Musculoskeletal Disorders in the Workplace Principles and Practice 2nd Edition - nordin

6C H A P T E R Wrist and Hand

6aC H A P T E R 200 log, a factor partially rectified in the early 1980s after OSHA levied large fines against some meat processing and automobile Epidemiology of Wrist manufacturers for under-reporting. A similar calendar trend in and Hand Disorders work-related hand/forearm problems has been observed in other countries such as Finland,46 Australia,7 and Japan.70 David Rempel and Laura Punnett Rates of hand and wrist symptoms and associated disability This chapter summarizes the findings of epidemiologic studies among working adults were assessed by a 1988 national interview that address workplace and individual factors associated with survey of 44,000 randomly selected U.S. adults (National Health hand and wrist musculoskeletal disorders (MSDs). From an Interview Survey).71 Of those who had worked any time in epidemiologic point of view, this topic is challenging because the past 12 months, 22% reported some finger, hand, or wrist although many specific hand and wrist disorders such as carpal discomfort that fit the category “pain, burning, stiffness, numb- tunnel syndrome (CTS) and hand-arm vibration syndrome ness, or tingling” for 1 or more days in the past 12 months. Only are recognized, no criteria for case definitions are universally one fourth were due to an acute injury such as a cut, sprain, accepted. More data are available for CTS than for other hand or broken bone. Nine percent reported having prolonged hand and wrist disorders because of its relatively well-defined pathology discomfort, that is, discomfort of 20 or more days during the last and available diagnostic methods such as nerve conduction 12 months or 7 or more consecutive days that was not due to velocity testing.79 an acute injury. Of those with prolonged hand discomfort, 6% changed work activities and 5% changed jobs because of the These disorders are not new; epidemics and clinical case hand discomfort. From the same data set it was estimated that in series of work-related hand and wrist tendinitis were reported 1988 alone there were 520,000 cases of work-related hand and throughout the 1800s and early 1900s.17,92 As summarized by a wrist disorders (CTS and tendon syndromes) in the United States.89 review by a National Academy of Sciences panel,65 many cross- sectional studies and more recent prospective studies consistently Administrative records (e.g., workers’ compensation) are identify certain key risk factors at the same time that they point frequently used to estimate incidence rates, but the data are to the multifactorial nature of work-related hand and wrist dis- extremely problematic to interpret because of varying decision orders. The etiology of these disorders includes both biomechani- rules that may have no clinical value in defining a “case.” For cal and work organizational factors, along with reporting and example, Fine et al26 evaluated multiple records for the same clinical progression that are likely affected by the worker’s per- time period at two U.S. automobile plants. Within each facility ception of the work environment and by medical management. the magnitude of the incidence rates of hand and arm disorders A conceptual model of this complicated relationship, adapted varied dramatically between data sources: The rates were 10 times from Armstrong et al4 and presented in Figure 6a.1, is based on higher in the workers’ compensation records than in the OSHA epidemiologic studies and pathophysiologic mechanisms clari- 200 log and 10 times higher in the plant medical records than in fied in laboratory studies. Health care providers can apply this the compensation data. Nevertheless, the relative ranking of the information and limit workplace exposures to risk factors both departments within each plant was similar, regardless of which to reduce the overall incidence of hand, wrist, and other mus- data source was used. culoskeletal disorders (primary prevention) and to prevent loss of function in patients (secondary and tertiary prevention) in whom The incidence of work-related CTS, impact of work disability, such disorders have occurred. and factors predicting disability have been assessed on a large scale in Washington State. A review of 7926 workers’ compensation claims for CTS from 1984 to 1988 yielded an industry-wide Work-related factors • Work organization • Repetition • Force • Posture FREQUENCY, RATES, AND COSTS Individual factors Internal load (dose) • Size Discomfort National incidence rates of work-related hand and wrist disorders • Capacity Pain in the United States are not easy to assess because of the difficulty • Behavior Disorder in attributing causation and the sparse data on background inci- • Repair Disability dence and prevalence. Annual incidence rates of all work-related repeated-motion disorders reported by U.S. private employers Figure 6a.1 A possible model of the relationship between exposure to the Bureau of Labor Statistics are shown for 1980 to 2000 in to work, worker attributes, and development of chronic musculoskeletal Figure 6a.2. Approximately 55% were hand or wrist disorders, disorders of the hands and wrist. Internal loads and individual capacity a percentage also reported in industrial studies60 and in studies result in a reversible cascading series of events ranging from minor from other countries.46 The dramatic rise after 1983 may be mechanical or biologic disturbances to tissue damage and disability. partially explained by early industry under-reporting on the (Modified from Armstrong TJ, Buckle P, Fine LJ, et al: Scand J Work Occupational Safety and Health Administration (OSHA) Environ Health 19:73-84, 1993.)

212 Chapter 6a ● Epidemiology of wrist and hand disorders Figure 6a.2 Incidence rates (per 1000 full-time employees) of repeated-motion disorders for all U.S. private-sector workers from 1980 to 2000. The lower curve is the incidence for industries with primarily office work (finance, insurance, and real estate). Approximately 55% are hand/wrist disorders. (From Bureau of Labor Statistics, 1980-2000.) incidence rate of CTS claims of 1.74 per 1000 full-time employees.27 highest cause of years of productivity lost, after sprains of the Rates up to 20 cases per 1000 full-time employees were observed back/neck and lower extremity, representing 1.8 years lost per in shellfish, fish, and other meat-packing industries. Industries thousand workers per year. CTS had a lower incidence rate but with the highest rates of occupational CTS are presented in caused more lost time per case, accounting for 0.5 years lost per Figure 6a.3. The ranking of these rates also shows a high 1000 worker-years. Approximately 40% of all the Washington correspondence with the occupations in Finland having the State workers with CTS went on to surgical treatment.1 Of these, highest rates of hand, wrist, and forearm disorders, despite some the mean duration of lost time was 4 months. The length of geographic differences in industry. time lost from work was not associated with demographic factors (age, gender, wage) or case severity as assessed by clinical staging Disability burden was quantified as “years of productivity or nerve conduction values. Most (67%) returned to the same lost,” addressing time lost from work for incident compensa- job, 15% found a different job, and 3 years after surgery 18% tion claims in 1986.30 Upper extremity strains were the third Incidence rate (per 1000 person-years) 3.0 2.5 2.0 1.5 1.0 0.5 0.0 16–24 25–34 35–44 45–54 55–64 >65 Age Figure 6a.3 Population age-specific incidence rates of carpal tunnel syndrome for Rochester, Minnesota, from 1961 to 1980 (——) (n = 1016)75 as compared with work-related incidence rates for the Washington State workers’ compensation system from 1984 to 1988 (...) (n = 7926).28

Chapter 6a ● Individual Factors 213 had not returned to work. Workers from jobs with elevated rates Whether these rates are higher among those performing repeti- of CTS or those involving repetitive hand activity were less likely tive hand activity versus those performing tasks with low repeti- to return to the same job. A return to repetitive or physically tiveness is unknown. demanding work is a predictor of poor long-term outcome after surgery.2,58 In the absence of universally accepted diagnostic criteria for CTS, some consider just an abnormal nerve conduction study Few data are available to assess the long-term financial and a gold standard.39,45,63 Relying exclusively on nerve conduction functional impact on patients and society, but best estimates by studies can lead to very high prevalences, however, such as the National Academy of Sciences panel place the average direct 28%63 and 19%8 in low-risk working populations. The usual signs cost per workers’ compensation case at over $8000, with total of CTS have relatively poor sensitivities and specificities28,39,45; cost estimates for all MSDs as high as $45 to $54 billion per year, only in the late stages of the disease or in the elderly are weak- around 0.8% of the nation’s gross domestic product.65 A popu- ness and thenar atrophy noticeable features, and in approxi- lation survey in Connecticut indicated that only about one in mately 25% of cases, CTS is accompanied by other disorders of five persons with medical treatment for work-related MSDs the hand or wrist.72 Although consensus criteria using symptom was reimbursed by compensation and that they had substantial history and nerve conduction study findings have been pro- other social and economic costs, ranging from loss of function to posed,79 the combination of a positive nerve conduction velocity decreased job advancement to losing a car or home for financial test and symptoms consistent with CTS represents a preferable reasons.62 case definition. DISORDER TYPES AND THEIR Few studies have evaluated how osteoarthritis of the hand NATURAL HISTORY and wrist relates to work.35,99 Hadler et al35 assessed the hands of 67 workers at a textile plant in Virginia. Significant differences Figure 6a.3 lists some hand and wrist disorders identified in in finger and wrist-joint range of motion, joint swelling, and occupational epidemiologic studies. Nonspecific hand/wrist pain radiograph patterns of degenerative joint disease were observed is the most common problem, followed by tendinitis, ganglion between three different hand-intensive jobs; the observed dif- cysts, and CTS.38,53,60,86 In their early stages, these disorders may ferences were reported to match the pattern of hand usage. be manifested by nonspecific symptoms without signs or labora- tory findings. It is important to remember that symptoms in the Hand-arm vibration syndrome, or vibration white finger hand may be due to nerve or vascular lesions further up the arm. disease, occurs in occupations involving many years of exposure to vibrating hand tools.66 This disorder of the small vessels and When measured in high-risk workplaces, rates of nonspecific nerves in the fingers and hands is manifested as localized blanch- symptoms, tendinitis, and CTS appeared to track each other; ing at the fingertips with numbness on exposure to cold or vibra- that is, specific disorders usually do not occur in isolation. For tion. The symptoms are largely self-limited if vibration exposure example, in a pork processing plant, the rank order of hand and is eliminated at an early stage,20,31 but with continuing exposure wrist problems as a percentage of all morbidity was nonspecific the condition becomes irreversible. hand/wrist pain, 39%; CTS, 26%; trigger finger, 23%; trigger thumb, 17%; and de Quervain tenosynovitis, 17%.61 Hypothenar hammer syndrome, or occlusion of the superfi- cial palmar branch of the ulnar artery, has been associated in Among packers in a bread factory, whose work involved repeti- clinical series and case-control studies with habitually using the tive and forceful gripping, approximately one half had wrist/hand hand for hammering52,69 and with exposure to vibrating hand tenosynovitis (compared with 14% among retail shop assistants).53 tools.44 The mean length of exposure before seeking medical The most common disorder of the hand or wrist was thumb attention was 20 to 30 years. Small case-control studies or clini- tenosynovitis, followed by finger/wrist extensor tenosynovitis. cal series have described factors associated with less common CTS was diagnosed in four packers and in no control subjects. disorders such as gamekeeper’s thumb,14,68 digital neuritis, ulnar Similar ratios of disorders have been observed in manufacturing neuropathy at the wrist,86 and Kienböck disease.32 workers,6,60,86 food processors,47,53 and computer operators.9,38 INDIVIDUAL FACTORS For the purposes of this chapter, tendinitis includes hand, wrist, and distal forearm tendinitis or tenosynovitis and trigger In general population studies and clinical case series, the average finger. Tendinitis occurs at discrete locations, the most common age of patients with CTS is approximately 55 years.10,72,88,100 site being the first extensor compartment (de Quervain disease), In contrast, the mean age for “occupational” cases, based on the followed by the five other pulley sites on the extensor side of the Washington State workers’ compensation study, is 37.5 years.27 hand and three on the flexor side. The diagnosis is based on the Furthermore, as displayed in Figure 6a.3, the incidence increases history, symptom location, and palpation and provocative with age in the general population but does not appear to do maneuvers on physical examination.34 No association of tendini- so in the occupational cohort. Only 3% of the variability in tis with age has been found, but a bimodal curve with seniority median nerve latency in a cross-sectional study of an industrial has been described; work-related tendinitis was higher among cohort is explained by age.63 In another prospective study, age workers with less than 3 years of employment, for example,60 was not a predictor for incidence of CTS or for wrist tendonitis suggesting that performance of unaccustomed tasks is a risk fac- in a mixed occupational cohort51 or of tendon-related disorders tor and/or that affected workers are less likely to remain in the job. of the hand and forearm among computer users.34 In cross-sectional workplace studies, the prevalence of ganglion Similarly, gender appears to play a greater role in population- cysts, as assessed by physical examination, is 2% to 3%.9,38,60 based studies of CTS than in industrial studies. In regional

214 Chapter 6a ● Epidemiology of wrist and hand disorders population studies and clinical series, the incidence of CTS is higher those of older cross-sectional studies of the same endpoints.95 in females than in males by a factor of 2.2:1 to 3.7:1,10,72,88,100 Tables 6a.1 and 6a.2 summarize selected studies of wrist and whereas in workplace studies, when employees perform similar hand tendinitis and CTS that included a control group. hand activities, the ratio is much closer to unity at 1.2:1.27,34,63,86 CTS can be a sequela (usually self-limiting) of pregnancy21; Hand/wrist pain and disorders have been associated with however, the role of other female reproductive factors such as repetitive hand and finger motions characterized by a variety of oophorectomy, hysterectomy,11,15,18,77 or the use of oral contra- metrics. Prevalences are generally high in manual-intensive ceptives82 is less certain. The overall implications are that when occupations such as data-entry work, postal sorting, cleaning, hand activities are taken into account, the differences between industrial inspection, and packaging.65 In a study relying exclu- working men and women are not particularly prominent, and sively on nerve conduction measurements, median nerve slow- hormonal influences likely account for relatively little morbidity ing occurred at a higher rate among assembly line workers than when ergonomic exposures are high.76 among administrative control subjects.64 Assembly line workers appeared to have more repetitive tasks than the control group. Other individual factors with strong associations to CTS Similar results were obtained in comparisons of garment workers are diabetes mellitus,72,88,100 rheumatoid arthritis,72,88,100 and obe- performing repetitive hand tasks with hospital employees not sity.18,23,63,94,97 For other factors, including thyroid disorders,38,72 using computer keyboards77 and in bread packers compared with vitamin B6 deficiency,3,22,59 wrist size and shape,5,12,33,43 and general retail shop attendants.53 A number of other cross-sectional and deconditioning,63 the associations are based on single studies or prospective studies have similarly observed the importance the studies present conflicting results. Nonspecific distal symptoms of high hand pace, short cycle time, little variation in tasks, and have also been associated with systemic disease, obesity, smoking, lack of rest breaks for risk of CTS,8,16,50,80,98 tendinitis,47 and hand and other nonoccupational factors.51,73,75 pain or combined disorders.25,49 This range of metrics illustrates the varied ways that “repetitive motion” may be operationalized WORK-RELATED FACTORS in addition to high velocity or acceleration of the wrist or rate of repetition of postural stress.57 Figure 6a.3 summarizes the characteristics of work that have been associated with elevated rates of hand and wrist symptoms The force applied to a tool or materials during repeated and with specific disorders like CTS and tendinitis. The number or sustained gripping is also a predictor of the risk for tendinitis, of prospective studies has increased substantially in recent years, CTS, and other distal extremity disorders. For example, in a and the risk factors identified tend to be quite consistent with study of the textile industry, the risk of hand and wrist tendinitis was 3.9 times higher among packaging and folding workers than among knitting workers, who performed work that was Table 6a.1 Selected controlled epidemiologic studies evaluating the association between work and wrist, hand, or distal forearm tendinitis* Authors Exposed population Control population Rate in Rate in exposed (%) control (%) Kuorinka et al, 1979 90 scissors makers 133 shop attendants 18 14 Luopajarvi et al, 197953† 152 bread packaging 133 shop attendants 53‡ 14 Silverstein et al, 198686§|| Industrial Industrial 143 low force/high rep 136 low force/low rep 3? 1.5 McCormack et al, 199060 153 high force/low rep 136 low force/low rep 4? 1.5 142 high force/high rep 136 low force/low rep 20‡ 1.5 Kurppa et al, 199147†¶ Manufacturing Manufacturing 369 packers/folders 352 knitting workers 3.3‡ 0.9 Latko et al, 199949 562 sewers 352 knitting workers 4.4‡ 0.9 296 boarding workers 352 knitting workers 6.4‡ 0.9 102 meat cutters 141 office workers 12.5? 0.9 107 sausage makers 197 office workers 16.3‡ 0.7 118 packers 197 office workers 25.3‡ 0.7 352 manufacturing workers (high/low rep) OR = 3.23 *Case criteria are based on history and physical examination. †All exposed and control subjects are female. ‡Significant difference from control. §Adjusted for age, sex, and plant. ||Analysis includes other disorders, although tendinitis was most common. ¶Cohort study with a 31-month follow-up. OR, odds ratio.

Chapter 6a ● Work-Related Factors 215 Table 6a.2 Selected controlled epidemiologic studies evaluating the association between work and carpal tunnel syndrome* Authors Exposed population Control population Criteria Rate in Rate in exposed (%) control (%) Silverstein et al, 198787† Industrial Industrial History and physical 5.1‡ 0.6 Nathan, 198864§|| High force/high rep Low force/low rep examination 22 keyboard operators 147 admin/clerical 27 28 Barnhart, 19918§ 164 assembly line 147 admin/clerical Electrodiagnostic 47 28 Roquelaure et al, 199780 115 general plant 147 admin/clerical Electrodiagnostic 38 28 23 grinders 147 admin/clerical Electrodiagnostic 61‡ 28 106 ski manufacturing 67 ski manufacturing Electrodiagnostic 15.4‡ 3.1 Electrodiagnosis and repetitive jobs nonrepetitive jobs OR = 9.0 (2.4-33.4) 65 factory workers/65 case signs for force and OR = 8.8 Symptoms, signs, (1.8-44.4) for repetition controls electrodiagnosis, surgery *Diagnoses are based on history and physical examination or nerve conduction study. †Controlled for age, gender, and years on job. ‡Significantly different from control group. §Controlled for age and gender. ||Low participation rate and limited exposure assessment. OR, odds ratio. much less physically demanding. In a study by Moore and other physical stressors.37, 77, 80 The importance of addressing all Garg61 at a pork processing plant, in the jobs that involved high such exposures simultaneously in workplace interventions is grip force or long grip durations such as Wizard knife operator, further demonstrated by the effect of multifaceted ergonomic snipper, feeder, scaler, bagger, packer, hanger, and stuffer, almost interventions in reducing upper extremity morbidity.13,25,67 every employee was affected. Others observed a similar relation- ship with work involving sustained or high force grip in grinders,64 Work involving increased wrist deviation from a neutral meatpackers and butchers,23,47 and other industrial workers.51,92,96 posture in either the extension/flexion or ulnar/radial direction has been associated with CTS and other hand and wrist prob- A comprehensive cross-sectional study of the combined fac- lems.40,92,93 de Krom et al18 conducted a case-control study of tors of repetition and force was conducted among 574 industrial 156 subjects with CTS versus 473 control subjects randomly workers by Silverstein et al.86,87 Disorders were assessed by phys- sampled from the hospital and population registers in a region ical examination and history and were primarily tendinitis fol- of the Netherlands. After adjustment for age and sex, a dose- lowed by CTS, Guyon tunnel syndrome, and digital neuritis. response relationship was observed for increasing hours of work Subjects were classified into four exposure groups based on force with the wrist in extension or flexion. No risk was observed for and repetition. The “high-force” work involved a grip force increasing hours performing a pinch grasp or typing, although averaging more than 4 kg of force, whereas “low-force” work methodologic limitations may have obscured such associations. involved less than 1 kg of grip force. The “high-repetition” work Some studies of computer operators have linked awkward wrist involved a repetitive task in which either the cycle time was less postures to severity of hand symptoms,24 risk of tendinitis or than 30 seconds (greater than 900 times in a work day) or more CTS,84 and arm and hand discomfort.19,41,83 In a large population than 50% of the cycle time was spent performing the same kind sample, both CTS and distal tendonitis were associated with of fundamental hand movements. After adjusting for plant, age, repetitive occupational bending and twisting of the hands and gender, and years on the job, the high-risk groups were compared wrists.89,90 Wrist angles measured by electrogoniometry were with the low-risk group. The odds ratio of all hand/wrist disor- strongly linked with wrist disorders in a range of service and ders for high force alone was 5.2 and that for high repetition manufacturing occupations; forceful exertions and repetitiveness alone was 3.3; this increased to 29 for jobs that required both were also risk factors, although they were correlated with each high force and high repetition. The identical analysis of just other too strongly to distinguish their effects.55 CTS revealed an odds ratio of 1.8 for force, 2.7 for repetition, and 14 for the combined high-force high-repetition group. Prolonged exposure to vibrating hand tools such as chain saws has been linked in prospective studies to hand-arm vibra- Years of exposure to both repetitive wrist movement and tion syndrome.20,31 The risks are primarily vibration acceleration, “heavy load on the wrist” were strongly associated with CTS.83 amplitude, and frequency; hand coupling to tool; hours per day Estimates of the CTS cases among workers who perform repeti- of exposure; and years of exposure. Based on existing studies, tive or forceful hand activity that can be attributed to work range however, no clear vibration acceleration/frequency/duration from 50% to 90%.36,91 Other investigations similarly highlighted threshold has been found that would protect most workers. the combined effects of repetition, force, postural load, and Medical surveillance is therefore recommended to identify

216 Chapter 6a ● Epidemiology of wrist and hand disorders cases early while the disease can still be reversed.66 Nonetheless, compensation system; however, a full accounting of their finan- both the American National Standards Institute and the cial impact has yet to be done. Hand and wrist problems may International Standards Organization have promulgated guide- present in any number of ways, from the most common pres- lines limiting the duration of exposure as a function of accelera- entation of nonspecific hand symptoms to discrete entities such tion and frequency. The use of vibrating hand tools may also as hand-arm vibration syndrome or de Quervain tenosynovitis. increase the risk of CTS,15,81,85,98 either by direct nerve injury The rates of specific disorders correspond to high symptom rates or by indirectly increasing applied grip force through a reflex in a work population. pathway.78 Prolonged or high-load localized mechanical stress over tendons or nerves from tools or from resting the hand on Studies point to a multifactorial relationship between hard objects has been associated with tendinitis93 and nerve work and these disorders. Some disorders such as tendinitis and entrapment40,72 in case studies. CTS are clearly associated with repetitive and forceful hand use, postural stress, and vibration. For other disorders such as gan- The average total hours per day that a task is repeated or glion cysts and osteoarthritis, the relationship to work has not sustained has been a factor in predicting hand problems.54,56 been well studied. Symptom severity and disorder rates—or For example, an increase in hours of computer use has consis- at least their reporting—appear to be influenced by work organi- tently been a predictor of increased symptom prevalence.9,24,26,41,74 zational factors such as decision latitude and cognitive demands. In prospective studies of computer users, increasing hours of In population-based studies and clinical case series, CTS in keyboard and mouse use predicted increased incidence of hand/ particular has been linked to individual factors. However, in wrist pain and tendonitis, especially above 20 hours per week.34,42 workplace studies when workplace exposure is high and quanti- fied, individual factors play a limited role relative to workplace In cross-sectional studies, work organizational factors (e.g., factors.5,15,24,38,41,87 work structure, decision control, workload, deadline work, supervision) and psychosocial factors (e.g., job satisfaction, social REFERENCES support, relationship with supervisor) appear to have some influ- ence on hand and wrist symptoms. Work organizational factors 1. Adams ML, Franklin GM, Barnhart S: Outcome of carpal tunnel surgery in Washington represent upstream determinants of both physical motion patterns State workers’ compensation. Am J Ind Med 25:527-536, 1994. and subjective psychosocial work experiences. For example, just- in-time production systems increase both the work pace48 and 2. 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Fulton-Kehoe D, Franklin G, Weaver M, Cheadle A: Years of productivity lost among of sensory conduction of the median nerve in industry. J Occup Med 34:379-383, injured workers in Washington State: modeling disability burden in workers’ 1992. compensation. Am J Ind Med 37:656-662, 2000. 64. Nathan PA, Meadows KD, Doyle LS: Occupation as a risk factor for impaired sensory conduction of the median nerve at the carpal tunnel. J Hand Surg Br 13B:167-170, 31. Futatsuka M, Ueno T: A follow-up study of vibration-induced white finger due to 1988. chain-saw operation. Scand J Work Environ Health 12:304-306, 1986. 65. National Academy of Sciences: Musculoskeletal disorders and the workplace. Washington, DC, 2001, National Research Council and Institute of Medicine, 32. Gelberman RH, Bauman TD, Menon J, Akeson WH: The vascularity of the lunate bone National Academy Press. and Kienböck’s disease. J Hand Surg 5:272-278, 1980. 66. National Institute of Occupational Safety and Health: Criteria for a recommended standard. Occupational exposure to hand-arm vibration. DDHS Publication No. 33. Gelmers H: Primary carpal tunnel stenosis as a cause of entrapment of the median 89-106. Cincinnati, 1989, The Institute. nerve. Acta Neurochir 55:317-320, 1981. 67. Nelson NA, Silverstein BA: Workplace changes associated with a reduction in musculoskeletal symptoms in office workers. Hum Fact 40:337-350, 1998. 34. Gerr F, Marcus M, Monteilh C, et al: A prospective study of computer users. I. Study 68. Newland CC: Gamekeeper’s thumb. Orthop Clin North Am 23(1):41-48, 1992. design and incidence of musculoskeletal symptoms and disorders. Am J Ind Med 69. Nilsson T, Burstrom L, Hagberg M: Risk assessment of vibration exposure and white 41:221-235, 2002. fingers among platers. Int Arch Occup Environ Health 61:473-481, 1989. 70. Ohara H, Aoyama H, Itani T: Health hazards among cash register operators and the 35. Hadler N, Gillings DB, Imbus HR, et al: Hand structure and function in an industrial effects of improved working conditions. J Hum Ergol 5:31-40, 1976. setting. Arthritis Rheum 21:210-220, 1978. 71. Park CH, Wagener DK, Winn DM, Pierce JP: Health conditions among the currently employed: United States, 1988. National Center for Health Statistics. Vital Health 36. Hagberg M, Morgenstern H, Kelsh M: Impact of occupations and job tasks on the Stat 10:186, 1993. prevalence of carpal tunnel syndrome. Scand J Work Environ Health 18:337-345, 72. Phalen GS: The carpal-tunnel syndrome. J Bone Joint Surg 48A:211-228, 1966. 1992. 73. Punnett L: Ergonomic stressors and upper extremity disorders in vehicle manufacturing: cross-sectional exposure-response trends. Occup Environ Med 55:414-420, 1998. 37. Häkkänen M, Viikari-Juntura E, Martikainen R: Incidence of musculoskeletal 74. Punnett L, Bergqvist U: Visual display unit work and upper extremity musculoskeletal disorders among newly employed manufacturing workers. Scand J Work Environ disorders. A review of epidemiological findings. Solna, Sweden, 1997, National Health 27:381-387, 2001. Institute of Working Life. 75. Punnett L, Gold JE, Katz JN, Gore R, Wegman DH: Ergonomic stressors and upper 38. Hales TR, Sauter SL, Peterson MR, et al: Musculoskeletal disorders among visual extremity disorders in automotive manufacturing: a one-year follow-up study. Occup display terminal users in a telecommunications company. Ergonomics 10: Environ Med 61:668-674, 2004. 1603-1621, 1994. 76. Punnett L, Herbert R: Work-related musculoskeletal disorders: is there a gender differential, and if so, what does it mean? In MB Goldman, MC Hatch, eds: Women 39. Heller L, Ring H, Costeff H, Solzi P: Evaluation of Tinel’s and Phalen’s signs in and health. San Diego, CA, 2000, Academic Press, pp. 474-492. diagnosis of carpal tunnel syndrome. Eur Neurol 25:40-42, 1986. 77. Punnett L, Robins JM, Wegman DH, Keyserling WM: Soft tissue disorders in the upper limbs of female garment workers. Scand J Work Environ Health 11:417-425, 40. Hoffman J, Hoffman PL: Staple gun carpal tunnel syndrome. J Occup Med 1985. 27:848-849, 1985. 78. Radwin RG, Armstrong TJ, Chaffin DB: Power hand tool vibration effects on grip exertions. Ergonomics 30:833-855, 1987. 41. Hunting W, Ldubli T, Grandjean E: Postural and visual loads at VDT workplaces. 79. Rempel D, Evanoff B, Amadio PC, et al: Consensus criteria for the classification Ergonomics 24:917-931, 1981. of carpal tunnel syndrome in epidemiologic studies. Am J Public Health 88: 1447-1451, 1998. 42. Jensen C: Development of neck and hand-wrist symptoms in relation to duration of 80. Roquelaure Y, Mechali S, Dano C, et al: Occupational and personal risk factors computer use at work. Scand J Work Environ Health 29:197-205, 2003. for carpal tunnel syndrome in industrial workers. Scand J Work Environ Health 23:364-369, 1997. 43. Johnson EW, Gatens T, Poindexter D, Bowers D: Wrist dimensions: correlation with median sensory latencies. Arch Phys Med Rehabil 64:556-557, 1983. 44. Kaji H, Honma H, Usui M, Yasuno Y, Saito K: Hypothenar hammer syndrome in workers occupationally exposed to vibrating tools. J Hand Surg Br 18B:761-766, 1993. 45. Katz JN,Larson MG, Fossel AH, Liang MH: Validation of a surveillance case definition of carpal tunnel syndrome. Am J Public Health 81:189-193, 1991. 46. Kivi P: Rheumatic disorders of the upper limbs associated with repetitive occupational tasks in Finland in 1975-1979. Scand J Rheumatol 13:101-107, 1984. 47. Kurppa K, Viikari-Juntura E, Kuosma E, Huuskonen M, Kivi P: Incidence of tenosynovitis or peritendinitis and epicondylitis in a meat processing factory. Scand J Work Environ Health 17:32-37, 1991. 48. Landsbergis PA, Cahill J, Schnall PL: The impact of lean production and related new systems of work organization on worker health. J Occup Health Psychol 4:108-130, 1999. 49. Latko WA, Armstrong TJ, Franzblau A, Ulin SS, Werner RA, Albers JW: Cross-sectional study of the relationship between repetitive work and the prevalence of upper limb musculoskeletal disorders. Am J Ind Med 36(2):248-259, 1999.

218 Chapter 6a ● Epidemiology of wrist and hand disorders 81. Rothfleisch S, Sherman D: Carpal tunnel syndrome: biomechanical aspects of 91. Tanaka S, Wild DK, Seligman PJ, et al: The US prevalence of self-reported carpal occupational occurrence and implications regarding surgical management. Orthop tunnel syndrome. Am J Public Health 84:1846-1848, 1994. Rev 7:107-109, 1978. 92. Thompson A, Plewes L, Shaw E: Peritendinitis crepitans and simple tenosynovitis: 82. Sabour M, Fadel H: The carpal tunnel syndrome, a new complication ascribed to the a clinical study of 544 cases in industry. Br J Ind Med 8:150-160, 1951. pill. Am J Obstet Gynecol 107:1265-1267, 1971. 93. Tichauer E: Some aspects of stress on forearm and hand in industry. J Occup Med 83. Sauter SL, Scheifer LM, Knutson SJ: Work posture, work station design, and 8:63-71, 1966. musculoskeletal discomfort in a VDT entry task. Hum Fact 33:151-167, 1991. 94. Vessey MP, Villard-MacInosh L, Yeates D: Epidemiology of carpal tunnel syndrome in 84. Seligman P, Boiano J, Anderson C: Health hazard evaluation of the Minneapolis women of childbearing age. Finding in a large cohort study. Am J Epidemiol Police Department. Springfield, VA, 1986, NIOSH HETA 84-417-1745, 19:655-659, 1990. U.S. Department of Commerce, National Technical Information Service. 95. Viikari-Juntura E, Silverstein BA: Role of physical load factors in carpal tunnel 85. Seppalainen AM: Nerve conduction in the vibration syndrome. Scand J Work Environ syndrome. Scand J Work Environ Health 25:163-185, 1999. Health 6:82-84, 1970. 96. Welch R: The causes of tenosynovitis in industry. Ind Med 41:16-19, 1972. 86. Silverstein BA, Fine LJ, Armstrong TJ: Hand wrist cumulative trauma disorders in 97. Werner RA, Albers JW, Franzblau A, Armstrong TJ: The relationship between body industry. Br J Ind Med 43:779-784, 1986. mass index and the diagnosis of carpal tunnel syndrome. Muscle Nerve 17: 87. Silverstein BA, Fine LJ, Armstrong TJ: Occupational factors and carpal tunnel 632-636, 1994. syndrome. Am J Ind Med 11:343-358, 1987. 98. Wieslander G, Norback D, Gothe CJ, Juhlin L: Carpal tunnel syndrome (CTS) and exposure to vibration, repetitive wrist movements, and heavy manual work: a 88. Stevens JC, Sun S, Beard CM, O’Fallon WM, Kurland LT: Carpal tunnel syndrome case-referent study. Br J Ind Med 46:43-47, 1989. in Rochester, Minnesota, 1961 to 1980. Neurology 38:134-138, 1988. 99. Williams WV, Cope R, Gaunt WD, et al: Metacarpo-phalangeal arthropathy associated with manual labor (Missouri meta-carpal syndrome). Arthritis Rheum 89. Tanaka S, Petersen MR, Cameron LL: Prevalence and risk factors of tendinitis and 30:1362-1371, 1987. related disorders of the distal upper extremity among U.S. workers: comparison to 100. Yamaguchi D, Liscomb P, Soule E: Carpal tunnel syndrome. Minn Med J 22-23, carpal tunnel syndrome. Am J Ind Med 39:328-335, 2001. 1965. 90. Tanaka S, Wild DK, Cameron LL, Fruend E: Association of occupational and non- occupational risk factors with the prevalence of self-reported carpal tunnel syndrome in a national survey of the working population. Am J Ind Med 35:550-556, 1997.

6bC H A P T E R Most wrist ligaments are considered true intracapsular ligaments and tend to be oriented obliquely, from the periphery of the Biomechanics of the wrist toward the midline, from a proximal to distal direction. Wrist and Hand The volar ligaments are well established as the primary stabilizers of the wrist joint. Studies investigated the anatomy and mechan- Rita M. Patterson and Kai-Nan An ical strength of the dorsal ligaments of the wrist. Together the dorsal intercarpal (DIC), dorsal radiocarpal, and dorsal scapho- The human hand is a relatively mobile three-dimensional structure lunate (SL) interosseous ligaments create a lateral “V” that deliv- capable of conforming to the shape of manipulated objects. The ers indirect dorsal stability between the scaphoid and the radius biomechanical structure of the hand can be considered a linkage while still allowing a threefold change in distance between the system of intercalated bony segments balanced by muscle and radius and the scaphoid dorsal groove. This unique design allows tendon forces and joint constraints. This chapter reviews some of dorsal stability of the scaphoid throughout the range of motion the unique qualities that affect the biomechanics of the hand and of the wrist that would require changes in the linear dimension wrist: normal skeletal and soft tissue anatomy, joint constraint of a “dorsal radioscaphoid ligament” far greater than any fixed and stability, range of joint motion and strength, and more basic ligament could accommodate (Fig. 6b.2). The combined mechan- biomechanical considerations of muscle-tendon function. ical properties of the DIC, dorsal SL interosseous, and dorsal radiocarpal ligaments together function to maintain scaphoid SKELETAL AND LIGAMENTOUS stability and alignment while allowing for carpal mobility.18 ANATOMY/JOINT CONSTRAINT Three distinct ligaments around the scaphoid trapezium Joint constraint and stability are provided by the joint articular and trapezoid (STT) joint have also been identified. The STT surfaces, the capsuloligamentous structures, and the musculo- ligaments extend distally (scaphoid trapezial ligament) and tendinous units. Primary joint stability is related to balance of ulnarly (scaphocapitate and scaphotrapezium ligaments) to form the muscle and tendon forces to an externally applied force, with a “V.” The plane of the V-shaped STT ligament is essentially par- the capsuloligamentous structures appearing to stabilize initially allel to that of the trapezium-trapezoid articulation and corre- against instantaneous loading and to provide secondary main- sponding interfacet ridge on the joint surface of the distal pole tenance of joint stability. The collateral ligaments of all the hand of the scaphoid. This ridge runs radiodorsal to ulnopalmar, a joints and the intercarpal ligaments in the wrist are important 45-degree angle from the sagittal plane13 (Fig. 6b.3). soft tissues for joint constraint. MOTION The locations and orientations of the ligament lines of action determine their characteristics in resisting loads on the joint. For The fingers and thumb consist of phalanges articulated at the example, the radial collateral ligament and the ulnar collateral interphalangeal joints. Within the physiologic range of motion, ligament are the primary ligaments of the metacarpophalangeal the interphalangeal joints can be considered hinges that allow joint. Originating from the radial-dorsal aspect of the metacarpal flexion/extension. In a normal hand, each interphalangeal joint head with insertion into the radial-volar aspect of the proximal has at least 90 degrees of motion. The proximal phalanx articu- phalanx, the radial collateral ligament is the primary ligament lates with the metacarpal at the metacarpophalangeal joints, resisting ulnar deviation and pronation of the proximal phalanx which are usually considered universal joints, allowing not only at the metacarpophalangeal joint. The ulnar collateral ligament, flexion/extension but also abduction/adduction. Normally, on the other hand, is the primary constraint in resisting radial the range of flexion/extension is about 90 degrees and that of deviation and supination of the proximal phalanx. abduction/adduction is 20 to 30 degrees. The relative contribution of each of the ligaments in resisting A composite articulation of eight carpal bones, the wrist joint joint displacement has been studied by sequential sectioning or connects the digits of the hand to the radius and ulna of the removal of the individual ligaments (Fig. 6b.1). The reduction of forearm. The range of wrist motions required to comfortably the load after removal of each ligamentous structure represents perform activities of daily living consists of 60 degrees of exten- the contribution of that ligament. sion, 54 degrees of flexion, 40 degrees of ulnar deviation, and 17 degrees of radial deviation. Most of the hand placement and Anatomic studies performed on the carpal bones and the range-of-motion tasks can be accomplished with 70% of wrist ligaments of the wrist in particular have identified several mor- motion maximum range. This converts to 40 degrees each of wrist phologic differences associated with degenerative changes and with flexion, wrist extension, and combined radial/ulnar deviation. specific kinematic (motion) patterns. Viegas and colleagues14 iden- tified two different lunate shapes. Type II has a facet that articu- Wrist flexion/extension and radial/ulnar deviation has tradi- lates with the hamate and has been associated with increased tionally been modeled as a fixed center of rotation through the arthritis in its proximal pole. Type I has no facet. proximal aspect of the capitate. However, studies have described the flexion/extension axis of the wrist as moving between the lunate and capitate. During global wrist motion, the radiolunate joint contributes more motion in flexion, whereas the lunocapi- tate joint contributes more motion in extension.16 Other studies described the kinematics of the lunate and the differences due to lunate type.13,18 The kinematics of type I lunate

220 Chapter 6b ● Biomechanics of the Wrist and Hand Extended MP joint 0.6 a 0.4 a: Intact 0.2 b c Sequential 0.2 sectioning of Torque (N-m) a b: RCL-P c: RCL-D b d: UCL-P c e: UCL-D Pronation 10 a d d 20 e a b c ab c 10 20 Supination a a 0.4 Figure 6b.1 Load-displacement curves were obtained by measuring the restraining torques when the metacarpophalangeal joints were displaced in supination and pronation. Curve a represents the torques with the entire capsule-ligament complex intact. Curves b and c represent the torques when the palmar and dorsal portions of the radial collateral ligament, respectively, were sectioned, whereas curves d and e represent those when the palmar and dorsal portions of the ulnar collateral ligament, respectively, were sectioned. The difference in load between each curve for a given displacement indicates the contribution of that particular sectioned element. For example, the difference in load between curves a and b represents the contribution of the palmar portion of the radial collateral ligament. N-m, newton-meter. (From An KN, Cooney WP III: Biomechanics, section II, the hand and wrist. In BF Morrey, ed: Joint replacement arthroplasty. New York, 1991, Churchill Livingstone International, pp. 137-146.) motion differs from that of type II. The total range of radial/ Forearm position has been shown also to affect key and ulnar translation of type II lunates was greater than that of type fingertip pinch strength but not three-jaw chuck pinch strength. I lunates during radial/ulnar deviation. Compared with that of The neutral forearm position rendered the highest mean score type I lunates, extension of type II lunates occurred later during and the pronated position the lowest mean score for key and ulnar deviation, whereas flexion of type II lunates occurred ear- fingertip pinch strength. Although these effects were consistent, lier. Describing the kinematics of the STT joint, Moritomo et al13 the statistically significant effects of forearm position were less found that the trapezium and the trapezoid rotate as a unit with than 1 pound of force and may not be clinically relevant. respect to the scaphoid during either flexion/extension or radial/ However, standardized forearm positioning during pinch ulnar deviation of the wrist. strength measurement is still recommended.17 The strength of the wrist joint is in the range of 10 to 20 Nm of flexion, 6 to 10 Nm STRENGTH of extension, 10 to 18 Nm of radial deviation, and 10 to 20 Nm of ulnar deviation. The potential strength of various joints in the hand and wrist in normal subjects has been studied with dynamometers. Normal TENDON EXCURSION pinch strengths ranged from 3 to 10 kg and grasp strengths from 20 to 40 kg. The wrist position and size of the grasped object have The ability to control the movement of an individual digit of the a significant influence on grip strength, which has been studied hand depends very much on the anatomic arrangement of the extensively as a function of wrist joint position. A self-selected musculotendinous complex. The magnitude of tendon excur- wrist position of 35 degrees of extension and 7 degrees of ulnar sion during joint movement for a given task would be important deviation has been identified as the position in which maximum also for assessing possible overuse injury caused by cumulative grip strength can be generated.15 For a given size of an object, trauma. grip strength is significantly reduced when the wrist position deviates from this self-selected position. For the finger and thumb, the pulley structures on the palmar side of the digits restrain bowstringing of the digital flexor

Chapter 6b ● Muscle and Joint Forces 221 Flexion Sc during joint flexion. Alteration of such a pulley system in the Tq hand disturbs the relationship between tendon excursion and joint angular displacement, and thus joint function. Parameters Radius have been defined from the curves of tendon excursion and joint motion for comparing tendon-pulley joint interactions Ulna under normal and abnormal conditions.9 The range of move- ment of the joint produced by a given standardized amount of Extension excursion is called the effective range of motion. Absolute Tq Sc tendon excursion is that from full extension to 90 degrees of flex- ion as measured with the flexor tendon set at its normal length Radius in the neutral position. Division of the pulley would result in bowstringing and adding slack to the tendon system, which Ulna would have to be taken up before any joint motion could occur. This amount of tendon slack is termed bowstring laxity. Subtracted Figure 6b.2 The lateral “V” configuration of the dorsal radiocarpal/ from absolute tendon excursion, bowstring laxity defines relative dorsal intercarpal construct allows dorsal stability of the scaphoid tendon excursion. along with a threefold change in the distance between the radius and the dorsal groove of the scaphoid between flexion and extension of the The biomechanical functions of the musculotendinous wrist (arrows). complex can be understood in terms of the relationship of ten- don excursion to joint angular displacement. The rate of change c in tendon excursion as the joint rotates is equal to the moment arm of the associated muscle or tendon for that specific joint motion.4 The moment arm defines not only the effectiveness of the tendon in joint rotation but also its mechanical advantage in resisting external loads. The larger the moment arm, the higher the torque and rotation angle generated for the same amount of muscle force and excursion. A determination of the potential moment arm contributions of muscles can provide insight into the balance of forces at a joint for planning tendon transfers or designing orthotics to help provide mobility or stability while minimizing loss of function. Tendon excursion and joint rotation angles of the wrist, for example, are measured by using an electric potentiometer and an electromagnetic tracking device, respectively.1 The instantaneous moment arms of each tendon are then calculated from the slope of the curve between the tendon excursion and the joint angular displacement. Calculated tendon moment arms are found to be consistent throughout a full range of flexion/extension and radio/ulnar deviation motion; they correspond closely to the anatomic location and orientation of the tendons (Fig. 6b.4). a MUSCLE AND JOINT FORCES FCR The potential force generated by a muscle depends on its size b and architecture. Three anatomic parameters of muscle morpho- logy have been recognized for their importance in defining its Figure 6b.3 The ligaments around the scaphoid trapezium and trapezoid biomechanical potential5: (1) muscle fiber length is related to joint at the palmar aspect of the left wrist. (a) The scaphotrapezial the potential range of physiologic excursion of the tendon and (S-Tm) ligament; (b) the scaphocapitate (S-C) ligament; (c) the muscle, (2) the physiologic cross-sectional area of a muscle is capitate-trapezium (C-Tm) ligament. FCR, flexor carpi radialis. proportional to its maximum tension potential, and (3) physi- cally, the product of the force and distance is work; therefore, the muscle mass or volume is proportional to its work capacity. In addition, potential force generation is further regulated by the velocity of shortening or lengthening of the muscle and, as is well known, its length at the time of contraction. Usually, an optimum length can be found for generating maximum con- tractile force. The arrangement of the muscle fiber architecture further influences the characteristics of the muscle contraction.8 It has been demonstrated that parallel muscle fibers produce a

222 Chapter 6b ● Biomechanics of the Wrist and Hand Figure 6b.4 (Left) Tendon excursion and moment arm of the five wrist motor tendons during flexion/extension motion. (A) Tendon excursion. The wrist joint was moved from full flexion to full extension passively. (B) Moment arms calculated from A. The flexors and extensors show the different directions of the moment arm: extensors show the plus, and flexors show the minus. (Right) Tendon excursion and moment arm of the five wrist motor tendons during radial/ulnar deviation. (A) Tendon excursion. The wrist joint was moved from radial deviation (R.D.) to ulnar deviation (U.D.) passively. (B) Moment arms calculated from A. The ulnar side tendons show the plus moment, and the radial side tendons show the minus moment. ERCB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; FCR, flexor carpi radialis; FCU, flexor carpi ulnaris. (From Horii E, An KN, Linscheid RL: Excursion of prime wrist tendons. J Hand Surg 18(1):83-90, 1993.) length-tension curve with maintained force throughout a wider grasp function. The corresponding moment arms of both the range of excursion than do muscles with a shorter fiber pennate intrinsic and extrinsic muscles at a particular joint configuration structure, which produce sharply peaked curves. The index of determine the mechanical advantage, tendon excursion, and muscle architecture, defined as the ratio of muscle fiber length to corresponding muscle length. Therefore, as mentioned earlier, muscle belly length, has been used to define such characteristics. the size and shape of the object are important considerations in determining the power and strength of the grasp. Furthermore, The orientation or constraint of muscles or tendons crossing a the extrinsic muscles of the fingers and thumb originate from the joint determines the characteristics of excursion and the moment forearm. Wrist joint motion therefore creates excursion of these arm. In general, the larger the moment arm, the better the tendons and modifies the muscle contraction characteristics mechanical advantage for the same amount of tendon or muscle because of the length-tension relationship. Thus grasp power and force. On the other hand, the larger the moment arm, the more strength are regulated by wrist joint configuration as well. tendon excursion expected for the same amount of joint rotation. The excursion of the tendon eventually affects the muscle length Because of the relatively smaller moment arms or mechanical of contraction and ultimately determines the potential force gen- advantage of the muscles and tendons across the joints as eration according to the muscle length-tension characteristics. compared with those of externally applied forces at the tip of the digits, the muscle force required to balance grip or pinch func- The size and shape of the object to be grasped determines tions is much higher. For example, in the tip and pulp pinch the joint configuration of the thumb and fingers involved in

Chapter 6b ● Force Through Wrist Carpal Joint 223 function, the forces of the flexor profundus and sublimis are CX4 = 4.9 CX2 = 2.7 about one to two times the force at the tip of the digits. The asso- ciated forces in the intrinsic muscles are in the range of 0.5 to CZ6 = 0.2 A=1 1.5 times the applied forces.2,3 Accordingly, with such a magnitude CX6 = 3.9 CY6 = 2.3 of muscle and tendon forces, the compressive and shear forces across the finger joints are quite significant (Fig. 6b.5). Figure 6b.5 Resultant joint forces during tip pinch function of one unit force, that is, A = 1. Forces represent the actions of the proximal FORCE THROUGH WRIST CARPAL JOINT segment applied onto the distal segment crossing the joint. CX, joint compressive joint force; CY, joint dorsal shear force; CZ, joint radial When the hand is used, the wrist joint encounters a tremendous shear force. (From An KN, Cooney WP III: Biomechanics, section II: the amount of force. The distribution of the forces among the hand and wrist. In BF Morrey, ed: Joint replacement arthroplasty. carpal bones has great potential for injury to the associated New York, 1991, Churchill Livingstone International, pp. 137-146.) bone and soft tissue. Cumulative trauma with compression of the lunate, for example, has been thought to result in avascu- lar necrosis of the lunate (Kienböck disease). It has been postu- lated that excessive and uneven loading is experienced by the lunate between the lunate fossa of the radius and the com- pressible triangular fibrocartilage of the ulna. The overall force transmitted from the proximal row of carpal bones to the distal radioulnar joint has been examined by numerous investi- gators. Although the findings have not been in complete agree- ment and probably depend on the measurement technique, trends of certain important characteristics have been quite consistent. On average, 15% to 20% of axial wrist joint force is trans- mitted by the distal end of the ulna, and 80% to 85% is trans- mitted through the radius in the neutral position (Fig. 6b.6A).7 Figure 6b.6 (A) Each arrow represents the cumulative compressive force vector between adjacent bones and between the carpal bones and distal ends of the radius and ulna. These joint compressive forces or pressures within the carpus are calculated by this model when all the joints and ligaments are intact and axial loads are applied along the metacarpals. (B) Predicted displacements of the carpal bones under the loading condition shown in A. Slight ulnar translation is present as a result of a component of force tangential to the radial articular surface. Carpal bone displacement must be considered when the concentration of the force vector across articular surfaces is analyzed. The dotted line represents the unloaded position and the solid line represents the loaded position of the carpus: S, scaphoid; L, lunate; Tq, triquetrum; Tr, trapezium/trapezoid; C, capitate; H, hamate; R, radius; U, ulna. (C) Each arrow represents the calculated tension for the different carpal ligaments under the same loading condition: 1, palmar radiolunate ligament; 2, dorsal radiotriquetral ligament; 3, palmar radiocapitate ligament; 4, palmar capitatotriquetral ligament; 5, dorsal scaphotriquetral ligament; 6, palmar/dorsal hamatocapitate ligaments; 7, flexor retinaculum. (From Horii E, Garcia-Elias M, Bishop AT, Cooney WP, Linscheid RL, Chao EY: J Hand Surg Am 15A(3):393-400, 1990.)

224 Chapter 6b ● Biomechanics of the Wrist and Hand The effect of joint position and forearm rotation on the percent- With OA age of load transmission across the radius and ulna has also been recognized. With the wrist in the neutral position, at the mid- Without OA carpal joint 30% of the total force was transmitted through the scaphotrapezial joint, 19% through the scaphocapitate joint, Radiographic TT 31% through the lunocapitate joint, and 21% through the tri- inclination quetrohamate joint. With the wrist loaded, the carpal bones translate in the ulnar direction down the inclined slope of the AB distal end of the radius (Fig. 6b.6B), and tensions in the inter- carpal ligaments are observed as well (Fig. 6b.6C). Interaction Figure 6b.7 (A) Radiographic measurements in the scaphoid axial of the carpal bones is conceptually analogous to a Rubik’s cube view. Radiographic trapezium-trapezoid (TT) inclination is an angle in which motion in one segment directly affects the position formed by a line running axially through the 3rd metacarpal and of another. another line running from the dorsal to the palmar articular edges of the proximal trapezium and trapezoid surfaces. (B) TT inclination is POSTTRAUMATIC INJURY associated with increased osteoarthritis (OA). Dobyns et al6 introduced the concept of traumatic carpal insta- ligament but also the DIC ligament at both its scaphoid and bilities, and many reports have described their clinical features, lunate attachments.10,19 treatments, and long-term consequences. The most common type of carpal instability is the dorsal intercalated segmental The second most common site of degenerative changes in instability (DISI). Although many reports describe the anatomy the wrist is scaphoid trapezium trapezoid degeneration. The eti- and function of the volar ligaments of the wrists, only recently ologic factors in the development of degenerative changes in the has the anatomy of the dorsal ligaments been better detailed STT joint are still unclear; studies have suggested, however, that and their function discussed. Most articles, which describe the degenerative changes are associated with scaphotrapezial ligament pathomechanism of SL instability (SLI), concentrate on the tears and increased trapezium-trapezoid inclination (the degree scaphoid instability. However, there has been relatively little of coverage by the facets of the trapezium and trapezoid over the information about lunate instability and no clear explanation distal pole of the scaphoid) (Fig. 6b.7).12 of the anatomic differences between dynamic and static SLI. Fractures of the scaphoid (the most commonly broken Studies suggested that the DIC ligament is important in main- carpal bone) are difficult to treat because of its complex three- taining the carpal alignment of both the scaphoid and lunate.19 dimensional shape and oblique orientation. Fractures of the When the DIC and the SL interosseous ligaments were disrupted proximal pole of the scaphoid have been associated with increased from the scaphoid but the DIC was still attached to the lunate, pressure and degenerative changes in the radius under its distal the resulting carpal instability demonstrated a flexed posture of pole. Whether the fracture line passes distal or proximal to the the scaphoid and a widened SL gap, but only when the hand was dorsal apex of the ridge of the scaphoid (where the DIC ligament loaded. This was comparable to a clinical dynamic SLI. and the dorsal component of the SL interosseous ligament attach) appears to determine the likelihood of subsequent DISI When the DIC ligament was also disrupted from the lunate, deformity and the pattern of degenerative changes, if the fracture the resulting instability demonstrated a flexed posture of the progresses to a scaphoid nonunion.11 In the volar type, the scaphoid and a widened SL gap in both loaded and unloaded distal fragment displaces volarly with respect to the proximal conditions. Furthermore, when the DIC was detached from the fragment, and in the dorsal type, the distal fragment displaces lunate, the latter changed position to an extended posture, also dorsally. in both loaded and unloaded conditions. This was comparable with a clinical static SLI with DISI. There was no apparent effect SUMMARY or further destabilization of the scaphoid or lunate resulting from disruption of the lunotriquetral interosseous ligament. Work-related injuries of the hand commonly occur. The nature of hand function places a tremendous amount of tension and The existence and progression of a dynamic SLI to a static SLI repetition on the tendons and intrinsic muscles. Although with a DISI deformity resulting from SL dissociation is well tension may not be high enough to cause great damage, it can accepted in the clinical setting. To date, however, there has create compressive and frictional forces on the tendons and adja- not been any detailed anatomic explanation and/or example of cent tissues around the pulley, bony surface, or other soft tissues. what the causes and the differences are between a dynamic These compressive and friction forces can potentially cause SLI and a static SLI with DISI. The anatomic and mechanical cumulative trauma disorders of the bone and soft tissue. integrity of the DIC ligament appears to play a significant role in SL stability and in determining whether the SL dissociation develops a dynamic or a static instability and DISI deformity. It is, of course, uncertain whether or not the progressive stages of instability simulated in these studies reflect actual clinical injury patterns. These results nevertheless propose that the treat- ment of the SLI should address not only the SL interosseous

Chapter 6b ● References 225 REFERENCES 11. Moritomo H, Viegas SF, Elder KW, et al: Scaphoid nonunion: a three dimensional analysis of patterns of deformity. J Hand Surg 25A(3):520-528, 1. An KN, Berger RA, Cooney WP: Biomechanics of the wrist. New York, 1991, Springer- 2000. Verlag. 12. Moritomo H, Viegas SF, Nakamura K, Patterson RM: The scaphotrapezio-trapezoidal 2. An KN, Chao EY, Cooney WP, Linscheid RL: Forces in the normal and abnormal hand. joint: Part 1. An anatomic and radiographic study. J Hand Surg 25A:899-910, J Orthop Res 3:202-211, 1985. 2000. 3. An KN, Cooney WP III: Biomechanics. Section II: The hand and wrist. In BF Morrey, 13. Nakamura K, Beppu M, Patterson RM, Viegas SF: Motion analysis in two dimensions ed: Joint replacement arthroplasty. New York, 1991, Churchill Livingstone of radial-ulnar deviation of type I versus type II lunates. J Hand Surg 25A:877-888, International, pp. 137-146. 2000. 4. An KN, Ueba Y, Chao EY, Cooney WP, Linscheid RL: Tendon excursion and moment 14. Nakamura K, Patterson RM, Moritomo H, Viegas SF: Type I vs. type II lunates: arm of index finger muscles. J Biomech 16:419-425, 1983. ligament anatomy and presence of arthrosis. J Hand Surg 26A:428-436, 2001. 5. Chao EYS, An KN, Cooney WP, Linscheid RL: Biomechanics of the hand. A basic 15. O’Driscoll SW, Horii E, Ness R, Cahalan TD, Richards RR, An KN: The relationship research study. Singapore, 1989, World Scientific. between wrist position, grasp size, and grip strength. J Hand Surg 17:169-177, 1992. 6. Dobyns JH, Linscheid RL, Chao EY, Weber ER, Swanson GE: Traumatic instability of the wrist. In A.A.O.S. 1975. St. Louis, MO, 1975, C.V. Mosby, pp. 182-199. 16. Patterson RM, Nicodemus CL, Viegas SF, Elder KW, Rosenblatt J: High speed, three dimensional kinematic analysis of the normal wrist. J Hand Surg 23A(3):446-453, 7. Horii E, Garcia-Elias M, Bishop AT, Cooney WP, Linscheid RL, Chao EY: Effect on force 1998. transmission across the carpus in procedures used to treat Kienböck’s disease. J Hand Surg Am 15A(3):393-400, 1990. 17. Stegink Jansen CW, Simper VK, Stuart HG Jr, Pinkerton HM: Measurement of maximum voluntary pinch strength: effects of forearm position and outcome score. 8. Kaufman KR, An KN, Chao EYS: Incorporation of muscle architecture into muscle J Hand Ther:16:326-336, 2003. length-tension relationship. J Biomech 22:943-948, 1989. 18. Viegas SF, Patterson RM, Hokanson JA, Davis J: Wrist anatomy: incidence, 9. Lin GT, Amadio PC, An KN, Cooney WP: Functional anatomy of the human digital distribution and correlation of anatomy, tears and arthritis. J Hand Surg flexor pulley system. J Hand Surg Am 14A:949-956, 1989. 18A:463-475, 1993. 10. Mitsuyasu H, Patterson RM, Shah M, Buford W, Iwamoto Y, Viegas SF: Role of the 19. Viegas SF, Yamaguchi S, Boyd NL, Patterson RM: The dorsal ligaments of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand wrist: anatomy, mechanical properties, and function. J Hand Surg 24A(3):456-458, Surg 29(2):279-288, 2004. 1999.

6cC H A P T E R and the hand that are considered tools of the trade, with atten- tion to each instrument’s stage of development and achieved Functional Evaluation reliability and validity. Although it is assumed that the use of of the Wrist and Hand reliable and valid tests increases the statistical probability for making correct clinical decisions and predictions about per- Jane Bear-Lehman formance potential, we are cautioned to not rely exclusively on these functional impairment or functional performance quanti- MULTIDIMENSIONAL ASSESSMENT PROCESS tative data alone. Qualitative data in terms of behavioral response, FOR THE WRIST AND HAND such as personal attitude and response to pain, fear, and loss of control, often influence the quantitative wrist and hand A comprehensive multidimensional assessment plan for the wrist functional evaluation results.10 Furthermore, in today’s clinic it and hand requires the selection and use of many different types is essential to have outcome documentation, including infor- of evaluation instruments to measure the outcomes of the mation about the patient’s health status, function, and overall patient’s health status, impairment level, functional limitations, satisfaction level, to understand the different kinds of results.3 and disability status. Assessment focuses on the outcome levels for those variables that can change because of time, treatment, The clinical assessment of a patient with a musculoskeletal or disease.27 Often generic or condition-specific self-report disorder affecting the wrist and hand follows a biomechanical questionnaires are now selected to measure health, function, and frame of reference to evaluate the results or outcomes. The prob- disability status from the patient’s perspective, and performance- lems are identified by gathering and then synthesizing subjec- based instruments known as the tools of our trade still provide tive, observational, and objective information about the patient to data about functional impairment and limitations. determine the quality of the result and the level of satisfaction.3 This information is derived from the patient, the clinician’s Clinical assessment of the wrist and hand is both a quanti- observation of the patient visually and through touch (palpation), tative and a qualitative process. Its aim is to help the clinician and the outcome measures the patient achieves on administered construct and then monitor the effectiveness of the treatment self-report and performance-based tests. The assessment relies on plan, the progression or the prevention of the disease or injury, the patient’s effort and voluntary cooperation with clinical stimuli, and the health status over time. Treatment of a patient who has inquiries, and directives. sustained a musculoskeletal occupational injury of the wrist and hand focuses on helping the patient achieve maximal function To begin the assessment, the clinician gathers a history from of both body and limb and regain independence in ordinary the patient’s perspective about the nature and the course of the activities of daily living while restoring health status. injury, prior medical and therapeutic attention sought, and success of these interventions. This report from the patient’s perspective Occupational musculoskeletal wrist and hand injuries can is compared for congruity with the written medical history. result from direct or indirect trauma in the workplace. The injury The clinician poses many questions about life-style adjustment, affects the musculoskeletal system, which includes the bone, its to document the alterations but more so to appreciate the joints, and their related structures: muscles, tendons, ligaments, patient’s ability to recognize, understand, and function within nerves, and arteries. Direct trauma injuries are usually a medical the restrictions imposed by the present physical problem(s). emergency; they have a date, time, and place of injury and may Patients are therefore asked to describe how the impact of the result from a fall in the workplace or adverse physical contact injury has affected their life-styles, namely, the changes in ability with tools or machinery. Indirect trauma is microtrauma to the to perform ordinary activities of daily living at home, at work, muscles, tendons, ligaments, nerves, or arteries that persists and and at leisure.25 The course, location, duration, and type of pain develops over time. The physical performance assessment of a are addressed through standardized questionnaires, such as the patient with direct or indirect trauma to the wrist and hand McGill Pain Profile or the Visual Analog Scale, to detect painful focuses specifically on the injured and adjacent body parts as reaction, patterns about the patient’s pain, and methods to appropriate for the medical and surgical stage of recovery; these control it.11,30 results are compared with function of the uninjured limb, if available. Outcome self-report instruments are administered to measure health status and function; some of the measures include infor- Several performance-based instruments that produce quanti- mation about pain level, performance of activities of daily living, tative measurements are used in the therapeutic setting to assess and satisfaction level. Generic or condition-specific scales in the functional impairment level, including range of motion self-report instruments are selected to help standardize the func- (ROM), muscle performance, edema (limb size), and sensation; tional assessments. These tools provide the clinician, the patient, functional limitations are assessed using instruments that meas- and others with basic functional information that is meaningful ure activities of daily living, dexterity, and physical capacity. This and helps serve as a screen at the outset of treatment.3 The chapter reviews the performance-based measures for the wrist SF-36, a widely used generic scale, measures health status in 36 items addressing key elements such as physical function, physical role, bodily pain, general health, social function, and emotional role.40 Many suggest that when assessing a patient with a wrist or hand injury, the highly regarded SF-36, with its impressive reliability and validity, should be combined with a more condition-specific instrument, of which several are avail- able for selection.8 Care in selection increases the quality of

228 Chapter 6c ● Functional Evaluation of the Wrist and Hand responsiveness and meaningfulness of the information. Attention of the wrist and the hand for actual measures of ROM, edema, should be directed to condition-specific regional self-report tests muscle performance testing, sensation, and pain, as follows. on function and health status such as the DASH (disabilities of the arm, shoulder, and hand), the Michigan Hand Questionnaire, Range of motion or the Upper Body Musculoskeletal Assessment for patients who have upper limb injuries.8,15,24 More focused questionnaires are Since the 1940s, clinicians have been reporting their use of appropriate for specific conditions, such as the Patient-rated the goniometric system to obtain accurate information about Wrist Evaluation Questionnaire for those who have sustained a patients’ joint status and movement capacity. Although techni- wrist fracture and the Carpal Tunnel Syndrome Questionnaire cally not a standardized assessment tool, the universal goniome- for individuals recovering from that syndrome. When matched ter is the most widely selected tool for measuring joint ROM. with the patient who has the targeted diagnosis, these highly The American Academy of Orthopaedic Surgeons guide is used specific instruments are more responsive than the DASH or the as a reference for normative values.4 In terms of reliability, SF-36.3,27 Hamilton and Lachenbruch20 found no difference in the results of determining joint angles with different goniometers. The reli- In the biomechanical component of the clinical hand and ability of readings by the same tester over time has shown a wrist assessment, the clinician observes the patient’s posture and 5-degree error when measuring joints in the wrist or the hand. attitude of the injured wrist or hand and its adjacent structures The method of recording continues to follow the Academy to answer the following questions: Is the patient favoring a guideline in which minus sign notation is used to show an exten- posture to protect the injured part from environmental contact sion limitation and a plus sign indicates hyperextension. through upper extremity flexion and adduction? Is there biome- chanical alteration in the body to compensate for the poverty The American Society for the Surgery of the Hand accepted of movement or the increase in pain? Is there symmetry in size the method of reporting goniometric scores in terms of the total and shape between the injured and uninjured wrist and hand? arc of movement at a given joint or a related series of joints. Does the body move symmetrically? What are the preferred Use of the arc measurement system for the digits is reported as postures during static positions such as sitting? What are the total active movement and as total passive movement for the transition patterns, that is, moving from sitting to standing, and summation of the angles of the three joints in each digit.14,18 the dynamic patterns of movement such as walking? What is That is, the total active movement or total passive movement the quality of movement at the injured site and in the adjacent represents the summation of the amount of movement available structures? Is there a change in coloration at the injured site; in all three joints, the metacarpophalangeal, proximal interpha- does the coloration vary? Palpation of the skin gives the clinician langeal, and distal interphalangeal, with full ROM yields a score more information about the skin’s temperature, the presence of approximating 260 degrees. This composite measurement does nodules, and the tightness of muscle-tendon units. not isolate the individual joint that is creating the deficit, but it is suited for graphic representations of the patient’s performance Physical or anatomic measurement is a continuous and ongo- over time; it is very useful after a tendon or nerve repair. ing process; it is carefully coordinated and monitored with the stage of healing, the plan for movement during healing, and the ROM measurements are conducted on the adjacent joints in trajectory of recovery. Physiologic changes can and do occur the acute stage of recovery; deficits in the adjacent joints that quite rapidly during the acute stage.18 Objective measures provide were not present before the injury are remediated in therapy. the treating clinician with information about the effectiveness of Depending on the nature of the injury and the medical or surgi- a given treatment, confirm the need to continue with a given cal protocol, measurements may be taken for active or passive treatment regimen, or signal the need for revision if the progress ROM at the injury site immediately or may be deferred until or response is not as anticipated. The data are used to justify the the integrity of the joint or the surrounding tissue allows a meas- need for continuation of treatment or the consideration of other urement. ROM assessment of the injured joints depends on therapies. the type of protection and stabilization used for healing. If com- plete rest of the injured region is required, measurements are CLINICAL ASSESSMENT OF THE delayed until movement is permissible. If controlled movement MUSCULOSKELETAL SYSTEM at the injured site is allowed, the clinician measures the type of movement (active or passive) within the range allowed and Physical performance measurements provide the clinician with restricts movement beyond the prescribed arc. information on the functional impairments affecting the wrist and the hand. These measurements rely on familiar hand care Edema tools of the trade; some of the tools or instruments, such as goniometers for measuring active or passive range of motion, Trauma or surgery is frequently followed by an abnormal accu- have remained the same. Others have been further developed mulation of fluid in the interstitial spaces of tissues, resulting in to improve the reliability of the measurement: Hydraulic pinch an increase in limb size. This edematous state limits ROM and, meters have replaced spring gauges, for example. Tools have ultimately, function. Measurement of wrist and hand size circum- also been redesigned to improve the quality of measurements, as ferentially with a tape measure is often done at three locations: in the continual instrument development for the measurement proximal to and distal from the edematous part and over the of light-touch deep pressure sensory response or two-point discrim- edematous part. To allow for a more valid comparison of ination testing. Functional impairment requires the assessment

Chapter 6c ● Clinical Assessment of the Musculoskeletal System 229 sequential measurements, anatomic landmarks are used as refer- Figure 6c.2 Finger circumference gauge is used for consistent ence points for placement of the tape measure. Placement and measurement in inches or centimeters. (NC70157-95: Courtesy of tension of the tape measure or finger gauge affect intertester and North Coast Medical, Inc., Morgan Hill, CA.) intratester reliability. In the past, clinicians have used jewelers’ rings to help reduce the measurement error related to tension on the tape measure. Now clinicians rely on the Gulick tape, which has a unique spring gauge, or the finger circumference gauge for more consistent measurements for repeated measures (Figs. 6c.1 and 6c.2). Because edema may be not localized in a digital segment but more generalized over the hand and arm, a volumeter method is preferred to accurately measure edema changes in the hand and wrist (Fig. 6c.3). The volumeter, based on Archimedes’ principle of water displacement, is used to measure composites of hand mass. Waylett and Seibly41 documented 10-ml test-retest reliability when the manufacturer’s guidelines are followed.23 Normative values for any of these measures are not available; the contralat- eral side is used as the approximate normal value for that patient. Because hand-size changes may be attributed to factors other than edema, such as normal asymmetry or muscle atrophy in the affected limb from disuse, care must be taken regarding generali- zation and interpretation of the findings. Muscle performance testing Muscle testing is used to evaluate the level of nerve injury and nerve The strength of muscle contractions can be measured clinically regeneration and preoperatively to determine potential donors in by means of spring scales, dynamometers, weights, or manual tendon transfer surgery. The manual muscle test designed by resistance. Manual resistance is added to voluntary maximal Lovett and Martin26 is a screening device that relies on the contraction once it has been established that the muscle exertion external forces of gravity and resistance to assess muscle strength. and the applied resistance will not adversely affect the healing bone, joints, and related structures. There is no agreement regarding whether isometric or isotonic contraction should be used in muscle testing or whether testing scores are best derived from the muscles’ isometric contractibil- ity under load at the end of the range, which is often chosen as the point for applied resistance.22 Few discrepancies are found in Figure 6c.1 Gulick tape measure has a unique spring gauge to Figure 6c.3 Hand volumeter is used to measure changes in provide consistent measurements. (NC70170-95: Courtesy of North hand size. (NC70310.00: Courtesy of North Coast Medical, Inc., Coast Medical, Inc., Morgan Hill, CA.) Morgan Hill, CA.)

230 Chapter 6c ● Functional Evaluation of the Wrist and Hand manual muscle testing procedures. Hislop et al21 used a gravity- Figure 6c.5 The hydraulic pinch gauge gives accurate and consistent eliminated position to test metacarpophalangeal joint extension, whereas Kendall et al22 did not distinguish the effect of gravity results, and like the Jamar dynamometer it can be calibrated. in the hand. The scoring methods of Lovett and Martin26 and Brunnstrom and Denner13 continue to be used: 0 (zero), 1 (trace), (NC70141_03: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.) and 2 (poor) represent test results in the gravity-eliminated posture; 3 (fair) uses the external force of gravity; and 4 (good) and 5 the hydraulic instruments. If regularly calibrated, the hydraulic (normal) add the dimension of resistance. Overall, reports of hand strength instruments have been shown to be reliable and reliability are descriptive. No predictive validity has been estab- produce consistent measurements.7,18 Both grip and pinch hand lished for grip and pinch scores, although many are hypothe- strength instruments allow for readings in kilograms-force and sized, nor is hand function predictive. pounds-force. Functional hand strength is measured by grip and pinch tests. The literature shows a variety of test procedures that can In the case of a distal forearm, wrist, or hand fracture, measure- have an impact on interrater and intrarater reliability, as well as ments are deferred for at least 2 to 4 weeks after the removal of on its normative data pool.29 The American Society for the immobilization. Hand strength measurement is the most com- Surgery of the Hand and the American Society of Hand Clinicians mon standardized assessment using hydraulic dynamometers. accept the seated posture with humeral adduction and neutral Figure 6c.4 shows the use of the Jamar hydraulic dynamometer humeral rotation, the elbow flexed to 90 degrees, and the fore- to measure hand-grip strength. Pinch patterns are measured arm and wrist in neutral position as the desired body posture for using the hydraulic pinch meter (Fig. 6c.5). Spring pinch gauges grip testing.28 are not recommended because they cannot be calibrated and have yet to prove as reliable or consistent in measuring as Norms have been established for age 5 to adulthood. Healthy adult grip strength values for the five handle positions, when providing full voluntary effort, yield a normal bell-shaped curve.36 The first position, the closest, is the least advantageous because it relies primarily on the ulnar nerve-innervated hand intrinsics, whereas the widest or fifth position relies on the median nerve- innervated long finger flexors. Middle-range handle positions require the intrinsic and extrinsic musculature to work together. A patient without neural or tendon damage who has a flattened curve may be suspected of providing submaximal voluntary effort. The traditional pinch patterns of lateral, palmar (also known as tripod or three-jaw chuck), and tip pinch are reported as the average of three trials for each type of pinch. The normative data tables are described on the basis of age and gender for both grip and pinch. Three test trials are recorded for each grip and pinch pattern tested. The mean (average of the three), the standard deviation, and the coefficient of variation (standard deviation/average) are computed to monitor the consistency or sincerity of effort.32,33,36 Figure 6c.4 The handheld Jamar dynamometer records grip strength Sensation in kilograms-force or pounds-force. The hand is a complex organ whose function depends on har- mony between sensory and motor abilities.16 Sensory testing

Chapter 6c ● Clinical Assessment of the Musculoskeletal System 231 can frequently identify sensorineural changes earlier than tradi- Figure 6c.6 The Touch-Test Sensory evaluators (Semmes-Weinstein tional motor examination. Studies have shown, for example, that monofilaments) are individually calibrated and accurately measure light in median nerve entrapment at the carpal canal level, sensory touch-deep pressure. (NC12757: Courtesy of North Coast Medical, changes precede motor changes. Clinical tests of vibration and Inc., Morgan Hill, CA.) Semmes-Weinstein monofilament testing show changes earlier than electromyographic studies because the latter does not show Touch-Test Two-Point discriminator provides the opportunity the process of change. Many of the tools used clinically to test for clinicians to have all points of measure on a single disk sensation are being revised and improved, and because of (Fig. 6c.7). Studies show that the amount of pressure offered the changes offered by microsurgery, more patients now have when two points are applied can be very different from that of greater potential to achieve sensory results of higher quantity and just one. quality. The ability to perceive vibratory stimuli is clinically valuable Sensory testing of a patient with a wrist and hand injury when the patient has undergone nerve repair or when nerve addresses the ability to perceive light touch and deep pressure, compression or a peripheral neuropathy is suspected. The 30-Hz to discriminate touch, and to detect vibration. To monitor the and 256-Hz tuning forks continue to be used to test for vibratory progress of a patient’s sensory status, particularly if a neural response. Clinical studies have proposed that both the 30-Hz injury is suspected, it is advisable to use instruments that yield and the 256-Hz tuning forks be used because it is believed ordinal rather than nominal data. Early methods to test light touch and deep pressure called for the use of a cotton ball or a Figure 6c.7 The Touch-Test Two-Point discriminator allows for cotton-tipped applicator. This form of testing yields the results two-point discrimination testing in one unit. (NC12776A: Courtesy of that the patient perceived the touch or is normal, may not North Coast Medical, Inc., Morgan Hill, CA.) have perceived or appreciated the stimulus fully or is impaired, or did not perceive the stimulus at all or is absent. This hierarchy represents an ordinal-level data system ranging from normal to absent response levels; the increment between the values is not known, nor is it equal. Abnormal results need to be monitored during the course of treatment. It is expected that sensitivity over scars and pin tracks is heightened. The deep pressure-to-light touch interval hierarchy for sen- sation in the hand resulted from the findings of von Frey,39 a surgeon who had a passion for learning about sensation and a love of horses. von Frey discovered that some of his patients could detect only the sensation of thicker horse hairs when applied to their skin surfaces, and as they healed, they could begin to feel finer horse hairs. The horse hairs that were first used are now 20 calibrated nylon monofilaments graded in diameter and individually attached to Plexiglas handles. The amount of force transmitted is related directly to the diameter of each fila- ment, which bends at a specific force controlling the magnitude of the touch-pressure stimulus.9 Weinstein42 developed a smaller more portable version of his original test, the Weinstein Enhanced Sensory Test (WEST), for ease of use in the clinic. Now clinicians use either the WEST or the Touch-Test Sensory Evaluators. The latter are individually calibrated within a 5% standard deviation of the predetermined targeted force. No other commercially available “monofilament type” testing device meets this scrutiny (Fig. 6c.6). The larger set of 20 still provides greater specificity for those patients who require it. To test for discriminatory touch sensation, the static or station- ary two-point discrimination instrument continues to be chal- lenged. The original Weber two-point discrimination instrument’s sliding scale allowed for adjustment of the spacing between the two points; however, the adjustment often did not allow the same precision as a tool with fixed points. Some practitioners open up paper clips to approximate distances, which leads to variability in spacing and uneven pressure between points. The two-point discrimination instrument, the Diskcriminator, designed by Dellon et al,17 controls for the precision between points and provides even application when two points are applied, and the

232 Chapter 6c ● Functional Evaluation of the Wrist and Hand that each elicits the response of an individual sensory neurite of the health and function status at the outcome evaluation by receptor. The 30-Hz fork is believed to evoke the response of the use of the McGill Pain Questionnaire or the Visual Analog the Meissner corpuscle and the 256-Hz fork from the Pacinian Scale,11,30 and it is monitored as treatment progresses. The patient corpuscle.16 Whether the prong or the stem should be applied is asked to describe the type, location, and threshold of pain per- to the skin surface is often debated; in either event, the lack of ceived before, during, and after each therapy session. Perception control of amplitude and variability in technique make the reli- of pain varies from one patient to the next with the same injury ability of the test inconsistent.7 Furthermore, the patient may as well as for the same patient over time. The clinician must also hear the sound of the tuning fork before perceiving it on the skin observe and address signs that may be causing pain, such as a surface, confounding the response. Only ordinal data are gleaned constrictive dressing, cast, or splint or an infection. Pain may and from this form of testing. often does occur at the onset of therapy; this form of pain is localized and should subside within 2 hours of the session. A vibrometer with a fixed frequency level provides a result measured in microns of motion at 120 c/s (Fig. 6c.8). The data FUNCTIONAL ASSESSMENT OF THE are interval and therefore quantifiable, allowing for specific MUSCULOSKELETAL SYSTEM tabulation of progress. The raw score is a logarithmic function of probe displacement measured in volts that is converted mathe- Critical to the assessment process is to appreciate wrist and hand matically into microns. Normal expected values of the displace- use in terms of functional limitations that result from the injury ment for skin surface are presented in an anatomic diagram and and to monitor change. Information about functional limitations table format. This instrument requires the use of an electrical can be derived from the self-report questionnaires such as the outlet and is not as readily portable as other hand assessment generic SF-36, the condition-specific DASH, or the diagnosis tools that fit into a laboratory coat pocket. condition-specific Patient-Rated Wrist Evaluation. Performance tests are administered, and the scores are compared with the Pain normative tables, if available. The performance scores can be compared also with the self-report questionnaire findings. Less Observed during the course of the assessment, pain can be often, clinicians may consider direct observation performance monitored over time in several ways. Pain is measured as part measures for activities of daily living; however, when this occurs, it is usually to resolve a specific concern or clarify a patient’s self-report. Figure 6c.8 The Bio-Thesiometer Vibrometer measures the threshold Information processing of appreciation of vibration. (Courtesy of Bio-Medical Instrument Company, Newbury, OH.) The patient comes to the medical setting mainly because of pain, fear, and disability.6 A satisfactory result depends not only on the technical skills of the team but also on the team’s ability to com- municate, engender confidence, and fully understand and explain the problem to the patient.12 It is necessary for the clinician to look at the process of therapy and the patient’s response to it. The clinician helps the patient by designing a learning environ- ment that emphasizes the salient traits and the characteristics of the problem to be solved or the condition to be learned. One method is to engage the patient in metacognitive experiences, that is, conscious thinking and awareness of feelings that accompany and pertain to the problem-solving task.1 Flavell19 defined metacognitive knowledge as information or beliefs about the course and outcome of the cognitive enterprise in three areas of cognitive awareness: person, task, and strategy. Every patient has a different level of cognitive awareness and a variety of beliefs, feel- ings, understanding of goals, and strategies for problem solving. In therapy, practice or instructional programs are systemati- cally used with a focus on the process rather than the content.35 Each task is analyzed relative to its repetition, imitation, and substitution. The training is assessed for the patient’s need to have cues or anchors and intermodal training and for the patient’s performance in a novel or new learning situation. How the patient accepts and responds to the information that has been shared is viewed in more than just a physical sense. Fear, pain, or side effects of medications often intervene in the patient’s ability to orientate to the therapy situation and to

Chapter 6c ● Functional Assessment of the Musculoskeletal System 233 focus attention (alertness); this also affects the patient’s ability patient’s job are delineated to develop the requirements for to learn. A patient in pain may find one voice instrumental in return to work and the goals for therapy. As treatment progresses, helping to learn the new way of moving the wrist. A verbal, the patient’s performance level is reviewed and compared visual, or kinesthetic voice (cue) from the clinician may be suffi- with the levels needed for safe return to work. The feasibility of cient as the patient learns to move the wrist and hand again. Two meeting the physical demand levels in terms of essentially voices, visual and verbal, may be needed, or the two voices may required dexterity, strength, or physical endurance are determined bombard the patient’s ability to concentrate if given at the same during the rehabilitation process. time because of the high threshold of pain. By observing how the patient learns to move again and how feedback is obtained Dexterity and used,2 the clinician determines whether the patient is reliant on others for direction and guidance to perform tasks or is self- Commonly defined as skill and ease in using the hands, dexterity directed and self-regulated.35 It is important to know whether is considered a functional limitation when impaired. To assess the patient can detect an error in movement alone, how the error manual dexterity or physical functioning efficiently, the examiner is corrected, and what kind of reinforcement is required. must select the standardized test that suits the patient’s abilities and needs. Most have a high index of reliability (greater than The clinician also observes the patient’s ability to cope with 0.75) and show good face and content validity; little has been the injury. After guidance in how to select and terminate activities done on concurrent validity or predictive validity, which is that correspond to the patient’s stage of healing, the clinician most needed for the clinical decision-making process.6 Predictive observes how the patient follows such guidelines in performing validity determines whether the patient, based on the perform- ordinary daily tasks, in participating in rehabilitation, and in ance on the test, is ready to return to work. Dexterity tests can assuming societal and family roles. The patient is observed for be classified by their demand for fine to gross motor movement the ability to adhere to safety precautions and exhibit self- patterns, requirement of one hand or integration of both to control in terms of physical limitations and reactions to pain. perform the task, requirement of a tool for their administration, and length of time the test takes to perform. Activities of daily living The Moberg Pick Up test can be classified as a sensory and The quantity and the quality of the patient’s performance of dexterity test because it brings together the sensate and motor activities of daily living are ascertained by interview. Information functions. This test is usually performed with unrestricted vision from the self-report health and functional status can be used and with vision occluded, and the patient is timed as the famil- or an additional inquiry may be conducted for more specific iar objects are scooped, handled, identified, and placed in a information as warranted. For problematic deficit areas, the designated location. clinician may observe the patient’s actual performance. Early in the healing process, when medical restrictions are in place as The Nine Hole Peg Test (Fig. 6c.9), the Purdue Pegboard (see to the amount of movement or force allowed at the site of injury Fig. 6c.10), the O’Connor Tweezer Dexterity Test, the O’Connor or the ability of the injured part to get wet, the patient must be assessed for methods of accommodation in activities of daily Figure 6c.9 The Nine-Hole Peg Test quickly measures fine motor living.5 For patients with a wrist or hand injury, this may require dexterity. (NC34547.d1: Courtesy of North Coast Medical, Inc., an assessment of eating, personal hygiene, dressing, bathing, Morgan Hill, CA.) and communication. Adaptive methods and devices may be indicated temporarily to facilitate one-handed methods, such as using a rocker knife for cutting meat or a button-hook for fasten- ing buttons, or the clinician might suggest purchasing precut or prepared foods. During the course of the rehabilitation program it is impor- tant for the clinician to guide the patient as to when and how the injured wrist and hand can be safely reintegrated into the performance of activities of daily living corresponding with the clinical progress. The first reintegration is in the performance of personal activities of daily living. When strengthening is intro- duced into the clinical program, the clinician needs to consider the patient’s need to perform such instrumental tasks, including those related to meal preparation, household management and shopping, and care of others. For many patients, work during the acute phase of recovery may not be possible due to extensive manual demands on the job, whereas others may not have a work interruption. For those who are working, the clinician identifies the components and demands of the patient’s job by interview and helps the patient assume those tasks that correspond to the achieved clinical status. For those unable to work, the demands essential to the

234 Chapter 6c ● Functional Evaluation of the Wrist and Hand Figure 6c.10 The Purdue Pegboard Test has four subtests: right hand placement, left hand placement, use of the hands in parallel, and, as shown, integrated use of the two hands on assembly. Finger Dexterity Test, and the Crawford Small Parts Test are all Figure 6c.11 The Minnesota Manual Dexterity Test measures eye- examples of fine-motor dexterity movement patterns. However, hand-finger movement in two subtests: one-handed placement and two- the Nine Hole Peg Test and the Purdue Pegboard Test are short handed turn and placement. (NC70030-96: Courtesy of North Coast tests that do not provide information about endurance; the Medical, Inc., Morgan Hill, CA.) Purdue Pegboard Test does require the use of one hand as well as that of both hands in a parallel and in an integrated fashion, The patient is observed for safety relative to the injured part, as shown in Figures 6c.9 and 6c.10. The O’Connor Tweezer him or herself, and others. Dexterity Test and the Crawford Small Parts Test both require the use of a small tool to handle and manipulate the test parts. Physical capacity evaluation The former requires the use of small tweezers, and testing is completed on the use of one hand at a time for all functions; the Most physicians and clinicians use a physical capacity evaluation latter requires the use of tweezers or a screwdriver in one hand to try to answer the question of whether a patient can safely while the alternate hand is assistive. The Minnesota Manual return to work. The capacity to perform work may be directly Dexterity Test (Fig. 6c.11) and the Bennett Hand-Tool Dexterity related to achieved physical performance but is more complex Test assess gross motor function; the former requires the patient due to the contribution of both philosophic and psychologic to handle the test items directly, whereas the latter requires issues.34 Many sophisticated instruments are available to assist the use of ordinary mechanic’s tools. Both allow for the direct in the evaluation process, but the level of validity for these use of both hands during some of the test components. Many instruments is less than is often required. Performance on these of the Valpar38 Corporation Work Samples (VCWS) are well suited systems is interpreted in a variety of ways, including MTM (motion- to assess precise finger and hand movements. In particular, times-measurement) standards, U.S. Dictionary of Occupational the VCWS 1 small tools (mechanical) work sample38 is helpful in Titles Worker Qualification Profiles37 or U.S. Department of Labor assessing the use of small tools in tight or awkward spaces requiring O*NET.31 The theoretical model that is followed is Parson’s trait use of the hand(s) without direct visual monitoring. factor from the early 1900s in industrial engineering. The proce- dure is to identify the traits that the patient now has physically, The outcome scores for manual dexterity performance are behaviorally, and cognitively; to keep symptoms under control reported as the amount of time (the speed) that the patient to work safely and effectively; and to match these to envi- required to perform the task, and the increments of time are ronmental factors, including the design of the work station, to compared with normal data based on age, gender, and occupa- determine safe maximum levels of functional work ability in tion published in the test manuals. The clinician also reports the work force. the preferred prehensile patterns used during the course of the tasks and the control the patient had over performance. Observations SUMMARY of motor control are discussed relative to the patient’s safe use of the injured part, biomechanical alignment of the injured part Success and satisfaction in rehabilitation of the wrist and the relative to the body, postural accommodation of the body to hand is measured by the patient’s ability to use the injured the injured part, and quality of task performance. Qualities of concern include the patient’s ability to integrate both the injured hand or wrist and the principles of joint protection sponta- neously into the dexterity pattern and the ability of the two hands to work together as a dominant and subdominant pair.

Chapter 6c ● References 235 part spontaneously in usual, customary, and ordinary activities. 15. Chung KC, Pillsbury MS, Walters MR, Hayward RA: Reliability and validity testing of Instruments that produce reliable and valid data assist in account- the Michigan Hand Outcomes Questionnaire. J Hand Surg 23A:575-587, 1998. ability for the assessment of upper extremity function and restora- tion of health status. The art of practice requires awareness and 16. Dellon AL: Evaluation of sensibility and re-education of sensation in the hand. documentation not just of the patient’s quantitative wrist and Baltimore, 1981, Williams & Wilkins. hand dysfunction characteristics, but also of the qualitative ones. To move effectively and efficiently, the patient needs to learn 17. Dellon AL, Mackinnon SE, Crosby PM: Reliability of two point discrimination again how to do so in a controlled rhythmic way. Today’s measurements. J Hand Surg Am 12A:693-696, 1987. practice requires the clinician to use standardized assessments and report results or outcomes that are meaningful to the clini- 18. Fess EE: Documentation: essential elements of an upper extremity assessment cian, the patients, and all who have access to the information. battery. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and Using an outcome model allows the clinician to understand upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 263-284. what is happening to the patients who are treated. 19. Flavell JH: Metacognition and cognitive monitoring: a new era of cognitive REFERENCES developmental inquiry. Am Psychol 34:906-911, 1979. 1. Abreu BC: Evaluation and intervention with memory and learning impairments. 20. Hamilton GF, Lachenbruch PA: Reliability of goniometers in assessing finger joint In C Unsworth, ed: Cognitive and perceptual dysfunction: a clinical reasoning angle. Phys Ther 49:465-469, 1969. approach to assessment and treatment. Philadelphia, 1999, F. A. Davis, pp. 163-207. 21. Hislop HJ, Montgomery J, Daniels I: Worthingham’s muscle testing techniques of manual examination, ed 7. Philadelphia, 2002, WB Saunders. 2. Abreu BC, Peloquin S: The quadraphonic approach: a holistic rehabilitation model for brain injury. In N Katz, ed: Cognition and occupation across the life span: Models for 22. Kendall FP, McCreary EK, Provance PG: Muscles: testing and function, ed 4. intervention in occupational therapy, 2nd ed. Rockville MD, 2005. AM. Occ Therapy Baltimore, 1993, Williams & Wilkins. Assoc. 23. King TI: The effect of water temperature on hand volume during volumetric 3. Amadio PC: Outcome assessment in hand surgery and hand therapy: an update. measurement using water displacement method. J Hand Ther 6:202-204, 1993. J Hand Ther 14:63-67, 2001. 24. Kramer JF, Potter P, Harburn KL, Speechly M, Rollman GB, Evans D: An upper 4. American Academy of Orthopedic Surgeons: Joint motion: method of measuring and body musculoskeletal assessment instrument for patients with work-related recording. Chicago, 1965, The Academy. musculoskeletal disorders: a pilot study. J Hand Ther 14:115-121, 2001. 5. Appelby MA, Schkade JK, Gilkeson GE: Timing of ADL education with hand surgery 25. Law M, Cooper BA, Strong S, Stewart D, Rigby P, Letts L: Theoretical contexts for the patients. J Hand Ther 5:218-225, 1992. practice of occupational therapy. In C Christiansansen, C Baum, eds: Occupational therapy enabling function and well-being, ed 2. Thorofare, NJ, 1997, Slack. 6. Bear-Lehman J: Factors affecting return to work after hand injury. Am J Occup Ther 37:189-194, 1983. 26. Lovett RW, Martin EG: Certain aspects of infantile paralysis and a description of a method of muscle testing. JAMA 6:729-733, 1916. 7. Bear-Lehman J, Abreu BC: Evaluating the hand: issues in reliability and validity. Phys Ther 69:1025-1033, 1989. 27. MacDermid JC: Outcome measurement in the upper extremity. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 8. Beaton DE, Katz JN, Fossel AH, Wright JG, Tarasuk V, Bombardier C: Measuring the 2002, Mosby, pp. 285-296. whole or the parts? Validity, reliability, and responsiveness of the disabilities of the arm, shoulder, and hand (DASH) outcome measure in different regions of the upper 28. Mathiowetz V, Kashman N, Volland G, et al: Grip and pinch strength: normative data extremity. J Hand Ther 14:128-146, 2001. for adults. Arch Phys Med Rehabil 66:69-74, 1985. 9. Bell-Krotoski JA: Sensibility testing with Semmes-Weinstein monofilaments. 29. Mathiowetz V, Kashmen N, Volland G, Weber K, Downe M, Rogers S: Reliability and In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper validity of hand strength evaluation. J Hand Surg Am 9A:222-226, 1984. extremity, ed 5. St. Louis, 2002, Mosby, pp. 194-213. 30. Melzack R, Mathiowetz V, Weber K, Volland G, Kashman N: Reliability and Validity of 10. Brand PW: The mind and spirit in hand therapy. J Hand Ther 1:145-147, 1988. grip and pinch strength evaluations. The McGill pain questionnaire: major properties 11. Briggs M, Closs JS: A descriptive study of the use of the visual analog scales and and scoring methods. Pain 1:265-276, 1975. verbal rating scales for the assessment of post-operative pain in orthopedic patients. 31. O*NET on-line. Retrieved from http://online.onetcenter.org J Pain Sympt Manage 18:438-446, 1999. 32. Schectman O: The coefficient of variation as a measure of sincerity of effort of grip 12. Brown PW: The role of motivation in patient recovery. Conn Med 42:555-557, 1978. strength. Part 1. The statistical principle. J Hand Ther 14:180-187, 2001. 13. Brunnstrom S, Denner M: Round table on muscle testing. Annual conference of 33. Schectman O: Using the coefficient of variation to detect sincerity of effort of grip American Physiotherapy Association, Federation of Crippled and Disabled, New York, 1931. strength: a literature review. J Hand Ther 13:25-32, 2000. 14. Cambridge-Keeling CA: Range-of-motion measurement of the hand. In J Hunter, 34. Schneider LH: Impairment evaluation. In J Hunter, E Mackin, A Callahan, eds: E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp 169-182. Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 297-307. 35. Schwartz RK: Therapy as learning. Rockville, MD, 1985, American Occupational Therapy Association. 36. Stokes HM: The seriously injured hand: weakness of grip. J Occup Med 25:683-684, 1983. 37. U.S. Dictionary of Occupational Titles: Worker qualification profiles. Retrieved from www.oalj:dol.gov/libdot.htm 38. Valpar Corporation Catalog. Retrieved from http://www.valparint.com 39. von Frey M: Zur physiologie der juckempfindung. Arch Neurol Physiol 7:142, 1922. 40. Ware JE, Kosinski M, Keller SD: SF-36 physical and mental health summary studies: a user’s manual. Boston, 1994, The Health Institute, The New England Medical Center. 41. Waylett J, Seibly D: A study of the accuracy of a commercially available volumeter. J Hand Ther 4:10-13, 1991. 42. Weinstein S: Fifty years of somatosensory research: from the Semmes-Weinstein monofilaments to the Weinstein enhanced sensory test. J Hand Ther 6:11-22, 1993.

6dC H A P T E R is occasionally palpable as are small ganglia arising from the diseased compartment. The best objective tool in confirming Wrist and Hand: the diagnosis of de Quervain disease is the Finkelstein test. By Treatment Options maximizing the excursion of the tendons through the stenotic first dorsal compartment, this maneuver produces significant David M. Kalainov and Mark S. Cohen discomfort for the patient if the condition is present. Disorders of the wrist and hand are common in the work Conservative treatment options for de Quervain disease include environment.23 Effective management frequently depends on a splinting, corticosteroid injections, nonsteroidal antiinflamma- multidisciplinary approach with coordinated input from a physi- tory medication, temporary job modifications, and therapy. cian, hand therapist, and nurse case manager. This chapter Splinting alone may be beneficial for management of acute pain, reviews several wrist and hand conditions that may occur in but symptom recurrence is common. A single corticosteroid an occupational setting, including tendinitis, peripheral nerve injection into the first extensor compartment successfully relieves compression lesions, sprains, fractures, arthritis, ganglia, and pain in 60% of cases, whereas two injections may provide relief complex regional pain syndrome. The underlying pathologies, in up to 80% of cases. Because the soft tissue in this region is thin, diagnostic methods, treatment options, and projected outcome however, repeated corticosteroid injections, with infiltration into for the various conditions are discussed. the subcutaneous tissues, can lead to localized depigmentation, fat necrosis, and subcutaneous atrophy. TENDINITIS If conservative measures fail, surgical release of the first Tendinitis is a general term used interchangeably with tenosyn- extensor tendon compartment may be considered. Surgery ovitis, stenosing tenosynovitis, and tendovaginitis. A thin involves incision of the retinacular sheath and division of low-friction envelope that surrounds individual tendons, the any septae separating the abductor pollicis and extensor pollicis tenosynovium, enhances tendon gliding around bony promi- brevis tendons. Vigorous retraction or injury of skin sensory nences and through retinacular sheaths. Tenosynovitis, which nerves intraoperatively can cause periincisional pain and/or refers to inflammatory changes in this lining, is often associated numbness. A therapist may be helpful in the early postoperative with a systemic disease process. A more frequently encountered period with scar desensitization and strengthening exercises. condition, termed stenosing tenosynovitis or tendovaginitis, involves Release of the first dorsal compartment predictably leads to a thickening of the tendon and overlying retinacular sheath with satisfactory result in over 90% of cases. Patients are generally only a paucity of tenosynovial inflammation. de Quervain disease able to return to unrestricted employment within 6 to 8 weeks and trigger digit are two common examples. after surgery. Trigger finger The flexor tendons projecting to each digit enter a retinacular sheath that begins in the distal palm. Thickening of the tendons and sheath at this point may obstruct normal tendon gliding, leading to catching and locking of the digit (Fig. 6d.2). de Quervain disease The dorsal wrist is comprised of six retinacular compartments Figure 6d.1 Wrist and finger extensor tendons. The first dorsal encompassing the extensor tendons of the wrist and hand. compartment contains the abductor pollicis longus and extensor The first compartment, which contains the abductor pollicis pollicis brevis tendons (arrow). Painful restricted tendon motion through longus and the extensor pollicis brevis tendons, is located directly this compartment is referred to as de Quervain disease. over the styloid process of the distal radius (Fig. 6d.1). Painful restricted tendon motion through this compartment is referred to as de Quervain disease.19 de Quervain disease is frequently associated with activities involving repetitive flexion and extension of the thumb and ulnar deviation of the wrist. The condition is also associated with direct trauma, rheumatoid arthritis, gout, and diabetes mellitus. A subdi- vision of the compartment by a septum is thought to predispose some individuals to the development of this condition. A patient with de Quervain disease presents with symptoms of pain, swelling, and tenderness over the radial styloid. Pain can be quite severe, with guarding and limitation of wrist and thumb motion. Crepitation with thumb flexion and extension

238 Chapter 6d ● Wrist and Hand: Treatment Options area four fingerbreadths proximal to the radial styloid. Often, palpable and audible crepitus occurs in this region with active wrist motion. Other tendons occasionally involved by inflam- mation and stenosis include the flexor carpi radialis, the exten- sor carpi ulnaris, and the extensor pollicis longus. In these cases, nonoperative treatment measures that may include splinting, ice, corticosteroid injection(s), antiinflammatory medications, activity modifications, and therapy are usually successful. Figure 6d.2 Digital flexor tendon sheath. Thickening of the tendons CARPAL TUNNEL SYNDROME and sheath proximally may lead to triggering (arrow). The median nerve passes across the wrist through an unyielding Examination often reveals a tender nodularity in the distal palm fibroosseous canal, termed the carpal tunnel (Fig. 6d.3). that moves with excursion of the tendons.26 Compression of the median nerve within this space is termed carpal tunnel syndrome. The condition occurs due to a mismatch Conservative care of a trigger digit entails activity modifica- between the volume of the canal and its contents: the median tions and a corticosteroid injection into the proximal flexor ten- nerve and the nine digital flexor tendons. don sheath. Single finger involvement, a discreet palpable nodule, and a short duration of symptoms are favorable prognostic Carpal tunnel syndrome is associated with diabetes, hypothy- indicators. Splinting of the metacarpophalangeal joint for a brief roidism, rheumatoid arthritis, and renal failure. Other contribu- period may be added to the treatment regimen. In individuals tory risk factors include wrist fractures, aging, obesity, female whose symptoms are aggravated by the use of small tools, modi- gender, smoking, pregnancy, and alcoholism. In the workplace, fication of these instruments to distribute forces over a greater area carpal tunnel syndrome has been attributed to repetitive forceful with a lesser requirement for digital flexion may be beneficial. use of the wrist and digits, repeated impact on the palm, and operation of vibratory tools. Task-related factors, however, The reported success rates after an injection range from are variable and inconsistent, and the mechanisms by which they 60% to 84%. If conservative management fails, surgical treat- may contribute to carpal tunnel syndrome are poorly understood. ment may be considered. Incision of the proximal portion of the flexor tendon sheath in the palm is curative in over 95% of The diagnosis of carpal tunnel syndrome relies initially on cases. Most patients are capable of returning to unrestricted work the patient history.8 Symptoms may include tingling and numb- activities within 4 to 8 weeks postoperatively. ness in the thumb and central digits, burning pain, weakness, and clumsiness of the hand, all corresponding to the motor and sensory distributions of the median nerve. Symptoms often appear after prolonged wrist flexion while sleeping and extended periods of wrist extension while driving. Loss of sensation (in the radial four digits) and atrophy of the thenar eminence muscles are symptoms of advanced median nerve compression. Carpal tunnel syndrome is diagnosed primarily through physical examination, including evaluation of thenar muscle Other tendonopathies Figure 6d.3 Wrist magnetic resonance image, axial view. The carpal tunnel (white arrow) contains the median nerve and the nine flexor Intersection syndrome refers to tenosynovitis of the radial wrist tendons. The adjacent ulnar tunnel (black arrow) contains the ulnar extensor tendons where they cross the first dorsal compartment nerve and artery. tendons in the distal forearm. Pain is typically localized to an

Chapter 6d ● Hand-Arm Vibration Syndrome 239 bulk and strength and performance of sensibility testing. A vari- passes the ulnar nerve and artery. Compression of the ulnar nerve ety of provocative maneuvers is used to reproduce or accentuate at this site can occur from trauma, use of vibrational tools, ulnar the symptoms. Phalen’s test refers to placing the wrist in a fully artery thrombosis or aneurysm, or presence of a space-occupying flexed posture, whereas Tinel’s test refers to percussion of the lesion such as a ganglion cyst. Symptoms include intrinsic median nerve over the wrist. The median nerve compression test muscle weakness, numbness, and tingling in the ring and small involves direct pressure on the median nerve over the carpal fingers, or a combination of motor and sensory abnormalities. canal. An electrodiagnostic study may be obtained to confirm the diagnosis of carpal tunnel syndrome and to quantify the degree The diagnosis depends on a thorough physical examination of median nerve injury. and pertinent ancillary studies. The examination should include palpation, percussion, vascular and motor evaluations, and In the absence of diminished sensation, muscle atrophy, or sensory testing. Wrist radiographs are helpful in excluding a denervation potentials on electrodiagnostic testing, initial treat- hook of hamate fracture in patients with a history of trauma. ment for carpal tunnel syndrome involves splinting the wrist Magnetic resonance imaging (MRI) or an ultrasound study may in neutral alignment and injecting corticosteroid into the carpal be valuable in identifying a ganglion cyst, ulnar artery aneurysm, canal.11 A neutral wrist position relaxes the median nerve and or arterial thrombosis. An electrodiagnostic study can assist in maintains a low pressure in the carpal tunnel. Splinting and locating the anatomic site of compression and in determining injection provide short-term relief of symptoms in over 75% the severity of the nerve involvement. of patients and continued symptomatic relief for 1 year or more in 13% to 40% of patients diagnosed early with mild symptoms. If a specific etiology for ulnar tunnel syndrome is identified, Presence of symptoms for less than 12 months, intermittent treatment is directed toward the cause. Examples include excision numbness, male gender, absence of advanced sensory changes, of a space-occupying lesion, resection of an arterial aneurysm, and normal thenar muscle bulk are good prognostic indicators and repair or resection of a hook of hamate fracture. When no for success. cause is found, conservative treatment measures such as wrist splints, antivibration gloves, activity modifications, and non- Activity modifications and use of antivibration gloves are steroidal antiinflammatory medication are instituted. Surgery is encouraged in manual laborers.16 Associated systemic diseases considered in these patients only if the diagnosis is certain and such as diabetes and hypothyroidism should be recognized nonoperative modalities fail. The procedure involves decom- and appropriately managed. Ergonomic changes may be consid- pression of the ulnar nerve and artery in the proximal palm. ered for general patient comfort and satisfaction. Many recom- mended measures have not, however, been scientifically proven Most patients with ulnar tunnel syndrome without a struc- to prevent or ameliorate symptoms of carpal tunnel syndrome. tural lesion do well with nonoperative management. In patients managed surgically, assistance from an occupational therapist If patients experience only partial or temporary relief with may be beneficial in the early postoperative period. Most patients conservative treatment measures, surgical decompression of are able to return to previous employment activities in 6 to the carpal tunnel may be considered. Individuals who report at 8 weeks, with maximum medical improvement expected from least temporary relief after an injection are more apt to obtain 3 to 6 months postoperatively. similar relief from carpal tunnel release surgery.10 Newer tech- niques such as limited-incision carpal tunnel releases and those An uncommon cause of ulnar tunnel syndrome that deserves performed endoscopically have been developed to decrease special mention is the hypothenar hammer syndrome.6,9 This palm discomfort and allow for a more rapid return to activities. condition results from repetitive impact to the ulnar aspect of Compared with a standard open decompression, the endoscopic the hand leading to ulnar artery damage and formation of a procedure has been found to shorten the recovery period, but pseudo-aneurysm and/or clot. Clinical findings include local it may be associated with a higher reoperation rate and possibly tenderness and ischemic changes with numbness in the ring an increased risk of nerve injury.20 and small fingers. A pathologic Allen test with compression of the radial artery and impaired blood flow to the ulnar digits sup- Operative release reliably diminishes tingling in the digits, ports the diagnosis. The location of the lesion can be determined whereas improvements in numbness and weakness are less with ultrasonography, selective angiography, or MRI angiography. predictable. In patients with severe chronic nerve compression, it is not unusual to have permanent low-grade symptoms after Initial treatment of hypothenar hammer syndrome includes uncomplicated carpal tunnel release surgery. Palm sensitivity cessation of impact trauma to the hand, elimination of tobacco around the scar, referred to as pillar pain, is fairly common products, and avoidance of prolonged cold exposure. Arterial and can be helped by scar desensitization performed by an occu- thrombosis may be addressed nonoperatively in some indi- pational therapist. Activity restrictions in a manual laborer are viduals with injection of a thrombolytic agent or surgically in typically recommended for a period of 6 to 8 weeks after surgery, others by resecting the damaged vessel segment. Because of the with maximum medical improvement anticipated between 3 and potential for repeated thrombi formation and emboli to the dig- 6 months postoperatively. Successful carpal tunnel release surgery ital arteries, an aneurysm is best managed operatively. Although usually produces no permanent impairment. residual cold intolerance can be expected, the results of surgical treatment are generally good. ULNAR TUNNEL SYNDROME HAND-ARM VIBRATION SYNDROME Neuropraxia of the ulnar nerve at the wrist is referred to as ulnar Hand-arm vibration syndrome, or vibration white finger, is a tunnel syndrome.3 The ulnar tunnel, or loge of Guyon, is a complex condition associated with vibration exposure and fibroosseous space adjacent to the carpal tunnel through which the use of hand-held vibrating tools.14,18,22 Symptoms include

240 Chapter 6d ● Wrist and Hand: Treatment Options white fingers, sensory disturbances, reduced hand dexterity, and include wrist arthrography (Fig. 6d.4), MRI arthrography, and diminished grip strength. Additional symptoms may include arthroscopy. cold intolerance, wrist and hand pain, and muscle cramps. Vibration exposure has a cumulative effect on both vessels and Initial nonoperative management is indicated for acute and nerves. The duration of exposure necessary to elicit symptoms, stable scapholunate interval injuries. Individuals with partial however, has never been clearly defined. ligament tears and no clinical or radiographic evidence of carpal instability can be treated by temporary wrist immobilization. The diagnosis of hand-arm vibration syndrome is based on a A nonsteroidal antiinflammatory medication and a localized history of vibration exposure and the presence of symptoms. The cortisone injection may also be considered. Patients with chronic Stockholm workshop scales are widely used in assessing the scapholunate ligament tears and evidence of marked degenera- severity of this condition in affected individuals. Electrodiagnostic tive arthritis can be initially managed similarly. If symptoms and vascular flow studies are helpful in excluding other etiolo- persist beyond approximately 4 months, surgical options may gies such as an arterial thrombosis or peripheral nerve compres- be discussed. sion lesion, although separate conditions may coexist. In patients with acute and unstable scapholunate ligament Prevention of hand-arm vibration syndrome is of paramount injuries, early operative intervention is recommended. The deci- importance, with measures including use of well-padded antivi- sion to intervene surgically, however, depends on additional bration gloves and frequent breaks from operating vibratory factors, including patient age, health status and expectations, machinery. If symptoms develop, avoidance of the inciting tool(s) and anticipated compliance with postoperative care. Because is essential. Discontinuation of smoking, oral vasodilators, and most individuals who sustain an acute scapholunate interval limitation of cold exposure may be beneficial in reducing associ- injury are physiologically young and active, direct ligament ated digital vasospasms. In early stages, the condition is typically repair with capsular augmentation is perhaps the best means reversible, but in long-standing cases, blanching of the fingers of managing this injury. However, other surgical procedures may persist indefinitely despite avoidance of vibration exposure. SPRAINS A sprain constitutes an injury to one or more ligamentous structures stabilizing a joint. The complex anatomy of the wrist ligaments includes thickened bands of capsular tissue inter- connecting the distal radius to the distal ulna and carpal bones, along with deeper structures such as the scapholunate and lunotriquetral interosseous ligaments linking adjacent carpal bones. The finger metacarpal and interphalangeal joints are stabilized by medial and lateral capsular thickenings termed collateral ligaments and a strong palmar structure designated the volar (palmar) plate. Scapholunate interval Stability of the scapholunate interval depends on the integrity of Figure 6d.4 Wrist arthrogram. Radiopaque dye injected into the the scapholunate interosseous ligament and secondary capsular radiocarpal interval with leakage into the midcarpal and distal ligament restraints.31 A history of falling onto the affected hand radioulnar joints. The appearance is diagnostic for tears of the is often described in association with a scapholunate interval scapholunate and lunotriquetral ligaments and the triangular injury, the symptoms of which include dorsoradial wrist pain fibrocartilage complex (TFCC). and a weakened grasp. Occasionally, active wrist flexion against resistance produces a painful snapping sensation. The diagnosis is suspected when pain is elicited with finger pressure over the scapholunate interval. The scaphoid shift test is helpful in excluding other causes of dorsoradial wrist pain, such as a ganglion cyst. A positive shift test is noted if the proximal pole of the scaphoid can be translated over the dorsal rim of the radius under dynamic load. In the initial evaluation, plain radiographs are useful. If an abnormality in carpal bone spacing is detected, comparative views of the contralateral wrist are obtained to distinguish a normal variation in carpal spacing from pathologic carpal align- ment. In equivocal cases, fluoroscopic imaging can be helpful. Additional studies that may assist in making the diagnosis

Chapter 6d ● Sprains 241 have been described for treatment of both acute and chronic in the soft tissues distal to the tip of the ulnar styloid scapholunate interval trauma. Depending to a large degree on predictably elicits discomfort. Stress testing of the stabilizing the specifics of the surgery, the course of rehabilitation and the function of the TFCC is performed by applying dorsal and results of treatment vary. palmar pressure to the interval between the distal ulna and the carpus. Wrist radiographs are recommended to assess arthritic Lunotriquetral interval changes, carpal instability patterns, and ulnar bone length relative to the radius (ulnar variance). MRI with or without intraarticular Analogous to scapholunate instability, pathologic laxity of contrast may assist in the diagnosis. the lunotriquetral interval requires injury to both the lunotrique- tral interosseous ligament and the secondary capsular restraints.27 In most patients, initial treatment of a TFCC injury involves The spectrum of pathology ranges from partial ligament tears a variable period of wrist immobilization and possibly a corti- with retained carpal stability to complete dissociation with carpal sone injection into the ulnocarpal joint. Exceptions include the collapse. Symptoms may include pain and crepitus with dimin- rare traumatic tear with gross instability at the distal radioulnar ished wrist motion, grip weakness, and sensation that the carpus joint. These cases usually require early operative intervention. is giving way. In those individuals who fail conservative measures and have To differentiate a lunotriquetral interval injury from other significant symptoms, surgical intervention may be indicated. lesions that can cause ulnar-sided wrist symptoms, a careful Simple arthroscopic debridement is effective in the management examination is necessary. Palpation over the lunotriquetral joint of many traumatic TFCC lesions, especially central tears predictably elicits pain. A ballottement test, performed by grasp- (Fig. 6d.5). In individuals with positive ulnar variance or lunotri- ing the pisotriquetral unit between the thumb and index finger quetral instability, this can be combined with formal ulnar short- of one hand and the lunate between the thumb and index finger ening. Open or arthroscopically assisted repairs of a peripheral of the other hand, reproduces symptoms and may demonstrate tear have exhibited results similar to or better than debridement abnormal joint laxity. alone. The expected postoperative recovery period depends to a large extent on the details of the operation performed. After Plain radiographs are recommended in the evaluation of discontinuation of splint immobilization, all patients may ulnar-sided wrist pain. Lunotriquetral instability may not be benefit from a short period of therapy. Maximum medical readily apparent on standard radiographic images, however. An improvement is expected 3 to 6 months postoperatively. MRI arthrogram can assist in diagnosis and occasionally reveal other lesions contributing to the symptom complex. Initial management is typically nonoperative, involving activity modifications and a 4- to 6-week course of wrist immo- bilization. A midcarpal corticosteroid injection and short-term use of an antiinflammatory medication may be beneficial also. Most patients with isolated lunotriquetral ligament tears respond well to conservative treatment. Persistent pain localized to the lunotriquetral interval with failure of conservative management is an indication to intervene surgically. The result depends on a variety of factors, including chronicity of the injury, associated carpal arthrosis, and specifics of the operation performed. Surgical options include simple ligament debridement, shortening of the ulna to decompress the lunotriquetral joint, lunotriquetral ligament reconstruction, and lunotriquetral fusion. Poor response to a previous injection and/or immobilization is a strong indicator of a potential surgical failure. Triangular fibrocartilage complex The triangular fibrocartilage complex (TFCC) is a soft tissue Figure 6d.5 Wrist arthroscopy. structure composed of seven contiguous elements that combine to stabilize the distal radioulnar joint and suspend the ulnar carpus.15 Traumatic disruption of the TFCC can lead to ulnar- sided wrist pain, instability of the distal radioulnar joint, and articular cartilage degeneration. Patients typically describe pain and a clicking sensation localized to the ulnar aspect of the wrist after known injury or repeated microtrauma. Symptoms are often aggravated by fore- arm rotation and ulnar deviation of the wrist. Applied pressure

242 Chapter 6d ● Wrist and Hand: Treatment Options Gamekeeper’s thumb rupture treated early with surgery, more than 90% of patients can expect a good to excellent result. Disruption of the ulnar collateral ligament of the thumb metacarpophalangeal joint occurs when a significant valgus stress Fingers is applied to the joint,13 often from a fall on the outstretched thumb. The injury may result in metacarpophalangeal joint The finger metacarpophalangeal and interphalangeal joints instability, causing pain with thumb motion and adversely affect- may be injured by a variety of different mechanisms, resulting in ing both grip and pinch strength. Two terms commonly used partial or complete disruption of the collateral ligaments and to describe this injury are the gamekeeper’s thumb and the palmar plate. Although the closely conforming articular surfaces skier’s thumb. of the proximal and distal interphalangeal joints usually afford residual stability, the metacarpophalangeal joints are less anatom- The anatomy of the thumb ulnar collateral ligament is ically constrained and may exhibit pathologic laxity with injury analogous to that of the collateral ligaments stabilizing the fin- to identical periarticular structures. ger metacarpophalangeal and interphalangeal joints. The thumb ulnar collateral ligament ruptures most often from its distal The diagnosis of a finger sprain is relatively straightforward. insertion at the base of the proximal phalanx. Displacement of The involved joint exhibits variable swelling and limited motion the ligament can occur such that it comes to lie superficial and with maximum tenderness in the area of soft tissue injury. Gentle proximal to the adductor pollicis muscle, a specific pattern of stress may elicit visible or palpable joint instability. Assessment injury referred to as a Stener lesion (Fig. 6d.6). and documentation of neurovascular status commonly reveals a digital neuropraxia. Radiographs are valuable in excluding The diagnosis of a gamekeeper’s injury involves a careful the presence of a fracture, joint subluxation, or joint dislocation. examination of the involved thumb. Plain radiographs should Ultrasound and MRI studies may be considered but are often be obtained to assess for an underlying bone injury. Stress radi- unnecessary for initial diagnosis. ographs with applied valgus force to the metacarpophalangeal joint can confirm the diagnosis and determine the degree of A stable sprain of the finger metacarpophalangeal joint is ligament disruption. Treatment of partial ligament tears involves treated with buddy strapping and immediate motion. Velcro a 4- to 6-week period of thumb immobilization. A hand-based straps or athletic tape is placed around the injured digit and spica splint or cast incorporating the thumb proximal phalanx adjacent finger, leaving the interphalangeal joints free for motion usually suffices. A complete ligament tear is an indication for exercises. An unstable metacarpophalangeal joint may be surgical intervention; in these cases a Stener lesion may preclude managed by buddy strapping and/or immobilization in a hand- effective ligament healing with nonoperative treatment. The based splint for 4 to 6 weeks. The decision to intervene surgically thumb is commonly immobilized for 4 weeks postoperatively. depends on several factors, including the presence of an associ- Unrestricted activities are permitted after 6 weeks in cases treated ated avulsion fracture and residual joint instability with splint nonoperatively and after 3 months in patients managed surgically. immobilization. In thumbs with partial ligament injuries, nonoperative Sprains of the proximal and distal interphalangeal joints treatment yields a stable and painless thumb with near-normal are managed by finger extension splinting for a brief period fol- motion in most cases. In thumbs with a complete ligament lowed by active motion exercises and protective buddy strap- ping. Progressive static or dynamic extension splinting may be indicated during the course of treatment to address a developing joint contracture. Supervised therapy is often helpful. Most finger sprains can be managed without surgical inter- vention. Some degree of permanent swelling is expected, and a small flexion contracture may persist. The deformity will unlikely impair hand function or preclude a return to gainful employment. Figure 6d.6 Torn and displaced ulnar collateral ligament of the FRACTURES thumb metacarpophalangeal joint, termed a Stener lesion (arrow). This pattern of displacement is often responsible for failure of Distal radius nonoperative management of complete ligament tears. Distal radius fractures, commonly called Colles’, Barton’s, Smith’s, and Chauffeur’s fractures, account for 14% of all extremity injuries.12,24 Approximately 50% of these injuries involve the articular surface of the distal radius. In healthy and active individuals, restoration of bone and joint alignment is indicated to preserve function and to deter posttraumatic arthrosis. The initial examination should include an assessment for concurrent bone and soft tissue injuries with specific attention to the stability of the distal radioulnar joint. Although vascular compromise occurs rarely, neurologic symptoms are relatively

Chapter 6d ● Fractures 243 frequent and typically involve the median nerve in the carpal Scaphoid tunnel with paresthesias in the radial four digits. The scaphoid is the most commonly fractured carpal bone.7 Radiographic evaluation is performed both before and after This type of injury typically results from a sudden impact on the attempted closed fracture reduction (Fig. 6d.7). Assessment of palm with the wrist hyperextended, such as occurs with a fall the intraarticular extent of the injury is crucial. A residual joint onto the outstretched hand. When the fracture is complete, incongruity of 2 mm or greater displacement has been associated intrinsic forces may lead to displacement of a scaphoid fracture with posttraumatic arthrosis. Special imaging studies such as into a flexed humpback position: The proximal pole extends, computed tomography are useful when the fracture pattern whereas the distal pole flexes. and/or magnitude of displacement is difficult to determine on plain radiographs. Classically, the patient presents with loss of wrist motion, snuff box tenderness, and pain with resisted forearm pronation Closed stable fractures in acceptable alignment can be treated and supination. Wrist swelling may be present, but this and nonoperatively. Serial radiographs are obtained, and a cast is other signs of local trauma are not always apparent. In many worn for approximately 6 weeks, followed by the use of a tem- instances the presentation and diagnosis are delayed, with the porary removable splint. Supervised therapy may be helpful injury initially attributed to a “sprain.” Although most scaphoid early during the course of healing to assist with finger motion fractures can be detected acutely on good quality plain radio- and later, after fracture consolidation, to help improve wrist graphs (Fig. 6d.8), some do not become apparent for several motion and grip strength. Displaced and unstable fractures weeks. Specialized imaging studies, including MRI, scintigraphy, usually require surgery. Procedural options include the use of and computed tomography, are occasionally helpful in early percutaneous pins, external fixation, open reduction and internal diagnosis and subsequent management. fixation, or a combination of methods. Closed treatment is indicated for acute nondisplaced The results of treatment vary, depending in part on the sever- scaphoid fractures. If diagnosed promptly and immobilized ity of the initial injury and the extent of articular surface involve- for an adequate duration, more than 90% of stable scaphoid ment. Although maximum medical improvement is anticipated injuries heal. Surgical intervention is indicated for acute fractures 6 months after injury or surgery, patients may continue to that are either displaced or unstable and for older fractures that demonstrate improvements in wrist motion, grip strength, and have failed to unite. Instability is defined as displacement greater endurance for well over 1 year. Figure 6d.7 Displaced distal radius fracture (arrow). Figure 6d.8 Scaphoid waist fracture (arrow).

244 Chapter 6d ● Wrist and Hand: Treatment Options than 1 mm in any direction and injuries associated with loss affecting the hands symmetrically. The distal interphalangeal of carpal bone alignment. Relative indications for surgical treat- joint of the finger is the most commonly involved hand joint, ment include a proximal pole fracture and prolonged wrist followed by the thumb basilar joint. In contradistinction to sys- immobilization that would be unacceptable to the patient for temic arthritic conditions such as rheumatoid arthritis, the finger social and/or economic reasons. metacarpophalangeal joints are usually spared. Although several studies have alluded to repetitive activities as having an influence Intramedullary pins or screws have become the standard of on the development of osteoarthritis in the wrist and hand, a fixation for scaphoid fractures, with union rates comparable causal relationship between repetitive activities and degenerative with those reported for closed-cast treatment. When screws are joint disease has never been conclusively proven. used and stability is achieved, early mobilization of the wrist is often permitted. In one study of military personnel, percutaneous Wrist screw fixation of nondisplaced scaphoid fractures was shown to result in more rapid radiographic union and return to duty when Osteoarthritis of the wrist most often develops secondary to compared with cast immobilization.5 Maximum medical a traumatic event. Intraarticular fractures of the distal radius, improvement is expected 4 to 6 months after injury or surgery malunited scaphoid fractures, scaphoid nonunions, and inter- but is contingent upon fracture healing. carpal ligamentous injuries all predispose the wrist to degenera- tion. In many cases, however, a specific cause is never identified. Metacarpals and phalanges Patients with wrist arthritis report pain, loss of mobility, and Fractures involving the metacarpals and phalanges occur in weakness in grip. Crepitation during motion or loading activities multiple patterns: transverse, oblique, spiral, and comminuted.4,17 and swelling over the dorsal carpus are common in advanced Most of these injuries may be evaluated using standard radio- disease. Plain radiographs confirm the diagnosis and assist in graphs. The rotational alignment of the digit is assessed with devising a treatment strategy (Fig. 6d.9). active finger motion or by generating finger motion through a tenodesis effect with passive wrist flexion and extension. The For early degenerative disease of the wrist, conservative phalanges should be parallel during extension and point toward measures are frequently successful. These include nonsteroidal the thenar eminence when flexed. Most metacarpal and phalangeal shaft fractures can be treated nonoperatively with protective casting or splinting. Clinical union usually requires 4 to 5 weeks for metacarpal injuries and 3 to 4 weeks for proximal and middle phalanx injuries. A distal phalanx fracture may take longer to unite. Metacarpal fractures are typically immobilized with a forearm-based cast or splint incorporating the metacarpophalangeal joint of the injured finger and one or two adjacent digits. Hand-based immobiliza- tion is indicated for proximal and middle phalanx shaft fractures, whereas distal phalanx fractures are treated with a simple finger splint. All cases require close radiographic follow-up to assess for loss of fracture alignment. Operative treatment is indicated for irreducible or unstable fractures and those associated with tendon lacerations. Articular injuries with marked incongruency and/or persistent joint subluxation are also considered for surgical repair. The type of fixation used depends on the fracture pattern, the soft tissue injury, and the judgment and experience of the surgeon. Depending in part on the severity of the fracture and associ- ated soft tissue trauma, the reported results after nonoperative and operative treatment of metacarpal and phalangeal fractures are variable. A successful outcome requires patient compliance with treatment and an appropriately structured rehabilitation program. In most cases maximum medical improvement is antici- pated approximately 3 to 4 months from injury or surgery. OSTEOARTHRITIS Osteoarthritis is a slowly progressive joint disease of multifactorial Figure 6d.9 Wrist degenerative arthritis developing after a etiology.21,29 Cartilage degeneration and osteophyte formation scapholunate interval injury (arrow). are often seen in association with advancing age, characteristically

Chapter 6d ● Osteoarthritis 245 antiinflammatory medication, wrist immobilization, activity modifications, and corticosteroid injection(s). Significant degenerative arthritic changes predict some degree of permanent functional impairment. Surgery is indicated if symptoms warrant and conservative treatment measures have failed. Procedures include proximal row carpectomy (excision of the three most proximal carpal bones), partial carpal bone fusions, and total wrist arthrodesis. The period of postoperative immobilization depends on the specifics of the operation performed, averaging 6 to 8 weeks for a fusion procedure. Results of surgical treatment are favorable in terms of pain relief. Motion-retaining procedures such as a partial wrist fusion and proximal row carpectomy require a considerable amount of therapy after cast removal. Total wrist fusion is the most reli- able in terms of relieving pain and improving grip strength but at the expense of wrist motion. Work restrictions after surgery must be determined on an individual basis, taking into account the specific job requirements. Maximum medical improvement is anticipated 6 months postoperatively. Thumb basilar joint The basilar joint of the thumb consists of the metacarpal base Figure 6d.10 Thumb basilar joint arthritis (arrow). and trapezium bone.2 Arthritis around the trapezium is the second most common site for degenerative joint disease in the grip/pinch strength improve slowly. Maximum medical improve- hand (preceded only by the distal interphalangeal joint). More ment is anticipated after approximately 6 months. frequent in females than males, the condition has been attrib- uted to laxity of the important stabilizing ligaments of the thumb. Proximal interphalangeal joint Patients with basilar thumb joint arthritis have pain localizing Osteoarthritis of the proximal interphalangeal joint is relatively to the base of the thenar muscles. Opening jars and turning rare. The condition typically arises after a dislocation or intraartic- door knobs are often difficult tasks to perform comfortably. ular fracture. The earliest signs of degenerative arthritis are swelling As the condition advances, pinch and grip strength diminish, and morning stiffness. Limited proximal interphalangeal joint and thumb range of motion may decrease as well. motion follows with the development of marginal osteophytes (Bouchard’s nodes). Late joint degeneration leads to an angular Examination reveals a tender and enlarged basilar joint. Axial deformity and joint instability. Radiographs confirm the diagno- grinding of the thumb metacarpal exacerbates the pain and may sis and reveal the degree of joint deterioration. elicit sensations of instability and crepitation. The Finkelstein test is usually negative, helping to distinguish basilar joint arthri- Conservative treatment measures include nonsteroidal anti- tis pain from de Quervain disease. The diagnosis is confirmed by inflammatory medication, activity modifications, and short-term plain radiographs (Fig. 6d.10). splinting. Early in the degenerative process, steroid injections can be helpful in ameliorating pain. If these measures fail and Initial treatment of basilar joint osteoarthritis includes considerable symptoms persist, surgical intervention may be activity modifications, splint immobilization, nonsteroidal anti- considered. inflammatory medication, thenar muscle strengthening exer- cises, and joint injection(s). If a patient’s symptoms are not Arthrodesis is the most reliable method of eliminating satisfactorily relieved by conservative means, surgical interven- pain. Fusion of the ulnar digits at the proximal interphalangeal tion may be considered. The most commonly performed opera- joint level impairs grip strength and finger dexterity to a greater tion entails partial or total excision of the diseased trapezium with stabilization of the thumb metacarpal base using local tendon graft. A significant hyperextension deformity of the thumb metacarpophalangeal joint may require a concomitant procedure to stabilize the metacarpophalangeal joint. The post- operative course typically involves a 4- to 6-week period of wrist and thumb immobilization followed by a supervised therapy program. Pain relief from surgery is nearly universal but not always complete, especially in younger and more active individuals. Activity modifications in the workplace may be indicated for an extended period of time after surgery. Thumb motion and

246 Chapter 6d ● Wrist and Hand: Treatment Options degree than it does in the radial digits. Fusion rates vary from 84% to 100%. Implant arthroplasty also provides pain relief with the added benefit of preserving partial joint motion. Joint replacement, however, carries an attendant risk of implant break- age and should be avoided in younger patients and/or manual laborers. Maximum medical improvement is expected 3 to 6 months postoperatively. Distal interphalangeal joint Idiopathic degeneration of the distal interphalangeal joint Figure 6d.11 Wrist magnetic resonance image, axial view. Dorsal commonly involves multiple digits in a symmetric distribution, ganglion attached to the scapholunate interval (arrow). whereas single finger joint degeneration is more suggestive of previous injury. In most cases, symptoms are mild and functional motion secondary to pain may result. In most cases, however, impairment is negligible. the cysts yield few or no symptoms and require no specific inter- vention. For a symptomatic dorsal wrist ganglion, aspiration of Swelling and stiffness are common symptoms in early degen- the cyst with or without a corticosteroid injection is initially rec- eration of the distal interphalangeal joint. As the disease progresses, ommended and successful in up to 50% of cases. Aspiration is joint enlargement is seen secondary to osteophyte formation relatively contraindicated for volar wrist ganglia because of the (Heberden’s nodes), resulting in limited motion. Late in the close proximity of the radial artery. In these cases temporary disease, angular and rotational deformities occur at the finger wrist splinting and use of a nonsteroidal antiinflammatory tip. Radiographs confirm the diagnosis and demonstrate the medication may be helpful. severity of joint destruction. Surgical excision of wrist ganglia is indicated for persistent In most individuals, conservative care is successful. Treatment pain, with reported recurrence rates averaging approximately measures include nonsteroidal antiinflammatory medication, 5%. The procedure is frequently performed in an open manner, activity modifications, corticosteroid injection(s), and splinting. although an arthroscopic technique for excising dorsal ganglia Surgery is reserved for symptomatic degenerative disease that was recently described.25 After ganglion excision, most patients does not respond to conservative measures. Distal interphalangeal experience continued low-grade discomfort for several weeks. joint fusion reliably relieves pain, restores stability and strength, Supervised therapy may be helpful in diminishing pain and and improves the appearance of the digit. Fusion rates vary from in restoring wrist motion and grip strength. Maximum medical 80% to 100%. Maximum medical improvement is expected 2 to improvement is anticipated 2 to 3 months postoperatively. 4 months postoperatively. Retinacular cysts GANGLIA Ganglia arising from the digital flexor tendon sheath are termed Ganglia are fluid-filled structures that arise from a joint, tendon, volar retinacular ganglia or retinacular cysts. Appearing as a small or tendon sheath.28,30 They contain lubricating fluid called bump at the base of a digit adjacent to the palmar digital flexion mucin that is similar in content to but more viscous than the crease, this type of cyst commonly causes discomfort during fluid found in joints and tendon sheaths. Ganglia can emanate activities that require gripping or holding objects in the palm. from almost any anatomic region, but they are most common at A painful cyst can usually be treated by needle aspiration. the wrist, the proximal margins of digital flexor tendon sheaths, Surgery to excise the lesion is considered in recalcitrant cases and and the finger distal interphalangeal joints. Cysts communicate when the diagnosis is uncertain. A rapid return to regular work with these structures through one or more ducts that account activities is expected. for their intermittent fluctuation in size. The true etiology of a ganglion is unknown, although approximately 10% have been Mucous cysts associated with previous trauma. Cysts arising from the distal interphalangeal joint, termed mucous Carpal ganglia cysts, are invariably associated with degenerative arthritic changes in the underlying joint. Because of their location, mucous cysts Ganglia of the wrist are seen most frequently dorsally, near the articulation of the scaphoid and lunate bones (Fig. 6d.11). They occur less commonly at the palmar aspect of the wrist, adjacent to the flexor carpi radialis tendon. Cysts may be multiloculated and much larger than clinically apparent, extending far away from their point of origin. Patients with carpal ganglia may complain of activity-related wrist pain and weakness. Guarding with minor loss of wrist

Chapter 6d ● References 247 may disrupt the germinal matrix of the nail bed and lead to CONCLUSION longitudinal nail plate grooves and ridges. Management of an occupational-related disorder of the wrist or Aspiration and instillation of a corticosteroid can be hand is contingent upon the recognition of factors related to attempted, but this treatment is rarely curative. Because the condition development, a coordinated team approach to care, distal interphalangeal joint is immediately deep to the skin and the patient’s active participation in recovery. Conservative surface, aspiration increases the likelihood of septic arthritis. treatment measures include supervised therapy, splinting, Simple cyst excision carries a recurrence rate of 25% or greater. corticosteroid injection, oral pain medication, and activity modi- Excision of the cyst in conjunction with debridement of mar- fications. Surgical intervention may be indicated for trauma, ginal joint osteophytes, however, is successful in over 95% of advanced nerve compression lesions, arterial thrombosis, recalci- cases. Recovery after surgery is relatively rapid, and unrestricted trant tendonitis, symptomatic degenerative arthritis, painful use of the hand should be possible within 6 weeks. ganglia, and various other conditions. The ultimate goals of treat- ment should include patient satisfaction, symptom resolution, COMPLEX REGIONAL PAIN SYNDROME and return to gainful employment. Complex regional pain syndrome (CRPS) is a neurogenic dis- REFERENCES order characterized by pain out of proportion to the level antic- ipated with the diagnosis, swelling, autonomic dysfunction, 1. Atkins RM: Aspects of current management complex regional pain syndrome. J Bone and joint stiffness.1,32 In the past, a variety of terms, including Joint Surg Br 85(8):1100-1106, 2003. reflex sympathetic dystrophy, causalgia, Sudeck’s atrophy, and shoulder-hand syndrome, has been used to describe this condi- 2. Barron OA, Glickel SZ, Eaton RG: Basal joint arthritis of the thumb. J Am Acad Orthop tion. Type 1 CRPS develops after a noxious event without iden- Surg 8:314-323, 2000. tifiable nerve injury, whereas type 2 CRPS occurs in association with a nerve injury. 3. Bednar MS: Ulnar tunnel syndrome. Hand Clin 12(4):657-663, 1996. 4. Blazar PE, Steinberg DR: Fractures of the proximal interphalangeal joint. J Am Acad The pathogenesis of CRPS remains poorly understood. Autonomic hyperactivity is implicated in syndrome development, Orthop Surg 8:383-390, 2000. and in many cases psychologic factors seem to play a role. Initially, 5. Bond CD, Shin AY, McBride MT, Dao KD: Percutaneous screw fixation or cast pain, swelling, restricted motion, and vasomotor changes (hyper- hidrosis, erythema, excessive warmth) predominate the symptom immobilization for nondisplaced scaphoid fractures. J Bone Joint Surg Am complex. After several months, swelling changes from a soft to a 83(4):483-488, 2001. hard brawny edema. Eventually, the skin appears shiny and glossy, 6. Cooke RA: Hypothenar hammer syndrome: a discrete syndrome to be distinguished and stiffness becomes marked with fixed joint contractures. from hand-arm vibration syndrome. Occup Med 53(5):320-324, 2003. 7. Cooney WP III: Scaphoid fractures: current treatments and techniques. Instr Course The diagnosis of CRPS is made on clinical examination but Lect 52:197-208, 2003. may be confirmed by a variety of objective tests. Radiographs 8. D’Arcy CA, McGee S: Clinical diagnosis of carpal tunnel syndrome. JAMA frequently reveal diffuse osteopenia secondary to bone dem- 284(15):1924-1925, 2000. ineralization. Three-phase bone scans show characteristic diffuse 9. De Monaco D, Fritsche E, Rigoni G, Schlunke S, Von Wartburg U: Hypothenar hammer uptake in the involved areas. Thermography can depict asym- syndrome: retrospective study of nine cases. J Hand Surg Br 24(6):731-734, 1999. metric temperature when compared with the contralateral limb. 10. Edgell SE, McCabe SJ, Breidenbach WC, LaJoie AS, Abell TD: Predicting the outcome Anesthetic blockade at the neck/shoulder level confirms the of carpal tunnel release. J Hand Surg Am 28(2):255-261, 2003. diagnosis in cases with primary involvement of the sympathetic 11. Gerritsen AA, de Krom MC, Struijs MA, Scholten RJ, de Vet HC, Bouter LM: nervous system. Conservative treatment options for carpal tunnel syndrome: a systematic review of randomized controlled trials. J Neurol 249(3):272-280, 2002. 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Kalainov DM, Culp RW: Arthroscopic treatment of TFCC tears. Tech Hand Upper adrenergic blocking agents, calcium channel blockers, and regional Extremity Surg 1(3):175-182, 1997. anesthetic injections. To address marked joint contractures late in 16. Kasdan ML, Lewis K: Management of carpal tunnel syndrome in the working the disease process, surgical intervention may be indicated. population. Hand Clin 18(2):325-330, 2002. 17. Kozin SH, Thoder JJ, Lieberman G: Operative treatment of metacarpal and phalangeal Evidence suggests that the earlier treatment is instituted, the shaft fractures. J Am Acad Orthop Surg 8:111-121, 2000. better the chance for a successful result. A significant percentage 18. Kurozawa Y, Nasu Y, Hosoda T, Nose T: Long-term follow-up study on patients with of patients, however, still complain of pain, cold intolerance, vibration-induced white finger (VWF). J Occup Environ Med 44(12):1203-1206, sensory disturbances, swelling, hand weakness, and stiffness years 2002. later. Once the chronic stages of CRPS have occurred, results are 19. Lane LB, Boretz RS, Stuchin SA: Treatments of de Quervain’s disease: role of less favorable, with expected varying degrees of permanent upper conservative management. J Hand Surg Br 26:258-260, 2001. extremity impairment. 20. Macdermid JC, Richards RS, Roth JH, Ross DC, King GJ: Endoscopic versus open carpal tunnel release: a randomized trial. J Hand Surg Am 28(3):475-480, 2003. 21. Palmieri TJ, Grand FM, Hay EL, Burke C: Treatment of osteoarthritis in the hand and wrist: nonoperative treatment. Hand Clin 3(3):371-383, 1987. 22. Pelmear PL: The clinical assessment of hand-arm vibration syndrome. Occup Med 53(5):337-341, 2003. 23. Piligian G, Herbert R, Hearns M, Dropkin J, Landsbergis P, Cherniack M: Evaluation and management of chronic work-related musculoskeletal disorders of the distal upper extremity. Am J Ind Med 37(1):75-93, 2000.

248 Chapter 6d ● Wrist and Hand: Treatment Options 24. Rettig ME, Raskin KB: Acute fractures of the distal radius. Hand Clin 16(3):405-415, 29. Steinberg DR: Management of the arthritic hand. In MW Chapman, ed: Operative 2000. orthopaedics, ed 2. Philadelphia, 1993, JB Lippincott. 25. Rizzo M, Berger RA, Steinmann SP, Bishop AT: Arthroscopic resection in the 30. Thornburg LE: Ganglions of the hand and wrist. J Am Acad Orthop Surg 7:231-238, management of dorsal wrist ganglions: results with a minimum 2-year follow-up 1999. period. J Hand Surg Am 29:59-62, 2004. 31. Walsh JJ, Berger RA, Cooney WP: Current status of scapholunate interosseous 26. Saldana MJ: Trigger digits: diagnosis and treatment. J Am Acad Orthop Surg ligament injuries. J Am Acad Orthop Surg 10:32-42, 2002. 9:246-252, 2001. 32. Zyluk A: The sequelae of reflex sympathetic dystrophy. J Hand Surg Br 26(2): 27. Shin AY, Battaglia MJ, Bishop AT: Lunotriquetral instability: diagnosis and treatment. 151-154, 2001. J Am Acad Orthop Surg 8:170-179, 2000. 28. Steinberg BD, Kleinman WB: Occult scapholunate ganglion: a cause of dorsal radial wrist pain. J Hand Surg Am 24:225-231, 1999.

6eC H A P T E R of screws and work situations. A screw is tightened usually by grasping the screwdriver handle and simultaneously applying Biomechanical Aspects a torque while exerting a push force. The amount of torque, of Hand Tools T, needed for tightening a screw depends on the kind of screw and the characteristics of the screw joint such as friction, screw Robert G. Radwin diameter, thread, and clamping load. The mechanical relationships between hands, tools, and tool The push force is often called feed force. Feed force, F, is the axial operation are important for understanding and controlling force applied against the screwdriver shaft that is required to thread physical stress of tool operators. Hand exertions needed for the screw and keep the screwdriver blade seated. Numerous task- many tool operations are affected directly by the selection of related factors affect feed force, including thread type (whether the specific tools and accessories for the task. Although many of screw is self-tapping or threaded), material hardness, thread size, the recommendations in this chapter are based on years of exten- and hole diameter. The choice of a particular size screwdriver can sive biomechanics research, others arise out of simple mechani- have a great effect on the hand exertion required for a task. cal principles and reasonable assumptions about mechanical relationships between tools and their operators. The objective is Handle length to illustrate how the characteristics of a particular tool (such as size, shape, output, and accessories) and its manner of use (such A question often asked is how does screwdriver length affect as orientation or location relative to the operator) can signifi- hand force? Experience has found that a longer screwdriver cantly affect the effort needed for performing specific tasks. handle generally results in less effort.32 This can be explained by considering the motions needed for tightening a screw. When Both manual (hand powered) and power (electric, pneumatic, a screw is tightened, torque is transferred to the handle, usually or hydraulic) hand tools require that operators produce forces by rotating the forearm in combination with flexion and ulnar at varying levels. Manual tools may require exertion of forces deviation of the wrist. The asymmetry of the hand, wrist, and to squeeze together tool handles, such as those of pliers and cut- forearm relative to the screwdriver’s radial axis produces ting tools. Other manual tools may require twisting, pulling, eccentric rotation of the handle that causes perturbation of or pushing. Safe operation of a power tool requires that an the handle and shaft along a horizontal displacement Δ from the operator support it adequately in a particular position and apply vertical axis (Fig. 6e.1). The magnitude of this displacement the necessary forces while reacting against the force generated depends on the particular action and anthropometry of the wrist. by the tool itself. Force demands that exceed an operator’s strength capabilities can cause loss of control and result in an F accident or an injury. If improper selection, installation, or use of a power tool requires an operator to make substantially greater Fx exertion than necessary, it may lead to muscle fatigue or a mus- Δ culoskeletal disorder.1,5,28,39,40 Tools that are selected to minimize hand forces are usually the best ones for the task. Fy The discussion begins with simple manually operated hand Direction tools, including screwdrivers and pliers. An investigation of of twist the means by which different kinds of screw fasteners can affect forces in the hands is followed by a description of how selection θ L and installation of power hand tools can control the static and dynamic hand forces associated with their use. Mathematical Direction and biomechanical calculations are provided to enable interested of rotation readers to follow them and to impress other readers less concerned with how objective conclusions can be ascertained through mostly deterministic methods. These principles should be applicable to occupational health professionals in the selection and installation of tools. Designers and engineers should be able to adapt these calculations to new tools and job designs. MANUAL SCREWDRIVERS One of the most commonly used hand tools, the screwdriver, Figure 6e.1 Rotation and perturbation of a manual screwdriver when is available in various sizes and forms suitable for different types the handle is twisted in the hand.

250 Chapter 6e ● Biomechanical aspects of hand tools This perturbation causes the screwdriver shaft to tilt to a maximum and Fy~~F cos 0 degrees ~~ F. This action therefore aids the angle, θ, as the screwdriver rotates. operator by keeping the axial feed force requirements minimal and unaffected by screwdriver length. When high feed forces If screwdriver handle size, diameter, and shape and shaft are required, screwdriver shafts should be long enough to be diameter remain the same, hand and wrist rotation is unaffected pinched or gripped by the other hand as a guide. Using a similar by the shaft length, so the handle perturbation remains constant. argument, the hand force needed for a nut driver should be Assuming that the handle displaces the same distance Δ from the mostly independent of the shaft length because the shaft is axis of the fastener shaft (Fig. 6e.1), the maximum angle, θ, that coupled to the nut, permitting concentric rotation with the the screwdriver shaft tilts as it is twisted can be described as handle despite the asymmetries of the hand and forearm. θ = sin−1 ⎛ Δ ⎞ Handle diameter ⎝⎜ L ⎠⎟ Another common question is how does a screwdriver handle Orthogonal feed force components (Fig. 6e.1) can be resolved diameter affect hand force? Several studies investigated the effect into of handle diameter on the torque capability of the hand. A study involving volitional torque exerted for different manual screw- Fy = F cosθ, Fx = F sinθ drivers, locking pliers, and wrenches found that the resulting torque magnitude was influenced strongly by the kind of tool If a screwdriver has a length, L, then the maximum component and the posture assumed.26 From a purely mechanical standpoint, parallel to the fastener shaft is Fy: a greater handle diameter should result in more torque at the screw- driver shaft for the same effort, provided that the frictional prop- Fy = F cos θ = F cos ⎣⎢⎡sin−1 ⎛ Δ⎞ ⎤ erties of the handles are similar and the diameter is not too large. ⎝⎜ L ⎠⎟ ⎥⎦ The diameter of a screwdriver handle plays a critical role in Solving for F, limiting a user’s torque-generating capability. Large grip forces are often needed for sustaining a grip and for coupling the hand F = Fy and the tool to prevent the handle from slipping. A simplified ⎣⎡⎢sin−1 ⎛ Δ ⎞ ⎤ relationship between the torque and diameter illustrates the cos ⎝⎜ L ⎠⎟ ⎥⎦ effect of mechanical advantage on torque: A consequence of this relationship is that if the required axial T = S G = μ FG G force component Fy remains constant, F decreases as L increases. Hence, the hand force exerted can be reduced by increasing L where T is torque, S is the shear grip force, G is the handle radius, and using the longest screwdriver available. For example, if the μ is the coefficient of friction between the hand and the handle, shaft of a 6-cm screwdriver displaces Δ = 3 cm, the feed force F and FG is grip force.32 If FG remained constant, torque would lin- needed to drive a screw is early increase as the handle diameter increased. As is well known, however, grip strength is not constant for all diameters but F = Fy = 1.15 × Fy rather is affected by handle size.4,17,19 If a handle is too large or too small, the strength of the hand is greatly compromised. The cos ⎡ sin−1 ⎛ 3⎞ ⎤ relationship between cylindrical handle size and grip strength is ⎣⎢ ⎝⎜ 6 ⎠⎟ ⎥⎦ summarized in Figure 6e.2.29 Maximum grip force occurs around 6 cm. Consequently, the optimal diameter is one in Therefore, the maximum feed force can be as much as 15% which a further increase in diameter increases the mechanical greater than the axial force needed. If the screwdriver length is advantage while simultaneously decreasing grip force. Research increased to 25 cm, the feed force needed to drive a screw would be has found that this optimum depends on handle design, friction, gender, and hand size.32 Torque performance diminishes when F = Fy ⎛ 3⎞ ⎤ = 1.01 × Fy handle diameters are greater than 5 cm,33 and a diameter of 4 cm cos ⎢⎣⎡sin−1 ⎝⎜ 25⎠⎟ ⎥⎦ is sometimes recommended for screwdrivers.7,8 which decreases the force feed to only as much as 1% more force Sufficient friction must be present between the handle and than is actually needed. the hand to provide a secure grip, exert force or torque, and prevent a tool from slipping. Surfaces that do not provide Of course, a very long screwdriver may not be practical under adequate friction require greater grip force that may result in all circumstances. Clearance and spatial constraints may limit greater effort and even loss of control of the tool. The amount the size of screwdriver that can be used. Furthermore, a very of friction depends on the coefficient of friction between the short screwdriver can facilitate the precision grip needed for light hand and the material or object grasped. Some materials have precise work, such as that afforded with a jeweler’s screwdriver. greater coefficients of friction and consequently better frictional characteristics than others. Another way to limit the horizontal perturbation of a screw- driver as it rotates in the hand is by supporting the screwdriver No one handle size is practical for all tasks, and certain handles shaft, as might be done when two hands are used. If the screw- serve some objectives better than others. A panel of ergonomics driver were held straight by supporting the shaft with the fingers experts recommends using a small-diameter handle (8-13 mm) of the free hand, then the tilt angle θ remains close to 0 degrees

Chapter 6e ● Screwdriver blades and screw heads 251 400 Allowances should be made for all these factors. The three most common threaded fastener heads are slotted, Phillips, and Torx™ (Fig. 6e.3), each of which has different feed force requirements. Grip strength Slotted screws 300 The oldest and simplest type of screw head, the slotted screw, has a single slot across the entire diameter of the head. When a screw- 200 7 driver blade is inserted inside a screw slot and rotated, contact is 456 usually made at the two edges of the blade, as shown in Figure 6e.4. The size of the screwdriver width, w, limited by the radius of the Handle span (cm) screw head provides a slight mechanical advantage for applying torque against the screw. Wider screw heads and screwdriver blades Figure 6e.2 Grip strength for a population of 29 subjects (19 university generally require less torque exertion at the screwdriver shaft. students and 10 factory workers). Error bars represent one standard error of the mean. We ignore frictional force by assuming that friction between the screw and screwdriver blade is zero. (Because in this case, friction assists the operator by helping keep the screwdriver blade in the screw slot, zero friction would be the worst-case condition.) If the width of the screwdriver blade is w and the applied torque at the screwdriver shaft is T, then the normal contact force, FC, between the blade and the screw head slot is for a precision grip and a large-diameter handle (50-60 mm) for FC = T a power grip.27 In one study, handles between 31 and 38 mm in W diameter were considered optimal for a power grip12; several studies recommend 50 mm as an upper limit diameter.4,33,38 SCREWDRIVER BLADES AND SCREW HEADS Because the blades of slotted screwdrivers are usually tapered to an angle φ to ease insertion of the screwdriver blade and Screwdriver feed force can be affected by the particular type of accommodate different size screw slots, the normal contact force screw fastener head and screw tip needed.6 Self-tapping screws FC is not actually perpendicular to the screwdriver shaft but require more feed force than do screws tightened through pre- rather acts at an angle perpendicular to the blade edge (Fig. 6e.4). tapped holes. Material hardness and friction are also important This results in an axial force at each contact point factors to consider for self-tapping screws. Feed force requirements increase as the torque level increases for cross-recess screws. Fy = FC sinφ = T sinφ W Slotted Phillips head Torx Figure 6e.3 Slotted head, Phillips head, and Torx™ head screws.

252 Chapter 6e ● Biomechanical aspects of hand tools Fy F = 4Fy = 4FC sinφ = 4 T sin φ. W T Because φ is typically greater for Phillips head screws and w is much smaller, Fy is considerably more than for slotted screw- drivers. The typical taper angle for a Phillips head screw is φ = 40 degrees, so F = 4 T sin(40°) = 2.57 T . W W φ which is more than six times the force needed for a slotted screw Fc with an equivalent diameter head. Fc Torx™ head screws W Torx™ screws offer the advantages of both slotted screws and Phillips Figure 6e.4 Static forces acting on a slotted screwdriver blade and shaft. head screws. Because φ = 0 for Torx™ head screws (Fig. 6e.3), no axial force component other than the actual feed force is that acts to push the screwdriver blade out of the slot as torque required to advance the fastener. Because the screwdriver blade is applied to the shaft. The hand must react against this force by cannot be tapered to accommodate different-size screws, Torx™ exerting an equal and opposite axial force Fy that is a component head screws are not as flexible as slotted or Phillips head screws. of the feed force. Because there are two contact points, the total The disadvantage of requiring a large assortment of screwdrivers axial force is 2Fy. Consequently, the axial force required to keep with corresponding blade sizes may be outweighed by the the blade from coming out of the slot is mechanical advantage of Torx™ head screws. Furthermore, they are more difficult to tamper with because Torx™ head screwdrivers are less readily available than slotted and Phillips head screw- drivers and an assortment of sizes are needed. The advantages and disadvantages of slotted, Phillips, and Torx™ head screws are summarized in Table 6e.1. F = 2Fy = 2 T sin φ. PLIERS AND CUTTING TOOLS W The particular finger or combination of fingers used can affect The greater the torque T, the greater the axial force needed to grip strength.2,37 As the strongest fingers, the thumb, index, and keep the screwdriver blade in the slot. If the screwdriver blade middle fingers should be used for producing the most grip force. taper angle φ is 12 degrees, The weaker ring and small fingers should be used for stabiliz- ing handles rather than acting as primary force contributors. F = 2 T sin(12°) = 0.42 T . Sometimes tool operators handle tools in ways that take these W W differences into account. If the screwdriver blade angle is not tapered but parallel to Table 6e.1 Summary of ergonomic advantages and disadvantages of different screw heads the slot, this force is negligible (Fy = 0) because no axial force acts to unseat the blade. Such a screwdriver, however, would be limited to certain size slots and more difficult to insert into them. Phillips head screws Screw Disadvantages head Advantages Although slotted screws are simpler, screwdriver blades some- times slip out of slotted heads and have the potential to damage Slotted Very flexible tool—one size fits all Difficult to keep seated in the or scratch the work piece. The Phillips head screw (Fig. 6e.3) slot gained popularity because it prevented slippage and discour- Phillips Requires little axial feed force aged vandals from removing screws in public places with a coin Torx™ Can slip and damage work or knife edge.31 Easy to keep seated in head piece Flexible tool A Phillips head screwdriver blade contains four wedges acting No axial feed force needed Requires more axial feed force on the blade. Similarly to the slotted screwdriver, the axial forces Easy to keep seated in head acting parallel to the fastener can be described by the equation Inflexible—must have a specific size for an associated screw head

Chapter 6e ● Power hand tools 253 Xj L1 θ L2 L3 Lj L4 X1 Figure 6e.6 Inverted pliers grip. X2 X3 X4 Figure 6e.5 Static forces acting on the hand when a pair of pliers is normal strengths for the distal phalanx while grasping handles of grasped. different sizes are taken from Amis.2 By summing the moments about the pivot point, the total moment is Offering the mechanical advantage provided from squeezing together two opposing lever arms, pliers are used often for pinch- MJ = F1L1 + F2L2 + F3L3 + F4L4 ing, grasping, and cutting. The common use of pliers involves a grip depicted in Figure 6e.5, where the pliers jaw is held on the This moment is counteracted by that produced from reaction radial side of the hand. In many instances, however, this grip forces at the jaw. Consequently, the maximum jaw force is does not optimize the mechanical advantage with finger strength and can result in greater exertion than necessary. Fj = Mj Lj Swedish researchers observed that some sheet metal workers held metal shear blades on the ulnar side of the hand by using an Using the dimensions provided in Table 6e.2, the maximum inverted grip (Fig. 6e.6) rather than that used with conventional jaw force available increases from 714 to 786 N (10) just by shears.10,41 Finger strength data revealed that the inverted grip inverting the handle. Because the index and middle fingers have allowed a greater span between the larger index finger and thumb the greatest strength, they are provided with larger moment than between the small finger and the palm, providing arms for generating force with the inverted grip, providing addi- a better-suited handle size for more force in each cut.14 tional mechanical advantage. One study observed that the max- imum force of one finger depended not only on its grip span but The articulation angle from the closed position to the pivot also on those of the other fingers.14 point is defined as θ. The jaw span Xj is related to the grip span Xi as POWER HAND TOOLS Xi = Xj Li One of the best methods of controlling applied hand exertion is Lj to substitute a power hand tool for a manual tool. In fact, many repetitive jobs could not be performed without the use of power where Li is the distance from the fulcrum to the finger i, Lj tools. Modern power hand tools can operate at high speeds and is the distance from the fulcrum to the jaw tip, and Xi is the produce very high forces. Exertions and forces acting against the grip span available for finger i. hand in power tool operation can be reduced by eliminating excess weight, by making the best use of the mechanical advantage, or by Assuming there are no coupling effects between fingers, the resultant force is the sum of all four fingers. Individual-finger

254 Chapter 6e ● Biomechanical aspects of hand tools Table 6e.2 Pliers handle dimensions and associated Si finger strength for showing the mechanical advantage Gi using an inverted grip Grip Index Middle Ring Small Total Conventional 6.0 6.6 6.4 5.4 204 LGY L1Y 60 63 44 37 Grip span Xi (cm) 7.0 8.3 10.2 11.4 1814 Grip strength Fi (N) 420 523 449 422 714 Finger distance Li (cm) 165 206 177 166 Torque (Nm) Jaw force FJ 5.4 6.4 6.6 6.0 204 Inverted 62 64 43 35 11.4 10.7 8.3 7.0 1994 Grip span Xi (cm) 707 685 357 245 786 Grip strength Fi (N) 278 270 141 97 Finger distance Li (cm) Torque (Nm) Jaw force FJ T providing mechanical aids for holding tools, parts, and materials. Figure 6e.7 Forces acting in the hand when an in-line nut runner is Selecting a power hand tool having certain dimensions and shapes operated. can often reduce tool reaction forces and provide mechanical advantages that assist the operator. Increasing friction between the Static forces hand and objects grasped can also reduce the forces required for gripping tools. Lin et al22 developed a mechanical model of power hand nut- runner operation for static equilibrium (no movement) con- Nut runners and power screwdrivers are widely used for ditions. Using hand force, reaction force from the work piece, tool securing screws and threaded fasteners in manufacturing and weight, and tool torque, the static force model calculates handle assembly operations, such as in the automotive, mechanical force when carrying tools and when spindle torque is constant. equipment, and electronics industries. Using electromyography as an index of muscle effort during pneumatic shut-off nut- The model uses a Cartesian coordinate system relative to the runner operation, Radwin et al37 observed that electromyographic orientation of the handle grasped using a power grip (Fig. 6e.7A). activity during threaded fastener torque buildup was affected by This coordinate system has the x-axis perpendicular to the axial tool torque output and torque buildup time. Electromyographic direction of the handle, the y-axis passed through the long axis activity during torque buildup was more than three times greater of the handle, and the z-axis perpendicular to both. The origin is than during preparation and shut-off. the end of the bit or socket. Oh and Radwin29 observed that the operator initially overcomes Hand forces are described here in relation to these coordinate the tool reaction force with a concentric muscle exertion. As the axes. To simplify the model, we assume that orthogonal forces force rapidly rises, the tool eventually overcomes the operator, can be summed along the handle without producing coupling causing the motion in opposition to muscle contraction and moments, an assumption that allows force to have a single point resulting in an eccentric muscle exertion. Due to passive prop- of application. The variables used in the model are summarized erties of the muscle, during an eccentric, or lengthening, con- in Table 6e.3 and illustrated in Figure 6e.7. traction the muscle acts like a spring, producing proportionally more force as it lengthens. When a tool is in static equilibrium, the sums of all forces (F), moments (M) about the origin, and grip moments generated by Because they directly affect handle force in a complex man- the spindle (MG) are zero. Therefore three vector equations can ner, tool geometry, mass, moment of inertia, and center of grav- be developed: ity are important factors in the design and selection of power hand tools. By providing mechanical advantages, the handle Σ Fi + Σ Ri + W + FF + Fs = 0 (Σ F = 0) length of pistol-grip and right-angle tools and the diameter of in-line tool handles likewise affect hand exertions.11,20,36 Tool Σ ( Fi + Ri) × Li + W × LG = 0 (Σ M = 0) load affects grip force,9,16,21,43 fatigue onset,18 task performance,13 and subjective preference by tool operators.3,30,42 In addition Σ Si × Gi + T = 0 (Σ MG = 0) to the static forces exerted by an operator when carrying and positioning tools or when a tool is running at a constant state, These vector equations can be written in matrix form: the impulsive forces and torques produced by rotating spindle The full model considers forces and moments exerted by power hand tools are dynamic. both hands (subscripts 1 and 2), but not all these equations are

Chapter 6e ● Power hand tools 255 ⎡ 1 0 0 1 0 0 0 0 0 0 0 0 1 0 0⎤ ⎢ 0 0 0 0 0 0 0 0 1 0⎥⎥ ⎢ 0 1 0 0 1 ⎢ 0 0 1 0 0 1 0 0 0 0 0 0 0 0 1⎥ ⎢ 0 0 0 0⎥⎥ ⎢ 0 L1z −L1y 0 L2z −L2y 0 0 0 0 0 ⎢ −L1z 0 L1x −L2z 0 L2x 0 0 0 0 0 0 0 0 0⎥⎥ × ⎢ ⎢ L1y −L1x 0 L2y −L2x 0 0 0 0 0 0 0 0 0 0⎥ ⎢ 0 0 0 0⎥⎥ ⎢ 0 0 0 0 0 0 G1x 0 0 G2x 0 ⎢ 0 0 0 0 0 0 0 G1y 0 0 G2y 0 0 0 0⎥ ⎢ 0 0 0 G1z 0 0 G2z 0 0 0⎦⎥ ⎣ 0 0 0 0 0 ⎡F1x ⎤ ⎢⎢F1y ⎥ ⎥ ⎢F1z ⎥ ⎢⎢F ⎥ 2x ⎥ ⎡ −Wx − R1x − R 2x − FFx ⎤ ⎢⎢F 2y ⎥ ⎢ −Wy − R1y − R 2y − FFy ⎥ ⎥ ⎢ ⎥ ⎢F2z ⎥ ⎢ ⎥ ⎢ −Wz − R1z − R 2z − FFz ⎥ ⎢⎢S1x ⎥ ⎢ ⎥ ⎥ L1zR1y − L1yR1z + L 2zR 2y − L 2yR 2z − LGzWy + LGyWz ⎢S1y ⎥ = ⎢ L1xR1z − L1zR1x + L 2xR 2z − L 2zR 2x − LGxWz + LGzWx ⎥ . ⎢⎢S1z ⎥ ⎢ − L1xR1y + L2yR 2x − L2xR 2y − LGyWx + ⎥ ⎥ ⎢L1yR1x LGxWy ⎥ ⎢ ⎥ ⎢⎢S2 x ⎥ ⎢ −Tx ⎥ ⎥ ⎢S2y ⎥ ⎢ −Ty ⎥ ⎢⎢S2z ⎥ ⎢ ⎥ ⎥ ⎣ −Tz ⎦ ⎢Fsx ⎥ ⎢⎢Fsy ⎥ ⎥ ⎣⎢Fsz ⎥⎦ required for all situations, and in certain cases the equations assumed always to act in a single axis. When the matrix becomes system may be reduced depending on tool shape and operating degenerate or singular, additional assumptions are needed to conditions. For example, the shear force needed for in-line tools solve for handle force. is insignificant for pistol grip tools except when a hand grasps the tool around the spindle. The tool torque and feed force are Nut runners are commonly configured as pistol grip, right angle, and in-line (Fig. 6e.7). Examples are provided in this Table 6e.3 Legend of variable notation article to demonstrate the resulting matrix reduction for these three common tool shapes. A set of more general cases are fully Variable* Description described in Lin et al.22 Fi Handle force acting on hand i Pistol-grip power drivers Si Shear force acting in hand i, applied when the handle rotates Consider the free-body diagram of the pistol-grip nut runner in in the y-axis Figure 6e.7B, which shows the use of the right hand (subscript 1), Ri Reaction force produced by the spindle torque at point i and the tool geometry shown in Figure 6e.8A. The spindle stall W Tool weight torque T acts clockwise in the xy-plane. The tool operator FF Feed force; not applicable when carrying a tool must oppose this equal and opposite reaction torque Tz counter- Fs Surface support force; not applicable when carrying a tool clockwise by producing a reaction force R1x along the x-axis that T Tool torque is equal to and opposite of the hand force component F1x. Li Location vector of point i LG Location vector of the center of gravity This is not, however, the only force that the tool operator Gi Grip radius at point i, applied when the handle rotates in must produce. A force acting along the z-axis F1z provides feed force FFZ and produces an equal and opposite reaction force FSz. the y-axis The operator must also react against the tool mass to support and position the tool by producing a vertical force component *All the variables in bold type are vectors. Subscript i represents a specific hand used in F1y. The tool weight Wy and push force F1z tend to produce a operating the tool. The right hand is annotated using subscript 1 and the left hand is clockwise rotation of the power tool about the spindle in the annotated using subscript 2. yz-plane that is countered by this vertical support force.

256 Chapter 6e ● Biomechanical aspects of hand tools L1z y LGz x z Tz LGy F1y FFz Wy L1y −Tz F1z F1x Figure 6e.8 Static forces during pistol-grip nut runner operation. In the case of one-handed operation, the right hand (subscript 1) selecting the tool requiring the least exertion. Consider the reacts against all tool forces and torques. The vector equations four hypothetical power nut runners shown in Figure 6e.9. can therefore be reduced to All four tools weigh the same (30 N) and have the same torque output with different dimensions and mass distribution. ⎡0 0 1 0 1⎥⎤ ⎡F1x ⎤ ⎡0⎤ Comparisons between the four tool dimensions are provided in ⎢ 0 1 0⎥ ⎢⎢F1y ⎥ ⎢ ⎥ Table 6e.4. ⎢0 1 ⎥ ⎢ −Wy ⎥ Assuming one-handed operation, resultant hand force was ⎢ 0 0 0 0 1⎥⎥ × ⎢F1z ⎥ = ⎢ −FFz ⎥. predicted by using the model for the four different tools and ⎢ L1z −L1y 0 0⎥ ⎢⎢Fsy ⎥ ⎢⎢− ⎥ plotted as a function of torque in Figure 6e.9. Hand force ⎢0 ⎥ WyLGz ⎥ was determined for both low-feed force (1 N) and high-feed force (100 N) conditions when the tools were operated against a ⎣⎢L1y 0 0 0 0⎥⎦ ⎣⎢Fsz ⎦⎥ ⎣⎢ −Tz ⎥⎦ vertical surface. When feed force was small, the resultant hand force was affected mostly by the torque reaction force, which These equations reveal several relationships between tool increased as torque increased for all four tools. Because the parameters and hand force. Torque reaction force R1x = F1x greatest force component in this case was the torque reaction is directly proportional to the reaction torque Tz and inversely force, tools 3 and 4 resulted in the least resultant hand force proportional to the handle length L1y. The torque reaction force because they had the longest handles (Table 6e.4). Tool 3, is therefore less for longer tool handles than for shorter handles. however, had a considerably greater resultant hand force when The vertical support force F1y is inversely proportional to the feed force was high because the hand was located farthest tool length L1z and dependent on tool weight, center of gravity from the spindle for that tool. This effect was not observed location, handle length L1y, and feed force FF = F1z. The equa- for tool 4, which also had a long handle, because of its greater tions indicate that less effort is probably needed for supporting tool body length. Although tool 4 had the least resultant hand a pistol-grip power hand tool when the tool body is long than force when both feed force and torque levels were high, tools 1 when it is short. When feed force is large, supporting force and 2 had less resultant hand force for high feed force and decreases when the handle length is short. low torque because these tools permitted the hands to grasp the tool close to the spindle axis. Consequently, the best tool This is why handles aligned close to the tool spindle axis and depended on both feed force and the torque requirements for with long tool bodies are advantageous for tools such as power the task. hand drills. These drills often require considerable feed force with torque reaction forces relatively less than for a nut runner, All tools were assumed to weigh the same; had they varied so a short handle is favorable. Alternatively, when torque is large weights, the differences might have been even greater. Additional and feed force is small, a tool with a long handle is advantageous. factors the model can consider include relative tool weight, mass When both feed force and torque are significant factors, how- distribution, and tool orientation. This analysis does not take ever, as when drilling large holes or shooting self-tapping screws into account the relative strength capabilities of the hand in the in hard wood, these parameters must be optimized. three component directions, although use of such a model does not exclude strength comparisons. The model can be used for comparing resultant hand forces associated with different tools for the same operation and for

Chapter 6e ● Power hand tools 257 Tool types 12 3 4 Figure 6e.9 Comparison of resultant hand forces acting on the hand for four equivalent power nut runners plotted against reaction torque. The reaction force transmitted to the hand for right-angle ⎡ 1 0 1 0 ⎤ ⎡F1x ⎤ ⎡ −Wx ⎤ power drivers is affected also by the magnitude of spindle torque ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ and the tool dimensions. Right-angle nut runner spindle torque ⎢ 0 1 0 −1 ⎥ × ⎢ F1z ⎥ = ⎢ 0 ⎥ can range from less than 0.8 Nm to more than 700 Nm. A tool L1y 0 L2y ⎥ ⎥ ⎢ −Tx ⎥ operator opposes these forces while supporting the tool and main- ⎢0 ⎥ ⎢F2x ⎥ ⎢ ⎥ taining control. This torque is transmitted to the operator as a ⎣⎢L1y ⎦ ⎢⎣F ⎦ ⎣ ⎦ reaction force and opposed by the great mechanical advantage 0 L2y 0 2z − W xLGy resulting from the long reaction arm created by the tool handle.37 These equations can be used to compare hand forces between Right-angle power drivers a right-angle and a pistol-grip power nut runner used on a horizontal surface (Fig. 6e.10). The right-angle nut runner in this A right-angle nut runner is functionally nothing more than a example weighs 20 N, whereas the pistol-grip nut runner weighs pistol-grip nut runner with a very short body and long handle. 50 N. A graph of torque reaction force plotted against torque The model for a right-angle nut runner is shown in Figure 6e.7C. shows that the mechanical advantage of the right-angle nut Because right-angle nut runners are usually operated with both runner for high torque levels is considerable. The other hand, hands, two-hand forces are now in the z-axis; F1z is applied at the however, exerts greater feed force for the right-angle nut runner handle for supporting the tool, and F2z is applied over the tool than for the pistol-grip nut runner. Because the pistol-grip nut spindle to help provide feed force. (When these tools are used runner weighs more and has its center of gravity closer to the one handed, the equations for a pistol grip nut runner apply.) tool spindle, it requires less support force for F1z and F2z than for the right-angle nut runner (Fig. 6e.10). Sometimes handle force Right-angle tools have short spindles perpendicular to the can be reduced further through the proper use of accessory long axes of the handles. Because the handle is usually longer handles and torque reaction arms. than the spindle, these tools are often held in two hands (Fig. 6e.7C). In this case, the right hand (subscript 1) grasps the In-line power drivers tool at the distal end of the tool handle, whereas the left hand (subscript 2) grasps it proximal to the spindle. It is further The form factor and associated forces and moments involved assumed that equal amounts of force are exerted by both hands in operating an in-line power tool are shown in Figure 6e.7D to react against tool torque along the long axis of the handle, and and dimensions in Figure 6e.8C. Assuming that the right hence F1z = F2z. The resulting matrix is hand (subscript 1) supports the tool, the static handle force matrix is ⎡1 0 ⎤ ⎡F1y ⎤ ⎡−Wy ⎤ ⎢⎣0 ⎥ × ⎢ ⎥ = ⎢ ⎥ G1x ⎦ ⎣ S1y ⎦ ⎣ −Ty ⎦ Table 6e.4 Pistol-grip nut runner dimensions, load, The static torque developed at an in-line power hand tool and center of gravity location spindle has an equal and opposite reaction torque Ty that must Tool Weight (N) L1z (m) L1y (m) L1z (m) be overcome by tangential shear forces between the hand and 1 30 0.09 0.06 0.07 the handle. The tangential shear force S1y produces torque about 2 30 0.40 0.09 0.26 the grip radius G. The shear force S1y is proportional to the com- 3 30 0.11 0.50 0.07 pressive hand force FG and the coefficient of friction μ between 4 30 0.40 0.50 0.32 the hand and the handle, similar to a manual screwdriver except in this case the spindle rather than the hand is producing the torque. In-line power driver operation is therefore limited by the

258 Chapter 6e ● Biomechanical aspects of hand tools z L1y x y LGy F1x Lzy F1z F2z L1z LGz Wz −Tz Tz FRz Figure 6e.10 Static forces for right-angle nut runner operation. maximum compressive grip force an operator can produce and the operator’s posture; (4) tool speed and weight are improved by the dimensions of the tool. The relationship between the over right-angle nut runners in most tool sizes; and (5) use of static torque, grip force, and tool diameter is similar to that of reaction bars can improve tool performance. manual screwdriver operation: The limitations are that (1) torque reaction bars must be Ty = S1yG = μFG G custom-made for each operation, (2) several attachments can make tool use difficult, (3) adding weight to the tool makes it Push-to-start activated power hand tools free the operator more cumbersome to handle, and (4) the intervention is not from having to squeeze a trigger or lever, but they can increase practical when the accessibility is limited, the manipulation is force requirements because they require more feed force to start restricted, or the reaction bar has no surfaces to contact. If a reac- them. A flange at the end of in-line handles helps prevent the tion bar is provided, however, a smaller tool handle can be used. hand from slipping during feed force exertion.15 When an accessory handle or torque reaction bar is used Accessory handles and torque reaction arms with a pistol-grip nut runner (Fig. 6e.11), the horizontal hand force F1x is reduced. If a vertical force is applied to a torque Accessory handles assist a pistol-grip power tool operator by reaction bar, as depicted in Figure 6e.12, an additional term is providing an additional handle for two-handed operation. needed for the sum of the moments in the z-axis: A torque reaction bar can sometimes be used to transfer loads back to the work piece. In fact, reaction torque can be com- T − F1x L1y + FSy LSx = 0 pletely eliminated from the operator’s hand by use of either a stationary reaction bar adapted to a specific operation so that As a result, F1x becomes reaction force can be absorbed by a convenient solid object or a torque-absorbing suspension system. F1x = −FSyLSx + T L1y A reaction bar can be installed on in-line, pistol-grip, and angled tools. The advantages of tool-mounted reaction devices If a torque reaction bar is used and all the torque reaction are that (1) all reaction forces are removed from the operator; force acts against a stationary object, then (2) one-hand-operated pistol-grip and in-line reaction bar tools can be used rather than right-angle nut runners, which usually T = −FSy LSx require two hands; (3) reaction bar tools can be less restricting on Consequently, F1x = 0

Chapter 6e ● Power hand tools 259 Tool types Right angle Pistol grip Figure 6e.11 Comparison of hand forces between a right-angle nut runner and a pistol-grip nut runner operated on a horizontal surface. Tool counterbalancers moment in the yz-plane, the counterbalance force FCy also influ- ences F1y. The moment is counteracted by a coupling moment, The force requirements for a job are often related to the weight C, from the hand, as described in the following equations: of the tools being handled. The effort needed for holding an object in the hands is usually associated with its mass,34,35 so that F1y + Wy + FCy = 0 heavier tools generally require greater exertion. There is a trade- off between the selection of a lightweight tool and the benefit F1yL1z + WyLGz + FCyLCz + C = 0 of the added weight for performing operations that require high feed force. A spring counterbalance or air balancer can help If the counterbalance force FCy is set to counteract the tool reduce the load from heavy tools that are operated frequently. weight Wy, then When used to support the tool, the counterbalance produces FCy = −WTy a force that opposes gravitational force. This is illustrated with a pistol-grip power tool in Figure 6e.13. When the tool is held Consequently, the y-axis component of the hand force freely in the hand, there is no torque to react against (T = 0) becomes F1y = 0. The location that the counterbalance force acts and consequently no reaction force (F1x = 0). Besides creating a against the tool can affect operator exertion when holding it. Solving for the coupling moment C, LSx −TZ C = FCy(LGz − LCz) FSy The equation shows that the coupling moment can be eliminated (C = 0), if F1x LGz = LCz Figure 6e.12 Force and moment arm for a pistol-grip nut runner equipped with a torque reaction bar. Balancers should therefore be attached to tools at or near their centers of gravity so as to avoid additional effort by the tool operator to counteract the handle moment. Balancers should be installed carefully so that minimal effort is needed when holding and using the tools in the desired work location. Spring counterbalances produce a force that opposes gravitational force so the tool weight is reduced. If installed incorrectly, however, these balancers can actually have the reverse effect of increasing force. Spring tension should be adjusted so that the operator does not have to counter more force than necessary and balancers so that the tool aligns as close to the work area as possible to prevent unnecessary reach- ing. The counterbalance should not lift the tool when it is released so that the operator must elevate the shoulder to reach it; the tool should remain suspended at the same height at

260 Chapter 6e ● Biomechanical aspects of hand tools FCy y x LCz L1z z LGz LGy L1y Wy F1y Figure 6e.13 Static forces when C handling a pistol-grip power hand tool with a counterbalance. Counterbalance force FCy creates a moment in the yz-plane that is counteracted by a coupling moment C. which it was released. Also, situations where operators tend to force of a threaded fastener is therefore proportional to torque, work ahead of or behind the assembly line should be avoided. with a desired clamping force achieved by rotating the fastener If a tool is moved horizontally, a trolley and rail system should to a specific target torque. Levels of joint stiffness range from be installed. Special attention may be required to be sure that a hard joint (30 degrees of spindle rotation) to a soft joint the balancer is attached directly above the work. (360 degrees of spindle rotation). Examples are illustrated in Figure 6e.14 Dynamic forces The spindle torque and angular displacement during torque Tool torque buildup model buildup have a linear relationship such that There are three elements involved in power nut runner operation θ( T ) = Tt θt (T − T0 ) using a threaded fastener: the operator, the tool, and the mechan- − T0 ical joint that joins or clamps two objects together, the hardness of which is analogous to the stiffness of a spring. The clamping where T is tool spindle torque, θ is spindle angular displacement, Tt is the target torque, T0 is the rundown torque, and θt is the target angle. Figure 6e.14 Recording of torque buildup profiles for hard (light line) and medium-soft (heavy line) joints. (From Lin JH, Radwin RG, Fronczak FJ, Richard TG: Ergonomics 46(12): 1161-1177, 2003.)

Chapter 6e ● Power hand tools 261 Pneumatic motors have a distinctive speed-torque relationship. following differential equation results in terms of the tool The motor does not produce torque at the free running speed, rotation θ: whereas it exerts maximum torque when the motor stalls. The spindle speed can be described using the equation ( JT + Msh2 ) d2θ + csh2 dθ + ksh2θ = T(t) dt 2 dt S( T ) = S (1 − T ), where T(t) is the tool torque, Ms, cs, and ks are the operator 0 T max mechanical parameters, JT is the mass moment of inertia of the tool about its spindle, and h is the distance between the hand where S is spindle speed expressed as a function of torque T, Tmax is the motor maximum torque output, and S0 is free run- and the tool spindle. ning speed. Because speed S(T) is the derivative of angular displacement θ(T), the unique solution for the differential equation is the torque delivered to the spindle )e− ( Tt −T0 )S0 t θtT max T(t) = T ma x + (−T ma x + T 0 The force experienced by the hand can be obtained by dividing the equation for T(t) by the distance of the hand from the rotating spindle. Handle force model: dynamics Figure 6e.15 A pistol-grip pneumatic hand tool is illustrated with a Lindqvist25 proposed that a simple mass-spring mechanical normal operator grip. The mechanical parameters can be defined as system might be sufficient to describe the handle response to follows: Ms = the total effective mass of the operator’s arm, hand, and impulsive reaction forces encountered in nut runner operation a portion of the upper body lumped at the distance h from the center but did not identify specific parameters for these elements. Lin et al23 advanced this model of the human operator; their of rotation of the tool spindle or line of action of the tool torque, T(t). method identifies these mechanical properties to predict the JT = the rotational mass moment of inertia of the tool about the center kinematic and kinetic response of the handle (motion and force) of mass of the tool. h = location of the center of pressure of the when an impulsive reaction force was encountered in threaded operator’s hand on the tool handle. ks = the effective stiffness of the fastener power hand tool operation. A brief description of the operator’s arm, hand, and a portion of the upper body. cs = the model is provided here. effective damping of the operator’s arm, hand, and a portion of the upper body. T(t) = the tool torque which is transmitted to the operator in The human operator is represented as a dynamic mechanical a typical mechanical fastening operation. θ = the rotation of the tool analog of a single degree-of-freedom mechanical system consist- and hand about the tool spindle axis. H = horizontal distance between ing of a linear spring, a mass, and a viscous damper (Fig. 6e.15). the floor and the handgrip. V = vertical distance between the ankles Instead of modeling for individual contributing muscles, the and the handgrip. (From Lin JH, Radwin RG, Richard TG: Handle model combines the loading of the muscles and joints into mechanical elements without considering the directions of the dynamics predictions for selected power hand tool applications. loads. The mechanical properties, Ms, ks, and cs, are assumed to be passive and invariant for an individual, a given posture, and Hum Fact 45(4):645-656, 2003.) a tool orientation. The effective mass Ms represents the total contributions of the standing operator coupled to the tool through the hands. The effective spring stiffness and damping represent the gross effect of the operator acting against the han- dle, including contributions from the entire body and nonspe- cific muscle groups. A system identification method using free oscillation measures these mechanical parameters for various work locations for three common tool shapes: pistol grip, right angle, and in-line. This method measures the influence of the operators’ mechanical elements on the system dynamic response (oscillation frequency and damping ratio) of a known mechani- cal system. The mechanical parameters are then extracted analytically.23 Given the mechanical parameters for an operator, the model estimates the dynamic response (angular displacement and force) when the operator encounters an impulsive reaction force from a power tool. A torsional dynamic equilibrium equation about the tool spindle axis can be written. The