262 Chapter 6e ● Biomechanical aspects of hand tools This second-order differential equation can be solved numer- situations can be assisted by comparing the mechanical rela- ically using finite difference techniques and a discrete time step tionships between the task and tool parameters. Other aspects variation of the tool torque, T(t). The result will be a description that should be considered but are not covered in this chapter of the time variation of the tool rotation, θ(t), include repetitive use, assumed postures, vibration exposure, and contact stress. ⎧⎫ ⎪ ⎪ ⎪ 1 ⎪ ⎡ ⎪⎧ 2(Msh2 + J) ⎪⎫ ⎪⎧ csh 2 2(Msh2 + J ) ⎪⎫ ⎤ θi = J ⎬ ⎢ ⎨ (Δt)2 T − ksh2 ⎬ θi (Δt)2 T ⎬ θ −1+ T ⎥ , +1 ⎨ ⎪ ⎣⎢ ⎪⎩ + ⎨ i i ⎪ Msh 2 + T csh2 ⎩⎪ 2Δt 2Δt ⎭⎪ ⎪⎭ ⎦⎥ ⎩⎪ (Δt)2 + ⎭⎪ where i is the iteration step, Δt is the time step, and T is the tool The following recommendations can be made: torque. 1. When large feed forces are necessary, use the longest manual With the rotational response of the tool predicted, the screwdriver available and provide a screwdriver shaft long motion of the handle can be defined as hθ(t). The force F(t) enough so that it can be gripped by the other hand as a guide. delivered to the handle can be approximated by Nut drivers and socket drivers also help reduce hand forces by providing concentric handle rotation and additional mechanical csh dθ + kshθ = F(t) advantage at the screw head. dt 2. Large-diameter manual screwdriver handles with high frictional characteristics are recommended; if the handle diameter is too Here the handle force F was estimated by solving the above large, however, the mechanical advantage may be counteracted equation. The tool operator mechanical model was also used to by reduced grip strength. estimate tool handle kinematics during torque buildup. The 3. Phillips head screws should be avoided because they require resultant handle displacement and force for using a right-angle greater axial push force as torque increases. Torx™ head tool having buildup times ranging from 35 (hard) to 1000 (soft) screws provide the least axial reaction force. ms was calculated and is plotted in Figure 6e.16 for the female 4. Pliers and shears can sometimes be used to a greater mechan- with the smallest stiffness and the male with the greatest stiffness.24 ical advantage by gripping them so that the pivot is on the ulnar rather than the radial side of the hand. CONCLUSIONS AND RECOMMENDATIONS 5. Torque reaction force is less for longer pistol-grip and right- angle nut runners than for equivalent tools with shorter han- Tool operator exertion can be minimized by considering the dles. forces acting on the tools and the way they are used for a specific 6. When pistol-grip power hand tools that have longer tool task. The selection of alternative hand tools for different work bodies are used, less vertical support force is required than for Figure 6e.16 Model prediction for handle displacement and force when using a right-angle nut runner on a horizontal surface for different torque buildup times. (From Lin JH, Radwin RG, Richard TG: Handle dynamics predictions for selected power hand tool applications. Hum Fact 45(4): 645-656, 2003.)
Chapter 6e ● References 263 equivalent tools with shorter tool bodies, provided that their 17. Greenberg L, Chaffin DB: Workers and their tools. Midland, MI, 1977, Pendell. mass distribution is similar. 18. Hallbeck MS, Sheeley GA, Bishu RR: Wrist fatigue in pronation and supination for 7. All other factors being equivalent, when feed force is large and torque is small, a pistol-grip power tool with a shorter dynamic flexion and extension: a pilot study. In S Kumar, ed: Trends in handle should be used. When feed force is small and torque ergonomics/human factors I. Amsterdam, 1984, Elsevier, pp. 51-57. is large, a pistol grip power hand tool with a longer handle is 19. Hertzberg T: Some contributions of applied physical anthropology to human more advantageous. engineering. Ann NY Acad Sci 63(4):616-629, 1955. 8. Torque reaction bars help eliminate torque reaction forces, 20. Huston TR, Sanghavi N, Mital A: Human torque exertion capabilities on a fastener and accessory handles help distribute torque reaction forces device with wrenches and screwdrivers. In A Mital, ed: Trends in ergonomics/human among the two hands. factors I. Amsterdam, 1984, Elsevier, pp. 51-57. 9. A tool counterbalance can help reduce the force needed to 21. Kattel BP, Fernandez JE: Criteria for selection of hand tools in the aircraft manufacturing support a power hand tool. The optimal location for attaching industry: a review. In MA Hanson, ed: Contemporary ergonomics. London, 1998, a balancer is at the tool center of gravity. Taylor & Francis. 22. Lin JH, Radwin RG, Fronczak FJ, Richard TG: Forces associated with pneumatic power REFERENCES screwdriver operation: statics and dynamics. Ergonomics, 46(12):1161-1177, 2003. 23. Lin JH, Radwin RG, Richard TG: Dynamic biomechanical model of the hand and arm 1. Aghazadeh F, Mital A: Injuries due to hand tools. Appl Ergonom 18(4):273-278, in pistol grip power hand tool usage. Ergonomics 44(3):295-312, 2001. 1987. 24. Lin JH, Radwin RG, Richard TG: A single-degree-of-freedom dynamic model predicts the range of human responses to impulsive forces produced by power hand tools. 2. Amis AA: Variation of finger forces in maximal isometric grasp tests on a range J Biomech 36(12):1845-1852, 2003. of cylinder diameters. J Biomed Eng 9:313-320, 1987. 25. Lindqvist B: Torque reaction in angled nutrunners. Appl Ergonom 24:174-180, 1993. 26. Mital A: Effect of body posture and common hand tools on peak torque exertion 3. Armstrong TJ, Punnett L, Ketner P: Subjective worker assessments of hand tools used capabilities. Appl Ergonom 17(2):87-96, 1986. in automobile assembly. Am Indust Hyg Assoc J 50:639-645, 1989. 27. Mital A, Kilbom A: Design selection and use of hand tools to alleviate trauma of the upper extremities. Part I. Guidelines for the practitioner. Int J Ind Ergonom 10:1-5, 1992. 4. Ayoub MM, LoPresti PL: The determination of an optimum size cylindrical handle 28. Myers JR, Trent RB: Hand tool injuries at work: a surveillance perspective. J Saf Res by the use of electromyography. Ergonomics 14(4):509-518, 1971. 19:165-176, 1988. 29. Oh S, Radwin RG: Pistol grip power tool handle and trigger size effects on grip 5. Cannon LJ, Bernacki EJ, Walter SD: Personal and occupational factors associated exertions and operator preference. Hum Fact 35(3):551-569, 1993. with carpal tunnel syndrome. J Occup Med 23:255-258, 1981. 30. Örtengren R, Cederqvist T, Lindberg M, Magnusson B: Workload in lower arm and shoulder when using manual and powered screwdrivers at different working heights. 6. Cederqvist T, Lindberg M: Screwdrivers and their use from a Swedish construction Intl J Indust Ergonom 8:225-235, 1991. industry perspective. Appl Ergonom 24(3):148-157, 1993. 31. Petroski H: The evolution of useful things. New York, 1992, Alfred A Knopf. 32. Pheasant S: Body space: anthropometry, ergonomics and design. London, 1988, 7. Cochran DJ, Riley MW: The effect of handle shape and size on exerted forces. Taylor & Francis, pp. 227-233. Hum Fact 27:253-265, 1986. 33. Pheasant S, O’Neill D: Performance in gripping and turning-a study in hand/handle effectiveness. Appl Ergonom 6(4):205-208, 1975. 8. Cochran DJ, Riley MW: An evaluation of handle shapes and sizes. Proceedings of the 34. Radwin RG, Armstrong TJ: Assessment of hand vibration exposure on an assembly 26th Annual meeting of the Human Factors Society, Seattle, WA, 1982, pp. 408-412. line. Am Ind Hyg Assoc 46(4):211-219, 1985. 35. Radwin RG, Armstrong TJ, Chaffin DB: Power hand tool vibration effects on grip 9. Cook TM, Rosecrance JC, Zimmerman CL: Work-related musculoskeletal disorders in exertions. Ergonomics 30(5):833-855, 1987. bricklaying: a symptom and job factors survey and guidelines for improvements. 36. Radwin RG, Oh S, Fronczak FJ: A mechanical model of hand force in power hand tool Appl Occup Environ Hyg 11:1335-1339, 1996. operation. In Proceedings of the Human Factors and Ergonomics Society, 39th Annual Meeting, San Diego, CA, October 1995, pp. 548-552. 10. Dahlman S, et al: Tools and hand function: requirements of the users and the use 37. Radwin RG, VanBergeijk E, Armstrong TJ: Muscle response to pneumatic hand tool situation. In Y Quéinnec, F Daniellou, eds: Designing for everyone. London, 1991, reaction forces. Ergonomics 32(6):655-673, 1989. Taylor & Francis. 38. Replogle JO: Hand torque strength with cylindrical handles. Proceedings of the 27th annual meeting of the Human Factors Society, Norfolk, Virginia, 1983, pp 412-416. 11. Deivanayagam S, Weaver T: Effects of handle length and bolt orientation on torque 39. Rothfleish S, Sherman D: Carpal tunnel syndrome: biomechanical aspects of strength applied during simulated maintenance tasks. In FI Aghazadeh, ed: Trends occupational occurrence and implications regarding surgical management. Orthop in ergonomics/human factors V. Amsterdam, 1988, Elsevier Science, pp. 827-833. Rev 7:107-109, 1978. 40. Silverstein BA, Fine LJ, Armstrong TJ: Occupational factors and carpal tunnel 12. Drury CG: Handles for manual materials handling. Appl Ergonom 11(1):35-42, 1980. syndrome. Am J Ind Med 11:343-358, 1987. 13. Drury CG, Hibschweiller ML: Size and weight effects on robot teach pendants. In SA 41. Swedish National Institute of Occupational Health: Forskning & Praktik. Vol. 2. 1993, The Institute, pp. 14-17 (English edition). Robertson, ed: Contemporary ergonomics. London, 1994, Taylor & Francis, pp. 417-423. 42. Ulin SS, Armstrong TJ, Snook SH, Monroe-Keyserling W: Perceived exertion and 14. Fransson C, Winkel J: Hand strength: the influence of grip span and grip type. discomfort associated with driving screws at various work locations and at different work frequencies. Ergonomics 36:833-846, 1993. Ergonomics 24(7):881-892, 1991. 43. Westling G, Johansson RS: Factors influencing the force control during precision grip. 15. Grant KA, Habes DJ: Effectiveness of a handle flange for reducing manual effort Exp Brain Res 53:277-284, 1984. during hand tool use. Int J Ind Ergonom 12:199-207, 1993. 16. Grant KA, Habes DJ, Steward LL: The influence of handle diameter on manual effort in a simulated assembly task. In S Kumar, ed: Advances in industrial ergonomics and safety IV. London, 1992, Taylor & Francis, pp. 797-804.
7C H A P T E R Hip and Knee
7aC H A P T E R Age, sex, and social life are of importance, along with occupa- tional factors. When compared with the upper extremities, neck, Epidemiology of the and lower back, diseases and disorders of the lower extremities Lower Extremity have less association to work.12 Workers’ compensation claims for disorders of the lower extremities account for fewer than 10% Gunnar B. J. Andersson of all musculoskeletal claims in Sweden. Musculoskeletal impairments increase with age. This is true for DEFINITIONS lower extremity impairments as well. Praemer et al26 concluded, based on 1995 data, that over 5% of the U.S. population had From an etiologic perspective, occupational musculoskeletal dis- lower extremity or hip impairments. This number is probably orders can be viewed as caused, aggravated, or accelerated by slightly higher today as the population has aged. Although the work. An occupational injury is defined as any injury that results percentile rates were 1.8% among those below age 17, it was 7.7% from a work-related accident or exposure involving a sudden in individuals 65 years of age and older. Women experience a event in the work environment.25 An occupational illness is any slightly smaller percentage of lower extremity impairments than abnormal condition or disorder other than that resulting from men. More than 20 million Americans have osteoarthritis (OA), occupational injury that is caused by exposure to factors associ- which makes OA the leading cause of long-term disability in per- ated with employment.25 Cumulative trauma disorders are con- sons older than age 65 years. Nonspecific knee pain is reported sidered occupational illnesses. by 4.6% of persons older than 18 years, and the corresponding number for hip pain is 3.1% (NHANES III). Specific to the work- OCCUPATIONAL INJURIES place, in 1996 there were about 5.7 million occupational injuries in the United States, of which 6.4% were fractures and 43.6% were In the United States, injuries to the musculoskeletal system in sprains and strains. Some 8.6% of fractures and 10.3% of sprains 1997 had an annual incidence of 7.1 per 100 full-time equivalent and strains involved the leg (excluding the foot and ankle); 71% of workers. Injuries among men are most common between 18 and injuries occur from knee causes: overexertion (28%), contact with 44 years of age. objects (26.2%), and falls (16.9%). Fractures resulting in work loss often involved the lower extremities (41.8%), but most of those Rupture of tendons and muscles is not often caused by occu- affect the foot and ankle. On the other hand, sprains and strains pational loading. The strength of tissues decreases with age, but involved the lower extremity frequently (20%), with the knee ruptures are most often seen in sports activities and as a result of being affected in 8.5% of cases (Table 7a.1). rather high-loading injuries. In a population-based study of 55 year olds (575 subjects), OCCUPATIONAL ILLNESS Bergenudd5 showed that 11% had femoropatellar pain and 10% had knee joint pain. The prevalence was higher in women than Joints are made for loading and movement. The cartilage of the in men. In a study correlating knee pain and low IQ measured joints is well designed to withstand compression, translation, and 40 years earlier, low job satisfaction, obesity, and increased s-glu- shear forces. Deleterious types of loading are loads in extreme tamyltransferase were found in men, whereas low education positions (nutcracker effect) and axial impact loads particularly at level, low income, low life success, and sleeping disturbances high speed.23 Low-frequency vibrational loading may be deleteri- were found in women. For the entire group, knee pain and high ous to the joints and the joint cartilage but is often attenuated by occupational workload were also correlated. Similar results were the time it reaches the knee and hip. High-frequency vibration is found for hip pain. Occupational workload correlated with hip unlikely to affect the lower extremities. Highly repetitive, monot- pain in men but not in women. Increased body weight correlated onous work can cause a variety of problems in the joints, bones, with knee pain in men and hip pain in women. tendons, and peripheral nerves. These types of loading condi- tions are not often seen in the lower extremities in relation to As with many other musculoskeletal conditions, the back- occupation but can occur during sports activities. ground for symptoms from the knee and hip is multifactorial. Tendinitis Table 7a.1 Occupational injuries of the lower Tendinitis, tenosynovitis, myalgia, and other conditions of mus- extremities as a percentage of all injuries: cles and tendons are uncommon in the lower extremities. U.S. data.25 Bursitis Diagnosis Hip Knee Lower leg Multiple Eighteen bursae surround the hip joint, and approximately 10 Fracture 0.3 2.6 2.0 1.2 surround the knee joint. Specific diagnoses are often difficult Sprain and strain 0.3 7.9 0.3 0.8
270 Chapter 7a ● Epidemiology of the lower extremity to make. Bursitis caused by sports overuse is not uncommon, but Table 7a.2 Prevalence of osteoarthritis as bursitis around the hip as an occupational illness is rarely seen. diagnosed by history or examination by gender Bursitis of the knee, especially prepatellar or infrapatellar, is often and age group: rate per 100 persons seen in jobs that require kneeling, for example, floor layers, fish- ermen, and plumbers.28-30 Diagnosis Diagnosis by by history examination Nerve entrapments Age Males Females Males Females Only occasionally is nerve entrapment seen in the lower extrem- ities. Ischial neuralgia, or “wallet sciatica,” a sensation along the Less than 20 years — —— — ischial nerve caused by compression at the infrapiriforme fora- 0.2 men, may be encountered by sitting, particularly when having a 20–39 years 0.2 0.4 — 8.9 well-filled wallet in the back pocket. Peroneal nerve compression 40.8 at the side of the knee may cause palsy and can result from work 40–59 years 3.4 8.4 4.0 5.0 activities. This may happen to tractor drivers during prolonged 9.0 sitting in a twisted position and from accidents. Ilioinguinal neu- Over 60 years 17.0 29.6 20.3 ralgia and lateral cutaneous nerve neuralgia are reported as occu- pational illnesses. The mechanism is often some type of pressure All ages 1.9 4.0 2.2 over the anterior part of the iliac crest from heavy belts or other equipment, especially if loaded with tools or other weights. All ages over 20 years 4.5 7.3 4.2 Edema, tiredness, and dull pain in the legs are more common in those with static sitting or standing occupations than in those Perthes disease). Primary OA has been shown to have a multifac- who work in a more varied posture.37 Compartment syndromes torial background. Bilateral hip and knee OA has been suggested are rarely due to occupational loading of the lower extremities. to have an etiology different from that of unilateral OA. This syndrome is more often seen as a result of sports activities Hochberg13 reported on a group of 1337 students who graduated and as a complication of fractures and other traumatic injuries. from The Johns Hopkins University School of Medicine from 1948 through 1964. The cumulative incident of knee OA at age Rheumatic diseases 65 was 6.3%, whereas hip OA existed in 2.9% of individuals. Cumulative knee OA relative rise was three times higher in those Arthritis and rheumatism account for 66% of the musculoskeletal with a history of knee injury (13.9% vs. 6%). The incidence of conditions among women and 51% among men. Osteoporosis knee OA was 7.5 per 1000 person-years among those with a knee accounts for an additional 11% of musculoskeletal disease, occur- injury compared with 1.2 per 1000 person-years, for a relative ring predominantly in females.25 Rheumatic diseases are not risk (RR) of 5.2. Similarly for the hip, the incidence was 3.2 per caused by occupational loading but may be worsened by it. 1000 person-years among those with hip injury compared with 0.7 without a hip injury (RR, 3.5). The increased risk remained Osteoarthritis significant even after adjustment for age, sex, body mass index, and physical activity at study entry. Clearly, lower leg injuries The prevalence of OA is greater in women than in men. Physical should be prevented to reduce the risk of knee and hip OA. examination more often results in a diagnosis of OA, as compared with radiographic examination, when narrowing of the joint Heredity space is used as the criterion. If osteophytosis is included as a sign of OA, the prevalence is much higher. Around 12% of the Most OA is not attributable to single genes. Rather, common U.S. population have OA in any joint.8,12,18 Table 7a.2 shows the OA appears to result from interactions between multiple genes prevalence of OA diagnosed by radiographic examination in dif- and the environment. In a comparative population study in San ferent age groups.18,25 Diagnosis by examination revealed more Francisco, standardized rates of primary hip OA, expressed as OA than diagnosis by history. The explanation is that many indi- numbers per 100,000 population per year, were 1.5 in Japanese, viduals are symptom free. 1.5 in Chinese, 1.6 in Filipinos, 5.1 in Hispanics, 8.3 in blacks, and 29.4 in whites. The hereditary factor often results in a more In the NHANES I study,2 the prevalence of OA of the knee generalized OA in different locations of the body.22 was 2.3% to 18% in those aged 45 to 74 years, with a larger pre- valence in the elderly and in women. Hip OA was found in The percentage of hip OA, defined as lowered height of the 0.2% to 6.6% in those aged 25 to 74 years, more in the elderly joint cartilage, at 70 years of age in Sweden is about 2% in both but with less sex difference than OA in the knee. OA of the hip sexes. Knee OA has a prevalence of 2% in men and 3% in women and knee has been studied in relation to occupational and other at 70 years of age in Sweden. However, a relation to occupational factors. These results were confirmed in recent studies.1,6 loading or sports is more clearly shown in men, whereas obesity correlates more with knee OA in women. Consequently, a hered- Secondary OA is due to previous known trauma (e.g., frac- itary factor increasing the risk for females to contract OA of the ture, surgery) or disease (e.g., hip dysplasia, osteochondritis, knee is likely.22 Obesity correlates with symptomatic OA in the hip31 and also in the knee, which is clearly shown in females, and has an RR of about 4.10,22 Hip OA Sports Lindberg and Montgomery20 found a 2.8% prevalence of hip OA in control subjects as compared with 5.6% in athletes
Chapter 7a ● References 271 and 14% in elite athletes (soccer players). Similar results have carry an increased risk for OA. Other physically demanding jobs been shown by Klunder et al.16 Among those undergoing a total have less of an increase in RR for OA, around 2 to 3, similar to hip procedure because of OA, Vingård et al32-34 found an RR of the RR for obesity and lower than the increased risk in some elite 4.5 for athletes. Those athletes who also had a physically athletes.22 demanding job had an RR of 8.5. Different results have been shown in studies of long-distance runners.9 REFERENCES Occupation Vingård et al32-36 found more symptoms caused by 1. Andersen RE, Crespo CJ, Ling SM, Bathon JM, Bartlett SJ: Prevalence of significant hip OA in men exposed to greater physically demanding jobs. knee pain among older Americans: results from the Third National Health and Farmers, construction workers, firefighters, and food processing Nutrition Examination Survey. J Am Geriatric Soc 47(12):1435-1438, 1999. workers had significantly more OA than expected (RR, 2.4). For those exposed to both occupational loading and sports activities 2. Andersson JJ, Felson DT: Factors associated with osteoarthritis of the knee in the first the RR was 8.5, and for sports alone the RR was 4.5. In this National Health and Nutrition Examination Survey (NHANES I): evidence for an asso- study, being overweight had an RR of 2.5. Disability pension for ciation with overweight, race, and physical demands of work. Am J Epidemiol hip OA was more often received by those with high occupational 128(179):89, 1988. load exposure than by those with low exposure (RR, 12.4).33 The risk occupations were construction workers, metal workers, 3. Andersson S, Nilsson B, Hessel T, et al: Degenerative joint disease in ballet dancers. farmers, and forestry workers. An increased risk for hip OA has Clin Orthop 238:233-236, 1989. been shown in farmers, with RRs of 9.7 to 12 in several studies.4,7,11,15,19,27 In female farmers, no difference from control 4. Axmacher B, Lindberg H: Coxarthrosis in farmers. Clin Orthop 287:82-86, 1993. subjects was found.4 5. Bergenudd H: Talent, occupation, and locomotor discomfort. Doctoral thesis. Malmö, Knee OA Sweden, 1989, Lund University. Sports A Swedish study22 found a knee OA prevalence of 7% in 6. Christmas C, Crespo CJ, Franckowiak SC, Bathon JM, Bartlett SJ, Andersen RE: How soccer players as compared with 1.6% in control subjects. The common is hip pain in older adults? Results from the Third National Health and prevalence was higher in those with known meniscal tears or Nutrition Examination Survey. J Fam Pract 51(4):345-348, 2002. anterior cruciate ligament ruptures. 7. Croft P, Coggon D, Cruddas M, Cooper C: Osteoarthritis of the hip: an occupational disease in farmers. BMJ 304:1269-1272, 1992. Occupation The Framingham study showed an odds ratio of 8. Cunningham LS, Kelsey JL: Epidemiology of musculoskeletal impairments and asso- 2.2 for OA of the knee in jobs requiring knee bending and at ciated disability. Am J Public Health 74:574-579, 1984. least a medium level of physical activity.10 The etiologic fraction 9. Ernst E: Jogging-for a healthy heart and worn out hips? J Intern Med 228:295-297, or attributable proportion of knee OA to occupational physical 1990. loading was 15%. Obesity accounted for 10%. Only a few females 10. Felson DT, Hannan MT, Naimark A, et al: Occupational physical demands, knee had physically demanding jobs in the study, and no gender asso- bending and knee osteoarthritis: results from the Framingham study. J Rheumatol ciation was found.10 In the NHANES study, knee OA was 18:1587-1592, 1991. increased among men and women with physically demanding 11. Forsberg K, Nilsson B: Coxarthritis on the island of Gotland. Increased prevalence in jobs: odds ratios of 1.88 in women (not significant) and 3.13 in a rural population. Acta Orthop Scand 63:1-3, 1992. men of younger ages, and odds ratios of 3.49 and 2.45, respectively, 12. Hadler NM: Occupational musculoskeletal disorders. New York, 1993, Raven at higher ages. The occupational etiologic fraction was estimated to Press. be 32%.2 13. Hochberg MC: Prevention of lower limb osteoarthritis: Data from the John Hopkins Precursor Study. In VC Hascall, KE Kuettner, eds: The many faces of osteoarthritis. Dock workers have been shown to have more knee OA than Berlin, 2002, Birkuauser. office workers.24 Lindberg and Montgomery20 found an increas- 14. Hult L: The Monkfors investigation. Acta Orthop Scand Suppl 16:1-76, 1954. ing risk for knee OA in shipyard workers as compared with office 15. Jacobsson B, Dalén N, Tjörnstrand B: Coxarthrosis and labour. Int Orthop workers and teachers. Vingård et al32-34,36 found an increased risk 11:311-313, 1987. for knee OA among farmers, construction workers, and firefighters. 16. Klunder KB, Rud B, Hansen J: Osteoarthritis of the hip and knee joint in retired That study also showed an increased risk of knee OA symptoms football players. Acta Orthop Scand 51:925-927, 1980. in female janitors and letter carriers. Therefore, a moderately 17. Kohatsu N, Schurman D: Risk factors for the development of osteoarthritis of the increased risk of symptom-giving knee OA has been shown in knee. Clin Orthop 261:242-246, 1990. physically demanding occupations.4,17,21 Overweight and some 18. Lawrence RC, Hochberg MC, Kelsey JL, et al: Estimates of selected arthritic and sports activities seem to increase the risk of symptom-giving knee musculoskeletal diseases in the U.S. J Rheumatol 16(4):427-441, 1989. OA more than any occupation. 19. Lindberg H, Axmacher B: Coxarthrosis in farmers. Acta Orthop Scand 59:607, 1988. 20. Lindberg H, Montgomery F: Heavy labor and the occurrence of gonarthrosis. A consensus discussion in 1992 in Malmö on the etiology of Clin Orthop 214:235-236, 1987. OA concluded that unfavorable weight bearing and repeated 21. Nicolaisen T: Health among postmen. Copenhagen, 1983, General Directorate for minor trauma may contribute to OA.22 This is in agreement with Post and Telegraph (in Danish). the current etiologic hypotheses. Static load, repeated trauma 22. Nilsson BE: The Tore Nilson Symposium on the etiology of degenerative joint disease. over long periods, and an unnatural use of joints are likely to con- Acta Orthop Scand Suppl 64(253): 54-61, 1993. tribute to OA. Regarding occupation, farmers, professional ballet 23. Nordin M, Frankel VH: Basic biomechanics of the musculoskeletal system, ed 2. dancers,3 and professional soccer players have a much higher fre- Philadelphia, 1989, Lea & Febiger. quency of OA than expected and are therefore considered to 24. Partridge REH, Dulthie JJR: Rheumatism in dockers and civil servants. Ann Rheum Dis 27:559-568, 1968. 25. Praemer A, Furner S, Rice DP: Musculoskeletal conditions in the United States. Park Ridge, IL, 1992, AAOS. 26. Praemer A, Furner S, Rice DP. Musculoskeletal conditions in the United States. Rosemont, IL, 1999, American Academy of Orthopedic Surgeons, pp. 1-182. 27. Thelin A: Hip joint arthrosis: an occupational disorder among farmers. Am J Ind Med 18:339-343, 1990. 28. Törner M: Musculoskeletal stress in fishery: causes, effects, and preventive measures. Doctoral thesis. Sweden, 1991, University of Göteborg. 29. Törner M, Zetterberg C, Anden U, Hansson T, Lindell V: Workload and musculoskeletal problems: a comparison between welders and office clerks. Ergonomics 34:1179-1196, 1991. 30. Törner M, Zetterberg C, Hansson T, Lindell V, Kadefors, R: Musculoskeletal symptoms and signs and isometric strength among fishermen. Ergonomics 33:1155-1170, 1990.
272 Chapter 7a ● Epidemiology of the lower extremity 31. Vingård E: Overweight predisposes to coxarthrosis. Body mass studied in 239 males 35. Vingård E, Alfredsson L, Hogstedt C, Goldie I: Ökad risk för arthros i knän och höfter with hip arthroplasty. Acta Orthop Scand 62:106-109, 1991. för arbetare i yrken med hög belastning på benen. Läkartidningen 87:4413-4416, 1990. 32. Vingård E: Work, sports, overweight and osteoarthrosis of the hip. Arbete och Hälsa 25, doctoral thesis, 1991, Karolinska Institute, Stockholm, Sweden. 36. Vingård E, Hogstedt C, Alfredsson L, Fellenius E, Goldie I, Koster M: Coxarthrosis and physical work load. Scand J Work Environ Health 17:104-109, 1991. 33. Vingård E, Alfredsson L, Fellenius E, Hogstedt C: Disability pensions due to musculoskeletal disorders among men in heavy occupations. Scand J Soc Med 37. Winkel J: On fast swelling during prolonged sedentary work and the significance of 20:31-36, 1992. leg activity. Arbete och Hälsa, doctoral thesis, Stockholm, 1985, National Institute of Occupational Health. 34. Vingård E, Alfredsson L, Goldie I, Hogstedt C: Sports and osteoarthrosis of the hip. Am J Sports Med 21(2):195-200, 1993.
7bC H A P T E R femoral condyles in the knee in extension precludes almost any motion in the frontal and transverse planes. The knee motion in the Biomechanics of the transverse plane increases as the knee is flexed toward 90 degrees, Hip and the Knee with a maximum of approximately 45 degrees in internal rotation and 30 degrees in external rotation, and then decreases primarily Ali Sheikhzadeh due to the soft tissue restrictions. Similarly, motion in the frontal plane increases as the knee is flexed toward 30 degrees, reaching a Biomechanical analysis of the hip and knee joints during daily maximum of only a few degrees of abduction and adduction, and activities that occur in the home and work environment can then decreases as the knee flexion goes beyond 30 degrees. identify tasks that are potentially harmful for a healthy and an injured joint. A kinematics and kinetic profile of uninjured joints Values for the average range of motion of the knee joint in provides an understanding of joint contribution during func- the sagittal plane during 11 common activities are reported in tional tasks, provides a baseline to identify abnormalities, and Table 7b.1. A range of motion of 130 degrees is required for com- thereby assists with diagnosis and treatment. Moreover, it facili- mon daily living activities. Excluding the range of motion tates the design and performance of reconstructive surgery and required to bathe, 11061 to 117 degrees51 of knee flexion would rehabilitation programs. seem a reasonable goal for the rehabilitation of its motion for the general population. The inability of the knee to move within the The kinematics and kinetics of the hip and knee joints and range of motion required for daily living activities would be the joint forces that occur during activities of daily living are the compensated for by increasing the motion of other joints51 or focus of this chapter. The application of biomechanical models avoiding trying to perform the task. for calculating external forces and moments at the hip and knee joints is explained first. The application of biomechanical con- Kinematics of the hip cepts in reducing joint forces and thereby risk of injury is then discussed. The activities discussed are mainly physical activities The hip joint is a synovial ball-and-socket joint with articulation of daily living and those commonly performed at work such as between the large nearly spherical head of the femur and the gait, stair climbing, rising from a chair, and lifting weights. acetabulum of the pelvis. With its inferior anterolateral and infe- rior opening, the acetabulum provides a wide range of motion. KINEMATICS OF THE HIP AND KNEE The concave acetabulum covers about two thirds of a spherical femur head. As the hip joint is loaded, the acetabulum deforms A three-dimensional measurement of relative motion among about the femoral head. The unloaded acetabulum has a smaller adjacent limb segments, comprehensive kinematics analysis is diameter than that of the femoral head.21 expressed by 6 degrees of freedom, generally three translational and three rotational angles. However, kinetics analysis involves Hip motion takes place in all three planes, with the greatest both static and dynamic analysis of internal and external forces motion in the sagittal plane. The extreme motion of the hip joint and moments acting on a joint. In the musculoskeletal system, is limited by passive tension of the surrounding ligaments external forces frequently include the ground reaction forces, the and muscles (Table 7b.2). Passive hip flexion is approximately weight of the limb segment, and the force of one segment on 140 degrees, whereas active hip flexion with the knee flexed is another. Muscle contractions, passive soft tissue stretch, and 125 degrees and with it extended is 90 degrees. Passive hip extension articular reaction forces generate primarily internal forces. is approximately 30 degrees, whereas active extension is 20 degrees.59 Kinematics of the knee Table 7b.1 The mean of the left knee joint angle performed by 20 normal elderly subjects during The knee joint is composed of the tibiofemoral joint and the 11 functional activities patellofemoral joint. The tibiofemoral joint has the greatest motion in the sagittal plane, 0 to approximately 140 degrees. Function Mean Provided by articulations between large convex femoral condyles and smaller or nearly flat tibia condyles, this large range allows Level walking 64.5 extensive knee motion in the sagittal plane for the activities such Ascend slope 61.6 as walking, running, squatting, and climbing. Descend slope 69.0 Ascend stairs 80.3 The knee motion in the transverse plane (internal and external Descend stairs 77.8 rotation) and in the frontal plane (abduction and adduction) is Sit down low chair 92.5 affected by the amount of joint flexion. The interlocking of the Sit to stand low chair 95.0 Sit down standard chair 91.0 Sit to stand standard chair 89.8 Into bath 123.3 Out of bath 131.3 Rowe PJ, Myles CM, Walker C, Nutton R. Gait Posture 12:143-155, 2000.
274 Chapter 7b ● Biomechanics of the hip and the knee Table 7b.2 Magnitude of hip range of motion and associated limiting ligaments and muscular tissues Hip motion Magnitude of hip motion Examples of tissues that may limit the extremes of motion Flexion 80° (with knee extended) Hamstrings and gracilis muscles 120° (with knee fully flexed) Inferior fibers of ischiofemoral ligament Extension Inferior capsule 20° of extension (with knee extended)* Predominantly iliofemoral ligament and anterior capsule; some components of the pubofemoral Abduction Adduction 0° (with knee fully flexed) and ischiofemoral ligaments Internal Rotation 40° Rectus femoris muscle Extrenal Rotation 25° Pubofemoral ligament, inferior capsule, adductor and hamstring muscles Superior fibers and ischiofemoral ligament, iliotibial band, and abductor muscles such as 35° 45° the tensor fasciae latae Ischiofemoral ligament external rotator muscles (e.g., piriformis) Lateral fasciculus of iliofemoral ligament, iliotibial band, and internal rotator muscles (e.g., gluteus minimus, tensor fasciae latae) *Implies 20° of extension beyond the neutral zero degree position. From Neumann, DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby; p. 400. The hip abduction range is about 30 degrees, and adduction range require gross oversimplification of forces and coincide with the is about 25 degrees. The external and internal rotations of the hip theoretical assumption of the model itself. However, the reliabil- are 90 and 70 degrees, respectively, when the joint is flexed. The ity and validity of biomechanical models depend on realistic internal and external rotations of the hip, when it is extended, are assumptions and representations of the mechanical system and approximately 15 and 35 degrees, respectively.59 accuracy of the experimental data that constitute the inputs and/or outputs. In addition, an important aspect of developing Most common daily activities require flexion, abduction, and a model is to decide what should be included or neglected. external rotation. The mean of motion during selected daily Although it is not always possible, generally the simplest model activities is shown in Table 7b.3. Most daily activities require more that provides a valid representation of reality should be used. than 100 degrees of hip flexion.30 Squatting and shoe tying with the foot across the opposite thigh require the greatest motion in Table 7b.3 Mean values for maximum hip range the frontal and transverse planes. Walking on a level surface of motion measured in three planes during several requires about 30 degrees of flexion and 10 degrees of extension, common activities for 33 healthy men with minimal abduction-adduction and internal-external rotation. Approximately 80 to 104 degrees of flexion and extension, respectively, is required to sit on or rise from a chair. The range of motion during daily activities should be inter- preted cautiously. The reported range has been shown to be influ- enced by age,23 speed of movement,15 and environmental task constraints such as chair46 and stair height. Mulholland and Wyss44 demonstrated the significance of cultural sensitivity in the interpre- tation of daily activities. In many parts of Asia and the Middle East, a chair is not commonly used at home or work, and sitting on the floor without support, sitting cross-legged, or kneeling are more common than in Western countries.22,44 Mulholland and Wyss44 suggested that even rural as opposed to urban life-styles in differ- ent geographic locations might demand significantly different ana- lytical approaches and should be considered in evaluations of daily physical activities. The current related literature on daily living activities, including data reported in Tables 7b.1 and 7b.3, reflects mainly the Western life-style and would not apply to the actual life-styles of many people in Asian and Middle Eastern cultures. There is a growing need for culturally and racially sensitive data that allow for individual variation in the normal range of motion. KINETICS OF THE HIP AND KNEE Generally, a biomechanical model attempts to represent a simpli- Johnston RC, Smidt GL: Hip motion measurement for selected activities of daily living, fied version of a complex task. Often these representations may Clin Orthop 72:205-215, 1970.
Chapter 7b ● Kinetics of the Hip and Knee 275 Superior SAGITTAL PLANE Posterior Anterior (from the side) (cm) 10.0 Inferior 5.0 Gluteus medius (post.) Gluteus minimus (ant.) Force P Gluteus maximus TeIllnsopors foaasscise latae ba 0.0 Sartorius Rectus femoris -5.0 Semimembranosus lAodndguucstor Pbrecetivinseus M=0 Bseicmepitesnfedmonoossisusand Adductor W×a−P×b−0 femoris W×a=P×b b P=W×a -10.0 Rectus Force W Adductor -5.0 (cm) Figure 7b.2 Free-body diagram of moments acting around the magnus center of motion of the tibiofemoral joint during stair climbing. The (post.) ground reaction force (W) and its lever arm (a) are counterbalanced by moments produced by the quadriceps muscle force through the 5.0 0.0 patellar tendon (P) and its lever arm (b). (From Nordin M, Frankel VH: Biomechanics of the knee. In M Nordin, VH Frankel, eds: Basic Figure 7b.1 A side view of the femoral head with the line-of-action of biomechanics of the musculoskeletal system. New York, 2001, several muscles crossing the hip in the sagittal plane. (From Neumann DA: Lippincott Williams & Wilkins, pp. 176-201.) Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby, p. 400.) The formulation of a comprehensive dynamic model of the of the knee flexion moment to the carrying of objects during knee and hip joints is challenging because of the complexity of occupational tasks can be determined by adding the weight of an internal forces acting on the joints and the difficulty of measur- object to the external weights acting on the body. ing anatomic parameters precisely. For instance, a comprehensive model of the hip joint should include the line-of-action of mus- Despite the oversimplification of the joint forces that may be cles crossing it with respect to its axes of rotation in the sagittal estimated based on a free-body diagram, a two-dimensional static and frontal plane, as presented in Figure 7b.1. In addition to model can be used to analyze occupational tasks or to design the line-of-action of muscles, such a model should consider the rehabilitation training. Typically, a person with arthritis pain or dynamic changes of these parameters during joint motion. The fol- patellofemoral joint pain is advised to avoid large forces created lowing methods are used to overcome the difficulty and complex- by the quadriceps.12 Figure 7b.3 illustrates the magnitude of the ity of estimating the internal joint forces during dynamic tasks. external forces on the knee during two physical tasks requiring knee extension, tibial-on-femoral knee extension (the line Analytical joint models between D and B) verses the femoral-on-tibial knee extension during the 0 to 90-degree joint angle (the line between A and C). Often, even the simplest model of external forces generated by During tibial-on-femoral knee extension, the external moment gravity acting on the body provides crucial functional and clini- arm of the weight of the lower leg increases from 90 degrees to 0 of cal information about a joint. As illustrated in Figure 7b.2, for knee flexion. In contrast, during femoral-on-tibial knee exten- instance, a simplified free-body diagram of the lower extremity sion, the external moment arm of the upper BW decreases from during a single leg stand phase of stair climbing presents a rea- 90 degrees to 0 of knee flexion. sonable estimate of the tibiofemoral joint forces and patella tendon force. The flexion moment of the lower leg is the product of the body A more realistic biomechanical model of the knee should weight (BW) and its lever arm, the perpendicular distance of the include a better representation of the patellofemoral stresses and BW to the center of the tibiofemoral joint motion. The sensitivity forces within the quadriceps muscle. The single line of quadri- ceps force in Figure 7b.2 should be replaced by four lines. The four heads of the quadriceps muscle consist of distinct fibers that
276 Chapter 7b ● Biomechanics of the hip and the knee A B 100% 70% External Torque-Angle Plot Relative external torque (% maximum) 0% 90º 70º 45º 20º 0º C D Knee angle (degrees) EXTENSION Figure 7b.3 The relative external torque generated by body weight acting on the knee joint between 90-degree flexion and full extension (0 degree) during two styles of knee extension: (1) during femoral-on-tibial extension (A to C line), the external moment arm of the weight of the lower leg increases from 90-degree knee flexion to full knee extension, and (2) during tibial-on-femoral extension (D to B line), the external moment arm of the upper-body weight decreases from 90 degrees to 0 knee flexion. (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby, p. 458.) approach the patella at different angles, especially the vastus medi- human concept aims at understanding human activities through alis fibers, which approach from two distinct directions. The more the simulation of accurate physiologic and anatomic models and distal oblique fibers approach the patella at 50 to 55 degrees, and data. This type of simulation combines biomechanical models of the remaining more longitudinal fibers approach it at 15 to joints and mechanical properties of connective tissues to visualize 18 degrees, both medial to the quadriceps tendon.49 Cohen et al12 presented a more comprehensive model of the knee joint, com- Figure 7b.4 Quadriceps muscle force exertion simulation based on puter simulated with geometric and anatomic details, to compare anatomical data from five cadavers for closed kinetic chain (CKC) and the patellofemoral stresses and quadriceps force during open (with open kinetic chain (OKC) exercises for knee flexion range of 20 to 0, 25-N, and 100-N load at ankle) and closed kinetic chain leg 90 degrees. The three OKC loading simulated conditions are OKC 0N, exercises in the flexion range of 20 to 90 degrees. As demonstrated knee extension with no load; OKC 25N, leg extension with 25-N external in Figure 7b.4, the quadriceps muscle force and the average force at the ankle; OKC 100N, leg extension with 100-N external force at patellofemoral contact forces increase progressively from 20 to the ankle. (From Cohen ZA, Roglic H, Grelsamer RP, et al: Patellofemoral 90 degrees. stresses during open and closed kinetic chain exercises: an analysis using computer simulation. Am J Sports Med 29:480-487, 2001.) To achieve a more realistic estimate of joint forces, a biome- chanical model of the hip and knee joint should include the soft tissues forces such as agonist-antagonist muscle forces in three- dimensional dynamic environments. The exclusion of agonist- antagonist muscle forces underestimates the internal joint forces. However, the inclusion of these forces adds another layer of complexity to the model and demands more advanced analytical methods to solve indeterminate systems. Generally, inverse dynamic models47 or optimization methods4,56 are used to solve the indeterminate problem of determining muscle and contact forces. For example, with the large number of muscles crossing the hip (Fig. 7b.1) and with at least 27 separate musculotendinous units crossing the joint, a unique demonstration of individual muscle force can be achieved only by oversimplification. Today’s advances in computer science and technology provide the possibility of creating “virtual human” reality.10 The virtual
Chapter 7b ● Reducing internal joint load: application of biomechanical concepts 277 the results in both static and animated forms. For surgical implan- of practical reasons only a limited number of subjects can be tation of a proximal femur/hip prosthesis, for example, graphic studied.69 Because the validity of collected information depends information about implants that is available directly from the on the extent to which joint mechanics and surrounding tissues manufacturers or CAD/CAM files can be added to real images of have been altered, generalizations cannot be made. the patients’ anatomic parameters taken from computed tomo- graphies. It can also be incorporated into the biomechanical REDUCING INTERNAL JOINT LOAD: models of joints and soft tissues in functional tasks. For surgical APPLICATION OF BIOMECHANICAL and medical education and for device development applications, CONCEPTS it is worthwhile to incorporate adaptive anatomic models, which include prosthetic implants and fracture fixation devices. Advanced Determining the consequence of daily physical activities of work computation environments for static posture, kinematics, kinetics, and leisure on lower extremity joints is difficult because of the and stress analysis under physiologic boundary and loading con- complexities of structural anatomy and dynamic movements ditions can be incorporated. combined with the calculation of internal and external forces act- ing on joints. Musculoskeletal loading is influenced by a number In vivo direct measurement of joint forces of individual differences such as age, weight, and gender; the activ- ity itself; and the variables of the task. Such factors help explain Although biomechanical models deal with indirect estimates of individual variation in functional abilities, biomechanical con- internal forces, the real-time continuous signal from an instru- sequences of physical performance on internal tissues, and poten- mented telemetric prosthesis has been used for direct measure- tial risk or mechanism of injury. Biomechanical analysis of ment of internal forces acting on the distal or proximal femur physical activities such as walking, running, and stair climbing during daily activities such as walking and stair climbing.69 Direct provides understanding of internal and external forces acting on measurement of the hip contact forces was first obtained by a joint and their significance for injury and pain. Biomechanical Rydell.62 The peak hip forces during gait vary from 1.8 to 4.3 analysis of task variables such as stair or chair height influence times the BW, with peak pressure occurring during heel strike and gait speed demonstrate the degree to which selected charac- and early midstance.4 These hip forces are related to the ground teristics of a task may influence the physical demands of execut- reaction forces acting on the superior anterior acetabulum. For ing it and its consequences for joints and surrounding tissues. The patients measured at 11-31 months postoperatively, the average following is a brief description of selected variables that directly hip forces during fast walking and climbing stairs was about or indirectly influence physical ability and musculoskeletal load- 250% BW and slightly less than going downstairs.7 ing during daily living activities. Taylor and Walker69 studied two patients over 2.5 years dur- Individual factors ing various daily activities. The average peak distal femoral shaft forces for one patient during various activities were jogging Individual factors such age, gender, anatomic variation, and 3.6 BW, stair descending 3.1 BW, walking 2.8 BW, treadmill medical history and disease stage are known directly or indirectly walking 2.75 BW, and stair ascending 2.8 BW. Bending moments to influence ability, internal resources for executing a task, and about the mediolateral axis (flexion-extension) and anteroposte- distribution of internal forces and tissue tolerance. Except for rior axis (varus-valgus) peaked in the range of 4.7-7.6 BW cm weight, individual factors cannot be controlled or altered, but and 8.5-9.8 BW cm, respectively, over the follow-up period. understanding a mechanism by which these factors may influ- During similar activities, however, forces and moments for the ence joint loading is important to explain injury mechanism, pre- second subject were generally 45-70% less than those for the first vent injury risk, and design rehabilitation programs for special subject due to inadequate musculature around the knee.69 groups of individuals. The joint forces and moments of patients who have had joint Age, weight, and gender arthroplasty are expected to return to the values of healthy indi- viduals within approximately 6 months after surgery.2 The discrep- Individual factors such as age,1,15,16,21,34,58 weight,1,11 and gender35,36,67 ancy between forces and moments reported by various authors, influence the internal joint forces and ultimately the injury for example, Bergmann et al7 and Taylor and colleagues,69,70 reflect mechanism and risk. Biomechanical properties of soft tissues and the variation among individuals, success of surgery, location of the hip and knee joints are known to be different between gen- measured forces, and time of study with respect to surgery. For ders and to change with age in a highly individualized process example, Taylor and Walker offer a good estimate of the loading and rate. They may be modified negatively or positively by many conditions (distal femoral) acting at the knee and are assumed to factors such as activity types and frequency, medical conditions, offer data different from what Bergmann and colleagues found and nutritional factors. The alteration of posture, active and pas- with respect to hip arthroplasty surgery. sive range of motion of the hip and knee joints, and gait during physical activities are associated with age and gender as well.51 In comparison with biomechanical models, direct measure- ment produces valid data on internal forces. The information An individual’s weight and height directly influence the hip serves mostly as validation9,39,65 for biomechanical models and and knee joint moments.71 Height can influence limb size and provides useful insight into wear, strength, and fixation stability. therefore lever arm. Daily physical activities such as walking and Direct measurement is otherwise difficult because of technologic restrictions and ethical considerations, and because of a variety
278 Chapter 7b ● Biomechanics of the hip and the knee stair climbing exert 3.5 BW on hip and knee forces. A change of into account their decrease in capacity.23 Using inverse dynamics 5 pounds of BW, for instance, may therefore result in 17.5 pounds analysis, Figure 7b.5 compares the knee joint moments of healthy of excess force in the knee and hip. Additionally, an individual’s young and older adults during stair ascent and descent and when weight has been associated with the prevalence of joint pain1 and rising from a chair compared with maximal isometric effort in supine change in properties of tissue characteristics.11 leg press. Although there is no significant difference between absolute knee moments during physical activities, motor tasks Aging is associated with a decrease in neuromuscular control demand substantially greater effort relative to available maximum characterized by the decline of maximum muscle force produc- capacity of elderly compared with young adults. As illustrated in tion, the velocity of contraction, and the dynamic stability.33 Figure 7b.5, relative effort was significantly higher for stair ascent, Human muscle strength attains its peak between the ages of 20 54% for younger compared with 78% for older adults, stair descent and 30 years and declines gradually until the age of 60 and rigor- required 42% compared with 88% relative effort, and chair rising ously thereafter.31 During the single-leg support phase of walking required 42% compared with 80%. Compared with young adults, and stair climbing, while the body is moving forward, lower the elderly walk at a significantly higher rate of oxygen uptake extremity muscular strength is required to control and support it.34 (about 20% more) and physiologic relative effort, that is, the ratio of Often a lack of joint strength or an inability to develop torque the required oxygen uptake to the available maximal capacity.5,23 within the appropriate time may contribute to the risk of injury.71 Stair descent by the elderly has previously been described as a Age has been hypothesized to cause a redistribution of joint “controlled fall” due to the lack of ankle flexibility and strength as torques and power during gait. DeVita and Hortobagyi15 reported well as the delay in developing torque rapidly.72 that during self-selected walking speed, elderly adults had 58% greater angular impulse and 279% more work at the hip and 50% It has been suggested that absolute task demands for perform- less angular impulse and 29% less work at the knee compared ing activities of daily living are not significantly high; however, with young adults. Similarly, they reported 23% less angular older adults’ difficulty in performing these activities must take Figure 7b.5 Mean of body mass-normalized knee joint moments for healthy young adults of 22 years and old adults with a mean age of 74 years during stair ascent (A), stair descent (B), and sit-to-stand (C). For stair ascent and descent, one cycle represents the initial foot contact (0) with the stair to toe-off (100%). For rising from a chair, one cycle corresponds to lift-off (0) to fully erect position at the end of the rise (100%). The bar graphs represent the group mean of the maximal isometric knee joint moments measured at specific knee joint positions in a leg press task. Solid lines and filled columns indicate older adults, and dashed lines and open columns denote young adults. (From Hortobagyi T, Mizelle C, Beam S, DeVita P: Old adults perform activities of daily living near their maximal capabilities. J Gerontol A Biol Sci Med Sci 58:M453-M460, 2003.)
Chapter 7b ● Reducing internal joint load: application of biomechanical concepts 279 impulse and 29% less work at the ankle for the elderly compared Maximum knee adduction momentadduction moments and more varus alignment than those in with young adults. The elderly use less of the ankle plantar (% body weight • height)which osteoarthritis is less severe.45 flexors and knee extensors and more of the hip extensors.15 Figure 7b.6 demonstrates the magnitude and slope of the the- Anatomic variation oretical relationship between the maximum knee adduction moments and the walking speeds for two groups of patients with In addition to variation in the size of muscle and bone, many different degrees of knee osteoarthritis severity compared with known anatomic variations directly influence the hip and knee asymptomatic control subjects matched for age and sex. The vari- joint forces. For instance, the femoral neck has two angular rela- ation of the slopes in Figure 7b.6 indicates that adopting differ- tionships with the femoral shaft: the neck-to-shaft or inclination ent walking speeds may not equally benefit osteoarthritis patients. angle and the torsion or anteversion angle. The inclination angle Patients with less severe knee osteoarthritis walk with unique gait of the femur is referred to the relation of the femur neck with the mechanics that are different from those of the control group and shaft in the frontal plane. The inclination angle is about 140 to those of patients whose knee osteoarthritis is more severe.45 150 degrees at birth and usually reduces to approximately Similarly, other studies have demonstrated the effects of hip 125 degrees, with a range of 90 to 135 degrees in adulthood. These osteoarthritis and pain on the hip forces and gait.25 abnormal angles alter the alignment between the acetabulum and femoral head and thereby alter the hip moments by chang- In summary, the kinematics and kinetics of the knee and hip ing the lever arm and the effect of upper body forces on the joints are directly or indirectly influenced by individual factors. joint. The inclination angle may have positive and negative bio- A brief discussion of some of these factors mainly serves as an mechanical effects.49 The torsion angle of the femur is the rela- example of how they may influence hip and knee joint forces. tive rotation that exists between the neck and the shaft. Although these individual factors cannot be controlled or mod- Normally, an infant is born with about 30 degrees of torsion ified, understanding their relationship with their influencing angle that usually decreases to 15 degrees by 6 years of age.55,75 mechanism helps to explain the individual’s tolerance, ability to Excessive anteversion is often associated with a tendency toward perform physical tasks, neuromuscular adaptation, and variation internal rotation of the leg during gait, change of contact area in the magnitudes of joint forces. Whereas most reported studies between the femoral head and the acetabular,50 and wear on the in this section discuss and compare healthy individuals with articular cartilage. certain groups such as the elderly or individuals with severe osteoarthritis, who may not represent the working population, The Q-angle is another reported anatomic variation. During the information can still demonstrate the process and direction of active knee extension and passive stretch, several structures guide biomechanical change. the patellar movement with respect to the tibiofemoral joint. Although each structure alone may force medial or lateral Less severe movement of the patella, the net result of these forces moves it knee OA through the groove with minimal stress to the articular surfaces. The degree that the quadriceps tends to pull the patella is known 4.0 as the Q-angle, which varies between the genders24 and is not bilaterally symmetric.37,38 A Q-angle of greater than 15-20 degrees 3.0 Asymptomatic is often thought to contribute to high articular stress and the poor tracking of the patella, thereby leading to arthritis, chondro- 2.0 More severe malacia, recurrent patellar dislocation, or patellofemoral joint knee OA pain syndrome. Although in apparently normal anatomic struc- ture the Q-angle and femoral neck angle of inclination and tor- sion is not necessarily consistent with the appropriate knee and hip joint loading during physical activities, the abnormal range of these angles is usually an indication of abnormal joint loading and pain. Medical history and disease stage 1.0 Medical history such as osteoarthritis45 and ligament deficiency35,67 0.5 1.0 1.5 may alter the kinematics and kinetics of the hip and knee joints Walking speed (m/s) directly or indirectly. Hip and knee osteoarthritis results from degenerative changes in cartilage that to some extent result from Figure 7b.6 Relationship between maximum knee adduction moment arbitrary increases in joint loading.19 For instance, patients with and self-selected walking speed for three groups of subjects: patients advanced knee osteoarthritis walk with lower ground reaction with knee osteoarthritis (OA) of lesser and greater severity and matched forces and reduced sagittal plane range of motion,45,66 increased control subjects. (From Mundermann A, Dyrby CO, Hurwitz DE, Sharma L, knee adduction moment,6 decreased stride length,3 and increased Andriacchi TP: Potential strategies to reduce medial compartment angling out of the toes.73 Although self-selected walking speed loading in patients with knee osteoarthritis of varying severity: reduced has been reported to explain only 8.9% of the variation in the walking speed. Arthritis Rheum 50:1172-1178, 2004.) maximum knee adduction moment, a patient’s walking style is associated with the severity of knee osteoarthritis.45 One study has shown that knees with more severe osteoarthritis have greater
280 Chapter 7b ● Biomechanics of the hip and the knee Reduction of joint forces and moments When the pelvis rotates and the trunk is laterally flexed toward the stance limb, the moment arm may reduce substantially with Many physical activities such as walking, running, and stair respect to the neutral trunk. If the lever arm decreases from 4 to climbing involve coordinated cyclic movements of several joints. 2 inches (Fig. 7b.7B), the hip joint moment proportionally Often, the comprehensive kinetic and kinematics analysis of reduces to half. single joints such as the hip or knee requires understanding their function in relation to other joints and their crossing muscles. In a series of three experiments, Neumann48 compared the The internal joint forces during dynamic physical activities are electromyography activity of the hip abductor muscles in sub- produced by BW, externally carried loads, and internal soft tissue jects with hip prostheses adopting different methods of walking forces such as muscles. A practical method of reducing joint force while using canes and carrying external loads. Twenty-four is to reduce the lever arm and impact of external forces. Several subjects with unilateral hip prostheses carried loads weighing biomechanical and physiologic factors underlie the mechanism 5%, 10%, or 15% BW and held by either their contralateral or to reduce joint loads during physical activities and thereby risk ipsilateral arms relative to their prosthetic hips. As shown in of injury. Figure 7b.8, it was assumed that during the midstance phase of walking, the hip abductor muscle generated a very large force Reducing the lever arm proportional to the BW and varied with a relatively small moment arm. Neumann found that the use of a cane on the con- The primary function of the hip joint is to support the weight of tralateral side and the ipsilateral load condition could reduce the the head, arm, and trunk both in static erect posture and in muscle activities by 40% of baseline as compared with walking dynamic activities such as walking, running, and stair climbing. without a load or a cane. The most effective means of reducing the joint forces during daily activities is to find a practical method of reducing the mag- Synergic movement and muscular coactivation nitude of either these forces or the lever arm. The hip and knee joint forces need to be understood largely in the context of The force produced by a given muscle with specific size and action of the upper BW on the lower extremity. For example, the structure depends on the activation level, length, and speed of magnitude of the torques on the hip joint during upright stand- contraction. The interaction of these parameters and their influ- ing is equal to the weight of the upper body (W), which is equal ence on muscle force production has been discussed in most to two thirds of BW50 times the distance of this force from the basic textbooks of skeletal muscle biomechanics and physiology. hip joint axis. As shown in Figure 7b.7A, during a single-legged Generally, it is known that tension generated in a skeletal muscle stance, assuming the lever arm is 4 inches,52 for a 180-pound is a function of its length and the magnitude of overlap between individual, the gravitational force at the hip is as follows: the actin and myosin filaments. As the load increases, the velocity at which a muscle shortens while undergoing maximal stimulation Hip joint moment = (upper BW + lower leg weight) × lever arm decreases. During physical activities involving the lower extremity, muscle length changes due to the synergy among the monoartic- Assuming the weight of lower leg is one sixth of BW, the acting ular and biarticular muscles of the hip and knee joints. moment is as follows: During functional activities, often the biarticular muscles have = (2/3 BW + 1/6 BW) × lever arm antagonistic activities at one joint and agonistic activities at = 5/6 BW × 4 = 150 × 4 = 600 lbs/in another.4 During stair climbing, for example, the rectus femoris acts as the knee agonist muscle by providing the knee extension Often individuals with painful hip or abductor weakness may moment and as the hip antagonist muscle by providing the hip lean their upper bodies over the painful hip to reduce the pain flexion moment.4 At times a muscle is even antagonist in one or may display a Trendelenburg (abductor lurch) gait pattern.59 plane and agonist in another. Except for the short head of the Weight Moment Arm Weight Moment Arm AB Figure 7b.7 Normal pelvis and hip orientation during upright standing (A) and pelvis position during abductor lurch and Trendelenburg (B). (From Robertson DD, Britton CA, Latona CR, Armfield DR, Walker PS, Maloney WJ: Hip biomechanics: importance to functional imaging. Semin Musculoskelet Radiol 7:28-41, 2003.)
Chapter 7b ● Reducing internal joint load: application of biomechanical concepts 281 flexors in a series of radiographs. He found that the hamstring moment arm is about 2.50 cm in 5- and 90-degree knee flexion, but it increases to 4.08 cm as the knee reaches 45 degrees. These findings suggest that besides the length-tension relationship, the hamstring lever arm compensates for the decrease of muscle length that occurs during knee flexion (Fig. 7b.9B).42 Two-joint muscles provide several advantages in the control of the musculoskeletal system during physical performance. First, biarticular muscles couple the motion of the two joints in that they cross and redistribute muscle torque, joint power, and mechanical energy throughout a limb. Second, the shortening velocity of biarticular muscles is less than that of monoarticular muscles. Therefore, a comprehensive biomechanical analysis of a physical task should include a careful analysis of co-contraction biarticular muscles and synergic activities among all joints in bal- ancing internal and external forces. Joint forces during daily living activities Figure 7b.8 The mean of normalized electromyography produced by The muscular demand and internal forces on the joint and soft tissues during daily physical activities may provide valuable the hip abductor muscles during three walking conditions: walking with information about how they interact. Understanding the factors that may modulate the demand of these activities on the inter- contralateral (CL) cane and ipsilateral (IL) load, with contralateral cane, nal forces can be extremely valuable for assessing the effects of tasks that occur routinely at home and at work. and with ipsilateral load. Loads are 5%, 10%, and 15% BW. The hip Squatting abductor electromyogram is normalized to normal control walking Dynamic squatting is an integral part of occupational27-29,68 and conditions. (From Neumann DA: An electromyographic study of the hip daily living activities, especially in non-Western cultures,22,44 and is the essential part of the strength and conditioning programs for abductor muscles as subjects with a hip prosthesis walked with rehabilitation and many sports that require high levels of strength and power.18 Half squatting, in which the posterior thighs are different methods of using a cane and carrying a load. Phys Ther parallel to the ground with approximately 0-100 degrees of knee flexion, is more commonly discussed and recommended in the 79:1163-1173, 1999.) literature rather than deep squatting, in which the posterior thighs and legs make contact. Dynamic squatting is generally biceps femoris and the popliteus, all knee flexors are biarticular discussed in the context of the tibiofemoral and patellofemoral muscles, and their ability to produce force is influenced by the rel- forces, the knee muscle activities, and the joint stability. ative position of the two joints over which they cross. And except for the gastrocnemius, all muscles that cross posterior to the knee Escamilla18 reviewed selected studies that have quantified the have the ability to flex and internally or externally rotate it. knee force during dynamic squatting. The posterior cruciate lig- ament restrains low to moderate posterior forces for all of the As a joint angle varies during physical activity, changes in the knee flexion angles throughout squatting. The anterior cruciate muscle length and in its effective moment arm at the joint result ligament restrains low forces from 0 to 60 degrees of knee flex- in torque variation.42 For the biarticular muscle of the hip and ion. During dynamic squatting, peak posterior cruciate ligament knee, it has been shown that change of angle at one joint and forces are estimated to range from 295 to 2704 N, peak anterior elongation of the muscle have been accompanied in most cases cruciate ligament forces from 28 to 500 N for 0 to 60 degrees of by greater torque production, an example being the effect of the knee flexion, and peak compression from 550 to 7928 N. hip angle on the knee extensor or flexor torque. Because the ultimate failure load is reported to be 4000 N54 for the posterior cruciate ligament and from 1725 to 2160 N for the Mohamed et al42 investigated the influence of length change anterior cruciate ligament,53,74 dynamic squatting should not on the electromyographic activity of six knee flexor muscles. As injure healthy joints.18 shown in Figure 7b.9A, regardless of the knee position, extended hip position was associated with significantly less torque than Although squatting and kneeling are common activities among that of the other two flexed hip positions. Similarly, 90-degree many populations,22,27-29,44 only a limited number of studies have knee flexion influenced the flexor muscle torque independent of investigated the biomechanical consequences during such deep the hip angle. Because the hamstring muscle length was short- flexion activities.22 Hefzy et al22 used biplanar radiographs to eval- ened at both joints, the extended hip position and the 90-degree uate knee kinematics in deep flexion and showed that the motion knee flexion resulted in the least torque production. of the femur did not reveal rollback on the tibia beyond 135 degrees of flexion. Another kinematic study by Dyrby et al17 The highest knee flexion torque was 90 degrees at the hip position and 45 degrees of knee flexion rather than extension. Similar results have been reported by other investigators that the peak torque occurred during the 45-degree knee flexion, where the flexor muscles were not fully stretched. In addition to the knee flexion torque, Smidt64 measured the lever arms of the knee
282 Chapter 7b ● Biomechanics of the hip and the knee Hip at 0° Knee at 0°(00-00) Hip at 0° Knee at 45°(00-45) Hip at 0° Knee at 90°(00-90) Hip at SLR Knee at 0°(SLR-00) Hip at SLR Knee at 45°(SLR-45) Hip at SLR Knee at 90°(SLR-90) Hip at 90° Knee at 0°(90-00) Hip at 90° Knee at 45°(90-45) Hip at 90° Knee at 90°(90-90) A The nine test positions. 800 Torque (kg•cm) 700 Hip position 600 0 degree 90 degree 500 45 degree 0 degree 400 300 90 degree 200 100 Knee position 0 B Figure 7b.9 (A) The maximum isometric knee torque and electromyographic data collected during a series of nine combinations of the knee and hip position for 19 healthy subjects. (B) The maximum isometric knee flexion torque for three positions of the knee and two hip angles. (From Mohamed O, Perry J, Hislop H: Relationship between wire EMG activity, muscle length, and torque of the hamstrings. Clin Biomech 17:569-579, 2002.) showed the relationship between deep knee flexion and Fry et al20 studied knee joints under external load, the barbell internal/external rotation during deep squatting. Dahlkvist et al14 squat technique, the restricted forward displacement of the knees calculated joint and muscle forces from data collected from six past the toes versus non-restricted movement, and the knee posi- subjects performing squatting and rising from a deep squat. tion on the hip and knee torques. Seven weight-trained men were Compared with the forces during normal walking,41,43 they esti- videotaped while performing parallel barbell squats with loads mated the tibiofemoral joint forces to vary from 4.7 to 5.6 times equal to their BWs. The study showed significant (p < 0.05) dif- the BW vertically and 2.9 to 3.5 times the BW horizontally. Other ferences between the static knee and the hip torques, and the investigators studied different styles of sitting and standing that restricted squat produced more anterior lean of the trunk and require deep knee flexion. As shown in Figure 7b.10, deep flexion shank and greater angles at the knees and ankles. The restricted activities generate large quadriceps moments and net posterior squat produced knee torque of 117.3 (34.2) Nm and hip torque forces depending on the style of ascension. The net moments of 302 (71) Nm, whereas the unrestricted squat produced knee and posterior forces increase along with the flexion angle. torque of 150 (50) Nm and hip torque of 28 (65.0) Nm. As Figure 7b.10 shows, net quadriceps muscle activity during double leg descending is about twice the single leg descending. The squat technique and stabilization mechanism to balance the whole body can affect the large net quadriceps moments and
Chapter 7b ● Reducing internal joint load: application of biomechanical concepts 283 Net moment (%BW*Ht) 16 Flexion moment Net moment (%BW*Ht) 16 14 N = 19 14 N = 19 12 12 Flexion moment 10 10 Posterior force 8 8 6 6 Inferior force 4 4 40 60 80 100 120 140 160 2 2 0 0 Knee angle (degrees) 100 Posterior force 100 80 80 Net force (%BW) 60 Inferior force Net force (%BW) 60 40 40 20 20 40 60 80 100 120 20 20 0 Knee angle (degrees) 0 – 20 – 20 – 40 – 40 – 60 – 60 – 80 – 80 –100 –100 0 0 A Single leg descending B Double leg descending Figure 7b.10 The mean and standard deviation of the net flexion moment (), net posterior force (᭹), and net inferior force (᭡) during single-leg (A) and double-leg (B) descent for 9 women and 10 men with a mean age of 29 years (range, 21-37). Stick figures indicate the sagittal image of the limb during each motion. Net moments are normalized to the percent of body weight times the height (%BW × Ht), and net force is normalized to the percent of body weight (%BW). (From Nagura T, Dyrby CO, Alexander EJ, Andriacchi TP: Mechanical loads at the knee joint during deep flexion. J Orthop Res 20:881-886, 2002.) net internal forces of the knee and hip joints. The loads on the knee and hip flexion.46 Bergmann et al8 reported the peak hip knee during deep flexion are important for both knee pathogene- contact forces and torsional moments measured by instrumented ses and rehabilitation programs for patients with total knee implants during different common physical activities. The average arthroplasty. Although some squatting techniques such as hip joint load was 238% BW while walking 4 km/h, 251% BW restricting forward movement of the knees may minimize their while ascending stairs, and 260% BW while descending stairs. stress, it is likely that such techniques may inappropriately trans- The most critical aspect of stair climbing is the inward torsion, fer mechanical stress to the hips and low back. which is 23% larger during ascent than walking. Stair climbing and walking The number of parameters studied during stair climbing has been limited, in particular in the frontal plane. Nadeau et al46 Like walking, stair climbing is a common daily activity that has studied and compared stair climbing and level walking during a been associated with a large number of cyclic joint loadings. If preferred speed in healthy adults over 40 years old. The net these activities are accompanied by pain and instability, they moments and powers were estimated with an inverse dynamic increase the perception of disability.13 Although stair climbing approach. The researchers reported a significantly shorter stance and walking are performed easily by healthy persons, they are time and longer mean cycle duration for stair climbing than for quite demanding when joints or motor functions have been level walking. In comparison with level walking, greater flexion altered by disease or injury. Especially during their single support of the lower limb was observed at the beginning of the stair phase, adequate joint strength and control are critical to support climbing cycle (foot strike) and less extension at the hip was the entire body mass and move the body forward. observed at toe-off with concentric action of the abductor mus- cles that raise the pelvis on the contralateral side. Although the Despite the similarity between these two physical activities, same muscle groups are used in stair climbing and walking, adequate muscle strength and joint range of motion for level major differences were observed in the patterns of the knee flex- walking does not ensure the individual’s ability for stair climbing. ors and extensors and the hip abductors and in the magnitude of The differences between these modes of locomotion might be the knee dorsiflexion during the swing phase. The moments and significant for individuals with physical impairments. Compared powers indicated a different action of the hip abductors across with level walking, stair climbing requires 15 to 20 degrees more
284 Chapter 7b ● Biomechanics of the hip and the knee tasks to control the pelvis in the front plane of the stance phase roles played by the hip and ankle.40 The ankle has the major role and the knee extensors in the sagittal plane. during forward continuance, with relatively little contribution from the knee and hip. If the ankle is restricted, the higher forces Costigan et al13 examined hip and knee joint kinetics during are therefore transferred to the hip and knee. stair climbing in 35 young healthy subjects using a subject- specific knee model to estimate the bone-on-bone tibiofemoral Task variables and patellofemoral joint contact forces. Net knee forces were below one BW, whereas peak posterior-anterior contact forces In addition to the lever arm and magnitude of the external forces, were close to one BW. The peak distal-proximal contact force various task variables are known to influence gait or movement was on average three times BW and could be as high as six times pattern and thereby change the forces of the muscles and internal BW. These contact forces occurred at a high degree of knee flex- joints. Task variables can be classified into two categories. The ion, where there is a smaller joint contact area resulting in high first is those that are defined by the environment and cannot be stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg, individually controlled, such as stair height and angle of inclina- whereas the flexion moment was 1.16 (0.24) Nm/kg. Similar peak tion and chair height, armrest,26,60 and surface condition.63 moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee For example, Riener et al57 studied the influence of stair flexion moment were higher during stair climbing than during climbing with three inclination angles of 24, 30, and 42 degrees level walking. The most striking difference between level walking on the hip and knee joint biomechanics and motor coordination and stair ascent was that the peak patellofemoral contact force (Figure 7b.11). The joint angles and moments showed relatively was eight times higher during the latter. small differences but depended significantly on the three inclina- tion angles. The temporal gait cycle parameters and ground The patterns for normal stair gait show the dominant role of the knee during weight acceptance and pull-up, with the supporting HIP POWER KNEE POWER ANKLE POWER Normalized joint power (W/kg) 1.4 3 Max 1.2 Ascent Level 2 Max 2 Level Norm Ascent 1 walking Norm Ascent walking Min Max Norm 1 Min 1 Min 0.8 Descent 0 0.6 Max Norm 0 0.4 –1 0.2 Min –2 Level –1 0 Min walking – 0.2 –3 Norm –2 Min Max Norm Descent – 0.4 –4 Descent –3 Max – 0.6 –5 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Cycle time (%) A Cycle time (%) Cycle time (%) MAXIMUM JOINT MOMENTS MAXIMUM JOINT POWERS Normalized joint moment (Nm/kg) 1.6 Hip Normalized joint power (W/kg) 4 1.4 Knee 3.5 Hip 1.2 Ankle 3 Knee 1 2.5 Ankle 0.8 0.6 2 0.4 1.5 0.2 1 0 0.5 – 0.2 – 0.4 0 – 0.5 –50 –40 –30 –20 –10 0 10 20 30 40 50 10 20 30 40 50 –1 B Inclination (deg) –50 –40 –30 –20 –10 0 Inclination (deg) Figure 7b.11 (A) Joint moments during level walking and stair ascent and descent at minimum (±24 degrees), normal (±30 degrees), and maximum (±42 degrees) inclinations, averaged for 10 healthy subjects. Joint moments are normalized by body weight. The cycle starts with foot contact. The vertical bar indicates the toe-off, which divides the entire cycle into stance and swing phase. (B) Group mean and standard deviation for joint powers and joint moments for hip (᭹), knee (), and ankle (᭡) during level walking (0-degree inclination), three-stair descent (at angles of −42, −30, and −24 degrees), and three-stair ascent (at angles of 24, 30, and 42 degrees). The solid lines show linear regressions. (From Riener R, Rabuffetti M, Frigo C: Stair ascent and descent at different inclinations. Gait Posture 15:32-44, 2002.)
Chapter 7b ● Conclusion 285 reactions were not significantly affected, but joint powers were adequate height, sufficient space underneath, and armrests significantly influenced by stair inclination. The maximum joint should therefore be recommended for patients with prosthetic powers in the hip and ankle change up to 67% with the inclina- devices,60 as well as for individuals with painful joints and low tion and can be attributed to the amount of potential energy hip and knee strength. produced during ascent or absorbed during descent by the muscles. The kinematics and kinetics of staircase walking differ The second category of task variables consists of those that considerably from those of level walking. individuals may be able to control such as shoes, speed of move- ment, and style of movement gait. Peak force is sensitive to walk- A review of the literature indicated that a chair seat’s height, ing speed.69 Bergmann et al8 studied the influence of footwear the use of armrests, and foot position have major influences on and walking or running style. One subject with an instrumented the sit-to-stand ability and the kinematics and kinetics of the hip implant wore different sports shoes, normal leather shoes, lower extremity joints. Using a higher chair seat results in signif- hiking boots, and clogs and walked barefoot with soft normal icantly lower moments at the knee (up to 60%) and hip (up to and hard heel strikes. The loads were the lowest while walking 50%) joints, whereas lowering the seat height makes sit-to-stand and jogging without shoes. The torsional loads rose up to 50% movement more demanding or even occasionally impossible.26 with shoes, whereas the hip bending moment at the implant Reducing the seat height can alter the body’s stabilizing strategy slightly changed. The investigators concluded that soft heel and biomechanical profile, such as the increase in its center of strikes with smooth gait patterns are the only means to reduce mass travel distance and momentum needed to initiate the move- joint loading. Soft heels, soles, or insoles did not offer advan- ment and the range of motion of the ankle, trunk, and knee.26 tages, and no relationship was found among different types of Conversely, maximum knee flexion moments were found to be shoes. Shoes with very hard soles, however, increased the joint highly dependent on chair height and nearly doubled from the load and were clearly disadvantageous. lowest to the highest position from 6 BW at 115% of knee height to 3 BW at 65% of knee height.60 As shown in Figure 7b.12, CONCLUSION moreover, a more posterior foot position allows both a lower maximum mean extension moment, 32.7 Nm at posterior versus Physical activities of daily living such as walking, running, and stair 148.8 Nm at anterior, and a shorter movement time.32 climbing involve cyclic activities coordinated among several joints. Additionally, the use of the armrests reduces the moments needed Kinetic and kinematic analyses of the hip and knee therefore at the knee and by 50% those needed at the hip. A chair with Figure 7b.12 The pathways of the center of gravity (COG) in a sagittal plane during two methods of foot placement in the initial stage of standing up from a chair (height, 40 cm). In the first method, with anterior foot placement, the COG moves forward and then up with the knee joint extension. In the second method, with posterior foot placement, the COG moves up from the early stage after lift-off with the hip joint and trunk extension. The initial position of the COG is defined as 0. The positive values correspond to forward and up. T1 indicates the beginning and T3 the end of the movement, whereas T2 indicates the beginning of different joint extensions. (From Kawagoe S, Tajima N, Chosa E: Biomechanical analysis of effects of foot placement with varying chair height on the motion of standing up. J Orthop Sci 5:124-133, 2000.)
286 Chapter 7b ● Biomechanics of the hip and the knee require an understanding of joint activities in relation to the 24. Horton MG, Hall TL: Quadriceps femoris muscle angle: normal values and whole body in the context of external loads and adapted posture. relationships with gender and selected skeletal measures. Phys Ther 69:897-901, Kinematic and kinetic analyses of the hip and knee joints 1989. enhance our understanding of factors influencing external and internal forces and injury risks. Additionally, biomechanical con- 25. Hurwitz DE, Hulet CH, Andriacchi TP, Rosenberg AG, Galante JO: Gait compensations cepts and simple biomechanical models provide reasonable esti- in patients with osteoarthritis of the hip and their relationship to pain and passive mates of factors differing among individuals, physical activities hip motion. J Orthop Res 15:629-635, 1997. being undertaken, and task variables. A careful analysis of these factors provides a practical method of reducing musculoskeletal 26. Janssen WG, Bussmann HB, Stam HJ: Determinants of the sit-to-stand movement: a loads by altering external loads or modifying techniques for exe- review. Phys Ther 82:866-879, 2002. cuting physical daily activities, thereby reducing risk of injury. 27. Jensen LK, Eenberg W: Occupation as a risk factor for knee disorders. Scand J Work REFERENCES Environ Health 22:165-175, 1996. 1. Andersen RE, Crespo CJ, Bartlett SJ, Bathon JM, Fontaine KR: Relationship between 28. Jensen LK, Kofoed LB: Musculoskeletal disorders among floor layers: is prevention body weight gain and significant knee, hip, and back pain in older Americans. possible? Appl Occup Environ Hyg 17:797-806, 2002. Obes Res 11:1159-1162, 2003. 29. Jensen LK, Mikkelsen S, Loft IP, Eenberg W: Work-related knee disorders in floor layers 2. Andersson L, Wesslau A, Boden H, Dalen N: Immediate or late weight bearing after and carpenters. J Occup Environ Med 42:835-842, 2000. uncemented total hip arthroplasty: a study of functional recovery. J Arthroplasty 16:1063-1065, 2001. 30. Johnston RC, Smidt GL: Hip motion measurements for selected activities of daily living. Clin Orthop Relat Res 72:205-215, 1970. 3. Andriacchi TP: Dynamics of knee malalignment. Orthop Clin North Am 25:395-403, 1994. 31. Jubrias SA, Odderson IR, Esselman PC, Conley KE: Decline in isokinetic force with age: muscle cross-sectional area and specific force. Pflugers Arch 434:246-253, 4. Andriacchi TP, Miksoz RP: Musculoskeletal dynamics, locomotion and clinical 1997. application. In VC Mow, WC Hayes, eds: Basic orthopaedic biomechanics. New York, 1991, Raven Press, pp. 51-93. 32. Kawagoe S, Tajima N, Chosa E: Biomechanical analysis of effects of foot placement with varying chair height on the motion of standing up. J Orthop Sci 5:124-133, 5. Astrand I, Astrand PO, Hallback I, Kilbom A: Reduction in maximal oxygen uptake 2000. with age. J Appl Physiol 35:649-654, 1973. 33. Lamoureux EL, Sparrow WA, Murphy A, Newton RU: Differences in the neuromuscular 6. Baliunas AJ, Hurwitz DE, Ryals AB, et al: Increased knee joint loads during walking capacity and lean muscle tissue in old and older community-dwelling adults. are present in subjects with knee osteoarthritis. Osteoarthr Cartil 10:573-579, J Gerontol A Biol Sci Med Sci 56:M381-M385, 2001. 2002. 34. Lark SD, Buckley JG, Bennett S, Jones D, Sargeant AJ: Joint torques and dynamic 7. Bergmann G, Deuretzbacher G, Heller M, et al: Hip contact forces and gait patterns joint stiffness in elderly and young men during stepping down. Clin Biomech from routine activities. J Biomech 34:859-871, 2001. 18:848-855, 2003. 8. Bergmann G, Graichen F, Rohlmann A: Hip joint loading during walking and running, 35. Lephart SM, Abt JP, Ferris CM: Neuromuscular contributions to anterior cruciate measured in two patients. J Biomech 26:969-990, 1993. ligament injuries in females. Curr Opin Rheumatol 14:168-173, 2002. 9. Brand RA, Pedersen DR, Davy DT, Kotzar GM, Heiple KG, Goldberg VM: Comparison 36. Lephart SM, Ferris CM, Riemann BL, Myers JB, Fu FH: Gender differences in strength of hip force calculations and measurements in the same patient. J Arthroplasty and lower extremity kinematics during landing. Clin Orthop 401:162-169, 2002. 9:45-51, 1994. 37. Livingston LA, Mandigo JL: Bilateral Q angle asymmetry and anterior knee pain 10. Chao EYS: Graphic-based musculoskeletal model for biomechanical analyses and syndrome. Clin Biomech 14:7-13, 1999. animation. Med Eng Phys 25:201-212, 2003. 38. Livingston LA, Mandigo JL: Bilateral within-subject Q angle asymmetry in young adult 11. Cimen OB, Incel NA, Yapici Y, Apaydin D, Erdogan C: Obesity related measurements females and males. Biomed Sci Instrum 33:112-117, 1997. and joint space width in patients with knee osteoarthritis. Ups J Med Sci 109:159-164, 2004. 39. Lu TW, O’Connor JJ, Taylor SJ, Walker PS: Validation of a lower limb model with in vivo femoral forces telemetered from two subjects. J Biomech 31:63-69, 1998. 12. Cohen ZA, Roglic H, Grelsamer RP, et al: Patellofemoral stresses during open and closed kinetic chain exercises: an analysis using computer simulation. Am J Sports 40. McFadyen BJ, Winter DA: An integrated biomechanical analysis of normal stair ascent Med 29:480-487, 2001. and descent. J Biomech 21:733-744, 1988. 13. Costigan PA, Deluzio KJ, Wyss UP: Knee and hip kinetics during normal stair 41. Mikosz RP, Andriacchi TP, Andersson GB: Model analysis of factors influencing the climbing. Gait Posture 16(1):31-37, 2002. prediction of muscle forces at the knee. J Orthop Res 6:205-214, 1988. 14. Dahlkvist NJ, Mayo P, Seedhom BB: Forces during squatting and rising from a deep 42. Mohamed O, Perry J, Hislop H: Relationship between wire EMG activity, muscle squat. Eng Med 11:69-76, 1982. length, and torque of the hamstrings. Clin Biomech 17:569-579, 2002. 15. DeVita P, Hortobagyi T: Age causes a redistribution of joint torques and powers during 43. Morrison JB: The mechanics of the knee joint in relation to normal walking. gait. J Appl Physiol 88:1804-1811, 2000. J Biomech 3:51-61, 1970. 16. DeVita P, Hortobagyi T: Age increases the skeletal versus muscular component of 44. Mulholland SJ, Wyss UP: Activities of daily living in non-Western cultures: range of lower extremity stiffness during stepping down. J Gerontol A Biol Sci Med Sci motion requirements for hip and knee joint implants. Int J Rehabil Res 24:191-198, 55:B593-B600, 2000. 2001. 17. Dyrby CO, Toney MK, Andriacchi TP: Relation between knee flexion and tibial-femoral 45. Mundermann A, Dyrby CO, Hurwitz DE, Sharma L, Andriacchi TP: Potential rotation during activities involving deep flexion. Gait Posture 5:179-180, 1997. strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity: reduced walking speed. Arthritis Rheum 18. Escamilla RF: Knee biomechanics of the dynamic squat exercise. Med Sci Sports 50:1172-1178, 2004. Exerc 33:127-141, 2001. 46. Nadeau S, McFadyen BJ, Malouin F: Frontal and sagittal plane analyses of the stair 19. Frost HM: Perspectives: a biomechanical model of the pathogenesis of arthroses. climbing task in healthy adults aged over 40 years: what are the challenges Anat Rec 240:19-31, 1994. compared to level walking? Clin Biomech 18:950-959, 2003. 20. Fry AC, Smith JC, Schilling BK: Effect of knee position on hip and knee torques 47. Nagura T, Dyrby CO, Alexander EJ, Andriacchi TP: Mechanical loads at the knee joint during the barbell squat. J Strength Cond Res 17:629-633, 2003. during deep flexion. J Orthop Res 20:881-886, 2002. 21. Greenwald AS, Haynes DW: Weight-bearing areas in the human hip joint. J Bone Joint 48. Neumann DA: An electromyographic study of the hip abductor muscles as subjects Surg Br 54:157-163, 1972. with a hip prosthesis walked with different methods of using a cane and carrying a load. Phys Ther 79:1163-1173, 1999. 22. Hefzy MS, Kelly BP, Cooke TD: Kinematics of the knee joint in deep flexion: a radiographic assessment. Med Eng Phys 20:302-307, 1998. 49. Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby. 23. Hortobagyi T, Mizelle C, Beam S, DeVita P: Old adults perform activities of daily living near their maximal capabilities. J Gerontol A Biol Sci Med Sci 58:M453-M460, 50. Nordin M, Frankel VH: Biomechanics of the hip. In M Nordin, VH Frankel, eds: 2003. Basic biomechanics of the musculoskeletal system. New York, 2001, Lippincott Williams & Wilkins, pp. 202-221. 51. Nordin M, Frankel VH: Biomechanics of the knee. In M Nordin, VH Frankel, eds: Basic biomechanics of the musculoskeletal system. New York, 2001, Lippincott Williams & Wilkins, pp. 176-201. 52. Norkin CC, Levangie PK: Joint structure and function: a comprehensive analysis. Philadelphia, 1992, F.A. Davis Company. 53. Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS: Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am 66:344-352, 1984. 54. Race A, Amis AA: The mechanical properties of the two bundles of the human posterior cruciate ligament. J Biomech 27:13-24, 1994.
Chapter 7b ● References 287 55. Reikeras OF, Bjerkreim IF, Kolbenstvedt A: Anteversion of the acetabulum and femoral implants: an evaluation of a three-dimensional mathematical model of the lower neck in normals and in patients with osteoarthritis of the hip. Acta Orthop Scand limb. J Biomech 36:929-936, 2003. 54:18-23, 1983. 66. Stauffer RN, Chao EY, Gyory AN: Biomechanical gait analysis of the diseased knee joint. Clin Orthop Relat Res 126:246-255, 1997. 56. Reinbolt JA, Schutte JF, Fregly BJ, et al: Determination of patient-specific multi-joint 67. Swanik CB, Lephart SM, Swanik KA, Stone DA, Fu FH: Neuromuscular dynamic kinematic models through two-level optimization. J Biomech 38:621-626, 2005. restraint in women with anterior cruciate ligament injuries. Clin Orthop 425:189-199, 2004. 57. Riener R, Rabuffetti M, Frigo C: Stair ascent and descent at different inclinations. 68. Tanaka S, Lee ST, Halperin WE, Thun M, Smith AB: Reducing knee morbidity among Gait Posture 15:32-44, 2002. carpetlayers. Am J Public Health 79:334-335, 1989. 69. Taylor SJ, Walker PS: Forces and moments telemetered from two distal femoral 58. Riley PO, DellaCroce U, Kerrigan DC: Effect of age on lower extremity joint moment replacements during various activities. J Biomech 34:839-848, 2001. contributions to gait speed. Gait Posture 14:264-270, 2001. 70. Taylor WR, Heller MO, Bergmann G, Duda GN: Tibio-femoral loading during human gait and stair climbing. J Orthop Res 22:625-632, 2004. 59. Robertson DD, Britton CA, Latona CR, Armfield DR, Walker PS, Maloney WJ: Hip 71. Thelen DG, Schultz AB, Alexander NB, Ashton-Miller JA: Effects of age on rapid ankle biomechanics: importance to functional imaging. Semin Musculoskelet Radiol torque development. J Gerontol A Biol Sci Med Sci 51:M226-M232, 1996. 7:28-41, 2003. 72. Townsend MA, Shiavi R, Lainhart SP, Caylor J: Variability in synergy patterns of leg muscles during climbing, descending and level walking of highly-trained athletes 60. Rodosky MW, Andriacchi TP, Andersson GB: The influence of chair height on lower and normal males. Electromyogr Clin Neurophysiol 18:69-80, 1978. limb mechanics during rising. J Orthop Res 7:266-271, 1989. 73. Wang JW, Kuo KN, Andriacchi TP, Galante JO: The influence of walking mechanics and time on the results of proximal tibial osteotomy. J Bone Joint Surgery Am 61. Rowe PJ, Myles CM, Walker C, Nutton R: Knee joint kinematics in gait and other 72:905-909, 1990. functional activities measured using flexible electrogoniometry: how much knee 74. Woo SL, Hollis JM, Adams DJ, Lyon RM, Takai S: Tensile properties of the human motion is sufficient for normal daily life? Gait Posture 12:143-155, 2000. femur-anterior cruciate ligament-tibia complex. The effects of specimen age and orientation. Am J Sports Med 19:217-225, 1991. 62. Rydell NW: Forces acting on the femoral head-prosthesis. A study on strain 75. Yoshioka YF, Cooke TD: Femoral anteversion: assessment based on function axes. gauge supplied prostheses in living persons. Acta Orthop Scand 37(Suppl):132, J Orthop Res 5:86-91, 1987. 1966. 63. Simpson AH, Lamb S, Roberts PJ, Gardner TN, Evans JG: Does the type of flooring affect the risk of hip fracture? Age Ageing 33:242-246, 2004. 64. Smidt GL: Biomechanical analysis of knee flexion and extension. J Biomech 6:79-92, 1972. 65. Stansfield BW, Nicol AC, Paul JP, Kelly IG, Graichen F, Bergmann G: Direct comparison of calculated hip joint contact forces with those measured using instrumented
7cC H A P T E R numbness and tingling (characteristic of lumbar radiculopathy) that suggest alternative sites for pathology are also important to Clinical Evaluation note. It is especially important to determine whether there are of the Hip and Knee activities that exacerbate or improve the patient’s symptomatology to ascertain return to work status. Craig J. Della Valle, Benjamin Crane, and Gunnar B. J. Andersson Although past treatment of a particular problem is generally A careful clinical evaluation of the hip and knee is important a crucial criterion for determining further treatment, in an occu- to determine the presence of disease or injury for the purpose pational injury the complaint is typically referable to a triggering of establishing the nature of a complaint. Only by means of an event (accident). It is important, however, to determine whether accurate diagnosis is it possible to determine an appropriate the present complaint is referable to a joint that has been treatment. Given the importance of a thorough history and phys- symptomatic or injured in the past, because this may be a criti- ical examination, textbooks are available that deal with this topic cal point in ascertaining whether the event in question caused in great detail. It is beyond the scope of this chapter to provide an initial injury or aggravated a preexisting condition. Specific a complete description of all the tests that are available to evalu- questions regarding childhood problems are particularly important ate the hip and knee. Rather our goal is to provide the clinician in patients with complaints of hip and groin pain because devel- with the basic skills needed to diagnose accurately and begin opmental problems can become symptomatic later in life. Past treatment appropriate for occupationally related complaints. medical history is important to ensure an appropriate evaluation (in a person with a history of malignancy, for example, metastatic Although advances in diagnostic imaging continue to improve disease can be considered among the potential diagnoses). The our ability to identify anatomic abnormalities, these often do not patient’s social history, including information about recreational correlate with clinical signs and symptoms. For this reason, indis- habits, smoking, alcohol intake, and family life, are all important criminate ordering of advanced imaging studies is discouraged, pieces of a thorough evaluation and paint a fuller picture of the particularly in patients with occupationally related complaints. person being examined. In cases for which they are deemed necessary, plain radiographs can point the physician to a correct diagnosis of most com- PHYSICAL EXAMINATION plaints when these tests are combined with a thorough history and physical examination. Hip The physical examination of a patient with a complaint of hip pain begins with an observation of the gait pattern. The patient needs to be sufficiently undressed so that movements of the hip and knee can be observed appropriately. The two most common HISTORY Table 7c.1 Example of structured history Obtaining a medical history from a patient with an occupation- History of present illness ally related complaint is somewhat different from doing so with a more general complaint: Occupational factors may provide What is the chief complaint (e.g., “left knee pain”)? additional information useful to obtain a correct diagnosis, When did the symptoms begin? and any relationship between the complaint and the patient’s How did they start? Was an accident or specific activity involved? vocation can have important legal, medical, and rehabilitative What do you believe caused the symptoms? Why? implications. The history should be structured, and the use of a Where exactly is the pain located (i.e., anterior knee, back of knee, inside “checklist” or standardized form is useful to ensure that all critical portions are carefully obtained and documented. An example of of knee)? a structured history is shown in Table 7c.1. How would you describe your pain (i.e., throbbing, sharp, dull, tightness)? Are there activities that make your pain worse? The history should begin by identifying the chief complaint What activities make your pain better? and injury mechanism. All events should be carefully documented Do you have any associated symptoms such as stiffness, swelling, in chronological order. Although patients with hip pathology typically report pain in the groin, pain in the area of the greater or weakness? trochanter or buttock is not uncommon. A history of difficulty What previous treatment have you had related to this complaint? in donning shoes suggests loss of hip range of motion and arthritis. Have radiographs or other tests been performed? In patients complaining of knee pain, it is important to docu- Previous history of injury or problems with the affected joint ment where the pain is located (anterior, posterior, medial, or lateral) and whether it is associated with swelling, sensations of Past medical history instability (suggestive of a ligamentous injury), or mechanical symptoms such as locking or clicking that may point to a Occupational history meniscal pathology or a loose body. Associated symptoms such as Social history Review of systems
290 Chapter 7c ● Clinical evaluation of the hip and knee gait patterns observed are an antalgic gait and a Trendelenburg Figure 7c.1 Trendelenburg test. The unaffected hip drops when or gluteus medius gait. standing on the affected leg. An antalgic gait pattern results from the patient’s attempt sought (see Chapter 4c). Range of motion is then measured with to decrease weight bearing on the painful hip by decreasing the patient supine. A complete examination includes measure- the amount of time spent in stance phase on the affected side ment of flexion, extension, internal rotation, external rotation, and thus the resulting pain. A Trendelenburg gait results from abduction, and adduction. To identify a hip flexion contracture, weakness of the hip abductor muscles (the luteus medius and the Thomas test is performed: The contralateral hip is maximally minimus). In its normal state, the abductor musculature holds flexed to eliminate the lumbar lordosis, and then residual flex- the pelvis level during the swing phase of gait; when the abduc- ion, if any, is measured (Fig. 7c.3). Normal range of hip flexion tors are weakened, the pelvis drops on the side contralateral is 120 to 135 degrees (Fig. 7c.4). Internal and external rotation of to the affected hip. The patient compensates by shifting the the hip are measured next with the patient still supine and the knee trunk in the opposite direction to maintain the center of gravity flexed 90 degrees; normal ranges for internal rotation are 30 to closer to the stance leg. 45 degrees and for external rotation, 45 to 60 degrees (Fig. 7c.5). The Trendelenburg test involves asking the patient to stand on one leg and then observing movements of the trunk and pelvis (Fig 7c.1). Normally, when the patient stands on the right leg, the gluteus medius on that side contracts to keep the pelvis level. If the muscle is weak or paralyzed, the pelvis on the con- tralateral side—the left side, for example—drops and the patient compensates by listing the trunk to the right. The test is typically recorded as positive (abnormal) or negative. It is positive most commonly in arthritic conditions, but patients with neurologic disease or with palsy of the superior gluteal nerve have similar, if not more dramatic, findings. With the patient still standing, the skin overlying the hip is inspected for abrasions, discoloration or ecchymosis, swelling, atrophy, or other deformity. The presence or absence of pelvic obliquity is determined next by identifying the anterior superior iliac spines, the iliac crest, and the greater trochanter; these struc- tures should be symmetrically level bilaterally, and if not, pelvic obliquity is present. The patient is then placed supine on an examination table for a determination of leg lengths. A general assessment involves examining the relative positions of the soles of the feet and the medial malleoli. Keep in mind, however, that this measurement will not differentiate between a “true” leg length discrepancy and an apparent discrepancy that can be caused by pelvic obliquity or more commonly a hip flexion contracture. Actual leg length can be measured with a tape measure as the distance between the anterior superior iliac spine and the medial malleolus bilaterally (Fig. 7c.2). Apparent leg length discrepancy is measured from the umbilicus to the medial malleolus. The hip is next palpated to determine areas of tenderness. The greater trochanter can be tender after a fall on the affected side, but tenderness is more commonly associated with a trochanteric bursitis or insertional tendonitis. The femoral triangle anteriorly, the sciatic notch posteriorly, and the individual mus- cles around the hip should be palpated also to determine areas of maximal tenderness; these may represent a contusion or strain injury secondary to acute trauma or tendonitis or bursitis from less acute processes. The patient is then asked to “straight leg raise” or to lift the leg off the examination table with the knee extended. An inability to do so may indicate a femoral neck fracture, particularly in the setting of acute trauma, and thus plain radiographs should be obtained before proceeding further with the examination. The leg can also be passively elevated with the knee extended, and if shoot- ing pain is experienced down the leg past the knee, particularly down the contralateral leg, a lumbar source of pain should be
Chapter 7c ● Physical examination 291 Figure 7c.4 Hip flexion is normally 120 to 135 degrees. true hip range of motion (Fig. 7c.6). Normal ranges for hip abduction are 45 to 50 degrees and for hip adduction, 20 to 30 degrees. Hip extension is measured next and is most com- monly performed with the patient prone; a normal range is 20 to 30 degrees (Fig. 7c.7). Muscular strength can be assessed next and should include direct testing of the hip flexors (iliopsoas and rectus femoris muscles), the hip extensors (gluteus maximus muscles), and the hip abductors and adductors. Hip flexion is tested most easily with the patient seated and asked to flex the hip against manual resistance; pain during this maneuver may indicate iliopsoas tendonitis. Hip extensor strength is most easily tested with the patient prone. Although the hip abductors have already been tested indirectly by gait observation and with the Trendelenburg test, with the patient in the lateral decubitus position, direct muscle strength testing can be performed. Pain with resisted Figure 7c.2 Leg length should be measured from the anterior superior iliac spine to the medial malleolus. Intraarticular conditions of the hip cause pain with rotatory movements, and a loss of internal rotation in particular is an early indicator of hip disease. Abduction and adduction are measured next while keeping one hand on the patient’s pelvis during testing to ensure that pelvic motion is not confused for 45° Figure 7c.3 The Thomas test is used to detect flexion contractures 35° of the hip and to evaluate the range of hip flexion. 0° Figure 7c.5 Rotation tested in the flexed position is normally 30 to 45 degrees internal and 45 to 60 degrees external.
292 Chapter 7c ● Clinical evaluation of the hip and knee AB Figure 7c.6 (A) Abduction and (B) adduction. Abduction is normally 45 to 50 degrees, and adduction is normally 20 to 30 degrees. hip abduction may be further evidence of a trochanteric bursitis. with hip pathology can present with pain that is primarily Hip adduction is tested most easily with the patient supine and referred to the knee. While the patient is still standing, examine asked to adduct the hip actively from an abducted position. the overall alignment of the extremity (Fig. 7c.8). Normally, the Although not directly related to the hip, a brief neurologic lower extremity is in slight (4-6 degrees) valgus alignment with examination of the lower extremities is imperative to ensure that larger amounts of varus or valgus typically associated with longer lumbar radiculopathy is not present; this should include a test of term pathology, such as arthritic conditions. Although unusual, deep tendon reflexes and a motor and gross sensory examination. muscular wasting should be sought, typically in association with neurologic pathology or disuse. Subtle muscular atrophy Knee indicative of more chronic pathology can be ascertained with a tape measure placed around the thigh at symmetric points on The physical examination of the knee follows closely the form the affected and unaffected limbs (e.g., at a specific distance as seen for that of the hip. As previously discussed, the patient must be sufficiently undressed to view the lower extremity in its entirety. Gait is typically examined first. Although an antalgic gait (decreased stance phase on the affected side to decrease pain) is most common, the presence of a Trendelenburg gait (indica- tive of hip pathology) is critical to identify because patients 30° Normal Valgus Varus 0° Figure 7c.8 Varus/valgus deformity of the knee. Figure 7c.7 Hip extension is normally 20 to 30 degrees.
Chapter 7c ● Physical examination 293 measured from the medial joint line). Long-standing subjective Figure 7c.10 Palpable defect in the quadriceps tendon, just proximal complaints of knee pain without substantial (more than 5 mm) side-to-side difference in girth should be viewed skeptically by to the patella, indicative of a quadriceps tendon rupture; the patient the examiner. was unable to extend the knee actively, and surgical repair was required. In the setting of an acute accident, the skin is carefully inspected for abrasions, ecchymosis, or swelling. The patient can The patella itself can also be examined to determine its then be placed supine and the knee examined for an effusion or mobility by gently moving it from side to side with the knee generalized knee swelling (Fig. 7c.9). In the setting of an acute extended; normally, the patella should be mobile in extension injury, a very large effusion may indicate an intraarticular frac- and fixed in flexion. Whether this maneuver is painful or not and ture, a ligamentous disruption, or an acute meniscal tear. With whether crepitation is sensed should be carefully noted because a more long-standing history of knee pain, an effusion can sug- these symptoms may indicate arthritis of the patellofemoral gest arthritis or a meniscal tear. More localized areas of swelling articulation or patellar instability. The examiner should not be can occur anteriorly (directly over the patella), indicating a able to dislocate the patella completely from within the trochlear prepatellar bursitis that can be associated with long periods of groove. Some patients may experience substantial apprehension kneeling. Some patients (particularly males) may have an area during these translational maneuvers, perhaps indicating patellar of apparent swelling anterior to the tibial tubercle, just distal to instability; in the setting of acute trauma, tenderness along the the insertion of the patellar tendon. When palpated, this area medial border of the patella may be secondary to its dislocation. is hard and represents bony overgrowth secondary to Osgood- Generalized pain with patellofemoral compression may indicate Schlatter disease, a self-limited process that is rarely problematic arthritis or early degenerative changes of the cartilage of the other than for a cosmetic protuberance in the area. A localized patellofemoral articulation. If the examiner suspects patellar area of swelling in the posterior aspect of the knee suggests instability, the “Q” angle can be assessed also by determining the a “Baker’s cyst.” Typically not the result of a primary process, angle tendered between a line drawn from the anterior superior a Baker’s cyst is secondary to arthritis or a meniscal tear, iliac spine and the quadriceps tendon and a second line drawn which induces an effusion that expands in the direction of least across the tibial tubercle and the central axis of the patella. resistance. Calculated with the knee extended and the patient supine, this value is expected to range from 15 to 20 degrees. Because many of the important anatomic structures about the knee are subcutaneous, careful palpation can often identify Next, the joint lines are carefully palpated both medially the site of pathology. Tenderness directly over the patella can and laterally; this is most easily accomplished with the patient indicate either a contusion or a fracture if the patient sustained supine and the knee flexed approximately 90 degrees. Localized a fall or a direct blow to the area; alternative causes of pain here tenderness along the joint lines may indicate meniscal pathology include prepatellar bursitis, as previously noted. Tenderness proximal to the patella most commonly represents tendonitis of the quadriceps or strain of the quadriceps muscle. If a frank tendon rupture is present, the examiner will clearly feel a palpa- ble defect (Fig. 7c.10), and in most cases, the patient is unable to extend the knee actively or lift the leg with it extended. Tenderness distal to the patella can indicate chronic tendonitis (“Jumper’s knee”) or an acute tear if a palpable defect is noted and the patient is unable to extend the knee actively. Figure 7c.9 Swollen right knee (typical appearance of an effusion).
294 Chapter 7c ● Clinical evaluation of the hip and knee 10° 0° 130° Figure 7c.12 Extensor lag is defined as an inability to actively extend 90° the knee. Figure 7c.11 Flexion-extension of the knee: normal extension, 10 degrees; flexion, 135 to 150 degrees. or arthritis. The collateral ligaments can also be palpated directly; some patients may present with a “locked knee” wherein the leg tenderness and localized swelling along the medial or lateral is held in mid-flexion and cannot be flexed or extended; most collateral ligament (including the fibular head where the lateral commonly involving a large meniscal tear or a loose body that collateral ligament inserts) can indicate acute rupture or strain. has become incarcerated in the joint, this symptom is associated often with acute severe pain and muscular guarding. Range of motion is measured as flexion and extension with normal values 0 to approximately 135 degrees. Here 0 degrees is Various special tests have been developed in an effort to described as “full extension,” and values of less than that are identify meniscal pathology: A history of acute injury with an referred to as a “flexion contracture” that is typically associated effusion and joint line tenderness or a subacute history of local- with knee arthritis or other long-standing pathology (Fig. 7c.11). ized joint line pain, recurrent effusions, and mechanical symp- Inability to extend the knee actively can indicate a disruption of toms such as locking suggest it as a cause. Most tests that follow the extensor mechanism (rupture of the quadriceps or patellar should not be performed in the setting of acute injury because tendon or fracture of the patella) and is referred to as an “exten- they not only cause substantial pain but also are relatively non- sor lag” (Fig. 7c.12). Hyperextension of the knee rarely exceeds specific. The McMurray test is performed by rotating the tibia 10 or 20 degrees and, if asymmetric, may represent cruciate liga- internally and externally while simultaneously flexing and extend- ment injury or, rarely, neurologic disease. Although uncommon, ing the knee with the patient in the supine position (Fig. 7c.13). AB Figure 7c.13 McMurray test. The knee is first rotated in full extension (A) and then extended (B).
Chapter 7c ● Physical examination 295 AB Figure 7c.14 Apley test. With the patient prone, the knee is flexed and the foot internally and externally rotated (A) with distraction and (B) with compression. The examiner’s fingers are placed at the joint line during this approximately 20 degrees (Fig. 7c.15). Testing is performed in maneuver, and a palpable sense of locking or clicking, particu- mid-flexion to avoid a false-negative result, as the geometry of larly when combined with recreation of the patient’s symptoms, the joint itself confers some stability when the knee is fully suggests a meniscal tear. Although similar, the Apley test is extended. If a sprain rather than a frank tear has occurred, the performed with the patient prone and the knee flexed 90 degrees application of these types of forces causes substantial pain without (Fig. 7c.14). The foot is rotated internally and externally while the examiner sensing frank instability. the joint is distracted or compressed; the test is considered positive if pain is recreated, particularly while the joint is Testing the stability of the anterior cruciate ligament can compressed. involve either the anterior drawer test or the Lachman test. An anterior draw test is performed with the knee in 90 degrees of Knee joint stability is tested by various means. As noted flexion while an anterior force is placed on the tibia (Fig. 7c.16); above, in the setting of acute trauma these tests should typically in the setting of acute trauma this test is particularly susceptible be deferred because they can be very painful and muscular guard- to a false-negative result because secondary restraints can com- ing secondary to pain compromises their sensitivity. Stability of pensate for a torn anterior cruciate ligament. Reputed to have the lateral and medial collateral ligaments is determined by higher sensitivity, the Lachman test is performed similarly, applying a lateral or medial moment to the knee while it is flexed but the knee is held in approximately 30 degrees of flexion. AB Figure 7c.15 Lateral stability is tested with the knee in approximately 15 to 20 degrees of flexion (A, medial; B, lateral).
296 Chapter 7c ● Clinical evaluation of the hip and knee Figure 7c.16 Anterior drawer test to detect cruciate ligament injury. stages of disease, weight-bearing views may be required to detect subtle joint space narrowing. Specifically, the examiner holds the femur in one hand while applying an anterior force to the tibia with the other. In both Rheumatoid arthritis is characterized by a more symmetric tests, the examiner notes how far forward the tibia moves on pattern of joint space narrowing along with periarticular osteope- the femur and whether or not there is a firm “endpoint” when nia; osteophytes are rarely seen until the later stages of the such forces are applied. A final test to determine anterior cruci- disease when secondary osteoarthritis develops. Seronegative ate ligament competency is the “pivot-shift” test; particularly arthritides (such as ankylosing spondylitis) usually present also uncomfortable for patients (and thus subject to false-negative with fusion of the sacroiliac joints, as seen on the pelvic AP view. results secondary to patient guarding), this test is probably most useful when performed in the anesthetized patient pre- Computed tomography is typically reserved for the evalua- operatively. Place the patient supine and flex the knee approx- tion of acetabular and pelvic fractures, but it may detect early imately 30 degrees. Internally rotate the foot and apply a valgus degenerative changes. Three-dimensional reconstructions made force on the extremity by the placing the opposite hand on the from high-resolution computed tomographies can be used for tibia. The knee is then extended, and if the anterior cruciate better understanding of complex hip anatomy such as in hip ligament is ruptured, a palpable subluxation of the joint may be dysplasia. Magnetic resonance imaging (MRI) is useful for iden- felt as the tibia jumps forward on the femur. Posterior cruciate tifying early osteonecrosis or avascular necrosis of the hip and ligament stability is tested using the posterior drawer test. Quite occult fractures and stress fractures that are not visible on plain similar to the anterior drawer test, this test includes placing radiographs. In the patient with a history of trauma who com- a posteriorly directed force on the tibia with the knee flexed plains of groin or hip pain and cannot raise the straight leg 90 degrees while the patient is supine; a firm endpoint should or ambulate, an MRI will most rapidly identify a nondisplaced be felt. fracture of the proximal femur. MR images can also detect loose bodies or pathology of the acetabular labrum; early degenerative IMAGING DIAGNOSIS changes also can be identified. Very sensitive but quite non- specific, nuclear medicine studies such as bone scans are rarely Hip useful, except for identifying metastatic disease. Although a bone scan also can identify subtle arthritis, joint inflammation, or Radiographic examination of the hip should include at least occult fracture, MRI is superior in showing the specific pathology an anteroposterior (AP) view of the hip and pelvis and a lateral so that appropriate treatment can be instituted. In the case of view of the hip. Oblique or Judet views may be useful when eval- occult fracture, whereas an MRI shows immediate changes, a uating a patient with a suspected or known acetabular fracture, bone scan may not be positive for several days. and pelvic inlet and outlet views are useful in patients with known or suspected pelvic fractures. Plain radiographs are the Knee standard technique for evaluation of trauma and arthritis. Routine radiographs of the knee include standing AP, lateral, Osteoarthritis is characterized by joint space narrowing and patellar (merchant or sunrise) views. Standing AP radio- (particularly in the superolateral or weight-bearing portion of graphs are recommended to assist in identifying subtle joint the joint), subchondral sclerosis, and osteophyte formation; space narrowing and determining overall alignment (normally subchondral cysts may also be seen. In advanced cases, erosion 7 degrees of valgus). Typically performed with the knee in of the femoral head or acetabulum can occur. In the earliest 30 degrees of flexion, the lateral view is non–weight bearing. Additional views that may be helpful include a weight-bearing AP view with the knee flexed 45 to 60 degrees. Commonly referred to as a “skier’s view,” this radiograph often identifies more subtle joint space narrowing as the posterior aspect of the femoral condyle is imaged. Radiographic markers of osteoarthritis include joint space narrowing, subchondral sclerosis, and osteophyte formation. Radiographic changes may affect the medial tibiofemoral, lateral tibiofemoral, or patellofemoral compartments. The most common pattern is a varus deformity with the most severe radiographic changes affecting the medial compartment, although patients can develop a valgus deformity or have arthritis that affects predominantly the patellofemoral joint. Inflammatory arthritis generally causes a more symmetric pattern of joint space loss with periarticular osteopenia and often a valgus deformity. Plain radiographs can be reviewed not only for bony pathology such as arthritis or fracture but also for soft tissue pathology because symptoms such as a large effusion are often identifiable radiographically. Stippled calcifications seen in the area of the joint space may represent chondrocalcinosis or pseudo-gout.
Chapter 7c ● Summary 297 A high riding patella or “patella alta” may indicate rupture of the Similarly, arthroscopy of the hip is used occasionally in situa- patellar tendon. MRI is used as a secondary test to identify pathol- tions where subtle pathology of the labrum or cartilage is sus- ogy of the ligaments and menisci; more subtle damage to the car- pected that may be unrecognized with other tests. The greatest tilaginous surfaces can be recognized also as can processes such as strength of arthroscopy is the ability to both diagnose and treat osteonecrosis. Although bone scans are used occasionally to iden- at the same time. tify early degenerative changes when plain radiographs are nega- tive, MRI is often both more sensitive and certainly more specific. SUMMARY ARTHROSCOPY Clinical evaluation of the hip and knee often allows the physician to make a diagnosis and plan for treatment. Imaging is some- In the patient with persistent complaints of pain or instability in times a necessary complement but should always be evaluated the face of plain radiographs and advanced imaging studies, in light of the clinical findings. Advanced imaging such as com- arthroscopic examination of the knee can be used for diagnostic puted tomography and MRI are rarely necessary and should purposes to directly view its anatomic structures. Although tests not be used for screening purposes, because the yield is low and such as MRI are quite sensitive, false-negative results can occur. false positive findings are not uncommon.
7dC H A P T E R the more common disorders affecting the hip are discussed in terms of treatment and work implications. Hip and Knee: Treatment Options Hip fractures are major acute injuries, generally from sig- nificant falls (Fig. 7d.1). Hip fractures are usually treated with James B. Talmage surgical internal fixation or prosthetic replacement. For example, significantly displaced femoral neck fractures are frequently Work-related problems in the lower limb are quite different from treated with prosthetic replacement of the proximal femur due those in the upper limb. Physicians frequently see patients with to the high probability of the complication of avascular necrosis occupational illnesses of the upper limb, where no major traumatic of the femoral head, whereas nondisplaced femoral neck frac- event has occurred, and the patient’s complaints are believed to tures are usually treated with internal fixation for stabilization be related to repetitively performing the same task(s). In the while the fracture heals. The orthopedic surgeon determines, lower limb, these “overuse” disorders are distinctly uncommon. based on the type of fracture and the type of surgery performed, Sports medicine physicians see overuse hip and knee injuries, when weight bearing on the affected limb is permissible. Until but these are very uncommon in workers’ compensation patients. weight bearing is permitted, a worker can only do work in a The lower limb seems to be built with more reserve capacity for sitting position. Ambulation at work would require crutches activity than is present in the upper limb. Thus, unlike when or a wheelchair and at least temporary access to handicapped treating upper limb disorders, physicians rarely treat lower limb parking. Periods of leg elevation may be required for preven- disorders and then have to ponder the wisdom of returning tion of thrombophlebitis. Workers with hip fractures may be workers to jobs in which the repetitive performance of simple using narcotic pain medication for several weeks or months. activities is alleged to have initiated the overuse illness. Most hip Company policies on work while using medications need to and knee problems that come to the attention of physicians are be considered. either gradually progressive age-appropriate degeneration (e.g., osteoarthritis), acute traumatic injuries (e.g., knee meniscal tear), Hip arthritis may be a cause for hip pain with work activity or rheumatologic illness (e.g., acute gout or rheumatoid arthritis). (Fig. 7d.2). Osteoarthritis is much more common than knee arthritis. It increases in prevalence with age. Other than in farm- Treatment of these hip and knee problems is the same for ers, epidemiologic studies have not associated hip osteoarthritis those patients in the workers’ compensation system (e.g., acute with work activity, so workers can continue to safely work knee meniscal tear at work) as it is for those who have the same despite osteoarthritis of the hip.17 The paradox of osteoarthritis problem but are not in the workers’ compensation system. The in the lower limbs is those who get osteoarthritis of the hip do results may not be as good. A recent meta-analysis showed that not usually get osteoarthritis of the knee, and those who get in 175 of 205 published studies, the results of surgical treatment osteoarthritis in the knee do not usually get it in the hip; neither of compensation patients were not as good as the results of treating group gets osteoarthritis of the ankle, and yet each joint carries the same condition with the same surgery in noncompensation the same body the same number of steps. Simple overuse or patients.7 The pooled odds ratio for an unsatisfactory outcome “wear and tear” does not explain osteoarthritis. Ten to 20% of in compensated patients compared with noncompensated osteoarthritis patients present with arthritis in both the hips and patients was 3.79 (95% confidence interval, 3.28-4.37). Decisions the knees, but these patients also have multiple other joints on return to work require consideration of the nature of the involved (spine, shoulders, wrists, hands, and/or feet), suggesting condition. Acute injuries generally show progressive improve- a genetic disorder.7 ment with time and treatment, whereas progressive diseases like osteoarthritis and rheumatoid arthritis may show progressive Nonoperative treatment includes trials of nonsteroidal anti- deterioration requiring job modification or career changes. inflammatory drugs (NSAIDs) and a cane in the contralateral hand. No NSAID has proven to be superior, and physicians THE HIP frequently prescribe several in serial trials, looking for the NSAID that gives the best relief and fewest side effects in the Hip problems in workers are uncommon and much less commonly individual patient. The COX-2–specific NSAIDs have not been seen than knee problems. For example, the American College of shown to provide better pain relief that the older traditional Occupational and Environmental Medicine’s Occupational mixed COX-1 and COX-2 NSAIDs. The COX-2–specific drugs Medicine Practice Guidelines, 2nd edition, contains a chapter on are suspected of having an association with myocardial infarction every part of the musculoskeletal system except for the hip. The and stroke and are being prescribed less frequently. Weight reduc- material in the preceding chapter on diagnosis is not repeated, tion is frequently recommended on biomechanical principles but and the reader is referred to that chapter for details. A few of is rarely achieved. Dietary supplementation with glucosamine and chondroitin sulfate can be tried. These “nutraceuticals” are safe because they are compounds found in the human diet. They may decrease symptoms in osteoarthritis, although their onset of action is slow (several months). Whether they have a disease- modifying affect is being debated.11,16 Glucosamine has not been shown to raise fasting blood glucose levels in diabetics. Severe hip pain is usually treated with total hip replacement. After hip replacement surgery, the surgeon determines when full weight bearing can occur. Cemented hip replacements are
300 Chapter 7d ● Hip and knee: treatment options B A CD Figure 7d.1 (A) Plain radiographs of a 65-year-old woman who complained of severe pain after a fall. No evidence of fracture is seen on the initial film (arrow). (B) Magnetic resonance imaging of the pelvis. T1-weighted spin echo and (C) STIR images demonstrate focal bone marrow edema (arrows) in the femoral neck and a difference in intensity, indicating the presence of a nondisplaced femoral neck fracture. (D) Bone scan shows intense focal uptake at the site of the fracture (arrow). Intense diffuse uptake in the contralateral hip is due to osteoarthritis. STIR, short inversion time inversion recovery.
Chapter 7d ● The knee 301 Figure 7d.2 Severe osteoarthritis of the left hip with cystic changes “bone bruise,” early avascular necrosis, transient osteoporosis of the hip, bursitis about a deep hip bursa (of which there are 13), in both the acetabulum and femoral head (arrow) in a 59-year-old or an acetabular labrum tear. Tears of the labrum do not always visualize on MRI, however, and hip arthroscopy may be neces- school teacher. The contralateral hip was treated with a cementless sary to exclude or to treat this diagnosis. For simple sprains and strains, a temporary period of reduced work activity may be help- total hip arthroplasty. ful, but it should not exceed 6 weeks. inherently stable, and full weight bearing can be permitted almost Sprains and strains of the hip region, like those of other joint immediately. Noncemented hip replacements require time for regions, heal in a known sequence. Muscles, ligaments, and ten- bone to grow into the porous coating of the implant or for the dons begin with an inflammatory phase of healing, progress to a patient to “heal to the implant” before full weight bearing can synthesis phase, and finish with a remodeling phase. Although it be permitted. After hip replacement, permanent restrictions against may decrease pain, antiinflammatory medication does not speed running, jumping, full squatting, kneeling, crawling, heavy lifting, up healing of muscles, ligaments, or tendons.6 Inflammation is and carrying are common to prevent loosening and dislocation a necessary part of tissue healing. “Muscle relaxants” are really of the prosthetic components. centrally acting minor tranquilizers, and sedation accounts for their “muscle relaxation.” If a patient is not sleeping well, one Avascular necrosis of the hip (osteonecrosis) is an uncommon dose a day at bedtime may improve his or her sleep pattern. problem (Fig. 7d.3). It may occur as a complication of femoral neck fracture or hip dislocation. It is seen without a history of Opioid analgesics, on occasion, are used for severe acute trauma in patients with a history of systemic corticosteroid use, pain symptoms. Opioid analgesics act primarily by binding to alcoholism, and as an idiopathic condition. In its early stages it opiate receptors in the central nervous system. They have poten- is treated much like hip osteoarthritis with NSAIDs and a cane tial problems of tolerance, dependence, addiction, and illicit or crutches. If femoral head collapse has not yet occurred when use/diversion with long-term administration. Even short-term use the condition is recognized, non–weight-bearing ambulation of these medications should be undertaken with caution because with crutches may be recommended. In these early cases, bone potential problems with demotivation, early reactive hyperalge- grafting surgery is frequently tried. Late cases with femoral head sia, and early dependency can occur in a select group of patients. collapse and severe pain are treated with hip replacement. Although more potent than NSAIDs and acetaminophen, in two of three clinical trials narcotic analgesics were not found Trochanteric bursitis is the most common bursitis about the hip. to be more effective. The dosage schedule should be defined This is painful but not serious, because no significant consequences (not “PRN”) and use limited to patients whose pain is unrespon- result from continued activity despite pain. Nonoperative treat- sive to alternative medications.10 ments include NSAIDs, stretching, and strengthening exercises frequently initially under the supervision of a physical therapist. Physical agents including ultrasound, electrical stimulation, For refractory cases a corticosteroid injection into the region of and heat and cold have been used to supposedly speed healing the bursa may be helpful. Surgery is rarely indicated. A tempo- by increasing circulation and decreasing inflammation while rary period of reduced work activity may be useful, but it should reducing pain. These passive modalities do not appear to have not exceed 6 weeks. any effect on clinical outcomes. No single modality has been shown to be superior to others for relief of musculoskeletal pain. Hip “sprains and strains” are uncommon in the workplace. Prolonged use of these passive modalities should be discouraged. They must be differentiated from inguinal and femoral hernias. Short-term use (1 to 3 weeks) of physical modalities may be They usually result from significant falls, because few jobs include appropriate for an acute musculoskeletal problem or a flare-up running or jumping activities likely to cause a hip strain or sprain. of a chronic condition, if they facilitate participation in active Heavy lifting rarely injures anything about the hip. Most sprains rehabilitative exercise.6 and strains recover in 6 weeks or less. Nonoperative treatment includes pain control and rehabilitation through stretching and THE KNEE strengthening exercises. Those that persist are usually evaluated by magnetic resonance imaging (MRI), looking for the unusual Acute knee injuries are common, although most are not work place injuries. Overuse syndromes about the knee are mainly a sports medicine problem and not a workers’ compensation problem. For example, the American College of Occupational and Environmental Medicine’s Occupational Medicine Practice Guidelines, 2d edition, discusses the treatment of many condi- tions affecting the knee, none of which is occupational overuse. Meniscal injuries are common (Fig. 7d.4). Small stable menis- cal tears may produce only occasional tolerable symptoms with heavier activity. For these minor tears, patients may be content with intermittent use of NSAIDs and a home strength- ening exercise program. A single intraarticular corticosteroid injection is sometimes given to decrease acute pain and effusion, hoping to permit earlier rehabilitative exercise. For patients
302 Chapter 7d ● Hip and knee: treatment options AB CD Figure 7d.3 (A) Severe avascular necrosis of the femoral head in a 35-year-old alcohol abuser. Note the incongruity of the femoral head with collapse (arrow). (B) Frog-leg lateral demonstrates severe collapse of the superior portion of the femoral head (arrows). (C) Magnetic resonance imaging of the pelvis. T1-weighted and T2-weighted (D) spin-echo images demonstrate the extent of osteonecrosis in the femoral head. with persisting major mechanical symptoms, arthroscopic partial young person without age-related osteoarthritis who sustains a meniscectomy is the now traditional treatment. For young large symptomatic meniscal tear, transplantation of a cadaveric patients with large peripheral tears (near the joint capsule where meniscus is occasionally performed. More often this is per- the meniscus still has a blood supply) that are discovered early, formed in the young patient without significant arthritis change meniscal repair instead of meniscectomy is sometimes performed. who remains symptomatic after total meniscectomy and who If the meniscal tear is repaired, and if it heals, hopefully knee does not have significant knee deformity or instability.12 function will be normal, and the late posttraumatic arthritis that usually develops in knees after meniscectomy can be prevented. Patients with isolated meniscal injuries can almost always Long-term studies on this procedure are in progress. For the return to the job they were doing before the injury. Arthroscopic partial meniscectomy usually permits return to even heavy
Chapter 7d ● The knee 303 AB Figure 7d.4 (A) Magnetic resonance imaging (MRI) of a normal meniscus appears black (arrows) in a proton-density-weighted image, as it does in this case. (B) MRI of a torn meniscus. The posterior horn tear appears as a high-intensity white line or band (arrows). work in 6 weeks (or at most 12 weeks).13 Patients with meniscal or grade 3 injuries to the medical collateral ligament are usually repair or meniscal transplantation require longer periods of treated nonoperatively. Grade 3 injuries to the lateral collateral activity restriction with emphasis on avoiding extreme flexion ligament may be treated with primary surgical repair. Grade and twisting. 3 injuries to a cruciate ligament do not heal and are not amenable to primary repair. A period of rehabilitative exercise after injury Knee ligament injuries are sprains (Figs. 7d.5 and 7d.6). permits a decision as to whether the residual symptoms can be Isolated grade 1 and grade 2 sprains typically heal in 6 weeks tolerated with NSAIDs, quadriceps and hamstring strengthening and leave no sequela. Partial injuries to a cruciate ligament are exercise, and bracing. If not, reconstruction of the involved sometimes treated with temporary protective bracing in addition to cruciate ligament is the surgical option. activity restriction to minimize the chance of reinjury. Complete AB Figure 7d.5 (A) T2-weighted magnetic resonance imaging (MRI) of a normal anterior cruciate ligament (ACL) that has a low-intensity (black edge) straight anterior margin (arrows). The posteroinferior edge of a normal ACL is variable in appearance; it is high in intensity in this case. (B) T2-weighted MRI of a torn ACL. Tissue in the expected region of the ACL is high in signal and disorganized, indicating a tear. Note the frayed ends of the torn ligament (arrows).
304 Chapter 7d ● Hip and knee: treatment options AB Figure 7d.6 (A) T2-weighted magnetic resonance imaging (MRI) of a normal posterior cruciate ligament (PCL) in a 25-year-old man. The ligament (arrows) is normally black, as it is in this case. (B) MRI, torn PCL. The bright appearance of the proximal end of the ligament and its discontinuity (arrows) indicates a tear at its attachment to the femur. If residual instability is present, and especially if instability is As in hip osteoarthritis, glucosamine and chondroitin present in two planes (both varus-valgus and anterior-posterior may be tried, and some patients improve symptomatically.11 instability), posttraumatic arthritis generally develops at an accele- Acetaminophen (paracetamol in Europe) for many arthritis rated rate. Bracing and permanent work activity restriction or a patients gives acceptable osteoarthritis pain relief with a better career change may be indicated if the patient usually performs side effect or safety profile, and many reviewers recommend this heavy work. drug be tried before NSAIDs are used.5,19,20 Osteoarthritis of the knee is very common. It increases If symptoms are more severe, injection therapy is frequently in prevalence with age, and it is associated with family history, used. Intraarticular corticosteroid injections may significantly knee varus or valgus deformity, obesity, prior intraarticular frac- decrease pain and effusion and may be repeated as often as ture, and prior significant meniscus or ligamentous injury. At every 3 months without documented worsening of the arthritis present, there are no conclusive data on the association of knee or other adverse effects.2,4 Intraarticular hyaluronic acid injection osteoarthritis and patients’ prior activity levels.3 Osteoarthritis of or “viscous supplementation” may also be tried. It is U.S. Food the knee is not a simple “wear and tear” problem. and Drug Administration approved as a series of three injections; however, it is much more expensive than simple corticosteroid Nonoperative treatments1 of knee arthritis include NSAIDs, injection, and its efficacy is controversial.8 use of a cane, and usually weight reduction (again, frequently prescribed but rarely accomplished). Physical therapy consulta- As in hip osteoarthritis, when pain and disease become severe, tion for training in quadriceps and hamstring strengthening surgical treatment is used. Arthroscopic debridement of the may help significantly with symptoms, because the developing degenerative knee was performed in the past, although since the arthritis has frequently resulted in favoring the symptomatic publication of a randomized controlled trial14 that showed no knee and thus quadriceps and hamstring weakness from disuse.15 benefit over placebo arthroscopy, this surgery is rarely performed. This exercise prescription does not result in further “wearing Arthroscopy is still indicated for comorbid osteoarthritis and out” of the knee, because osteoarthritis is not a simple wear and significant mechanical pathology, like a major meniscal tear or a tear problem. Unlike automobile tires, knees do not have a fixed loose body. number of miles they can travel. For early varus deformity with medial compartment arthritis For patients with a significant knee varus deformity (bow legs), or for early valgus deformity with lateral compartment arthri- lateral wedge shoe insoles decrease the external varus moment tis, if the other compartment is still relatively normal, a weight- and the estimated medial compartment load, resulting some- transferring osteotomy of the proximal tibia is sometimes times in pain improvement, especially in early stage arthritis. performed. Varus deformities are usually treated by lateral closing An unloader brace, which applies a varus or valgus moment to wedge osteotomy and valgus deformities by medial closing wedge reduce force transmission in the most involved knee compart- osteotomy (Fig. 7d.7). The ideal patient for osteotomy has single- ment (medial or lateral), can be tried in an active patient with compartment arthritis, ligamentous stability, and is “young” and isolated unicompartmental disease. Most patients discontinue physically active.13 Absolute contraindications include inflam- brace use as the arthritis progresses. Work activity modification matory arthritis, severe tricompartmental disease, a flexion arc may be necessary as the arthritis progresses. of 90 degrees or less, marked tibiofemoral subluxation, and
Chapter 7d ● The knee 305 Figure 7d.7 Bilateral varus deformities with medial joint arthritis in a previous meniscectomy in the contralateral compartment. 41-year-old woman treated with a high tibial osteotomy on the left side Relative contraindications include age older than 60 years, to correct her varus alignment. patellofemoral arthritis, collateral ligament insufficiency, lateral tibial subluxation, or a varus deformity more than 10 degrees. Once the osteotomy (“broken tibia”) has healed, activity restric- tions may not be needed. Osteoarthritis is a progressive disease, so results deteriorate with time, and up to 40% of patients undergo knee replacement in 5 years and 50% in 10 years.9 For patients with severe arthritis and pain who are not candi- dates for osteotomy, unicompartmental knee replacement or total knee replacement are the surgical options (Figs. 7d.8 and 7d.9). Current knee replacement designs can be expected to last at least 15 years before wear requires revision.14 As in hip replacement, cemented knee replacements are immediately stable, whereas noncemented units require time for the patient to heal to the implant before full weight bearing is allowed. Rehabilitation after knee replacement is slower than after hip replacement. After successful replacement arthroplasty, the worker requires permanent restrictions prohibiting jumping, heavy lifting, and so forth. Knee tendonitis is an occasional problem, although again is much more frequently seen in a sports medicine practice than in an occupational medicine practice. It may involve the quadriceps AB Figure 7d.8 (A) A severe varus deformity in an 8-year-old girl with partial loss of the medial tibial plateau (arrow). (B) Total knee arthroplasty required a bone graft fixed with screws on the medial side to support the tibial plate (arrow).
306 Chapter 7d ● Hip and knee: treatment options AB Figure 7d.9 (A) Bilateral degenerative joint disease in a 56-year-old woman rheumatoid patient. Note the complete loss of joint space, severe osteopenia, and lack of osteophytes typical of rheumatoid arthritis. (B) Bilateral total knee arthroplasties were cemented in place because of poor bone quality in this patient. tendon, the patellar tendon, the iliotibial band, the popliteus so that surgeons can charge more (therapeutic arthroscopy tendon, or the medial hamstring tendon insertions (pes anserine is reimbursed at a higher level than a “negative” diagnostic bursitis). Treatment is usually symptomatic with a brief period of arthroscopy). activity restriction, NSAIDs, and stretching and strengthening exercises. There is very little quality evidence on the role of phys- Other than for obvious patellar malalignment or instability, ical therapy for knee tendinitis syndromes.1 For the patellar the treatment for anterior nonspecific knee pain is usually non- tendon, use of a “strap” orthosis may provide partial symptom operative. NSAIDs are tried, although they may be ineffective. relief. For refractory cases a corticosteroid injection may be used Physical modalities have not been proven to be effective treat- (but not for the quadriceps or patellar tendons because of the ment.1 Aerobic conditioning and quadriceps and hamstring possibility of steroid induced tendon weakness predisposing to stretching and strengthening exercises are usually tried. Closed- tendon rupture). In athletes, a shoe orthotic to alter knee chain knee extension strengthening exercises between 0 and mechanics is sometimes helpful. Surgery is used only for serious 30 degrees of flexion put the least compression load on the patella complications like complete rupture of a quadriceps or patellar and may be tolerated and thus performed. Surgical debridement tendon. (patellar chondroplasty) has variable to disappointing results. “Patellofemoral pain” is a frequent complaint and is some- Like the patient with chronic low back pain, the patient what like chronic headache and chronic low back pain in that with chronic anterior knee pain without objective findings is at the findings in patients with anterior knee pain are usually non- times a problem in the workplace. There is no risk of serious con- specific and commonly seen in asymptomatic individuals. sequences if the patient/worker remains active at work despite Anterior knee pain in patients with obvious patellar malalignment pain. The crucial issue is the patient’s tolerance for workplace or patellar instability (subluxations) can be rationally treated symptoms, and in the absence of major objective findings, there surgically, although with less than ideal results in many cases. is not usually physician agreement on the appropriateness of advising employers or patients to decrease the job demands on Patients with anterior knee pain without obvious patellar the patient.18 malalignment or instability are challenging. In many patients the pain is attributed to chondromalacia of the patella, although REFERENCES arthroscopy studies have shown that the patella has normal cartilage in many of these cases.10 A patellar plica is a fold of 1. Archibeck MJ, Ayers DC, Berger RA, et al: Knee reconstruction. In KJ Koval, ed: synovium present in embryologic life that does not always resorb Orthopaedic knowledge update 7. Rosemont, IL, 2002, American Academy of in childhood. In some adults it is postulated to be a cause of Orthopaedic Surgeons, pp. 513-536. anterior knee pain. However, results from excising the plica arthroscopically are variable, and the persisting plica was not 2. Arroll B, Goodyear-Smith F: Corticosteroid injections of osteoarthritis of the knee: considered to be a source of symptoms when knee surgery was meta-analysis. BMJ 328:869-873, 2004. by open arthrotomy. Cynics believe that the plica is implicated 3. Clyman B: Sports, exercise, and arthritis. Bull Rheum Dis 50(6):1-3, 2001.
Chapter 7d ● References 307 4. Cole BJ, Schumacher HR Jr: Injectable corticosteroids in modern practice. 13. http://www.mdainternet.com/V5/mdaTopics.aspx. Accessed 05/28/05. JAAOS 13(1):37-46, 2005. 14. Mosely JB, O’Malley K, Petersen NJ, et al: A controlled trial of arthroscopic surgery 5. Courtney P, Doherty M: Key questions concerning paracetamol and NSAIDs for for osteoarthritis of the knee. N Engl J Med 347(2):81-88, 2002. osteoarthritis. Ann Rheum Dis 61:767-773, 2002. 15. Philadelphia panel evidence-based clinical practice guidelines on selected 6. Dahners LE, Mullins BH: Effects of nonsteroidal anti-inflammatory drugs on bone rehabilitative interventions for knee pain. Phys Ther 81(10):1675-1700, 2001. formation and soft-tissue healing. JAAOS 12(3):139-143, 2004. 16. Richy F, Bruyere O, Ethgen O, et al: Structural and symptomatic efficacy of 7. Harris I, Mulford J, Solomon M, et al: Association between compensation status and glucosamine and chondroitin in knee osteoarthritis: a comprehensive outcome after surgery. JAMA 293:1644-1652, 2005. meta-analysis. Arch Intern Med 163:1514-1522, 2003. 17. Sherrer YS: Working with common rheumatologic disorders. In JB Talmage, 8. Lo GH, LaValley M, McAlindon T, et al: Intra-articular hyaluronic acid in treatment of JM Melhorn, eds. A physician’s guide to return to work. Chicago, 2005, AMA Press. knee osteoarthritis: a meta-analysis. JAMA 290(23):3115-3121, 2003. 18. Talmage JB, Melhorn JM: How to think about work ability and work restrictions: risk, capacity, and tolerance. In JB Talmage, JM Melhorn, eds. A physician’s guide to 9. Lonner JH: Clinical crossroads: a 57 year-old man with osteoarthritis of the knee. return to work. Chicago, 2005, AMA Press. JAMA 289(8):1014-1025, 2003. 19. Zhang W, Doherty M, Arden N, et al: EULAR evidence based recommendations for the management of hip osteoarthritis: report of a task force of the EULAR standing 10. Mayer TG, Press J: Musculoskeletal rehabilitation. In AR Vaccaro, ed: Orthopaedic committee for international clinical studies including therapeutics (ESCISIT). Ann knowledge update 8. Rosemont, IL, 2005, American Academy of Orthopaedic Rheum Dis 64(5):669-681, 2005. Surgeons, pp. 655-660. 20. Zhang W, Jones A, Doherty M: Does paracetamol (acetaminophen) reduce the pain of osteoarthritis? A meta-analysis of randomized controlled trials. Ann Rheum Dis 11. McAlindon T: Glucosamine and chondroitin for osteoarthritis? Bull Rheum Dis 63:901-907, 2004. 50(7):1-4, 2001. 12. McCarty EC, Spindler KP, Bartz R: Knee and leg: soft-tissue trauma. In AR Vaccaro, ed: Orthopaedic knowledge update 8. Rosemont, IL, 2005, American Academy of Orthopaedic Surgeons, pp. 443-456.
7eC H A P T E R lost of 15. Furthermore, in the construction industry, muscu- loskeletal disorders involving the knee resulted in a median of Workplace-Related Lower 29 lost work days, a severity higher for the knee than any of the Extremity Disorders: industry groups having more total lower extremity musculoskeletal Workplace Adaptations disorders. with Case Studies Despite these facts from the Bureau of Labor Statistics, scien- Amit Bhattacharya, Daniel J. Habes, and James A. Dewees tific studies and journal articles found in the literature predom- inantly address the upper extremity. Entering the key words MAGNITUDE OF THE PROBLEM “upper extremity musculoskeletal disorders” and “lower extremity musculoskeletal disorders” into a popular search engine yields Work-related lower extremity 877 and 20 hits, respectively. musculoskeletal disorders There is additional justification for this new emphasis area A significant amount of research has been performed in the area based on the following facts: The working population is aging, of cumulative trauma disorders of the upper extremity and and because age-induced muscle strength impairment affects low back pain of occupational origin.127 Although studies on this the lower extremity and the upper extremity, it stands to reason topic are important enough to warrant further investigation, it that tasks requiring repetitive and sustained use of lower limbs is becoming more important to address the need to evaluate the detrimentally affect this part of the body. In contrast to the lower extremity cumulative trauma syndrome. According to upper extremity, the lower limbs are under sustained static and the Bureau of Labor Statistics, there were 1.4 million injuries dynamic loading due to weight bearing. When a person is and illnesses in private industry that required days away from simply standing upright, the lower extremity joints (such as work in 2002. Of these, 488,000 (34%) were musculoskeletal ankle, knee, and hip joints) experience sustained biomechanical disorders, defined as injuries or disorders of the muscles, nerves, loading. These loadings become significantly high and repetitive tendons, joints, cartilage, and spinal disks. Twenty-one percent (2 to 20 times the body weight) during simple walking and run- of these musculoskeletal disorders occurred in manufacturing ning.16,43 With an aging musculoskeletal system, such high repet- and about 9% occurred in construction. The back accounts for itive loading may detrimentally affect the health of the joints. the greatest number of occupational injuries and illnesses, but reports for the upper extremity (hand, finger, wrist) and lower Furthermore, with the aging process, it is well established extremity (knee, foot, toe) are comparable with each other for that in the general population the incidence of musculoskeletal both total injuries and illnesses (Fig. 7e.1A) and for muscu- disorders such as osteoarthritic knee is very high. It is estimated loskeletal disorders only (Fig. 7e.1B). Moreover, the severity that over 80% of people over the age of 55 have a clinically diag- of injuries and illnesses to the lower extremity exceeds that for nosed osteoarthritic condition.64,138 In the aged population the both the upper extremity and back, trailing only that of the shoul- joint complaints of the lower extremities are more frequent der (Fig. 7e.1C). For the years 2000-2002 the median number of than that of the upper extremities.11 There is sufficient evidence days away from work for back, upper extremity, lower extremity, in the literature4 that osteoarthritis causes more absenteeism than and shoulder injuries and illnesses has averaged 6, 6, 8, and any other joint trauma. Therefore, a worker population chosen 12 days, respectively. from such a sample is at a high risk of developing significant musculoskeletal disorders of the lower extremity. According to 2002 Bureau of Labor Statistics data, the services industry, which includes health care and social assistance, Keeping in mind the changing demographics of the aging accounted for more lower extremity musculoskeletal disorders work force and the fact that lower extremity injuries account for with days away from work than any other broad industry cate- about 20% of all compensable injuries, it is rather important that gory (11,092). Manufacturing (5759) and transportation and pub- we further study this particular cumulative trauma. In particular, lic utilities (5668) were next, with about half the number of lower because most of the industrial tasks require some amount of extremity musculoskeletal disorders with days away from work as sustained standing, it places excessive loading on the already services but higher severity rates with median days away from traumatized lower extremity joints due to aging. Furthermore, work of 11 and 15 days, respectively. Construction, which was jobs requiring excessive kneeling and walking further traumatize fifth on the list of industries having lost work-day lower extrem- the aging lower extremity joints. ity musculoskeletal disorders (4748), also experienced more severe cases than services, having a median number of days A review of the literature indicates that a variety of occupa- tions that require excessive use of the lower extremities shows a high incidence of musculoskeletal disorders. For example, osteoarthritic/arthritic and other types of musculoskeletal con- ditions of the knee, ankle, and hip have been documented in carpet layers, ballet dancers, housemaids, miners, and construc- tion workers.13,24,26,38,63,66,69,105,107,108,122 Similar findings of lower extremity trauma have been documented in people involved in professional athletics such as soccer, football, bicycling, and running.8,24,60,101 Coggon et al33 concluded that there is strong evidence for occupational osteoarthritis from prolonged kneeling and squatting but reported that obesity may be a factor in such workers. A study by Lindberg and Montgomery67 reported that
310 Chapter 7e ● Workplace-related lower extremity disorders 700000 Number of injuries Trunk 600000 Upper Ext 500000 Lower Ext 400000 300000 2000 2001 2002 200000 100000 Year 0Number of MSK Trunk Upper Ext A Lower Ext 450000 2000 2001 2002 400000 350000 Year 300000 250000 200000 150000 100000 50000 0 B 30 25 Percentage 20 Trunk 15 Upper Ext Lower Ext 10 5 0 2000 2001 2002 C Year Figure 7e.1 (A) Number of nonfatal occupational injuries and illnesses with days away from work for select parts of the body, years 2000-2002. (B) Number of musculoskeletal disorders (MSK) involving days away from work for selected body parts, years 2000-2002. (C) Percentage of nonfatal injuries and illnesses with days away from work exceeding 30 days for selected body parts, years 2000-2002.
Chapter 7e ● Magnitude of the problem 311 osteoarthritic knee conditions in 322 shipyard workers (average The carpet layers further heighten the trauma to their knees age, 66 years) were significantly related to long-term (30 years) by impacting on a carpet stretching device called a “knee-kicker” exposure to heavy labor rather than age. An epidemiologic at a rate of about 140 kicks per hour with impact peak forces study106 of 342 chain saw operators and 277 rock drill operators averaging around 3000 N15 (Fig. 7e.2A). Similar research found indicated that these workers showed not only classic cases of that seven male carpet layers using a knee-kicker over 39 trials vibration white finger disorders but symptoms of numbness and demonstrated peak forces of 2933 N.128 In general, the carpet coldness in the legs as well. The workers with the most frequent installation task requires use of awkward body posture, high symptom were older and had longer exposures to vibration. The impact forces to the knees, high acceleration of lower legs, and results imply vibration-induced disturbance of circulation of the repetition that is biomechanically demanding and, therefore, lower limbs. Earlier studies14,139 showed that whole body vibra- provides reasons for high risk of knee disorders (Fig. 7e.2, B to D). tion can cause modification of the cardiovascular system relevant The epidemiologic data of high morbidity (107.8) among for the lower extremities. Such disorders do not occur suddenly; carpet layers compared with tile setters and general floor layers rather, it is the long-term insult by the externally applied forces substantiate the fact that these workers are at a relatively high that gives rise to microtrauma of the biologic issues in question. risk of developing lower extremity musculoskeletal disorders.117 According to the Industrial Commission of Ohio’s report,3 the The human body undergoes microtrauma on a daily basis percentage of carpet layers’ knee injury claims was about four from performing routine tasks such as walking, running, and times higher than knee injury claims filed by all other Ohio climbing stairs. For normal tissue, exposure to such a low level workers. In an epidemiologic/medical study of 112 carpet layers, of force causes gradual replacement of microscopically injured 42 tilers and terrazzo setters, and 243 millwrights and bricklayers, tissues with new ones. However, when the activities become Thun et al122 reported that carpet and floor layers have a high more stressful and repetitive and the loading envelope reaches a frequency of bursitis, needle aspiration of knee fluid, and skin certain limit, the biologic system no longer is able to respond by infections compared with the other workers in the study. Their regeneration, and the result is pathologic conditions. Furthermore, study also showed that the frequency of impacting on the the onset of such pathologic response is highly dependent on the knee-kicker was the only statistically significant predictor of existing health status of the tissue. For example, with the aging bursitis. The act of kneeling was one of several descriptors of process, the susceptibility of injury to tissues under loading to knee aspiration and skin infection of the knee. externally applied forces is high. Middle-aged or elderly workers who are exposed to repetitive loading of certain parts of their The above summary12,17-19,54,55,68,117,122,128 of existing research bodies may be highly susceptible to injury due to declining studies on carpet installers clearly indicates a serious knee morbid- health status in their tissue properties and not being able to ity problem exists among these workers. The data so far supports sustain the insult caused by the external loading. the fact that the knees of these workers are actually traumatized by their occupation, and the resulting cost of medical expenses, Case study of carpet layers earning loss, and physical and psychologic suffering compels Lower extremity trauma in carpet installers The concept us to investigate further monitoring and prevention of such a disability of the lower extremity. of microtrauma induced by repetitive loading as described above is used for analyzing the job of carpet layers in our laboratory. Biomechanical basis for clinical responses to the carpet This section presents the approach involving ergonomic/ installation task Most of the postures used during the carpet biomechanical principles to better understand, characterize, and installation phase of the job of installing carpet pose unusual monitor lower extremity trauma experienced by these workers biomechanical demands on the musculoskeletal system. In our and to provide some solutions to help minimize this trauma. previous study with carpet layers,17 we were able to identify typical postures that produce either static or dynamic sustained There are occupations (such as carpet laying) where knee loading on the lower extremities (in particular, the knee joint). injury claims have been significantly higher than knee injury In Figures 7e.2A and 7e.3, we present examples of typical body claims from all occupations. Morbidity data indicate that carpet postures that produce sustained static biomechanical loading installers experience more than 10 times the number of lower of the knee joint. Such kneeling postures are maintained about extremity disorders than expected, given the percentage of 75% of the work period. The arrows in Figure 7e.3 indicate the these workers in the United States.117 Although others such as potential areas of pressure points due to distributed ground reac- tile setters, floor layers, drywall installers, cement and concrete tion forces acting at the interface of the ground and the body. finishers, and carpenters also use their lower extremities in the Because of excessive knee flexion angles and direct ground pres- performance of their jobs by kneeling, the carpet layers’ exposure sure at the infrapatellar region associated with these postures, to mechanical loading to the knee is not limited to the task of the infrapatellar bursa is susceptible to injuries. This conclusion kneeling. A comparison of knee disorders among essentially agrees with the finding of investigators at the National Institute equal numbers of carpet and floor layers to painters indicated for Occupational Safety and Health (NIOSH) who reported that the former group reported more knee pain, knee accidents, more frequent infrapatellar bursitis than prepatellar bursitis in and treatment regimens for the knees than the latter group. this work force.122 Osteophytes of the patella were more common among the carpet and floor layers as measured by radiographic changes.55 In Figure 7e.3D, a typical posture is shown which describes Ultrasonography performed by these same authors found thick- the dynamic act of knee-kicking with the suprapatellar region ening of the prepatellar or superficial infrapatellar bursa in of the knee. In our previous study17 we found that most of the 49% of carpet installers versus 7% of house painters.54
312 Chapter 7e ● Workplace-related lower extremity disorders Angular 24 Angular acceleration of thigh C.G. (rad/s2) 60 20 –20 1 –60 –100 Z –140 –180 3 X 0 10 20 30 40 (0,0,0) 0 1.35 A Knee kicker B Time (sec) Horiz. and vert. joint reaction forces at knee (N) Vertical 0 Horiz. linear acc. of shank C.G. (m/s2) 60 –400 40 –800 20 –1200 Horizontal 0 –20 –1600 –40 10 20 30 –2000 10 20 30 40 0 Film frame number 40 0 Film frame number 1.35 0 Time (sec) 1.35 0 Time (sec) C D Figure 7e.2 (A) Schematic of coordinate system for carpet stretching task. (B) Angular acceleration of thigh center of gravity (C.G.). (C) Horizontal linear acceleration of shank C.G. (D) Joint reaction forces at knee. time (70%) workers were involved in carpet stretching tasks, using posterior and anterior to the patella and the infrapatellar bursa the knee-kicker to stretch the carpet. The knee-kicking motion are in direct contact with the quadriceps muscle and the patellar required vigorous and quick extension and subsequent flexion of tendon, respectively. Under such a repetitive movement condi- the knee joint as the carpet stretching tool was struck. Therefore, tion, the tendon moves repeatedly over the bursae, causing this movement of the leg and the direct impact on the knee- mechanical irritation that gives rise to inflammation, causing kicker with the knee potentially exposes the bursae (fluid-filled fluid to be released into the bursae. Fluid in the bursae produces sacs whose function is to reduce friction and distribute stress) swelling and tenderness. If the inflammation is intense, the over- located anterior and posterior to the patella to trauma (Fig. 7e.4). lying skin becomes red and feels hot when touched. Symptoms The epidemiologic/medical evaluation study on carpet layers typical of inflammation include95 swelling caused by accumula- by Thun et al122 concluded that only the use of the knee-kicker tion of fluid that may require knee tapping, redness and local predicted the occurrence of bursitis and to some extent knee rise of skin temperature caused by increased blood flow around tapping (using a needle to withdraw fluid from the knee). Our the injured area, tenderness on touching the affected area, and biomechanical explanation presented above and shown in Figure impaired function. Early signs of superficial tissue damage due to 7e.4 supports the findings of Thun et al.122 sustained kneeling or impacting a knee-kicker may be indicated by skin redness caused by increased blood flow and therefore local In the case of carpet layers performing the carpet-stretching rise of skin temperature. Therefore, one of the medical/physiologic task (using a knee-kicker), it appears that the bursae located
Chapter 7e ● Magnitude of the problem 313 A Sustained static loading B Sustained static loading C Sustained static loading D Repetitive dynamic loading Figure 7e.3 (A-D) Lower extremity locations of potential pressure points and/or vigorous impact force on body postures of the carpet installation process. Rk R parameters of measurement should be skin temperature distri- bution and the degree of skin redness that could be used as Rpf preclinical indicators of inflammation/bursitis. Figure 7e.4 Force configuration in the sagittal plane during impact phase of the knee kicking cycle. Ground reaction forces are assumed In comparison with frictional bursitis, the condition of hemo- to be negligible. RK, Impact knee force on the knee-kicker; bursa (bleeding into a bursa) may be produced in people whose Rpf, patellofemoral force; R, resultant force. activities require them to make repeated contact with a hard surface or object, such as those experienced by carpet layers. In the case of carpet layers, sheer impact force on the knee-kicker may be sufficient to injure the bursae located posterior and anterior (pre) to the patella. Blood within the bursae causes chemical irritation, and in severe cases it may clot, causing adhe- sion of connective tissue and loose bodies. At this stage, chronic inflammation is likely to set in. The presence of loose bodies causes a specific cracking and grating sound when the knee is flexed and extended. Chu et al32 showed that the presence of loose bodies can be quantified by noninvasively measuring and characterizing the “acoustic signature” using a special purpose (20 to 20,000 Hz) microphone (attached to a waveform analyzer) in an auscultation examination of the knee joint. Development of this kind of methodology is highly recommended for a future project because this technique may be sensitive enough to iden- tify the preclinical signs of the existence of loose bodies as well as some degenerative knee joint disorders. In addition to the trauma to the bursae, Thun et al122 also reported the existence of arthritic conditions in the carpet layers. They did not specifically distinguish between osteoarthritis and
314 Chapter 7e ● Workplace-related lower extremity disorders rheumatoid arthritis. In the carpet layers’ case, biomechanics can Figure 7e.5 Tibial damping calculated by accelerometric technique. be used to explain the existence of potential osteoarthritis. (From Huang S, Bhattacharya A: Chin J Med Biol Eng 13:255-264, Previous investigators77,100 implied and showed that with increase 1993.) of articular stresses and asymmetric loads beyond the capacity of resistance of bone and cartilage tissues, osteoarthritic lesions spring and viscous damper.10,34 During a force plate event appear and develop. From our field study and biomechanical (patient steps across force plate), the single degree of freedom analysis of the impact data and the position of the knee during system responds to the transient force in accordance with the the impact phase of the kicking cycle, we see that the result of solution to the second-order differential equation. Using a Rk (impact knee force on knee-kicker) and Rpf (patellofemoral frequency response function (transfer function between the force) (Fig. 7e.4) either (1) acts eccentrically at the articulating force plate and the acceleration at the tibia), the solution to a surface, creating uneven pressure distribution on the cartilage differential equation, a trabecular-damping fraction (ratio, ζ), and therefore present conditions for developing osteoarthritis, was obtained directly from a measured frequency response func- or (2) acts laterally, resulting in eccentric squeezing of the patella tion using a technique adapted from Coleman34 and Bendat and against the femur that increases localized stress with bone osteo- Piersol.10 The results showed that the osteoarthritic subjects have phytes, destruction of cartilage, and narrowing of joint space. higher resonant frequency and decreased damping (Fig. 7e.5) Either of the above two conditions in conjunction with the than the normal subjects. It implies that the subjects with impacting nature of the load experienced by the carpet layers osteoarthritis have a decreased shock-absorbing capacity in the give sufficient biomechanical reasons to promote osteoarthritis tibia and stiffer bone compared with normal subjects. Therefore of the knee. Whatever the nature of the underlying cause, it it is a worthwhile effort to investigate this technique for iden- appears that there is a need to quantify the existence of knee tifying preclinical signs of osteoarthritis in the carpet layers. osteoarthritis in carpet layers at a preclinical stage. To date, this type of degenerative disease (generally irreversible) can be Based on the above discussion and our previous studies, the identified only when the actual sclerotic lesions have appeared following parameters should be measured as descriptors of on the tibiofemoral joint surface. These lesions are visible on an mechanical loading of the knee joint in carpet layers: kneeling x-ray film. time, knee-kicking frequency, kneeling pressure/force, and knee- kicking impact force. The above parameters can be used to In our laboratory we have further developed, refined, and vali- define new indices of biomechanical loading of the knee joint dated a previously reported133 noninvasive method for quantifying for carpet layers. One such index, called the Cumulative Impact preclinical biomechanical parameters of knee osteoarthritis.2,50,111 Loading Index, is described in our earlier publication.18 The Briefly, this technique allows noninvasive quantification of corresponding clinical/physiologic response variables should stiffening (or damping) properties of subchondral bone in the include (1) location and size of inflammation region, (2) skin osteoarthritic patients compared with normal subjects. Previous temperature distribution of the inflamed region, (3) degree of study101 has shown that stiffening of subchondral bone may be skin redness, (4) range of motion of knee joint, (5) acoustic iden- used as a preclinical indicator of knee osteoarthritis. The experi- tification of the existence of loose bodies, and (6) noninvasive mental protocol involves attaching single-axis accelerometers preclinical quantification of an osteoarthritic condition. at the tibial tuberosity and femoral condyles of each subject for collecting heel-strike–induced acceleration waveforms. The Work-related lower extremity rationale is that the stiffer subchondral bone of osteoarthritic vascular problems patients produces high-frequency bone vibration compared with those produced by normal subjects. Because of decreased Many occupations require long periods of standing, including damping capacity of the subchondral bone, harmful forces workers in the manufacturing, service, and retail sectors. due to external loads (either produced by the occupational task Epidemiologic studies have shown certain health outcomes to and/or natural heel strike events) damage the knee cartilage and be associated with occupational prolonged standing, including eventually traumatize the tibiofemoral bony surfaces. Ultimately, the incoming forces continue to progress toward the hip, causing it to become the next target of trauma. The results from our previous and ongoing studies with clinically diagnosed osteoarthritic patients2,52,113 (Bhattacharya, Watts, and Waters, 2004, unpublished data) indicate that this technique can differentiate osteoarthritic acceleration patterns from those obtained from normal subjects. The purpose of this study52 was to describe the accelerometric technique used to estimate tibial damping properties among osteoarthritic subjects. Tibial tuberosity bone vibration was captured in 8 osteoarthritic patients and 10 normal subjects with a skin-mounted low-mass accelerometer described in the literature.7,25,130-132 The subject was asked to walk on a force plate. Trabecular damping was estimated assuming a single degree of freedom model in which the tibia and foot were considered together as a lumped mass and the trabecular behaves as a linear
Chapter 7e ● Workplace adaptation/recommendations 315 chronic venous insufficiency,41,57,58,125 varicose veins,1,56,114,126 low stimuli to initiate neural/humoral responses are a decrease in back pain,73,85,105 symptom-free venous reflux,61 hip osteoarthritis,37 central venous pressure, arterial pulse pressure, and arterial mean leg and foot pain,105 varicose symptoms without varicose veins pressure. The neural/humoral responses are an increase in sympa- (hypotonic phlebopathy),5 venous disease,42 arthrosclerotic pro- thetic activity, plasma norepinephrine, heart rate, vasoconstric- gression (as measured by ultrasound of carotid intima media tion, and vasopressin or antidiuretic hormones.104 The release of thickness),56 and trunk varices.116 Abramson et al1 estimated the antidiuretic hormones is modulated by the atrial mechanorecep- prevalence of varicose veins in the general population to be tors that sense the shift in fluid volume to the lower leg as a 10% in men and 29% in women. Krijnen et al57,58 found the decrease in fullness of the vascular system. This hormone has water prevalence of venous insufficiency in a population exposed to and salt retention properties that may constitute an effective occupational standing to be 29%. Chronic venous insufficiency long-term adjustment to the upright posture. is often unrecognized in the occupational population because it is sometimes asymptomatic.58 Much more research is needed The mechanism behind muscle pain/discomfort due to to investigate causes of venous insufficiency.41 prolonged standing is not well understood.52,113-115 Some human studies113-115 using thermodilution techniques (along with hema- Biomechanical studies have shown prolonged standing to tocrit, hemoglobin, lactic acid, and muscle biopsy) have shown be associated with increased plantar pressures81 and pain and that submaximal static muscle contraction (such as prolonged increased leg internal fluid volume.57,58 Prolonged standing can standing) causes an increase in muscle water content due to an cause lower leg and back discomfort.102 Magora75 reported a high increase in extracellular water (possibly affecting muscle mem- incidence of lower back pain for workers standing more than brane potential due to changes in potassium and sodium con- 4 hours a day. In addition to lower back pain, supermarket tents of the muscle as per Sjogaard et al113), and with maximal workers such as checkout personnel have a high incidence of static contraction intracellular water increases. One reason for lower limb discomfort and pain.105 Leg discomfort and fatigue is an increase in water in the muscle is because lactate formed also found in assembly and quality control inspection workers.103 during fatigue is transported into the t-tubules where it attracts Eighty-four percent of French female health care workers stand water and causes t-tubule swelling and vacuolation.62 Bakke et al9 more than 4 hours a day, compared with 43% in the general in a study on humans showed significant correlation between population.39 German laundry workers stand 70-80% of their muscle edema (as measured by an increase in extracellular fluid work time per day.39 retention by the muscle) and subjective pain/discomfort. Therefore, previous studies,28 in which external leg volume was Physiology/biomechanics of prolonged standing measured before and after prolonged standing, showed no statis- tically significant correlations between leg discomfort and leg The upright posture poses a challenge for the human cardiovas- volume change. This insignificant relationship could be due to cular system. In the upright position about 70% of the total the fact that an increase in leg discomfort may not be linearly blood volume is below the heart level and three fourths of the related to venous pooling, because with sustained standing, com- blood volume is located in the compliant veins.104 With upright pensatory mechanisms may actually reduce the venous pooling posture, the increased hydrostatic pressure causes marked dis- temporarily.9,104 tension of the veins, causing pooling of the blood as increased filtration of fluid from the capillaries remain in the interstitial WORKPLACE ADAPTATION/ space (extracellular fluid) of the legs instead of returning to the RECOMMENDATIONS heart. In the upright position, the mean capillary pressure of a person of average height may increase by 80 mm Hg to a value Injury/disease prevention plan for jobs of about 125 mm Hg. requiring use of knee: carpet layers’ tasks During sudden upright position, the hydrostatic column of The development of an effective injury prevention program the blood in the vein between foot level and the heart level is involves three phases: (1) identification and estimation of the broken up by a series of one-way venous valves. However, as the level of the health hazard/injury for a specific job, (2) develop- standing time progresses, the blood continues to flow from the ment of a hazard/injury monitoring program, and (3) control arteries into the lower extremity veins, causing the blood to pool of the hazard. As far as the carpet layers study is concerned, and thereby forcing the valves to open, causing an uninterrupted the hazard has been identified and its potential risk determined. hydrostatic column of blood to form between the foot vein and We, in our laboratory, and others developed techniques to the right atrium. Under these conditions, about 600 ml of blood estimate the level of biomechanical loading and estimation/ usually shifts from the central circulation to the veins in the measurement of medical/physiologic variables of lower extrem- lower legs.72 Up to 30 minutes of standing causes the following ity trauma. For example, to monitor and quantify the level of responses to take place. When humans stand upright, both cen- external loading exposure to the knee joints during daily carpet tral venous and arterial pulse pressures fall, causing an increase installation activities, we designed and developed an “electronic in venous muscle tone via innervation of the sympathetic vaso- kneeling meter” that can measure and record the number of constrictor nerves supplying the smooth muscles of the venous kneelings, length of kneeling time, and number of kicks applied walls. The increase in venous muscle tone increases the stiffness by a worker during a working day15,20,46 (Fig. 7e.6). These parame- of the vein walls, causing the pressure of the blood within the ters are then used for calculating a cumulative loading parameter veins to rise; this increased venous pressure then drives the blood for the knee joint. This unit is a self-sustaining microcomputer out of the vein toward the right heart.114 Once the standing task continues beyond 30 minutes, both the neural and humoral responses play significant roles. With prolonged standing, the
316 Chapter 7e ● Workplace-related lower extremity disorders RCX accurate in detecting joint inflammation in the absence of 7 visible impairment. Figure 7e.6 Kneeling/knee-impact meter. This thermography system was tested at the site of a local hotel undergoing renovation.46 Two carpet-installer tradesmen system controlled by a microprocessor through a software pro- volunteered to undergo a day of testing with the thermography gram stored in a nonvolatile microprocessor chip. This device sheets. Both were experienced workers with 10 and 11 years is worn as a knee pad on the infrapatellar and suprapatellar experience as carpet installers, respectively. Measurements were regions. The entire system is designed for portability, and the taken before work began, at mid-morning and mid-afternoon display and storage of kneeling parameters remains intact for breaks, just before lunch, and at the end of the work day. Because at least 4 hours before the data need to be downloaded (on a the thermography sheets we used had a narrow temperature laptop computer) and stored for future analysis. The use of this range and we did not know what temperatures to expect from device allows quantification and characterization of the dose of the workers’ knees, we assembled a collection of thermography external loading on knee joints associated with tasks requiring sheets that could detect temperatures from 22 to 42°C. The two the use of the lower extremities. tradesmen went about their typical work activities that included a mix of unloading rolls of carpet from the delivery truck, cut- For the quantification and characterization of early medical/ ting carpet and pads to size, laying tack strip and molding, and physiologic effects of exposure to chronic low-level biomechani- stretching carpet. We assumed that the workers were spending cal loading of the knee, a microprocessor-based liquid crystal about 75% of the work time on their knees as indicated by our thermography technique was developed in our laboratory.46 The previous study.18 The individual and combined results for the developed system, which is inexpensive and portable for field upper knee (suprapatellar) of the two workers over the course of use, uses flexible sheets embedded with liquid crystals that the work day are presented in Figure 7e.7. have both thermal and fluid properties. These sheets are factory calibrated to produce different colors for known temperature Measurements were taken on both the prepatellar and supra- ranges. The flexible liquid crystal sheets are cut to fit the surface patellar regions of the knee, but only the suprapatellar are of the suprapatellar and prepatellar regions of the knee joints. presented because this part of the knee, which makes contact For the evaluation of the temperature profile of the knee regions with the knee-kicker, produced the most dramatic results. The exposed to knee-kicker impact and kneeling tasks, the subject is highest knee temperature detected was 30.1°C. The percentage first seated in an air-conditioned room with his or her leg inside of total patch area for each temperature color was calculated by a glare-free box. Once the liquid crystal patch is placed on the outlining each color with the computer mouse and using the knee joint (either suprapatellar region or the prepatellar region), customized computer program to calculate the total area for the colors are allowed to change and finally stabilize. An indi- each color outlined. vidual thermographic sheet displays its full range of colors from brown (coldest) to blue (hottest) within a range of 3 or 4°C. The results of this case study indicate that the use of contact These color changes are continuously recorded on tape with a thermography, in conjunction with the analytical methods video camera. The video data are analyzed off-line with the help described above, may be an effective and expedient means of of a TARGA-16 based video-digitization system with custom- obtaining quantitative measures of knee temperature patterns developed software that allows calculation of liquid crystal areas in response to work involving the knee. Although the increase of equal temperature zones. The output of this software allows in the size of the “hot spots” on the knees of the two volunteer us to identify the “hot spot” regions of the knee joint of the carpet installers was steady and consistent over the course of subject. This technique has been evaluated on arthritic and the day, the exact cause of the inflammatory response cannot be rheumatic patients, and the results suggest that the technique is ascertained from an analysis of thermographic records alone. Questions to be answered are whether or not the observed inflammatory response was due to the work that was performed that day or to an existing knee inflammation that the workers may have developed over the course of their careers. Other questions that are raised include whether or not recovery to the knees would occur overnight, and whether these workers would demonstrate similar patterns of knee temperature increases while performing other knee-intensive activities such as walking, stair climbing, or crouching with a bended knee. A larger more in-depth study is needed to address these issues. Nonetheless, we conclude the following from this study: 1. Knee temperatures appear to increase consistently as cumula- tive biomechanical loading increases. 2. Contact thermography is able to detect these changes. 3. The thermographic system we developed provides a feasible means of measuring knee temperature at the work site. Some of the techniques such as those described above are tested and validated, and others may require some refinement. What remains to be done is the development and validation of a
Chapter 7e ● Workplace adaptation/recommendations 317 WORKER 1 100 Percentage of patch area Tan 90 Green 80 Blue 70 60 Pre work Mid morn Lunch Mid aft End work 50 Time of day 40 30 20 10 0 A WORKER 2 100 Percentage of patch area Brown 90 Tan 80 Green 70 Blue 60 50 Pre work Mid morn Lunch Mid aft End work 40 Time of day 30 20 10 0 B BOTH WORKERS COMBINED 100 Percentage of patch area Brown 90 Tan 80 Green 70 Blue 60 50 Pre work Mid morn Lunch Mid aft End work 40 Time of day 30 20 10 0 C Figure 7e.7 Histograms showing the distribution of thermography patch colors for each worker separately and combined results for both workers. (From Habes D, Bhattacharya A, Millliron M: Appl Ergonom 24:111-115, 1994.)
318 Chapter 7e ● Workplace-related lower extremity disorders dose-response curve in a long-term prospective study that would be possible by suggesting proper work practice procedures and be appropriate for development of a trauma/injury monitoring work rotation (rotating workers from knee-kicking activity, which program. The methods and device(s) described here set the frame- is more traumatic, to other tasks of the carpet installation job). work within which a long-term prospective study can be devel- oped in the future. It is through such prospective study that one We drafted a preliminary guideline for the development of can determine the dose-response characteristics of job-related a work practice guide.16 It is envisioned that with the avail- lower extremity cumulative trauma caused by external loading. ability of such a monitoring program, one can make significant improvement in arresting and minimizing the high morbidity The biologic system is capable of tolerating short-term low ratio found among carpet layers. Some of the information that levels of external loading with complete recovery. However, it is will be generated for carpet layers can be modified for use by possible, after a certain amount of biomechanical insult to the other professions (tile setters, floor layers, etc.), and in other knee region, that the biologic system will show early (preclinical) occupations where the kneeling posture is also common. signs of tissue damage/trauma as manifested by the inflam- matory process. Even before the inflammatory process sets in In addition to the above-mentioned significance to worker permanently, the workers may show an increasing level of dis- health associated with the proposed development of a dose- comfort of the knee joint region as the biomechanical loading response curve, tool redesign is certainly another approach that increases due to daily exposure to kneeling and knee-kicking. needs to be explored to investigate methods to further reduce In summary, it appears that the dose-response curve may have injury among carpet layers. A study conducted by Liu et al68 in several dimensions, including cross-correlation among variables which the knee-kicker pad was modeled as a viscoelastic solid, of biomechanical loading, knee joint discomfort rating, medical/ concluded that the typical pad does little to attenuate the physiologic response, and incidence of permanent knee injury. impulse of the kick stroke. That is, the pad is effective in trans- Such a dose-response curve (once established with a large popu- mitting the force produced by the worker’s knee to the carpet lation) could be made available to the worker or trade groups, being stretched but does little or nothing to cushion the blow to such as unions, to show its application regarding identifying the worker’s knee. The authors concluded that different pad their members’ state of risk by measuring certain cumulative materials need to be developed that better absorb harmful force biomechanical parameter(s) on a regular basis along with proper transmissions and distribute the forces more evenly to the knee and periodic medical evaluation. The primary objective would and for a longer time. They believed that with future research be to avoid getting close to the “irreversible trauma zone” of the such a material could be found that reduces the trauma to the proposed dose-response curve shown in Figure 7e.8. This could worker’s knee while maintaining the sharp impulse applied to the carpet. Transition zone In response to the research described above, NIOSH published Increase in severity of health hazard an Alert entitled “Preventing Knee Injuries and Disorders in Clinical/physiological outcomes* Reversible Irreversible Carpet Layers.”83 The purpose of a NIOSH Alert is to inform trauma zone trauma zone workers and employers of a health hazard, solicit the public for assistance in preventing the described health hazard, and provide Increase in cumulative biomechanical loading** recommendations for injury prevention and control based on what is known at the time. In the Alert, NIOSH recommended Hypothetical relationship the following: 1. Employers educate workers about the hazards of kneeling and * Skin temperature distribution pattern captured by thermography ** Cumulative impact loading index, kneeling time, skin pressure using a knee-kicker. 2. Workers wear protective knee pads while working on hard distribution by kneeling meter floor surfaces. Figure 7e.8 Schematic of hypothetical association between 3. Power stretchers should be used wherever possible. cumulative biomechanical loading of the knee and the early symptoms 4. Conduct research to develop carpet installation methods that of clinical/physiologic outcomes. further reduce the physical stress and trauma incurred by carpet layers. A power stretcher is a tool that looks like a typical knee-kicker but is anchored to the opposite wall by attaching a series of telescoping tubes to its end. Once the power stretcher is spanned across the width of the room, force is produced by pushing downward on a handle that uses the leverage obtained from the stationary wall. Power stretchers are effective and relieve the worker from impact forces to the knee but are not used as often as possible because they are expensive, require more setup time, often lack portability, and cannot be used in small spaces such as hallways and stairs. A new type of carpet stretcher mechanism has emerged that promises to remedy some of the inconveniences of the power stretcher while maintaining its ability to stretch carpet. Called the “stretcher adapter,” it is a short piece of tube attached to
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