["Copyright \u00a9 2005 by F. A. Davis. 13 Chapter Posture Cynthia C. Norkin, PT, EdD Introduction Vertebral Column Head Static and Dynamic Postures Frontal Plane Optimal Alignment and Analysis Postural Control Deviations from Optimal Alignment in the Frontal Plane Major Goals and Basic Elements of Control Foot and Toes Absent or Altered Inputs and Outputs Knees Muscle Synergies Vertebral Column Kinetics and Kinematics of Posture Analysis of Sitting Postures Inertial and Gravitational Forces Muscle Activity Ground Reaction Forces Muscle Activity in Sitting versus Standing Coincident Action Lines Postures Sagittal Plane Interdiskal Pressures and Compressive Loads on the Spine Seat Interface Pressures Optimal Posture Effects of Changes in Body Posture Effects of Alterations in the Position of the Chair Analysis of Standing Posture Sagittal Plane Alignment and Analysis Analysis of Lying Postures Ankle Interdiskal Pressures Knee Surface Interface Pressures Hip and Pelvis Lumbosacral and Sacroiliac Joints Effects of Age, Pregnancy, Occupation, The Vertebral Column and Recreation on Posture Head Alignment of Body Segments in the Sagittal Plane Age Deviations from Optimal Alignment in the Sagittal Plane Infants and Children Foot and Toes Elderly Knee Pelvis Pregnancy Occupation and Recreation Introduction will consider the internal and external forces acting on the body in relation to standing, sitting, and lying pos- In this chapter, the focus is on how the various body tures, and we will explore how these forces will affect structures are integrated into a system that enables the the patient in the following case. Throughout the chap- body as a whole to maintain a particular posture. We ter, we will include discussions in relation to a patient\u2019s will use our knowledge of individual joint and muscle ability to function without many of the normal postural structure and function as the basis for determining how control mechanisms and the internal lower extremity each structure contributes to the equilibrium and sta- forces necessary to maintain his body in the standing bility of the body in the optimal standing posture We posture, as well as potential problems that he might have in the sitting and lying postures 479","Copyright \u00a9 2005 by F. A. Davis. 480 \u25a0 Section 5: Integrated Function 13-1 Patient Case standing posture before he can attempt walking. Later he will progress to walking in the parallel bars and Dave Nguyen, a 19-year-old college varsity ice hockey player, was finally will be able to use crutches. Walking for any injured during a game when two members of the opposing team extended length of time or distance may not be a realis- checked him against the boards. The impact of the collision tic goal for Dave because of the high energy cost knocked all three players down onto the ice, with Dave on the bot- involved when walking with crutches with his extent of tom and the other players on top. Dave sustained fractures of two lower extremity paralysis. thoracic vertebrae (T9 and T10) and a complete spinal cord injury (SCI) which resulted in paraplegia (muscle paralysis in both lower Erect bipedal stance gives us freedom for the upper extremities). He has functioning lower abdominal and lower erec- extremities, but in comparison with the quadrupedal tor spinae muscles but no function in his hip or lower extremity posture, erect stance has certain disadvantages. Erect muscles. bipedal stance increases the work of the heart; places increased stress on the vertebral column, pelvis, and When we first meet Dave, his surgically repaired vertebral lower extremities; and reduces stability. In the quad- fractures have healed, and he is medically cleared to begin an rupedal posture, the body weight is distributed between aggressive rehabilitation program. the upper and lower extremities. In human stance, the body weight is borne exclusively by the two lower Dave\u2019s main goal at this point is to become independent as extremities. The human species\u2019 base of support (BoS), soon as possible, including being able to walk again. He admits defined by an area bounded posteriorly by the tips of that his legs probably will not regain their function, but he is deter- the heels and anteriorly by a line joining the tips of the mined to be able to get around with crutches. toes, is considerably smaller than the quadrupedal BoS (Fig. 13-1). The human\u2019s center of gravity (CoG) is the His youth, his good physical condition, and the fact that he is point where the mass of the body is centered and will used to the discipline required for participation in a varsity sport be referred to in this chapter as the center of mass should be helpful in the rehabilitation process. (CoM). The position of the CoM is not fixed and changes in different postures such as sitting and kneel- Static and Dynamic Postures ing, with movements of the extremities or trunk, and when a person is carrying something.1 When a person Posture can be either static or dynamic. In static pos- is wearing a leg cast on one leg, the CoM moves lower ture, the body and its segments are aligned and main- and towards the casted leg. In the sitting posture, the tained in certain positions. Examples of static postures CoM of the body above the seat is located near the include standing, sitting, lying, and kneeling. Dynamic armpits.2 In the young child in the standing posture, posture refers to postures in which the body or its seg- the CoM is located within the body about at the level of ments are moving\u2014walking, running, jumping, throw- the 12th vertebra. As the child becomes less \u201ctop ing, and lifting. An understanding of static posture heavy,\u201d the CoM moves lower to a location in the stand- forms the basis for understanding dynamic posture. ing adult at about the level of the second sacral seg- Therefore, the static postures of standing and sitting ment in the midsagittal plane. The adult position of the are emphasized in this chapter. The dynamic postures CoM is relatively distant from the BoS. Despite the of walking and running are discussed in Chapter 14. instability caused by a small BoS and a high CoM, main- taining stability in the static erect standing posture The study of any particular posture includes kine- tic and kinematic analyses of all body segments. Humans and other living creatures have the ability to arrange and rearrange body segments to form a large variety of postures, but the sustained maintenance of erect bipedal stance is unique to humans. The erect standing posture allows persons to use their upper extremities for the performance of large and small motor tasks. If the upper extremities need to be engaged by the use of crutches, canes, or other assistive devices to maintain the erect posture, an important human attribute is either severely compromised or lost. C a s e A p p l i c a t i o n 1 3 - 1 : Predicted Rehabilitation \u25b2 Figure 13-1 \u25a0 A comparison between the base of support in Progression quadripedal stance and bipedal stance. Note the small BoS and high CoM in the human figure, in comparison with the dog\u2019s relatively Initially our patient, Dave, will be able to attain a stand- large BoS and low CoM. ing posture on a tilt table, which will provide support for his entire body. He will progress to standing in the par- allel bars, on which he can use his upper extremities to provide support. Standing will not be as much of a problem as walking, but he will have to learn how to transfer from wheelchair to standing and to maintain the","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 481 requires only low levels of muscle activity. Passive tension the person\u2019s posture may be altered and stability com- in the joint capsules, muscles, and ligaments are able promised. Alteration or absence of inputs may occur to provide some of the forces needed to counteract for a number of reasons, including, among others, the gravity. absence of the normal gravitational force in weightless conditions during space flight or decreased sensation Postural Control in the lower extremities. Although only a relatively small amount of muscular Example 13-1 activity is required to maintain a stable erect standing posture, the control of posture is complex and is a part Astronauts aboard the U.S. Space Shuttle Discovery in of the body\u2019s motor control system. The main focus of June 1985 assumed a position in space in which the this text is not on the motor control aspects of human neck, hip, and knee were flexed significantly more function; however, a discussion of some features of pos- than they were in preflight. They maintained the same tural control is necessary for an understanding of pos- flexed posture initially when they returned to earth.6 tural stability in standing. Another group of astronauts exhibited changes in mul- tijoint coordination that was attributed to a reweighting Postural control, which can be either static or of inputs to the vestibular system in the gravity- dynamic, refers to a person\u2019s ability to maintain stability eliminated condition.7 The postural changes that have of the body and body segments in response to forces that been observed in astronauts upon their return to earth threaten to disturb the body\u2019s equilibrium. According are thought to be due to alterations in tactile, articular, to Horak and associates,3 the ability to maintain stabil- vestibular, and proprioceptive inputs used in postural ity in the erect standing posture is a skill that the cen- control.6,7 tral nervous system (CNS) learns, using information from passive biomechanical elements, sensory systems, A more common example of altered inputs occurs and muscles. The CNS interprets and organizes inputs when a person attempts to attain and maintain an erect from the various structures and systems and selects standing posture when a foot has \u201cfallen asleep.\u201d responses on the basis of past experience and the goal Attempts at standing may result in a fall because input of the response. Reactive3 (compensatory4) responses regarding the position of the foot and ankle, as well as occur as reactions to external forces that displace the information from contact of the \u201casleep\u201d foot with the body\u2019s CoM. Proactive3 (anticipatory4) responses occur supporting surface, is missing. in anticipation of internally generated destabilizing forces such as raising arms to catch a ball or bending Another instance in which inputs may be disturbed forward to tie shoes. is after injury. A disturbance in the kinesthetic sense about the ankle and foot after ankle sprains has been Major Goals and Basic implicated as a cause of poor balance or loss of stabil- Elements of Control ity.8 Forkin and colleagues,9 in a study of gymnasts 1 to 12 months after an ankle sprain, found that these indi- The major goals of postural control in the standing viduals were less able to detect passive ROM in the pre- position are to control the body\u2019s orientation in space, viously injured ankle than they were in the uninjured maintain the body\u2019s CoM over the BoS, and stabilize ankle. The gymnasts in the study also reported that they the head with regard to the vertical so that the eye gaze believed that they were less stable in the standing pos- is appropriately oriented. According to DiFabio and ture than before their injury. Sometimes ankle sprains Emasithi,5 stabilizing the head with regard to the vertical are followed by chronic functional instability.10 is the primary goal of postural regulation. Maintenance and control of posture depend on the integrity of the In addition to altered inputs, a person\u2019s ability to CNS, visual system, vestibular system, and musculo- maintain the erect posture may be affected by altered skeletal system. In addition, postural control depends outputs such as the inability of the muscles to respond on information received from receptors located in and appropriately to signals from the CNS. In sedentary around the joints (in joint capsules, tendons, and liga- elderly persons, muscles that have atrophied through ments), as well as on the soles of the feet. The CNS disuse may not be able to respond with either the must be able to detect and predict instability and must appropriate amount of force to counteract an opposing be able to respond to all of this input with appropriate force or with the necessary speed to maintain stability. output to maintain the equilibrium of the body. In persons with neuromuscular disorders, both agonists Furthermore, the joints in the musculoskeletal system and antagonists may respond at the same time, thus must have a range of motion (ROM) that is adequate reducing the effectiveness of the response. for responding to specific tasks, and the muscles must be able to respond with appropriate speeds and forces. C a s e A p p l i c a t i o n 1 3 - 2 : Missing Inputs and Outputs \u25a0 Absent or Altered Inputs and Outputs Dave is missing some of the inputs and outputs neces- sary for normal postural control. He is not able to When inputs are altered or absent, the control system must respond to incomplete or distorted data, and thus","Copyright \u00a9 2005 by F. A. Davis. 482 \u25a0 Section 5: Integrated Function naturally occuring perturbations is to produce mechan- ical perturbations experimentally by placing subjects receive input for standing postural control either from on a movable platform. The platform can be moved receptors located around his ankle, knee, and hip joints forward, backward, or from side to side. Some platforms or from the soles of his feet. He is unable to provide can be tipped, and the velocity of platform motion can output in response to signals from the CNS because his be varied. The postural responses to perturbations lower extremity muscles are paralyzed. Consequently, we caused by either platform movement or by pushes and must look at other aspects of postural control because pulls are reactive or compensatory responses in that Dave will have to rely on other mechanisms to monitor they are involuntary reactions. These postural respon- and maintain a standing posture. His vestibular and ses are referred to in the literature as either synergies3 visual systems are intact and able to provide input. or strategies.4 Therefore, in this text, the terms will be Proprioceptive input from his trunk and upper extremi- used interchangeably. The synergies are task specific ties is also intact, and they are able to provide input and and appear to vary with a number of factors, including output. the amount and direction of motion of the supporting surface; width and compliance of the supporting sur- \u25a0 Muscle Synergies face and the location, magnitude, and velocity of the perturbing force; and initial posture of the individual at Although static posture is emphasized in this chapter, the time of the perturbation. the term static can be misleading, especially with regard to standing posture, because the maintenance of stand- Fixed-Support Synergies ing posture is the result of dynamic control mecha- nisms. Postural control researchers have suggested that Horak and associates3 described synergies as centrally for any particular task such as standing on a moving organized patterns of muscle activity that occur in re- bus, standing on a ladder, or standing on one leg, many sponse to perturbations of standing postures. Fixed- different combinations of muscles may be activated to support synergies are patterns of muscle activity in which complete the task. A normally functioning CNS selects the BoS remains fixed during the perturbation and the appropriate combination of muscles to complete recovery of equilibrium. Stability is regained through the task on the basis of an analysis of sensory inputs. movements of parts of the body, but the feet remain Dietz11 suggested that afferent input from Golgi tendon fixed on the BoS. Two examples of fixed-support syner- organs in the leg extensors signals changes in the pro- gies are the ankle synergy and the hip synergy. jection of the body\u2019s CoM with regard to the feet. Variations in an individual\u2019s past experience and cus- The ankle synergy consists of discrete bursts of mus- tomary patterns of muscle activity will also affect the cle activity on either the anterior or posterior aspects of response. Allum and coworkers12 suggested that propri- the body that occur in a distal-to-proximal pattern in oceptive input from the hip or trunk may be more response to forward and backward movements of the important than input from the legs in signaling and ini- support platform, respectively. Forward motion of the tiating responses. According to these authors, muscle platform results in a relative displacement of the line activation is based primarily on input from the hip and of gravity (LoG) posteriorly and would be similar to trunk proprioceptors. A second level of input includes starting to fall backward in a free-standing posture (Fig. cues from the vestibular system and proprioceptive 13-2A). The group of muscles that responds to the per- input from all body segments. turbation is activated in an attempt to restore the LoG to a position within the BoS. Bursts of muscle activity Monitoring of muscle activity patterns through occur in the ankle dorsiflexors, hip flexors, abdominal electromyography (EMG) and determinations of mus- muscles, and possibly the neck flexors. The tibialis ante- cle peak torque and power outputs are some of the rior muscle contributes to the restoration of stability by methods used to study postural responses during per- pulling the tibia anteriorly, and hence the body for- turbations of upright postural stability. A perturbation ward, so that the LoG remains or centers within the BoS is any sudden change in conditions that displaces the (see Fig. 13-2B). Backward motion of the platform body posture away from equilibrium.3 The perturba- results in a relative displacement of the LoG anteriorly tion can be sensory or mechanical. A sensory perturba- and is similar to starting to fall forward in a free- tion might be caused by altering of visual input, such as standing posture. The muscles responds in an attempt might occur when a person\u2019s eyes are covered unex- to restore the LoG to a position within the BoS (Fig. pectedly. Mechanical perturbations are displacements 13-3A). Bursts of activity in the plantarflexors, hip that involve direct changes in the relationship of CoM extensors, trunk extensors, and neck extensors are used to the BoS. These displacements may be caused by to restore the LoG over the BoS (see Fig. 13-3B). movements of either body segments or the entir body.12 Even breathing can displace the CoM. Perturbations in The hip synergy consists of discrete bursts of mus- standing that result from respiratory movements of the cle activity on the side of the body opposite to the ankle rib cage are counterbalanced by movements of the pattern in a proximal-to-distal pattern of activation.14 trunk and lower limbs. As detemined by EMG, muscle Maki and McIlroy4 suggested that the fixed-support hip activity in the trunk and hip muscles provides a coun- synergy may be used primarily in situations in which terbalance to motions of the rib cage.13 change-in-support strategies (stepping or grasping syn- ergies) are not available. One method of studying how people respond to","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 483 CoM CoM LoG LoG \u1b63 Figure 13-2 \u25a0 Perturbation of erect stance equilib- rium caused by forward horizontal platform movement. A. Anterior (forward) movement of the platform causes poste- rior (backward) movement of the body and, as a conse- quence, displacement of the body\u2019s CoM posterior to the base of support. B. Use of the ankle strategy (activation of the flexors at the ankle, hip, trunk, and possibly neck) is necessary to bring the body\u2019s CoM back over the base of sup- port and reestablish stability. CONCEPT CORNERSTONE 13-1: Summary of Fixed moves or enlarges the body\u2019s BoS so that it remains Support Strategies under the body\u2019s CoM (Fig. 13-4).15,16 Previously, it was thought that the stepping synergy was used only as a last Ankle Strategies resort, being initiated when ankle and hip strategies Perturbations were insufficient to bring and maintain the CoM over the BoS.15,17 However, Maki and McIlroy suggested that Forward translation of Backward translation of change-in-support strategies are common responses to support surface support surface*(forward perturbations among both the young and the old.4 (backward motion motion of the body) Furthermore, these authors observed that change-in- of the body) support synergies are the only synergies that are suc- cessful in maintaining stability in the instance of a large Muscles Distal to Proximal Response perturbation.4 Comparisons of the stepping strategies used by the young and the old show that the younger Tibialis anterior Gastrocnemius subjects have a tendency to take only one step, whereas the elderly subjects have a tendency to take multiple Quadriceps femoris Hamstrings steps that are shorter and of less height than those of their younger counterparts.4,18 However, no differences Abdominals (neck Paraspinals (neck are apparent in the speed at which the young and the flexors)5 extensors)5 elderly initiate the change-in-support stepping strategy. Luchies and associates19 found that older subjects lifted Hip Strategies their feet just as quickly as did the younger subjects. Perturbations However, Wojcik and associates found distinct age and gender differences in the magnitudes of joint torques Forward translation of Backward translation of sup- in the stepping extremity that were used to regain bal- support surface port surface* (forward ance.20 Van Wegen and colleagues determined that in (backward motion motion of the body) quiet standing, the older person\u2019s center of pressure of the body) (CoP) is located closer to edge of the BoS than in younger subjects.21 Therefore, the older individuals Muscles Proximal to Distal Response may have less time to react to a perturbation before exceeding stability limits. Abdominals Paraspinals Quadriceps femoris Hamstrings Dave cannot respond to a perturbation by moving Tibialis anterior Gastrocnemius his lower extremities; therefore, not only does he need to develop alternative strategies for dealing with per- *Increasing the velocity of backward platform translations may lead turbations but also he needs to try to avoid sudden per- to a mixed ankle-and-hip strategy.14 turbations of his standing posture. Change-in-Support Strategies Head-Stabilizing Strategies The change-in-support strategies include stepping (for- Two head-stabilizing strategies have been described by ward, backward, or sidewise) and grasping (using one\u2019s DiFabio and Emasithi.5 These proactive strategies differ hands to grab a bar or other fixed support) in response to shifts in the BoS. Stepping and grasping differ from fixed-support synergies because stepping\/grasping","Copyright \u00a9 2005 by F. A. Davis. 484 \u25a0 Section 5: Integrated Function CoM \u1b63 Figure 13-3 \u25a0 Perturbation LoG of erect stance equilibrium caused by backward horizontal platform move- ment. A. Posterior movement of the platform causes anterior movement of the body and, as a consequence, dis- placement of the body\u2019s CoM anterior to the base of support. B. Use of the ankle strategy (activation of the exten- sors at the ankle, hip, back, and possi- bly neck) is necessary to bring the body\u2019s CoM over the base of support and reestablish stability. from the previously described reactive strategies Continuing Exploration: Recent Evidence on the because head-stabilizing strategies occur in anticipation Nature of Postural Control of the initiation of internally generated forces caused by changes in position from sitting to standing. The Although in the past muscle synergies have been con- head-stabilizing strategies are used to maintain the sidered fairly automatic responses to perturbations, head during dynamic tasks such as walking, in contrast some evidence suggests that postural control, instead to ankle and hip strategies, which are used to maintain of requiring only a minimal amount of attention, the body in a static situation. The authors described the appears to require a significant amount of atten- following two strategies for maintaining the vertical sta- tion,22\u201324 especially the sensory integration aspects.25 bility of the head: head stabilization in space (HSS) and The amount of attention required varies according to head stabilization on trunk (HST).5 The HSS strategy is the complexity of the postural task (such as bending a modification of head position in anticipation of dis- the trunk backward while standing with the feet close placements of the body\u2019s CoG. The anticipatory adjust- together), the age of the individual, balance abilities, ments to head position are independent of trunk and the type of secondary task (such as a math prob- motion. The HST strategy is one in which the head and lem) being performed.23,24,26 Postural challenges trunk move as a single unit. appear to influence reaction time for task perform- ances in both young and old, but under some condi- tions, older individuals also demonstrate an increase in postural sway.23,25 Kinetics and Kinematics of Posture CoM The muscle strategies described in response to pertur- LoG bations are examples of the active internal forces em- ployed to counteract the external forces that affect the \u25b2 Figure 13-4 \u25a0 Perturbation of erect stance equilibrium equilibrium and stability of the body in the erect stand- caused by backward platform movement. The person in this illustra- ing posture. The following section examines the effects tion is using a stepping strategy to keep from falling forward in of both external and internal forces on the body in the response to backward movement of the platform. Stepping forward standing posture. The external forces that will be con- brings the body\u2019s CoM over a new base of support. sidered are inertia, gravity, and ground reaction forces (GRFs). The internal forces are produced by muscle activity and passive tension in ligaments, tendons, joint capsules, and other soft tissue structures. The sum of all of the external and internal forces and torques acting on the body and its segments must be equal to zero for the body to be in equilibrium. Stability is maintained by keeping the body\u2019s CoM over the BoS and the head in a position that permits gaze to be appropriately oriented.","Copyright \u00a9 2005 by F. A. Davis. Inertial and Gravitational Forces Chapter 13: Posture \u25a0 485 In the erect standing posture, little or no accleration of CoP[1] the body occurs, except that the body undergoes a con- stant swaying motion called postural sway or sway enve- CoP[1] lope.16 The extent of the sway envelope for a normal individual standing with about 4 inches between the feet can be as large as 12\u040a in the sagittal plane and 16\u040a in the frontal plane.16 The inertial forces that may result from this swaying motion usually are not consid- ered in the analysis of forces for static postures.27 However, in a postural study using laser technology, Aramaki and colleagues investigated angular displace- ments, angular velocity and acceleration around the hip and ankle joints.28 Naturally, inertial forces must be considered in postural analysis of all dynamic postures such as walking, running, and jogging in which the forces needed to produce acceleration or a change in the direction of motion are important for understand- ing the demands on the body.29 Ground Reaction Forces Whenever the body contacts the ground, the ground \u25b2 Figure 13-5 \u25a0 Path of the center of pressure (CoP) in erect pushes back on the body. This force is known as the GRF, stance. A. A CoP tracing plotted for a person standing on a force and the vector representing it is known as the ground plate. The rectangle represents the outline of the force plate. The reaction force vector (GRFV). The GRF is a composite tracing shows a normal rhythmic anterior-posterior \u201csway envelope\u201d (or resultant) force that represents the magnitude and during approximately 30 seconds of stance. B. A CoP tracing showing direction of loading applied to one or both feet. The relatively uncontrolled postural sway. (CoP tracings courtesy of GRF is typically described as having three components: Leonard Elbaum, Director of Research at the Physical Therapy a vertical component force (along the y-axis), and two Laboratory, Florida International University, Miami, Florida. Data force components directed horizontally. One of the two were collected with an Advanced Material Technology, Inc. (AMTI), horizontal forces is in a medial-lateral direction (along Force Platform, Newton, Massachusetts. Analysis and display software the x-axis) , whereas the other horizontal force is in an were provided by Ariel Life Systems, Inc., La Jolla, California.) anterior-posterior direction (along the z-axis) on the ground. The composite or resultant GRFV is equal in ing static stance, we would expect the force of gravity-on- magnitude but opposite in direction to the gravitational person (represented by the LoG) to be equal in magni- force in the erect static standing posture. The GRFV tude and opposite in direction to the GRF represented indicates the magnitude and direction of loading ap- by the GRFV. In many dynamic postures, the intersec- plied to the foot. The point of application of the GRFV tion of the LoG with the supporting surface may not is at the body\u2019s CoP, which is located in the foot in uni- coincide with the point of application of the GRFV. The lateral stance and between the feet in bilateral standing horizontal distance from the point on the supporting postures. If a person were doing a handstand, the CoP surface where the LoG intersects the ground and the would be located between the hands. The CoP, like the CoP (where the GRFV acts) indicates the magnitude of CoG, is the theoretical point where the force is consid- the external moment that must be opposed to maintain ered to act, although the body surface that is in contact a posture and keep the person from falling. with the ground may have forces acting over a large portion of its surface area. The path of the CoP that The technology required to obtain GRFs, the CoP, defines the extent of the sway envelope can be deter- and muscle activity may not be available to the average mined by plotting the CoP at regular intervals when a evaluator of human function. Therefore, in the follow- person is standing on a force plate system (Fig. 13-5). ing sections, a simplified method of analyzing posture Much of the research on postural control uses the pat- will be presented with the use of diagrams and with tern of displacements of the CoP to evaluate the effects the combined action of the LoG and the GRFV as a ref- of attentional demands and perturbations on standing erence. posture. Coincident Action Lines The GRFV and the LoG have coincident action lines in the static erect posture. The LoG represents the In an ideal erect posture, body segments are aligned force of gravity-on-person and is generally equal in so that the torques and stresses on body segments are magnitude to and in the same direction as the force of person-on-ground. The GRF is a more common name for the force of ground-on-person. In equilibrium dur-","Copyright \u00a9 2005 by F. A. Davis. 486 \u25a0 Section 5: Integrated Function Sagittal Plane minimized and standing can be maintained with a min- The effect of external forces on body segments in the imal amount of energy expenditure. The coincident sagittal plane during standing is determined by the action lines formed by the GRFV and the LoG serve as location of the LoG in relation to the axis of motion of a reference for the analysis of the effects of these forces body segments. When the LoG passes directly through on body segments (Fig. 13-6). When the LoG and the a joint axis, no external gravitational torque is created GRFV coincide, as they do in static posture, it is possi- around that joint. However, if the LoG passes at a dis- ble to assess the effects at each joint by using one or the tance from the axis, an external gravitational moment other. However, the reader should be aware that the is created. This moment will cause rotation of the super- horizontal forces are not being considered separately. imposed body segments around that joint axis unless it We will use the LoG in the remainder of this chapter. is opposed by a counterbalancing internal moment (an The location of the LoG shifts continually (as does the isometric muscle contraction). The magnitude of the CoP) because of the postural sway. As a result of the gravitational moment of force increases as the distance continuous motion of the LoG, the moments acting between the LoG and the joint axis increases. The around the joints are continually changing. Receptors direction of the external gravitational moment of force in and around the joints of lower body segments and on depends on the location of the LoG in relation to a par- the soles of the feet detect these changes and relay this ticular joint axis. If the LoG is located anterior to a par- information to the CNS. ticular joint axis, the gravitational moment will tend to cause anterior motion of the proximal segment of the C a s e A p p l i c a t i o n 1 3 - 3 : Information from Knee body supported by that joint. If the LoG is posterior to and Ankle Receptors the joint axis, the moment will tend to cause motion of the proximal segment in a posterior direction . In a pos- Dave will not be able to access information from recep- tural analysis, external gravitational torques producing tors in his knee and ankle, even though the receptors sagittal plane motion of the proximal joint segment are around these joints are able to transmit the information referred to as either flexion or extension moments. to the lower spinal cord below the injury. The informa- tion cannot go up the spinal cord beyond the level of Example 13-2 the injury because of the disruption in the cord at the T10 vertebral level. Under normal conditions, the CNS If the LoG passes anterior to the ankle joint axis, the would analyze the inputs and make an appropriate out- external gravitational moment will tend to rotate the put response to maintain postural stability. tibia (proximal segment) in an anterior direction (Fig. 13-7). Anterior motion of the tibia on the fixed foot will result in dorsiflexion of the ankle. Therefore, the \u25b2 Figure 13-6 \u25a0 Location of the combined action line formed \u25b2 Figure 13-7 \u25a0 The anterior location of the LoG in relation by the ground reaction force vector (GRFV) and the line of gravity to the ankle joint axis creates an external dorsiflexion moment. The (LoG) in the optimal standing posture. arrow indicates the direction of the dorsiflexion moment. The dotted line indicates the direction in which the tibia would move if the dor- siflexion moment were unopposed.","Copyright \u00a9 2005 by F. A. Davis. moment of force is called a dorsiflexion moment. An Chapter 13: Posture \u25a0 487 internal plantarflexion moment of equal magnitude will be necessary to oppose the external dorsiflexion Optimal Posture moment and establish equilibrium. Because the force of gravity is constantly acting on the Example 13-3 body, an ideal standing posture would be one in which the body segments were aligned vertically and the LoG If the LoG passes anterior to the axis of rotation of the passed through all joint axes. Normal body structure knee joint, the gravitational moment will tend to rotate makes such an ideal posture impossible to achieve, but the femur (proximal segment) in an anterior direction it is possible to attain a posture that is close to the ideal. (Fig. 13-8). An anterior movement of the femur will In an optimal standing posture, the LoG is close to, but cause extension of the knee. Therefore, the moment of not through, most joint axes. Therefore, the external force is called an extension moment. An internal flex- gravitational moments are relatively small and can be ion moment of equal magnitude will be necessary to balanced by internal moments generated by passive balance the external extension moment. capsular and ligamentous tension, passive muscle ten- sion (stiffness), and a small but continuous amount of C a s e A p p l i c a t i o n 1 3 - 4 : Tilt Table Standing muscle activity. After his injury, Dave\u2019s first exposure to the standing Slight deviations from the optimal posture are to posture will be on a tilt table. Standing in the tilt be expected in a normal population because of the table will provide compression on Dave\u2019s bones and many individual variations found in body structure. joints and will get him used to the upright position. However, deviations from an optimal standing posture Wide straps across his legs and trunk will hold Dave that are large enough to cause excessive strain in pas- to the table and provide the necessary counterbalanc- sive structures and to require high levels of muscle ing forces to oppose the external gravitational activity need to be identified, and remedial action must moments. be taken. If faulty postures are habitual and assumed continually on a daily basis, the body will not recognize these faulty postures as abnormal, and over time, struc- tural adaptations such as ligamentous and muscle short- ening or lengthening will occur. Analysis of Standing Posture Observational analysis of posture in the sagittal plane involves locating body segments in relation to the LoG. A plumb line, or line with a weight on one end, dropped from the ceiling and passing through the external auditory meatus of the ear may be used to rep- resent the LoG. Evaluators of posture should be able to determine whether a body segment or joint deviates widely from the normal optimal postural alignment by using their observational skills. A skilled observational analysis can yield basic information about an individ- ual\u2019s posture that can be used either for developing a treatment regimen for the correction of poor posture or to decide whether a more sophisticated analysis such as radiography is warranted. \u25b2 Figure 13-8 \u25a0 The anterior location of the LoG in relation CONCEPT CORNERSTONE 13-2: Effects of Anterior to the knee joint axis creates an external extension moment. The and Posterior Gravitational Moments on arrow indicates the direction of the extension moment. The dotted Body Segments line indicates the direction in which the femur would move if the extension moment were unopposed. If the LoG passes anterior to the head, vertebral column, or joints of the lower extremities, the gravitational moment will tend to force the segment of the body superior to the joint in an anterior direc- tion. Conversely, when the LoG passes posterior to the joints the body, the gravitational moment will tend to force the body seg- ment that is superior to the joint in a posterior direction.","Copyright \u00a9 2005 by F. A. Davis. 488 \u25a0 Section 5: Integrated Function ing are the tibialis anterior, peroneal, and tibialis pos- terior muscles.34 It is possible that these muscles may be Sagittal Plane Alignment and Analysis helping to provide transverse stability in the foot during postural sway rather than acting to oppose the external \u25a0 Ankle dorsiflexion at the ankle joint. In the optimal erect posture, the ankle joint is in the neutral position, or midway between dorsiflexion and \u25a0 Knee plantarflexion. The LoG passes slightly anterior to the lateral malleolus and, therefore, anterior to the ankle In optimal posture, the knee joint is in full extension, joint axis.30,31 The anterior position of the LoG in rela- and the LoG passes anterior to the midline of the knee tion to the ankle joint axis creates an external dorsi- and posterior to the patella. This places the LoG just flexion moment that must be opposed by an internal anterior to the knee joint axis (see Figs. 13-8 and 13-9). plantarflexion moment to prevent forward motion of The anterior location of the gravitational line in rela- the tibia. In the neutral ankle position, there are no tion to the knee joint axis creates an external extension ligamentous checks capable of counterbalancing the moment.35 The counterbalancing internal flexion external dorsiflexion moment; therefore, activation of moment created by passive tension in the posterior the plantarflexors creates the internal plantarflexion joint capsule and associated ligaments is usually suffi- moment that is necessary to prevent forward motion of cient to balance the gravitational moment and prevent the tibia. The soleus muscle contracts and exerts a knee hyperextension. However, a small amount of activ- posterior pull on the tibia and in this way is able to ity has been identified in the hamstrings. Activity of the oppose the dorsiflexion moment (Fig. 13-9). If the soleus muscle may augment the gravitational extension force that the muscle can exert is less than the gravita- moment at the knee through its posterior pull on the tional moment, the tibia will move the ankle into dorsi- tibia as it acts at the ankle joint. In contrast, activity of flexion and the soleus muscle will undergo an eccentric the gastrocnemius muscle may tend to oppose the grav- contraction while trying to oppose the forward motion itational extension moment because the muscle crosses of the tibia. the knee posterior to the knee joint axis. EMG studies have demonstrated that soleus32,33 and C a s e A p p l i c a t i o n 1 3 - 5 : How to Oppose External gastrocnemius33 activity is fairly continuous in normal Gravitational Moments in Standing Posture subjects during erect standing. This activity suggests without Muscle Activity that these muscles are exerting a minimal but constant internally generated plantarflexion torque about the When Dave progresses from standing on the tilt table to ankles to oppose the normal external gravitational dor- standing in the parallel bars, he will need some means siflexion moment. Ankle joint muscles that have shown of opposing the external gravitational moments affecting inconsistent activity in EMG recordings during stand- his lower extremities. He has no musculature capable of resisting the external dorsiflexion moment at the ankle \u25b2 Figure 13-9 \u25a0 The external extension moment acting and no tilt table straps to help him maintain the stand- around the knee joint is balanced by an internal opposing moment ing posture. Therefore, one or more forces will have to created by passive tension in the posterior joint capsule. The external be found to substitute for the internal plantarflexor dorsiflexion moment at the ankle is counterbalanced by an internal moment that would have been applied by activity in his moment created by activity of the soleus muscle. plantarflexors. Orthoses (braces) at his ankles and the push of the parallel bars or crutches on his head and trunk (HAT) will be able to provide the necessary oppos- ing forces. All orthoses apply forces to the body that can be used to either resist motion or to protect a body part.36 Orthoses are based on a three-point pressure system with one force acting in one direction and two forces directed in the opposite direction. The type of orthoses that Dave will use are knee-ankle-foot orthoses (KAFOs), which are deemed sufficient for low thoracic lesions (T9 to T12).37 These orthoses have standard double metal uprights, posterior thigh bands, plates under the sole of the foot, and anterior knee flexion pads (Fig. 13-10). Locking joints are positioned at the knee and ankle; they are locked when the person is standing but can be unlocked to allow for sitting. There are locks at the ankle and knee to keep the knee and ankle stabilized during standing and to allow knee flexion when sitting. When Dave is standing, the knee pads on his KAFOs will provide posteriorly directed external forces to oppose the gravitational dorsiflexion moments. The pads and locks at the knee will maintain the knees in","Copyright \u00a9 2005 by F. A. Davis. Thigh band Chapter 13: Posture \u25a0 489 Tibial band (ASISs) are vertical, and the lines connecting the ASISs and posterior-superior iliac spines (PSISs) are horizon- Sole plate tal.38 In this optimal position, the LoG passes slightly \u25b2 Figure 13-10 \u25a0 Features of the KAFO. The KAFO\u2019s sole posterior to the axis of the hip joint, through the plate attachment at the foot and posterior thigh band provide anteri- greater trochanter.30,31,35,39 However, during postural orly directed forces, and the tibial pad below the knee provides a pos- sway, the LoG may pass anterior to the hip joint axis, teriorly directed force. and contraction of the hip exterior may be required. The posterior location of the gravitational line in rela- extension in the event that the LoG passes behind the tion to the hip joint axis creates an external extension knee joint axis. The metal uprights will help to support moment at the hip that tends to rotate the pelvis (prox- the weight of the body. Anteriorly directed external imal segment) posteriorly on the femoral heads40 (see forces coming from the posterior calf pads and sole Fig. 13-11B). EMG studies have shown activity of the plates under the shoe will help ensure that his knees do iliopsoas muscle during standing,41 and it is possible not go into excessive hyperextension. that the iliopsoas is acting to create an internal flexion moment at the hip to prevent hip hyperextension. If \u25a0 Hip and Pelvis the gravitational extension moment at the hip were In optimal posture, according to Kendall and allowed to act without muscular balance, as in a so- McCreary,38 the hip is in a neutral position and the called relaxed or swayback posture,38 hip hyperexten- pelvis is level with no anterior or posterior tilt (Fig. 13- sion ultimately would be checked by passive tension in 11A). In a level pelvis position, lines connecting the the iliofemoral, pubofemoral, and ischiofemoral liga- symphysis pubis and the anterior-superior iliac spines ments. In the swayback standing posture, the LoG drops farther behind the hip joint axes than in the opti- mal posture (Fig. 13-12). Therefore, the swayback pos- ture does not require any muscle activity at the hip but causes an increase in the tension stresses on the ante- rior hip ligaments, which could lead to adaptive length- ening of these ligaments if the posture becomes habitual. Also, because of the diminished demand for hip extensor activity, the gluteal muscles may be weak- ened by disuse atrophy if the swayback posture is habit- ually adopted.42 The relaxed standing or sway posture may also increase the magnitude of the gravitational torque at other joints in the body. C a s e A p p l i c a t i o n 1 3 - 6 : Swayback Posture 38, 42 Although a swayback posture is considered to be a poor posture because of its stress on anterior hip ligaments, Dave has to adopt a swayback standing posture in order to ensure that the LoG remains well behind his hip joints and in front of his knee and ankle joints. In this posture, he does not need to have any hip extensors or any brac- LoG \u1b63 Figure 13-11 \u25a0 The location of the LoG in relation to the axis of the hip joint. A. The LoG passes through the greater trochanter and posterior to the axis of the hip joint. B. The posterior location of the LoG creates an external extension moment at the hip, which tends to rotate the pelvis posteriorly on the femoral heads. The arrows indicate the direction of the gravita- tional moment.","Copyright \u00a9 2005 by F. A. Davis. 490 \u25a0 Section 5: Integrated Function angle and results in an increase in the shearing stress at the lumbosacral joint and may result in an increase in Line of the anterior lumbar convexity in standing (Fig. 13-13A). gravity Continuing Exploration: Controversy regarding Hip joint Relationship between Sacral Inclination and axis Lumbar Lordosis \u25b2 Figure 13-12 \u25a0 In the swayback posture, the LoG passes well However, the nature of the relationship between posterior to the hip joint axis, which eliminates the need for activity sacral inclination and lumbar lordosis remains con- of the hip extensor muscles. The pelvis is posteriorly rotated, and the troversial. Youdas and associates,45 in a study of 90 hips are hyperextended. male and female subjects, found only a weak associa- tion between lumbar lordosis and sacral inclination. ing at the hip to keep his hip in extension. The KAFOs On the other hand, Korovessis and coworkers,46,47 allow him to balance his weight over his feet with his using x-ray evaluations of erect posture, found that hips hyperextended (see Fig. 13-12). the sacral inclination correlated strongly with both \u25a0 Lumbosacral and Sacroiliac Joints thoracic kyphosis and lumbar lordosis.46 The average lumbosacral angle measured between the bottom of the L5 vertebra and the top of the sacrum In the optimal posture, the LoG passes through the (S1) is about 30\u040a but can vary between 6\u040a and 30\u040a.43,44 body of the fifth lumbar vertebra and close to the axis Anterior tilting of the sacrum increases the lumbosacral of rotation of the lumbosacral joint. Gravity therefore creates a very slight extension moment at L5 to S1 that tends to slide L5 and the entire lumbar spine down and forward on S1. This motion is is opposed primarily by the anterior longitudinal ligament and the iliolumbar ligaments. Bony resistance is provided by the locking of the lumbosacral zygapophyseal joints. When the sacrum is in the optimal position, the LoG passes slightly ante- rior to the sacroiliac joints. The external gravitational moment that is created at the sacroiliac joints tends to cause the anterior superior portion of the sacrum to rotate anteriorly and inferiorly, whereas the posterior inferior portion tends to move posteriorly and superiorly (see Fig. 13-13B). Passive tension in the sacrospinous and sacrotuberous ligaments provides the internal moment that counterbalances the gravitational torque by pre- venting upward tilting of the lower end of the sacrum.43 \u25a0 The Vertebral Column There is considerable variation among individuals, as can be seen in Table 13-1, but the average values are fairly close to one another in the studies presented. In the optimal configuration, the curves of the vertebral column should be fairly close to average or normal con- \u1b63 Figure 13-13 \u25a0 A. The average lumbosacral angle in optimal erect posture is about 30\u040a. B. The grav- itational moment tends to rotate the superior portion of the sacrum anteriorly and inferiorly. Consequently, the inferior portion tends to thrust posteriorly and superi- orly. Passive tension in the sacrotuberous ligament pre- vents the upward motion of the inferior sacral segment.","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 491 Table 13-1 Variations in Spinal Curves in the Sagittal Plane in Standing Posture: Mean Values in Degrees Hardacker Lord et al49 Jackson and Jackson et Jackson and Gelb et al 53 et al48 McManus50* al 51\u2020 Hales52\u2021 40\u201370 yrs 21\u201383 yrs 20\u201370 yrs n=109 20\u201365 yrs 26\u201375 yrs 20\u201363 yrs n=100 n=100 Mean (SD) n=100 n=20 n=75 Mean (SD) Mean (SD) Mean (SEM) Mean (SD) Mean (SD) \u03ea64 (10) Cervical \u03ea40 (10) \u03ea49 (15) 42 (9) 43 (9) 46 (11) Thoracic 49 (11) \u03ea61 (12) \u03ea62 (13) \u03ea63 (12) Lumbar \u03ea60 (12) * Ranges: thoracic curve 22 to 68\u040a and lumbar curve \u03ea88 to \u03ea31\u040a \u2020 Ranges: thoracic curve 23 to 61\u040a and lumbar curve \u03ea81 to \u03ea38\u040a \u2021 Ranges: thoracic curve 22 to 75\u040a and lumbar curve was \u03ea90 to \u03ea35\u040a figuration described in Chapter 4. The optimal position would tend to pull the thorax and upper lumbar of the plumb line LoG is through the midline of the spine anteriorly would be present. Activity of the trunk (Fig. 13-14). erector spinae would be necessary to counteract the moment and maintain the body in equilibrium. Continuing Exploration: Controversy regarding Location of the LoG above the Fifth Lumbar According to Cailliet\u2019s frame of reference, the Vertebra LoG will pass posterior to the axes of rotation of the The location of the LoG in relation to the vertebral cervical and lumbar vertebrae, anterior to the tho- column above the fifth lumbar level is controversial. racic vertebrae, and through the body of the fifth Cailliet54 reported that the LoG transects the verte- lumbar vertebra. In this situation, the gravitational bral bodies at the level of T1 and T12 vertebrae and moments tend to increase the natural curves in the at the odontoid process of the C2 vertebra. Duval- lumbar, thoracic, and cervical regions. Moreover, Beaupere et al.,39 using x-ray examinations of the according to Cailliet,54 the maximal gravitational vertebral columns of 17 young adults, found that torque occurs at the apex of each curve at C5, T8, the LoG in these individuals was located anterior to and L3, because the apical vertebrae are farthest the anterior aspect of the T8 to T10 vertebrae. from the LoG and the moment arms are longest at According to Bogduk,43 the LoG passes anterior to these points. However, as Table 13-2 shows, there is L4 and thus anterior to the lumbar spine in many considerable individual variation in the apices for individuals. In this instance, a flexion moment that both thoracic and lumbar curves, but the means are similar among investigators. Cailliet\u2019s apices are \u25b2 Figure 13-14 \u25a0 Location of the LoG in relation to the within the ranges shown in the table. trunk. According to Kendall and McCreary,38 the LoG passes through the bodies of the lumbar and cervical vertebrae and anterior to the thoracic vertebrae in the optimal posture. In this instance, the stress on the supporting structures would be greatest in the thoracic area, where the LoG would pass at a great- est distance from the vertebrae. Stress in the lumbar and cervical regions would be comparatively less because the LoG passes close to or through the joint axes of these regions. Although not confirming either Cailliet\u2019s or Kendall and McCreary\u2019s hypotheses, EMG studies have shown that the longissimus dorsi, rotatores, and neck exten- sor muscles exhibit intermittent electrical activity dur- ing normal standing.56 This evidence suggests that ligamentous structures and passive muscle tension are unable to provide enough force to oppose all external gravitational moments acting around the joint axes of the upper vertebral column. In the lumbar region, where minimal muscle activity appears to occur, passive tension in the anterior longitudinal ligament and pas- sive tension in the trunk flexors apparently are suffi- cient to balance the external gravitational extension moment.","Copyright \u00a9 2005 by F. A. Davis. 492 \u25a0 Section 5: Integrated Function Table 13-2 Variations in Apices of Thoracic and Lumbar Curves in the Sagittal Plane in Standing Posture Author Vendantam Jackson and Gelb et al.55 McManus50 et al.53 10\u201318 yr 20\u201365 yr 40\u201370 plus yr Subjects n \u03ed 88 n \u03ed 100 n \u03ed 100 Mean Range Mean Mean Range Thoracic T6 T3\u2013T9 T7\u201378 T7 T5 disk\u2013T10 apex L4 L2\u2013L5 disk Lumbar L4 L2\u2013L5 apex \u25a0 Head \u25b2 Figure 13-15 \u25a0 The anterior location of the LoG in relation to the transverse axis for flexion and extension of the head creates an The LoG in relation to the head passes slightly anterior external flexion moment. to the transverse (frontal) axis of rotation for flexion and extension of the head and creates an external flex- reader must realize that the swaying motion that occurs ion moment (Fig. 13-15). This external flexion in the normal erect posture will change the position of moment, which tends to tilt the head forward, may be the LoG in relation to individual joint axes. The CoP counteracted by internal moments generated by ten- also will move during swaying. For example, if the sion in the ligamentum nuchae, tectorial membrane, amount of forward sway is large enough, the LoG may and posterior aspect of the zygapophyseal joint capsules move from the optimal posterior location in relation to and by activity of the capital extensors.54 Ideally, a plumb the hip joint axis to a position anterior to the hip joint line extending from the ceiling should pass through axis. The CoP will move anteriorly toward the toes. The the external auditory meatus of the ear, and the head resulting external flexion moment at the hip created by should be directly over the body\u2019s CoM at S2.54,57 the change in position of the LoG may be counteracted by activity of the hip extensors, which will move the Continuing Exploration: Configuration of the LoG and CoP posteriorly. On the other hand, increased Cervical Spine in Standing activity in the soleus muscles rather than in the hip extensors might be used to bring the entire body and In a lateral radiographic study of the spines of 100 thus the LoG back into a position posterior to the hip standing men and women between 20 and 70 years joint axis. Some independent motion may occur in of age, plumb lines extending from the odontoid each leg, and relative motion may occur between body process to C7 fell within a relatively narrow range of segments in response to postural sway.57 16.8 mm anterior to the center of C7. The greatest lordosis was at C1 to C2 (\u03ea31.9; standard deviation If your body is suddenly thrust forward, either by [SD] \u03ed 7.0), with little lordosis found in the rest of someone bumping into you or by a sudden backward the cervical spine. On average, the occiput-C1 seg- movement of the supporting surface, a large and force- ment was kyphotic, and a segmental kyphosis of 5\u040a or ful movement of the LoG will occur. Consequently, flex- greater was present in 39% of the total group, ion moments will be created at the neck and head; although no total kyphosis (occiput to C7) was pres- cervical, thoracic, and lumbar spines; hip; and ankle. ent. In this study, as cervical lordosis increased, tho- To counteract these moments, the neck, back, hip racic kyphosis increased also.48 extensor, and ankle plantarflexor muscles may have to contract. The CNS responds with activation of a muscle In a study in which they used slightly different or pattern of muscles that will counteract the inertial reference points on radiographs, Visscher et al. iden- and flexion moments, bring the LoG back over the tified the following two types of cervical spine con- CoM, and reestablish static erect equilibrium and sta- figurations in 54 men and women students standing bility. Furthermore, individual variations in the curves in a neutral position: a lordotic curvature and a pre- and apices will cause changes not only in external grav- dominately straight spine with an occasional high itational moments but also in the amount of internal lordosis and low kyphosis.58 counterforce that is necessary. \u25a0 Alignment of Body Segments in the Sagittal Plane Table 13-3 shows the relationship of the LoG to various body segments in the sagittal plane. However, the","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 493 Table 13-3 Alignment in the Sagittal Plane in Standing Posture Joints Line of Gravity External Moment Passive Opposing Forces Active Opposing Forces Atlanto-occipital Anterior Anterior-to- Flexion Ligamentum nuchae and alar liga- Rectus capitus posterior Cervical ment; the tectorial, atlantoaxial, major and minor, semi- Thoracic transverse and posterior atlanto-occipital spinalis capitus and cervi- axis for membranes cis, splenius capitis and Lumbar flexion and cervicis, and inferior and extension Extension Anterior longitudinal ligament, superior oblique muscles. Sacroiliac joint Posterior Flexion anterior anulus fibrosus fibers, Hip joint and zygapophyseal joint capsules Anterior scaleni, longus Knee joint Anterior Extension capitis and colli Ankle joint Posterior longitudinal, Posterior Nutation supraspinous, and interspinous Ligamentum flavum, longis- Extension ligaments simus thoracis, iliocostalis Anterior Extension thoracis, spinalis thoracis, Dorsiflexion Zygapophyseal joint capsules and and semispinalis thoracis Posterior posterior anulus fibrosus fibers Anterior Rectus abdominis and exter- Anterior Anterior longitudinal and iliolum- nal and internal oblique bar ligaments, anterior fibers of muscles the anulus fibrosus, and zygapophyseal joint capsules Transversus abdominis Sacrotuberous, sacrospinous, ili- Ilipsoas olumbar, and anterior sacroiliac Hamstrings, gastrocnemius ligaments Soleus, gastrocnemius Iliofemoral ligament Posterior joint capsule Deviations from Optimal Alignment amount of energy required to maintain erect standing in the Sagittal Plane posture. Postural problems may originate in any part of the body and cause increased stresses and strains in Minimizing energy expenditure and stress on support- throughout the musculoskeletal system. Postures that ing structures is one of the primary goals of any pos- represent an attempt to either improve function or nor- ture. Any change in position or malalignment of one malize appearance are called compensatory postures.59 body segment will cause changes to occur in adjacent Evaluators of posture need not only to identify the devi- segments, as well as changes in other segments, as the ation but also to determine the cause of the deviation, body seeks to adjust or compensate for the malalign- compensatory postures, and possible effects of the devi- ment (closed-chain response to keep the head over the ation on bones, joints, ligaments, and muscles support- sacrum).58 Large changes from optimal alignment ing the affected structures. increase stress or increase force per unit area on body structures. If stresses are maintained over long periods \u25a0 Foot and Toes of time, body structures may be altered. Muscles may lose sarcomeres if held in shortened positions for Claw Toes extended periods. Such adaptive shortening may accen- tuate and perpetuate the abnormal posture, as well as Claw toes is a deformity of the toes characterized by prevent full ROM from occurring. Muscles may add sar- hyperextension of the metatarsophalangeal (MTP) comeres if maintained in a lengthened position, and as joint, combined with flexion of the proximal interpha- a consequence, the muscle\u2019s length-tension relation- langeal (PIP) and distal interphalangeal (DIP) ship will be altered. Shortening of the ligaments will joints.60\u201362 The abnormal distribution of weight may limit normal ROM, whereas stretching of ligamentous result in callus formation under the heads of the structures will reduce the ligament\u2019s ability to provide metatarsals or under the end of the distal phalanx. sufficient tension to stabilize and protect the joints. Sometimes the proximal phalanx may subluxate dor- Prolonged weight-bearing stresses on the joint surfaces sally on the metatarsal head (Fig. 13-16A).60 Calluses increase cartilage deformation and may interfere with may develop on the dorsal aspects of the flexed pha- the nutrition of the cartilage. As a result, the joint sur- langes from constant rubbing on the inside of shoes. In faces may become susceptible to early degenerative essence, this deformity reduces the area of the BoS and, changes. The following sections illustrate how deviation as a result, may increase postural sway and decrease sta- from normal alignment of one or two body segments bility in the standing position. causes changes in other segments and increases the A few of the many suggested etiologies for this condition are as follows: the restrictive effect of","Copyright \u00a9 2005 by F. A. Davis. 494 \u25a0 Section 5: Integrated Function \u1b63 Figure 13-16 \u25a0 Claw toes and hammer toes. A. The drawing of claw toes shows hyperextension at the metatarsophalangeal joint and flexion of the interpha- langeal joints. B. Hammer toes are characterized by hypertension of the metatarsophalangal and distal inter- phalangeal joints and by flexion of the proximal inter- phalangeal joints. shoes, a cavus-type foot, muscular imbalance, ineffec- the amount of quadriceps force is required between 15\u040a tiveness of intrinsic foot muscles, neuromuscular disor- and 30\u040a of knee flexion. When the knee reaches 30\u040a of ders, and age-related deficiencies in the plantar flexion, the necessary quadriceps force rises to 51% of structures. a MVC.63 The increase in muscle activity needed to maintain a flexed knee posture subjects the tibiofemoral Valmassy61 suggested that the claw toe deformity is and patellofemoral joints to greater-than-normal com- actually the same condition as hammer toe because the pressive stress and can lead to fatigue of the quadriceps only difference in the conditions is that a claw toe de- femoris and other muscles if the posture is maintained formity affects all toes (second through fifth), whereas for a prolonged period. hammer toe usually affects only one or two toes. Other consequences of a flexed-knee erect standing Hammer Toes posture are related to the ankle and hip. Because knee flexion in the upright stance is accompanied by hip flex- In general, hammer toe is described as a deformity ion and ankle dorsiflexion, the location of the LoG also characterized by hyperextension of the MTP joint, flex- will be altered in relation to these joint axes. At the hip, ion of the PIP joint, and hyperextension of the DIP the LoG may pass anterior to the hip joint axes, creating joint (see Fig. 13-16B). Callosities (painless thickenings an external flexion moment. Activity of the hip exten- of the epidermis) may be found on the superior sur- sors may be necessary to create an internal extensor faces of the PIP joints over the heads of the first pha- moment to balance the external flexion moment acting langes as a result of pressure from the shoes. The tips of around the hip. Increased soleus muscle activity may be the distal phalanges also may show callosities as a result required to create an internal plantarflexion moment to of abnormal weight-bearing.61,62 The flexor muscles are counteract the increased external dorsiflexion moment stretched over the MTP joint and shortened over the at the ankle (Fig. 13-17). The additional muscle activity PIP joint. The extensor muscles are shortened over the subjects the hip and ankle joints to greater-than-normal MTP joint and stretched over the PIP joint. If the long compression stress. Overall, the increased need for and short toe extensors and lumbrical muscles are quadriceps, gastrocnemius, soleus and, perhaps, hip selectively paralyzed, the instrinsic and extrinsic toe extensor activity appears to substantially increase the flexors acting unopposed will buckle the PIP and DIP energy requirements for stance. joints and cause a hammer toe. \u25a0 Knee C a s e A p p l i c a t i o n 1 3 - 7 : Sitting from Standing Flexed Knee Posture Dave needs to make sure that that the LoG does not pass anterior to the hip joint, because his hip extensors In the flexed-knee standing posture, which can result are paralyzed and unable to counteract a flexion from knee flexion contractures, the LoG passes poste- moment at the hip. When he is going to sit down, he rior to the knee joint axes. The posterior location of the needs to make sure that he reaches back for the arm- LoG creates an external flexion moment at the knees rests on the wheelchair or other chair so that he can that must be balanced by an internal extension control the flexion moment at the hip when his trunk moment created by activity of the quadriceps muscles begins to flex in preparation for sitting. Therefore, devel- in order to maintain the erect position. The quadriceps opment of his upper extremity strength is of utmost force required to maintain equilibrium at the knee in importance in his being able to control the lowering of erect stance increases from zero with the knee his body into the chair. extended to 22% of a maximum voluntary contraction (MVC) with the knee in 15\u040a of flexion. A rapid rise in","Copyright \u00a9 2005 by F. A. Davis. Hip joint axis Flexion Chapter 13: Posture \u25a0 495 Flexion moment moment extension and puts the posterior joint capsule under Knee considerable tension stress. A continual adoption of the Ankle joint axis joint hyperextended knee posture is likely to result in adap- axis tive lengthening of the posterior capsule and of the cru- ciate ligaments and, consequently, in a more unstable Dorsiflexion joint. The anterior portion of the knee joint surfaces on moment the femoral condyles and anterior portion of the tibial plateaus will be subject to abnormal compression and \u25b2 Figure 13-17 \u25a0 Gravitational moments in a flexed-knee pos- therefore are subject to degenerative changes of the car- ture. External flexion moments are present, acting around the hip, tilaginous joint surfaces. The length-tension relation- knee, and ankle joints. The external flexion moments are opposed by ship of the anterior and posterior muscles also may be internal extension moments acting at the hip and knee and by a plan- altered, and the muscles may not be able to provide the tarflexion moment at the ankle. force necessary to provide adequate joint stability and mobility. Hyperextended Knee Posture (Genu Recurvatum) Hyperextension at the knee is usually caused either The hyperextended knee posture (Fig. 13-18) is one in by limited dorsiflexion at the ankle or by a fixed plan- which the LoG is located considerably anterior to the tarflexion position of the foot and ankle called equinus. knee joint axis. The anterior location of the LoG causes It may also be the result of habits formed in childhood an increase in the external extensor moment acting at in which the child or adolescent always elects to stand the knee, which tends to increase the extent of hyper- with hips and knees hyperextended in the relaxed or swayback standing posture. \u25b2 Figure 13-18 \u25a0 In a hyperextended knee posture, the ante- rior aspect of the knee is subjected to abnormal compressive forces, C a s e A p p l i c a t i o n 1 3 - 8 : Knee Hypertension whereas the posterior aspect is subjected to abnormal tensile forces. Note the limitation of dorsiflexion at the ankle. Although our patient, Dave, needs to stand in a swayback posture, he has some protection from knee hyperexten- sion because of the anteriorly directed counterforce pro- vided by the posteriorly placed thigh and calf pads on his KAFOs. However, we need to check for excessive knee hyperextension because Dave will not be aware of his knee joint position or be able to feel pain from his knee. \u25a0 Pelvis Excessive Anterior Pelvic Tilt In a posture in which the pelvis is excessively tilted ante- riorly, the lower lumbar vertebrae are forced anteriorly. The upper lumbar vertebrae move posteriorly to keep the head over the sacrum, thereby increasing the lum- bar anterior convexity (lordotic curve). The LoG is therefore at a greater distance from the lumbar joint axes than is optimal and the extension moment in the lumbar spine is increased. The posterior convexity of the thoracic curve increases and becomes kyphotic to balance the lordotic lumbar curve and maintain the head over the sacrum. Similarly, the anterior con- vexity of the cervical curve increases to bring the head back over the sacrum (Fig. 13-19). Table 13-4 illus- trates the changes that may result from an excessive anterior tilt. In the optimal posture in erect standing, the lum- bar disks are subject to tension anteriorly and compres- sion posteriorly. A greater diffusion of nutrients into the anterior than into the posterior portion of the disk occurs in the optimal erect posture.64 Increases in the anterior convexity of the lumbar curve during erect standing increases the compressive forces on the poste- rior annuli and may adversely affect the nutrition of the","Copyright \u00a9 2005 by F. A. Davis. 496 \u25a0 Section 5: Integrated Function posterior portion of the intervertebral disks. Also, excessive compressive forces may be applied to the zygapophyseal joints.65 Gravity \u25a0 Vertebral Column line Lordosis and Kyphosis \u25b2 Figure 13-19 \u25a0 An excessive anterior pelvic tilt results in an increase in the lumbar anterior convexity. To compensate for the The term lordosis refers to the normal sagittal plane increased lumbar convexity, there is an increase in the posterior con- anteriorly convex curves in the cervical and lumbar vexity of the thoracic region and an increase in the anterior convex- regions of the vertebral column. The term kyphosis ity of the cervical curve. refers to the normal sagittal plane posteriorly convex curves in the thoracic and sacral regions of the verte- bral column.66 Sometimes an abnormal increase in the normal posterior convexity may occur, and this abnor- mal condition also may be called a kyphosis.67,68 This condition may develop as a compensation for an increase in the normal lumbar curve, as seen in Figure 13-19, or the kyphosis may develop as a result of poor postural habits or ostoporosis. Dowager\u2019s hump is an easily recognizable excessively kyphotic condition that is found most often in postmenopausal women who have osteoporosis.60 The anterior aspect of the bodies of a series of vertebrae collapse as a result of osteo- porotic weakening. The vertebral body collapse causes an immediate lack of anterior support for a segment of the thoracic vertebral column, which bends forward, causing an increase in the posterior convexity (the hump) and an increase in compression on the anterior aspect of the vertebral bodies (Fig. 13-20A).The LoG passes at a greater distance from the thoracic spine, and the gravitational moment arm increases. Compression Table 13-4 Possible Effects of Malalignment on Body Structures Deviation Compression Distraction Stretching Shortening Excessive Abdominal muscles Posterior aspect of vertebral Lumbosacral angle Iliopsoas, lumbar anterior tilt bodies increased Anterior longitudinal extensors of pelvis ligament Interdiskal pressure at L5 Shearing forces at Posterior longitudi- Excessive to S1 increased L5 to S1 Dorsal back extensors nal ligament lumbar lordosis Posterior ligaments Posterior vertebral bodies Likelihood of for- Scapular muscles Interspinous liga- Excessive and facet joints ward slippage of ments dorsal kyphosis L5 on S1 Interdiskal pressures increased Ligamentum flavum increased Lumbar extensors Anterior annulus Anterior longitudinal Intervertebral foramina fibers narrowed ligament Facet joint cap- Upper abdominal Anterior vertebral bodies sules and poste- Intradiskal pressures rior annulus muscles fibers Anterior shoulder increased girdle musculature Excessive cer- Posterior vertebral bodies Anterior annulus Anterior longitudinal Posterior ligaments vical lordosis and facet joints fibers ligament Neck extensors Interdiskal pressure increased Intervertebral foramina narrowed","Copyright \u00a9 2005 by F. A. Davis. A Dowager's hump B Gibbus Chapter 13: Posture \u25a0 497 \u25b2 Figure 13-20 \u25a0 A. Dowager\u2019s hump. B. Gibbus deformity. (hump), which forms a sharp posterior angulation in the upper thoracic vertebral column. on the anterior aspects of the vertebral bodies and ante- rior annulus increases, and the posterior aspect (con- \u25a0 Head vexity of the curve) is subjected to tensile stresses in the fibers of the posterior annulus and apophyseal joint Forward Head Posture capsules. A forward head posture is one in which the head is posi- Diseases such as tuberculosis or ankylosing spondy- tioned anteriorly and the normal anterior cervical con- losis also may cause abnormal increases in the posterior vexity is increased with the apex of the lordotic cervical convexity of the thoracic region. A gibbus or humpback curve at a considerable distance from the LoG in com- deformity may occur as a result of tuberculosis, which parison with optimal posture. The constant assumption causes vertebral fractures (see Fig. 13-20B). Gibbus or of a forward head posture causes abnormal compres- humpback deformity is easily recognized by the gibbus sion on the posterior zygapophyseal joints and poste- rior portions of the intervertebral disks and narrowing of the intervertebral foramina in the lordotic areas of the cervical region. The cervical extensor muscles may become ischemic because of the constant isometric contraction required to counteract the larger than nor- mal external flexion moment and maintain the head in its forward position. The posterior aspect of the zygapophyseal joint capsules may become adaptively shortened, and the narrowed intervertebral foramen may cause nerve root compression. In addition, the structure of the temporomandibular joint may become altered by the forward head posture, and as a result, the joint\u2019s function may be disturbed. In the forward head posture, the scapulae may rotate medially, a thoracic kyphosis may develop, the thoracic cavity may be dimin- ished, vital capacity can be reduced, and overall body height may be shortened. Other possible effects of habitual forward head posture, including adverse effects on the temperomandibular joint, are presented in Table 13-5. Dave will need to be aware of his head and neck posture because most of the time he will be working and\/or relaxing in a seated posture. Table 13-5 Forward Head Posture Deviation Structural Components Long-Term Effects on Structural Function Forward head Anterior location of LoG causes an increase in Muscle ischemia, pain, and fatigue and possi- the flexion moment, which requires constant ble protrusion of nucleus pulposus isometric muscle tension to support head Retruded mandible position causes compres- Stretch of suprahyoid muscles pulls mandible sion and irritation of retrodiskal pad and posteriorly into retrusion may result in inflammation and pain Increase in cervical Narrowing of intervertebral foramen and com- Reduction in range of motion lordosis pression of nerve roots Damage to spinal cord and\/or nerve roots Compression of zygapophyseal joint surfaces and leading to paralysis increase in weight-bearing Damage to cartilage and increased possibility Compression of posterior annulus fibrosus of arthritic changes; adaptive shortening Adaptive shortening of the posterior ligaments and possible formation of adhesions of Adaptive lengthening of anterior ligaments joint capsules with subsequent loss of ROM Increase in compression on posterior vertebral Changes in collagen and early disk degenera- tion; diminished ROM at the intervertebral bodies at apex of cervical curve joints Decrease in cervical flexion ROM Medial rotation of Adaptive lengthening of upper posterior back Decrease in cervical extension ROM and the scapula muscles decrease in anterior stability Osteophyte formation Adaptive shortening of anterior shoulder muscles Increase in dorsal kyphosis and loss of height Decrease in vital capacity and ROM of shoul- der and arm","Copyright \u00a9 2005 by F. A. Davis. 498 \u25a0 Section 5: Integrated Function and gluteal folds should be equal, and the ASIS and PSIS should lie on a line parallel to the ground, as well as being equidistant from the LoG. The joint axes of the hip, knee, and ankle are equidistant from the LoG, and the gravitational line transects the central portion of the vertebral bodies. When postural alignment is optimal, little or no muscle activity is required to main- tain medial-lateral stability. The gravitational torques acting on one side of the body are opposed by equal torques acting on the other side of the body (Tables 13-6 and 13-7). Deviations from Optimal Alignment in the Frontal Plane \u25b2 Figure 13-21 \u25a0 In anterior view of the human body, the Any asymmetry of body segments caused either by LoG, in optimal posture, divides the body into two symmetrical parts. movement of a body segment or by a unilateral postural deviation will disturb optimal muscular and ligamen- Frontal Plane Optimal Alignment tous balance. Symmetrical postural deviations, such as and Analysis bilateral genu valgum (knock knee), that disturb the optimal vertical alignment of body segments cause an In an anterior view, the LoG bisects the body into sym- abnormal distribution of weight-bearing or compressive metrical halves (Fig. 13-21). The head is straight, with forces on one side of a joint and increased tensile forces no tilting or rotation evident. The LoG bisects the face on the other side. The increased gravitational torques into equal halves. The eyes, clavicles, and shoulders that may occur require increased muscular activity and should be level (parallel to the ground). In a posterior cause ligamentous stress. view, the inferior angles of the scapulae should be parallel and equidistant from the LoG. The waist angles \u25a0 Foot and Toes Pes Planus (Flat Foot) An evaluation of standing posture from the anterior- posterior aspect should include a careful evaluation of the feet. Normally the plumb line should lie equidistant from the malleoli, and the malleoli should appear to be of equal size and directly opposite from one another. When one malleolus appears more prominent or lower than the other and calcaneal eversion is present, it is possible that a common foot problem known as pes planus, or flat foot, may be present. Calcaneal eversion Table 13-6 Alignment in the Coronal Plane in the Standing Posture: Anterior Aspect Body Segment LOG Location Observation Head Neck\/shoulders Passes through middle of the forehead, nose Eyes and ears should be level and symmetrical. and chin. Chest Right and left angles between shoulders and neck Abdomen\/hips Passes through the middle of the xyphoid should be symmetrical. Clavicles also should be Hips\/pelvis process. symmetrical. Knees Passes through the umbilicus (navel). Ribs on each side should be symmetrical. Ankles\/feet Passes on a line equidistant from the right and Right and left waist angles should be symmetrical. left anterior superior iliac spines. Passes Anterior superior iliac spines should be level. through the symphysis pubis. Passes between knees equidistant from medial Patella should be symmetrical and facing straight femoral condyles. ahead. Passes between ankles equidistant from the medial maleoli. Malleoli should be symmetrical, and feet should be parallel. Toes should not be curled, overlapping, or devi- ated to one side.","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 499 Table 13-7 Alignment in the Coronal Plane in the Standing Posture: Posterior Aspect Body Segment LoG Location Observation Head Passes through middle of head. Head should be straight with no lateral tilting. Arms Angles between shoulders and neck should be Shoulders\/spine Passes along vertebral column in a straight equal. line, which should bisect the back into two Hips\/pelvis symmetrical halves. Arms should hang naturally so that the palms of the hands are facing the sides of the body. Knees Passes through gluteal cleft of buttocks and Ankles\/feet should be equidistant from posterior supe- Scapulae should lie flat against the rib cage, be rior iliac spines. equidistant from the LoG, and be separated by about 4 inches in the adult. Passes between the knees equidistant from medial joint aspects. The posterior superior iliac spines should be level. The gluteal folds should be level and sym- Passes between ankles equidistant from the metrical. medial malleoli. Look to see that the knees are level. The heel cords should be vertical and the malleoli should be level and symmetrical. of 5\u040a to 10\u040a is normal in toddlers, but by 7 years of age, results in a relatively overmobile foot that may require no calcaneal eversion should be present.61 muscular contraction to support the osteoligamentous arches during standing. It also may result in increased Flat foot, which is characterized by a reduced or weight-bearing on the second through fourth meta- absent medial arch, may be either rigid or flexible. A tarsal heads with subsequent plantar callus formation, rigid flat foot is a structural deformity that may be especially at the second metatarsal. Weight-bearing hereditary. In the rigid flat foot, the medial longitudi- pronation in the erect standing posture causes medial nal arch is absent in non\u2013weight-bearing, toe-standing, rotation of the tibia and may affect knee joint function. and normal weight-bearing situations. In the flexible flat foot, the arch is reduced during normal weight- Dave has depressed navicular bones on both feet. Do bearing situations but reappears during toe-standing or you think that this condition will be a problem for him? non\u2013weight-bearing situations. Can you think of a possible remedy if it is a problem? In either the rigid or flexible type of pes planus, the Pes Cavus talar head is displaced anteriorly, medially, and inferi- orly. The displacement of the talus causes depression of The medial longitudinal arch of the foot, instead of the navicular bone, tension in the plantar calcaneonav- being low (as in flat foot), may be unusually high. A icular (spring) ligament, and lengthening of the tibialis high arch is called pes cavus (Fig. 13-24). Pes cavus is a posterior muscle (Fig. 13-22). The extent of flat foot more stable position of the foot than is pes planus. The may be estimated by noting the location of the navicu- weight in pes cavus is borne on the lateral borders of lar bone in relation to the head of the first metatarsal. the foot, and the lateral ligaments and the peroneus Normally, the navicular bone should be intersected by longus muscle may be stretched. In walking, the cavus the Feiss line (Fig. 13-23). If the navicular bone is foot is unable to adapt to the supporting surface depressed, it will lie below the Feiss line and may even because the subtalar and transverse tarsal joints tend to rest on the floor in a severe extent of flat foot. Flat foot be near or at the locked supinated position. \u1b63 Figure 13-22 \u25a0 In pes planus (\u201cflat foot\u201d), there is displacement of the talus anteriorly, medially, and infe- riorly; depression and pronation of the calcaneus; and depression of the navicular bone.","Copyright \u00a9 2005 by F. A. Davis. 500 \u25a0 Section 5: Integrated Function A. B. \u25b2 Figure 13-23 \u25a0 In the normal foot, the medial malleolus, the tuberosity of the navicular bone, and the head of the first metatarsal lie in a straight line called the Feiss line. \u25a0 Knees \u25b2 Figure 13-25 \u25a0 A. In genu valgum (\u201cknock knee\u201d), the medial aspect of the knee complex is subjected to tensile stress, and Genu valgum (knock knee) is considered to be a nor- the lateral aspect is subjected to compressive stress. B. In genu varum mal alignment of the lower extremity in children from (\u201cbowleg\u201d), the lateral aspect of the knee complex is subjected to ten- 2 to 6 years of age.69 However, by about 6 or 7 years of sile stress, and the medial aspect of the knee complex is subjected to age, the physiologic valgus should begin to decrease, compressive stress. and by young adulthood, the extent of valgus angula- tion at the knee should be only about 5\u040a to 7\u040a. In genu tibia. Cortical thickening on the medial concavity of valgum, the mechanical axes of the lower extremities both the femur and tibia may be present as a result of are displaced laterally. If the extent of genu valgum the increased compressive forces,70 and the patellae may exceeds 30\u040a and persists beyond 8 years of age, struc- be displaced medially. Some of the more commonly tural changes may occur. As a result of the increased suggested cause of genu varum are vitamin D deficiency, external torque acting around the knee, the medial renal rickets, osteochondritis, or epiphyseal injury. knee joint structures are subjected to abnormal tensile or distraction stress, and the lateral structures are sub- Squinting or cross-eyed patella (patella that faces jected to abnormal compressive stress (Fig. 13-25A). medially) is a tilted\/rotated position of the patella in The patella may be laterally displaced and therefore which the superior medial pole faces medially and the predisposed to subluxation. inferior pole faces laterally (Fig. 13-26A). This abnor- mal patella position may be present in one or both The foot also is affected as the gravitational torque knees and may be a sign of either increased femoral tor- acting on the foot in genu valgum tends to produce sion (excessive femoral anteversion)61 or medial tibial pronation of the foot with an accompanying stress on rotation.60 The Q-angle may be increased in this condi- the medial longitudinal arch and its supporting struc- tion, and patella tracking may be adversely affected. tures, as well as abnormal weight-bearing on the poste- Grasshopper-eyes patella refers to a high, laterally dis- rior medial aspect of the calcaneus (valgus torque). placed position of the patella in which the patella faces Additional related changes may include flat foot, lateral upward and outward (see Fig. 13-26B). An abnormally tibial torsion, lateral patellar subluxation, and lumbar long patella ligament may be responsible for the higher spine contralateral rotation.60 than normal position of the patella (patella alta). Femoral retroversion or lateral tibial torsion may be Genu varum (bowleg) is a condition in which the responsible for the rotated position of the patella. knees are widely separated when the feet are together Grasshopper-eyes patella leads to abnormal patella and the malleoli are touching (see Fig. 13-25B). Some tracking and a decrease in the stability of the patella. extent of genu varum is normal at birth and during infancy up to 3 or 4 years of age.62,70 Physiologic bowing \u25a0 Vertebral Column is symmetrical and involves both the femur and the Scoliosis \u25b2 Figure 13-24 \u25a0 Pes cavus. Another segment of the body that requires special con- sideration when posture is evaluated from the anterior or posterior view is the vertebral column. Normally, when viewed from the posterior aspect, the vertebral column is vertically aligned and bisected by the LoG. The structures on either side of the column are sym- metrical. The LoG passes through the midline of the occiput, through the spinous processes of all vertebrae, and directly through the gluteal cleft. In an optimal","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 501 \u1b63 Figure 13-26 \u25a0 A. In squint- ing or cross-eyed patella, the superior medial pole of the patella faces medi- ally, and the inferior patellar pole faces laterally. B. In grasshopper-eyes patella, the patellae are high and lat- erally situated and face upward and outward. posture, the vertebral structures, ligaments, and mus- located between the body of T2 and the disk between cles are able to maintain the column in vertical align- T11 and T12.73 ment with little stress or energy expenditure. If one or more of the medial-lateral structures fails to provide Investigators have postulated that AIS may result adequate support, the column will bend to the side. from a dysfunction in the vestibular system,74 a distur- The lateral bending will be accompanied by rotation of bance in control of the muscle spindle,75 an inherited the vertebrae because lateral flexion and rotation are connective tissue disorder,76 subcortical brain stem coupled motions below the level of the second cervical abnormalities,77\u201380 developmental instability,81,82 mela- vertebra. tonin production abnormality, growth hormone secre- tion, and platelet abnormalities.83 Furthermore, in a Consistent lateral deviations of a series of vertebrae recent study, Chan and associates found a genetic locus from the LoG in one or more regions of the spine may indicate the presence of a lateral spinal curvature in the \u25b2 Figure 13-27 \u25a0 A lateral curvature of the vertebral column frontal plane called a scoliosis (Fig. 13-27). There are that is convex to the right in the thoracic region and convex to the two classifications of curves: functional curves and left in the lumbar region. Note the rotation of the vertebra and asym- structural curves. Functional curves are called non- metry of the rib cage. structural curves in that they can be reversed if the cause of the curve is corrected. These curves are the result of correctable imbalances such as a leg length dis- crepancy or a muscle spasm. Structural curves, as the name implies, involve changes in bone and soft tissue structures. Although scoliosis is usually identified as a lateral curvature of the spine in the frontal plane, the defor- mity also occurs in the transverse (as vertebrae rotate) and sagittal planes (as the column buckles). Idiopathic scolioses are catagorized by age at onset : infantile (0 to 3 years), juvenile (4 to 10 years) and adolescent (older than 10 years).70 The adolescent idiopathic scoliosis (AIS) type makes up the majority of all scolioses71,72 and affects up to 4% of schoolchildren worldwide.72 The term idiopathic means that the cause of the condition is unknown. The curves in scoliosis are named accord- ing to the direction of the convexity and location of the curve. If the curve is convex to the left in the cervical area, the curve is designated as a left cervical scoliosis. If more than one region of the vertebral column is involved, the superior segment is named first (e.g., left cervical, right thoracic). A double major curve is pres- ent when there are two structural curves of the same size. A triple curve includes three regions of the verte- bral column.The curve shown in Figure 13-27 is a struc- tural curve called a right thoracic, left lumbar scoliosis. In a study of 606 AIS cases, the most prevalent (51%) type of curve was the main thoracic curve with its apex","Copyright \u00a9 2005 by F. A. Davis. 502 \u25a0 Section 5: Integrated Function B. Unequal A. Unequal arm shoulder angles distance from for AIS.72 Lidstrom and coworkers84 found differences body in postural sway in 100 children aged 10 to 14 years; 35 Prominent hip of the children were siblings of scoliotic patients, and C. Unequal 65 were control subjects. This is another finding that waist angles suggests the possibility of a genetic component as the causative agent. Nault and associates80 found a decrease \u25b2 Figure 13-28 \u25a0 A lateral curvature of the vertebral column in standing stability among 43 girls diagnosed with sco- that is convex to the right in the thoracic region and convex to the liosis in comparison with 28 girls without scoliosis. Sway left in the lumbar region. areas, as measured by variations in the CoP and CoM, were larger in the scoliotic group than in the nonscoli- well as being cosmetically unacceptable. Observation otic group. As of this writing, however, no evidence has combined with periodic follow-up to watch for curve been presented that unequivocally points to a single progression is indicated for curves of less than 25\u040a. etiology for adolescent idiopathic scoliosis,85 and Ahn Bracing is used for flexible curves between 25\u040a and et al.83 suggested that the etiology is multifactorial. 40\u040a.70 Adolescents whose vertebral columns are still Despite the ambiguity surrounding the cause or causes immature and who have curves between 25\u040a and 40\u040a are of adolescent idiopathic scoliosis, the effects of unequal considered to be at high risk because curves of this torques on the structures of the body are dramatic and extent tend to progress.86 Bracing is successful in pre- can be devastating to those affected. AIS involves changes venting additional progression of the curve in 70% to in the structure of the vertebral bodies, transverse and 80% of the cases in which it is used.86 Curves that have spinous processes, intervertebral disks, ligaments, and progressed beyond 40\u040a may necessitate surgical inter- muscles. Asymmetrical growth and development of the vention to prevent further progression. If a curvature is vertebral bodies lead to wedging of the vertebrae. recognized early in its development, then measures Growth on the compressed side (concavity) is inhibited may be instituted either to correct the curve or to pre- or slower than on the side of the convexity of the curve. vent its increase.87 However, some curves may progress even after surgery.88 The following example depicts a hypothetical series of events for AIS. The first step in the process is un- According to the second phase of the 1988 Utah known because researchers have been unable to identify study in which a visual assessment (scoliosis screening) the supporting structure involved in the initial failure. of 3000 college-aged women (19 to 21 years of age) was Therefore, it is just as possible that the sequence of performed in 34 states and 5 foreign countries, 12% of events begins with a developmental disturbance that this population had a previously undetected lateral results in asymmetrical growth of the vertebrae rather deviation of the spine.89 In consideration of the fact than a failure in the muscular or ligamentous support that AIS may be progressive in some cases and lead to a system, as suggested in the model. considerable amount of deformity without treatment, early recognition is important. The vertebral deviations Example 13-4 in scoliosis cause asymmetrical changes in body struc- tures, and several of these changes may be detected Hypothetical Series of Events in Adolescent through simple observation of body contours either at Idiopathic Scoliosis (Fig. 13-28) home or in the schools. Usually, home or school screen- ing programs are designed for identification of the fol- 1. possible failure of support as a result of a defect in muscular and\/or ligamentous support systems dur- ing a period of rapid growth 2. creation of an external lateral flexion moment 3. deviation of the vertebrae with rotation 4. compression of the vertebral body on the side of the concavity of the curve 5. inhibition of growth of vertebral body on the side of the concavity of the curve in a still immature spine 6. wedging of the vertebra in a still immature spine 7. head out of line with sacrum 8. compensatory curve 9. adaptive shortening of trunk musculature on the concavity 10. stretching of muscles, ligaments, and joint capsules on the convexity These changes may progress to produce a severe defor- mity as growth proceeds unless intervention occurs at the appropriate time. Deformities can interfere with breathing and the function of other internal organs, as","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 503 Unequal Rib hump shoulder angles Unequal arm Prominent hip distance from body Unequal waist angles \u1b63 Figure 13-29 \u25a0 Typical changes in body contours used in scoliosis screen- ing programs. A. Uneven waist angles or difference in arm to body space and unequal shoulder height or unequal A B scapula levels. B. A rib hump during for- ward trunk flexion. lowing: unequal waist angles, unequal shoulder levels loads on body structures. Our patient, Dave, will have to or unequal scapulae (see Fig. 13-29A), rib hump, and spend a great deal of time in the sitting position in a obvious lateral spinal curvature (see Fig. 13-29B). The wheelchair, and so we will have to consider the effects American Academy of Orthopedic Surgeon\u2019s Patient of prolonged sitting as well as the type of wheelchair Service Brochure on scoliosis, which is available online, that he will need. recommends that parents check their children\u2019s spines for any assymetry in body contours beginning at age 8 In a way, sitting postures are more complex than years. If the parents observe any postural asymmetries standing postures. The same gravitational moments as in their child, they should inform the child\u2019s physi- in standing posture must be considered, but, in addi- cian.90 The American Physical Therapy Association\u2019s tion, we must consider the contact forces that are cre- (APTA\u2019s) pamphlet on scoliosis (also available online) ated when various portions of the body interface with suggests that home screening should take place every 6 various parts of chairs, such as head, back, and foot months for both boys and girls starting at age 9 years rests, and seats. The location and amount of support and continue until the child is 14 years of age.91 provided to various portions of the body by the chair or stool may change the position of the body parts and Analysis of Sitting Postures thus the magnitude of the stresses on body structures. The overall goal for sitting posture is the same as the Example 13-5 goal for standing posture: to attain a stable alignment of the body that can be maintained with the least The use of a lumbar support can help to maintain the expenditure of energy and the least stress on body normal lumbar lordotic curve and reduce the compres- structures. In our analysis of standing posture, we saw sive stress on the spine in comparison with sitting with- that moments at the spine and extremity joints were out a lumbar support.92 created when the LoG was at a distance from either a portion of the vertebral column or the axes of the There are many different sitting postures, but we extremity joints. The greater the distance that the LoG will direct our attention to the active erect sitting pos- was from the joint axes, the larger the moment that was ture, which is defined in this chapter as an unsupported created and, as a result, the more muscle activity posture in which a person attempts to sit up as straight and\/or passive tension in ligaments and joint capsules as possible. A consideration of muscle activity, inter- that was required to maintain equilibrium and a stable diskal pressures, and seat interface pressures in the posture. The necessary increase in muscle activity active erect sitting posture will be compared to forces in resulted in more energy expenditure and increased relaxed erect, slumped, and slouched sitting and to","Copyright \u00a9 2005 by F. A. Davis. 504 \u25a0 Section 5: Integrated Function sitting and relaxed erect sitting but not in active erect sitting. Muscle activity in the lumbar erector spinae erect standing postures. In addition, we will discuss how remained the same in both postures. The authors pos- these forces may affect Dave. tulated that the passive tissues were able to assume the load in the relaxed erect and slumped postures and Muscle Activity that was why the thoracic erector spinae muscles ceased their activity.94 The LoG passes close to the joint axes of the head and spine in active erect sitting posture. (Fig. 13-30A and Muscle activity in the active erect sitting posture is B). In the slumped posture, the LoG is more anterior to also greater than in both relaxed erect and slouched sit- the joint axes of the cervical, thoracic, and lumbar ting. In relaxed erect sitting, the LoG is only slightly spines than it is in either active or relaxed erect sitting anterior from its position in active erect sitting. In the (see Fig. 13-30C). Therefore, we would expect that slouched posture, the LoG is posterior to the spine and more muscle activity would be required in the slumped hips, but body weight is being supported by the back of posture than in the other sitting postures. In contrast to the chair, and so less muscle activity is required than in these expectations, researchers have found that main- active erect posture (Fig. 13-31).95 taining an active erect sitting posture requires not only a greater number of trunk muscles but also an C a s e A p p l i c a t i o n 1 3 - 9 : Strengthening of Trunk increased level of activity in some of these muscles than Muscle for Sitting and Transfers in both relaxed erect and slumped postures. O\u2019Sullivan and associates93 used EMG to monitor activity in the Dave\u2019s trunk muscles are not paralyzed but are weak- superficial lumbar multifidus, thoracic erector spinae, ened from the surgery and subsequent bed rest. There- and internal oblique abdominal muscles in erect and fore, one goal that we will have for Dave is to strengthen slumped sitting postures. These authors found a signifi- his trunk muscles so that he will be able to maintain his cantly greater amount of activity in these muscles in stability in sitting as well as in transfer and other daily erect sitting than in slumped sitting. living activities. (Individuals with a SCI below T3 may use the latissimus dorsi and lower trapezius muscles to help The flexion relaxation (FR) phenomenon may pro- maintain stability in sitting, but it appears that Dave will vide a possible reason why the slumped sitting posture not need these muscles to help in sitting.)96 requires less muscle activity than does the active erect sitting posture. Flexion relaxation is a sudden cessation \u25a0 Muscle Activity in Sitting versus Standing Postures of muscular activity, as manifested by electrical silence of the back extensors during trunk flexion in either sit- The amount of muscle activity employed to maintain a ting or standing postures. In a study by Callaghan and particular posture affects the amount of interdiskal Dunk, FR occurred in the thoracic erector spinae muscles (thoracic components of the longissimus thoracis and iliocostalis lumborum) in 21 of 22 subjects in slumped A Active erect sitting B Relaxed erect sitting C Slumped sitting \u25b2 Figure 13-30 \u25a0 A. In the active erect sitting position, the LoG is close to the axes of rotation of the head, neck, and trunk. B. In the relaxed erect sitting posture, the LoG still is relatively close to those axes of rotation. C. In the slumped position, the LoG is relatively distant from the axes of rotation of the head, neck, and trunk.","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 505 identical conditions in their research or did not con- sider all of the variables that might affect muscle activ- ity in erect sitting versus erect standing. For instance, something as simple as changing from a hard seat to a soft seat will decrease the amount of activity in the internal and external oblique muscles.99 Supporting one\u2019s arms on a table when using both hands for data entry100 can reduce the load on the left and right trapezius and erector spinae muscles in comparison with working with unsupported arms. Interdiskal Pressures and Compressive Loads on the Spine Slouched sitting Direct determinations of interdiskal pressures haveNormalized to Standing in % been made through the insertion of pressure sensitive \u25b2 Figure 13-31 \u25a0 In the slouched sitting posture, the LoG is at sensors or transducers101\u2013104 into one or more interver- a distance from the axes of rotation at the head, neck, and trunk, but tebral disks. Indirect determinations of interdiskal pres- the back of the chair is providing support in lieu of muscle support. sures have used measurements of spinal shrinkage (creep)105\u2013108 and calculation of compressive forces pressure and energy expenditure. Increases in muscle based on information obtained from EMGs about mus- activity cause increases in interdiskal pressures and de- cle activity.98,99 creases in muscle activity are accompanied by decreases in interdiskal pressures. Callaghan and McGill97 noted Active erect sitting requires co-contractions of that the upper and lower erector spinae muscles shifted trunk extensors (erector spinae muscles) and flexors to higher levels of activity during active erect sitting (abdominal muscles), which cause higher pressures in than during standing. This increase in muscle activity the disk between L4 and L5 than does slumped sitting. has been attributed in part to the differences in the One of the most well-known studies in which direct extent of lumbar lordosis observed between sitting and interdiskal pressure measurements in erect sitting were standing. Sitting forces the pelvis into a posterior tilt compared with pressures in erect standing and other and, as a result, causes a reduction in the lumbar curve postures was by Nachemson,101 who reported that there in comparison with that observed in standing.92 In one was a 40% increase in pressures in the disk between L4 radiographic study of 109 patients, the average lumbar and L5 in erect sitting in comparison with erect stand- curve (L1 to S1) was 15\u040a less in active erect sitting than ing. However, the results of some studies102\u2013104 in which was an average lumbar curve of 49\u040a in the same popu- advanced sensor technology was used suggest that inter- lation in standing posture.49 The LoG would be farther diskal pressures\/loads on the spine in active erect sit- away from the apex of the joint axes of the lumbar ver- ting are either only slightly higher than102 or equal to103 tebrae in a flexed or more kyphotic lumbar spine than pressures in erect standing (Fig. 13-32). in a lordotic lumbar spine. Therefore, one would expect that more muscle activity would be required to 500 maintain the active erect sitting posture than to main- tain standing. However, the results of the following 450 Nachemson study raise questions about a more kyphotic lumbar 400 Wilke et al spine\u2019s being responsible for all of the increase in mus- cle activity in active erect sitting versus standing. 350 Continuing Exploration: Muscle Activity and Lumbar Text3\/0i0mage rights not available. Lordosis in Standing and Sitting Postures 250 When the lordotic lumbar curve in standing was replicated in unsupported active erect sitting in 30 200 subjects, the EMG activity level of the extensor mus- cles was significantly higher than in standing.98 It 150 thus appears from this study that the loss of lordosis in the sitting posture is not totally responsible for the 100 greater amount of muscle activity observed in erect sitting than in standing. 50 Many variables need to be considered, and it is 0 possible that investigators either did not employ \u25b2 Figure 13-32 \u25a0 Interdiskal pressures in different sitting and standing positions. (From Wilke H-J, Neef P, Caimi M, et al.: New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 24:755, 1999. Reprinted with permission from Lippincott Williams & Wilkins.)","Copyright \u00a9 2005 by F. A. Davis. 506 \u25a0 Section 5: Integrated Function Continuing Exploration: Comparison of Interdiskal dynamic chairs than in chairs with fixed seats and Pressures in Standing and Sitting backs. Although dynamic chairs may be more desirable than fixed chairs, the task being performed had greater One of the problems in interpreting the results of effects on spinal stature than did the type of chair. investigations is that it is not always possible to deter- mine whether the researchers are referring to active Very few studies have investigated either the con- erect sitting or relaxed erect sitting. Undoubtedly, triution of soft tissue deformation to measurements of the controversy will continue until enough addi- total height loss or the shrinkage of the cervical spine. tional studies are performed to either confirm or In an investigation of the soft tissue contribution to deny Nachemson\u2019s findings. Some researchers agree total seated height, one group of researchers found that interdiskal pressures in relaxed or slouched sit- that deformation of muscle and fat below the sacrum ting postures are lower than in erect standing.102,103 contributed 28% to 30% at 5 and 10 minutes of load- Wilke and colleagues reported that the interdiskal ing, respectively. Soft tissue deformation always con- pressure at the disk between L4 and L5 disk in tributed a small amount to total height loss, but early in relaxed erect sitting was 0.46 MPa, in comparison the loading cycle, height loss mostly occurred in the with 0.50 MPa in relaxed standing.102 Straightening spine, whereas at the end of the loading cycle, the loss the back to attain an active erect sitting posture was a combination of spine and soft tissue.107 Cervical increased interdiskal pressures by approximately spine shrinkage was investigated after 1 hour of televi- 10% to 0.55 MPa.102 Rohlmann and associates found sion watching in a sitting position in the follow- that bending moments on an internal spinal fixation ing three different head\/neck positions: neutral, 20\u040a of device were, on average, 13% lower for relaxed erect flexion, and 40\u040a of flexion. The neutral head position sitting than for relaxed erect standing103 (Fig. 13-33). had no effect on spinal shrinkage, in contrast to the head held at a 40\u040a angle, when the most cervical shrink- The results of spinal shrinkage measurements com- age (approximately 1 mm) occurred in 1 hour.108 paring sitting and standing work lend some support to the findings that, in general, loads in sitting are less After a literature review, Harrison and colleagues92 than in standing. Leivseth and Drerup106 showed that concluded that the lowest lumbar interdiskal pressures shrinkage of the lumbar spine in sitting (1.73 mm) was and lowest EMG readings are produced by seat back much less than the shrinkage in standing (4.16 mm). In inclinations between 110\u040a and 130\u040a, combined with a a comparison of spinal shrinkage between 2 hours of lumbar support that protrudes 5 cm from the back of relaxed sitting versus 2 hours work in standing, there the seat back and a posterior seat inclination of 5\u040a. The actually was a gain in stature in the lumbar spine in the use of armrests produces further reductions.92 relaxed sitting position. Working in a standing position caused a reduction in height of 0.8 mm per lumbar Seat Interface Pressures disk, in comparison with 0.3 mm for work in a sitting position.106 In another study of spinal shrinkage, van Pressure is force per unit area and is measured in pas- Dieen and colleagues105 found that a larger stature gain cals (Pa or N\/m2 [pounds per square inch]). The pres- occurred when a person spent 2 hours working in sure caused by contact forces between the person\u2019s body and the seat is referred to as the seat interface Standing pressure. Pressure mapping techniques using sensor- containing mats that can be placed on the seat of a Sit: Relaxed chair are used to measure average and maximum seat interface pressures (Fig. 13-34A and B). Average seat Sit: Ventral flexion interface pressure is the mean of pressure sensor val- ues, and the maximum seat interface pressure is the Text\/imageSit: Extension rights not available. highest individual sensor value.109 Sit: Lateral bending Studies have shown that individuals with physical Sit: Axial rotation disabilities (myelomeningocele and paraplegia) have significantly higher seat interface pressures than do 0 25 50 75 100 125 150 people without such disabilities.110,111 The higher maxi- Relative Bending Moment (%) mum seat interface pressures observed in individuals with SCI than in healthy individuals have been attrib- \u25b2 Figure 13-33 \u25a0 A comparison of average relative bending uted to asymmetrical ischial loading resulting from moments in internal fixation devices from 10 patients in different spinal\/pelvic deformities and atrophy of soft tissue over sitting positions. Values are related to the corresponding value for the ischiae. Kernozek et al. studied peak interface pres- standing. Note that bending moment in relaxed sitting is less than sures in a group of 75 elderly persons with different the bending moment in standing, but the erect sitting (shown as body mass indices (BMIs). Peak seat interface pressures extension) bending moment is greater than in standing. (From were found to be highest in the thin elderly persons Rohlmann A, Graichen F, Bergmann G: Loads on an internal spinal (ones with the lowest BMI), who had the least amount fixation device during physical therapy. Phys Ther 82:49, 2002. of soft tissue over the ischiae.112 These individuals prob- Reprinted with permission from the American Physical Therapy ably had a smaller contact area with more concentra- Association.) tion of pressure than did individuals with a greater","Copyright \u00a9 2005 by F. A. Davis. A Chapter 13: Posture \u25a0 507 Text\/image rights not available. \u25a0 Effects of Changes in Body Posture B Changes in the posture of the body such as forward and \u25b2 Figure 13-34 \u25a0 A. Tactilus seat pad sensor used for mapping lateral trunk flexion can be effective means of reducing seat interface pressures in individuals like Dave who seat pressures. B. Three-dimensional image of the pressure distribu- must spend long periods of time in a wheelchair.111 tion, which shows where highest pressures are located. (Courtesy of Vaisbuch et al.110 compared maximum seat interface Sensor Products, Inc., 188 Rt. 10, Suite 307, East Hanover, NJ 07936.) pressures in different body positions (neutral, recline, tilt, lean forward, and lateral flexion) in a group of 15 body mass with increased surface contact area and nondisabled children and in a group of 15 children better pressure distribution. The fact that seat interface with myelomeningocele. Maximum pressures for the pressure has been found to be a good indicator of sub- myelomeningocele group were significantly higher cutaneous stress (with the latter being higher than the than those found in the nondisabled group for the neu- former)113 demonstrates the importance of minimizing tral and lean forward positions.The disabled group seat interface pressure. Changes in the position of the experienced significantly lower maximum seat inter- body, position of the chair, and the type of seat cushion face pressures in the forward and lateral flexed posi- employed can be employed to minimize the interface tions than in the neutral position. Hobson111 compared pressure.114 seat interface pressure and shear in 10 healthy subjects and in 12 persons with SCIs. The individuals with SCIs had maximum seat interface pressures that, depending on which of the eight positions were assumed in the wheelchair, were 6% to 46% higher than the pressures found in the healthy group. Maximum seat interface pressures could be reduced from neutral position val- ues by 9% when the trunk was flexed forward to 50\u040a and reduced on the unweighted side by 30% to 40% when the trunk was laterally flexed to 15\u040a (Fig. 13-35). C a s e A p p l i c a t i o n 1 3 - 1 1 : Pressure-Reducing Activities The performance of seat interface pressure\u2013reducing activities is an essential activity for our patient. Dave C a s e A p p l i c a t i o n 1 3 - 1 0 : Need to Minimize Seat \u25b2 Figure 13-35 \u25a0 The patient is able to relieve interface pres- Interface Pressure sure by leaning to the side. Leaning is recommended every few minutes. Minimizing seat interface pressure is an extremely important consideration for our patient, Dave, who may have to spend a great deal of his time in a wheelchair. A reduction in seat interface pressures reduces the risk of developing pressure sores, which are caused by unre- lieved pressure and shearing forces. When soft tissue is compressed between the seat and bony prominences (such as the ischial spines) for an extended period of time, the external pressure is higher than capillary blood flow pressure. The higher external pressure leads to ischemia (decrease in blood flow) and may lead to death of cells and tissue. Shear pressure (the horizontal force component) also may cause obstruction of blood flood and tissue death. Dave is at high risk because he has lost muscle bulk in his buttocks as a result of the paral- ysis affecting his hip extensor muscles.","Copyright \u00a9 2005 by F. A. Davis. 508 \u25a0 Section 5: Integrated Function must be able to maintain stability while performing Interdiskal pressures in supine lying (0.10 MPa) were activities to alleviate pressure and be able to develop less than in either lying prone (0.11 MPa) or lying on sufficient upper extremity strength to elevate his body the side (0.12 MPa), and in all of these postures the vertically by performing push-ups on the armrests of his interdiskal pressure was less than in sitting and standing wheelchair. He needs to understand why these activities postures. Lying prone with the back extended and sup- are important so that he will be motivated to perform ported on one\u2019s elbows had the largest interdiskal pres- them on a continual basis while he is in the wheelchair. sure (0.25 MPa) among the lying postures tested and was only slightly less than in slouched sitting (0.27 \u25a0 Effects of Alterations in the Position of the Chair MPa). Rohlmann and associates conducted a study of the bending moments on spinal fixation devices in 10 Alterations in the angulation of the chair\u2019s back rest in patients. Movements in the lying posture such as lifting combination with footrest and seat inclinations are an extended arm or leg in the supine and prone posi- another method utilized to reduce seat interface pres- tions did not raise the bending moments above bend- sure. ing moments in standing (Fig. 13-36). However, when the patients raised both extended legs in the supine Continuing Exploration: Positioning to Reduce Seat position, peak bending moments exceeded the mo- Interface Pressure ments in the standing posture.101 Reclining the backrest posteriorly by 30\u040a from 0\u040a has Surface Interface Pressures been found to significantly reduce average seat inter- face pressure (but not maximum seat interface pres- In order for pressure-relieving surfaces to be effective, sure). Supporting a person\u2019s feet on blocks of wood they should be able to reduce the interface pressure to produce 90\u040a of flexion at the hips, knees, and below capillary closing pressure (12 mm Hg). Other- ankles caused an increase in the average seat inter- wise, blood flow may be compromised, and this may face pressure.109 In another study, the maximum seat result in tissue breakdown. Also, a uniform pressure dis- interface pressure was observed to be significantly tribution over the entire available surface is desirable to lower when sitting with a 0\u040a backrest inclination prevent sections of increased pressure over certain when the feet were on the floor rather than when legs areas. Examples of some pressure-reducing mattress were supported on a rest.115 Hobson111 found that a surfaces include foam, air, gas, water, and gel. Other recline of the back rest to 120\u040a reduced the neutral pressure-relieving surfaces include movable surfaces, backrest position values by 12%. Full body tilt to 20\u040a usually powered by a motor or pump, which can alter- reduced seat interface pressure values by 11%. natively inflate and deflate.116 Also, cushions of various compositions and depths Standing are used to reduce seat interface pressures. Materials used in the composition of cushions include synthetic SP: Lifting left leg materials, air, water, and gels of various kinds. Cushion thicknesses up to 8 cm have been found to be success- SP: Lifting both legs ful in reducing maximum subcutaneous stress inferior to the ischial tuberosity, but increasing the thickness SP: Lifting pelvis beyond 8 cm failed to cause an additional decrease in seat interface pressure.113 SP: Lifting upper body The selection of an appropriate cushion for Dave\u2019s SP: Cycling one leg wheelchair will be extremely important, and different materials will need to be tried. Ideally, we should map Text\/image rightsPP: Lifting right arm not available. the seat interface pressure in order to customize his PP: Lifting right leg seating. PP: Lifting right arm + left leg Analysis of Lying Postures SLP: Abduction of a leg Interdiskal Pressures SLP: Lifting both feet In general, interdiskal pressures are less in lying pos- tures than in standing and sitting postures. Wilke and SLP: Lifting both knees colleagues104 measured interdiskal pressures over a 24- hour period from a pressure transducer implanted in 0 25 50 75 100 125 150 the nucleus pulposus of the nondegenerated disk Relative Bending Moments (%) between L4 and L5 of a 45-year-old healthy man. \u25b2 Figure 13-36 \u25a0 Bending moments that occurred when body parts were moved as they might be in an exercise program when the body is positioned in the supine lying position (SP), prone position (PP), and side-lying position(SLP).The bending moments are com- pared with the moments in standing. (From Rohlman, A, Graichen, F, Bergmann, G: Loads on an internal spinal fixation device during physical therapy. Physical Theraphy 82:48, 2002. Reprinted with per- mission from the American Physical Therapy Association.)","Copyright \u00a9 2005 by F. A. Davis. C a s e A p p l i c a t i o n 1 3 - 1 2 : Risk of Pressure Chapter 13: Posture \u25a0 509 Sore Development times for muscle activation than in either adults or We need to be concerned about lying postures because older children.118 Newell and colleagues119 investigated of the danger of developing pressure sores. Dave is at CoP motion (postural sway) in different age groups risk for skin breakdown because his lower extremity from 3 years to 92 years of age. The young adult group muscles may have atrophied, with an accompanying loss of students in their 20s had the least amount of move- of protective soft tissue over bony prominences. In the ment of the CoP; the individuals in the youngest and supine lying posture, the areas at risk are the backs of oldest groups had the greatest amount of CoP motion. his heels and head, his lower vertebral spine, and the sacrum. In the side-lying posture, the areas at risk are The erect standing posture in infancy and early his malleoli and the heads of the femur and fibula. childhood differs somewhat from postural alignment in adults, but by the time a child reaches the age of 10 or Effects of Age, Pregnancy, 11 years, postural alignment in the erect standing posi- Occupation, and Recreation tion should be similar to adult alignment.120 However, on Posture poor postural alignment in a 7- or 8-year-old child can be recognized because it is similar to poor postural Age alignment in adults. For example, the poor posture may include forward head, kyphosis, lordosis, and \u25a0 Infants and Children hyperextended knees.120 Postural control in infants develops progressively dur- The following two studies investigated the effects of ing the first year of life, from control of the head to age and gender on the thoracic and lumbar curves. control of the body in a sitting posture and then to con- Widhe121 monitored 90 Swedish boys and girls over a trol of the body in a standing posture. Stability in a pos- 10-year period, examining them first at 5 to 6 years of ture, or the ability to fix and hold a posture in relation age and again at 15 to 16 years of age. Between the first to gravity, must be accomplished before the child is able and second measurements, both thoracic kyphosis and to move within a posture. The child learns to maintain lumbar lordosis increased by 6\u040a (Table 13-8). Sagittal a certain posture, usually through co-contraction of mobility decreased in the thoracic region by 27\u040a (9\u040a in antagonist and agonist muscles around a joint, and flexion and 18\u040a in extension). Lumbar flexion then is able to move in and out of the posture (sitting decreased by 9\u040a and extension by 5\u040a. In the second to standing and standing to sitting). Once stability is study, 847 Finnish boys and girls were examined annu- established, the child proceeds to controlled mobility ally from ages 10.8 years to 13.8 years.The normal tho- and skill. Controlled mobility refers to the ability to racic kyphosis was greater and the normal lumbar move within the posture\u2014for example, weight shifting lordosis less in boys than in girls both at the beginning in the standing posture. Skill refers to performance of and at each annual examination..122 Mean thoracic activities such as walking, running, and hopping, which kyphosis increased and mean lumbar lordosis are dynamic postural activities.117 decreased with increasing age. Despite wide variations, thoracic kyphosis was between 20\u040a and 40\u040a and lordosis According to Woollacott,118 by the time a child was between 20\u040a and 50\u040a in both genders.122 reaches 7 to 10 years of age, postural responses to plat- form perturbations are less variable and also compara- \u25a0 Elderly ble with those of adults in patterns of muscle activity and timing of responses. Responses of children Postural alignment in elderly people may show a more younger than 7 years of age included greater coactiva- flexed posture than in the young adult; however, many tion of agonists and antagonists and slower response elderly individuals in their 70s and 80s still demonstrate a close-to-optimal posture. Hardacker and colleagues found that cervical lordosis increased with increasing age48 (Fig. 13-37). Hammerberg and Wood123 in a study of the radiographic profiles of 50 elderly individuals 70 to 85 years of age showed an average kyphosis angle of 52\u040a, with a range of 29\u040a to 79\u040a, and an anterior position Table 13-8 Age Variations in Spinal Curves in the Sagittal Plane in Standing Posture: Values in Degrees Widhe121* Vendantam et al.55\u2020 Gelb et al.53 Hammerberg and Wood123 5\u20136 yr 15\u201316 yr 10\u201318 yr 40\u201349 yr 70\u201385 yr n \u03ed 90 n \u03ed 90 n \u03ed 88 n \u03ed 27 n \u03ed 50 Mean (SD) Mean (SD) Mean (SD) Mean (SD) Mean Range Thoracic 29 (9) 35 (8) 38 (10) \u03ea68 (11) 52 29\u201379 Lumbar \u03ea31 (8) \u03ea38 (7) \u03ea64 (10) \u03ea57 \u03ea96 to \u03ea20 *Widhe measured the thoracic curve from a point between the spinous processes of T2 and T3 to T12. The lumbar curve was measured from a point between T11 and T12 to a point between S1 and S2. The same 90 subjects were measured at different ages. \u2020Vendantam et al. measured the thoracic curve from T3 to T12 and the lumbar curve from T12 to S1.","Copyright \u00a9 2005 by F. A. Davis. 510 \u25a0 Section 5: Integrated Function -50 -40 Cervical Lordosis-30 Tex-2t0\/image rights not available. -10 0 \u25b2 Figure 13-38 \u25a0 Changes in posture as a result of aging. 20-30 21-30 41-50 51-60 61-70 times in elderly people appear to be longer than in young people, elderly persons may elect to stand with a Age wide BoS to have a margin of safety. Postural responses of older adults, aged 61 to 78 years, to platform pertur- \u25b2 Figure 13-37 \u25a0 The graph indicates that for the 100 volun- bations show differences in timing and amplitude and teers in the study, the mean cervical lordosis increased with increas- include greater coactivation of antagonist and agonist ing age. (From Hardacker JW, Shuford RF, Capicotto PN, et al.: muscles in comparison with younger subjects, aged 19 Radiographic standing cervical segmental alignment in adult volun- to 38 years. Iverson and associates,125 who tested nonin- teers without neck symptoms. Spine 22:1477, 1997. Reprinted with stitutionalized men 60 to 90 years of age on two types of permission from Lippincott Williams & Wilkins.) balance tests that involved one-legged stance, found that balance time and torque production decreased sig- of C7. The LoG passed, on average, 40 mm anterior to nificantly with age. In some of the tests, the authors the posterosuperior corner of S1. Gelb and colleagues53 found that torque production was a significant predic- in a study of 100 middle-aged and older volunteers tor of balance time; that is, the greater the torque pro- (average age of 57 years) noted that as age increased, duction, the longer the balance time. These authors the LoG was located more anteriorly with a loss of lum- also found that men who exercised five to six times per bar lordosis and an increase in thoracic and thora- week had greater torque production than did men who columbar kyphosis. However, the mean values of 34\u040a for exercised less frequently. This finding suggests that thoracic kyphosis and 64\u040a for lumbar lordosis values fell high levels of fitness and activity may have beneficial within normally accepted ranges for younger popula- effects on the aging person\u2019s ability to perform one- tions. No correlations were found between age and legged balancing activities that are needed for activities kyphosis either in the thoracic region or at the thora- of daily living such as walking.125 columbar junction. Only the loss of lumbar lordosis at the proximal levels showed the strongest correlation C a s e A p p l i c a t i o n 1 3 - 1 3 : Osteoporosis Risk with age.53 The flexed posture observed in some elderly persons is probably due to a number of factors, some of Osteoporosis may be a problem for Dave even before which may relate to aging processes (Fig. 13-38). any significant aging because of the lack of weight- Conditions such as osteoporosis may affect posture in bearing on his his lower extremities. However, if Dave elderly persons. Osteoporosis (abnormal rarefaction of happens to enter one of the newer rehabilitation pro- bone) weakens the vertebral bodies and makes them grams that employ treadmill walking for spinal liable to fracture. After the collapse of a series of the cord\u2013injured patients, osteoporosis may not be as much anterior portions of the weakened vertebrae, the nor- of a problem. It even may be possible that Dave might mal posterior convexity of the thoracic curve increases (kyphosis). In kyphosis, the anterior trunk flexor mus- cles shorten as the posteriorly located trunk extensors lengthen. Teramoto and coworkers124 evaluated the effects of kyphosis in subjects from 20 to 90 years of age. The authors found that the extent of kyphosis signifi- cantly decreased lung volume and maximal inspiratory pressure in the elderly subjects. The ROM at the knees, hips, ankles, and trunk may be restricted because of muscle shortening and disuse atrophy. Furthermore, as voluntary postural response","Copyright \u00a9 2005 by F. A. Davis. be able to gain back muscle strength in his legs and be Chapter 13: Posture \u25a0 511 able to walk with minimal assistance.126,127 postures. Bricklayers, surgeons, carpenters, and cashiers Another aging consideration for Dave will be a assume and perform tasks in standing postures for a decrease in the thickness of the skin that occurs with majority of the working day. Others, such as secretaries, normal aging, including reductions in collagen, elastin, accountants, computer operators, and receptionists, proteoglycan, and water content. Therefore, Dave will assume sitting postures for a large proportion of the have to be extremely careful with his skin as he ages, day. Performing artists often assume asymmetrical pos- because his skin is already at risk. tures while playing a musical instrument, dancing, or acting. Running, jogging, and long-distance walking are Pregnancy dynamic postures with which very specific injuries are associated. Normal pregnancies are accompanied by weight gain, an increase in weight distribution in the breasts and Different sitting postures and their effects on abdomen, and softening of the ligamentous and con- intradiskal pressures in the lumbar spine have been nective tissue. The location of the woman\u2019s CoG analyzed.131 Wheelchair postures and the effects of dif- changes because of the increase in weight and its distri- ferent degrees of anterior-posterior and lateral pelvic bution anteriorly. Consequently, postural changes in tilt on the vertebral column and trunk muscle activity in pregnancy include an increase in the lordotic curves in sitting postures in selected work activities also have been the cervical and lumbar areas of the vertebral column, investigated.132 A large portion of the research suggests protraction of the shoulder girdle, and hyperextension that many back problems are preventable because they of the knees. Franklin and Conner-Kerr128 compared result from mechanical stresses produced by prolonged postural evaluations of 12 pregnant volunteers in their static postures in the forward stooping or sitting posi- first trimester with evaluations of the same women in tions and the repeated lifting of heavy loads. their third trimester. These investigators found changes in lumbar angle, head position, and anterior pelvic tilt. Many of the injuries sustained during both occupa- The lumbar angle increased by an average of 5.9\u040a, the tional and recreational activities belong to the category anterior pelvic tilt increased by an average of 4\u040a, and of \u201coveruse injuries.\u201d This type of injury is caused by the head become more posterior as pregnancy pro- repetitive stress that exceeds the physiologic limits of gressed from the first through the third trimesters.128 the tissues. Muscles, ligaments, and tendons are espe- These changes in posture represent adaptations that cially vulnerable to the effects of repetitive tensile forces, help to maintain the CoM centered over the BoS. whereas bones and cartilage are susceptible to injury Softening of ligamentous and connective tissues, espe- from the application of excessive compressive forces. A cially in the pelvis, sacroiliac joints, pubic symphyses, random sample of professional musicians in New York and abdomen change the support and protection revealed that violin, piano, cello, and bass players were offered by these structures and predispose pregnant frequently affected by back and neck problems.133 In a women to strains in supporting structures.129 Many larger study involving 485 musicians, the authors found women experience backache during pregnancy, and all that 64% had painful overuse syndromes. The majority of the women in the study by Franklin and Conner-Kerr of problems were associated with the musculotendinous complained of backache.128 unit, and others involved bones, joints, bursae, and muscle. String players experienced shoulder and neck Continuing Exploration: Effects of Pregnancy on problems caused by the maintenance of abnormal head Sitting and Standing Postures and neck positions, whereas flute players had shoulder problems associated with maintaining an externally Gilleard and coworkers,130 however, did not find any rotated shoulder position that has to be assumed for significant effects of pregnancy on upper body pos- prolonged periods during performances and prac- ture of nine pregnant women during sitting and tices.134 Peripheral nerve disorders, including thoracic quiet standing in films taken at intervals during ges- outlet syndrome, ulnar neuropathy at the elbow, and tation and at 8 weeks post partum. A flattening of the carpal tunnel syndrome, also appear to be common thoracolumbar curve was observed in some subjects playing-related disorders.135,136 in the sitting posture as pregnancy progressed. No significant differences were found between the post- C a s e A p p l i c a t i o n 1 3 - 1 4 : Succeptibility to partum group and a control group in the cervical or Overuse Injuries thoracic spines, but the postpartum group stood with more thoracolumbar flexion than did the con- Dave will be succeptible to the same type of upper trol group. extremity overuse injuries that are incurred by any sitting worker performing a repetitive task such as data entry. If Occupation and Recreation he chooses to use a hand-propelled wheelchair as his main method of transportation, he could be at risk for shoulder, elbow, and wrist overuse injuries. If he is able to use crutches, he may incur shoulder and wrist over- use injuries. Each particular occupational and recreational activity Each occupational and recreational activity requires has unique postures and injuries associated with these a detailed biomechanical analysis of the specific postures","Copyright \u00a9 2005 by F. A. Davis. 512 \u25a0 Section 5: Integrated Function the treatment of SCI is changing dramatically, and Dave may not be confined to a wheelchair. Advances in treat- involved to determine how abnormal and excessive ment are helping some individuals regain sufficient stresses can be relieved. Sometimes the analysis involves muscle strength to be able to walk without braces, and not only a person\u2019s posture but also features of the work- we hope that Dave will be able to benefit from these site such as chair or table height, weight of objects to be new treatment programs.126,127 lifted or carried, and weight and shape of a musical instrument or tool. Intervention may involve a combi- Summary nation of modifications of the environment, adaptations of the instrument or tools, and modifications of posture. In this chapter, we introduced the basic aspects of postural control and analyzed normal postural alignment in the erect C a s e A p p l i c a t i o n 1 3 - 1 5 : Future Progression from standing position. Also, we discussed some of the internal Static to Dynamic Postures and external forces affecting sitting and lying postures pri- marily in relation to how they may affect our patient, Dave. We have identified some of the problems that may face The kinematic and kinetic information provided in this chap- our patient, Dave, in static postures. He will now ter and previous chapters forms the basis for the analysis of progress from static sitting and standing postures to static posture as well as the dynamic posture of gait. walking. Because he is a former athlete, we hope that he may want to participate in activities such as wheel- chair basketball or in wheelchair marathons. However, Study Questions 1. What is a \u201csway envelope\u201d? 2. Is quadriceps muscle activity necessary to maintain knee extension in static erect stance? Explain your answer. 3. Is activity of the abdominal muscles necessary to keep the pelvis level in static standing posture? Explain your answer. 4. How does the lumbar curve change from standing to sitting, and what effect does the change have on interdiskal pressures? 5. In which areas of the vertebral column would you expect to find the most stress in the erect stand- ing posture? Why? 6. For the erect standing posture, identify the type of stresses that would be affecting the following structures: apophyseal joints in the lumbar region, apophyseal joint capsules in the thoracic region, anulus fibrosus in L5 to S1, anterior longitudinal ligament in the thoracic region, and the sacroiliac joints. 7. What effect might tight hamstrings have on the alignment of the following structures during erect stance: pelvis, lumbosacral angle, hip joint, knee joint, and the lumbar region of the verte- bral column? 8. How would you describe a typical idiopathic lateral curvature of the vertebral column? 9. Describe the moments that would be acting at all body segments as a result of an unexpected for- ward movement of a supporting surface. Describe the muscle activity that would be necessary to bring the body\u2019s LoG over the CoP. 10. Identify the changes in body segments that are commonly used in scoliosis screening programs. 11. Explain how our patient manages to stand when he lacks lower extremity musculature and ele- ments of postural control. 12. How do postural responses to perturbations of the erect standing posture in elderly persons com- pare with responses of children who are 1 to 6 years of age? 13. Compare a flexed lumbar spine posture with an extended posture in terms of the nutrition of the disks and stresses on ligaments and joint structures. 14. What is the relationship between the GRFV, LoG, and CoM in the erect static posture? 15. Explain how a hallux valgus deformity develops. 16. Describe the effects of a forward head posture on the zygapophyseal joints and capsules, inter- vertebral disks, vertebral column ligaments, and muscles. 17. Explain the possible effects on body structures in a young person with a double major curve (right thoracic, left lumbar) 18. Explain how changes in body position affect seat interface pressures. 19. Compare interdiskal pressures in erect standing with erect, slumped, and relaxed sitting. 20. Compare interdiskal pressures in sitting postures with pressures in lying postures.","Copyright \u00a9 2005 by F. A. Davis. Chapter 13: Posture \u25a0 513 References 1. Panjabi MM, White AA: Biomechanics in the Therapy Research Association Section on Research, Musculosketal System. Philadelphia, Churchill New Orleans, LA, 1990. Livingstone, 2001. 18. Luchies CW, Alexander NB, Schultz AB, et al.: Stepping responses of young and old adults to pos- 2. Nordin M, Frankel VH: Basic Biomechanics of the tural disturbances: Kinematics. J Am Geriatr Soc Musculoskeletal System, 3rd ed. Philadelphia, 42:506, 1994. Lippincott Williams & Wilkins, 2001. 19. Luchies CW, Wallace D, Pazdur R, et al.: Effects of age on balance assessment using voluntary and 3. Horak FB, Henry SM, Shumway-Cook A: Postural involuntary step tasks. 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Olney, PT, OT, PhD Introduction Mechanical Energy: Kinematic Approach General Features Mechanical Power and Work Gait Initiation Muscle Activity Ground Reaction Force: Sagittal Plane Analysis Kinematics Phases of the Gait Cycle Kinematics and Kinetics of the Trunk and Events in Stance Phase Upper Extremities Subphases of Stance Phase Swing Phase Trunk Gait Terminology Upper Extremities Joint Motion Sagittal Plane Joint Angles Stair and Running Gaits Frontal Plane Joint Angles Stair Gait Transverse Plane Joint Angles Running Gait Saunders\u2019 \u201cDeterminants\u201d of Gait Joint Motion and Muscle Activity Moments, Powers, and Energies Kinetics Summary Ground Reaction Force Center of Pressure Effects of Age, Gender, Assistive Devices, Kinetic Analysis and Orthoses Internal and External Forces, Moments, and Conventions Moment Conventions Age Sagittal Plane Moments Gender Frontal Plane Moments Assistive Devices Transverse Plane Moments Orthoses Energy Requirements Mechanical Energy of Walking Abnormal Gait Structural Impairment Functional Impairment Pain Adaptation\/Compensation Introduction Human locomotion, or gait, may be described as a In human locomotion (ambulation, gait), the reader is translatory progression of the body as a whole, pro- given the opportunity to discover how individual joints and muscles function in an integrated manner both to duced by coordinated, rotatory movements of body seg- maintain upright posture and to produce motion of the ments.1 The alternating movements of the lower body as a whole. Knowledge of the kinematics and kinetics of normal ambulation provides the reader with extremities essentially support and carry along the head, a foundation for analyzing, identifying, and correcting arms, and trunk (HAT).2 HAT constitutes about 75% of abnormalities in gait. total body weight, with the head and arms contributing about 25% of total body weight and the trunk con- tributing the remaining 50%.3 Walking is probably the most comprehensively studied of all human movements, and the variety of technologies, coupled with the diver- 517","Copyright \u00a9 2005 by F. A. Davis. 518 \u25a0 Section 5: Integrated Function a several-segment body with joint centers and centers of mass. One or more force platforms provide simul- sity of disciplinary perspectives, has produced a complex taneous foot-floor forces. EMG systems provide simul- and sometimes daunting literature. Nevertheless, the taneous information from surface or, sometimes, biomechanical requirements of the movement that indwelling electrodes. An excellent and engaging explain gait are logical and easily understood if the report of the evolution of clinical gait analysis, includ- detail is not permitted to cloud comprehension. The ing motion analysis and EMG, can be found in purpose of this chapter is to provide this comprehen- Sutherland\u2019s articles.5,6 sion of gait that will serve as the foundation for analysis of normal walking and of gait deviations. To understand gait, let us first identify the funda- mental purposes. Winter7 proposed the following five General Features main tasks for walking gait: In early gait analysis, investigators used cinemato- 1. maintenance of support of the HAT: that is, pre- graphic film. Until about 20 years ago, sophisticated venting collapse of the lower limb analysis required frame-by-frame hand-digitizing of markers that had been placed on body landmarks. 2. maintenance of upright posture and balance of the These data were coupled with knowledge of the center body of pressure (CoP) of the foot-floor forces derived from a force platform to give complete, if simplified, kinetic 3. control of the foot trajectory to achieve safe ground information. This is referred to as the inverse dynamic clearance and a gentle heel or toe landing approach with link segment mechanics. Electrogonio- meters fastened to joints were also commonly used to 4. generation of mechanical energy to maintain the describe joint motion and still have applications.4 present forward velocity or to increase the forward Similarly, electromyography (EMG) has been used for velocity many decades, although the expectation that it would be possible to convert those signals to force values in 5. absorption of mechanical energy for shock absorp- simple, useful ways has not been fulfilled. The past two tion and stability or to decrease the forward velocity decades have witnessed an explosion of technical of the body advancements in motion analysis whose greatest virtue is the ability to collect and process large amounts of The professional staff at Rancho Los Amigos data. As with the development of any science, the National Rehabilitation Center in California identified knowledge available far exceeds its current applica- three main tasks in walking: (1) weight acceptance tions. A modern gait laboratory (Fig. 14-1) includes (WA), (2) single-limb support, and (3) swing limb some kind of motion analysis system that gives precise advancement.8 Although worded differently, these con- marker locations that are subsequently used to model cepts correspond to Winter\u2019s first three tasks. However, the body moves only because energy is generated by means of concentric contraction of muscle groups. In fact, normal walking at a constant velocity requires small bursts of energy from three muscle groups at two important times in the gait cycle. Likewise, unless energy is removed with each step through eccentric muscle contractions, the velocity of walking would con- tinue to increase. \u25b2 Figure 14-1 \u25a0 A modern gait laboratory. 14-1 Patient Case Marlene Brown is a 63-year-old woman who sustained a stroke 15 days ago and shows right hemiparesis of her arm and leg. She has been in a rehabilitation unit for 10 days and is making good progress walking, although she is ambulating at only 0.20 m\/sec. She has weakness in several muscle groups of her lower limb, notably the ankle plantarflexors, ankle dorsiflexors, knee exten- sors, and hip flexors, with distal muscles more affected than prox- imal ones. Particularly troublesome is the inability to clear her foot during the swing phase of gait. She uses a cane with a large base (a four-point cane) in her unaffected hand for stability. What will you expect to be the main difficulties with her gait, and what will you attempt to change with rehabilitation? \u25a0 Gait Initiation Gait initiation may be defined as a stereotyped activity that includes the series or sequence of events that occur from the initiation of movement to the beginning of the gait cycle. Gait initiation begins in the erect stand-","Copyright \u00a9 2005 by F. A. Davis. ing posture with an activation of the tibialis anterior Chapter 14: Gait \u25a0 519 and vastus lateralis muscles, in conjunction with an inhibition of the gastrocnemius muscle. Bilateral con- fected leg. The time when the affected leg initiates gait centric contractions of the tibialis anterior muscle the pattern of events is practically the same as in a non- (pulling on the tibias) results in a sagittal torque that affected person, but when the person with paralysis inclines the body anteriorly from the ankles. Initially, attempts gait initiation with the nonafffected leg, the the CoP is described as shifting either posteriorly and pattern of events is erratic, and stability is seriously laterally toward the swing foot (foot that is preparing to threatened10. take the first step)9 or posteriorly and medially toward the supporting limb.10 Abduction of the swing hip Kinematics occurs almost simultaneously with contractions of the tibialis anterior and vastus lateralis muscles and pro- Phases of the Gait Cycle duces a coronal torque that propels the body toward the support limb. According to Elble and colleagues,9 Gait has been divided into a number of segments that the support limb hip and knee flex a few degrees (3\u040a to make it possible to describe, understand, and analyze 10\u040a), and the CoP moves anteriorly and medially toward the events that are occurring. A gait cycle spans two suc- the support limb. This anterior and medial shift of cessive events of the same limb, usually initial contact the CoP frees the swing limb so that it can leave the (also called heel contact or heel strike) of the lower ground. The gait initiation activity ends when either extremity with the supporting surface. During one gait the stepping or swing extremity lifts off the ground9 or cycle, each extremity passes through two major phases: when the heel strikes the ground.10 The total duration a stance phase, when some part of the foot is in contact of the gait initiation phase is about 0.64 second.8 A with the floor, which makes up about 60% of the gait healthy individual may initiate gait with either the right cycle,11 and a swing phase, when the foot is not in con- or left lower extremity, and no changes will be seen in tact with the floor, which makes up the remaining the pattern of events. 40%11,12 (Fig. 14-2). There are two periods of double support occurring between the time one limb makes C a s e A p p l i c a t i o n 1 4 - 1 : Avoiding Instability initial contact and the other one leaves the floor at toe- in Initiation of Gait off. At a normal walking speed, each period of double support occupies about 11% of the gait cycle, which Patients with hemiplegia (one-sided paralysis), like Ms. makes a total of approximately 22% for a full cycle.13 Brown, demonstrate a considerable difference between The body is thus supported by only one limb for nearly gait initiation that begins with a step by the affected leg 80% of the cycle. The approximate value of 10% and gait initiation that begins with a step by the nonaf- for each double-support phase is usually used. The approximate value of 10% for each double-support Right Right Right Right Left Right Right Right initial foot flat 7% midstance heel off initial toe off midswing initial contact contact 60% contact 0% Left toe off 30% 40% 50% 100% 10% 90% 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% GAIT CYCLE RIGHT STANCE RIGHT SWING Left LEFT SWING LEFT STANCE stance Double Right single Double Left single support limb support support limb support \u25b2 Figure 14-2 \u25a0 A gait cycle spans the period between initial contact of the reference extremity (right) and the successive contact of the same extremity. This figure shows the gait cycle with major events: stance and swing phases for each limb and periods of single and double sup- port. The stance phase constitutes 60% of the gait cycle, and the swing phase constitutes 40% of the cycle at normal walking speeds. Increases or decreases in walking speeds alter the percentages of time spent in each phase.","Copyright \u00a9 2005 by F. A. Davis. 520 \u25a0 Section 5: Integrated Function % Gait 0% 10% 20% 30% 40% 50% 60% Cycle Traditional Event Phase Phase Event Initial Foot Heel off Toe off % Gait contact flat 7% 40% 60% Cycle 0% Heel strike Midstance Push off Rancho Loading Midstance Terminal stance Preswing Los Amigos response Initial Toe off 20% Midstance 40% Initial Initial contact (left) 30% contact contact 10% (left) 50% 0% 30% 60% 10% 50% 0% \u25b2 Figure 14-3 \u25a0 The stance phase of a gait cycle of the right lower limb with comparisons between traditional and Rancho Los Amigos terminologies. The events that delimit subphases are shown for each terminology and expressed as percentages of full gait cycle. FF, foot flat; HO, heel-off; IC, initial contact; IC(L), initial contact of left (contralateral) limb; MS, midstance. phase is usually assigned to each of the two double- and toe-off (RLA and T). In both conventions, the gait support periods. cycle is divided into percentiles that will be used to clar- ify events and phases. Values for normal walking appear The two most common terminologies for the fur- in the figures. ther division of these major phases into sub phases are shown in Figures 14-3 and 14-4, where one will be \u25a0 Events in Stance Phase referred to as traditional (T), and one derived from Rancho Los Amigos (RLA). Both terminologies define 1. Heel contact or heel strike (T) refers to the instant at \u201cevents\u201d that mark the start and end of defined sub- which the heel of the leading extremity strikes the phases. ground (Fig. 14-5). The word \u201cstrike\u201d is actually a misnomer inasmuch as the horizontal velocity Figure 14-3 identifies the events delimiting the reduces to about 0.4 m\/sec and only 0.05 m\/sec ver- major phases in both terminology conventions as initial tically.14 Initial contact (T and RLA) refers to the contact (T and RLA) or heel contact or heel strike (T) instant the foot of the leading extremity strikes the ground.8 In normal gait, the heel is the point of con- Traditional Early swing Midswing Late swing tact. In abnormal gait, it is possible for the whole 60-75% 75-85% 85-100% foot or the toes, rather than the heel, to make initial contact with the ground. The term initial contact Ranchos Initial swing Midswing Terminal swing will be used in referring to this event. Los Amigos 60-73% 73-87% 87-100% 2. Foot flat (T) in normal gait occurs after initial contact \u25b2 Figure 14-4 \u25a0 The swing phase of a gait cycle of the right at approximately 7% of the gait cycle (Fig. 14-6). It lower limb with comparisons between traditional and Rancho Los is the first instant during stance when the foot is flat Amigos terminologies. Differences are insignificant. on the ground. 3. Midstance (T) is the point at which the body weight is directly over the supporting lower extremity (Fig. 14-7), usually about 30% of the gait cycle. 4. Heel-off (T) is the point at which the heel of the ref- erence extremity leaves the ground (Fig. 14-8), usu- ally about 40% of the gait cycle. 5. Toe-off (T and RLA) is the instant at which the toe of the foot leaves the ground (Fig. 14-9), usually about 60% of the gait cycle.","Copyright \u00a9 2005 by F. A. Davis. Chapter 14: Gait \u25a0 521 \u25b2 Figure 14-7 \u25a0 Midstance is the point at which the body weight passes directly over the supporting lower extremity. \u25b2 Figure 14-5 \u25a0 Initial contact refers to the instant at which gait cycle and ends with heel-off at about 40% of any part of the reference extremity contacts the supporting surface. the gait cycle. Midstance phase (RLA) begins when If the heel is first, it may be referred to as heel contact or heel strike. the contralateral extremity lifts off the ground at Right heel strike in the diagram constitutes the beginning of the about 11% of the gait cycle and ends when the body stance phase of gait for the right lower extremity. is directly over the supporting limb at about 30% of the gait cycle, which makes it a much smaller por- \u25a0 Subphases of Stance Phase tion of stance phase than the T midstance phase. 4. Terminal stance (RLA) begins when the body is 1. Heel strike phase (T) begins with initial contact and directly over the supporting limb at about 30% of ends with foot flat and occupies only a small per- the gait cycle and ends a point just before initial centage of the gait cycle (see Fig. 14-3). contact of the contralateral extremity at about 50% of the gait cycle. 2. Loading response (RLA), or WA, begins at initial con- 5. Push-off phase (T) begins with heel-off at about 40% tact and ends when the contralateral extremity lifts of the gait cycle and ends with toe-off at about 60% off the ground at the end of the double-support of the gait cycle (see Fig. 14-2). phase8 and occupies about 11% of the gait cycle (see 6. Preswing (RLA) is the last 10% of stance phase and Fig. 14-3). begins with initial contact of the contralateral foot (at 50% of the gait cycle) and ends with toe-off (at 3. Midstance phase (T) begins with foot flat at 7% of the 60%). \u25b2 Figure 14-6 \u25a0 Foot flat occurs immediately after initial con- \u25b2 Figure 14-8 \u25a0 Heel-off is the point at which the heel of the tact and is defined as the point at which the foot is flat on the ground. reference extremity (right extremity in the diagram) leaves the sup- porting surface.","Copyright \u00a9 2005 by F. A. Davis. 522 \u25a0 Section 5: Integrated Function For most purposes, including patient report writ- ing, it is preferable to refer to events as occurring in early, middle, or late stance phase or in early, middle, or late swing phase, and this will be the practice in this chapter. For detailed description or quantitative analy- sis, more specific events and phases may be needed, but it is most important that the student grasp the overall picture and understand the major events of gait, which can become buried in excessive terminology. \u25b2 Figure 14-9 \u25a0 Toe-off is defined as the point in which only CONCEPT CORNERSTONE 14-1: Normative Values the toe of the reference extremity (right extremity) is touching the for Time and Distance Gait Variables ground. The following mean and standard deviation (SD) or range of mean \u25a0 Swing Phase values for time and distance variables for normal gait are derived from the classic work of Finley and Cody,15 who surreptitiously 1. Acceleration, or early swing phase (T), begins once the measured the gait of 1100 pedestrians, and from Kadaba et al.,16 toe leaves the ground and continues until midswing, Oberg et al.,17 and colleagues of Ranchos Los Amigos National or the point at which the swinging extremity is Rehabilitation Center8 who obtained gait laboratory measure- directly under the body (see Fig. 14-3). ments (Table 14-1). 2. Initial swing (RLA) begins when the toe leaves the Gait Terminology ground and continues until maximum knee flexion occurs. Time and distance are two basic parameters of motion, and measurements of these variables provide a basic 3. Midswing (T) occurs approximately when the description of gait. Temporal variables include stance extremity passes directly beneath the body, or from time, single-limb and double-support time, swing time, the end of acceleration to the beginning of deceler- stride and step time, cadence, and speed. The distance ation. Midswing (RLA) encompasses the period from variables include stride length, step length and width, maximum knee flexion until the tibia is in a vertical and degree of toe-out. These variables, derived in clas- position. sic research of over 30 years ago, provide essential quantitative information about a person\u2019s gait and 4. Deceleration (T), or late swing phase, occurs after should be included in any gait description.8,15\u201318 Each midswing when limb is decelerating in preparation variable may be affected by such factors as age, sex, for heel strike. Terminal swing (RLA) includes the height, size and shape of bony components, distribu- period from the point at which the tibia is in the ver- tion of mass in body segments, joint mobility, muscle tical position to a point just before initial contact. strength, type of clothing and footgear, habit, and psy- chological status. However, a discussion of all the fac- tors affecting gait is beyond the scope of this text. Stance time is the amount of time that elapses dur- ing the stance phase of one extremity in a gait cycle. Single-support time is the amount of time that Table 14-1 Normative Values for Time and Distance Variables Characteristic Male: Mean (SD) Female: Mean (SD) Source Speed of walking in meters 1.37 (0.22) 1.23 (0.22) Finley and Cody15 per second (m\/sec) 1.37 (0.17) 1.32 (0.16) RLA8 Range of means, 1.22\u20131.32 Range of means, 1.10\u20131.29 Oberg et al.17 Length of one 1.34 (0.22) 1.27 (0.16) Kadaba et al.16 stride in 1.48 (0.18) 1.27 (0.19) Finley and Cody15 meters (m) 1.48 (0.15) 1.32 (0.13) RLA8 Range of means, 1.23\u2013130 Range of means 1.07\u20131.19 Oberg et al.17 Step cadence in 1.41 (0.14) 1.30 (0.10) Kadaba et al.16 steps per 110 (10) 116 (12) Finley and Cody15 minute 111 (7.6) 121 (8.5) RLA8 Range of means, 117\u2013121 Range of means, 122\u2013130 Oberg et al.17 112 (9) 115 (9) Kadaba et al.16","Copyright \u00a9 2005 by F. A. Davis. elapses during the period when only one extremity is Chapter 14: Gait \u25a0 523 on the supporting surface in a gait cycle. Step duration refers to the amount of time spent Double-support time is the amount of time spent during a single step. Measurement usually is expressed with both feet on the ground during one gait cycle. The as seconds per step. When there is weakness or pain in percentage of time spent in double support may be an extremity, step duration may be decreased on the increased in elderly persons and in those with balance affected side and increased on the unaffected disorders. The percentage of time spent in double sup- (stronger) or less painful side. port decreases as the speed of walking increases. Cadence is the number of steps taken by a person Stride length is the linear distance between two suc- per unit of time. Cadence may be measured as the num- cessive events that are accomplished by the same lower ber of steps per second or per minute, but the latter is extremity during gait.11 In general, stride length is more common: determined by measuring the linear distance from the point of one heel strike of one lower extremity to the Cadence \u03ed number of steps\/time point of the next heel strike of the same extremity (Fig. 14-10). The length of one stride is traveled during one A shorter step length will result in an increased gait cycle and includes all of the events of one gait cadence at any given velocity.20 Lamoreaux found that cycle. Stride length also may be measured by using when a person walks with a cadence between 80 and other events of the same extremity, such as toe-off, but 120 steps per minute, cadence and stride length had a in normal gait, two successive heel strikes are usually linear relationship.11 As a person walks with increased used. A stride includes two steps, a right step and a left cadence, the duration of the double-support period step. However, stride length is not always twice the decreases. When the cadence of walking approaches length of a single step, because right and left steps may 180 steps per minute, the period of double support dis- be unequal. Stride length varies greatly among individ- appears, and running commences. A step frequency or uals, because it is affected by leg length, height, age, cadence of about 110 steps per minute can be consid- sex, and other variables. Stride length can be normal- ered as \u201ctypical\u201d for adult men; a typical cadence for ized by dividing stride length by leg length or by total women is about 116 steps per minute.3 Sometimes body height. Stride length usually decreases in elderly authors report values that refer to stride cadence, persons12,13,19 and increases as the speed of gait which is exactly half the step cadence. increases.20 The length of one stride is traveled during one gait cycle. Walking velocity is the rate of linear forward motion of the body, which can be measured in meters Stride duration refers to the amount of time it takes or centimeters per second, meters per minute, or miles to accomplish one stride. Stride duration and gait cycle per hour. Scientific literature favors meters per second. duration are synonymous. One stride, for a normal The term velocity implies that direction is specified, adult, lasts approximately 1 second.21 Complex fluctua- although this is frequently not included, and the more tions in stride duration during slow, normal, and fast correct term walking speed should be used if direction walking have been identified as being statistically corre- is not reported. In instrumented gait analyses, walking lated with variations in stride duration thousands of velocity is used, inasmuch as the velocities of the seg- strides earlier. These fluctuations appear to be a char- ments involve specification of direction: acteristic of normal gait.22 Walking velocity (meters\/second) \u03ed distance walked Step length is the linear distance between two suc- (meters)\/time (seconds) cessive points of contact of opposite extremities. It is usu- ally measured from the heel strike of one extremity to Women tend to walk with shorter and faster steps the heel strike of the opposite extremity (see Fig. than do men at the same velocity.20 Increases in velocity 14-10). A comparison of right and left step lengths will up to 120 steps per minute are brought about by in- provide an indication of gait symmetry. The more equal creases in both cadence and stride length, but above the step lengths, the more symmetrical is the gait. 120 steps per minute, step length levels off, and speed Variability in step length is at a minimum when the increases are achieved with only cadence increases. ratio of step length to step rate is about 0.006 m\/step or at a person\u2019s preferred walking speed.23 Speed of gait may be referred to as slow, free, and fast. Free speed of gait refers to a person\u2019s normal walk- ing speed; slow and fast speeds of gait refer to speeds slower or faster than the person\u2019s normal comfortable Right step length Left step length Left foot angle Right foot angle \u1b63 Figure 14-10 \u25a0 Stride length, step length, and width shown Stride length with foot angle placements. The midpoint of the heel is used as a point of reference for measuring step width.","Copyright \u00a9 2005 by F. A. Davis. 524 \u25a0 Section 5: Integrated Function must have equal stride lengths but may have unequal step lengths, you understand the concepts of steps walking speed, designated in a variety of ways. There is and strides. a certain amount of variability in the way an individual elects to increase walking speed. Some individuals in- Joint Motion crease stride length and decrease cadence to achieve a fast walking speed. Other individuals decrease the Another way in which gait may be described is through stride length and increase cadence. measuring the trajectories of the lower extremities and the joint angles. Sophisticated equipment\u2014at first, stro- Step width, or width of the walking base, may be boscopic photography; then cinematography and elec- found by measuring the linear distance between the trogoniometers; and, more recently, many types of midpoint of the heel of one foot and the same point on computerized motion analysis systems\u2014have provided the other foot (see Fig. 14-10). Step width has been comprehensive information about joint angles and found to increase when there is an increased demand limb trajectories in normal and abnormal gait.5,6,26\u201328 for side-to-side stability, such as occurs in elderly per- The most valuable analyses express findings in joint sons and in small children. In toddlers and young chil- angle plots, frequently three-dimensional. dren, the center of gravity is higher than in adults, and a wide base of support is necessary for stability. In the Less sophisticated and less objective methods are normal population, the mean width of the base of sup- used in observational gait analysis, whereby an observer port is about 3.5 inches and varies within a range of 1 to makes a judgment as to whether a particular joint angle 5 inches. or motion varies from a norm. Usually observational gait analysis is used to hypothesize causes of deviations and Degree of toe-out represents the angle of foot direct treatment objectives. One disadvantage of the placement (FP) and may be found by measuring the observational method of analysis is that it requires a angle formed by each foot\u2019s line of progression and a great deal of training and practice to be able to identify line intersecting the center of the heel and the second the particular segment of gait in which a particular joint toe. The angle for men normally is about 7\u040a from the angle deviates from a norm while a person is walking. line of progression of each foot at free speed walking Videotaping with slow playback can improve this greatly. (see Fig. 14-10).12 The degree of toe-out decreases as Another disadvantage of observational gait analysis the speed of walking increases in normal men.12 methods is that they frequently have low reliability, although recent reports have identified some variables Power generation is accomplished when muscles and conditions under which reliability is satisfactory.29 shorten (concentric contraction). They do positive work and add to the total energy of the body. Power is \u25a0 Sagittal Plane Joint Angles the work or energy value divided by the time over which it is generated. The power of muscle groups perform- The approximate range of motion (ROM) needed in ing gait is calculated through an inverse dynamic normal gait and the time of occurrence of the maxi- approach. The power generated or absorbed across a mum flexion and extension positions for each major joint is the product of the net internal moment and the joint may be determined by examining the joint angle net angular velocity across the joint.24 If both are in the profiles in Figures 14-11 and 14-12. The standard devia- same direction (flexors flexing, extensors extending, tion bars (dotted lines) around the mean profile (solid for example), positive work is being accomplished by lines) give an indication of how much person-to-person energy generation. The most important phases of variation exists, demonstrating that 67% of subjects\u2019 power generation and absorption have been designated values fell within the range shown. Results reported in by joint (H \u03ed hip, K \u03ed knee, A \u03ed ankle) and plane (S gait studies vary with age, gender, and walking speed of \u03ed sagittal, F \u03ed frontal, T \u03ed transverse).25 subjects and with the method of analysis. Data pre- sented here were derived from three-dimensional Power absorption is accomplished when muscles analyses.24 For simplicity, the mean value shown in the perform a lengthening (eccentric) contraction. They figures will be referred to in the text, taken to the near- do negative work and reduce the energy of the body. If est 5\u040a, and, to remind the reader that these are not joint motion and moment are in opposite directions, fixed values, the \u201capproximately\u201d sign (~) will be used. negative work is being performed through energy In the anatomical position, the hip, knee, and ankle are absorption. at approximately 0\u040a. Flexion for the hip and knee and dorsiflexion for the ankle are given positive values, and C a s e A p p l i c a t i o n 1 4 - 2 : Effects on Time and extension and plantarflexion are given negative values. Distance Gait Variables From the appearance of, first, the hip in Figure 14- Ms. Brown walks with a speed of 0.20 m\/sec and a 11, it can be seen that the hip achieves maximum flex- cadence of 25 steps per minute. It is evident even on ion (~\u03e920\u040a) around initial contact at 0% of the gait visual inspection that double-support time is consider- cycle and its most extended position (~\u03ea20\u040a) at about ably longer than normal on both steps. Stance phase 50% of the gait cycle, between heel-off and toe-off. The is more than 60% of the gait cycle on her affected side, knee is straight (0\u040a) at initial contact and nearly straight but she spends an even greater proportion of time in stance on the unaffected side. Her left step length (unaffected side) is shorter than her right (affected side), but her stride lengths are equal. Why? If you understand that a person walking in a straight line","Copyright \u00a9 2005 by F. A. Davis. Chapter 14: Gait \u25a0 525 JOINT ANGLES SAGGITAL PLANE +20\u02da 15\u02da 0\u02da 10-20\u02da flexion flexion flexion hyperextension 0\u02da 15\u02da 5\u02da 0\u02da flexion flexion 0\u02da 5\u02da 5\u02da 0\u02da Plantar Dorsal Initial contact flexion flexion Heel off 0% 40% Foot flat Midstance 10% 30% 10-20\u02da 20\u02da 30\u02da 30\u02da hyperextension flexion flexion flexion 30\u02da 60\u02da 30\u02da flexion flexion flexion 0\u02da 20\u02da 10\u02da 0\u02da 0\u02da Plantar Plantar Midswing Deceleration flexion flexion Toe off Acceleration 60% DEGREES HIP DEGREES KNEE dorsi ANKLE flex ext flex Saggital Sagittal 70 DEGREES Joint Angle 60 10 ext 30 50 plant 20 40 0 10 30 -10 0 20 -20 -10 10 -30 -20 -30 0 20 40 60 80 100 20 40 60 80 100 20 40 60 80 100 % Gait Cycle % Gait Cycle % Gait Cycle \u25b2 Figure 14-11 \u25a0 Joint angles in degrees at the hip, knee, and ankle angles in the sagittal plane. The dotted lines in the angle diagrams represent the standard deviation values, and the solid lines represent the mean values. (Joint angle diagrams redrawn from Winter DA, Eng JJ, Isshac MG: A review of kinetic parameters in human walking. In Craik RL, Otis CA [eds]: Gait Analysis: Theory and Application, pp 263-265. St. Louis, Mosby\u2013Year Book, 1994, with permission from Elsevier.)","526 A HIP JOINT A FRONTAL Frontal Joint Angle KNE ANGLE (deg) 12.5 ANGLE (deg) 5.0 abduction adduction 10.5 abduction adduction 2.5 0.0 7.5 20 40 60 80 100 -2.5 20 4 5.0 -5.0 2.5 -7.5 0.0 -10.0 -2.5 -5.0 0 -7.5 0 % Gait Cycle % Gait B TRANSVER HIP KNE Transverse Joint Angle DEGREES 3 DEGREES 10.0 Ext. Rot Int.Rot 1 Ext. Rot Int.Rot 5.0 -1 0.0 -3 20 40 60 80 100 20 4 -5 -5.0 -7 -10.0 0 0 \u25b2 Figure 14-12 \u25a0 A. Joint angles in degrees in the frontal plane at the hip, knee, and ankle. and transverse planes redrawn from Winter DA, Eng JJ, Isshac MG: A review of kinetic parameters 265. St. Louis, Mosby\u2013Year Book, 1994, with permission from Elsevier.)","ANGLES ANKLE L PLANE EE ANGLE (deg) 15.0 eversion inversion 10.0 40 60 80 100 5.0 20 40 60 80 100 0.0 -5.0 0 % Gait Cycle t Cycle RSE PLANE ANKLE EE 15.0 DEGREES 10.0 Ext. Rot Int.Rot 5.0 0.0 40 60 80 100 -5.0 20 40 60 80 100 0 % Gait Cycle . B. Transverse plane hip knee and ankle motion in degrees. (Joint angle diagrams for the frontal s in human walking. In Craik RL, Otis CA [eds]: Gait Analysis: Theory and Application, pp 263-","Copyright \u00a9 2005 by F. A. Davis. again just before heel-off at 40% of the gait cycle. Chapter 14: Gait \u25a0 527 During the swing phase, the hip reaches its maximum flexion of ~\u03e960\u040a at ~70% of the gait cycle. (Note that a Saunders\u2019 \u201cDeterminants\u201d of Gait small knee flexion phase occurring at 10% of the gait cycle peaks at ~\u03e915\u040a.) The ankle reaches maximum Another way of looking at gait using \u201cdeterminants\u201d was dorsiflexion of ~\u03e97\u040a at approximately heel-off at about first described by Saunders and coworkers in 1953.30 40% of the gait cycle and reaches maximum plan- The \u201cdeterminants\u201d were supposed to represent adjust- tarflexion (\u03ea25\u040a) at toe-off (60%). ments made by the pelvis, hips, knees, and ankles that help to keep movement of the body\u2019s center of mass to CONCEPT CORNERSTONE 14-2: Hip, Knee, and Ankle a minimum. By decreasing the vertical and lateral Range of Motion Needed for Normal Walking excursions of the body\u2019s center of mass it was thought that energy expenditure would be less and gait more For normal walking, we need a hip ROM from approximately 20\u040a efficient. The determinants are pelvic rotation in the of extension to 20\u040a of flexion, a knee range from straight (0\u040a) to 60\u040a transverse plane of about 8\u040a, which is thought to flatten flexion, and an ankle range from 25\u040a of plantarflexion to 7\u040a dorsi- the arc of the passage of the center of mass; lateral flexion. If these joint ranges are not available, a gait pattern would pelvic tilt in the frontal plane, in which the pelvis drops be expected to show considerable deviation from the norm. on the side of the swing leg, which is thought to keep the peak of the rise lower than if it did not drop; knee \u25a0 Frontal Plane Joint Angles flexion in stance phase, which should keep the center of mass from rising as much as it would have to if the During the first 20% of stance, the pelvis or the con- body had to pass over a completely extended knee; tralateral side drops about 5\u040a, which results in adduc- interaction of the movements of the foot, knee, and tion of the hip (see Fig. 14-12A). The hip abducts ankle, which may work together to minimize the excur- smoothly to about 5\u040a of abduction, peaking about toe- sion of the center of mass; and physiologic valgus of the off, then returns to neutral at initial contact. The knee knee, which is said to reduce side-to-side movement of remains more or less neutral, except for a brief abduc- the center of mass in frontal plane. Although still use- tion peaking at about 7\u040a in midswing, and then returns ful as descriptors of gait, biomechanical analyses that to neutral.28 From the figure, it can be seen that the were not available at Saunders\u2019 time do not support ankle everts from about 5\u040a of inversion to 5\u040a of eversion these factors as guiding principles of walking (see the in early stance and inverts about 15\u040a during push-off. following Continuing Exploration). \u25a0 Transverse Plane Joint Angles Continuing Exploration: Problems with Saunders\u2019 \u201cDeterminants\u201d Theory The hip, knee, and ankle show a great deal of variabil- ity in profiles. With regard to the laboratory (global) The premise upon which the classic \u201cdeterminants\u201d coordinates, the hip externally rotates until approxi- theory of Saunders30 was based is erroneous: that the mately midswing and then internally rotates to near energy costs of the body are reflected in the move- neutral before initial contact (see Fig. 14-12B). The ment of the center of mass. Movements of limbs in knee joint remains relatively neutral throughout most opposite directions tend to cancel each other and do of the gait cycle but externally rotates in late stance not appear as energy costs, despite the fact that until about foot flat. The ankle has three rapid reversals energy is required both to accelerate and to deceler- of rotation from about 40% of the gait cycle until initial ate them. Furthermore, energy conservation be- contact and reaches a point of maximum external rota- tween potential and kinetic types, which is discussed tion at about foot flat. later in the chapter, was not considered. Authors more than two decades ago31 and recently32 con- C a s e A p p l i c a t i o n 1 4 - 3 : Effects on Joint cluded that energy conservation of the HAT segment Angle Patterns is very high in normal walking, and that lower limb movement dominates the energy picture. Other An examination of videotaped joint angles reveals that research also questions the influence of the \u201cdeter- Ms. Brown has no knee flexion phase in early stance, minants\u201d on the excursion of the HAT.33,34 In sum- and she tends to fully extend her knee in midstance. mary, Saunders\u2019 theory of the determinants of She has minimal ability to dorsiflex her ankle and has walking probably should be abandoned. difficulty clearing the floor with her affected limb as a result of poor dorsiflexion and because she does not Kinetics bend her knee more than a few degrees during swing phase. Instead, she tends to lift her pelvis (\u201chike\u201d) to Ground Reaction Force clear her foot during swing on the affected side. Her affected hip does not extend beyond neutral. How do When a person takes a step, forces are applied to the Ms. Brown\u2019s joint angle profiles vary from the normal in ground by the foot and by the ground to the foot. stance and swing phases? These forces are equal in magnitude but opposite in direction. We are usually more interested in the forces being applied to the foot, which are termed ground"]
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