The Unique Features of Human Foot - Book Report/Review Example

FOOT AND GAIT Table of Contents INTRODUCTION 4 FOOT ARCHES 4 Longitudinal Arches 6 Medial Longitudinal Arch 7 Lateral Longitudinal Arch 7 Transverse Arch 8 MECHANISM OF WALKING 8 The Six Determinants of Gait Theory 9 The Inverted Pendulum Model 10 Mechanism of Dynamic Walking 13 GAIT 15 NORMAL GAIT 16 ABNORMAL GAIT 17 Musculoskeletal Causes of abnormal gait patterns: 18 Neurological Causes of Abnormal Gait: 20 Conclusion 21 References 22 Bipedalism is a unique ability of the human beings that involves locomotion with the help of two feet along with maintenance of balance. Besides the many joints of the lower limb, the longitudinal and transverse foot arches play a significant role in facilitating human gait. The structure of these arches is maintained by the intricate bones and connective tissues that enable the unique function of human gait. The human gait has intrigued mankind since the beginning of civilization and several researches have contributed to the understanding of the mechanism of walking. The attention on the understanding gait mechanism has stemmed from the realization of the importance of normal gait on one hand; and on the debilitating impact of abnormal gait that itself can arise from varied neuromuscular and musculoskeletal causes since these three systems; skeletal, muscular and nervous; are involved in accomplishment of the feat of walking. This article makes an attempt to understand the anatomical and functional aspects of walking by reviewing the available literature. FOOT & HUMAN GAIT INTRODUCTION Human beings have been bestowed with the unique though not exclusive ability of bipedalism without contributing a thought to it. This is an ability the lack of which leads to severe disability, dependence and hence distress (Nutt et al., 1993). The significance and uniqueness of this ability, has captivated the attention of man since the beginning of history. Illustrations of walking men and women have been found in caves and mythological literatures of all cultures describe walking devices. Authors such as Aristotle and Borelli have made investigations in to science of locomotion and have written descriptive treatise on study of human gait and muscular movement and body dynamics respectively (Zielinska, 2004). A clear understanding of human locomotion, the human foot and gait; is of immense significance for both health and sports management. This review addresses the unique features of human foot, types of arches, mechanism of walking and human gait; both normal and abnormal; on the basis of available literature. FOOT ARCHES Human body comprises multiple joints designed to enable functional stability and functional locomotion. However, almost all joints are capable of bestowing only one of these functions; i.e. either mobility or locomotion, except the ankle (talcoural) and foot joint. These joints of the foot are therefore unique in that they form a complex that at times renders the foot mobile and at other makes it stable. This unique ability is provided by the foot anatomy, especially the shape of the foot bones (Riegger, 1988). This section enables an understanding of foot stability and mobility by discussing the foot anatomy with special reference to foot arches. Figure 1: Human Foot Anatomy The foot is made of 26 bones including 7 tarsals (the calcaneus, talus, navicular, cuboi; and medial, intermediate and lateral cuneiforms), 5 metatarsals, and 14 phalanges; along with tibia and fibula. These 26 bones of the foot form multiple arches (figure 1). In between the calcaneus and metatarsal heads are formed two longitudinal arches: the medial and lateral arches; by interlocking together of the 14 phalanges. Posterior to metatarsal head is formed a comparatively less clearly identified transverse arch. The three arches together constitute the plantar volt. The plantar volt is not present in a new born but develops usually by the time he reaches approximately six years of age (Riegger, 1988). The maintenance of the arches is ensured by the unique shape of the foot bones, foot musculature and their functional ability; and the connective tissue including multiple ligaments and tendons that provide additional support. The elasticity of the arches provides a ‘spring’ to the walk thus reducing energy consumption during running and walking by alleviating forces during impact (Chang et al., 2010). Figure 2: Foot Arches: Transverse and Longitudinal Figure 3: Medial and Lateral Longitudinal Arches Longitudinal Arches Longitudinal arches are the key features of the human foot compared to the animal foot. It enables prolonged walking but renders the foot comparatively unfit for climbing and running. It serves the twin functions of enabling shock absorption during walking and allowing vessels and nerves to reach the forefoot without being damaged. Most importantly it provides stability by functioning as the long lever arm for the Achilles tendon rendering the calcaneous and metatarsal joint rigid allowing for rotation at the ankle as the forces at the Achilles tendon pass from the calcaneal tuberosity to the metatarsal head. This rigidity of the lever provides gait propulsion that enables bipedalism in humans (Greisberg, 2007). Medial Longitudinal Arch The medial longitudinal arch is the longest and clinically most significant foot arch (Chang et al., 2010). It curves up to 15-18mm above the ground, reaching the level of the navicular, and denotes the part of the foot absent from the footprint; but is most clearly visible in the foot. It is formed by the calcaneus, talus, navicular, and the three cuneiforms along with three metatarsals; the first second and the third; and is supported mostly by the planter fascia and the spring ligament. At its apex is the superior articular surface of talus and the lower ends are formed by the tuberosity on the plantar surface of calcaneus along with heads of three metatarsals present anteriorly. These are the two extremities at lower end that rest on the ground during standing. The medial arch is characterized by elasticity contributed by the elevation and the numerous joints constituting the arch. The talus navicular joint is the most vulnerable part of the medial arch and has the highest probability to yield under pressure. Hence it is provided with additional support by the spring ligament or the plantar calcaneonavicular ligament. This ligament is highly elastic and reverts the arch to its original condition upon removal of pressure. The spring ligament is further strengthened by the deltoid ligament of ankle joint and the Tibialis posterior tendon that is fan-shaped insertion preventing the irreversible damage to ligament as a consequence of excessive tension leading to permanent extension. Further support to the medial arch is provided by the small muscles in foot sole; plantar sponeurosis, tensons of Peroneus longus and anterior and posterior tibilais; and also by the ligaments of all the joints involved (Snell, 2004). Lateral Longitudinal Arch The lateral longitudinal arches are lower to medial arch (3-5 mm form base) reaching the level of cuboid and are made of the calcaneus bone, fourth and fifth metatarsals and the cuboid. These are lower than medial arch. The apex of the lateral arch is formed by talocalcaneal articulation and calcaneocuboid is the major joint. In contrast to the medial arch, the lateral arch contributes rigidity to the foot and this factor is mainly contributed by the calcaneocuboid joint. Further support ot the arch is provided by the long plantar, the plantar calcaneocuboid; the two ligaments characterized by high strength. Besides these the extensor tendons and the short muscles of the little toe also contribute to its stability (Snell, 2004). The lateral and medial longitudinal arches together form the anterioposterior foot arches; and along with some other anatomical parts constitute the fundamental longitudinal arch of the foot. These parts include calcaneus, cuboid, third metatarsal and the third cuneiform. Transverse Arch Foot is formed by a series of transverse arches that are complete at the anterior and posterior ends but form a semi-circle in the middle or in the foot concavity. These arches are supported by plantar and the dorsal ligaments, the interosseous, and by the short muscles of the first and fifth toes. The tendons of Peronaeus longus spanning between the piers of the arches provide additional support. In a typical transverse arch the angle formed between the metatarsal and the ground at toes one to five is 18-25◦, 15◦, 10◦, 8◦, and 5◦ respectively (Riegger, 1988). The foot arches are responsible for carrying weight of the body, enabling it to walk and provide additional support without additional and irreversible impact on the foot anatomy. The elevation of arches and shape of foot as a consequence of the precise structure of arches controls energy expenditure in walking and prevents wear and tear. An arch elevation higher or lower than the precise limits leads to foot dysfunctions and results in abnormal gait on one hand and to dysfunctionality of distant body parts since the functional abnormalities of the foot result in additional forces on other body parts (Chang et al., 2010). MECHANISM OF WALKING Before we address the question “how do we walk”, we need to find “what are the requirements for normal walking or bipedalism in human beings”. Nutt and colleagues (1993), provide two prerequisites for walking: equilibrium or the ability to maintain balance while maintaining the erect posture. This involves getting up from a sitting position to acquire a vertical posture. The second prerequisite for walking is locomotion or the ability to begin and continue movement in a rhythmic pattern. Mechanism of walking has been explained using two theories; both prevailing, and still contradictory. The first theory, six determinants of gait, provides the kinematic features of gait that are involved in reduction of energy cost by alleviating the vertical displacement of centre of mass (COM) of body during locomotion, emphasizing instead a flattened movement of COM (Kuo, 2007). COM is located immediately anterior to sacral vertebra, in between the hip joints (Malanga & Delisa, 1998). In contrast the second theory, the inverted pendulum model proposes that the leg behaves like an inverted pendulum, moving in a circular arc. This kind of motion is more economical for the movement of COM instead of horizontal movement (Kuo, 2007). The Six Determinants of Gait Theory Proposed by Saunders and colleagues (Saunders et al., 1953) in the seminal publication “The Major Determinants of Normal and Pathological Gait” the theory was revered and used to explain the gait mechanism for five decades. However the theory has come under considerable criticism in the last two decades. The six determinants of gait theory provides six kinematic features that prove to be more economical for locomotion in terms of energy. It is based on two hypotheses: Locomotion can be considered as the transfer of centre of gravity of a body in space along a specific pathway with minimal metabolic energy expenditure (Saunders et al., 1953). Another aspect of energy saving mechanism involves taking the shortest possible pathway for transfer of centre of gravity along the specific pathway; thereby keeping the energy expenditure for muscular movement as low as possible (Kuo & Donelan, 2010). Thus both hypotheses of six determinants of gait theory lay stress on keeping the walking process economical in terms of metabolic energy costs. The theory remained approved till the 1990s, before researchers began to quantify and assess the six kinematic features enlisted in the theory (Gard & Childress, 2001). The six determinants (D1, D2, D3 etc) enlisted in the theory are (Saunders et al., 1953): Pelvic list or the frontal plane tilt of the pelvis in single limb support conditions Stance phase knee flexion Pelvic rotation about the vertical axis Foot mechanism Knee mechanism Lateral displacement of body Besides this two minor determinants have also been listed: Neck movement and swinging of arms. Later researchers have criticized the six determinants of gait theory since the determinants fail to be economical and at best have mild impact on lowering COM and hence alleviating energy cost of walking. In fact some of them are expensive in terms of energy (Della et al, 200; Kerrigan et al., 2001). Kuo (2007) reports that an almost horizontal movement of centre of mass as determined by the theory; leads to elevated muscular work, has higher force requirements and is therefore more expensive. It has now been determined by various researchers that COM lowering has no impact on lowering energy expenditure of walking, instead energy expenditure is optimized by phase relationship maintenance correlation of gravitational and kinetic energy amplitudes during walking (Baker et al., 2004). The Inverted Pendulum Model The inverted pendulum model proposes that legs perform a movement that traces the path of movement of an inverted pendulum thereby facilitating an energy saving mechanism of walking (Cavagna & Margaria 1966). Kuo and colleagues have further specified that walking can be described as simultaneous movement of two pendulums; with the stance leg behaving as an inverted pendulum moving with respect to stance foot; while the swing leg can be likened to a regular pendulum oscillating about the hip. This mechanism has been proposed to explain energy economy in walking. The movement of stance leg facilitates movement of COM of body in an arc allowing for mechanical energy conservation. Unlike the six determinants theory, in inverted pendulum model, no mechanical force is required for keeping the vertical posture or for locomotion; and knee torque is also not required to support body weight. Swine leg also performs ballistic motion which requires no physical effort and hence energy consumption is minimal. The inverted pendulum theory finds support in the leg length alterations and mechanical energy exchange pattern during single limb support (Lee & Farley, 1998). Figure 4: Inverted Pendulum Model (Kuo, 2010) The chief advantage of inverted pendulum model lies in energy conservation since change in kinetic energy is completely accounted for to an opposing and correlated change in gravitational potential energy if the model is exhibiting conservative performance. Thus there is no need for muscular effort. Another advantage of this model is that a leg can act as an inverted pendulum even when it is not in a straight position since the distance between the hip and the base contact of foot remains same. Energy Considerations of Inverted Pendulum Model of Walking The stance phase in inverted pendulum model can be divided in to four sub phases: Collision: During this phase redirection of COM occurs with active negative work being performed by the ankle and subsequently by the knee. Passive work is performed by the rest of the body. Rebound: During this phase there is straightening of stance leg around mid-stance and positive work is done by the knees Pre-load: At preload continued negative work is performed by the ankle, the slowing down of the motion of the inverted pendulum occurs along with gathering of elastic energy needed for the push off that follows. Push Off: During push off the elastic energy stored during pre-load performs the major proportion of the work with positive work done by the ankles. Figure 5: Sub phases of Stance phases (a) with energy considerations (b) (Kuo et al., 2005) Despite effectively explaining energy conservation and differences in walking and running mechanisms; there are several limitations to inverted pendulum model. It is unable to explain differences in energy expenditure at different speeds of walking. At higher speeds the stance legs behaves unlike a pendulum and hence there would be variations in exchanges of kinetic energy and gravitational potential energy. The inverted pendulum model does not account for this variation (Cavagna et al., 1977). Finally, the model suggests that once started the process of walking does not require any input of mechanical energy. Thus even though it provides an energy economic model for walking it fails to explain why walking requires any energy input at all (Kuo, 2007). Mechanism of Dynamic Walking McGeer (1990) has extended the model of ballistic motion of stance and swine leg to include collision in order to explain dynamic walking. It describes the passive control of gait cycle on basis of heel strike collision of ground with the leading leg which facilitates periodic walking without mechanical effort. The collision shifts the COM of body from one inverted pendulum arc to other and facilitates the next step. The direction of COM velocity is almost perpendicular to the trailing limb and shifts ahead and downwards at the end of the gait cycle. During the next cycle, the COM proceeds on a new arc that is directed upward and forward on the leading leg. Figure 6: Mechanism of Dynamic walking This mechanism predicts that walking with larger steps keeping step frequency constant, should lead to a rise in energy costs since it would mean increased COM velocity in terms of both magnitude and frequency of directional change. This has been proved experimentally providing support to the mechanism. The energy economy in walking is made by a trade of between step to step transition and forced leg motion; both of which contribute to most of the metabolic energy cost of gait cycle; thus striking balance between wider steps and frequent steps (Kuo et al., 2010). GAIT Simply put gait is the medical terminology describing human locomotion or the manner of walking. Physiologically gait is defined as a cumulative activity of an individual’s bones, muscles and nervous system (both peripheral and central) leading to locomotion. Figure 7: Step and Stride (Uustal & Baerga 2004) Gait cycle or stride refers to the chain of events during walking involving one limb. It can be considered as the functional unit of gait, and is divided into following two phases (figure 7): Swing phase during which the specific limb is in touch with ground. Stance phase during which the limb has lost touch with ground and is in position of moving upward and forward in the air. The two phases of stride are further divided in to sub phases (table). Table 1: Phases of Stride Stance Phase Swing Phase Initial contact Initial swing Loading Response Midswing Midstance Terminal swing Terminal stance Preswing Figure 8: Gait Cycle: A: New Gait Terms. B: Classic Gait Terms. C: The normal distribution of time during the gait cycle at normal walking speed (Uustal & Baerga 2004) Gait patterns are determined by the manner of integration of the systems involved, i.e. bone, muscles and nervous system; and defect in either of these can adversely affect the gait pattern. Thus gait can be normal, or abnormal. Abnormal gait pattern can either be unsteady or antalgic (Malanga & Delisa, 1998). NORMAL GAIT In a normal gait cycle, stance phase comprises of 60% of the cycle and remaining 40% is swing phase. Faster walking reduces time spent in stance phase and running eliminates it almost completely. During normal gait COM undergoes rhythmic upward and downward movement as it moves forward; with the peak reaching during midstance and the lowest point being reached during double support. Simultaneously it also deviates from the vertical straight line as body moves in a specific direction. Vertical as well as lateral displacement during the normal gait of a human adult male is approximately 5 cm (Whittle, 1996; Lehmann et al., 1992). Figure 9: Characteristics of Normal Gait (Uustal & Baerga 2004) ABNORMAL GAIT Abnormal gait can arise due to defect in either of the muscular, skeletal or nervous systems. On the basis of pathology, gait abnormality can be either neuromuscular or musculoskeletal (Schneck, 1998). Structural defects of the bone, joints and/or soft tissues may result in abnormal gait patterns (Lehmann et al., 1992). Further it has been observed that efficiency of gait pattern is inversely proportional to energy consumption during walking (Malanga & Delisa, 1998). Table 2: Gait pathology, major points of observation (Malanga & Delisa, 1998) Cadence Symmetrical, Rhythmic Pain Where, when Stride Even/ uneven Shoulders Dipping, elevated/ depressed/ protracted/ retracted Trunk Fixed deviation, lurch Pelvic Anterior/posterior tilt, hike, level Knee Dorsiflexion, eversion/inversion Foot Heelstrike, push off Base Stable/unstable, wide/narrow Musculoskeletal Causes of abnormal gait patterns: 1. Hip Pathology: The most common hip pathology responsible for abnormal gait is osteoarthritis. It is observable in form of reduced range of hip motion with lesser internal rotation and flexion. This reduction in motion of affected hip is compensated by motion of healthy hip and the lumbar spine. In cases of painful hip osteoarthritis patterns of antalgic gait are observed characterized by effort to avoid weight bearing by the affected hip and consequent reduction of stance phase for the corresponding limb (Malanga & Delisa, 1998). 2. Knee Pathology: Knee pathology resulting in pain is manifested in gait patterns by continuous maintenance of knee in flexion cycle especially in instances of intra-articular effusion. In order to avoid stress on the affected knee, heelstrike and toe walking is avoided for that limb (Lehmann et al., 1992). Other abnormal gait patterns associated with knee pathology include varus thrust gait pattern associated with injury of posterior lateral corner of knee; quadriceps avoidance gait pattern in individuals with anterior cruciate ligament injury, and abnormal gait patterns due to knee joint contractures (Andriacchi, 1990; Berchuk et al., 1990). 3. Foot and Ankle Pathology: Antalgic gait patterns result from injury to foot and ankle resulting in avoidance of weight bearing by the affected region. The gait pattern is characterized by shorter strides and lack of heel to toe motion. Forefoot injuries would lead to complete avoidance of plantarflexion and toe off. In hindfoot injuries, individual will tend to walk on toes instead, and will completely limit hindstrike. Ankle instability results in antalgic gait due to unstable ankle and compensatory weight bearing on the unaffected side. Joint contractures such as gastrocsoleus complex; resulting as a consequence of injury, immobilization or neurological causes result in steppage gait during which swing phase exhibits increased hip and knee flexion while normal heel contact and heel to toe motion is entirely lost in order to avoid toe contact. Hindfoot pathology especially of the calcaneus such as calcaneal fractures, stress fractures of calcaneus or ankle and plantar fasciitis result in antalgic gait characterized by lowering of stress on the heels. 4. Leg length Discrepancy: Asymmetry of the pelvis, femur or tibia length results in leg length discrepancy that is manifested in gait pattern by pelvic obliquity, reduced hip and knee flexion, ankle plantarflexion; all of these observed ipsilateral to the side shorter in comparison (Song et al., 1997). Table 3: Gait Pathology (Tan, 1998) Abnormal Gait Probable causes Foot strike to foot flat Foot slap Moderately weak dorsiflexors Foot strike through midstance Genu recurvatum Weak, short, or spastic quadriceps; compensated hamstring weakness; Achilles tendon contracture; plantarflexor spasticity Excessive foot supination Compensated forefoot valgus deformity; pes cavus; short limb; uncompensated external rotation of tibia or femur Excessive trunk extension Weak hip extensor or flexor; hip pain; decreased knee ROM Excessive trunk flexion Weak gluteus maximus and quadriceps Foot strike through toe off Excessive knee flexion Hamstring contracture; increased ankle dorsiflexion; weak plantar flexor; long limb; hip flexion contracture Excessive medial femur rotation Tight medial hamstrings; anteverted femoral shaft; weakness of opposite muscle group Excessive lateral femur rotation Tight hamstrings; retroverted femoral shaft; weakness of opposite muscle group Increased base of support Abductor muscle contracture; instability; genu valgum; leg length discrepancy Decreased base of support Adductor muscle contracture; genu varum Foot flat through heel off Excessive trunk lateral flexion (Trendelenburg gait) Ipsilateral gluteus medius weakness; hip pain Pelvic drop Contralateral gluteus medius weakness Waddling gait Bilateral gluteus medius weakness Midstance through toe off Excessive foot pronation Compensated forefoot or rearfoot varus deformity; uncompensated forefoot valgus deformity; pes planus; decreased ankle dorsiflexion; increased tibial varum; long limb; uncompensated internal rotation of tibia or femur; weak tibialis posterior Bouncing or exaggerated plantar flexion Achilles tendon contracture; gastroc-soleus spasticity Insufficient push-off Gastroc-soleus weakness; Achilles tendon rupture; metatarsalgia; hallus rigidus Inadequate hip extension Hip flexor contracture; weak hip extensor Swing phase Steppage gait Severely weak dorsiflexors; equinus deformity; plantarflexor spasticity Circumduction Long limb; abductor muscle shortening or overuse Hip hiking Long limb; weak hamstring; quadratus lumborum shortening Neurological Causes of Abnormal Gait: 1. Hemiplegic Gait: resulting from cardiovascular injuries, the hemiplegic gait pattern is characterized by distinct arm swing along with shoulder, wrist, fingers and elbow flexion (Wagenaar & Beek, 1992). 2. Spastic Gait: Problem with the central nervous system affecting the motor tone of lower limbs are manifested in Spastic gait patterns. Enhanced pelvic tilt along with increased flexion of the hip and knee is observed. Crouch gait is also commonly observed. A narrow base that results in crossing and hip adductor over activity causes the scissoring effect of legs. The individual is therefore forced to tiptoe in order to maintain balance. Forward swing required additional effort result in an unsteady and energy consuming gait (Opheim et al., 2013). 3. Parkinsonian Gait: This gait pattern is characterized by limited movement of upper and lower limbs and also that of trunk and facial muscles. As a consequence the gait comprises of slow steps with intermittent rapid small steps. This results due to impact of the disease on motor control resulting as a consequence of lesions of basal ganglia (Lehmann et al., 1992). 4. Ataxic Gait: Unsteady gait with broad base along with lower limb and trunk staggering result as a consequence of disturbance to the motor function coordination and accuracy as a consequence of cerebellum injury. The gait is unsteady, lacks coordination and definitely exaggerated (Lehmann et al., 1985). Conclusion The ability to walk with coordinated, steady steps in a specific and desired direction is a unique ability of human beings that is dependent on the foot anatomy, and neuromuscular coordination. It not only affects our physical and mental well being but is also a prerequisite for personal and financial independence. An understanding of the mechanism of walking and the characteristics of normal gait have facilitated researches to focus on developing a deeper understanding of the gait abnormalities and therefore allowed for therapies, surgeries and treatments to overcome them. Further gait patterns and mechanism have enabled understanding of healthy lifestyle, improvement of fitness levels and enhanced performance in sports activities. References 1. Baker et al., 2004. 8th International Symposium on the 3-D Analysis of Human Movement. Florida, USA, s.n. 2. Andriacchi, T. P., 1990. Dynamics of pathologica; motion: applied to the anterior cruciate deficient knee. Journal of Biomechanics, Volume 23, pp. 99-105. 3. Berchuk, M., Andriacchi, T. P., Bach, B. R. & Reider, B., 1990. Gait adaptations by patients who have a deficient anterior cruciate ligament. The journal of bone & joint surgery, Volume 72A, pp. 871-7. 4. Cavagna, G. A., Heglund, N. C. & Taylor, C. R., Am J Physiol . 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Biological aspects of locomotion. In: F. Pfeiffer & T. Zielinska, eds. Walking: Biological and Technological Aspects. New York: Springer, pp. 1-22. Read More