Ankle & foot biomechanics

this PPT contains details about ankle joint & foot complex like anatomy, kinetics, kinematics, arches, weight bearing, etc.

1. Dr. meghan phutane (pt) Cardio-respiratory physiotherapist ANKLE & FOOT BIOMECHANICS

2. CONTENTS Anatomy review – Joints of ankle & foot Ligaments Muscles Biomechanics – Artho -kinematics Osteo -kinematics

3. FUNCTIONS OF ANKLE & FOOT Stability Provide stable base of support in variety of weight bearing postures Acts as a rigid lever for effective push off during gait Mobility Absorbs stress & shock – pliability of foot Propulsion of body in walking Protection – sensation of sole of foot

4. BONES 26 bones & 2 sesamoid bones; divided into 3 functional segments – Forefoot – (Anterior) Metatarsals 5 Phalanges 14 Midfoot – (Middle) Navicular Cuboid Cuneiform 3 Hindfoot – (Posterior) Talus Calcaneus

5. JOINTS 25 component joints Proximal & distal tibiofibular joints Ankle (Talo-crural ) joint Talo-calcaneal (subtalar) joint Talo-navicular joint Calcaneo-cuboidal joint 5 tarso -metatarsal joints 5 metatarso-phalangeal joints 9 interphalangeal joints Transverse tarsal joint

6. DEFINITIONS OF MOTION

7. Cont…

8. MUSCLES OF ANKLE & FOOT

9. Muscle activity is critical for dynamic stability & integration of movements at multiple joints of foot. No muscle is single joint muscle. Muscle function depends on – Muscle structure & Position of muscle in relation to joint axis Anterior compartment muscles – Dorsiflexion Posterior compartment muscles – Plantarflexion Lateral compartment muscles – Pronation Medial compartment muscles - Supination

10. Peroneus longus FHL Triceps surae FDL TP DORSIFLEXION PLANTARFLEXION PRONATION SUPINATION Peroneus brevis TA EHL EDL Peroneus tertius Ankle joint axis Subtalar joint axis

11. Posterior compartment muscles Passes posterior to the ankle joint & so all are plantarflexors . The muscles are – Gastrocnemius Soleus Tibialis posterior Flexor digitorum longus (FDL) Flexor hallucis longus (FHL) Peroneus longus Peroneus brevis Plantaris

12. Triceps surae Two heads of gastrocnemius & soleus together Strongest plantarflexor Inserts perpendicular on the calcaneum – provides large moment arm to provide plantarflexion torque. Passes medial to the subtalar joint axis – supination During weight bearing, helps lock the foot into a rigid lever Eccentrically control dorsiflexion in weight bearing

13. Tibialis posterior – Important dynamic contributor to the arch support. Controls & reverse foot pronation during gait cycle. FHL & FDL – Spans the medial longitudinal arch & supports arch during gait cycle. Also causes subtalar joint supination & flexion of toes. FHL causes flexion of IP joints.

14. Lateral compartment muscles Muscles are – Peroneus longus Peroneus brevis Primary pronators of subtalar joint.

15. Anterior compartment muscles The muscles are – Tibialis anterior Extensor hallucis longus (EHL) Extensor digitorum longus (EDL) Peroneus tertius Strong ankle dorsiflexors . Tibialis anterior – strong supinator of subtalar joint. EHL – extension of MTP joint of hallux EDL & peroneus tertius – pronation EDL – extension of MTP joint of lesser toes

16. Intrinsic musculature Important functions – Stabilizes toes Dynamic spport to the arches during gait Muscles are – Lumbricals Dorsal & plantar interossei muscles

17. ANKLE JOINT

18. Also called as talocrural joint. Synovial hinge joint Calcaneus Talus Fibula Tibia Medial Lateral

19. STRUCTURE Proximal articular surface – Concave surface of distal tibia & of tibial & fibular malleoli . Extends more distally on lateral than medial & on posterior than anterior. (Mortise) Proximal tibiofibular joint – Plane synovial joint Distal tibiofibular joint – Syndesmosis or fibrous union

20. Distal articular surface – Body of talus – 3 articular surfaces Large lateral fibular facet Smaller medial tibial facet Trochlear (superior facet) Body – wider anteriorly than posteriorly (Wedge shape) Cuboid Head of calcaneus Fibular/lateral facet Navicular Head of Talus Body of Talus Tibial facet

21. CAPSULES & LIGAMENTS Capsule – thin & weak anteriorly & posteriorly. So stability depends on intact ligaments. Ligaments of proximal & distal tibio -fibular joints – For stability of mortise & therefore ankle. Crural tibiofibular interosseus ligament Anterior & posterior tibiofibular ligaments Tibiofibular interosseus membrane Other ligaments - Medial collateral ligament [MCL] Lateral collateral ligament [LCL] Extensor & peroneal retinaculae Key support to subtalar joint also

22. MCL – Called as Deltoid ligament Fan shaped Superficial & deep fibers from borders of tibial malleolus to navicular , talus & calcaneus. Extremely strong ligament Controls medial distraction forces on ankle Checks motions at extremes of joint range

23. LCL – 3 separate bands referred as separate ligaments- Anterior talofibular ligament Posterior talofibular ligament Calcaneofibular ligament LCL components are weaker & more susceptible to injury than MCL Control varus (lateral distraction) forces

24. Other structures

25. MOVEMENTS MOVEMENT AXIS PLANE RANGE Plantarflexion / dorsiflexion Coronal Saggital 20-50 / 10-20 Talar rotation (abduction / adduction) Vertical Transverse 10 / 7 Talar tilt (inversion / eversion) Longitudinal (AP) Frontal ≤ 5

26. AXIS Through fibular malleolus, body of talus & just below or through tibial malleolus. Tibial torsion – more posterior position of fibular malleolus, due to normal torsion or twist in distal tibia in relation to proximal tibia.

27. FUNCTION Dependant on stability of tibiofibular mortise & for mobility role mortise belongs primarily to fibula. Shape of talus facilitate ankle stability. Trochlea – wedge shape – in weight bearing, during dorsiflexion tibia rotates over talus, wider anterior part wedges into mortise to enhance stability. This allows ankle to withstand compression forces of 450% of body weight. This joint motion is necessary for – Normal load distribution Cartilage nutrition Lubrication of ankle joint

28. Cont… Plantarflexion – loosepacked position of ankle – less stable – higher incidence of ankle sprain. Asymmetry in size & orientation of lateral & medial facets of talus – changes ankle mortise during dorsiflexion – causes greater displacement of fibula over lateral malleolus during dorsiflexion.

29. Muscles protecting

30. SUBTALAR JOINT (TALO-CALCANEAL)

31. STRUCTURE 3 separate plane articulations between talus superiorly & calcaneus inferiorly. Triplanar movement around a single joint axis. Variable articulating surfaces, posterior being consistent & largest. Posterior facet receives 75% of stress of subtalar joint.

32. Between posterior articulation & anterior & medial articulation, forms a bony tunnel – tarsal canal. Runs obliquely across foot. Sinus tarsi – laterally, large end, anterior to the fibular malleolus. Sustentaculum tali – medially, small end, below tibial malleolus & above calcaneus. Ligaments running through, divides posterior articulation from anterior & medial articulations. Posterior has its own capsule whereas anterior & medial articulations share capsule with talonavicular joint.

33. MEDIAL VIEW LATERAL VIEW

34. LIGAMENTS All ligaments of ankle joint. Other ligaments – Calcaneofibular ligament Lateral talocalcaneal ligament Cervical ligament Strongest ligament Interosseus talocalcaneal ligament Has anterior & posterior bands

35. FUNCTION 3 articulations – alternating convex-concave – limits potential mobility of joint. Motion of talus on calcaneus is complex twisting or screw like motion that proceeds till the facets can accommodate simultaneous & opposite motions across the surfaces. Triplanar motion – around a single oblique joint axis – supination / pronation .

36. Cont… The subtalar axis – TP SP Component motions; can’t occur independently. Includes about equal magnitude of eversion/inversion & abduction/adduction but a very small component of dorsiflexion/ plantarflexion.

37. NON WEIGHT BEARING WEIGHT BEARING DEFORMITY Calcaneus moves on stationary talus(Proximal) Talus moves on stationary calcaneus (Distal) SUPINATION Calcaneal inversion Calcaneal adduction Calcaneal plantarflexion Calcaneal inversion Talar abduction Talar dorsiflexion Tibiofibular lateral rotation Supinated / Cavus foot PRONATION Calcaneal eversion Calcaneal abduction Calcaneal dorsiflexion Calcaneal eversion Talar adduction Talar plantarflexion Tibiofibular medial rotation Pronated / Pes planus / Flat foot

38. MITERED HINGE – Representation of interdependence of leg & foot

39. RANGE Difficult to determine objectively because of triplanar nature of movement & as the component contribution vary with inclination of subtalar joint. Normally calcaneal eversion ( valgus ) is 5-10 & inversion is 20-30 degrees. (usually easy to measure component) Dorsi /plantarflexion can’t be assessed properly except static radiograph; abduction/adduction even difficult on radiogram so can be estimated by degree of tibial rotation. Change in inclination in subtalar joint axis, changes ROM of component movements & affect both foot & leg position in weight bearing.

40. Subtalar neutral position – point from which calcaneus will invert twice of eversion. (Root & colleagues) The main function of subtalar joint in weight bearing is to absorb the imposed lower extremity transverse plane rotations that occur during walking & other weight bearing activities.

41. TRANSVERSE TARSAL JOINT

42. Also called as mid-tarsal or Chopart joint. Compound joint formed by – Talonavicular joint & Calcaneo-cuboid joint S-shaped joint line – transects foot horizontally – divides hindfoot from midfoot & forefoot. During weight bearing, navicular & cuboid bones are considerably immobile – so talus & calcaneus has to move on relatively fixed naviculo-cuboid unit.

43. Talonavicular joint Proximal articulation by anterior portion of head of talus (convex) & distal by concave posterior aspect of navicular bone. Ball & socket joint Shares joint capsule with anterior & medial facets of subtlar joint. Inferior aspect of capsule is formed by plantar calcaneonavicular (spring) ligament. Capsule is reinforced medially by deltoid & laterally by bifurcate ligament.

44. Cont… Spring ligament – Triangular sheet from sustentaculum tali to inferior navicular bone. Continuous medially with deltoid ligament & laterally with medial band of bifurcate ligament. Little or no elasticity; resist tensile stresses. Supports head of talus & talonavicular joint. Provides support to medial longitudinal arch.

45. Cont… During weight bearing, talonavicular joint is linked to the subtalar joint. In weight bearing supination & pronation , talus moves on calcaneus that causes movement of talus on navicular bone. The talonavicular joint & subtalar joint are anatomically & functionally related in weight bearing. Ligaments reinforcing talonavicular joint – Spring & bifurcate ligament Dorsal talonavicular ligament MCL & LCL Inferior extensor retinaculum Cervical & interosseous talocalcaneal ligament

46. Calcaneo-cuboid joint Formed proximally by anterior calcaneus & distally by posterior cuboid bone. Articular surfaces are complex; reciprocally concave/convex both side to side & top to bottom – restricts motion. Saddle joint Linked to subtalar joint in weight bearing. Has own capsule.

47. Cont… Reinforced by several ligaments – Laterally by lateral band of bifurcate ligament ( calcaneocuboid Ligament) Dorsally by dorsal calcaneocuboid ligament Inferiorly by plantar calcaneocuboid ligament (short plantar) & long plantar ligament. Long plantar ligament – Most important Significant contribution to transverse tarsal joint stability & to related support of the lateral longitudinal arch of foot.

48. Transverse tarsal joint axis Movements are more difficult to study because multiple joints & axes are involved. Talonavicular and calcaneocuboid joints have some independent movement, but motion at one is generally accompanied by at least some motion of the other because of their functional, bony, and ligamentous connections. The longitudinal axis is nearly horizontal, being inclined 15 upward from the transverse plane and angled 9 medially from the sagittal plane. Triplanar movement, predominated by inversion / eversion.

49. Longitudinal axis 15º 9º

50. The oblique (transverse) axis of the transverse tarsal joint is positioned approximately 57 medial to the sagittal plane and 52 superior to the transverse plane. This triplanar axis also provides supination/pronation with coupled component movements of the talus and calcaneus segments moving together on the navicular and cuboid bones, but dorsiflexion/plantarflexion and abduction/adduction components predominate. Motions about the longitudinal and oblique axes are difficult to separate and to quantify. The longitudinal and oblique axes together provide a total range of supination / pronation of the talus and calcaneus that is about one third to one half of the range available at the subtalar joint.

51. Oblique axis 57º 52º

52. Transverse tarsal joint function Function similar to that of the subtalar joint. The subtalar and the transverse tarsal joints are linked mechanically. Any weight-bearing subtalar motion causes motion at the talonavicular joint and the calcaneocuboid joint. As the subtalar joint supinates / pronates , its linkage to the transverse tarsal joint causes both the talonavicular joint and the calcaneocuboid joint to begin to supinate / pronate also.

53. The transverse tarsal joint is the transitional link between the hindfoot and the forefoot, & serves to add to the supination / pronation range of the subtalar joint and compensate the forefoot for hindfoot position. Compensation refers to the ability of the forefoot to remain flat on the ground while the hindfoot (talus and calcaneus) pronates or supinates in response to the terrain or the rotations imposed by the leg.

54. Weight-Bearing Hindfoot Pronation and Transverse Tarsal Joint Motion – In the weight-bearing position, during pronation on the subtalar joint; if the force continued distally through the foot, the lateral border of the foot tends to lift from the ground, diminishing the stability of the base of support, resulting in unequal weight-bearing, and imposing stress at multiple joints. This undesirable effect of weight-bearing subtalar joint pronation may be avoided if the forefoot remains flat on the ground. This can occur if the transverse tarsal joint is mobile and can effectively “absorb” the hindfoot pronation . Relative supination of the bony segments distal to the transverse tarsal joint, with the result that the forefoot remains relatively flat on the ground. When the weight-bearing hindfoot (subtalar joint) is pronated – the transverse tarsal joint will supinate.

55. Weight-Bearing Hindfoot Supination and Transverse Tarsal Joint Motion A lateral rotatory force on the leg will create subtalar supination in the weight-bearing subtalar joint with a relative pronation of the transverse tarsal joint. Transverse tarsal joint mobility is increasingly limited as the subtalar joint moves toward full supination . the transverse tarsal joint cannot absorb the additional rotation but begins to move toward supination as well.

56. TARSO-METATARSAL JOINT

57. The tarsometatarsal (TMT) joints are plane synovial joints formed by the distal row of tarsal bones (posteriorly) and the bases of the metatarsals . The first (medial) TMT joint is composed of the articulation between the base of the first metatarsal and the medial cuneiform bone and has its own articular capsule. The second TMT joint is composed of the articulation of the base of the second metatarsal with a mortise formed by the middle cuneiform bone and the sides of the medial and lateral cuneiform bones. This joint is set more posteriorly than the other TMT joints; it is stronger and its motion is more restricted. The third TMT joint, formed by the third metatarsal and the lateral cuneiform, shares a capsule with the second TMT joint. The bases of the fourth and fifth metatarsals, with the distal surface of the cuboid bone, form the fourth and fifth TMT joints. These two joints also share a common joint capsule.

58. Small plane articulations exist between the bases of the metatarsals to permit motion of one metatarsal on the next. Ligaments reinforcing TMT joint - Numerous dorsal, plantar, and interosseous ligaments Deep transverse metatarsal ligament - spans the heads of the metatarsals on the plantar surface & so contributes to stability of the proximally located TMT joints by preventing excessive motion and splaying of the metatarsal heads.

59. Axes Each TMT joint is considered to have a unique, although not fully independent, axis of motion. A ray is defined as a functional unit formed by a metatarsal and (for the first through third rays) its associated cuneiform bone. The cuneiform bones are included as parts of the movement units of the TMT rays because of the small and relatively insignificant amount of motion occurring at the cuneonavicular joints. The fourth and fifth rays are formed by the metatarsal alone because these metatarsals share an articulation with the cuboid bone. most motion at the TMT joints occurs at the first and fifth rays. Each axis is oblique and, therefore, triplanar . The first has the largest ROM.

60. The axis of the first ray is inclined in such a way that dorsiflexion of the first ray also includes inversion and adduction, whereas plantarflexion is accompanied by eversion and abduction. The abduction/adduction components normally are minimal. Movements of the fifth ray around its axis are more restricted and occur with the opposite arrangement of components: dorsiflexion is accompanied by eversion and abduction, and plantarflexion is accompanied by inversion and adduction. The axis for the third ray nearly coincides with a coronal axis; the predominant motion, therefore, is dorsiflexion/plantarflexion. The axes for the second and fourth rays were considered to be intermediate between the adjacent axes for the first and fifth rays, respectively.

61. Function The motions of the TMT joints are interdependent. TMT joints contribute to hollowing and flattening of the foot. The greatest relevance of TMT joint motions is found during weight-bearing. In weightbearing , the TMT joints function primarily to augment the function of the transverse tarsal joint; (attempt to regulate position of the metatarsals and phalanges in relation to the weight-bearing surface). As long as transverse tarsal joint motion is adequate to compensate for the hindfoot position, considerable TMT joint motion is not required. However, when the hindfoot position is at an end point in its available ROM or the transverse tarsal joint is inadequate to provide full compensation, the TMT joints may rotate to provide further adjustment of forefoot position.

62. Supination twist When the hindfoot pronates in weightbearing , the transverse tarsal joint generally supinate to some degree to counterrotate the forefoot and keep the plantar aspect of the foot in contact with the ground. If the range of transverse tarsal supination is not sufficient to meet the demands of the pronating hindfoot , the medial forefoot will press into the ground, and the lateral forefoot will tend to lift. The first and second ray will be pushed into dorsiflexion by the ground reaction force, and the muscles controlling the fourth and fifth rays will plantarflex the TMT joints in an attempt to maintain contact with the ground. Both dorsiflexion of the first and second rays and plantarflexion of the fourth and fifth rays include the component motion of inversion of the ray. Consequently, the entire forefoot undergoes an inversion rotation around a hypothetical axis at the second ray. This rotation is referred to as supination twist of the TMT joints.

63. Pronation twist When both the hindfoot and the transverse tarsal joints are locked in supination , the adjustment of forefoot position must be left entirely to the TMT joints. With hindfoot supination , the forefoot tends to lift off the ground on its medial side and press into the ground on its lateral side. The muscles controlling the first and second rays will cause the rays to plantarflex in order to maintain contact with the ground, whereas the fourth and fifth rays are forced into dorsiflexion by the ground reaction force. Because eversion accompanies both plantarflexion of the first and second rays and dorsiflexion of the fourth and fifth rays, the forefoot as a whole undergoes a pronation twist.

64. METATARSO-PHALANGEAL JOINT

65. The five metatarsophalangeal (MTP) joints are condyloid synovial joints with two degrees of freedom: extension/ flexion (or dorsiflexion/plantarflexion) and abduction/adduction. Although both degrees of freedom might be useful to the MTP joints in the rare instances when the foot participates in grasplike activities, flexion and extension are the predominant functional movements at these joints. During the late stance phase of walking, toe extension at the MTP joints permits the foot to pass over the toes, whereas the metatarsal heads and toes help balance the superimposed body weight through activity of the intrinsic and extrinsic toe flexor muscles.

66. Structure The MTP joints are formed proximally by the convex heads of the metatarsals and distally by the concave bases of the proximal phalanges. The range of MTP extension exceeds the range of MTP flexion. All metatarsal heads bear weight in stance. Consequently, the articular cartilage must remain clear of the weight-bearing surface on the plantar aspect of the metatarsal head. This structural requirement restricts the available range of MTP flexion. The first MTP joint has two sesamoid bones associated with it that are located on the plantar aspect of the first metatarsal head . In the neutral position of the first MTP joint, the sesamoid bones lie in two grooves on the metatarsal head that are separated by the intersesamoid ridge.

67. The ligaments associated with the sesamoid bones form a triangular mass that stabilizes the sesamoid bones within their grooves. The sesamoid bones serve as anatomic pulleys for the flexor hallucis brevis muscle and protect the tendon of the flexor hallucis longus muscle from weight-bearing trauma as the flexor hallucis longus passes through a tunnel formed by the sesamoid bones and the intersesamoidal ligament that connects the sesamoid bones across their plantar surfaces. In toe extension greater than 10, the sesamoid bones no longer lie in their grooves and may become unstable. Chronic lateral instability of the sesamoid bones may lead to MTP deformity.

68. Stability of the MTP joints is provided by a joint capsule, plantar plates, collateral ligaments, and the deep transverse metatarsal ligament. The plantar plates are the fibrocartilaginous structures in the four lesser toes that are connected to the base of the proximal phalange distally and blend with the joint capsule proximally. The plates of the four lesser toes are interconnected by the deep transverse metatarsal ligament and by the plantar aponeurosis.

69. The collateral ligaments of the MTP joints, have two components: a phalangeal portion that parallels the metatarsal and phalange, and an accessory component that runs obliquely from the metatarsal head to the plantar plate. The plantar plates protect the weight bearing surface of the metatarsal heads and, with the collateral ligaments, contribute to stability of the MTP joints. Long flexor tendons run in grooves in the plates that help maintain tendon position as the MTP joints are crossed. At the first MTP joint, the sesamoid bones and thick plantar capsule are in place of the plantar plates found at the other toes.

70. Function The MTP joints have two degrees of freedom, but flexion/extension motion is much greater than abduction/adduction motion, and extension exceeds flexion. Although MTP motions can occur in weight-bearing or non–weight-bearing, the MTP joints serve primarily to allow the weight-bearing foot to rotate over the toes through MTP extension (known as the metatarsal break) when rising on the toes or during walking.

71. MTP extension & metatarsal break The metatarsal break derives its name from the hinge or “break” that occurs at the MTP joints as the heel rises and the metatarsal heads and toes remain weight bearing. The metatarsal break occurs as MTP extension around a single oblique axis that lies through the second to fifth metatarsal heads. The range of MTP extension will also vary somewhat, depending on the relative lengths of the metatarsals and whether the motions occur in weight-bearing or non–weight-bearing activities. Limited extension ROM at the first MTP joint will interfere with the metatarsal break and is known as hallux rigidus . The obliquity of the axis for the metatarsal break allows weight to be distributed across the metatarsal heads and toes more evenly than would occur if the axis were truly coronal.

72. Axis of metatarsal break 54-73 degrees

73. MTP flexion, abduction & adduction Flexion ROM at the MTP joints can occur to a limited degree from neutral position but has relatively little purpose in the weight-bearing foot other than when the supporting terrain drops away distal to the metatarsal heads. Abduction and adduction of the MTP joint appear to be helpful in absorbing some of the force that would be imposed on the toes by the metatarsals as they move in a pronation or supination twist. An increase in this normal valgus angulation of the first MTP joint is referred to as hallux valgus and may be associated with a varus angulation of the first metatarsal at the TMT joint, known as metatarsus varus.

74. INTERPHALANGEAL JOINTS

75. Synvial hinge joints with one degree of freedom : flexion/ extension Great toe has only one IP joint whereas lesser toes has 2 IP joints The toes function to smooth the weight shift to the opposite foot in gait & help maintain stability by pressing against the ground in standing.

76. PLANTAR ARCHES

77. The foot typically is characterized as having three arches: medial and lateral longitudinal arches and a transverse arch, of which the medial longitudinal arch is the largest. The arches are fully integrated with one another and enhance the dynamic function of the foot. The arches are not present at birth but evolve with the progression of weight-bearing. By 5 years of age, as children approached gait parameters similar to those of adults, the majority of children had developed an adult like arch.

78. Structure of arches The longitudinal arches are anchored posteriorly at the calcaneus and anteriorly at the metatarsal heads; the arch is higher medially, than laterally so the medial side usually is the side of reference. The talus rests at the top of the vault of the foot and is considered to be the “keystone” of the arch. All weight transferred from the body to the heel or the forefoot must pass through the talus. The transverse arch, At the anterior tarsals, the middle cuneiform bone forms the keystone of the arch.

79. The shape and arrangement of the bones are partially responsible for stability of the plantar arches. The wedge-shaped mid tarsal bones provide an inherent stability to the transverse arch. The inclination of the calcaneus and first metatarsal contribute to stability of the medial longitudinal arch, particularly in standing.

80. LATERAL LONGITUDINAL ARCH MEDIAL LONGITUDINAL ARCH

81. Although the structure of the tarsal bones provides a certain inherent stability to the arches, the arches would collapse without additional support from ligaments and muscles. Because the three arches can be thought of as a segmented vault or one continuous set of interdependent linkages, support at one point in the system contributes to support throughout the system.

82. The plantar calcaneonavicular (spring) ligament, the interosseous talocalcaneal ligament, and the plantar aponeurosis have been credited with providing key passive support to the arch . The cervical ligament is credited with contributing particularly important support of the posterior aspect of the longitudinal arch. Support from the more laterally located long and short plantar ligaments appeared to be important but less influential than support from the spring and cervical ligaments.

83. Function of arches The plantar arches are adapted uniquely to serve two contrasting mobility and stability weight-bearing functions. First, the foot must accept weight during early stance phase and adapt to various surface shapes. To accomplish this weight-bearing mobility function, the plantar arches must be flexible enough to allow the foot to Dampen the impact of weight-bearing forces Dampen superimposed rotational motions Adapt to changes in the supporting surface. To accomplish weight-bearing stability functions, the arches must allow Distribution of weight through the foot for proper weight-bearing Conversion of the flexible foot to a rigid lever.

84. Plantar aponeurosis The role of the plantar aponeurosis (the plantar fascia) is particularly important. The plantar aponeurosis is a dense fascia that runs nearly the entire length of the foot. It begins posteriorly on the medial tubercle of the calcaneus and continues anteriorly to attach by digitations to the plantar plates and then, to the proximal phalanx of each toe. From the beginning to the end of the stance phase of gait, tension on the plantar aponeurosis increases.

85. For this reason, the function of the aponeurosis in supporting the arches has been compared to the function of a tie-rod on a truss. The truss and the tie-rod form a triangle; the two struts of the truss form the sides of the triangle and the tie-rod is the bottom. The talus and calcaneus form the posterior strut, and the remaining tarsal and metatarsals form the anterior strut. The plantar aponeurosis, as the tie-rod, holds together the anterior and posterior struts when the body weight is loaded on the triangle.

86. This structural design is efficient for the weight-bearing foot because the struts (bones) are subjected to compression forces, whereas the tie-rod (aponeurosis) is subjected to tension forces. The fibrocartilaginous plantar plates of the MTP joints are organized not only to resist compressive forces from weight-bearing on the metatarsal heads but also to resist tensile stresses presumably applied through the tensed plantar aponeurosis. Therefore, each biological structure is positioned to maximize its optimal loading pattern and minimize the opportunity for injury.

87. When the toes are extended at the MTP joints the plantar aponeurosis is pulled increasingly tight as the proximal phalanges glide dorsally in relation to the metatarsals or as the metatarsal heads glide in a relatively plantar direction on the fixed toes. The metatarsal heads act as pulleys around which the plantar aponeurosis is pulled and tightened. As the plantar aponeurosis is tensed with MTP extension, the heel and MTP joint are drawn toward each other as the tie-rod is shortened, raising the arch and contributing to supination of the foot.

88. This phenomenon allows the plantar aponeurosis to increase its role in supporting the arches as the heel rises and the foot rotates around the MTP joints in weight-bearing (during the metatarsal break). The reduction in tension in the plantar aponeurosis will allow an increase in the range of MTP extension. Through the pulley effect of the MTP joints on the plantar aponeurosis, it acts interdependently with the joints of the hindfoot to contribute to increasing the longitudinal arch.

89. The tightened plantar aponeurosis also increases the passive flexor force at the MTP joints, preventing excessive toe extension that might stress the MTP joint or allow the LoG to move anterior to the toes. Finally, the passive flexor force of the tensed plantar aponeurosis also assists the active toe flexor musculature in pressing the toes into the ground to support the body weight on its limited base of support.

90. Weight distribution Because the foot is a flexible rather than fixed arch, the distribution of body weight through the foot depends on many factors, including the shape of the arch and the location of the LoG at any given moment. The pattern of weight distribution through the foot can be seen by looking at the trabeculae in the bones of the foot. In static standing, the distribution of weight-bearing on the plantar foot is highly variable and depends on a number of postural and structural factors. Load distribution analysis during quiet standing showed that the heel carried 60%, the midfoot 8%, and the forefoot 28% of the weight bearing load. The toes were minimally involved in bearing weight. Plantar pressures are much greater during walking than during standing, with the highest pressures typically under the metatarsal heads and occurring during the push-off phase of walking (~80% of stance), when only the forefoot is in contact with the ground and is pushing to accelerate the body forward.

91. 50 % 50 % 2 / 3 1 / 3

92. Excessive plantar pressures can contribute to pain and injury in otherwise healthy people or contribute to skin breakdown in patients with diabetes and peripheral neuropathy. Pressure under the first metatarsal head also increases as arch height increases. As one might expect, the soft tissue under the forefoot and the heel acts as a cushion, and as this soft tissue thickness decreases, pressures increase. The greatest stresses to the heel during walking occur at heel strike and typically are 85% to 130% of body weight. Running with a heel contact pattern increases this force to 220% of body weight. The heel pad is composed of fat cells that are located in chambers formed by fibrous septa attached to the calcaneus above and the skin below. The effectiveness of the cushioning action of the heel pad decreases with age and with concomitant loss of collagen, elastic tissue, and water.

93. Muscular Contribution to the Arches Muscle activity appears to contribute little to arch support in the normal static foot. The small intrinsic muscles of the foot contract periodically during quiet stance, presumably to provide brief periods of unloading for the many ligaments supporting the foot. Key muscular support is provided to the medial longitudinal arch during gait is by tibialis posterior, the flexor digitorum longus , and the flexor hallucis longus muscles. The peroneus longus muscle provides important lateral stability as These medial and lateral muscles provide a dynamic sling to support the arches of the foot during the entire stance phase of walking and enhance adaptation to uneven surfaces.

94. THANK YOU