Regional Biomechanics Ankle Joint & Foot Kinematics Kinetics Pathomechanics

Biomechanics of Ankle joint 1- Bony structure Proximal: Mortise. stable mortise is maintained by the ligaments of the distal tibiofibular joint. The lateral malleolus is bigger than the medial and extends distally. Distal: body of talus Tibiofibular joints: - superior, inferior, and the intermediate tibiofibular. They do not add any degree of freedom to the ankle joint.

Bony structure of the ankle and foot

2- Axis of the ankle joint rotate laterally 6 in the horizontal plane and inclined 10 down on the lateral side. It passes through the fibular malleolus and the body of the talus and through or just below the tibial malleolus. The inclination of the axis results in motion across two planes: dorsiflexion with increased toe out ( foot up & lateral) and plantar flexion with decreased toe out ( foot down & medial).

3- ligaments of the ankle (1) medial collateral ligament “Deltoid ligament” Position: medial aspect of ankle. Attachment: Apex of med. Malleolus navicular, spring ligament (plantar calcaneonavicular ligament),and calcaneus. Orientation: Fan shaped Functions: 1- Control eversion stress. 2- Compensates shortness of the medial malleolus. 3- Help to maintain the arches of the foot

(2) Lateral Collteral ligament Position: lateral aspect of ankle Jt. Attachment: Lat. Malleolus talus and calcaneus. Orientation: 1- Ant. talofibular run inferiorly and anteriorly. 2- Post. talofibular from the medial aspect of medial malleolus and run posterior, horizontal, and medially. 3- Calcaneofibular run inferiorly and posteriorly. Function: 1- control varus stress. 2- resist forward slide of tibia. 3- posterior talofibular limits excessive abduction of talus “dorsiflexion” 4- anterior talofibular limits excessive inversion & adduction of ankle “ planter flexion”

(3) Anterior and posterior ligaments of the ankle Anterior ligaments run obliquely from the anterior margin of the lower end of tibia to the talus. Posterior ligament consists of fibers attached to tibia and fibula and insert into the talus.

Functions of the ankle joint Stability function: 1- provide stable base of support. 2- acting as a rigid lever for effective push off during gait. Mobility function: 1- Absorbs the rotation imposed by the more proximal joints. 2- Absorbs the shock as the foot hits the ground. 3- Permits the foot to be adjusted over the variety of surfaces.

Mobility of ankle joint Since the trochlear surface of talus is longer posteriorly than anterior, extension has greater range than flexion. The tibial surface represents an arc of 70º compared to the arc of the talus which is 140-150º, so the total range of flexion and extension is 70º- 80º.

Stability of ankle joint Closed packed position: Dorsiflexion as the wider anterior part of the talus is grasped between the 2 malleoli. Loose packed position: planter flexion as the narrower posterior part of the talus comes between the 2 malleoli so side to side rocking can take place leading to ankle instability.

Biomechanics of the foot 1- Bony structure 1- Hind foot: talus and calcaneus. 2- Mid foot: navicular, cubiod, and three cuneiforms. 3- Forefoot: 5 long metatarsals and 14 long phalanges.

Bony structure

2- joints of the foot Subtalar: (talocalcaneal). Transverse tarsal: (talocalnavicular and calcneocubiod). Tarsometatarsal: between cuboid and 3 cuneiforms and the bases of metatarsals. Metatarsophalangeal: between the metatarsals and the phalanges. Interphalangeal: between phalanges.

3- ligaments of the foot (A) spring (planter calcneonavicular) Position: Med. Aspect of the foot. Attachment: sustentaculum tali of calcaneus inferior navicular. Orientation: posterior anterior. Functions: 1- Support head of talus. 2- Support longitudinal arch of the foot. If it becomes weak, the space between the calcaneus and the navicular becomes wider& the talar head sinks in this space resulting in flat foot.

(b) Planter Aponeurosis Position: dense fascia on the solar surface of the foot. Attachment: from calcaneus to the proximal phalanx of each toe via deep transverse metatarsal ligaments.. Orientation: Posterior Anterior. Function: tie rod on a truss. hold the anterior and posterior struts so maintain the triangle reduce shear stress and provide shock absorption. Increase of the load on the truss will increase tension in the tie rod.

Windlass mechanism When toe extended at the MTP joints tension on the aponeurosis increased the distance between calcaneus and metatarsal heads shorten increased curvature.

(C) Long planter ligament Position: solar surface of the foot. Attachment: calcaneus and cuboid base of 2nd , 3rd , 4th metatarsals. Orientation: posterior anterior. Function: Provides longitudinal support of the foot arches. (D) Short planter ligament Extend between calcaneus and cubiod. Supports the lateral longitudinal arch of the foot

Structure of the subtalar joint (talocalcaneal) 1- bony structure Three separate between talus and calcaneus. Anterior, middle, posterior articulations. Allow triplanar motion around a single oblique joint axis. ”uniaxial joint 1 degree of freedom” supination and pronation. Axis: anterior, medial, and superior

2- ligaments of subtalar joint 1- interossous talocalcaneal ligament. 2- MCL and LCL. 3- posterior and lateral talocalcaneal ligament.

Motion of subtalar joint Non weight bearing motion (OKC): Supination: Adduction, Inversion, Planter flexion. Pronation: Abduction, Eversion, Dorsiflexion. Weight bearing motion (CKC): In CKC, the calcaneus can evert and invert but can not dorsiflex, plantar flex, adduct or abduct. Motion cannot consist of inversion and eversion in isolation. So adduction and planter flexion of calcaneus “supination” reversed by abduction and dorsiflexion of talus.

Summary of subtalar component motion Weight bearing Non-weight bearing Cal. Inversion (Varus). Talar Abd (lat.rot). Talar Dorsiflexion. Cal.Inversion (varus). Cal.Adduction. Cal.Planterflexion Supination Cal. Eversion (valgus). Talar add (med rot). Talar planter flexion. Cal. Abduction. Cal. Dorsiflexion. Pronation

Effect of subtalar joint motion on the leg Non weight bearing the motions of the subtalar joint and the leg are independent. Weight bearing subtalar pronation creates medial rotatory force on the leg (tibial tuberosity is carried medially with increased patellar tendon obliquity and Q angle). Medial rotation of the leg cause foot pronation of the foot and lateral rotation causes foot supination.

Structural of transverse tarsal joint Structure: Talonavicular and Calcaneocubiod. Motion: - Like subtalar triplaner with 1° of freedom: supination & pronation. - Med. Rotation tibia pronation of the hind foot lateral border of the foot tends to be lift from the ground diminish the stability transverse tarsal joint supinate the forefoot distal to the joint. - During the first half of the gait cycle, the hindfoot pronate while the forefoot supinate for proper WB. Hindfoot supination occurs at the second half of the stance phase Convert the foot to rigid lever.

Structure of tarsometatarsal joints The ray is a functional unit formed by a metatarsal and its associate cuneiform. Motion: The 1st ray motion is the largest of metatarsal: it is inclined so dorsiflexion is accompanied by inversion and adduction while planter flexion is accompanied by eversion and abduction. 5th ray motion is restricted its dorsiflexion is accompanied by eversion and abduction. Function: the TMT joints contribute to hollowing and flattening of the foot.

Supination and pronation twist Supination twist Hind foot pronation medial forefoot will press into the ground and lateral side will lift 1st and 2nd ray dorsiflex while 4th and 5th planter flex to maintain the foot contact with the ground the entire forefoot undergoes an inversion rotation. Pronation twist Hindfoot and transverse tarsal joint are locked in supination med. Forefoot will lift and lat. Side will press into the ground. 1st and 2nd rays planter flex while 4th and 5th dorsiflex. Supination and pronation twist occur only when the transverse tarsal joint function is inadequate.

Structure of the metatarsophalangeal Motion & Function 1- Extension range exceeds the flexion range 2- MTP allow the foot to act as hinge at the toes so that the heel may rise off the ground. Metatarsal break Single oblique axis of the MTP joints. The obliquity distributes the body weight across the toes. If the axis is not oblique, excessive amount of weight would be placed on the 1st & 2nd metatarsals. The obliquity shifts the weight laterally.

Arches of the foot Twisted osteoligamentous plate with anterior margin is horizontal (metatarsal heads) and posterior margin is vertical (Calcaneus). loading the plate will untwist and flatten the plate. We have 3 supports and 3 arches: 3 supports: head of the first metatarsal (A), head of fifth metatarsal (B), and the calcaneus (C). 3 arches: medial longitudinal arch (AC), lateral longitudinal arch (BC), and anterior transverse arch (AB).

Medial longitudinal arch Components: 9 bones, calcaneus, talus, navicular (keystone of the arch 15-18mm above ground), 3 cuneiform and heads of the medial 3 metatarsals. Factors maintaining the arch: 1- shape and arrangement of the bone. 2- spring ligament & plantar aponeurosis 3- muscles: tibialis posterior (TP), peroneus longus (PL), flexor hallucis longus (FHL), and Abd. HL. Stress transmission through the arch: controlled by the direction of the trabeculae. Posterior tibial trabeculae arising from the ant. tibia run inf. and post. to the post. support of the arch. Anterior tibial trabeculae arising from the post. tibia run inf. and ant. to the ant. support of the arch.

Lateral longitudinal arch of the foot Component: 3 bones calcaneus, cuboid, and 5th metatarsals (3-5mm above the ground) Factors maintaining the arch: 1- shape and arrangement of the bones 2- long and short plantar ligaments. 3- muscles: peroneus brevis (PB), peroneus longus (PL), abductor digiti minimi. Stress transmission: 1- Trabecular system of the tibia. 2- Trabecular system of calcaneus : superior arcuate to resist compression and inferior arcuate to resist tension.

Transverse arch of the foot Components: 1- At the level of metatarsals: 1st metatarsals to the 5th metatarsals (2nd metatarsals 9mm). 2- At the level of cuneiforms: 4 bones three cuneiforms and cubiod bones (Middle cuneiform). 3- At third level: navicular and cubiod. Factors maintaining the arch: 1- shape of the articulating bones. 2- dorsal and plantar interossous ligaments. 3- muscles: add. Hallucis, peroneus longus (PL), plantar expansion of the tibialis posterior.

Functions of the foot arches Stability functions: 1- distribute the weight through the foot. 2- conversion of the foot to rigid lever. Mobility functions: 1- shock absorption. 2- adaptation to changes in the supporting surface. 3- provide elastic propulsion of the body during walking and running.

Load transmission through the foot (stability component) Load distribution begins with the talus which receives all the weight that passes down through the leg. This load is 50% of BW in bilateral stance and 100% in unilateral stance. The weight transmitted the talus is divided into 2 pathways comprising 7 weight bearing points. (1)- 50% of BW passes anteriorly through the transverse tarsal joints to the forefoot. In static standing, the weight distribution at the metatarsal heads is 2:1:1:1:1 proportion with 6 WB points. Loads on the 1st and 2nd rays increase in the late stage of the stance phase when BW shifts medially. (2)- 50% of BW passes posteriorly to the calcaneus. WB at this point is dissipated by the heel pad which plays critical role at heel contact (80-100% BW) and running (250% of BW).

Load transmission through the foot (mobility component, shock absorption) With loading there is: 1- Eversion of the calcaneus and adduction and plantar flexion of the head of talus (foot pronation). 2- Talar motion causes slight depression of navicular (checked by the spring ligament). 3- Slight flattening in the longitudinal arch. 4- Elasticity of the supporting structures absorbs the shock. 5- Shape of the foot is adapted according to the supporting surface.

Kinetics: 1- statics Two leg stance: each ankle carries ½ of BW. During postural sway the JRF changes according to the position of GRFV. JRF increases if the GRFV passes more ant. To the ankle joint increasing the moment arm of GF with increased demand on the calf muscles. one leg stance: carries 100% of BW. Unilateral standing on tiptoe: Achilles tendon force 1.2 w & JRF 2.1 W. This explains why patient with ankle O.A will have pain on rising up on tiptoes.

2- Dynamics Compressive force during stance phase: - Produced by contraction of gastrocnemius and soleus. - 5W at the late stance phase ( when the Achilles tendon produces torque for plantar flexion at push off). During fast walking there are 2 peaks of JRF: 3w in early stance and 5w in late stance. Shear force: - 0.8 W just after the middle of the stance phase

Pathomechanics 1- Flatfoot (pronated foot or pes planus) Plantar fascia over stretched, subtalar joint excessively pronated cause rear foot valgus posture. 1- Medial rotatory stresses on the leg excessive angulations of patellar tendon & excessive pressure on the lateral patellar facet. 2- Asymmetrical flat foot inequality of the leg length.

Types of flat foot are: rigid & flexible For flexible flat feet when the person is asked to stand on tip-toe, the arch usually reconstitutes, and the heel goes into mild varus

2- Supinated foot (Pes cavus, raised medial longitudinal arch) Subtalar and transverse tarsal joint locked in supination prevent the foot to participate in shock absorption or adaptation to uneven surface. Supinated position: 1- Lat. Rot. Stress on the leg. 2- Planter aponeurosis remain slack and may shorten over time. 3- TMT joints undergo a pronation twist to maintain appropriate weight bearing of the foot. 4- Callus formation under the metatarsal heads.

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