Regional BiomechanicsRegional BiomechanicsAnkle Joint & FootAnkle Joint & Foot

KinematicsKineticsPathomechanics

Biomechanics of Ankle jointBiomechanics of Ankle joint1- Bony structure1- Bony structureProximal: 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 talusTibiofibular 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 Bony structure of the ankle and footfoot

2- Axis of the ankle joint2- Axis of the ankle jointrotate laterally 6 in the horizontal plane rotate laterally 6 in the horizontal plane and inclined 10 down on the lateral side.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 ankle3- ligaments of the ankle(1) medial collateral ligament “Deltoid (1) medial collateral ligament “Deltoid ligament”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(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 (3) Anterior and posterior ligaments of the anklethe 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 Functions of the ankle jointjointStability 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 jointMobility of ankle jointSince 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 jointStability of ankle jointClosed 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 footBiomechanics of the foot1- Bony structure1- Bony structure1- Hind foot: talus

and calcaneus.

2- Mid foot: navicular, cubiod, and three cuneiforms.

3- Forefoot: 5 long metatarsals and 14 long phalanges.

Bony structureBony structure

2- joints of the foot2- 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 foot3- ligaments of the foot(A) spring (planter calcneonavicular)(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(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 mechanismWindlass 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(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 jointStructure of the subtalar joint(talocalcaneal)(talocalcaneal)1- bony structure1- 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 2- ligaments of subtalar jointjoint

1- interossous talocalcaneal ligament.

2- MCL and LCL.3- posterior and lateral

talocalcaneal ligament.

Motion of subtalar jointMotion 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 Summary of subtalar component motionmotion

Non-weight bearing

Weight bearing

SupinationCal.Inversion (varus).

Cal.Adduction.

Cal.Planterflexion

Cal. Inversion (Varus).

Talar Abd (lat.rot).

Talar Dorsiflexion.

PronationCal. Eversion (valgus).

Cal. Abduction.

Cal. Dorsiflexion.

Cal. Eversion (valgus).

Talar add (med rot).

Talar planter flexion.

Effect of subtalar joint motion on Effect of subtalar joint motion on the legthe 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 Structural of transverse tarsal jointjoint 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 Structure of tarsometatarsal jointsjointsThe 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 twistSupination and pronation twistSupination 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 Structure of the metatarsophalangealmetatarsophalangeal

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 footArches of the footTwisted 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 archMedial 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 Lateral longitudinal arch of the footfoot 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 Transverse arch of the footfootComponents: 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 Functions of the foot archesarches

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 Load transmission through the foot (stability component)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 Load transmission through the foot the foot (mobility component, (mobility component, shock absorption)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: Kinetics: 1- statics1- staticsTwo 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- Dynamics2- DynamicsCompressive 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

PathomechanicsPathomechanics1- Flatfoot (pronated foot or pes 1- Flatfoot (pronated foot or pes planus)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 & Types of flat foot are: rigid & flexibleflexible

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 2- Supinated foot (Pes cavus, raised medial longitudinal (Pes cavus, raised medial longitudinal arch)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.