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