Foot and Ankle Bio-Mechanics
The foot and ankle combine flexibility (propulsion) with stability(support) structure because they consist of a
complex of joints, bony structure, ligamentous attachments, and muscle contraction. The flexible/rigid characteristics
of the ankle/foot complex provide multiple functions, including:
1. Ankle joint forces up to 4.5 times body weight to occur while walking.
2. It provides a base of support.
3. It acts as a lever during push-off period of stance.
4. It provides adequate flexibility for absorption of the shock of the body weight and for accommodation to uneven terrain.
5. Prehensile.
Structure of the ankle and foot
Bony Parts: It contains a total of 26 bones
1. Leg
Tibia and fibula
2. Hindfoot
Talus and calcaneus
3. Midfoot
Navicular, cuboid, and three cuneiforms
4. Forefoot
Five metatarsals and 14 phalanges, which make up the 5 toes (3 phalanges for each toe except the large toe, which has 2 phalanges)
Figure 1: Structure of the ankle and foot
Arches of the Foot
They are formed by the structure and arrangement of the bones (tarsus and metatarsus) and maintained by
ligaments and tendons the arches are not rigid; they “give” when
weight is placed on the foot, and they spring back as the weight is lifted.
There are 2 types of arches:
Longitudinal arch: divided into medial and lateral parts
The medial part originates at the calcaneus, rises at the talus, and descends to the first three metatarsal bones and
receives weight of the body. The medial arch is supported by the spring ligament. Lateral part consists of the
calcaneus,cuboid, and fourth and fifth metatarsal bones and acting essentially as a space through which tendons canpass.
It is supported by the long and short plantarligaments.
Transverse Arch – side to side concavity from anterior tarsal bones (calcaneus, navicular, and cuboid) to all fivemetatarsal bones.
Arches of the Foot
The factors maintaining the arches of the foot:
Functions of the arches:
1. Support the weight of the body in standing.
2. Act as a lever to propel the body in walking and running.
3. During weight bearing,
mechanical energy is stored released to assist with push-off of the foot from the surface.
Transmission of body weight:
The structures of the foot are anatomically linked such that the load is evenly distributed over the foot during weight bearing.
Approximately 50% of body weight is distributed through the subtalar joint to the calcaneus, with the remaining 50% transmitted
across the metatarsal heads.
The head of the first metatarsal sustains twice the load borne by each of the other metatarsal heads. Tibia is the only true
weight-bearing bone in the body.
Muscle Function in the Ankle and Foot
Both the extrinsic muscles (11) and the intrinsic (22) muscles of the foot play a vital role in the mechanics of the foot.
Muscles
Muscle control of the ankle during gait
1. The muscles of the anterior compartment (dorsiflexors) actprimarily during swing and early stance phase. This action
enables the foot to clear the ground during swing phase and then allows it to be placed gently on the ground after heel strike.
2. The posterior, or calf, group acts from midstance to toe-off.
3. In normal standing, the gravitational line falls anteriorly to the axis of the ankle joint, creating a dorsiflexion moment.
The soleus muscle contracts to counter the gravitational moment through its pull on the tibia.
4. The intrinsic muscles of the foot activity in the last half of the stance phase.
Joints
The joints of the foot are divided into three sections—hindfoot
(rearfoot), midfoot, and forefoot ankle and foot joints.
Joints:
Hindfoot (Rearfoot)
1. Talocrural (Ankle) Joint.
2. Subtalar (Talocakanean).
Midfoot (Midtarsal Joints, Transverse Tarsal Joint, Chopart’s amputation) .
1. Talocalcaneonavicula r joint.
2. Cuneocuboid Joint.
3. Cuneonavicular Joints
4. Cuboideonavicular joint
5. Calcaneocuboid Joint.
Fore foot
1. Tarsormetatarsal Joints.
2. Metathrsophafangeat Joints.
3. Interphalangeal joints.
Important joints of the foot:
Ankle Joint (Talocrural): The talocrural joint is a uniaxia (,modified hinge, synovial joint) located between the talus,
themedial malleolus of the tibia, and the lateral malleolus of thefibula and the movements possible at this joint are dorsiflexion
and plantar flexion.
Subtalar (Talocakanean) Joint: A gliding multiaxialsynovial joint which consists of the talus on top and calcaneuson the bottom.
The subtalar joint allows movements about an oblique axis, allowing the foot to side to side motion (inversion and eversion).
Transverse tarsal joint: It is formed of 2 joints that lie sideby-side. These are the talo-navicular joint (between the head
of talus and navicular), and calcaneo-cuboid joint (between the caleaneus. and cuboid). It is little to no motion
and assists in eversion and inversion.
Locking and unlocking of the ankle joint: During
dorsiflexion, the wide anterior part of the trochlear surface of the talus is lodged into the narrow posterior part of the superior
articular surface (socket). In this position, the ankle joint is locked as the foot cannot be moved from side to side.
During plantar flexion, the narrow posterior part of the trochlear surface is lodged in the wide anterior part of the socket.
In this position, the ankle joint is unlocked as the foot can be movedslightly from side to side.
Accordingly, the ankle joint is locked during dorsiflexion and unlocked during plantar flexion.
Ligaments:
Ankle Ligaments
Lateral Ankle Ligaments:
Talofibular ligaments: from the lateral malleolus of the fibula to connects the talus and support the lateral side of the joint.
Divided in:
Anterior Talofibular Ligament: It is prevents anterior subluxation of talus when ankle is in plantar flexion.
Posterior Talofibular Ligament: it is prevents posterior and rotatory subluxation of the talus.
Calcaneofibular: connecting lateral malleolus to calcaneus.
It acts primarily to stabilize sub-talar joint & limit inversion. it is lax in normal, standing position due to relative valgus
orientation of calcaneus
Medial Ankle Ligaments
Deltoid ligaments: supports the medial side, triangular shaped, apex at tip of medial malleolus,, base at talus, navicular,
calcaneus which has two major components;
Superficial deltoid which resist talar abduction and primarily resists eversion of hindfoot. Tibionavicular portion prevents inward
displacement of head of talus, while tibiocalcaneal portion prevents valgus displacement. Deep deltoid ligament is prevents
lateral displacement of talus & prevents external rotation of the talus and latter effect is pronounced in plantar flexion, when
deep deltoid tends to pull talus into internal rotation.
Ligaments of the Foot:
Spring ligament: attaches from calcaneus to navicular. It is supports longitudinal arch and the head of talus especially in standing.
Plantar aponeurosis: runs from calcaneus to proximal phalanges, ties posterior an anterior sections together and windlass action
in ankle, where full dorsflexion is limited by plantar aponeurosis.
Movements of the Foot and Ankle
1. Primary plane motions defined
a. Sagittal plane motion is dorsflexion and plantarfiexion.
b. Frontal plane motion is inversion and eversion .
c. Transverse plane motion is abduction and adduction.
2. Triplanar motions occurring about oblique axes defined
a. Pronation is a combination of dorsiflexion, eversion, and
abduction.
b. Supination is a combination of plantarfiexion, inversion, and
adduction.
ROM:
Plantar flexion(55°), Dorsiflexion(15°), Inversion(35°),
Eversion(20°), Pronation (20°)and Supination(35°).
The ankle and foot during gait:
The biomechanics of the foot are best explained by describing
what happens to the foot during the stance phase of the gait
cycle.
Stance phase:
Heel strike
The impact of the heel as it contacts the floor, with subsequent rapid loading of the foot, results in a floor reaction that exceeds
the body weight by 20 per cent. The sudden impact is partially absorbed by lowering the body through plantar flexion of the ankle.
It is during this phase that the foot begins to act like a shock absorber. The ankle dorsiflexors function during the initial foot
contact to counter the plantarflexion torque and to control the lowering of the foot to the ground.
Midstance
During midstance the entire foot is in contact with the ground (ankle is neutral again) and the weight of the body is directly over
the foot. The vertical floor reaction is less than the body weight because of the falling CM. The longitudinal arch of the foot
is elevated and the foot everts, with concomitant motion in the subtalar joint due to the eversion, pronation and external rotation
of the lower limb. As the body weight shifts forward the foot begins to return to a neutral position in preparation for heel lift.
Push-off
The ankle plantarflexors , supinates and the metatarsal phalangeal joints go into extension begin functioning near the end of
mid-stance and during terminal stance and preswing (heel-off to toe-off) to control the rate of forward movement of the tibia
and also to plantarfiex the ankle for push-off. During this period the heel rises rapidly with increased ground reaction, up to
40 per cent above body weight.
Swing Phase of Gait:
Much of kinetic energy for swinging limb is provided by inertia, which is augmented by the plantarflexors (85%) and hip flexors (15%).
During swing, the ankle dorsiflexes by the concentric contraction of anterior tibialis muscle and all other muscles are silent.
Sub-talar joint assumes near neutral position, and toes dorsiflex slightly as foot prepares for next episode.
Common injuries of the ankle and foot
Foot injuries may develop from various causes, such as congenital malformations of bones, muscular paralysis or spasticity,
stresses and strains in weight-bearing.
Alignment Anomalies of the Foot and Abnormal foot contact:
1. Pes varus (Club foot).
2. Pes valgus (Pes planus or flat foot).
3. Pes equines.
4. Pes cavus.
5. Pes Calcaneus.
Injuries Related to High and Low Arch Structures:
Arches that are higher or lower than the normal range have been found to influence lower extremity kinematics and kinetics,
with implications for injury. High- arched exhibit increased vertical loading rate, with related higher incidences of ankle sprains,
plantar fascitis, and 5° metatarsal stress fractures. Low-arched exhibit increased range of motion and velocity in rearfoot eversion,
as well as an increased eversion to tibial internal rotation ratio.
Injuries of the Ligaments
Ankle sprains
Injuries of the lateral ligament
Ankle sprains usually occur on the lateral side because the joint capsule and ligaments are stronger on the medial side of the ankle.
Mechanism injury of ankle sprain is inversion of the supinated, plantarflexed foot. It usually occurs when the foot rolls over on
the outside of the ankle. When the ligament is completely torn or detached from the fibula, the talus is free to tilt in the mortice
of the tibia and fibula. If the lateral ligament fails to heal, chronic instability of the ankle results.
Fractures with Deloid Injury ligament (Maisonneuve fracture):
The medial ligament is immensely strong and if stressed in ankle joint injuries generally avulses the medial malleolus rather than
itself tearing. Nevertheless tears do occur, and are seen particularly in conjunction with lateral malleolar fractures. A mechanism
is combination of external rotation at ankle, abduction of hindfoot,& eversion of forefoot while the upper body externally rotates
over the fixed foot.
Paralysis or Spasticity:
Tibialis Posterior:
Paralysis of tibialis posterior alone causes a planovalgus deformity. Spasticity of Tibialis Posterior cause dynamic varus
deformities of foot.
Tibialis Anterior:
Paralysis (polio) results in development of equinovalgus deformity this is seen initially during swing phase of gait. Failure to
raise the foot sufficiently during the early swing phase causes Toe drag.
gastrocnemius-soleus paralyzed:
The patient cannot rise on tiptoes, and the gait is severely affected because inability to increase walking speeds beyond the
normal pacing. However, despite uneven step lengths, she had uniform forward progression. She had excessive dorsiflexion
of the ankle and diminished plantar flexion on the involved side . The act of climbing stairs is awkward and slow, and activities
such as running and jumping are all but impossible.
Other soft tissues injuries:
Footballer’s ankle:
Repeated incidents of forced plantar flexion of the foot which result in tearing of the anterior capsule of the ankle joint.
These may lead to mechanical restriction of dorsiflexion.
Peroneal tendon disruption (peroneus brevis tear):
Mechanism of this injury is forced dorsiflexion with slight inversion and concomitant eccentric contraction of the peroneal
muscles may produce a subluxation or dislocation of the peroneal tendons.
Anterior (Talotibial) Impingement Syndrome:
The mechanism of injury is repetitive forced dorsiflexion as demiplie position in ballet can lead to impingement of anterior
lip of tibia on talar neck.
Posterior (Talotililal,) Impillgement Syndrome:
The mechanism of injury is repetitive, forced plantarflexion such as may occur with practicing karate kicks or dancing en pointe.
Shortening of the Achilles tendon
Mechanisms for tendinitis have been proposed by repeated tension or repeated loading .Shortening results in plantar flexion of
the foot and clumsiness of gait as the heel fails to reach the ground (Insufficient push off).
Plantar Fasciltis:
Mechanism of Injury are overuse or repetitive stretching of the plantar fascia associated with training errors or associated
with incomplete rehabilitation (strengthening) following a previous ankle injure because weak peroneal muscles may inadequately
support the arch. Thus placing additional stress on the plantar fascia. All of which reduce the foot’s shockabsorbing capability.
Fracture:
Both the end of the fibula (1) and the tibia (2) are broken .If both malleoli are broken, this is called a bimallolar fracture
or Pott's fracture.
Stress Fractures
The shafts of the second through the fifth metatarsals are the most common sites of injury. These injuries are perhaps most
commonly seen in athletes involved in endurance running activities.
Pediatric Ankle Fractures
The age distribution of was typical: malleolar fractures predominated among the younger children, epiphyseal fractures among the
older.
Most common epiphyseal injury to ankle is distal tibia caused by supination and external rotation. Complications of this fracture is :
1. Growth Plate Arrest.
2. Angular Deformities - varus or valgus deformity.
3. Leg Length Discrepancy.
