Ankle Foot Anatomy

Anatomy of the ankle and foot

The ankle

The ankle is a complex joint articulating the lower extremity with the foot.

It permits the flexion, extension and rotation of the foot. The ankle bears the full weight of the body, which is enhanced with the forces applied in activities such as running and jumping. For this reason, the ankle is subject to a wide range of injuries. 

The foot

The foot is the terminal end of the lower extremities on which we stand and walk. It is articulated to the lower leg through the ankle joint. The multitude of functions of the foot is the result of a sophisticated, biomechanical anatomy comprising several bones, joints, ligaments, muscles and tendons that allow for its versatility. Because of the its role in ambulation and weight bearing, the foot is subject to several pathologies that can limit our mobility in daily activities and professions.

Ankle bones

The ankle is a synovial joint formed by the bones of the lower leg tibia and fibula and the bones of the foot, the talus and calcaneus. 

The landmarks of the lower extremity forming the ankle are the:

lateral malleolus situated at the edge of the fibula

posterior malleolus on the back side of the tibia

medial malleolus in the medial lower edge of the tibia

Foot bones

The foot is equipped with 26 bones including :

14 phalanges

5 metatarsal bones

7 tarsal bones (calcaneus, talus, cuboid, navicular and medial, middle and lateral cuneiform bones)

These bones are grouped into three sections:

fore-foot formed by the phalanges and metatarsal bones

mid-foot comprising 5 tarsal bones, 3 cuneiform bones, cuboid bone and navicular bone

hind-foot comprising 2 tarsal bones, the talus and calcaneus

The dorsal or upper side of the foot is opposed to the lower, plantar side facing the ground.

Tarsal bones

Calcaneus is the largest bone of the foot protruding at the heel. It is the first part of the foot to touch the ground when walking. This bone inserts the Achilles tendon arising from the calf muscles (gastrocnemius and soleus) in the posterior side. This muscles extend the ankle and flex the foot when raising the body on the balls of the foot. In the anterior or articular side the calcaneus has a convex shape and faces the posterior side of the talus.

Talus is the second largest tarsal bone of the hind-foot. It is situated anterior to the calcaneus and is almost completely covered by cartilage due to its vast articular surface. Multiple articulations are present at the talus with the calcaneus, lateral and medial malleoli and navicular bone. The talus comprises the head, neck, body, and two lateral processes.

Cuboid is a smaller bone situated on the lateral side of the foot between the calcaneus and the 4th and 5th metatarsal bones. It takes the name from its cuboid shape. It is used for the insertion of ligaments and forms four articulations with the following bones: calcaneus, 3rd cuneiform, 4th and 5th metatarsal.

Navicular bone is located in the mid-foot, anterior to the cuboid and before the cuneiform bones. It forms part of the dorsum of the foot. The boat-like bi-concave shape gives the name to this bone.

Cuneiform bones

The cuneiforms are three bones, named medial, middle and lateral cuneiform, having a convex shape. They are situated in the foot dorsum. They form multiple joints:

The medial articulates with the navicular, 1st cuneiform and 1st and 2nd metatarsal bones.

The middle smallest cuneiform bone articulates with the navicular, 1st and 3rd cuneiform, 2nd metatarsal bone.

The lateral cuneiform articulates with the navicular, 2nd cuneiform, cuboid, 2nd, 3rd, 4th metatarsal bones. 

Metatarsal bones

The metatarsal bones are interposed between the tarsal bones and the phalanges, or toes bones. The have a cylindrical elongated shape divided into a head (distal end), neck, shaft and base (proximal end). The shaft is slightly curved to provide a a concave shape to the foot plantar and convex to the dorsal foot side. 

The 1st metatarsal corresponds to the phalange of the hallux, or big toe. The other metatarsal bones follow sequentially with the 2nd, 3rd, 4th and 5th in continuity with the corresponding proximal phalanges and toes.

Each metatarsal articulates with at least one tarsal bones of the mid-foot, whereas the metatarsal heads articulate with the proximal phalanges. 

Phalanges

The phalanges are the most distal bones of the toes forming two rows: the proximal phalanges opposed to the metatarsal bones, the middle and the distal phalanges. Except for the the hallux with two (proximal and distal), all other toes have three phalanges, mirroring the anatomy of the hand.

Proximal phalanges present a cylindrical and curved shape similar to the metatarsal bones, with the largest one being the proximal phalange of he hallux.

Distal phalanges have a flat shape to accommodate for the toe nail bed.

Sesamoid bones

The sesamoid bones are unusual in that they are embedded into a tendon rather than being free. The foot has two small sesamoid bones at either side of the1st metatarsal bone head of the hallux, forming the ball of the foot. They have the shape of the bean and function as pulleys for the tendons during motion. These bones absorb shock and assist during walking when pressure is put on the ball of the foot. 

Cartilage

The edges of the bones forming the ankle joint are protected by articular cartilage. This is a rubbery, shiny and smooth tissue, which reduces the friction between bones during movement and absorbs the impact, thus preventing the degeneration of the bones.

The joints of the ankle

The ankle consists of three distinct joints:

talo-crural or true ankle joint involves the tibia, fibula and talus, the small bone between the tibia and calcaneus bones. This joint is responsible for flexion extension of the foot

sub-talar joint or talo-calcaneal joint is formed by the talus and the calcaneus (side rotation of the foot)

Inferior tibio-fibular joint (or syndesmosis joint) between the tibia and fibula.

 

Joints of the foot

The foot has over 30 distinct joints, which articulates the bones with one another. Only the subtalar and transverse tarsal joints control foot motion (inversion and eversion). The other joints allow for small movements only.

At each joint the bone ends are covered with articular cartilage, to absorb sock and create a smooth surface for the movement of the bones at the joint.

subtalar joint (synovial joint) articulates the talus and calcaneus. It allows side to side movement of the foot

transverse tarsal joint (or Chopart’s joint) articulates the talus and calcaneus on one side and the navicular and cuboid on the other. It allows some pivoting movements of the forefoot on the hind-foot and flattening of the arch. It includes the talo-calcaneo-navicular and the calcaneo-cuboid joints (synovial joints), which articulates the anterior calcaneus and the navicular and cuboid, respectively

cuneo-navicular joint (synovial joint) between the navicular bone and the three cuneiform bones

cuboideo-navicular joint between the cuboid and the navicular bones

tarso-metatarsal joint (or Lisfranc’s joint) articulates the distal tarsal bones, (cuneiforms and cuboid) with the metatarsals

inter-metatarsal joints are located at the base of the metatarsal bones

metatarso-phalangeal joints (MTP) are five joints between each metacarpals and the corresponding phalanges. These are visible when bending and straightening the toes and permit the flexion and extension of the toes

inter-phalangeal joints are two in each toe and connect the three phalanges with one another with the exception of the hallux that has only one. They are used when curling the toes.

 

Ligaments of the ankle

The ankle is supported by a number ligaments, which are elastic fibrous bands of connective tissue, joining bones to bones.

The main ligaments of the ankle are named according to the bones they connect with one another:

The lateral ligament complex is a key structure located on the outer side of the ankle consisting of three ligaments:

Anterior talo-fibular ligament (ATFL) connects the talus with the fibula on the ankle front side

Calcaneo-fibular ligament (CFL) connects the fibula to the calcaneus on the lateral side

Posterior talo-fibular ligament (PTFL) runs from the back of the fibula to the posterior side of the calcaneus

deltoid or medial ligament is situated in the medial, internal side of the ankle

anterior inferior tibio-fibular ligament (AITFL) keeps the tibia and fibula together on the front side.

posterior fibular ligaments (PTFL) keep ends of tibia and fibula together from the back side and comprise the posterior inferior tibio-fibular ligament (PITFL) and the transverse ligament

interosseus ligament is a large membrane that runs throughout the length of the tibia and fibula to connect these bones of the lower leg.

The retinaculum

The retinacula comprise a system of ligaments forming fibrous bands, which support the tendons of the lower leg and ankle/foot during flexion, extension and rotation movements.

Superior extensor retinaculum is the higher retinaculum located in front of the lower leg. It inserts in the middle of the tibia and extends to the fibula across the ankle. It keeps together the extensor tendons

Inferior extensor retinaculum is the lower band of ligaments attaching from one malleolus to the other finally attaching to the dorsal foot

Superior peroneal retinaculum and Inferior peroneal retinaculum are located over the tendons of the peroneal muscles. The superior holds the tendons in position below the lateral malleolus and the inferior holds them at the lateral side of the calcaneus.

Ankle joint capsule

The ankle is surrounded by a fibrous capsule enclosed by a synovial membrane, which produces a lubricating synovial fluid to facilitate the sliding of the ankle bones.

The ankle capsule is held together by the deltoid and medial ligaments; in the outer layer by the anterior talo-fibular, calcaneo-fibular and posterior talo-fibular ligaments.

These structures together permit a wide range of movements of the ankle joint and stabilise the ankle to avoid excessive extension/flexion and rotation. 

Muscles

Muscles of the anterior lower leg controlling the foot

The movement of the foot is controlled by muscles situated in the lower leg, also named extrinsic muscles, as well as muscles residing in the foot itself or intrinsic muscles.

The anterior part of the lower leg (shin) comprises the following muscles:

tibialis anterior

extensor digitorum longus

extensor hallucis longus

peroneus tertius

These muscles dorsiflex the foot and toes upward. The tibialis anterior also controls turning the foot inward.

At the the lateral side of the lower leg are the muscles:

peroneus longus

peroneus brevis

These muscles are used to pull the foot outward and to flex the toes (pointing the foot).

Muscles of the posterior lower leg

The posterior compartment of the lower leg, commonly named calf, consists of two large muscles:

gastrocnemius

soleus

The gastrocnemius begins on the femur above the knee, whereas the soleus inserts below the knee at the tibia. These muscles merge as they descend towards the ankle to form the Achilles tendon, which raps around the calcaneus or heel bone.

The calf muscles flex the ankle and lift the heel when raising the body on the ball of the feet.

In the deep posterior compartment of the lower leg are the following muscles:

tibialis posterior

flexor digitorum longus

flexor hallucis longus

The tibialis muscle pulls the foot inward and the flexor muscles flex the toes and hallux, respectively. Together they also control the flexion of the foot plantar.

Muscles of the foot

The largest muscles of the foot are mostly located on the plantar side and distributed on four layers which are described below from the inner to the outer layer.

First layer: originate at the calcaneus and extend up to the toes:

abductor hallucis and abductor digiti minimi muscles contribute to the abduction of the hallux and small toe, respectively. However, their function is mostly to relieve the tension in the plantar aponeurosis when we lift the toes

flexor digitorum brevis muscles insert at the remaining four toes and flex them

Second layer:

quadratus plantae arises from the calcaneus and joins with tendon of the muscle flexor digitorum longus

lumbricals (I to IV) connect to each lateral toe (except hallux) by inserting to the proximal phalanges. They are used to flex the toes.

 

Third layer:

flexor hallucis brevis runs from the cuboid and lateral cuneiform bones to the proximal phalanx to flex the big toe

flexor digit minimi brevis begins at the 5th metatarsal and inserts in the proximal phalanx of the little toe and is used to its flexion

adductor hallucis originates in the 2nd,3rd,4th metatarsal bones and connects to the proximal phalanx of the hallux

 

Fourth layer:

Plantar and dorsal interossei begin at the metatarsal bones and insert in the proximal phalanges. They are used to adduct and abduct the toes, respectively.

Extensor digitorum brevis and extensor hallucis brevis muscles join to form one muscle and run from the upper-lateral part of the calcaneus to the proximal phalanges of the toes and are used to extend them.

Tendons of the ankle and foot

The function of the muscles of the foot is coordinated by numerous tendons connecting the muscles to the bones. These tendons begin in the lower leg and descend to the foot where they assist in the movement of the toes.

peroneal or fibularis tendons (longus and brevis) run behind the fibula, along the lateral side of the calf to the foot. These tendons are named after their corresponding muscles:

peroneal brevis (short) tendon attaches to the 5th metatarsal bone of the foot (little toe)

peroneal longus (long) tendon runs under the foot and inserts to the 1st metatarsal bone of the foot

The extensor longus digitorum and extensor hallucis longus tendons are the continuation of the muscles carrying the same names and extend to the foot and toes.

extensor longus digitorum longus arises at the tibial condyle, runs along the lateral side and inserts at the dorsal foot. It divides into four branches, each inserting in the small toes.

extensor hallucis longus insert on the dorsal side of the big toe and extends it upward. It is clearly visible with foot/hallux flexion

The posterior tibial tendon arises from the calf muscle. It runs on the back side of the leg near the Achilles tendon and bends at the ankle to insert to the bones on the inner foot. It holds the arch and support the foot when walking.

Peroneal tertius tendon enters the dorsal surface of the 5th metatarsal bone.

Achilles tendon

The Achilles tendon is the largest and strongest tendon in the body. It connects the calf muscles to the back of the foot or calcaneus. It is also named the calcaneal tendon.

This tendon is formed conjointly by the gastrocnemius and soleus muscles of the calf and inserts into the calcaneus.

With the flexion of the calf muscles, the Achilles tendon will raise the calcaneus. This movement occurs when we stand on our toes, or during running, sprinting and jumping. Due to the poor blood flow, all tendons including the Achilles are prone to injury causing tears and severing.

The retinaculum

The retinacula are actually a system of ligaments forming fibrous bands, which support the tendons of the lower leg and ankle/foot to keep them in place during flexion, extension and rotation movements.

Superior extensor retinaculum is the higher retinaculum located in front of the lower leg. It inserts in the middle of the tibia to the fibula across the ankle with the function to keep together the extensor tendons

Inferior extensor retinaculum is the lower band of ligaments attaching from one malleolus to the other finally attaching to the dorsal foot

Superior peroneal retinaculum and Inferior peroneal retinaculum are located over the tendons of the peroneal muscles. The superior holds the tendons in position below the lateral malleolus and the inferior holds them at the lateral side of the calcaneus.

Arteries and veins of the ankle and foot

Arteries

The arteries supplying the ankle and foot arise from the arteries of the thigh and lower leg.

The popliteal artery originates from the femoral artery in the thigh and branches below the knee into the anterior tibial artery, posterior tibial artery and the fibular or peroneal artery. These arteries supply the frontal, medial and lateral leg, respectively.

The anterior tibial artery runs through the entire length of the leg into the foot, where it becomes the dorsal pedis artery (used to feel the pulse on the foot dorsum).

The dorsal pedis artery supplies with its branches the dorsal side and the sole of the foot. In the dorsum, it forms the lateral tarsal artery, the arcuate artery and the metatarsal arteries, which further divide into the plantar digital arteries to supply the lateral toes.

The posterior tibial artery descends through the deep posterior compartment of the lower limb and supplies the inner leg. It can be felt as the pulse of the medial malleolus. Downstream it forms the medial and lateral plantar arteries of the foot.

The fibular artery runs between the tibia and fibula and divides further to supply the posterior side of the heel (rete calcaneum).

Rete calcaneum or calcaneal anastomosis consists of a network of arteries over the calcaneus, formed by branches of the fibular and posterior tibial arteries and branches of the malleolar networks.

Veins

Deoxygenated blood flows through the veins from the lower extremities and ascends to the heart.

The main veins of the foot and lower leg are:

digital veins exit from each toe and join into the plantar venous arch, which divides into each side of the foot to merge into the posterior tibial vein

lesser or small saphenous vein originates at the foot and runs subcutaneously along the medial aspect of the calf to merge with the greater saphenous vein in the thigh

poplitear vein is located posteriorly in the subcutaneous region of the knee and continues upstream to merge with the femoral vein

anterior and posterior tibial veins and the fibular (or peroneal) vein run along the anterior and posterior side of the tibia, respectively

fibular vein runs at the lateral aspect of the calf along the fibula bone. These last three veins merge into the popliteal vein at the knee region.

Plantar pump

The plantar pump is composed of large medial and lateral plantar veins (plantar venous arch), which converge posteriorly into the deep tibial veins and anteriorly into the anterior tibial veins. The function of the plantar pump is to decrease hydrostatic pressure and pump venous blood upstream towards the lungs where it becomes oxygenated. This is facilitated during motion and weight bearing.

Nerves of the lower extremity

The innervation of the lower leg, ankle and foot begins upstream at the lombo-sacral region of the spine with a bundle of nerves that together form the lumbo-sacral plexus. The nerves exiting the 4th and 5th lumbar vertebrae form the lumbo-sacral trunk merge with the sacral plexus, which consists of the sacral nerves from the 1st to the 4th sacral vertebrae. The sacral plexus descends along the posterior pelvic wall.  The most important nerve of the lower extremity is the sciatic nerve and its branches extending from the spine to the foot.

Sciatic nerve

Sciatic nerve is the largest human nerve; it consists of nerves arising from the 4th lumbar to 3rd sacral vertebrae. It leaves the sciatic foramen to first innervate the gluteal muscle.

The sciatic nerve with all its components innervate several muscles of the leg.

It provides motor innervation to the muscles of the posterior thigh, and extends to all muscles of the lower leg and foot

It also provides sensory innervation to the skin of the leg anterolateral and postero-lateral aspects

Injury to the sciatic nerve produces a number of neurological deficits including motor and sensory loss of the posterior thigh, leg and foot.

Above the knee the sciatic nerve divides into two branches: the tibial nerve medially and the common fibular nerve, laterally.

Tibial nerve bifurcates into the medial and lateral plantar nerves in the sole of the foot

The medial plantar nerve innervates the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis muscles.

The lateral plantar nerve innervates the abductor digiti minimi, flexor accessorius, interossei and lumbricals, adductor hallucis and flexor minimi brevis muscles

Injury to the tibial nerve typically produces: loss of plantar flexion, loss of flexion of the toes and poor foot inversion and sensory loss of these regions.

Tibial nerve

The tibial nerve runs in the posterior aspect of the leg along the tibial artery to reach the medial malleolus of the distal tibia at the ankle.

Below the medial malleolus, the tibial nerve bifurcates into the medialandlateral plantar nerve innervating the sole of the foot.

The tibial nerve affords motor and sensory innervation to the muscles of the posterior compartment of the leg and sensory function in the sole of the foot.

Injury to the tibial nerve causes:

loss of foot flexion (plantar flexion)

loss of toe flexion

reduced inversion of the foot

sensory loss throughout the areas above

Common fibular nerve

The common fibular nerve, or common peroneal nerve, originates from the tibial nerve and bends around the proximal fibula subcutaneously, which makes it prone to injury.

At the fibular head, the common fibular nerve bifurcates into the superficial and deep fibular nerves.

The superficial fibular nerve is situated on the lateral aspect of the lower leg where it controls motor function during outwards movement (eversion) of the foot

It also provides sensory function in the antero-lateral compartment of the leg and the dorsum of the foot.

Injury to this nerve impairs the motor and sensory functions described above.

The deep fibular nerve runs in the anterior aspect of the lower leg along the tibial artery. It confers motor function to the frontal muscles of the leg to control foot dorsiflexion and toe extension.

It also regulates sensory innervation between hallux and second toe.

Injury to the deep fibular nerve causes the so called “foot-drop”, and deficits in the functions described above.