Anatomy of the Foot & Ankle
The foot consist of 26 bones and 28 joints which are controlled by 42 muscles that are arranged in 9 compartments and are held together by multiple ligaments. There are 19 tendons that cross the ankle joint and insert on different parts of the foot.
The term ‘ankle’ refers to the ‘talocrural’, or the true ankle joint, which is a hinge joint between the talus and the distal end of tibia and fibula. The talus fits right in between the latter two bones and sits on top of the calcaneus. The body of talus is slightly wider anteriorly than posteriorly.
The subtalar joint is made by an articulation between the talus and the calcaneus. The mid-tarsal joints are formed between the talus and the navicular and between the calcaneus and the cuboid. In full extension (dorsiflexion), the talus becomes firmly wedged between the two malleoli. In flexion (planterflexion), there is slight laxity in the joint and allowing some side to side movements, which occur at the subtalar joint and mid-tarsal joint.
The bones of the foot are arranged in the form of two longitudinal arches. The medial arch comprises calcaneus, talus, navicular, the three cuneiforms and the three medial metatarsals; the apex of this arch is made by the talus. The lateral arch comprises calcaneus, cuboid and the lateral two metatarsals.
The principle dorsiflexors of the ankle include tibialis anterior assisted by extensor digitorum longus, extensor hallucis longus and peronius tertius. The main planterflexors include gastrocnemius and solius assisted by tibialis posterior, flexor hallucis longus and flexor digitorum longus.
The anterior tibiofibular ligament connects the tibia to the fibula. The lateral ligaments attach the fibula to the calcaneus. There are three main lateral ligaments; the anterior and the posterior talofibular ligaments (ATFL & PTFL) and the calcaneofibular ligament (CFL). The anterior talofibular ligament is a flat band that extends from the anterior malleolus forward to the talus and is relatively weak. The posterior talofibular ligament is thicker and stronger than the former ligament and runs horizontally from the back of the malleolus to the posterior surface of the talus. The calcaneofibular ligament, the longest of the three, is a round cord that goes from the tip of the lateral malleolus down to the lateral surface of the calcaneus.
On the medial side, the deltoid ligaments (superficial & deep) connect the tibia to the talus and calcaneus and are stronger than the lateral ligaments. Other important ligaments include spring ligament (from sustantaculum tali to the navicular), short planter ligament (between the calcaneus and the cuboid) and long planter ligament (between the calcaneus and the 2nd-4th metatarsals). All these ligaments are further supported by planter aponeurosis, a thickened fibrous band, which contributes significantly toward the stress of weight bearing.
Branches of the Tibial nerve
Medial calcaneal nerve innervates plantar medial heel
Medial plantar nerve innervates Abductor Hallucis, FHB, FDB and lumbircals to 2nd and 3rd toes. Cutaneous distribution to the medial sole and medial three and a half toes including the nail beds on the dorsum
Lateral plantar nerve innervates adductor hallucis, quadratus plantae, all interossei muscles, lateral two lumbricals, abductor digiti minimus (via Baxter's nerve - the first branch of LPN). Cutaneous innervations to the lateral sole and lateral one and a half toes.
It consists of the collateral branches of the tibial nerve and common peroneal nerve. Provides sensations to the lateral aspect of the foot and in 4th web space (70-80% of time)
Deep Peroneal Nerve
Innervates muscles of the anterior compartment of the leg including tibialis anterior,extensor digitorum longus, peronius tertius and extensor hallucis longus and in the foot it supplies extensor digitorum brevis and extensor hallucis brevis
The medial branch provides sensation to the first dorsal webspace
Superficial Peroneal Nerve
Innervates peroneus longus and peroneus brevis muscles and the skin over the antrolateral aspect of the leg and the dorsum of the foot with the exceotion of the 1st web space
Largest cutaneous branch of the femoral nerve
Supplies sensation to medial aspect of foot
The three primary sources of blood supply to the foot and ankle are posterior tibial, anterior tibial and peroneal arteries.
Posterior Tibial Artery is the larger of the two branches of polpliteal atrery and is the main blood supply to the superficial and deep compartments of the leg. In the ankle it gives rise to posteromedial malleolar artery, artery of the tarsal canal and a communicating branch. In the foot it divides into lateral and medial plantar arteries.
Anterior tibial artery is the smaller of the two branches of poploiteal artery and supplies the muscles of the anterior compartment of the leg. In the ankle it gives rise to antero-medial and antero-lateral malleolar arteries. In the foot it continues as dorsalis pedis artery and terminates into deep plantar arch as first dorsal metatarsal artery.
Peroneal Artery is a branch of posterior tibial artery. It divides at the ankle to give rise to posterolateral malleolar artery and a communicating branch. Its terminal branch in the foot is lateral calcaneal artery that is an imporatnt source of blood supply to the fasciocutaneous flap raised during the extensile approach to the calcaneus.
Blood supply to the plantar aspect of the foot and the toes comes from the plantar arch that is formed by the anastmosis of lateral plantar artery and the dorsalis pedis artery. It gives off plantar metatarsal arteries and plantar digital arteries
The dorsal venus arch drains into the great saphenous and short saphensous veins.
GRAY H, C. C. 1985. Gray’s Anatomy of the Human Body, Lippincott Williams & Wilkins.
ELLIS, H. 2006. Clinical Anatomy, Blackwell Publishing.