The foot and ankle are the anatomic result of evolution from species that primarily used their feet to grasp objects into a species that relies on their feet principally for bipedal gait. Inherent to this transformation was the ability to transmit the physiologic forces of upright gait through an interconnected network of 26 separate foot bones. These bones are linked through a series of joints, stabilizing ligaments, and tendons. Many conditions can compromise these interconnections, including trauma, which abruptly disrupts normal anatomy, or rheumatologic conditions, which may gradually compromise or erode these links. Persistent application of a substantial physiologic load through such compromised structures can result in the pain and deformity frequently observed among afflicted patients. Understanding and diagnosing such pathology in the foot and ankle requires an intricate knowledge of the underlying anatomy, as well as a recognition of how disruption of one facet of normal anatomy may predicate pathology elsewhere.
There are 7 tarsal, 5 metatarsal, and 14 phalangeal bones. An additional two sesamoid bones are located within the short flexor tendon of the hallux, and accessory ossicles may also be present in various locations. The bones of the foot are generally divided into the hindfoot (calcaneus and talus), midfoot (navicular, three cuneiforms, and cuboid), and forefoot (metatarsals, phalanges, and sesamoids).
The ankle (tibiotalar) joint allows dorsiflexion and plantar flexion range of motion. The mortise, which articulates with the talus, is comprised of the tibital plafond (the horizontal weight-bearing portion of the distal tibia), the medial malleolus, and the lateral malleolus. The deltoid ligament linking the medial malleolus to the talus is the main ligamentous ankle stabilizer during the stance phase and resists an outward valgus and external rotation force on the ankle. Three lateral ankle ligaments of the ankle resist an inward varus force.
The ankle is a mortise joint, a reference to a carpentry term in which a recess is cut into a piece of wood in order to stabilize its linkage to another piece of wood that is inserted into the mortise. The ankle mortise specifically consists of the fibula and tibia, which in turn stabilize the talus between them. To do so, the fibula and tibia are linked together by multiple ligaments which, in concert, span the inferior tibiofibular joint in a complex known as the syndesmosis. The syndesmosis consists of four ligaments, the strongest of which is the posterior inferior tibiofibular ligament.
Hindfoot joints include the subtalar and transverse tarsal (Chopart) joints (the talonavicular and calcaneocuboid joints). While the ankle joint allows the foot to dorsi- and plantarflex, the subtalar joint is an oblique-axis joint that allows 20 degrees of hindfoot inversion and 10 degrees of hindfoot eversion. The spring (plantar calcaneonavicular) ligament spans the inferior medial calcaneus to the navicular and is critical ...