Ankle and Foot

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The bones of the ankle and foot form the most distal region of the lower limb in the appendicular skeleton. These bones are responsible for the propulsion, balance, and support of the body's weight through many diverse activities, such as standing, walking, running, and jumping.

The ankle joint is formed by the union of the lower leg bones --- the tibia and fibula --- and the talus bone (one of a group of bones collectively known as the tarsus, located in the foot). Together, these three bones form a tight synovial hinge joint that permits the plantarflexion and dorsiflexion of the foot. Plantarflexion is the movement that describes the pointing of the foot toward the ground, as in standing on one's tiptoes. Dorsiflexion is the opposite of plantarflexion and involves the movement of the foot away from the ground, as in pulling the toes up and walking on one's heels. The medial malleolus of the tibia and the lateral malleolus of the fibula form a cup surrounding the rounded tarsus to prevent lateral movement at the ankle joint. The fibula is united to the bones of the foot on the lateral side of the ankle by the anterior and posterior talofibular ligaments and the calcaneofibular ligament. On the medial side, the wide deltoid ligament binds the tibia to the tarsal bones of the foot. All of these ligaments work together to limit extreme movements and dislocations of the ankle joint while providing slight lateral flexibility that helps the body walk on uneven surfaces and maintain its balance.

Twenty-six small bones of the foot provide the strength and flexibility necessary for bipedal locomotion. The seven tarsal bones form the posterior portion of the foot nearest to the heel. Each tarsal bone is a short bone with many flat facets that allow the tarsals to glide past one another. This gliding motion provides lateral mobility to the foot below the level of the ankle joint and allows the foot to bend to adjust the body's balance. Anterior to the tarsals are the five long metatarsal bones of the foot and the fourteen phalanges of the toes. The metatarsals, phalanges, and tarsals form the longitudinal and transverse arches of the foot to divide the body's weight across the entire foot and act as a spring to absorb and release the force of the body's weight on the ground. These bones also act as a lever to increase the strength of the muscles acting on the ankle joint, allowing the body to easily lift its entire weight up on the balls of the foot and the toes. This leverage is essential to rapid locomotion and jumping as it greatly increases the strength and speed of the legs.

Many different ligaments hold the bones of the foot firmly together while providing flexibility to the bones. Amongst the tarsal bones, the plantar calcaneonavicular ligament joins the navicular bone to the calcaneus (heel bone), while the plantar cuboideonavicular ligament joins the navicular bone to the cuboid bone. The dorsal and plantar tarsometatarsal ligaments bind the tarsal and metatarsal bones together, support the arches of the foot, and strengthen overall structure of the foot. In the anterior of the foot, the plantar metatarsal ligaments bind the instep across the sole of the foot.