Ankle Anatomy and Sprains

The ankle is formed by a joint known as the talocrural joint. The two bones of the lower-leg, the tibia and the fibula, form a pocket at the bottom that houses the talus bone to form the ankle joint. During activity your body weight is transferred from the tibia, the stronger of the two lower-leg bones, to the talus where the weight is then distributed between the front and back of the foot. The distal end (farthest point from the point of origin) of the fibula extends farther than that of the tibia, which provides the medial (inside) ankle with greater support than the lateral (outside) ankle. This discrepancy is a big reason why inversion ankle sprains are much more common than eversion sprains.

The bones of the ankle joint are held together by stiff, fibrous bands called ligaments. There are two ligament groups that support the ankle joint, known as, the lateral collateral ligaments and the medial collateral ligaments. The medial (inside) ankle is supported by a group called the deltoid ligament complex, which provides strong medial stability against eversion. As was mentioned above, the lateral (outside) ankle has limited bony support from the tibia. To compensate the lateral ankle receives support from three ligaments, the anterior talofibular ligament (ATFL), posterior talofibular ligament (PTFL), and the calcaneofibular ligament (CFL).