The ankle joint is a hinged synovial joint with primarily up-and-down movement (plantarflexion and dorsiflexion). However, when the range of motion of the ankle and subtalar joints (talocalcaneal and talocalcaneonavicular) is taken together, the complex functions as a universal joint (see the image below).
Anatomy of the lateral ankle ligamentous complex and related structures.
The combined movement in the dorsiflexion and plantarflexion directions is greater than 100°; bone-on-bone abutment beyond this range protects the anterior and posterior ankle capsular ligaments from injury. The anterior and posterior ankle capsular ligaments are relatively thin compared with the medial and lateral ankle ligaments.
Type I collagen tissue constitutes the bulk of the capsule and supporting ligaments of the ankle joint. The fiber density and orientation are arranged dynamically according to the typical mechanical stress experienced by the joint. Within limits, the greater the excursion of the joint capsule and ligaments, the less likely sprains are to occur. With increased motion, the muscles absorb the mechanical force energy without exceeding the tensile limits of either the joint capsule or the ligaments.