The ankle (talocrural) joint is a mortise-and-tenon synovial hinge joint formed by the tibia (plafond and medial malleolus), fibula (lateral malleolus), and talar dome. The talar dome is wider anteriorly, so the mortise grips the talus firmly in dorsiflexion but is relatively lax in plantarflexion, which is why most sprains happen with the foot pointed. The fibula carries roughly one sixth of axial load, and its position is essential for mortise stability. The joint axis is inclined downward and laterally, explaining the coupled eversion with dorsiflexion.
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Lateral ankle sprains tearing the ATFL, sometimes with the CFL, are the most common musculoskeletal sport injury. The Ottawa Ankle Rules guide radiography: bone tenderness at the posterior edge or tip of either malleolus, or inability to bear weight, indicates the need for X-ray. Ankle fractures are classified by the Weber system based on fibular fracture level relative to the syndesmosis, and an unstable mortise (widened medial clear space or syndesmotic injury) needs open fixation. High ankle (syndesmotic) sprains are less common but take longer to recover than standard lateral sprains. Ankle arthritis is most often post-traumatic, unlike hip and knee arthritis, and is managed by arthrodesis or total ankle replacement. The anterior joint line lies about 1 cm above the tip of the medial malleolus, a reference for anteromedial arthroscopy portal placement.
Plantarflexion-inversion tearing the ATFL, the most common musculoskeletal sport injury, managed with early functional rehabilitation.
Malleolar fractures from rotation classified by the Weber system. Mortise stability determines operative versus conservative management.
High ankle sprain disrupting the distal tibiofibular syndesmosis, requiring prolonged rehabilitation or fixation with a screw or suture button when unstable.
