Ankle Joint Anatomy
The ankle joint is a synovial hinge joint between the lower ends of the tibia and fibula and the upper part of the talus (Fig. 6.84), and all the articular surfaces are
covered by hyaline cartilage. The proximal articular surface comprises the distal end of the tibia and the medial and lateral malleoli, which together form a deep socket (Fig. 6.85), completed posteriorly by the posterior tibiofibular ligament (see below). The socket is wider anteriorly than posteriorly and is completely congruous with the upper part of the talus, which is reciprocally wedgeshaped (Figs 6.84 & 6.86). The articular surface on the lateral side of the talus is more extensive than that on the medial side.
The fibrous capsule attaches to the margins of the articular surfaces, but anteriorly extends forwards onto the neck of the talus (Fig. 6.86). The capsule is thin anteriorly and posteriorly, but is reinforced on each side by ligaments. Synovial membrane lines the capsule internally and covers the intracapsular part of the neck of the talus.
The posterior tibiofibular ligament spans the gap between the distal ends of the tibia and fibula, contributing to the articular socket posteriorly (Fig. 6.85). There are two collateral ligaments. The medial (deltoid) ligament (Fig. 6.89) is attached by its apex to the tip of the medial malleolus. Its deeper fibres descend to the margin of the articular surface on the medial side of the talus and its longer superficial fibres attach to the tuberosity of the navicular, the medial border of the spring (plantar calcaneonavicular) ligament and the sustentaculum tali.
The lateral ligament has three components: the anterior and posterior talofibular and the calcaneofibular ligaments (Figs 6.87 & 6.88). All attach to the lateral malleolus. The anterior talofibular ligament passes forwards to the lateral side of the neck of the talus, the posterior talofibular ligament medially to the posterior tubercle of the talus, and the calcaneofibular downwards and backwards to the side of the calcaneus. Tearing of the medial and/or lateral collateral ligaments occurs with fractures of one or both malleoli.
They are known by the clinical eponym of Pott’s fracture.
Only extension (dorsiflexion) and flexion (plantar flexion) occur at the ankle joint, around a transverse axis between the malleoli. Plantar flexion is produced by soleus and gastrocnemius, assisted by tibialis posterior, flexors hallucis longus and digitorum longus, and fibularis longus and brevis. Extension (dorsiflexion) is produced by tibialis anterior, extensors hallucis longus and digitorum longus, and fibularis tertius.
The joint is very stable due to the wedge shape of the articulating surfaces and the strong collateral ligaments. During standing and walking, body weight tends to dis place the tibiofibular socket forwards so that it becomes closely packed against the wider anterior part of the talus, which further enhances stability during dorsiflex ion. Excessive forward displacement of the tibia and fibula on the talus is prevented by the posterior fibres of the medial (deltoid) ligament and by the calcaneofibular and posterior talofibular ligaments. However, in plantar flexion the narrow part of the talus articulates with the wider anterior part of the socket, allowing some sidetoside movement. In this position, forced inversion of the foot may damage the anterior talofibular ligament, one form of sprained ankle.
Branches of the anterior and posterior tibial arteries, including the fibular, anastomose at the level of the malleoli and supply the joint. Innervation is from the deep fibular and tibial nerves.
The sides of the joint, the bony malleoli, are superficial (Fig. 6.90) and easily palpable. Passing subcutaneously in front of the joint are branches of the superficial fibular nerve and, just anterior to the medial malleolus, the saphenous nerve and great saphenous vein. On a deeper plane are the tendons of tibialis anterior and extensor hallucis longus, the dorsalis pedis artery, the deep fibular nerve, and the tendons of extensor digitorum longus and fibularis tertius (Fig. 6.91).
Posteriorly, the tendo calcaneus (Achilles) lies separated from the joint capsule by a bursa and pad of fat. Behind the medial malleolus are the tendons of tibialis posterior, flexor digitorum longus and flexor hallucis longus (Fig. 6.90), accompanied by the tibial nerve and posterior tibial artery (Fig. 6.91). Passing below the medial malleolus, they enter the foot beneath the flexor retinaculum. Passing superficially behind the lateral malleolus are the small saphenous vein and sural nerve and, more deeply, the tendons of fibularis longus and brevis (Fig. 6.91).