Overview
The ankle (talocrural) joint is a synovial hinge joint located in the lower limb, formed by the tibia, fibula and talus. It permits dorsiflexion and plantarflexion of the foot.
The tibia and fibula are bound by tibiofibular ligaments and form a bracket-shaped socket known as a mortise, which is covered in hyaline cartilage. The body of talus fits within the mortise joint.
Articular Surfaces
Tibia and Fibula
- Roof: Inferior surface of distal end of tibia
- Medial side: Medial malleolus of tibia
- Longer lateral side: Lateral malleolus of fibula
Talus
- Superior part of talus (talar dome and its medial and lateral surfaces)
- The articulating part of the talus is wedge shaped – it is broad anteriorly, and narrow posteriorly:Dorsiflexion – the anterior part of the talus is held in the mortise, and the joint is more stable.
Plantarflexion – the posterior part of the talus is held in the mortise, and the joint is less stable.
Capsule & Ligaments
Medial collateral (deltoid) ligament – Triangular-shaped ligament attached above from medial malleolus and fans out with a broad base attached to medial surfaces of navicular, talus and calcaneus. Its primary purpose is to resist over-eversion of the foot. It consists of four parts:
- Tibionavicular part – attaches to tuberosity of navicular and calcaneonavicular (spring ligament)>
- Anterior tibiotalar part – attaches deep to tibionavicular part of medial ligament
- Posterior tibiotalar part – attaches to medial side and medial tubercle of talus
- Tibiocalcaneal part (central) – attaches to sustentaculum tali of calcaneus
Lateral collateral ligament
Composed of 3 separate ligaments. It’s primary purpose is to resist over-inversion of the foot.
- Anterior talofibular ligament – lateral malleolus to lateral surface of talus
- Posterior talofibular ligament – malleolar fossa of lateral malleolus to posterior process of talus
- Calcaneofibular ligament – lateral malleolus to posterior tubercle of calcaneus
Synovium
- Synovial membrane attaches to margins of the articular surfaces
- A fibrous membrane covers the synovial membrane attached to adjacent bone
Muscles
- Plantarflexion – some muscles in the posterior compartment of the leg (gastrocnemius, soleus, plantaris and posterior tibialis)
- Dorsiflexion – some muscles in the anterior compartment of the leg (tibialis anterior, extensor hallucis longus, extensor digitorum longus and fibularis tertius)
Arterial Supply
Anterior Tibial Artery – anterior tibial artery passes in front of the ankle joint, passing under the Y-shaped flexor retinaculum to continue as the dorsalis pedis artery. It gives branches to supply the medial and lateral malleoli before branching to supply the dorsum of the foot
Fibular (Peroneal) Artery
Venous Drainage
- Dorsal venous arch forms medial marginal and lateral marginal vein
- The medial marginal vein continues to become the great saphenous vein, which drains into the femoral vein at the upper thigh
- The lateral marginal veins continues to become the small saphenous vein, which drains into the popliteal vein at the knee
- Deep plantar venous arch forms medial plantar and lateral plnatar veins
- The confluence of the medial and lateral plantar veins at the medial malleolus forms the posterior tibial and the fibular (peroneal) veins
Innervation
- Tibial nerve – terminal branch of the sciatic nerve (L4 – S3), derived from the sacral plexus
- Deep fibular – terminal division of the common fibular nerve
Relations
Superior
- Distal tibiofibular joint – a fibrous joint (therefore no joint capsule), formed by the articulation between the fibular notch, distal tibia and fibula. Supported by the following ligaments:
- Interosseous membrane – a fibrous structure spanning the length of the tibia and fibula.
- Anterior and posterior inferior tibiofibular ligaments
- Inferior transverse tibiofibular ligament – a continuation of the posterior inferior tibiofibular ligament.
Posteromedial
- Tarsal tunnel posterior to medial malleolus (tendons of tibialis posterior, flexor digitorum longus, flexor hallucis longus, posterior tibial artery, tibial nerve)
- Flexor retinaculum
Anterior
- Tendons of extensor digitorum longus, extensor hallucis longus, tibialis anterior
Posterior
- Achilles (calcaneal) tendon – the common tendon of the gastrocnemius (medial and lateral heads), soleus and plantaris, which attaches to the calcaneal tuberosity of the calcaneus
- Subcutaenous calcaneal bursa – permits movement of skin over the flex tendon
- Deep bursa of the Achilles tendon – reduces friction between tendon and calcaneus
Lateral
- Tendons of fibularis longus and brevis, fibular retinuluca
- Superior and inferior fibular retinaculum
Anatomical Variants
- Absent anterior tibiotalar ligament
- Os subtalare
- Os subfibulare – accessory ossicle inferior to the tip of the lateral malleolus
- Os subtibiale – accessory ossicle inferior to the posterior colliculus of the medial malleolus
- Os trigonum
- Talocalcaneal coalition
- Synovial plicae – folds of the synovium, though to represent embryologic remnants