Ankle joint, also known as talocrural joint, consists of a deep socket formed by the lower ends of the tibia and fibula, into which the upper part of the body of talus fits. It is approximately a uniaxial hinge joint, where movements are possible through only one axis. The talus moves on a transverse axis and produces dorsiflexion and plantar flexion of the foot. The shape of articulating bones, strength of the ligaments and the surrounding tendons make this joint strong and stable.
Articular surfaces of ankle joint:
The articulation takes place between the lower end of tibia, the two malleoli and the body of talus. All of these are covered with articular cartilage. The socket created by the medial and lateral malleoli, into which the body of talus fits, is deepened by the inferior transverse tibiofibular ligament.
Fibrous capsule of ankle joint:
The fibrous capsule surrounds the joint and is attached to the bones near their articular margins. It is thin in front and behind and is strengthened by strong collateral ligaments.
Ligaments of ankle joint:
Two important ligaments are associated with this joint: Medial ligament and Lateral ligament.
- Medial Ligament: Also known as deltoid ligament, it is the stronger of the two important ligaments of ankle joint. It is attached by its apex to the tip of the medial malleolus. Below it has two places of attachment. The deep fibers are attached to the non-articular area on the body of talus. The superficial fibers are attached to medial side of talus, sustentaculum tali and the tuberosity of navicular bone. The medial ligament consists of 4 bands.
- Posterior tibiotalar ligament
- Anterior tibiotalar ligament
- Tibiocalcaneal ligament
- Tibionavicular ligament
- Lateral ligament: It is weaker than the medial ligament and consists of three bands;
- Anterior tibiofibular ligament: It runs from the lateral malleolus to the lateral surface of talus.
- Calcaneofibular ligament: It runs from the tip of lateral malleolus to lateral surface of calcaneum.
- Posterior talofibular ligament: It runs from the lateral malleolus to the posterior tubercle of the talus.
Blood supply of ankle joint:
The ankle joint receives its blood supply form malleolar rami of the anterior and posterior tibial and peroneal arteries.
Lymphatic drainage of ankle joint:
Lymphatic drainage is through the vessels accompanying the arteries.
Nerve supply to ankle joint:
The ankle joint receives its nerve supply from deep peroneal, saphenous, sural and tibial nerves. Occasionally, the superficial peroneal nerve also supplies the ankle joint.
Movements of ankle joint:
As stated above, the ankle joint is a uniaxial hinge joint permitting only two types of movements: Dorsiflexion and Plantal flexion. The movements of inversion and eversion of foot seem to occur and ankle but actually they take place at the tarsal joints.
- Dorsiflexion: It is the movement in which the dorsal surface of foot is flexed. In this movement the toes point upward. Muscles responsible for it include;
- Tibialis anterior
- Extensor hallusic longus
- Extensor digitorum longus
- Peroneus tertius
Dorsiflexion is limited by the tension of the tendo calcaneus (Achilles’ tendon), posterior fibers of the medial ligament and the calcaneofibular ligament.
- Plantar flexion: It is the movement of foot in which its plantar surface is flexed. The toes point downward in this movement. Muscles responsible for plantar flexion include;
- Peroneus longus
- Peroneus brevis
- Tibialis posterior
- Flexor digitorum longus
- Flexor hallucis longus.
From the above list of muscles, it is quite clear that more muscle mass is involved in plantar flexion than in dorsiflexion, therefore, plantar flexion is much more powerful. It is limited by the tension of the opposing muscles, the anterior fibers of the medial ligament and the anterior talofibular ligament.