The ankle-joint is a ginglymus, or hinge-joint. The lower end of the tibia and its malleolus, the malleolus of the fibula, and the inferior transverse tibiofibular ligament enter into its formation, and together form a mortise for the reception of the body of the talus. The bones are connected by the following ligaments; capsular, lateral collateral, anterior and posterior, anterior and posterior talofibular, deltoid & calcaneofibular.
The capsular ligament (fig. 570) surrounds the joint and is attached, above, to the borders of the articular surfaces of the tibia, and malleoli, and below, to the talus.
The anterior ligament is a broad, thin, membranous layer, attached above to the anterior margin of the lower end of the tibia, and below to the talus, some distance in front of its superior articular surface. It is in relation, in front, with the extensor tendons of the toes, the tendons of the tibialis anterior and peroneus tertis, and the anterior tibal vessels and nerve.
A synovial membrane lines the capsular ligament, and the joint-cavity ascends for a short distance between the tibia and fibula (fag. 573).
The deltoid ligament (figs. 570, 573) is a strong, triangular band attached, above, to the apex and anterior and posterior borders of the medial malleolus. It consists of two sets of fibers, superficial and deep. Of the superficial fibers the anterior (tibionavicular) pass forwards to be attached to the tuberosity of the navicular bone; and immediately behind this they blend with the medial margin of the plantar calcaneonavicular ligament; the middle fibers (calcaneotibial) descend almost perpendicularly and are fixed to the whole length of the sustentaculum tali of the calcaneum; the posterior fibers (posterior talotibial) pass backwards and laterally to be attached to the medial side of the talus, and to its medial tubercle. The deep fibers (anterior talotibial) are fixed above, to the tip of the medial malleolus, and, below, to the non-articular part of the medial surface of the talus. The deltoid ligament is crossed by the tendons of the tibialis posterior and flexor digitorum longus.
The anterior talofibular ligament (fig. 572) passes from the anterior margin of the fibular malleolus, forwards and medially, to the talus, where it is attached in front of the lateral articular facet and to the lateral aspect of the neck.
The posterior talofibular ligament (fig. 569), strong and deeply seated, runs almost horizontally from the lower part of the malleolur .fossa to the posterior tubercle of the talus.
The calcaneofibular ligament (fig. 572) is a long rounded cord, running from the depression in front of the apex of the fibular malleolus downwards and slightly backwards to a tubercle on the lateral surface of the calcaneum. It is crossed by the tendons of the peroneus longus and brevis.
Relations.-The tendons, vessels, and nerves in relation with the joint are in front, from the medial side, the tibialis anterior, extensor hallucis longus, anterior tibial vessels, anterior tibial (deep peroneal) nerve, extensor digitorum longus, and peroneus tertius; behind, from the medial side, the tibialis posterior, flexor digitorum longus, posterior tibial vessels, posterior tibial nerve (tibial nerve), flexor hallucis longus : and, in the groove behind the fibtilar malleolus, the tendons of the peroneus longus and brevis (fig, 571).
The nerves are derived frorn the anterior and posterior tibial (deep peroneal and tibial).
Movements.-When the body is in the erect position the foot is at right angles to the leg. The movements of the ankle-joint are those of dorsif exion and plantar-flexion; in dorsiflexion the angle between the front of the leg and the dorsum of the foot is diminished; in plantar-flexion the angle is increased, the heel being raised and the toes pointed downwards. The malleoli embrace the talus tightly in the position of rest, so that any slight degree of side-to-side movement which may exist is simply due to stretching of the ligaments of the inferior tibiofibular joint, and slight bending of the fibula. The superior articular surface of the talus is broader in front than behind. In dorsiflexion, therefore, greater space is required between the two malleoli. This is obtained by a slight lateral rotatory movement of the lower end of the fibula and a stretching of the ligaments of the inferior tibiofibular joint; this lateral movement is facilitated by a slight gliding at the superior tibiofibular joint, and possibly also by the bending of the shaft of the fibula. The deltoid ligament is exceedingly strong-so much so, that it usually resists a force which fractures the process of bone to which it is attached. Its middle portion, together with the oalcaneofibular ligament, binds the bones of the leg firmly to the foot, and resists displacement in every direction. The posterior talofibular ligament assists the calcaneofibular in resisting the displacement of the foot backwards, and deepens the cavity for the reception of the talus. The anterior talofibular ligament is a security against the displacement of the foot forwards. Plantar-flexion of the foot is limited by the anterior fibers of the deltoid and by the anterior talofibular ligament. Dorsiflexion of the foot is limited by the posterior fibers of the deltoid and by the calcaneofibular ligament.
Muscles producing the movements:
- Dorsiflexion.—Tibialis anterior, Extensor digitorum longus, Extensor hallucis longus, Peroneus tertius.
- Plantar flexion.—Gastrocnemius, Soleus, Plantaris, Tibialis posterior, Flexor digitorum longus, Flexor hallucis longus, Peroneus longus and brevis.
Applied Anatomy.–As the ankle-joint is a very strong and stable articulation, displacement of the talus from the tibiofibular mortise is a rare accident, and great force is required to produce it.
The ankle-joint is more frequently sprained than any joint in the body, and this may lead to acute synovitis. In these cases, when the synovial sac is distended with fluid, the bulging appears principally in the front of the joint, beneath the anterior tendons, and on either side, between the tibialis anterior and the deltoid ligament on the medial side, and between the peroneus tertius and the anterior talofibular ligament laterally. In addition to this, bulging often occurs posteriorly and a fluctuating swelling may be detected on either side of the tendo calcaneus. A large proportion of so-called `sprains’ of the ankle have been proved by x-ray examination to be some variety of fracture about the malleoli, with or without displacement.
When disease or injury of the ankle-joint is likely to lead to ankylosis, the joint is kept dorsiflexed to rather less than a right angle.
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