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7d. Talocrural Articulation or Ankle-joint
FIG. 354 - Ligaments of the medial aspect of the foot. (Quain.) (Articulatio Talocruralis; Tibiotarsal Articulation)
The ankle-joint is a ginglymus, or hinge-joint. The structures entering into its formation are the lower end of the tibia and its malleolus, the malleolus of the fibula, and the transverse ligament, which together form a mortise for the reception of the upper convex surface of the talus and its medial and lateral facets. The bones are connected by the following ligaments:The Articular Capsule. The Anterior Talofibular. The Deltoid. The Posterior Talofibular. The Calcaneofibular. The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule surrounds the joints, and is attached, above, to the borders of the articular surfaces of the tibia and malleoli; and below, to the talus around its upper articular surface. The anterior part of the capsule (anterior ligament) is a broad, thin, membranous layer, attached, above, to the anterior margin of the lower end of the tibia; below, to the talus, 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 Peronæus tertius, and the anterior tibial vessels and deep peroneal nerve. The posterior part of the capsule (posterior ligament) is very thin, and consists principally of transverse fibers. It is attached, above, to the margin of the articular surface of the tibia, blending with the transverse ligament; below, to the talus behind its superior articular facet. Laterally, it is somewhat thickened, and is attached to the hollow on the medial surface of the lateral malleolus. 
FIG. 355 - The ligaments of the foot from the lateral aspect. (Quain.) The Deltoid Ligament (ligamentum deltoideum; internal lateral ligament) (Fig. 331).—The deltoid ligament is a strong, flat, 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 most anterior (tibionavicular) pass forward to be inserted into the tuberosity of the navicular bone, and immediately behind this they blend with the medial margin of the plantar calcaneonavicular ligament; the middle (calcaneotibial) descend almost perpendicularly to be inserted into the whole length of the sustentaculum tali of the calcaneus; the posterior fibers (posterior talotibial) pass backward and lateralward to be attached to the inner side of the talus, and to the prominent tubercle on its posterior surface, medial to the groove for the tendon of the Flexor hallucis longus. The deep fibers (anterior talotibial) are attached, above, to the tip of the medial malleolus, and, below, to the medial surface of the talus. The deltoid ligament is covered by the tendons of the Tibialis posterior and Flexor digitorum longus. The anterior and posterior talofibular and the calcaneofibular ligaments were formerly described as the three fasciculi of the external lateral ligament of the ankle-joint. The Anterior Talofibular Ligament. (ligamentum talofibulare anterius) (Fig. 355).—The anterior talofibular ligament, the shortest of the three, passes from the anterior margin of the fibular malleolus, forward and medially, to the talus, in front of its lateral articular facet. The Posterior Talofibular Ligament (ligamentum talofibulare posterius) (Fig. 355).—The posterior talofibular ligament, the strongest and most deeply seated, runs almost horizontally from the depression at the medial and back part of the fibular malleolus to a prominent tubercle on the posterior surface of the talus immediately lateral to the groove for the tendon of the Flexor hallucis longus. The Calcaneofibular Ligament (ligamentum calcaneofibulare) (Fig. 355).—The calcaneofibular ligament, the longest of the three, is a narrow, rounded cord, running from the apex of the fibular malleolus downward and slightly backward to a tubercle on the lateral surface of the calcaneus. It is covered by the tendons of the Peronæi longus and brevis. 
FIG. 356 - Capsule of left talocrura articulation (distended). Lateral aspect. Synovial Membrane (Fig. 356).—The synovial membrane invests the deep surfaces of the ligaments, and sends a small process upward between the lower ends of the tibia and fibula. Relations.—The tendons, vessels, and nerves in connection with the joint are, in front, from the medial side, the Tibialis anterior, Extensor hallucis proprius, anterior tibial vessels, deep peroneal nerve, Extensor digitorum longus, and Peronæus tertius; behind, from the medial side, the Tibialis posterior, Flexor digitorum longus, posterior tibial vessels, tibial nerve, Flexor hallucis longus; and, in the groove behind the fibular malleolus, the tendons of the Peronæi longus and brevis. The arteries supplying the joint are derived from the malleolar branches of the anterior tibial and the peroneal. The nerves are derived from the 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 joint are those of dorsiflexion and extension; dorsiflexion consists in the approximation of the dorsum of the foot to the front of the leg, while in extension the heel is drawn up and the toes pointed downward. The range of movement varies in different individuals from about 50° to 90°. The transverse axis about which movement takes place is slightly oblique. The malleoli tightly embrace the talus in all positions of the joint, so that any slight degree of side-to-side movement which may exist is simply due to stretching of the ligaments of the talofibular syndesmosis, and slight bending of the body of the fibula. The superior articular surface of the talus is broader in front than behind. In dorsiflexion, herefore, greater space is required between the two malleoli. This is obtained by a slight outward rotatory movement of the lower end of the fibula and a stretching of the ligaments of the syndesmosis; this lateral movement is facilitated by a slight gliding at the tibiofibular articulation, and possibly also by the bending of the body of the fibula. Of the ligaments, the deltoid is of very great power—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 calcaneofibular ligament, binds the bones of the leg firmly to the foot, and resists displacement in every direction. Its anterior and posterior fibers limit extension and flexion of the foot respectively, and the anterior fibers also limit abduction. The posterior talofibular ligament assists the calcaneofibular in resisting the displacement of the foot backward, and deepens the cavity for the reception of the talus. The anterior talofibular is a security against the displacement of the foot forward, and limits extension of the joint. The movements of inversion and eversion of the foot, together with the minute changes in form by which it is applied to the ground or takes hold of an object in climbing, etc., are mainly effected in the tarsal joints; the joint which enjoys the greatest amount of motion being that between the talus and calcaneus behind and the navicular and cuboid in front. This is often called the transverse tarsal joint, and it can, with the subordinate joints of the tarsus, replace the ankle-joint in a great measure when the latter has become ankylosed. Extension of the foot upon the tibia and fibula is produced by the Gastrocnemius, Soleus, Plantaris, Tibialis posterior, Peronæi longus and brevis, Flexor digitorum longus, and Flexor hallucis longus; dorsiflexion, by the Tibialis anterior, Peronæus tertius, Extensor digitorum longus, and Extensor hallucis proprius. (*74
Note 74. The student must bear in mind that the Extensor digitorum longus and Extensor hallucis proprius are extensors of the toes, but flexors of the ankle; and that the Flexor digitorum longus and Flexor hallucis longus are flexors of the toes, but extensors of the ankle. [back]
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