Surgical Anatomy.—For the study of injuries in the region of the ankle-joint it is of importance to define the terms employed in describing the movements of the foot. Thus by flexion or dorsiflexion is meant that movement which approximates the dorsum of the foot to the front of the leg; while extension or plantar flexion means the drawing up of the heel so that the toes are pointed. In inversion the medial edge of the foot is drawn up so that the sole looks towards the middle line of the body, an attitude which is analogous to supination of the hand. In eversion the lateral edge of the foot is drawn up, the sole looking away from the middle line—analogous to pronation of the hand. Adduction indicates the rotation of the foot so that the toes are turned towards the middle line of the body; while in abduction the toes are turned away from the middle line.
The most prominent bony landmarks in the region of the ankle are the two malleoli, the lateral lying slightly farther back, and about half an inch lower than the medial. On the medial side of the foot from behind forward may be felt the medial process (internal tuberosity) of the calcaneus; the sustentaculum tali, which lies about 1 inch vertically below the tip of the malleolus; the tubercle of the navicular, about 1 inch in front of the malleolus, and at a slightly lower level; the first (internal) cuneiform, and the base, shaft, and head of the first metatarsal.
On the lateral side may be recognised the lateral process (external tuberosity) of the calcaneus; the trochlear process (peroneal tubercle) on the same bone; the cuboid; and the prominent base of the fifth metatarsal.
The talo-navicular joint lies immediately behind the tuberosity of the navicular, and a line drawn straight across the foot at this level passes over the calcaneo-cuboid joint.
The ankle-joint, formed by the articulation of the tibia and fibula with the talus, lies about half an inch above the tip of the medial malleolus, and is so constructed that when the foot is at a right angle with the leg it is only possible to flex and extend the joint. When the toes are pointed, however, slight side-to-side and rotatory movements are possible. The chief seat of side-to-side movement of the foot is at the talo-navicular and calcaneo-cuboid articulations—“the mid-tarsal or Chopart's joint.”
The ankle-joint owes its strength chiefly to the malleoli and the collateral ligaments, and to the inferior tibio-fibular ligaments, which bind together the lower ends of the bones of the leg. The numerous tendons passing over the joint on every side also add to its stability.
The synovial membrane of the ankle-joint passes up between the bones of the leg to line the inferior tibio-fibular joint; but it is distinct from that of the intertarsal joints, which communicate with one another in a complicated manner. The epiphysial cartilage at the lower end of the fibula lies on the level of the talo-tibial articulation, while that of the tibia is about half an inch higher ([Fig. 93]).
Fig. 93.—Section through Ankle-Joint showing relation of epiphyses to synovial cavity.
a, Lower epiphysis of tibia.
b, Lower epiphysis of fibula.
c, Talus.
d, Calcaneus.
(After Poland.)