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). [Illustration: 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.)] FRACTURES IN THE REGION OF THE ANKLE #Pott's Fracture.#--It must be understood that various lesions occurring in the region of the ankle-joint are included under the clinical term "Pott's fracture." Although of a similar nature, and produced by the same forms of violence, these vary considerably in their anatomy and clinical features. They are all the result of _combined eversion and abduction_ of the foot--produced, for example, by slipping off the kerbstone, or by jumping from a height and landing on the medial side of the foot. When forcible _eversion_ is the chief movement, the tightening of the deltoid (internal lateral) ligament usually tears off the medial malleolus across its base. The talus is then brought to bear on the lateral malleolus, and the force continuing to act, the lower end of the fibula is pressed laterally, and breaks close above the malleolus. The tibio-fibular interosseous ligament may rupture, or the outer portion of the tibia, to which it is attached, may be avulsed. This form is sometimes called _Dupuytren's fracture_. When the bones are widely separated in Dupuytren's fracture the talus may be forced up between them. When the movement of _abduction_ predominates, the deltoid ligament is usually ruptured, or the anterior edge or tip of the medial malleolus torn off. The tibio-fibular interosseous ligament usually resists, and an oblique fracture of the fibula 2 or 4 inches above its lower end results.