Injuries to the lateral ligament of the ankle.

The tendency for the foot to “ give way “ (a complaint here referred to as functional instability) after an ankle sprain has been attributed to a number of pathological processes, among which the most widely accepted are varus instability of the talus in the ankle mortise (Nilsonne 1932, Elmslie 1934, Watson-Jones 1955, Dziob 1956, Wiles 1959, Perkins 1961) and adhesion formation at the subtalar joint (McMurray 1934, Lake 1952, Watson-Jones 1955, Perkins 1961). Other pathological processes to which functional instability ofthe foot has been attributed include antero-posterior instability of the talus in the ankle mortise (Anderson, LeCocq and LeCocq 1952), instability at the subtalarjoint (Bosien, Staples and Russell 1955; Perkins 1961), inferior tibio-fibular diastasis (Mullins and Sallis 1958), peroneal muscle weakness (Bonnin 1950, Bosien et a!. 1955) and a “ weak spot “ in the ligament (Thorndike 1959). The evidence that these pathological processes are etiological is slender, and it is accepted by some surgeons that there is a group of patients who, following a sprain, develop a foot which tends to “ give way,” but in which no abnormality is detectable on examination (Wiles 1959). The attribution of the symptom of functional instability to these pathological processes has usually been based upon the detection of abnormal physical signs in patients presenting with the established disability. The demonstration of such associations, however, does not show which is cause and which is effect. It is possible for instance that the repeated sprains suffered by a patient with a functionally unstable foot finally lead to substantial varus instability of the talus rather than that the mechanical instability initiates the tendency for the foot to give way. In this study a group of previously asymptomatic patients presenting with a recent ankle sprain have been followed for one year and the physical and radiological findings upon the completion of treatment have been correlated with the symptom of functional instability of the foot one year later.