Abstract
1. Forty-two previously asymptomatic patients presenting with a recent rupture of the lateral ligament of the ankle, and twenty similar patients with a simple sprain of this ligament, have been followed for one year. The physical and radiological findings upon the completion of treatment have been related to functional instability of the foot one year later.
2. Persistent mechanical varus instability of the talus in the ankle mortise was a possible cause of functional instability one year after injury in four (or perhaps six) patients.
3. Adhesion formation was a possible cause of functional instability in one patient.
4. Seventeen patients finally displayed no clinical or radiological abnormality after injury, but noted functional instability of the foot one year later.
5. It is concluded that the pathological process which is usually responsible for functional instability of the foot after a lateral ligament injury is at present unknown.
