Radiological assessment of chronic instability of the ankle

Chronic instability of the ankle can be assessed clinically and radiologically. Radiological assessment should include stress views of the ankle. We examined radiologically 115 patients with chronic instability of the ankle. Anteroposterior and lateral stress view of both ankles were performed using the TELOS instrument. We found a significant change in lateral tilt (L.T.) of the talus 4° in the normal ankle; 7.6° in the injured ankle. The average difference between the two ankles was 3.5°. The change in the posterior opening (P.O.) of the tibio-talar joint was from 4.7 mm in the normal ankle to 5.6 in the injured ankle. The average difference was 1 mm. A significant correlation was found between P.O. and L.T. in the injured ankle. However, there was no correlation between P.O. and L.T. of the differences between injured and non-injured ankles. About 40% of the patients had a difference of 4° or less in the L.T. and 60% had 1 mm or less in the P.O. Only about 30% had an L.T. of 5° or more and 2 mm P.O. Therefore, about 40% had functional instability without radiological evidence of instability, and about 30% had mechanical instability. Clinical relevance-stress views of the ankle in patients with chronic instability of the ankle may demonstrate only mechanical instability. They are of limited value in such patients.