A study of the roentgenograms of 554 patients who had triple arthrodesis of the tarsus revealed ten anterior subluxations of the tarsus in eight patients. In most instances the subluxation was combined with internal rotation of the foot referable to the ankle mortise.

Recent follow-up studies in five patients indicated that four had some pain or swelling of the foot brought on by activity and relieved by rest. Follow-up roentgenograms of five ankles in four patients revealed degenerative changes three and a half to seven years after operation.

Experimental studies, performed on the ankles of twelve amputated legs, suggested that anterior subluxation of the lateral part of the trochlea tali can be produced after severing the anterior talofibular ligament and, even more readily, after cutting the anterior talofibular together with the fibulocalcaneal ligaments or the anterior talofibular together with the posterior talofibular ligaments. Posterior subluxation of the lateral part of the trochlea can be produced only after cutting the fibulocalcaneal and posterior fibulotalar ligaments and inverting the foot. The talus can be tilted into inversion of 15 degrees after cutting the anterior talofibular ligament alone, 30 degrees after cutting the anterior talofibular and fibulocalcaneal ligaments, 30 degrees after cutting the anterior and posterior talofibular ligaments, and 15 to 30 degrees after cutting the fibulocalcaneal and posterior talofibular ligaments. Cutting the fibulocalcaneal and posterior talofibular ligaments also permits posterior displacement of the lateral portion of the trochlea.

Despite the fact that muscle imbalance or weakness was present in each of the patients with subluxation, we believe, as suggested by our study of amputated legs, that muscle abnormalities alone cannot explain the occurrence of talar subluxation—some ligamentous damage must be present. This must involve at least the anterior talofibular ligament.

Recommendations to prevent unnecessary damage to the ankle joint during triple arthrodesis include: (1) avoid cutting the anterior talofibular ligament, (2) remove little bone from the inferior surface of the talus (thus leaving attachments of ligaments to the talus), (3) hold the foot gently in neutral position and support the leg while applying the cast if injury to the anterior talofibular ligament is suspected, and (4) obtain roentgenograms after each cast change.