Plantar flexion injuries of the ankle. An experimental study.

A biomechanical study was designed to test the hypothesis that isolated plantar flexion of the ankle can produce avulsion fractures of the medial and lateral malleoli without fracture of the posterior articular surface of the tibia. Cadaver specimens were subjected to a standard plantar flexion force in the Burstein torsion testing machine. They showed the following typical patterns of injury in 26 of 32 ankles: (1) avulsion of the anterior ankle capsule; (2) a short oblique distal fibular fracture or fibular avulsion of the anterior talofibular ligament; and (3) an oblique medial malleolar fracture or a tear of the deep fibers of the deltoid ligament. Of particular interest was the direction and location of the medial malleolar fracture. This pattern, previously identified with supination-external rotation injuries, was also produced by isolated plantar flexion, which may be attributed to the anatomical attachments of the deltoid ligament on the medial malleolus, as well as the position of the foot and direction of the injuring force.