The purpose of this study was to classify posterior malleolar fractures according to the position of fragments and to analyze radiologic features of each type.

We analyzed forty-six patients of ankle fractures involving a posterior malleolus who were treated between January 2004 and December 2007. The posterior malleolar fractures were categorized into three types (posterolateral, posteromedial, shell) based on the major fracture line. In each type, we analyzed amount of displacement, involvement of articular surface, existence of subluxation and osteochondral impacted fragments.

The forty-six patients were categorized into three types: Posterolateral (PL) type (33 cases, 72%), Posteromedial (PM) type (8 cases, 17%), shell type (5 cases, 11%). Of the 8 cases with PM type, 7 cases showed displacement more than Grade II, 4 cases showed subluxation of ankle joint, and 3 cases showed osteochondral impacted fragment. Average involvement of articular surface of PM type is 35% (15~65%).

Posterior malleolar fractures with medial extension tended to have adverse effect on ankle stability and Preoperative CT scan is essential for evaluation of fracture type and determination of appropriate surgical approach.