Acetabular depression fracture accompanying posterior fracture dislocation of the hip.

The acetabular depression fracture is defined as a rotated, impacted, osteocartilaginous fragment of the posteromedial acetabulum that occurs in conjunction with a posterior fracture dislocation of the hip. Displacement of this fracture fragment creates incongruity of the posterior acetabular articular surface and the potential for hip joint instability. A retrospective review of hip dislocations over a 3-year period disclosed 75 posterior fracture dislocations of the hip. A total of 71 hips had computerized tomography (CT) scanning after successful closed reduction of the dislocation. Of the 75 dislocations, 58 were treated with open reduction and internal fixation for reproducible posterior subluxation or redislocation upon clinical examination, non-concentric closed reduction, and/or unacceptable articular fracture displacement. The acetabular depression fracture was identified in 17 cases (23%). A total of 16 were found on preoperative CT scans, and one was discovered at the time of open reduction. Preoperatively, each of these injuries demonstrated posterior instability with hip flexion less than 90 degrees. Treatment consisted of disimpaction of the fragment with elevation to the level of the concentrically reduced femoral head. The fragment was stabilized with packed cancellous bone graft obtained from the greater trochanter. The separate posterior lip fragment was then reduced and internally stabilized to ensure reduction of the acetabular depression fragment. We conclude that this variant of the posterior fracture dislocation of the hip occurs in a significant percentage of these injuries. Preoperative recognition of this fracture may correlate with posterior hip instability, and its presence may be an indication for open reduction and internal fixation of the fracture. Long-term studies of this lesion are still needed.