Posterior acetabular spike: an obstacle to reduction in long-standing hip dislocations.

The posterior insertion of the transverse acetabular ligament can be transformed into a toothlike bony prominence narrowing the acetabulum in its distal part. This deformity can impede the placement of the femoral head deep in the acetabulum, making a complete reduction impossible. The toothlike spike can be detected by computed tomography or by intraoperative palpation, and can be corrected by pushing it back with a punch under palpatory control.