OBJECTIVETo evaluate the safe zones of screw fixations of Jumbo cup and reinforcement rings in acetabular revision surgery.

METHODSFrom December 2006 to January 2008, 11 fresh frozen human cadaver pelvises were prepared by removing all soft tissues except the medial neurovascular structures, each specimen was held in supine position with clamps. The anteroposterior radiographs were taken after the Jumbo cups or reinforcement rings were fixed in places. Left sides of acetabulum were used to create the models to evaluate the safe zones of the high hip center and Jumbo cups. Right sides were used to evaluate the safe zones of 3 different designs of acetabular reinforcement rings (Müller, Ganz, Burch-Schneider cage).

RESULTSJumbo cups: screws in the superoanterior and anteroinferior quadrants could cause neurovascular injuries. High hip center: neurovascular injuries could be expected in all quadrants except the inferoposterior and posterior half of superoposterior quadrant. Müller ring: screws placed in the intra-acetabular and extra-acetabular areas of the superoanterior quadrant could cause neurovascular injuries. Ganz ring:the screws placed in superoanterior quadrant and apex area were dangerous. The insults were confirmed in all of the specimens. Burch-Schneider cage: the medial nervous and vasculature structures were injured in all of the specimens if the screws placed in the superoanterior (intra-acetabular and extra-acetabular) quadrant. Screws for ischial fixation could cause sciatic nerve injury.

CONCLUSIONSIn revision acetabular surgery, the superoanterior quadrant, the anterior half of the superoposterior quadrant and the implant's central area are unsafe for screw fixation, especially when the exposed thread is longer than 15 mm.