Abstract
Introduction: From June 1991 to June 1995, 256 consecutive total hip arthroplasties using the Duraloc 100 TM acetabular shell, manufactured by Depuy, were performed by two surgeons. The acetabular component featured a non-locking apex hole eliminator. In January 1995 the first patient with extrusion of the apex hole eliminator was seen. Since that time 21 patients, or 8% (21/256) have been seen with partial or complete extrusion. This study reports the outcomes and discusses a possible rationale for this finding.
Methods: The study group comprises 12 men, nine women, mean age was 59 years (32-86), mean weight 180 lbs. 18 (86%) femurs were cementless, three (14%) were cemented. Mean acetabular component size was 58 mm (52-64), with 18 acetabular liners manufactured with HylamerTM, and three liners EnduronTM. Sixteen (76%) liners were 10 degree hooded, and five (24%) were non-hooded. Eighteen (86%) femoral heads were ceramic, and three (14%) were chrome-cobalt. 15 (71%) femoral heads were 28 mm diameter, and six (29%) were 32 mm.
Results: Radiographs were obtained at routine follow-up in 20 (95%) patients. One (5%) patient had groin pain as the indication for radiographs. Four (19%) patients had complete extrusion in to the pelvis of the apex hole eliminator, and 17 (81%) had partial backout with the apex hole eliminator still within the confines of the acetabular component. On the antero-posterior radiograph visible pelvic osteolysis was seen in the four patients with complete extrusion of the apex hole eliminator, all in zone B. Zone one femoral osteolysis was seen in one patient with incomplete extrusion of the apex hole eliminator. Sixteen patients had incomplete extrusion of the apex hole eliminator associated with no visible radiographic pelvic or femoral osteolyisis. Two (10%) patients have undergone revision with curettage and allografting of the pelvic lesion and head and liner exchange. At the time of revision surgery liner motion was grossly obvious.
Discussion: The apex hole eliminator is neither watertight nor locking. Our hypothesis is that activity-related hydraulic pressure generated from excessive liner motion causes a high-pressure fluid leak into the pelvis. This fluid contains sub-micron particles generated by backside wear. The combination of particulates and fluid under pressure produces retro-acetabular osteolysis. The cyclic pressure then allows the non-locking plug to advance into the osteolytic pelvic defect.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
