SEVERE POLYETHYLENE WEAR IN TOTAL HIP-ARTHROPLASTY - OBSERVATIONS FROM RETRIEVED AML PLUS HIP IMPLANTS WITH AN ACS POLYETHYLENE LINER

A retrospective review was performed of 94 consecutive Anatomic Medul lary Locking Plus (AML+, DePuy, Warsaw, IN) cementless acetabular comp onents implanted between January 1988 and January 1990. All acetabular cups utilized the Acetabular Cup System (ACS) polyethylene liner (Dep uy). Of these hips, 72 had been followed for more than 2 years (averag e, 43 months). There have been 15 (21%) clinical failures, all due to catastrophic wear of the acetabular polyethylene component surfaces. O f the 15 failures, clinical symptoms were absent in 7, an audible sque ak was present in 3, and 5 patients reported having pain. All clinical failures had accelerated acetabular wear necessitating revision. Pati ents in the failure population were younger (56 years vs 62 years) tha n the remainder of the patients, and had greater cup abduction angles (55 degrees vs 49 degrees). All of the failed ACS polyethylene compone nts had a 32 mm inner diameter articulating surface. The AML + acetabu lar component outer diameter averaged 56 mm (range, 50-64 mm). Six of 15 failures occurred in cups 58 mm or larger. Acetabular wear in the f ailure group was 0.77 mm/y (average). The incidence of acetabular (78% ) and femoral (71%) osteolysis in the failure population is alarming. The rate of failure (21%) at 46 months of the AML+ acetabular componen t with the ACS polyethylene liner appears to be related to design. The ACS design is flawed by a lack of hemispherical geometry, leading to failure at the superior rim with penetration of the femoral head throu gh the polyethylene and against the metal shell. All patients with tot al hip arthroplasties of this design, regardless of implant size, shou ld be carefully observed for evidence of polyethylene wear.