Severe polyethylene wear in total hip arthroplasty. Observations from retrieved AML PLUS hip implants with an ACS...

A retrospective review was performed of 94 consecutive Anatomic Medullary Locking Plus (AML+, DePuy, Warsaw, IN) cementless acetabular components implanted between January 1988 and January 1990. All acetabular cups utilized the Acetabular Cup System (ACS) polyethylene liner (Depuy). Of these hips, 72 had been followed for more than 2 years (average, 43 months). There have been 15 (21%) clinical failures, all due to catastrophic wear of the acetabular polyethylene component surfaces. Of the 15 failures, clinical symptoms were absent in 7, an audible squeak was present in 3, and 5 patients reported having pain. All clinical failures had accelerated acetabular wear necessitating revision. Patients in the failure population were younger (56 years vs 62 years) than the remainder of the patients, and had greater cup abduction angles (55 degrees vs 49 degrees). All of the failed ACS polyethylene components had a 32 mm inner diameter articulating surface. The AML + acetabular 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 failure 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 component 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 through the polyethylene and against the metal shell.(ABSTRACT TRUNCATED AT 250 WORDS)