204. ALUMINA-POLYETHYLENE BEARING AT TWENTY YEARS FOLLOW-UP: POLYETHYLENE WEAR AND OSTEOLYSIS

Abstract

Purpose of the study: The alumina-polyethylene bearing has been used for many years but no study has evaluated polyethylene wear and osteolysis with a 32 mm head with a follow-up exceeding 20 years.

Material and methods: Thirty-six arthroplasties implanted between 1983 and 1985 (26 patients, mean age 54 years, range 35–65 years) were studied. The same cemented implants were used in all cases, with no loosening. Penetration of the head into the polyethylene was measured annually on digital radiographs and with computer assistance. Osteolysis was quantified in mm² on the merckel.

Results: At 20 years follow-up (minimum) or more, penetration of the femoral head into the cup was on average 0.07mm/y. The characteristic feature of the wear curve was the perfect stability after the third year and the absence of any increase over time. Extrapolation of the straight part of the curve to the origin determined the creep. True wear was limited: 0.05mm/y. It was not modified by the polyethylene thickness (eight 52mm cups, twenty-three 50mm and five 48mm). Corresponding volumetric wear was estimated at 640 mm3 at maximum follow-up. At last follow-up, osteolysis measured in mm² on the meckel was 65 mm² on average. In general, this osteolysis appeared around the second year with an imprint on the merckel; it then increased linearly and regularly to the 20th year. Acetabular osteolysis was nevertheless greater than that observed with the Al/Al bearing of controlateral hips implanted at the same period when evaluated on the scan for both hips (20 cases).

Discussion: The alumina-polyethylene bearing enables long implant survival for at least 20 years, even for relatively thin polyethylene thicknesses. The characteristic feature of the bearing is the linear polyethylene wear which does not increase with time but remains constant, undoubtedly in relation to the absence of any change in the roughness of the head despite the very long follow-up. Osteolysis remains minimal, but superior to that observed with Al/Al bearings implanted during the same period in controlateral hips.