THE POROUS-COATED ANATOMIC TOTAL HIP-PROSTHESIS - FAILURE OF THE METAL-BACKED ACETABULAR COMPONENT

One hundred and ninety-nine total hip arthroplasties were performed, b etween 1983 and 1987, in 173 patients by three surgeons using the init ial design of the porous-coated anatomic prosthesis. The acetabular co mponent was a preassembled, metal-backed polyethylene device, with bea ds sintered to the metal backing to allow bone ingrowth and two pegs f or initial fixation. Twenty-three acetabular components (12 per cent) failed because of either migration or severe osteolysis. The radiograp hic appearance of osteolysis was positively associated with the durati on that the implant had been in situ (p < 0.001). The prevalence of os teolysis was also significantly greater in acetabular components with an outer diameter of fifty-five millimeters or less (a polyethylene th ickness of 8.5 millimeters or less) (p = 0.03). Thirteen hips were rev ised at a mean of 69.5 months (range, thirty-three to ninety-one month s) after the index operation. Examination of the retrieved acetabular components revealed extensive polyethylene damage on the articular and back surfaces of the liners. Cracks in the polyethylene rim of the li ner and deformation of the anti-rotation notch in the polyethylene rim were common findings. The density of the polyethylene was greater tha n expected, and more particles than anticipated had not fused,vith the surrounding polyethylene. The results of this study suggest that fact ors related to both the design and the material contributed to the fai lure of these porous-coated anatomic acetabular components. CLINICAL R ELEVANCE: Patients who have had a total hip arthroplasty with the init ial design of the porous-coated anatomic acetabular component should b e closely monitored clinically for the onset of pain and radiographica lly for the development of osteolytic lesions or migration of the comp onent. These findings are associated with impending failure of the com ponent and may warrant revision of this portion of the hip replacement .