PROSPECTIVE CLINICAL AND JOINT SIMULATOR STUDIES OF A NEW TOTAL HIP-ARTHROPLASTY USING ALUMINA CERAMIC HEADS AND CROSS-LINKED POLYETHYLENE CUPS

We report the findings from independent prospective clinical and labor atory-based joint-simulator studies of the performance of ceramic femo ral heads of 22.225 mm diameter in cross-linked polyethylene (XLP) ace tabular cups. We found remarkable qualitative and quantitative agreeme nt between the clinical and simulator results for the wear characteris tics with time, and confirmed that ceramic femoral heads penetrate the XLP cups at only about half the rate of otherwise comparable metal he ads. In the clinical study, 19 hips in 17 patients were followed for a n average of 77 months, In the hip-joint simulator a similar prosthesi s was tested for 7.3 million cycles. Both clinical and simulator resul ts showed relatively high rates of penetration over the first 18 month s or 1.5 million cycles, followed by a very much lower wear thereafter , Once an initial bedding-in of 0.2 mm to 0.4 mm had taken place the s ubsequent rates of penetration were very small, The initial clinical w ear during bedding-in averaged 0.29 mm/year; subsequent progression wa s an order of magnitude lower at about 0.022 mm/year, lower than the 0 .07 mm/year in metal-to-UHMWP Charnley LFAs. Our results show the exce llent tribological features of alumina-ceramic-to-XLP implants, and al so confirm the value of well-designed joint simulators for the evaluat ion of total joint replacements.