Purpose To compare 4 different bearings in total hip arthroplasty (THA) in a randomised controlled clinical study on clinical performance. Methods 393 patients with osteoarthritis of the hip or avascular necrosis were included and allocated to 1 of the head-and-cup couples zirconia-on-polyethylene (group A), metal-on-metal (group B), zirconia-on-polyethylene with the liner moulded into the shell (group C), or alumina-on-alumina (group D). In the individual case the surgeon could choose other implants if indicated. Results 299 patients were operated with the allocated prosthesis. The estimated cumulated prosthesis survival percentages and 95% confidence interval after 10 years were: group A 84.6 (75.8-93.4); group B 95.0 (89.5-100); group C 93.2 (86.7-99.7); group D 66.1 (54.5-77.7). The patients' physical function was significantly improved and remained equally good in all 4 groups, however slightly declining with ageing. The luxation rate was initially high, and equal between the groups, but was reduced by improving the surgical procedure introducing capsule repair by reinsertion of the short external hip rotators. Conclusions The metal-on-metal or zirconia-on-polyethylene prostheses had high 10-year survival percentages. The longevity of these bearing couples by themselves was not related to the combination of materials. The zirconia-on-polyethylene prosthesis with the liner mounted peroperatively possibly exhibited cases of backside wear which the corresponding bearing couple with moulded polyethylene (Asian) did not. The alumina-on-alumina bearing performed poorly - it was redesigned after our study initiation and later withdrawn from the market.
Implications of component size and calibration error on digital templating for total hip arthroplasty. A visual matrix from a simple mathematical model