EBRA migration patterns of the Plasmacup with ceramic or polyethylene inserts: a randomised study

In this prospective randomised study, the influence of different bearing materials on migration and wear was measured and their effect on the function of the artificial joint and the patient outcome was investigated. Mid-term results were recorded so that recommendations can be made on the use of certain bearings, which minimise wear and thus the danger of subsequent aseptic loosening.

Sixty-six patients met the inclusion criteria and were willing to take part in the study. These patients were randomised to 2 groups. All of them had total hip arthroplasty with implantation of a cementless Bicontact stem and Plasmacup using a cementless press-fit technique. Thirty-five of these patients were given a ceramic-ceramic bearing and 31 patients a ceramic-polyethylene bearing (gamma sterilised/nitrogen environment). At the most recent follow-up, they underwent detailed clinical and radiological examination and evaluation by means of the Harris Hip Score, Hannover function questionnaire and single-film X-ray analysis (EBRA).

The overall follow-up rate was 65.2 % (43 of 66) and the mean follow-up period was 8.1 (7.1 - 9.2) years. The median Harris Hip Score at the time of follow-up was 90.1 (58.7 - 99.9) points. The average Hannover function score was 87.14 % (63.9 - 100). In 4 of 66 cases (6.1 %) there was a tendency for the Plasmacup to subsidence in the first postoperative months that was slight but detectable by EBRA; however, this stopped subsequently. This primary subsidence was independent of the chosen bearing material. No significant difference in the clinical and radiological parameters was found between the two groups.

The very good results with regard to the rate of loosening confirm the press-fit cup fixation concept. The study shows a similar medium-term result for the ceramic-ceramic and ceramic-polyethylene bearing so that use of both bearings can continue to be recommended. Only long-term studies with sufficiently large numbers of patients will be able to show whether significant differences can be detected between the two slide bearings with regard to wear and migration behaviour and so that a recommendation can be given to the surgeon.