Cementless Plasmacup-Bicontact Total Hip Arthroplasty. Results of a Minimum of Ten-Year Follow-up

PURPOSE OF THE STUDY The aim of the study was to analyse the long-term clinical and radiographic results of total hip arthroplasty (THA) with the Bicontact-Plasmacup prosthesis, MATERIAL AND METHODS In this retrospective observational study, 34 consecutive patients undergoing Bicontact-Plasmacup THA between August 1998 and July 2000 were evaluated. The group included 15 women and 19 men with an average age of 56 years (30 to 67 years). The mean +/- SD of follow-up was 132 +/- 9 months (122 to 149 months). Patients' satisfaction with the treatment outcome and selected clinical and radiographic features were evaluated. The data were analysed using the concordance test, Spearman's correlation coefficient and chi-square test. RESULTS At the final follow-up, 94% of the interviewed patients reported satisfaction with the surgery outcome. The mean Harris score was 93 (67 to 98) points, with excellent or very good results in 91% of the patients. Compared with the post-operative radiographs, the mean +/- SD value for vertical migration of the acetabular cup was 2.43 +/- 3.21 mm (0 to 12 mm) and that for horizontal migration was 0.35 +/- 1.0 mm (0 to 4.3 mm). The mean stem subsidence was by 3.87 mm (range, 0.36 to 21.11 mm; SD 4.03). At the final follow-up, all implants showed radiographic stability and absence of radiolucent lines. Early acetabular osteolysis was detected in two patients (5.9 %). In 19 patients (56%) a change in bone architecture, similar to alterations due to weight-bearing adaptation, was seen around the cup following surgery. The stress shielding effect of the femoral component was recorded in 79%, bypass phenomenon in 41 % and pedestal formation under the apex of the stem in 18% of the patients. The mean rate of polyethylene wear measured by the Dorr and Wan method was 0.106 mm per year (range, 0.00 to 0.267 mm) or it was 0.078 mm per year (0.00 to 0.19 mm) when assessed by a modification of the method described by Kang et al. DISCUSSION The clinical and radiographic findings presented here are in accordance with the relevant literature data. This implant design is associated with a relatively infrequent osteolysis around the cup probably due to a low wear rate of polyethylene and a stable polyethylene liner-metal cup interface. Based on this work and some other studies it can be concluded that a post-operative migration of several millimetres is compatible with a long-term, stable cementless THA. CONCLUSIONS The Bicontact-Plasmacup THA meets the National Institute for Health and Clinical Excellence (NICE) criteria for a very good implant (ten-year survival rate of over 90%). At 10 years after surgery, however, the first signs of complaints about surgery outcome II dissatisfaction with surgery outcomes were recorded. This may, at least partly, be related to aseptic loosening which is one of the symptoms of particle disease.