Long term results with the BiCONTACT system--aspects to investigate and to learn from

Abstract

The BiCONTACT femoral stem for cementless fixation is being used without any technical modification after 15 years. The long-term results should be evaluated in this study. A consecutive series was continuously monitored in a prospective follow-up study. A survival analysis was performed, clinical results were rated according to the Harris score. There were 236 patients with 250 total hip replacements (THR); mean age at time of implantation was 58.2 years. Indications for THR included osteoarthritis (62.4%), dysplasia (16.8%), trauma (8.4%) and femoral-head necrosis (16.8%). Average time of follow-up evaluation was 8.9 years (range 7.4-10.7 years). At follow-up, 27 patients had died and two could not be located. Seven patients were revised--two for infection, one for recurrent dislocation, two for component undersizing with rapid subsidence, and one for aseptic loosening of a varus-malaligned stem; one radiologically well-fixed stem had been revised during acetabular revision. Survival estimate showed an overall survival rate of 97.1% after 11 years (confidence limits: 98.7% upper and 93.6% lower). Radiologically, tiny reactive lines (< 2 mm) were present in the distal zones of the femoral shaft, but no radiolucencies could be found in the proximal anchoring zone. Migration analysis with Ein-Bild-Röntgen-analyse/femoral component analysis (EBRA/FCA) demonstrated a very small amount of migration: in 31.0%, the overall migration was between 0.5 and 1 mm after 120 months; 8.5% had an absolute amount of subsidence exceeding 2 mm after 120 months (one case more than 3 mm). Mean subsidence was 0.2 mm after 3 months and 6 months, 0.3 mm after 12 months, and reached 0.5 mm after 10 years. An initial small amount of subsidence could be detected in 45.1%, and 15.5% had a late onset of subsidence. Continuous sinking could be found in 12.7%, while 26.8% had irregular patterns of migration. Clinical results were somewhat compromised by a higher-than-average rate of cup loosening (uncoated threaded cup). The average Harris hip score at follow-up was 84.3 points. Interestingly, no femoral osteolysis could be detected, even in cases with severe acetabular osteolyses, indicating sealing of the stem interface by tight osseointegration of the proximally-coated stem.