Midterm follow-up study of metal on metal total hip replacement

Abstract

Background: Metallosis and pseudotumors are long discussed complications with metal on metal bearing total hip replacement which has increased the rate of revision total hip replacements in these patients. Aims and Objective: To evaluate the levels of metal ion (Cobalt and Chromium), factors affecting theses metal ion levels and incidence of pseudotumors in metal on metal total hip replacement patients. Materials And Methods: Prospective descriptive study done on 25 patients who had metal on metal bearing surface replacement and total hip replacement with a mean post-op period of 6 years. Serum metal ion levels (Cobalt and Chromium), MARS-MRI (Metal Artifact Reduction Sequence) and acetabular cup inclination angle on X-rays and functional score were recorded in theses patients on two follow-up visits with mean follow-up period of 1 year. Result: Mean cobalt was 1.64 and mean chromium was 3.06. 28% of the study population showed asymptomatic pseudotumors but were less than 5cm. Mean cup inclination angle was 41.8* on X-rays which did not have any influence on serum metal ions and functional score. Gender (Male / Female) and type of arthroplasty (Articular surface replacement / Total hip replacement) has no affect on serum metal ions. Functional scores of these metal on metal patients comparable to metal on polyethylene bearing patients. Revison total hip replacement done in one metal on metal THR patient who had a dislocated cup in his second follow-up. Conclusion: Metal on metal hip arthroplasty patients were functionally doing well like the regular metal on polyethylene patients. Chromium values were significant and higher than cobalt. Incidence of asymptomatic pseudotumors was 28%.