CANCER RISK AFTER METAL ON METAL AND POLYETHYLENE ON METAL TOTAL HIP-ARTHROPLASTY

The incidence of cancer after metal on metal total hip arthroplasty (M cKee-Farrar) and polyethylene on metal total hip arthroplasty (Brunswi k, Lubinus) was compared with that of the general population in Finlan d. The mean followup time for the patients who had metal on metal tota l hip arthroplasty was 15.7 (9092 person years) and for the patients w ho had polyethylene on metal total hip arthroplasty it was 12.5 years (19,846 person years), One hundred thirteen malignant cancers were obs erved in patients who had metal on metal total hip arthroplasty and 21 2 were observed in patients who had polyethylene on metal total hip ar throplasty. The standardized incidence ratio for all cancers of the me tal on metal arthroplasty group was 0.95 (95% confidence limits 0.79-1 .13) and that of the polyethylene on metal arthroplasty group was 0.76 (95% confidence limits 0.68-0.86). The risk of total cancer in the pa tients who had metal on metal total hip arthroplasty was 1.23-fold com pared with that of the patients who had polyethylene on metal total hi p arthroplasty. Both groups had significantly less lung cancer than th e general population: the leukemia incidence in the patients who had m etal on metal total hip arthroplasty was slightly increased (observed to experienced 7/3.03, standardized incidence ratio 0.61; 95% confiden ce limits 0.17-1.56). The leukemia rate of the patients who had metal on metal total hip arthroplasty was 3.77-fold compared with that of th e patients who had polyethylene on metal total hip arthroplasty, but t his difference was not statistically significant. No sarcomas were obs erved at the site of the prosthesis. The incidence of the other forms of cancers did not differ significantly from those in the general popu lation. The observed variation in the incidence of different cancers a mong patients who had total hip arthroplasty compared with the general population suggests that factors other than total hip arthroplasty pl ay a major role in the origin of cancer.