Cancer risk after hip replacement with metal implants: a population-based cohort study in Sweden.

Background: Joint replacement with metal implants has been the standard procedure for surgical treatment of irreversible degeneration of hip and knee joints for more than two decades. However, reports of local malignancy after joint replacement and experimental studies that suggest a carcinogenic action of metal ions and polymethylmethacrylate (an acrylic compound used to stabilize the implant in the host) have raised concern about the possible long-term risks associated with metal implants.
Purpose: Our aim was to study cancer risk in a Swedish cohort of patients who had hip replacement surgery during the period 1965 through 1983.
Methods: We studied the risk of cancer in a cohort of 39 154 patients (14 869 men and 24 285 women), identified in the nationwide Swedish Inpatient Register with at least one hip replacement during the period 1965 through 1983. The patients were followed through 1989 by means of record linkage to the Swedish Cancer Register. The cohort contributed a total of 327 922 person-years at risk. Standardized incidence ratios (SIRs) were computed using age-, sex-, and period-specific incidence rates derived from the entire Swedish population.
Results: The overall relative risk of cancer was increased by only 3%. Bone cancer--the focus of previous concerns--occurred in six cases versus 4.3 expected, and connective tissue cancer occurred in 28 cases versus 25.9 expected. Increased risks were observed for kidney cancer (SIR = 1.31; 95% confidence interval [CI] = 1.13-1.51), prostate cancer (SIR = 1.13; 95% CI = 1.04-1.22), and melanoma (SIR = 1.23; 95% CI = 1.00-1.50). The relative risk of gastric cancer steadily declined with increasing follow-up time, in both men and women (SIR = 0.58; 95% CI = 0.39-0.84 more than 10 years after hip replacement).
Conclusion: In this study, the largest study to date to evaluate hip replacement and subsequent cancer risk, the overall cancer risk appears to be negligible from a public health perspective, and our results have not produced any strong evidence against the continued use of these devices. Nevertheless, the small but statistically significant increases in kidney and prostate cancers and the decrease in gastric cancer deserve further study.