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All patients with total hip arthroplasty (THA) are exposed to soluble or particulate forms of Co and Cr. Adverse effects of these wear products are not known. Data from Nordic registries is used to estimate adverse effects on a large scale, based mostly on metal-on-polyethylene bearings. Cancer incidence was in line with the general population when the patients were operated on for all indications and significantly decreased when the indication was primary osteoarthritis. Stomach cancer and colorectal cancers were significantly reduced and prostate cancer and skin melanoma significantly increased. There was no significant excess of cancer in target organs, i.e. liver, kidney, or haematopoietic cancers. THA patients had reduced mortality and extended life expectancy compared with standard Nordic populations. All-site cancer incidence of the first-generation metal-on-metal McKee-Farrar patients operated on for primary osteoarthritis was in line with the general population after follow-up for up to 28 years. General mortality of these patients was also reduced and they also had an extended life expectancy. Temporary increases in haematopoietic cancers at different follow-up periods were seen in some cohorts. This malignancy deserves a special record linkage monitoring while large numbers of young patients are provided with the second generation of metal-on-metal prostheses.

3 Nordic cohorts of total hip (THA) and total knee arthroplasty (TKA) in patients operated on for primary osteoarthrosis during 1967-1995 were partly adapted and combined for meta-analysis. THA was performed in 49,000 patients and TKA in 24,000 totaling 497,000 person years. The mean and maximum follow-up times were 6.8 and 30 years, respectively. Standardized incidence ratios (SIRs) with 95% confidence intervals (95% CI) were calculated for the observed and expected number of cancers. The expected numbers were based on national incidence rates. The overall SIRs as well as the site-specific ones were similar in the THA and TKA patients. The observed number of cancers at all sites was 7,639 and the expected one was 8,202 (SIR 0.93, 95% CI 0.91-0.95). The SIRs for lung cancer (0.69, 0.64-0.75) and laryngeal cancer (0.64, 0.44-0.92) were reduced. The incidence was also low for cancers of the stomach (SIR 0.76, 0.67-0.84), colon (SIR 0.86, 0.79-0.93) and rectum (SIR 0.89, 0.80-0.98). Among TKA patients, the only increases in SIRs were seen in cancers of the endometrium (SIR 1.36, 1.05-1.74), prostate (SIR 1.19, 1.02-1.38) and, among both THA and TKA patients, in skin melanoma (combined SIR 1.21, 1.03-1.41).