Cancer incidence after total knee arthroplasty: a nationwide Finnish cohort from 1980 to 1996 involving 9,444 patients.

A nationwide, computer-based survey of all total joint arthroplasties performed in Finland has been carried out since January 1980. From these records, a cohort of 9,444 patients, with 51,756 person-years, after primary operation with a total polyethylene-on-metal knee arthroplasty (TKA) was followed up for cancer through the Finnish Cancer Register up to December 31, 1996. During the follow-up, 706 cancers were observed. The expected number, based on national rates, was 719; therefore, the standardized incidence ratio (SIR) for all cancers was 0.98. The SIRs for non-Hodgkin's lymphoma (1.40), Hodgkin's disease (1.24) and multiple myeloma (1.54) were increased, but only that of non-Hodgkin's lymphoma was statistically significant 3-10 years after the operation. The numbers of observed cases of prostate cancer exceeded that of expected, with a SIR value of 1.49. A low SIR of lung cancer was observed among men, especially during the first 3 years (0.61), but not in women. The SIR for colon cancer was below unity in women only (SIR 0.70). The SIR for cancer of the urinary organs was close to unity (0.97). SIR relating to soft tissue and bone cancer did not differ significantly from unity, and none of the 6 sarcomas was observed at the site of a prosthesis. The overall cancer risk after TKA done for primary osteoarthrosis seems not to be increased. The increases in lymphoma and prostate cancer risk, however, are observations that could be related to TKA and justify further follow-up of the cohort.