Unicondylar knee replacement for primary osteoarthritis: a prospective follow-up study of 1,819 patients from the Finnish Arthroplasty Register.

BACKGROUND: The choice and use of unicondylar knee arthroplasty (UKA) has gone through a nation wide resurgence at the start of the 21st century in Finland. We evaluated the population-based survival of UKA in patients with primary osteoarthritis (OA) in Finland, and the factors affecting their survival.

METHOD: The Finnish Arthroplasty Register was established in 1980. During the years 1985-2003, 1,928 primary UKAs were recorded in the register; 1,819 of these were performed for primary OA. Of these 1,819 UKAs, we selected for further analysis implants that had been used in more than 100 operations during the study period. The survival rates of UKAs were analyzed using Kaplan-Meier analysis and the Cox regression model.

RESULTS: Analysis of the whole study period showed that UKAs had a 73% (95% CI: 70-76) survival rate at 10 years, with revision for any reason as the end point. Those patients who received the Oxford menisceal bearing unicondylar (n = 1145) had a survival rate of 81% (95% CI: 72-89) at 10 years. The group that received the Miller-Galante II unicondylar (n = 330) had a 79% survival rate (95% CI: 71-87) at 10 years, whereas the Duracon (n = 196) had a survival rate of 78% (95% CI: 72-84) and the PCA (n = 146) had a survival rate of 53% (95% CI: 45-60) at 10 years. The number of UKA operations in Finland has increased markedly in recent years. At the time of operation, the mean age of the patients was 65 (38-91) years. Younger patients (<or= 65 years of age) were found to have a 1.5-fold (95% CI: 1.1-2.0; p = 0.04) increased risk of revision compared to older patients (< 65 years).

INTERPRETATION: UKA is a viable option for the treatment of unicompartmental osteoarthritis of the knee. However, patients should be made aware of the lower survival of the UKAs compared with total knee arthroplasties.