Lifetime revision risk for medial unicompartmental knee replacement is lower than expected.

PURPOSE: Unicompartmental knee replacement (UKR) is widely considered to be a pre-total knee replacement (TKR) particularly in the young. The implication of this is that it is sensible to do a UKR, even though it will be revised at some stage, as it will delay the need for a TKR. The chance of a UKR being revised during a patient's life time has not previously been calculated. The aim of this study was to estimate this lifetime revision risks for patients of different ages undergoing UKR. METHODS: Calculations were based on data from a designer series of 1000 medial Oxford UKR with mean 10-year follow up. These UKR were implanted for the recommended indications using the recommended surgical technique. Parametric survival models were developed for patients of different ages based on observed data, and were extrapolated using a Markov model to estimate lifetime revision risk. RESULTS: The estimated lifetime revision risk reduced with increasing age at surgery. Lifetime revision risk at age 55 was 15% (95% CI 12-19), at 65 it was 11% (8-13), at 75 it was 7% (5-9), and at 85 it was 4% (3-5). CONCLUSION: Provided UKR is used appropriately, the lifetime revision risk is markedly lower than expected. UKR should be considered to be a definitive knee replacement rather than a Pre-TKR even in the young. These lifetime estimates, alongside established benefits for UKR in speed of recovery, morbidity, mortality and function, can be discussed with appropriate patients when considering whether to implant a UKR or TKR. LEVEL OF EVIDENCE: III.