Candidacy for medial unicompartmental knee replacement declines with age.

BACKGROUND: The effect of age on the percentage of primary knee replacements appropriate for unicompartmental replacement (UKR), defined as candidacy, is unknown. The aim was to determine the candidacy and outcome of UKR in different age groups. HYPOTHESIS: Age is associated with candidacy for medial UKR. PATIENTS AND METHODS: This cross-sectional study determined UKR candidacy from preoperative radiographs, including stress views, from 457 consecutive knee replacements (TKR or UKR) in a specialist joint replacement centre. Candidacy, estimated from radiographs and from usage, was determined for all knees and then stratified by age group<50, 50-60, 60-70, 70-80, and 80+. The outcome of UKR implanted in these groups was also assessed. To avoid overestimating, candidacy estimated by usage was used for the primary analysis. RESULTS: Candidacy decreased with age (OR 0.98, p=0.008) and was 61% (CI 42-78), 52% (CI 43-61), 43% (CI 35-51), 41% (CI 31-52), and 36% (CI 22-52) respectively. Candidacy estimated by radiographs was slightly higher overall (49% compared to 46%) and in all age groups than candidacy estimated from usage. Neither functional outcome (p=0.47) nor implant survival (p=0.54) was affected by age. Overall 80% achieved good/excellent Knee Society objective scores, and the five-year implant survival was 99%. DISCUSSION: There is a strong association of candidacy for UKR with age in that younger patients are more likely to be candidates (61% in those<50 and 36% in those 80+). Good outcomes can be expected in patients of all ages who are appropriate for UKR. LEVEL OF EVIDENCE: IV, Prognostic cross-sectional study.