Safety of single‐anaesthetic versus staged bilateral primary total knee replacement: experience from the New Zealand National Joint Registry

BACKGROUND: Surgical management options for bilateral knee osteoarthritis comprise staged or single-anaesthetic bilateral total knee replacements (SABTKRs). We examined the New Zealand Joint Registry hypothesizing there would be no difference between these practices compared to unilateral total knee replacement (TKR) examining 30-day mortality, all-cause revision rate and function. METHODS: For this study, 84 946 primary TKRs were identified. We compared three groups: unilateral TKRs, all SABTKRs and all staged bilateral TKRs with intervals of 1 to 90 days, 91 days to 1 year and >1 year. Cumulative revision rates were calculated (Kaplan-Meier method). Mortality risks were compared to unilateral TKR and hazard ratios (HRs) calculated. Six-month Oxford scores were compared using analysis of variance. RESULTS: Thirty-day mortality for SABTKR was 0.219%: unilateral TKR 0.236% (HR 0.43; 95% confidence interval (CI) 0.38-0.48; P < 001). Staged TKR had lower mortality than unilateral TKR at three time interval groups unless performed within 90 days (adjusting for age and American Society of Anesthesiologists grade) TKR (<90 days HR 0.92; 95% CI 0.703-1.371; P = 0.915; 91-365 days HR 0.783; 95% CI 0.687-0.891; P < 0.001; >365 days HR 0.394; 95% CI 0.344-0.451; P < 0.001). Revision risk with SABTKR was lower at 0.43/100 component years (95% CI 0.37-0.49/100 component years) compared to unilateral 0.56/100 component years (95% CI 0.53-0.59; P < 0.05). Six-month Oxford scores were superior in SABTKR versus unilateral TKR (38.6 (95% CI 38.2-39) versus 36.9 (95% CI 36.8-37.1); P < 0.001). CONCLUSIONS: SABTKR is at least as safe as unilateral TKR or staged bilateral TKR in appropriately selected cases. Surgeons should wait at least 90 days before the second procedure.