Effect of axial alignment on patient outcomes following total knee replacement (TKR): a systematic review and meta analysis.

INTRODUCTION: With robotic-assisted precision, total knee replacement (TKR) alignment has regained attention to address 20% post-operative dissatisfaction. While coronal alignment has been studied extensively, the impact of axial alignment on patient-reported outcome measures (PROMs) remains unclear. METHODS: Five databases were searched (to 15/02/2025). Random-effects meta-regression models, weighted by number of TKRs, assessed associations between each axial alignment parameter and PROMs. Analyses were conducted using individual PROMs and then with all PROMs combined as standardised-mean-differences(SMD), at individual timepoints, pooled, and time-adjusted levels. RESULTS: Sixty-five studies were included (n = 8392 TKRs, 8113 patients). Most (86%) studies reported only one or two axial parameters, with fewer than half assessing more than one and measurement protocols varied widely. Greater external femoral-component-rotation (FCR, range: -2.60° to 2.63°) improved Knee-Society-Score (KSS)-Overall (Regression-Coefficient (RC) = 33.2, p < 0.001, n = 323) and KSS-Function (RC = 11.5, p < 0.001, n = 327) at 12 months, and Standardised-Mean-Difference(SMD) PROM scores (RC = 3.38, p = 0.042, n = 1112). Higher external tibial-component-rotation (TCR, range: -4.30° to 19.0°) improved KSS-Function at 12 months (RC = 1.90, p = 0.030, n = 234), Western-Ontario-and-McMaster-Universities-Arthritis-Index (WOMAC)-Total in pooled/time-adjusted analyses (RC = - 4.62/-4.57, p < 0.001, n = 2221), and SMD PROMs at 3 months (RC = 0.57, p < 0.001, n = 149). Lower mismatch-rotation (MR) improved SMD PROM in pooled/time-adjusted analysis (RC = -0.55/-0.52, p < 0.001, n = 786, MR Range: -10.5°-9.30°). Combined-rotation (CR) showed no significant individual timepoint, pooled or time-adjusted effects on PROMs or SD PROMs. CONCLUSION: This review provides an up-to-date quantitative synthesis demonstrating that higher FCR, higher TCR, and lower MR, are associated with improved PROMs, emphasising the importance of considering axial alignment alongside coronal plane in TKR. However, heterogeneity in measurement protocols, underreporting of parameters limit comparability and generalisability. Standardised, multiplanar reporting is essential to establish evidence-based alignment targets and guide surgeons in optimising patient outcomes.