Effect of sagittal alignment on patient outcomes following total knee replacement: A systematic review and correlation analysis

Abstract Purpose With enhanced implant precision facilitated by robotic technologies, there is renewed attention on the contribution of total knee replacement (TKR) alignment to the 20% post‐operative dissatisfaction rate. Although coronal alignment has been extensively studied, the impact of post‐operative sagittal alignment on patient‐reported outcome measures (PROMs) remains unclear. This review addresses this gap. Methods We searched five electronic databases (inception‐15 February 2025) for studies reporting post‐TKR sagittal alignment and PROMs. Case‐weighted regression models examined sagittal alignment—PROM relationships at individual post‐operative timepoints, across pooled timepoints and using time‐adjusted aggregated analyses. Risk of Bias was assessed using ROB2 and ROBINS‐I V2 tools. Results Of 622 studies, 52 were included ( n  = 11,180 TKRs, 9431 patients). Most (92%) studies reported only one or two sagittal parameters, with fewer than five assessing more than two, and measurement protocols varied widely. Higher posterior‐tibial‐slope (PTS) was associated with improved visual analogue scale pain scores at 1 month (regression‐coefficient [RC] = 1.00, p  < 0.001, n  = 90 TKR, PTS range: 6.80–6.90), Oxford‐knee‐score (OKS) at 6 months (RC = 3.28, p  = 0.009, n  = 117, PTS range: –5.00 to 4.38) and pooled OKS across all timepoints. Higher femoral flexion (FF) was associated with improved OKS at 24 months (RC = 4.05, p  = 0.004, n  = 539, FF range: 3.00–4.96) and improved knee‐society‐score‐overall (KSS‐overall), KSS‐function, short‐form‐survey‐12 and knee‐injury‐and‐osteoarthritis‐outcome‐score. Lower femoral‐sagittal‐angle (FSA; range: 1.30–3.80) was significantly associated with improved KSS‐knee at 12 months (RC = –6.20, p  = 0.008, n  = 160), and when pooled across timepoints (RC = –5.32, p  < 0.001, n  = 280), and in time‐adjusted aggregated analysis (RC = –6.09, p  < 0.001, n  = 280). Higher posterior‐condylar‐offset (PCO) was associated with improved KSS‐overall at 12 months (RC = 42.945, p  = 0.002, n  = 613, PCO range: 30.40–33.60 mm), higher KSS‐knee (RC = 0.67, p  = 0.019, n  = 175, PCO range: 24.5–33.6 mm) in pooled analysis, and improved KSS‐overall (RC = 31.64, p  < 0.001, n  = 2338, PCO range: 24.0–33.6 mm) in time‐adjusted analysis. Conclusion This review provides the first quantitative synthesis linking post‐operative sagittal alignment parameters with PROMs. Higher posterior‐tibial‐slope, femoral flexion, and posterior‐condylar offset, and lower femoral‐sagittal angle were each significantly associated with improved PROMs, underscoring the importance of sagittal alignment beyond the coronal plane. However, heterogeneity in measurement protocols, underreporting of parameters limit comparability and generalisability. Standardised, multiplanar reporting is essential to help define evidence‐based alignment associations and inform surgeons about how best to improve patient outcomes. Level of Evidence Level I.