Association of Flexion Gap Balancing with Postoperative Knee Stability and Functional Outcome after Total Knee Arthroplasty: A Prospective Observational Study

Background: The relationship between intraoperative flexion-gap symmetry, postoperative stability, and functional recovery after total knee arthroplasty (TKA) remains uncertain. Objective: To examine associations between medial lateral flexion-gap difference and six-month stability and functional outcomes after posterior stabilised TKA. Methods: A total of 80 primary unilateral TKA cases were analysed, with six-month outcomes available for 76. Absolute medial lateral gap difference at 90° flexion was the principal exposure. Outcomes included coronal laxity, anteroposterior laxity, and Oxford Knee Score (OKS). Multivariable linear regression incorporated prespecified covariates and robust standard errors. Results: Median absolute gap difference was 1.0 mm (interquartile range 0.5–1.0). Each additional millimetre was associated with 1.03° greater coronal laxity after adjustment (95% CI 0.72–1.34; p<0.001). No independent association was identified with anteroposterior laxity or six-month OKS. Mean OKS increased from 18.6±4.2 to 38.1±3.7, representing an improvement of 19.5 points (95% CI 18.3–20.7; p<0.001). Conclusion: Greater flexion-gap asymmetry was associated with increased six-month coronal laxity, but not with anteroposterior laxity or Oxford Knee Score, suggesting that mechanical stability and short-term functional recovery may reflect different aspects of postoperative outcome.