CT-based estimation of medial and lateral femoral joint lines in extension and flexion: A large three-dimensional validation study.

Purpose: Successful total knee arthroplasty relies on precise joint line restoration, but anatomical variations and bone loss complicate this intraoperatively. This study aimed to develop computed tomography (CT)-based estimates of the medial and lateral femoral joint lines in extension and flexion using three-dimensional imaging. Methods: Using a Computed Tomography database, the medial and lateral joint lines in extension and in flexion relative to the medial and lateral epicondyles were analysed in 724 nondegenerative femora. Linear regression models were developed using femoral width as the predictor. Independent validation was performed in 264 femora, not included in the regression analyses, to analyze prediction accuracy. Results: The linear regression models predicted the medial and lateral extension joint lines with an Conclusion: This study presents CT-based regression models that characterise native femoral joint line anatomy using a large cohort of nondegenerative femora. By defining reproducible relationships between femoral geometry and joint line position, the proposed approach provides imaging-derived reference values that may support preoperative planning and joint line estimation. These findings contribute to a more detailed anatomical understanding of joint line morphology and offer a quantitative framework that could be integrated into image-based planning workflows, although clinical validation is still required. Level of Evidence: Level IV.