Preoperative MRI measurement of condylar twist angle to optimise femoral component rotation in total knee arthroplasty: A prospective study.

Background: Rotational malalignment of the femoral component is a recognized cause of early failure after total knee arthroplasty (TKA). Conventional techniques often rely on fixed external rotation values or bony landmarks, which may be unreliable in arthritic knees. The condylar twist angle (CTA) - the angle between the posterior condylar axis (PCA) and anatomical transepicondylar axis (aTEA) - offers a patient-specific reference. This study evaluated whether preoperative magnetic resonance imaging (MRI) measurement of CTA, reproduced intraoperatively, enhances the accuracy of femoral component rotation. Methods: A prospective study was performed on 23 knees in 12 patients undergoing primary TKA for osteoarthritis between 2014 and 2016. Preoperative MRI was used to calculate the CTA, which was reproduced intraoperatively using a posterior condylar referencing jig. Postoperative computed tomography (CT) was performed to validate femoral component rotation relative to the aTEA. The primary outcome was the difference between planned and achieved CTA. Results: The mean preoperative CTA was 6.47° (range: 3-9°), with higher values in males (7.44°) than females (5.85°). The mean error between planned and postoperative CTA was 0.60°. Parallel alignment to the aTEA was achieved in 8 knees (34.8 %) and a further 14 knees (60.9 %) were 1° or less. All patients demonstrated balanced flexion gaps, stable patellofemoral tracking, and no requirement for lateral release. Conclusions: Preoperative MRI-based CTA measurement provides a highly accurate, patient-specific method for guiding femoral component rotation in TKA, achieving near-parallel alignment with the aTEA. This approach may overcome the limitations of fixed external rotation techniques and reduce the risk of malrotation-related complications. Larger, multicentre studies are warranted to validate these findings and assess long-term outcomes.