FEMORAL COMPONENT ROTATION IN TOTAL KNEE ARTHROPLASTY: WHICH AXIS IS BEST?

Abstract

Femoral component malrotation is a major cause of patello-femoral complications in total knee arthroplasty. In addition, it can affect varus/valgus stability during flexion which can lead to increased tibiofemoral wear.

Debate exists on where exactly to rotate the femoral component. The three principal methods utilise different anatomical landmarks: the posterior condylar axis, the transepicondylar axis and the antero-posterior axis (Whiteside’s line).

A prospective randomised controlled trial was undertaken. Sixty consecutive patients undergoing total knee arthroplasty by a single surgeon (LML) at the Royal Perth Hospital were randomised into 3 groups based on the intra-operative method for measuring femoral rotation using the PFC sigma prosthesis (Depuy) with computer navigation (Depuy/Brainlab). All patients received the usual post-operative treatment, rehabilitation and JRAC (Joint Replacement Assessment Clinic) follow up. All underwent a CT scan according to the Perth CT protocol designed specifically to accurately measure component alignment and rotation.

No significant difference in femoral rotation was found between the three groups using a one-way analysis of variance (p=0.67). However, Whiteside’s line had a significantly greater variability than the posterior condylar or transepicondylar axis using the F Test for variances (p=0.02, p=0.03). In conclusion, whilst there was no significant difference in femoral rotation, Whiteside’s line did show greater variability (−6° to 3°), and therefore we recommend the use of either the transepicondylar or posterior condylar axis in Total Knee Replacement.