Reproducibility of measurement of femoral component rotation after total knee arthroplasty using computer tomography

Both the condylar twist angle (CTA) and the posterior condylar angle (PCA) describe rotational alignment of the femoral component after total knee arthroplasty. The purpose of this study was to assess the reliability of the measured axes which determine these angles. Measurements were independently performed on transverse computer tomography sections of 61 knees at 18, 24, 30, and 36 mm above the joint line by 2 experienced musculoskeletal radiologists. The most prominent point of the medial epicondyle which is required for the CTA was much better identifiable than the medial sulcus which is required for the posterior condylar angle. The best interobserver correlation was obtained for the CTA at 30 mm above the joint line (R = 0.91).