Background: Total knee arthroplasty is an accepted method for treatment of osteoarthritis of the knee. Measuring the distal femoral rotation is one of the most important problems in such operations. In the conventional 2D method, measuring the angle is based on CT scan images but these methods usually contain errors. In this study, the three-dimensional measurement of the aforementioned angle was investigated.

Methods: In this research, using CT scans and 3D modeling, 3D lower extremity models of 40 patients were extracted. The rotation of distal femur was measured for plane perpendicular to the anatomical and the plane of mechanical axis of femur. Four axes were drawn on these planes using anatomical landmarks: posterior condylar line (PCL), anatomical and surgical transepicondylar line (ATEA+STEA), and the Whiteside line (WL).  

Results: The mean difference of these measurements on the plane perpendicular to the mechanical axis of the femur, between PCL and WL,  STEA,  ATEA was 3.41, -1.31, 5.53; and angles on the plane perpendicular to the anatomical axis of femur were -0.74, -1.26, and 5.67, respectively. In addition, Bland-Altman diagram was plotted between every two measurements and no relationship found, except for STEA and ATEA.

Conclusions: The measurements between PCL, ATE, and STEA are not affected by the plane on which these measurements are carried out on, except for the 4 degrees difference present in WL axis. With a greater sample size and proper grouping, some relationship might be found between the aforementioned axes.