The accuracy of femoral component rotational measurements using computed tomography—a cadaveric study

Abstract

Background CT scans can be used to assess the rotational alignment of the femoral component following total knee arthroplasty (TKA). This is done by calculating the posterior condylar angle (PCA). However, the methods used may not account for the biomechanical functionality of the TKA components. This cadaveric study aimed to determine whether the axis of scanning (mechanical or anatomical) alters the results of PCA calculations. Methods CT scans of 12 cadaveric adult femora were performed along the anatomical axis and the mechanical axis. The PCA was determined on each CT scan by measuring the relationship of the prosthetic posterior condyles to the surgical epicondylar axis of the femur. The mechanical and anatomical axis groups were further subdivided into best-fit and multi-slice subgroups. As a control, the posterior condylar angle was also calculated on photographic images of each femur. Bland-Altman plots were used to determine the correlation between the PCA values obtained from the different scanning axes and measurement techniques. Results There was no significant difference between the PCA measurements derived from anatomical and mechanical axis CT scans. The Pearson correlation co-efficient also indicated good correlation between the two scanning axes. Conclusion The axis of scanning does not significantly affect the PCA measurements. Therefore, the measurements may be reliably used for clinical decision-making, regardless of the axis of CT scanning.

Comparison of the femoral condylar ellipse line and the surgical epicondylar axis: 3D measurement by MRI scans in healthy Chinese people

“…Some in vitro and in vivo studies have shown that the posterior condyles appear circular and the centers pass through the medial and lateral femoral epicondyles, which coincides with the epicondylar axis 1,9 . Therefore, the epicondylar axis has been proposed as a reliable reference for determining the rotational alignment of the femoral component in total knee arthroplasty 21 . However, some studies have come to a different conclusion, that the epicondylar axis does not coincide with the contour of the femoral condyles 12,13,27 .…”

“… 1 , 9 Therefore, the epicondylar axis has been proposed as a reliable reference for determining the rotational alignment of the femoral component in total knee arthroplasty. 21 However, some studies have come to a different conclusion, that the epicondylar axis does not coincide with the contour of the femoral condyles. 12 , 13 , 27 Lustig et al investigated the existence of a circle centering on the epicondyles and fitting the whole femoral contours.…”

“…The SEA connects the most prominent point of the lateral epicondyles and the deepest point of the sulcus on the medial epicondyles 19,20 . In this study, we focused on the SEA because it is more reproducible, and is widely used during total knee arthroplasty 19–21 . On a 3D model of the distal femur, angular measurement of the CEL and SEA was performed on the axial view and the coronal view.…”

“… 19 , 20 In this study, we focused on the SEA because it is more reproducible, and is widely used during total knee arthroplasty. 19 , 20 , 21 On a 3D model of the distal femur, angular measurement of the CEL and SEA was performed on the axial view and the coronal view. The horizontal and vertical distances from the outlet point of the CEL to the SEA were measured on the sagittal MRI slices.…”