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

OBJECTIVE: The sagittal shapes of the femoral condyles were thought to consist of circles. However, the line connecting the centers of circles was not consistent with the surgical epicondylar axis (SEA) which was commonly used in surgery. Recently, ellipses have been proposed as an alternative method to represent the sagittal femoral condylar shape. Does the condylar ellipse line (CEL) coincide with the SEA in 3D MRI reconstruction analysis? METHODS: From May to August 2021, a total of 80 healthy subjects were scanned by MRI on the right knee in this retrospective study. The ellipses on the most distal slices of the medial and lateral condyles were determined. A line connecting the centers of the medial and lateral ellipses was the CEL. A line connecting the deepest point of the medial sulcus and the most prominent point of the lateral epicondyle was the SEA. Angular measurement of the SEA and the CEL relative to the posterior condylar line (PCL) and the distal condylar line (DCL) was performed on an axial and coronal view of the 3D model, respectively. Measurements were compared between males and females by using the independent‐samples t‐test. Pearson correlation was used to analyze the relationship between SEA‐PCL and CEL‐PCL, SEA‐DCL, and CEL‐DCL. RESULTS: On the axial view, the mean SEA‐CEL was 0.35° ± 0.96°. SEA‐PCL (2.91° ± 1.40°) had a high correlation with CEL‐PCL (3.27° ± 1.11°) (r = 0.731, p < 0.001). On the coronal view, the mean coronal SEA‐CEL was 1.35° ± 1.13°. SEA‐DCL (1.35° ± 1.13°) had a low correlation with CEL‐DCL (0.18° ± 0.84°) (r = 0.319, p = 0.007). On the sagittal view, the outlet points of the CEL on the medial and lateral epicondyles were anatomically located in the anteroinferior direction to the SEA. CONCLUSIONS: CEL traversed the medial and lateral epicondyles, which has a mean deviation of 0.35° with SEA on axial view and a mean deviation of 0.18° with DCL on coronal view. This study suggested that the ellipse approach is an improved scheme for representing the femoral condylar shape.