A computerized analysis of femoral condyle radii in ACL intact and contralateral ACL reconstructed knees using 3D CT

The bony geometry of the distal femoral condyles may have a significant influence on knee joint kinematics. The aim of this study was to analyze the relationship between the size of the medial and lateral femoral condyles in different planes. Seventy-four three-dimensional (3D) CT reconstructions of 37 patients with ACL intact and contralateral ACL reconstructed knees were used and the data were imported into a graphical software program. The radii of the medial and lateral femoral condyles were analyzed in the sagittal, coronal, and axial planes by digitally reconstructed circular arcs along the bony condylar profiles marked with multiple digital surface points. Intra- and interobserver testing was performed. In the intact knees the average sagittal radius of the distal medial and lateral femoral condyles was similar. There was a significant difference between the radii of the distal medial femoral condyles compared to lateral femoral condyles in the coronal plane (22.4 vs. 27.8 mm, P < 0.001) as well as between the radii of the medial femoral condyles in the axial plane in 90A degrees knee flexion compared to the lateral femoral condyles (21.3 vs. 18.3 mm, P < 0.001). The average radius of the medial femoral condyles was significantly smaller in extension compared to 90A degrees of flexion (21.2 vs. 22.4 mm, P = 0.05) and the average radius of the lateral femoral condyles was significantly larger in extension compared to 90A degrees of flexion (27.8 vs. 18.3 mm, P < 0.001). The 37 ACL reconstructed knees demonstrated similar radii in all three planes when compared to the intact knees without any significant difference. The described method of assessing the architecture of the distal femoral condyles is non-invasive, reproducible, and provides reliable geometric parameters necessary for the 3D reconstruction of the femoral geometry in vivo. The radii of the FC were similar in the sagittal planes but demonstrate a significant asymmetry in the axial and coronal planes. The average radius of the lateral femoral condyles was significantly larger in extension whereas the radius of the medial femoral condyles was significantly larger in flexion. We did not find any significant difference in the shape of the femoral condyles in ACL intact and contralateral ACL reconstructed knees indicating that the geometry of the femoral condyles might not influence the injury mechanism of ACL rupture. The asymmetry between the femoral condyles may be considered when designing new anatomical femoral components in knee arthroplasty.