Objective: To investigate the reference role of the plane of the distal femur anterior cortex in determining the lateral rotation angle of femoral component in total knee arthroplasty (TKA).
Methods: Computed tomography (CT) scan was performed for full length of both lower limbs in 27 patients, and a total of 53 legs were examined by radiological department of the First Affiliated Hospital of Sun Yat-sen University. Case inclusion criteria were as follows: no obvious congenital bone deformity on the lower limbs, no knee purulent infection, and no severe knee deformity after surgery. 3D reconstruction was performed by Mimics 16.0 software for the scan images to calculate the angle between the plane of the distal femur anterior cortex and the Posterior Condylar Line (PCL) (defined as FPA), and the angle between the plane of the distal femur anterior cortex and the Clinical Epicondylar Axis (CEA) (defined as ACA), as well as the angle between the CEA and PCL, known as the condylar twist angle (CTA). Finally, Kolmogorov-Smirnov test and Student's t test were used to analyze the measured value.
Results: The average value of FPA was -4.70 ± 3.77°, that of CTA, +5.04 ± 2.36°, and that of ACA, -9.17 ± 5.78°. Each angle measured above has no significant differences in the gender (P > 0.05).
Conclusion: ACA was measured to be 9.17 ± 5.78° on the direction of medial femoral rotation, proving that the plane of distal femur anterior cortex plays a relatively accurate reference role in determining the lateral rotation angle of the femoral component in TKA.
Keywords: Anterior femoral cortex; Clinical Epicondylar Axis; Condylar twist angle; Total knee arthroplasty.