Abstract
Purpose
Reproducing a functional flexion-extension axis (FEA) of the femur is key to achieving successful collateral ligament balance and joint line in total knee arthroplasty (TKA). This study assessed the feasibility of cylindrical axis (CA)-reference bone-cut and articular surface-reference bone-cut to reproduce FEA in Japanese osteoarthritis patients.
Methods
The study enrolled 122 knees from 86 patients who underwent primary TKA due to grade III or IV osteoarthritis. Data from preoperative CT were reconstructed into 3-dimensional (3D) models using 3D-planning software. Cylindrical radii of the condyles were measured, and femoral bone-cut angles relative to anatomical landmarks were determined in the coronal and axial reference planes based on CA-reference and articular surface-reference methods.
Results
Mean cylindrical radii for medial and lateral femoral condyles were 17.4±1.6 mm and 17.3±1.4 mm, respectively. Of the 122 knees, 46 exhibited >1 mm of difference between condyles (Fig.1). Fifty-three and 22 knees exhibited >2º of angular difference between CA-reference and articular surface-reference bone-cuts in the coronal and axial planes (Fig.2). Mean angle of the CA and surgical epicondylar axis in 3D space was 4.6±2.1º. As practical parameters for TKA, the angle between CA and IM rod was significantly larger than that between the distal articular surface line and IM rod in the coronal plane (p<0.0001), indicating that CA-reference involves a smaller valgus bone-cut of the distal femur than articular surface-reference.
Conclusions
CA-reference bone-cut of the femur is preferable to articular surface-reference bone-cut for reproducing FEA in OA patients, in whom more than one-third of knees exhibited asymmetry of radii between medial and lateral condyles.
