Clinical three-dimensional anatomy of the femur considering navigation-aided surgery of total knee arthroplasty in Japanese patients.

Purpose: Few studies exist regarding sagittal alignment describing femur morphology in navigation-aided surgery. This study investigated the three-dimensional (3D) sagittal femoral alignment of the whole femur.

Methods: Seventy-three consecutive patients (59 females, 14 males, mean age: 76.1 years), yielding 140 femurs, were included in this study. A computed-tomography-based patient-specific 3D femur model was used to define a mechanical axis-based reference plane. Proximal and distal femoral axis angles (PFA, DFA) to the reference plane were measured in 3D using custom software. PFA and DFA represent the proximal and distal inclination of the femoral anatomical axis in sagittal plane, respectively.

Results: PFA (10.6 ± 1.5°) was greater than DFA (2.6 ± 1.6°; P < 0.0001). DFA in females (2.3 ± 1.4°) was smaller than in males (3.9 ± 1.7°; P < 0.0001).

Conclusion: This is the first report of measurement of femoral sagittal alignment related to both 3D anatomy and decision making of femoral flexion angle using navigation surgery for total knee arthroplasty. This report shows a robust DFA measurement that could be used as a template for femoral implants flexion angle when performing both conventional and navigated total knee arthroplasty.