2016 年 35 巻 1 号 p. 25-30
Objective: In total knee arthroplasty, most of the femoral components should be placed perpendicular to the mechanical axis of the femur in the coronal plane. However, in the sagittal plane, a suitable flexion angle from the mechanical axis is unknown. Although determining the center of the femoral head and mechanical axis is possible by navigation systems used intraoperatively, the position of the cutting block depends on the surgeon’s preference. Planning the flexion angle of the femoral component from the mechanical axis is necessary preoperatively. We measured the angle between the mechanical axis and anatomical axis of the distal femur in the sagittal plane using three-dimensional imaging.
Methods: Sixty-seven femurs of patients with knee osteoarthritis were examined by computed tomography preoperatively, and the data were transferred into three-dimensional images by preoperative planning software. The coronal plane of each femur was defined by the femoral head center and the surgical epicondylar axis. The sagittal plane was orthogonal to the coronal plane. The angle between the mechanical axis and distal femoral axis in the sagittal plane (flexion angle) was then measured. The shape of each femur with large and small flexion angles was observed.
Results: The mean flexion angle was 3.1°±1.6° (range, 0° to 7.4°). At the extremes of the measured angles, the femur with 0°flexion angle had a linear shaft, and the femur with 7.4°flexion angle had severe bowing.
Conclusion: The angle between the mechanical axis and anatomical axis of the femur in the sagittal plane was 3.1°±1.6°. It is suggested that the flexion angle is related to bowing of the femur.