Three-dimensional Effect of the Single Plane Proximal Femur Osteotomy

PURPOSE: Three-dimensional (3D) effects of the single plane osteotomies of the proximal femur are compared and analyzed by the trigonometric method. MATERIALS AND METHODS: The shape of proximal femur was simplified as a bent line. The bent line is the continuation of the three points-the center of the femoral head, the center of femoral neck at the base, and the center of the femoral shaft. Then rotated the proximal femur at the junction of the neck and shaft with the each rotation axis of X, Y, Z, defined the frontal plane as a XY plane, sagittal plane as a YZ plane, and transverse plane as a XZ plane. RESULTS: The varus osteotomy of the proximal femur in the frontal plane with the rotation axis 'Z' that meant the increase of the X coordinate and the decrease of Y coordinate with constant Z coordinate (Δx>Δy, Δz=0) resulted in decreased anteversion in the transverse plane and increased flexion in the sagittal plane. The derotation osteotomy (Δx>Δz, Δy=0) resulted in varus in the frontal plane and extension in the sagittal plane. The flexion osteotomy (Δz>Δy, Δx=0) resulted in increased anteversion in the transverse plane and varus in the frontal plane. CONCLUSION: Single plane osteotomy for the proximal femur results in the angular correction in all three planes and may have the similar 3D effect of the certain double or triple osteotomy. So single plane osteotomy could be enough to correct some complex deformities.