Planning of Correctional Osteotomies Based on 3D Computer Models

Conventional planning methods of osteotomies are traditionally focused on the amount of slippage of the femoral epiphysis to improve the alignment of the acetabulum and the proximal femur. The acetabular orientation and the geometry of the proximal femur are generally not taken into consideration for preoperative planning of correctional osteotomies. It is known, that the slippage of the femoral head and the deformation of the proximal femur cause an impingement between the acetabulum and the femoral neck. This impingement and the changed distribution of forces between femur and acetabulum may lead to an early arthritic degeneration. Therefore it is necessary to address the amount of slippage, the acetabular orientation and the geometry of the proximal femur when planning correctional osteotomies.

FIGURE 3 "Frogleg"-radiograph of both hips with a SCFE on the left hip (same patient as in Fig. 2). Sketched on the image is also the information about the torsion of the neck (red, right hip) and physis (blue, left hip). Note the asymmetrical positioning. See also Plate 40.

FIGURE 4 Axial CT-cross-sections through the knee condyles (left image) and the upper femoral neck (right image). The way to determine the torsion of the neck (red, right hip) and physis (blue, left hip) is also shown. In the depicted method the line sketched on the left image is transferred to the right images and titled 1 in the latter. See also Plate 41.

FIGURE 4 Axial CT-cross-sections through the knee condyles (left image) and the upper femoral neck (right image). The way to determine the torsion of the neck (red, right hip) and physis (blue, left hip) is also shown. In the depicted method the line sketched on the left image is transferred to the right images and titled 1 in the latter. See also Plate 41.

Projectional errors which reduce the accuracy of plain radiographs preclude the determination of crucial angles such as the orientation of the acetabulum. After further processing, 2D CTs of the pathological hip joint provide all essential angles but inaccuracies caused by positioning and projection errors remain. In contrast, 3D-CT analysis for preoperative planning enables the surgeon to take all important angles into consideration and provides accurate measurements.

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