Anatomical analysis and preoperative planning of correctional osteotomies: slipped capital femoral epiphysis (SCFE).

SCFE is defined as the slippage of the femoral head relative to the femoral neck along the proximal femoral growth plate. The femoral head shifts and rotates along the proximal end of the femoral neck, usually posteriorly and interiorly. The pathoanatomical findings are characterised by the changed relationship between the femoral head and femoral metaphysis, and between the femoral head and the acetabulum. A reduced femoral anteversion, a varus deformity of the femur, a shortening of the femoral metaphysis and an anterior metaphyseal prominence are also regularly observed. This may lead to impingement between the femoral metaphysis and the acetabular rim. Potential consequences of this complex 3D deformity are pain, a reduced range of hip motion and an early degenerative joint disease. In moderate and severe cases a redirectional femoral osteotomy is recommended. Different techniques, such as subcapital, base-of-neck, intertrochanteric and subtrochanteric osteotomies, have been described. These correctional osteotomies aim towards a reconstruction of the hip joint geometry, to prevent early arthritic degeneration. Currently, the planning of surgical treatment in these cases is based on measurements on antero-posterior and lateral plain radiographs. The relevant angle for planning of correctional osteotomies is the physis-shaft angle, determined in both plains. These angles describe the degree of slippage, thereby helping the surgeon to indicate and plan a correctional osteotomy. However, plain radiographs are projectional images and therefore carry inaccuracies caused by the overlay of anatomical structures and an incorrect positioning of the patient. 3D reconstructions are more accurate and provide substantial additional information for the surgeon, such as, for example, the anteversion of the acetabulum. We have developed interactive 3D software to measure projected angles, to analyse the geometry of the proximal femur and to determine the orientation of the acetabulum based on 3D reconstructions of CT data-sets. A program was also developed to simulate different techniques of osteotomies and to evaluate the postoperative range of hip motion and the hip-joint geometry. Accurate 3D measurements, additional anatomical information, simulations of different techniques of osteotomies and the evaluation of simulated postoperative results enables the surgeon to determine the best surgical treatment, based on the clinical findings.