Progressive Femoral Varus Osteotomy and its Mechanical Implications : A Cadaver Study.
Background : Proximal femoral varus wedge osteotomy alters hip mechanics. Quantifying radiographic changes seen with increasing varus angulation can provide valuable information in the preoperative decision to determine the optimum degree of varus angulation. Questions/Purpose s: The purpose of this study is to measure the effect of varus angulation on radiographic indices such as femoral neck-shaft angle (NSA), acetabulo-trochlea distance (ATD), and femoral length. Finally, the mechanical implications of varus osteotomy will be considered, including changes in the hip's range of motion and its effect on gait. Patients and Methods : Progressive varus osteotomies were performed on a cadaver femur in 15° wedges. AP radiographs were taken following each varus osteotomy and neck-shaft angle, articulotrochanteric distance, and femoral length were recorded. Results : Preoperatively, the neck-shaft angle measured 132° and articulotrochanteric distance measured 20.4 mm. With each 1° wedge varus angulation, the mean reduction in neck-shaft angle was 0.448°, mean reduction in articulotrochanteric distance was 0.29 mm, and mean femoral shortening was 0.157 mm. Conclusion: When determining the degree of varus angulation for a proximal femoral wedge varus osteotomy, it is important to consider abductor lurch, limb length discrepancy, and changes to the hip's range of motion, especially when varus angulation exceeds a neck-shaft angle of less than 110°.