Influence de l'antéversion fémorale pré-opératoire et de l'orientation du plan d'ostéotomie intertrochantérien sur la morphologie du fémur proximal après ostéotomie intertrochantérienne de rotation: une étude simulée en scanner 3D

Background Transtrochanteric anterior rotational osteotomy (ARO) is joint-preserving surgery for patients with osteonecrosis of the femoral head (ONFH). During ARO, femoral neck-shaft varus angulation by changing intertrochanteric osteotomy plane is often designed to obtain a sufficient post-operative intact ratio. However, the effect of intertrochanteric osteotomy plane on post-operative femoral anteversion has not been well examined. Therefore we performed a simulation study of ARO to determine how intertrochanteric osteotomy plane and pre-operative femoral anteversion affect both femoral neck-shaft varus angle and post-operative femoral anteversion. Hypothesis Both femoral neck-shaft varus angle and post-operative femoral anteversionare predicted by intertrochanteric osteotomy plane and pre-operative femoral anteversion in ARO. Materials and methods Using CT-data obtained from 10 hips in 10 patients with ONFH, ARO was simulated. On anteroposterior view, basic intertrochanteric osteotomy line (AP-view line) was defined as the perpendicular line to the femoral neck axis. On lateral view, basic intertrochanteric osteotomy line (lateral-view line) made through the cut surface of greater trochanter was defined as the perpendicular line to the lateral axis of the femur. By changing either AP-view or lateral-view line, 49 ARO models/hip were produced, in which femoral neck-shaft varus angle and post-operative femoral anteversion were assessed. Results With increase in the vertically-inclined degree of AP-view line, both neck-shaft varus angle and post-operative femoral anteversion increased. With increase in the posteriorly-tilted degree of lateral-view line, neck-shaft varus angle increased, whereas post-operative femoral anteversion decreased. The approximation equations based on the multiple regression analyses were as follows: neck-shaft varus angle ≈ vertically-inclined degree of AP-view line × 0.9 + posteriorly-tilted degree of lateral-view line × 0.8 + pre-operative femoral anteversion × 0.7; post-operative femoral anteversion ≈ vertically-inclined degree of AP-view line × 1.1–posteriorly-tilted degree of lateral-view line × 0.8. Discussion The post-operative morphology of proximal femur was nearly defined by intertrochanteric osteotomy plane with pre-operative femoral anteversion, which is useful for pre-operative planning in terms of both achieving asufficient post-operative intact ratio and maintaining femoral anteversion. Level of evidence Level IV case series without control group.