BACKGROUND Subtrochanteric or supracondylar femoral rotational osteotomies are established surgical treatments for femoral rotational deformities. Unintended change of the mechanical leg axis is an identified problem. Different attempts exist to plan a correct osteotomy plane, but implementation of the preoperative planning into the surgical situation can be challenging. Goal of this study was to identify the critical threshold of mal-angulation of the osteotomy plane and of femoral rotation that leads to a relevant deviation of the postoperative mechanical leg axis using a computer simulation approach. METHODS Three-dimensional (3D) surface models of the lower extremity of two patients (Model 1: 42° femoral antetorsion; Model 2: 6° femoral retrotorsion) were generated from computed tomography data. First, baseline subtrochanteric and supracondylar rotational osteotomies, perpendicular to the femoral mechanical axis were simulated. Afterwards, mal-angulated osteotomies in sagittal and frontal plane followed by different degrees of rotation were simulated and frontal mechanical axis was analyzed. RESULTS 400 mal-angulated osteotomies have been simulated. Mal-angulation of ±30° with 30° rotation showed maximum deviation from preoperative mechanical axis in subtrochanteric osteotomies (4.0° ± 0.4°) and in supracondylar osteotomies (12.4° ± 0.8°). Minimal mal-angulation of 15° in sagittal plane in subtrochanteric osteotomies and mal-angulation of 10° in sagittal plane in supracondylar osteotomies altered the mechanical axis by > 2°. Mal-angulation in sagittal plane showed higher deviations of the mechanical axis (up to 12.4° ± 0.8°), than in frontal plane mal-angulation (up to 4.0° ± 1.9°). CONCLUSION A femoral rotational osteotomy, perpendicular to the femoral mechanical axis, has no considerable influence on the mechanical leg axis. However, mal-angulation of femoral rotational osteotomies showed relevant changes of the mechanical leg axis. In supracondylar respectively subtrochanteric procedures, mal-angulation of only 10° in combination with already 15° of femoral rotation respectively mal-angulation of 15° in combination with 30° of femoral rotation, can lead to a relevant postoperative mechanical leg axis deviation of more than 2°, wherefore these patients probably would benefit from the use of navigation aids.

中文翻译：

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股骨旋转畸形截骨术对机械性腿轴的影响：计算机仿真模型。

背景技术转子粗隆或con上股骨旋转截骨术是针对股骨旋转畸形的外科治疗方法。机械腿轴的意外更改是已发现的问题。存在计划正确的截骨平面的不同尝试，但是在手术情况下实施术前计划可能具有挑战性。这项研究的目的是使用计算机模拟方法确定截骨平面和股骨旋转的角度偏差的临界阈值，该临界阈值导致术后机械性腿轴发生相关偏差。方法根据计算机断层扫描数据生成两名患者下肢的三维（3D）表面模型（模型1：42°股骨前倾；模型2：6°股骨后倾）。第一，模拟垂直于股骨机械轴的股骨转子下和sub上旋转截骨术。然后，模拟矢状面和额叶面的角度不正确的截骨术，然后进行不同程度的旋转，并分析额叶的机械轴。结果已模拟了400例角度不正确的截骨术。旋转30°时±30°的角度不正确显示在转子下截骨术（4.0°±0.4°）和con上截骨术（12.4°±0.8°）中，与术前机械轴的最大偏差。转子粗隆下截骨时矢状面的最小角度为15°，而con上截骨中矢状面的最小角度为10°，使机械轴改变了> 2°。矢状面的角度差显示机械轴的偏差较大（最大为12.4°±0.8°），比额角不正的情况下（最大4.0°±1.9°）。结论垂直于股骨机械轴的股骨旋转截骨术对腿部机械轴没有重大影响。但是，股骨旋转截骨的角度不正确显示了腿部机械轴的相关变化。在con上，粗隆下手术中，仅10°的不正确角度结合已经有15°的股骨旋转，或者15°的不正确角度结合股骨的30°旋转，可能导致相关的术后机械性腿轴偏斜。角度小于2°，因此这些患者可能会受益于使用导航工具。对机械腿轴没有太大影响。但是，股骨旋转截骨的角度不正确显示了腿部机械轴的相关变化。在con上，粗隆下手术中，仅10°的不正确角度结合已经有15°的股骨旋转，或者15°的不正确角度结合股骨的30°旋转，可能导致相关的术后机械性腿轴偏斜。角度小于2°，因此这些患者可能会受益于使用导航工具。对机械腿轴没有太大影响。但是，股骨旋转截骨的角度不正确显示了腿部机械轴的相关变化。在con上，粗隆下手术中，仅10°的不正确角度结合已经有15°的股骨旋转，或者15°的不正确角度结合股骨的30°旋转，可能导致相关的术后机械性腿轴偏斜。角度小于2°，因此这些患者可能会受益于使用导航工具。