Background

In total hip arthroplasty the surgeon aims to restore the biomechanics of the joint. Femoral height has the greatest influence on restoring limb length and contributes equally to the restoration of femoral head centre. On X-ray, the level of femoral neck resection is most often referenced off the upper border of lesser trochanter. Less frequently, femoral head centre is referenced from the tip of the greater trochanter. The error in measurement of femoral height resulting from unknown femoral rotation is crucially important and can result in inappropriate surgical planning for implant selection and placement. It is unknown which reference produces lower error.

Methods

A sample of femoral shapes was generated using a femoral statistical shape model. These were placed in a range of orientations in terms of external rotation and flexion, at intervals of 10°. Simulated X-rays were then produced and the distances from the tip of either greater or lesser trochanter to femoral head centre were measured.

Findings

Although using greater trochanter as a reference demonstrated greater errors at the extremes, both techniques resulted in errors of 7–8 mm with 20° of both femoral external rotation and flexion.

Interpretation

Moderate degrees of femoral external rotation combined with flexion can result in unsatisfactory errors when templating limb length. There should be greater focus and an agreed definition for femoral height. There is a clinical need for a method with a lower error in determining true femoral height and the level of neck resection.

中文翻译：

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术前股骨方向对全髋关节置换术中股骨头高度的影像学测量的影响

背景

在全髋关节置换术中，外科医生旨在恢复关节的生物力学。股骨高度对恢复肢体长度影响最大，并且同样对股骨头中枢的恢复有贡献。在X射线检查中，股骨颈切除的水平通常是在小转子的上边界以外进行参考的。较不常见的是，股骨头中心是从大转子的尖端开始参考的。股骨旋转不明导致的股骨高度测量误差至关重要，可能会导致不合适的外科手术计划进行植入物的选择和放置。未知哪个参考会产生较低的误差。

方法

使用股骨统计形状模型生成股骨形状的样本。根据外部旋转和屈曲，将它们放置在一系列方向上，间隔为10°。然后产生模拟的X射线，并测量从大转子或小转子的尖端到股骨头中心的距离。

发现

尽管使用更大的转子作为参考，在极端情况下显示出更大的误差，但两种技术均导致7-8 mm的误差以及股骨外部旋转和弯曲20°。

解释

在对四肢长度进行模板化时，适度的股骨外旋度和屈曲度会导致不令人满意的错误。应该更多地关注股骨高度，并达成一致的定义。临床上需要一种在确定真正的股骨高度和颈部切除水平时误差较小的方法。