Objective: The purpose of this study was to explore if the dimensions of the ischiofemoral space on MRI vary with changes in external femoral rotation in Ischifemoral Impingement patients relative to healthy control; if so, to determine the optimal diagnostic cutoff values of these dimensions in Ischifemoral Impingement.

Methods: The study included 43 clinically confirmed Ischifemoral Impingement patients and 50 healthy volunteers. All subjects underwent hip MRI examinations with their hips externally rotated at 0°, 30° and 60°. The IFS and QFS were measured respectively at each angle. The measurements were compared between the IFI group and the control group to determine the optimal diagnostic cutoff values for diagnosing IFI by using IFS and QFS measurements.

Results: In the IFI group, the spaces were smaller than those of the control group at all rotation angles (P < 0.05 for each). When external rotation angles were increased, the IFS and QFS tended to decrease. QFSs were smaller in the case group than the control group at each rotation angle. The receiver operating characteristic areas under the curves of IFS and QFS in a neutral position of 0° were highest.

Conclusion: Both of the IFS and QFS spaces of IFI patients were found to be smaller than those of control group, regardless of the external hip rotation angles. A neutral position of 0° was deemed the best position for diagnosing IFI. The diagnostic cutoff values of IFS and QFS were 2.44cm and 1.34cm in the neutral position, respectively.

目的：本研究的目的是探讨与健康对照相比，坐骨撞击症患者的 MRI 上坐骨股间隙的尺寸是否随着股骨外旋的变化而变化；如果是这样，确定坐骨撞击中这些尺寸的最佳诊断临界值。

方法：该研究包括 43 名经临床证实的坐骨关节撞击症患者和 50 名健康志愿者。所有受试者均接受髋关节 MRI 检查，髋关节外旋 0°、30°和 60°。在每个角度分别测量 IFS 和 QFS。比较 IFI 组和对照组的测量值，以确定使用 IFS 和 QFS 测量值诊断 IFI 的最佳诊断临界值。

结果：IFI组所有旋转角度的间隙均小于对照组（P < 0.05）。当外旋角增加时，IFS 和 QFS 趋于减小。在每个旋转角度，病例组的 QFS 均小于对照组。在 0°中立位置的 IFS 和 QFS 曲线下的接收者操作特征区域最高。

结论：无论髋关节外旋角度如何，IFI患者的IFS和QFS间隙均小于对照组。0°的中立位被认为是诊断 IFI 的最佳位置。在中立位，IFS 和 QFS 的诊断临界值分别为 2.44 厘米和 1.34 厘米。