The Utility of MRI to Diagnose Ischifemoral Impingement by Assessing the Ischiofemoral and Quadratus Femoris Spaces During Femoral Exter-nal Rotation

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 degrees, 30 degrees and 60 degrees. 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 degrees 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 degrees 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.