Hip MRI in flexion abduction external rotation for assessment of the ischiofemoral interval in patients with hip pain-a feasibility study

Alexander F Heimann; Jonas Walther; Moritz Tannast; Joseph M Schwab; Moritz Wagner; Alexander Brunner; Till D Lerch; Simon D Steppacher; Peter Vavron; Ehrenfried Schmaranzer; Florian Schmaranzer

doi:10.1186/s13244-023-01524-4

Hip MRI in flexion abduction external rotation for assessment of the ischiofemoral interval in patients with hip pain-a feasibility study

Insights Imaging. 2023 Oct 15;14(1):172. doi: 10.1186/s13244-023-01524-4.

Authors

Affiliations

¹ Department of Orthopaedic Surgery, HFR - Cantonal Hospital, University of Fribourg, Chemin des pensionnats 2 - 6, CH-1700, Fribourg, Switzerland. alexander.heimann@unifr.ch.
² Department of Orthopaedic Surgery, Inselspital Bern, University Hospital, University of Bern, Freiburgstrasse 18, Bern, CH-3010, Switzerland.
³ Department of Orthopaedic Surgery, HFR - Cantonal Hospital, University of Fribourg, Chemin des pensionnats 2 - 6, CH-1700, Fribourg, Switzerland.
⁴ Department of Orthopaedic Surgery, District Hospital St. Johann in Tirol, Bahnhofstraße 14, 6380, St. Johann in Tirol, Austria.
⁵ Department of Diagnostic-, Interventional- and Pediatric Radiology, Inselspital Bern, University Hospital, University of Bern, Freiburgstrasse 18, Bern, CH-3010, Switzerland.
⁶ Department of Radiology, District Hospital St. Johann in Tirol, Bahnhofstraße 14, St. Johann in Tirol, 6380, Austria.
⁷ Department of Radiology, Balgrist University Hospital, Forchstrasse 340, Zurich, CH-8008, Switzerland.

Abstract

Objectives: To assess the feasibility of flexion-abduction-external rotation (FABER) magnetic resonance imaging (MRI) of the hip to visualize changes in the ischiofemoral interval and ability to provoke foveal excursion over the acetabular rim.

Methods: IRB-approved retrospective single-center study. Patients underwent non-contrast 1.5-T hip MRI in the neutral and FABER position. Two readers measured the ischiofemoral interval at three levels: proximal/distal intertrochanteric distance and ischiofemoral space. Subgroup analysis was performed for hips with/without high femoral torsion, or quadratus femoris muscle edema (QFME), respectively. A receiver operating curve with calculation of the area under the curve (AUC) for the prediction of QFME was calculated. The presence of foveal excursion in both positions was assessed.

Results: One hundred ten patients (121 hips, mean age 34 ± 11 years, 67 females) were evaluated. FABER-MRI led to narrowing (both p < .001) of the ischiofemoral interval which decreased more at the proximal (mean decrease by 26 ± 7 mm) than at the distal (6 ± 7 mm) intertrochanteric ridge. With high femoral torsion/ QFME, the ischiofemoral interval was significantly narrower at all three measurement locations compared to normal torsion/no QFME (p < .05). Accuracy for predicting QFME was high with an AUC of .89 (95% CI .82-.94) using a threshold of ≤ 7 mm for the proximal intertrochanteric distance. With FABER-MRI foveal excursion was more frequent in hips with QFME (63% vs 25%; p = .021).

Conclusion: Hip MRI in the FABER position is feasible, visualizes narrowing of the ischiofemoral interval, and can provoke foveal excursion.

Critical relevance statement: FABER MRI may be helpful in diagnosing ischiofemoral impingement and detecting concomitant hip instability by overcoming shortcomings of static MR protocols that do not allow visualization of dynamic changes in the ischiofemoral interval and thus may improve surgical decision making.

Key points: • FABER MRI enables visualization of narrowing of the ischiofemoral interval proximal to the lesser trochanter. • Proximal intertrochanteric distance of ≤ 7 mm accurately predicts quadratus femoris muscle edema. • Foveal excursion was more frequent in hips with quadratus femoris muscle edema.

Keywords: Femoroacetabular impingement; Hip; Hip arthroscopy; Ischiofemoral impingement; Magnetic resonance imaging.