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Objectives and questions: Ischiofemoral impingement (IFI) is characterized by narrowing of the space between the lesser trochanter and the ischium, resulting in irritation of the quadratus femoris muscle. Patients typically report deep posterior hip pain, but the condition is often overlooked because symptoms overlap with other causes of hip pain. Although bony morphology influences the ischiofemoral space, the role of pelvic position and spinal alignment remains unclear. The primary aim was to determine the prevalence of MRI-confirmed IFI in young patients with non-arthritic hip pain. The secondary aim was to assess whether specific femoral, acetabular, pelvic, and static and dynamic spinopelvic parameters are associated with IFI.

Material and methods: A retrospective analysis of a prospectively maintained cohort included 250 patients (35.1±8.6 years; 67.2% female) with standardized MRI, CT, and lateral standing and deep-seated radiographs. IFI was defined by quadratus femoris edema and/or atrophy on MRI. Hip and pelvic morphology were assessed by CT and radiographs. Spinopelvic parameters (LL, PT, PI, SS, PI–LL mismatch) were measured in standing and seated positions; dynamic mobility was calculated as standing–sitting differences (Δ). Multivariate logistic regression identified independent predictors of IFI, and linear regression determined factors associated with quadratus femoris space (QFS).

Results: IFI was identified in 14/250 patients (5.6%), all female. IFI hips showed smaller ischiofemoral space (24.8±6.7 mm vs. 34.9±10.2 mm; p<0.001) and QFS (9.2±3.4 mm vs. 20.7±7.0 mm; p<0.001), greater ischial angle (135.7°±3.0° vs. 132.2°±4.0°; p=0.002) and femoral version (16.5°±10.3° vs. 10.4°±12.3°; p=0.031), and reduced femoral (34.2±5.6 mm vs. 37.7±5.9 mm; p=0.016) and acetabular offset (29.4±3.5 mm vs. 32.0±4.8 mm; p=0.036). Spinopelvic analysis demonstrated higher standing PT (15.7°±4.7° vs. 12.4°±6.2°; p=0.047), smaller PI–LL mismatch (–2.4°±7.2° vs. –7.8°±10.0°; p=0.034), and lower ΔLL (50.3°±10.9° vs. 56.9°±10.6°; p=0.020). Multivariate analysis identified reduced QFS (OR=1.92; p<0.001) and greater standing LL (OR=1.16; p=0.047) as independent predictors (Nagelkerke R²=0.615). QFS correlated positively with femoral offset (β=0.35; p<0.001) and PI–LL mismatch (β=0.18; p=0.028), and negatively with ischial angle (β=–0.33; p<0.001), femoral version (β=–0.13; p=0.018), and standing PT (β=–0.16; p=0.026).

Discussion and conclusions: IFI occurred in 5.6% of young non-arthritic patients and exclusively in females. IFI was characterized by a distinct morphometric profile including increased femoral version, larger ischial angle, and reduced offsets, leading to posterior space narrowing. In addition, patients demonstrated a characteristic sagittal alignment pattern with increased pelvic tilt, relative flattening of lumbar lordosis, and reduced lumbopelvic mobility. These findings suggest that IFI is not solely a local morphological phenomenon but reflects a complex interaction between hip morphology and sagittal balance.