What hip and spinopelvic characteristics are associated with ischiofemoral impingement?

To determine the prevalence of MRI-confirmed ischiofemoral impingement (IFI) in young patients with nonarthritic hip pain, and to evaluate the associations of femoral, acetabular, pelvic, and spinopelvic parameters with IFI.

We included 250 patients with nonarthritic hip pain who underwent standardized imaging (MRI and CT, lateral standing and deep-seated spinopelvic radiographs). IFI was diagnosed by quadratus femoris oedema/atrophy. IFI-positive/negative hips were compared for morphological and spinopelvic parameters. Underlying pathologies (e.g. femoroacetabular impingement, dysplasia) were documented. Multivariate regression identified independent predictors of IFI and determinants of quadratus femoris space (QFS).

IFI was identified in 14/250 patients (5.6%), all female. IFI cases had significantly reduced ischiofemoral space (24.8 mm (SD 6.7) vs 34.9 mm (SD 10.2); p < 0.001) and QFS (9.2 mm (SD 3.4) vs 20.7 mm (SD 7.0); p < 0.001). IFI cases demonstrated larger ischial angle (135.7° (SD 3.0°) vs 132.2° (SD 4.0°); p = 0.002), higher femoral version (16.5° (SD 10.3°) vs 10.4° (SD 12.3°); p = 0.031), and reduced femoral (34.2 mm (SD 5.6) vs 37.7 mm (SD 5.9); p = 0.016) and acetabular offset (29.4 mm (SD 3.5) vs 32.0 mm (SD 4.8); p = 0.036). In standing, IFI cases tended to have lower lumbar lordosis (LL) (55.31° (SD 7.95°) vs 59.91° (SD 10.50°); p = 0.077), higher pelvic tilt (15.68° (SD 4.73°) vs 12.39° (SD 6.20°); p = 0.047), and smaller mismatch between pelvic incidence and LL (-2.39° (SD 7.18°) vs -7.82° (SD 10.00°); p = 0.034). The change in LL across standing to deep-flexed sitting transition (ΔLL) was lower in IFI cases (50.31° (SD 10.89°) vs 56.89° (SD 10.64°); p = 0.020). Multivariate regression identified reduced QFS (odds ratio (OR) 1.92, 95% CI 1.30 to 2.89; p < 0.001) and greater LL (OR 1.16, 95% CI 1.00 to 1.33; p = 0.047) as independent predictors of IFI. Size of QFS was associated positively with femoral offset (β = 0.35; p < 0.001) and mismatch between pelvic incidence and LL (β = 0.18; p = 0.028), and negatively with ischial angle (β = -0.34; p < 0.001), femoral version (β = -0.14; p = 0.016), and standing pelvic tilt (β = -0.16; p = 0.026).

IFI occurred in 5.6% of patients and was characterized by a distinct morphometric and sagittal alignment profile, including increased femoral version, reduced offset, greater ischial angle, reduced LL, increased pelvic tilt, and diminished spinal motion. These findings support a multifactorial model in which hip morphology and spinopelvic alignment jointly influence posterior hip clearance in IFI.