Spinopelvic mobility and rotational morphology in patients with femoroacetabular impingement‐like hip pain without classical imaging findings

PURPOSE: To evaluate spinopelvic mobility and rotational morphology in patients with femoroacetabular impingement (FAI)-like hip pain without classical radiographic or magnetic resonance imaging (MRI) findings. METHODS: This retrospective comparative study included 54 patients with FAI-like hip pain without classical imaging findings (alpha angle <55°, lateral centre-edge angle 20°-40° and no significant labral/chondral pathology on conventional MRI) and 36 matched controls. Spinopelvic parameters (pelvic incidence, pelvic tilt [PT], sacral slope (SS) and anterior pelvic plane [APP]-based PT) were measured on standing and sitting lateral radiographs. Spinopelvic mobility was assessed using difference between standing and sitting pelvic tilt (ΔPT), difference between standing and sitting sacral slope (ΔSS) and difference between standing and sitting anterior pelvic plane angle (ΔAPP) tilt. Patients were classified as having rigid (ΔSS < 10°) or non-rigid (ΔSS ≥ 10°). Acetabular version, supratrochanteric femoral torsion, Visual Analogue Scale (VAS), modified Harris Hip Score and International Hip Outcome Tool-12 (iHOT-12) were evaluated. RESULTS: Compared with controls, the patient group had significantly lower sitting PT, ΔPT (mean difference -10.0°, 95% confidence interval [CI] -12.0 to -8.0), ΔSS (-12.4°, 95% CI -15.1 to -9.7), sitting APP tilt and ΔAPP tilt (-14.4°, 95% CI -17.1 to -11.7), whereas standing APP tilt and sitting SS were significantly higher (all p < 0.01). Among patients, 34 were classified as rigid pelvis and 20 as non-rigid pelvis. The non-rigid subgroup showed higher sitting PT, ΔPT, ΔSS, sitting APP tilt and ΔAPP tilt, lower sitting SS, lower acetabular version (-3.8°, 95% CI -5.7 to -1.9; p < 0.001) and higher supratrochanteric torsion (4.4°, 95% CI 0.7-8.1; p = 0.02). Clinical scores did not differ between subgroups. ΔPT and ΔAPP tilt correlated with clinical outcome measures. In multivariable regression, ΔPT was independently associated with VAS and mHHS, whereas ΔAPP tilt was independently associated with VAS and iHOT-12. CONCLUSIONS: Patients with FAI-like hip pain without classical imaging findings demonstrated reduced spinopelvic mobility. Rotational morphology may represent an additional biomechanical contributor, although its clinical relevance remains uncertain. Assessment of these parameters may provide additional information in selected patients with persistent symptoms and inconclusive imaging findings. LEVEL OF EVIDENCE: Level III, retrospective comparative study.