Objective: To examine the effect of external hip rotation on ischiofemoral (IF) and quadratus femoris (QF) spaces using real-time kinematic MRI, with the hypothesis that hips with IF and QF space narrowing have distinct motion patterns compared with control hips.
Materials and methods: This prospective study was IRB-approved and complied with HIPAA guidelines. We recruited women (≥ 18 years) with and without ischiofemoral impingement to undergo kinematic MRI of the hips. A kinematic imaging protocol using T2-HASTE was performed beginning at maximal internal rotation followed by active external hip rotation. The duration of each acquisition was 30 s, providing 8 images/3 s. IF and QF spaces, and femoral metaphyseal and lesser trochanter centroid coordinates were measured on sequential images. Hips were classified as controls or narrowed based on IF and QF space thresholds and compared statistically throughout motion stages.
Results: The cohort comprised 12 women (24 hips; 10 control and 14 narrowed hips) aged 58 ± 10 years. External rotation caused IF space reduction of 59% in narrowed hips versus 41% in control hips. QF space decreased 71% in narrowed hips versus 50% in control hips. IF and QF spaces differed significantly between groups only when external rotation exceeded the neutral position (P < 0.02 for both). The lesser trochanter terminated more posteriorly in narrowed hips compared with controls (P = 0.03).
Conclusions: Kinematic MRI during external hip rotation in women with narrowed and control hips reveals dynamic differences in IF and QF spaces and lesser trochanter terminal position.
Keywords: Anatomy; Hip; Ischiofemoral impingement; Kinematic MRI; Quadratus femoris muscle.