Narrowing of ischiofemoral and quadratus femoris spaces in pediatric ischiofemoral impingement.

OBJECTIVE: To correlate MRI findings of quadratus femoris muscle edema (QFME) with narrowing of the ischiofemoral space (IFS) and quadratus femoris space (QFS) in children, and to identify threshold values reflecting an anatomic architecture that may predispose to ischiofemoral impingement. MATERIALS AND METHODS: A case-control retrospective MRI review of 49 hips in 27 children (mean, 13 years) with QFME was compared to 49 hips in 27 gender and age-matched controls. Two radiologists independently measured IFS and QFS. Generalized linear mixed-effects models were fit to compare IFS and QFS values between cases and controls, and adjust for correlation in repeated measures from the same subject. Receiver operating characteristic (ROC) analysis determined optimal threshold values. RESULTS: Compared to controls, cases had significantly smaller IFS (p < 0.001, both readers) and QFS (reader 1: p < 0.001; reader 2: p = 0.003). When stratified as preteen (< 13) or teenage (≥ 13), lower mean IFS and QFS were observed in cases versus controls in both age groups. Area under ROC curve for IFS and QFS was high in preteens (0.77 and 0.71) and teens (0.94 and 0.88). Threshold values were 14.9 mm (preteens) and 19 mm (teens) for IFS and 11.2 mm (preteens) and 11.1 mm (teens) for QFS. IFS and QFS were modestly correlated with age among controls only. CONCLUSIONS: Pediatric patients with QFME had significantly narrower QFS and IFS compared with controls. IFS and QFS were found to normally increase in size with age. Optimal cutoff threshold values were identified for QFS and IFS in preteens and teenagers.