Purpose: Ischiofemoral impingement (IFI) is defined by hip pain related to narrowing of the space between the ischial tuberosity and the femur. The presence of quadratus femoris muscle (QF) edema on MRI is a sensitive imaging finding for IFI. Its prevalence in asymptomatic adults is as low as 1.5%, however the prevalence in pediatric population was not yet reported. In our practice we seem to relatively often encounter QF edema in pediatric pelvic MRI examinations. Therefore, the purpose of our study was to assess the prevalence of QF edema in children.
Material and Methods: In this retrospective study, pediatric (1-18 years) pelvic MRI examinations performed at our institution between 03/2012 - 05/2017 were retrieved. In each examination axial T2 with fat saturation sequence (ax-T2-FS) was evaluated independently by two musculoskeletal radiologists for the presence of edema in the right and left QF space. In case of reader`s disagreement a consensus was reached by an additional reading session. Studies without axial-T2-FS sequence and studies of reduced quality were excluded.
Results: 212 pediatric pelvic MRI studies were identified. A total of 57 studies were excluded (38: no axial-T2-FS sequence, 8: the QF space was not included in the axial-T2-FS, 10: reduced quality of of one study after reconstructive surgery of the pelvis). The remaining 155 MRI studies of 130 children (M:F 1:28, average age 12±3) were evaluated (154 right QF, 154 left QF). Twelve patients had more than one exam. Discrepancy between readers was found in 3 muscles out of 308 evaluated (0,97%). QF edema was identified in 48 muscles of 25 children: in 40 QF muscles (20 right, 20 left, 25 exams, 20 children) isolated QF edema was found and in additional 8 muscles (1 right, 7 left, 7 exams, 5 children) QF edema resulting from a nearby pathology was detected. In 8 other studies a linear high signal, potentially representing a blood vessel, was detected anterior to the QF muscle (5 right, 8 left). In the 12 children with repetitive studies: six had no QF edema in all studies, two had edema appearing on the same side in all studies and in four, edema presence was inconsistent.
Conclusion: The prevalence of isolated QF edema in children is 13%, the clinical significance of this finding requires further evaluation.
