MRI is Better Than CT Scan for Detection of Structural Pathologies After Traumatic Posterior Hip Dislocations in Children and Adolescents.

BACKGROUND: Traumatic posterior hip dislocations in children and adolescents requires emergent closed reduction. Postreduction imaging is necessary to assess the concentricity of reduction and structural injuries to the hip. There is no a consensus for which imaging is a modality of choice in such condition. The purposes of this study are to describe magnetic resonance imaging (MRI) findings of traumatic posterior hip dislocations and to compare the effectiveness of MRI with computerized tomography (CT) in detecting structural abnormalities of the hip that impact patient management.

METHODS: This study is a retrospective review of imaging in traumatically dislocated hips in patients who were treated at our institution. All CT and MRI imaging were reviewed and specific osseous and soft tissue injuries documented by consensus among 2 musculoskeletal pediatric radiologists who interpreted the MRI and CT scans of each patient in a blinded manner.

RESULTS: In total, 27 patients (23 males, 4 females) with mean age of 12.5 years (range, 2 to 19 y) with postreduction MRI were evaluated. MRI findings revealed femoral head injuries in 17 (62.9%), posterior labral entrapments in 6 (22.2%), posterior labral tears in 17 (62.9%), posterior wall fractures in 15 (55.5%), fracture of the posterior unossified part of acetabulum in 4 (14.8%), and ligamentum teres injuries in 8 (29.6%). Of 16 patients who had postreduction CT scans, 6 (37.5%) had femoral head fractures, 9 (56.3%) had posterior wall fractures, and 8 (50%) had intra-articular osseous entrapments. All bony fractures and intra-articular entrapment could be seen on MRI imaging. In 16 patients with both CT and MRI, posterior acetabular injury was detected in 10/16 (62.5%) on MRI and 9/16 (56.3%) on CT. Three patients with entrapment of labrums identified on MRI could not be seen on CT scan. One patient with persistently unstable hip after reduction had an entrapped unossified portion of acetabular fracture which was seen on MRI but not on CT.

CONCLUSIONS: MRI is superior to CT scan for detection of structural injuries in children and adolescents with traumatic hip dislocation. The unique structural injuries included entrapment of posterior labrum and posterior unossified acetabular fractures could be seen only at MRI. These findings will impact surgical decision making of these injuries.

LEVEL OF EVIDENCE: Level IV.