MRI assessment of the posterior acetabular wall fracture in traumatic dislocation of the hip in children.

Traumatic hip dislocations associated with posterior wall fractures of the acetabulum in the pediatric population are in general a consequence of high-energy trauma. After expeditious reduction, instability mandates for further diagnosis and intervention. Plain radiographs or computerized tomography (CT) scans can misjudge the involvement of the posterior wall of the acetabulum due to the partially calcified nature of the pediatric bone. We present two cases of pediatric traumatic hip dislocation associated with posterior wall fractures of the acetabulum. In both cases, obvious postreduction instability was noted without conclusive findings of etiology on plain X-rays or CT scans. Magnetic resonance imaging (MRI) disclosed an extensive posterior wall traumatic involvement in both cases and helped to decide in favor of open reduction of the hip and internal fixation of the posterior wall fragment.