Magnetic resonance imaging in the evaluation of suspected hip sepsis in children

Background: Rapid and accurate diagnosis of musculoskeletal infection in children is critical to enable appropriate, targeted surgical interventions. Distinguishing between septic arthritis, myositis, and osteomyelitis around the hip can be difficult using clinical criteria and ultrasound scan alone. Materials and methods: We performed a retrospective 5-year observational review of selective magnetic resonance imaging scanning for hip sepsis in a pediatric tertiary referral center. Included were children with atraumatic hip pain with symptom duration <2 weeks, minimum of two positive modified Kocher's criteria, and a hip effusion on ultrasound. All cases were followed up to discharge. We evaluated hip ultrasound and magnetic resonance imaging findings, operative procedures, microbiology results, duration of treatment, outcomes, and complications. Results: Fifty-one patients, 55% male, with a mean age 6.4 (0-16) years were included. Thirty-nine underwent magnetic resonance imaging scan for suspected septic arthritis of the hip; 24 prior to surgical washout (pre-emptive), and 15 afterwards (postoperative). In the pre-emptive group, 1/24 had septic arthritis, 7/24 had osteomyelitis, 6/24 had myositis, 5/24 had osteomyelitis and myositis, and 5/24 had no evidence of infective pathology. In the postoperative group, 3/15 had myositis, 3/15 had osteomyelitis, 3/15 had re-accumulation of the hip effusion requiring repeat washout, 3/15 had myositis and osteomyelitis, and 1/15 had septic arthritis of a contiguous joint. Conclusion: Pre-emptive magnetic resonance imaging scanning avoided unnecessary hip washout in 23 cases and enabled targeted drainage of an alternative focus in four of those. Magnetic resonance imaging scanning after hip washout indicated that four cases required further surgery to drain a different focus of infection.