Abstract
The unwell child with an acutely irritable hip poses a diagnostic dilemma. Recent studies indicate that pericapsular myositis may be at least as common as joint infection in the septic child. MRI might therefore be a critical first step to avoid unnecessary hip drainage surgery in the septic child with hip symptoms.
We reviewed our own experience with MR imaging in this setting.
We searched our PACS system to retrieve MRI scans performed for children with suspected hip sepsis from August 2008 to August 2014 using the following terms: hip, septic arthritis, osteomyelitis, mysositis, abscess, femur, acetabulum. 56 cases fulfilled inclusion criteria that included acute presentation with hip symptoms and 2 or more Kocher criteria for septic arthritis. Recent unsuccessful hip washout was not a contra-indication.
56 patients presented with acute infection around the hip. 47 (84%) had MRI scans before any surgical intervention and 9 (16%) had scans promptly following unsatisfactory hip washout with failure to improve.
20 (36%) were found to have pericapsular myositis. In this group, the infection commonly involved the iliopsoas (4), gluteal (4), piriformis (5) or obturator (7) muscles. 15 (27%) children had proximal femoral or acetabular osteomyelitis and 8 (14%) were diagnosed with septic arthritis. The 13 (23%) remaining scans did not show infection around the hip.
This study confirms a high rate of extracapsular foci in septic children presenting with hip irritability. Less than 20% had actual septic arthritis in this series. While drainage of a septic joint should never be delayed in the face of a large joint effusion with debris on US, there is a clear role for MRI scanning in the acute setting when the diagnosis is less certain.
