Acute sacral osteomyelitis mimicking hip pathology in a child: A diagnostic challenge.

Pelvic osteomyelitis is rare in children, and sacral involvement is particularly unusual. Due to its deep anatomical location, clinical presentation is often nonspecific, frequently leading to diagnostic delays or misdiagnosis as hip arthritis or abdominal pathology. We report the case of a 10-year-old boy who presented with high-grade fever, right hip pain, and inability to bear weight. Initial hip ultrasonography was normal, but careful clinical examination revealed sacral tenderness, prompting pelvic magnetic resonance imaging (MRI). MRI demonstrated acute osteomyelitis of the right hemi-sacrum associated with a small paravertebral collection, diffuse iliopsoas muscle infiltration, and a minimal sacroiliac joint effusion, without spinal canal or neural foraminal involvement. Blood cultures remained negative. The patient was treated with 10 days of intravenous antibiotics followed by 3 weeks of oral therapy, resulting in complete clinical, biological, and radiological recovery. Follow-up MRI confirmed resolution of the marrow edema and disappearance of the paravertebral collection. This case highlights the diagnostic challenge of sacral osteomyelitis presenting as hip pathology and emphasizes the pivotal role of MRI in establishing an early diagnosis, assessing disease extent, and guiding appropriate management.