Paediatric Pelvic Osteomyelitis & Sacroiliac Joint Infection

Pelvic osteomyelitis and septic sacroiliitis present vaguely: a child with a limp or refusal to weight-bear, fever, and pain that may localise to the hip, buttock, groin, thigh or low back - so they are frequently mistaken for a septic hip, transient synovitis, discitis or even appendicitis, and diagnosis is often delayed. The reason the pelvis is involved is the metaphyseal-equivalent concept: flat/irregular bones have regions adjacent to cartilage with metaphysis-like vascularity that seed haematogenous infection, and the sacroiliac joint region is the most frequent pelvic site (with ilium, pubis, ischium and triradiate cartilage). MRI is the key test - sensitive early and able to define an abscess - while plain films are often normal early; Staphylococcus aureus predominates.

• Get a diagnosis where possible. Inflammatory markers (CRP/ESR), blood cultures, and - for a localised or atypical focus - image-guided aspiration/biopsy; a subacute pelvic focus may be a Brodie's abscess that mimics tuberculosis and bone tumours, so biopsy/curettage is sometimes needed to confirm and exclude tumour.
• Cover the likely organism. S. aureus predominates; consider Kingella kingae in younger children and Salmonella in sickle-cell disease. Start empirical antibiotics per local protocol after sampling.
• Antibiotics are the mainstay. Most children respond to appropriately chosen antibiotics alone, with the usual transition from intravenous to oral guided by clinical and biochemical response.
• Drain when needed. Surgical drainage is reserved for a drainable abscess, for SI-joint sepsis not responding, or for failure to improve on antibiotics.