The radiograph is normal for 10–14 days; MRI shows marrow oedema, subperiosteal abscess and physeal involvement early, and ultrasound finds the joint effusion to aspirate — the report says where the pus is.
Orient first
- Haematogenous spread to the metaphysis (slow flow in the capillary loops); in infants vessels cross the physis to the epiphysis and joint.
- Staphylococcus aureus is commonest; Kingella kingae in young children.
- Subperiosteal abscess and pyomyositis change management (drainage).
Acquire the study
- Two orthogonal views of the affected bone including adjacent joints.
The manoeuvre
- Soft tissue swelling and loss of fat planes (early).
- Metaphyseal lucency and periosteal reaction (after 10–14 days).
- Compare with the other side.
What confirms it
- Marrow signal abnormality on T1 and STIR with a compatible clinical picture, or pus on aspiration.
What licenses you to exclude it
- A normal MRI excludes osteomyelitis.
The classic misread
- A normal radiograph reassuring anyone.