Staphylococcal diaphyseal subacute osteomyelitis of the ulna in a child: an unusual cause of post-traumatic forearm swelling.

Paediatric subacute osteomyelitis (SAO) presents a diagnostic and therapeutic challenge to clinicians. Typically located in the metaphysis of long bones, diaphyseal SAO of the upper limb is rare. We present the case of a three-year-old girl referred to our fracture clinic as an occult fracture following trauma to her forearm with normal initial radiographs. Follow-up radiographs one week later showed cortical erosion of the distal ulna, while a subsequent MRI scan showed soft tissue swelling with an area of high signal in the distal ulna. A limited biopsy diagnosed staphylococcal subacute osteomyelitis of the ulna. The patient responded to high dose antibiotic therapy and made a full recovery. We present this case to highlight the high index of suspicion required to diagnose and appropriately manage this insidious condition, which may easily be confused with any number of benign and malignant bony lesions and provide a review of the relevant literature.