Introduction and aim: The resemblance of acute osteomyelitis and primary bone tumor is well established. However, pubic osteomyelitis presents particular diagnostic dilemmas and acute osteomyelitis of the distal femur resembling soft tissue sarcoma has not previously reported in the English literature.

Patients and methods: We report two cases of acute osteomyelitis in 6-year and 7-year old children, affecting the pelvis and the distal femur respectively. Both patients reported previous trauma and presented with a painful limp. Clinical examination revealed a painful mass in both. Laboratory screening and imaging modalities were inadequate to establish the correct diagnosis.

Results: ESR and CRP were raised in both patients, however blood cultures were negative. Plain x-rays showed a lytic lesion at the pelvic site and were unremarkable for the femur. Bone scan was not specific. MRI Scan suggested primary bone tumor in both cases, i.e. Ewing’s sarcoma and liposarcoma/rabdomyosarcoma respectively. Open biopsy established the correct diagnosis and S. Aureous was isolated in both cases. Treatment was conservative

Conclusion: Acute osteomyelitis may cause diagnostic confusion especially if its location and/or presentation are particularly unusual. Blood investigations are frequently inconclusive. Even the most sophisticated imaging modalities may fail to establish the diagnosis and biopsy is then necessary. This should be always performed in specialized centers, in order to minimize complications. Treatment is fairly straightforward.