Subacute Osteomyelitis

Subacute osteomyelitis is an infection of bone with distinct characteristics that distinguish it from both acute and chronic osteomyelitis. These include mild localized bone pain and tenderness usually of over 2 week’s duration, absence of constitutional symptoms, a negative blood culture and an osteolytic lesion in the metaphysis or epiphysis of a long bone. Based on the features of the bone surrounding the lytic area, subacute osteomyelitis is classified into five types. The plain radiographic appearances may mimic benign or malignant neoplastic lesions, and hence MR imaging and a needle biopsy are warranted in many instances. Frank suppuration may not occur in subacute osteomyelitis and hence aspiration of the lesion may not yield pus, but granulation tissue often lines the cavity, and this is responsible for the “penumbra sign” on unenhanced T1-weighted MRI. Medical treatment with antibiotics is often sufficient to eradicate the infection. Surgical intervention is needed in children with a poor response to conservative treatment and in children with high risk of sustaining a fracture. Though the frequency of complications is low following subacute osteomyelitis, all children must be followed until skeletal maturity to detect subtle growth abnormalities.