Fatigue fractures of the femoral diaphysis in the skeletally immature simulating malignancy.

The clinical and radiological features of three fatigue fractures developing along the medial aspect of the distal femoral diaphysis are described. All three patients were skeletally immature and were referred with the radiographic diagnosis of a probable sarcoma of bone. The plain radiographic findings consisted of an uninterrupted single lamella of periosteal new bone arising medially from the distal femoral diaphysis. Bone scans showed no evidence of hyperaemia on the vascular phase and revealed a fusiform focus of increased uptake in the postero-medial cortex of the lower femoral diaphysis on the 3-h images. Computed tomography showed increased attenuation of the medulla due to fibrosis and an absence of a soft-tissue mass. Periosteal callus was present and a cortical fracture through the medial femoral cortex was identified in two cases. The features that distinguish a fatigue fracture of the femur from a sarcoma are discussed.