Fatigue Fractures of the Shaft of the Femur: Simulation of Malignant Tumor

It is not generally appreciated that “fatigue” or “stress” fractures can occur in the shaft of the femur. This type of injury is usually encountered in the metatarsals of runners or military personnel on prolonged training marches. Here they are so common that few radiologists or orthopedists have trouble correctly diagnosing them. However, the occurrence of these injuries in the larger and seemingly less vulnerable bones can lead to erroneous diagnosis by the examiner who is unfamiliar with them. It is only in rare instances that this injury occurs in the shaft of the femur. A search of the English literature reveals only 8 such cases previously reported (2, 3, 7–11), most of them during World War II and presumably the result of intensive army training. The clinical history, physical examination, and radiographic findings are similar to those of fatigue fractures of the metatarsals. The presenting complaint is simply of pain in the thigh, insidious in onset, aching in nature, and of several days to several weeks duration. There is no history of sudden trauma to which the fracture can be ascribed. Physical findings are limited to localized tenderness and impairment of ability to bear weight. Roentgenograms taken shortly after the onset of pain will usually show no abnormalities. Approximately three or four weeks later, however, periosteal reaction and small amounts of amorphous soft-tissue calcification occur locally as a result of the healing process. At this stage a thin fracture line may be barely visible. The fracture is more readily seen on these later films because of increased osteoclastic activity along its edges. It can be transverse, oblique, or almost longitudinal, and is often incomplete. Still later, considerable localized cortical thickening occurs as a result of periosteal new-bone formation. The fracture line will gradually be bridged, but the cortex does not revert to its normal thickness for several years. If the fracture line is not visualized during the first month, it usually will be seen later on during the healing process. The treatment customarily consists of no more than cessation of weight-bearing for three to six weeks. It is important, however, to adhere carefully to this restriction, as complete transverse fracture can occur if weight-bearing and exercising are continued (11). Immobilization in a plaster cast is necessary only if the patient is unreliable. Diagnosis of this lesion may prove quite difficult if one is not aware of its existence. The discovery of soft-tissue calcification and periosteal reaction along the shaft of the femur in a young adult with no history of sudden trauma is generally cause for alarm. These lesions may be initially misdiagnosed as Ewing's sarcoma or osteogenic sarcoma, osteomyelitis, syphilis, osteitis or periostitis, osteoid osteoma, pseudofracture, or traumatic myositis ossificans.