STUDY DESIGN: Resident's case problem BACKGROUND: Nonossifying fibroma (NOF) is the most common fibrous bone lesion in children. The lesion is usually asymptomatic, and rarely leads to pathological fractures. DIAGNOSIS: We present the case of a 12-year-old boy who appeared to be normally developed but had a pathological insufficiency fracture associated with NOF in the distal femur. He was a member of a track athletics club and ran more than 5 km every day. Seven weeks prior to the initial evaluation he felt discomfort in the left distal thigh when running and felt pain upon knee flexion. The amount of discomfort increased gradually and he began to experience pain while running 4 weeks prior to his initial evaluation. At the time of the initial evaluation, he had tenderness over the distal thigh region and there was increased pain with weight bearing. Plain radiographs showed an irregular, well-defined cortical bone lesion, suggesting NOF, with vague increased density in the bone marrow across the femur and periosteal new bone, suggesting a fracture. Computed tomography confirmed a linear fracture with increased density across the femur leading to the cortical lesion. In the process of differential diagnosis osteosarcoma, or Ewing sarcoma, and bone/joint infection were ruled out using magnetic resonance imaging. The final diagnosis based upon the images and clinical course was pathological insufficiency fracture associated with NOF. The patient was treated with initial avoidance of weight bearing using 2 crutches for ambulation, followed by progressive weight bearing over a period of 5 weeks. Active range of motion of the knee joint was allowed. Three months after onset (5 weeks after the initial evaluation), the patient had normal gait without pain, whereupon the patient resumed his sport activities, beginning with jogging. DISCUSSION: Although pathological fractures secondary to NOF in the femur are rare, NOF can cause pathological insufficiency fractures in athletes, even if the lesion is confined and small. The current case is a reminder of such a possibility. This case also provides a time course as a reference for the rehabilitation of patients in similar cases. LEVEL OF EVIDENCE: Diagnosis, level 4.

J Orthop Sports Phys Ther. 2008;38(7):434-438, published online 12 March 2008. doi:10.2519/jospt.2008.2655

KEY WORDS: athletes, bone lesion, femur, fibroxanthoma