HISTORY: A 66-year-old female avid distance runner complained of anterior right thigh pain for four months. She was diagnosed with a quadriceps strain and restricted her running for several weeks. Further evaluation revealed a healing stress fracture of the right proximal femur. After seven weeks of low impact exercise and radiographic evidence of a healed stress fracture, the patient began a gradual return to running. In the first week of this program, the patient fell at home and fractured her right proximal femur. Past history was notable for a stress fracture of the right proximal femur five years earlier which healed with six weeks of low impact exercise. Since then she continued to run 10k and half marathon races without right thigh pain and even qualified for the senior Olympics. Patient was treated with bisphosphonates for over five years. Her DEXA scan from the previous year revealed osteopenia of the spine (T-score= -2.3) but normal bone mineral density of her femurs (T-scores of -0.7 left and 0.0 right). PHYSICAL EXAMINATION: On initial presentation, the patient appeared healthy and athletic. Her lower extremities showed no gross deformities and had full active range of motion. There was tenderness to palpation along the middle third of the right thigh, and pain with single leg standing on the right. DIFFERENTIAL DIAGNOSIS: Completed femoral stress fracture from incomplete healing Femoral fracture secondary to osteoporosis Pathologic femoral fracture Low-energy mid shaft femoral fracture associated with longstanding bisphosphonate use TEST AND RESULTS: Initial right femur radiographs (7 weeks prior to fracture): - 2 cm sclerotic cortical lesion at the lateral proximal femur consistent with prior stress fracture Three phase bone scan (7 weeks prior to fracture): - Increased activity in the proximal shaft of the right femur mainly in the cortical region Follow up right femur radiograph (1 week prior to fracture): - Increased callus formation in the area of previously noted sclerosis in proximal femur FINAL WORKING DIAGNOSIS: Low-energy femoral fracture possibly complicated by long-term bisphosphonate use TREATMENT AND OUTCOMES: 1. Intramedullary nailing of femur for acute displaced fracture management 2. Stop bisphosphonate 3. Gradual return to running after adequate rest and rehabilitation