Paget’s disease of bone (PDB) is a progressive bone disorder characterized by increased osteoclast-mediated bone resorption and abnormal bone formation. Incomplete atypical femoral fracture, appearing radiographically as a stress fracture at the lateral aspect of the femur, is an uncommon low-trauma fracture frequently seen in association with long-term bisphosphonate therapy. We describe the case of a 61-year-old female patient with PDB who developed a stress fracture at the lateral femoral cortex after 5 doses of intravenous bisphosphonate. The conservative treatment plan included discontinuation of bisphosphonate, a continuation of calcium and vitamin D supplementation, and limited weight-bearing for 3 months. The patient’s pain level gradually improved after switching to the new treatment plan. At the latest follow-up, approximately 5 years after the initiation of conservative treatment, the patient remained pain-free, and her PDB was well-controlled. However, the fracture line was still visible on the most recent radiograph. Although it remains unclear whether a stress fracture at the lateral femoral cortex occurred due to bisphosphonate therapy or PDB, this case highlights the importance of careful evaluation of any lesion that appears in PDB patients receiving bisphosphonate therapy.

Paget’s disease of bone (PDB) is a progressive bone disorder characterized by increased osteoclast-mediated bone resorption and abnormal bone formation. Incomplete atypical femoral fracture, appearing radiographically as a stress fracture at the lateral aspect of the femur, is an uncommon low-trauma fracture frequently seen in association with long-term bisphosphonate therapy. We describe the case of a 61-year-old female patient with PDB who developed a stress fracture at the lateral femoral cortex after 5 doses of intravenous bisphosphonate. The conservative treatment plan included discontinuation of bisphosphonate, a continuation of calcium and vitamin D supplementation, and limited weight-bearing for 3 months. The patient’s pain level gradually improved after switching to the new treatment plan. At the latest follow-up, approximately 5 years after the initiation of conservative treatment, the patient remained pain-free, and her PDB was well-controlled. However, the fracture line was still visible on the most recent radiograph. Although it remains unclear whether a stress fracture at the lateral femoral cortex occurred due to bisphosphonate therapy or PDB, this case highlights the importance of careful evaluation of any lesion that appears in PDB patients receiving bisphosphonate therapy.