Disclosures: Ryan P. Dunn, DO: Nothing to disclose

Case Description:  While being treated with anastrazole (Arimidex), the patient began experiencing thigh pain with running. With normal radiographs, she was diagnosed clinically with a femoral stress fracture. After 6 weeks of non-weight bearing, her symptoms improved. Due to low bone density noted in the femur on Dexa studies (T-score of -2.0), the patient was started on denosumab (Prolia) and received 2 doses separated by 6 months. She began having a return of thigh symptoms after repeat initiation of running. MRI subsequently showed periosteal thickening consistent with a femur stress fracture. Despite extended activity restrictions, her pain continued, and she was referred to the bone health clinic. Radiographs continued to show periosteal thickening.

Setting: Outpatient Sports Medicine Clinic

Patient: A 37-year-old female with a history of breast cancer status post chemotherapy (on daily anastrozole [Arimidex]), radiation therapy, and bilateral mastectomies/salpingo-oophorectomy.

Assessment/Results: Given her continued discomfort in conjunction with the fact that she had developed this stress fracture in the setting of anti-resorptive therapy, there was concern for an atypical femur fracture. She underwent surgical stabilization of her left femur with TFN. Post-operatively, both anastrazole and denosumab were discontinued.

Discussion: In recent years, there have been reports of atypical fractures developing in the setting of denosumab therapy. Denosumab works by preventing osteoclastic activity with the goal of inhibiting bone resorption. If a microcrack is present at the time of initiation of denosumab, as is certainly possible in an athlete, the process of bone repair is disrupted and could ultimately contribute to a fracture.

Conclusion: The possibility of denosumab therapy leading to an increased risk of atypical femur fractures is debatable, as is the recommendation for or against running in a patient with osteoporosis. Specific activity recommendations need to be tailored to each individual patient with osteoporosis, particularly when undergoing anti-resorptive therapy.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/leg-pain-in-a-runner-on-denosumab-prolia-a-case-report/