Atypical Ulnar Fracture in an Older Woman with Osteoporosis with a Five-Year History of Denosumab Treatment: A Case Report.

Atypical ulnar fracture (AUF) is a rare condition that may occur in patients treated with bisphosphonates. We describe the clinical course of a patient who had an AUF during treatment with denosumab. An 86-year-old woman treated with denosumab for 5 years experienced a complete transverse fracture of the proximal left ulna after falling from a standing height. Intraoperative photographs showed cortical thickening around the fracture site. Therefore, we diagnosed the patient with AUF and performed internal fixation with a locking plate. However, a re-fracture occurred 2.5 months after surgery, which was treated with locking plate replacement with a longer one with a bone graft. One year after the second surgery, the fracture healed. To our knowledge, this is the second case report of an AUF occurring during denosumab treatment. Our case highlights the importance of careful follow-up of patients receiving not only bisphosphonate, but also denosumab. Levels of Evidence: Level V (Therapeutic).