SUN-710 A "Typical" Atypical Femur Fracture in an Adult Patient with Osteogenesis Imperfecta without Bisphosphonate Exposure

Abstract Disclosure: J. Patton: None. S.D. Rao: None. A. Rothstein Costris: None. Introduction: Atypical femur fractures (AFF) are a known complication of long-term bisphosphonate (BP) therapy in patients with osteoporosis and other metabolic bone diseases including Osteogenesis Imperfecta (OI). AFF are sub trochanteric extending from 4-5 cm below lesser trochanter proximally to the femoral metaphyseal flare distally. While first reported in patients receiving BP therapy, fractures resembling AFF have been reported in conditions such as RA, OI, and CKD. Here we present a case of AFF in an adult patient with OI without prior BP therapy. Narrative: A 45 year-old male with a history of OI presented after a fall at home. He was diagnosed with OI as a child following a fracture of the left femoral diaphysis. It is unclear if he had confirmatory genetic testing but his son was also diagnosed with OI. While watering flowers, he tripped on a rock and fell on his right hip. On presentation, he was in severe pain with limited mobility of right leg. X-ray revealed sub trochanteric transverse fracture of the proximal right femoral diaphysis with varus angulation. An open reduction with fixation was performed and the patient was advised to follow up in endocrinology clinic. On follow up, review of imaging studies showed no local or generalized cortical thickness in either femur. Pharmacologic therapy was deferred until repeat imaging could be obtained to assess fracture healing and bone turnover status. Discussion: AFFs are fragility fractures located in the sub trochanteric region 4-5 cm below the lesser trochanter and femoral metaphyseal flare. Since the first report in 2005, AFFs are now a known complication of BP therapy. The risk of AFF increases with duration of BP therapy and decreases precipitously with BP cessation. AFFs have also been reported in the absence of BP therapy. Our case illustrates an unusual fracture similar to AFF in a patient with OI. In contrast to AFF in BP treated patients, AFF type fracture in patients with OI is usually due to cortical thinning, but our patient had neither cortical thickening nor cortical thinning representing a unique type of fracture. Conclusion: This case highlights an unusual presentation of AFF in an adult with OI without prior BP therapy. Since BPs are an important therapeutic tool for patients with OI, a fracture mimicking AFF should not deter use of BPs in the management of OI. Presentation: Sunday, July 13, 2025