Atypical femoral fractures: an update

This narrative review provides an up-to-date overview of atypical femoral fractures (AFFs), emphasizing diagnostic criteria, epidemiology, pathophysiology, risk factors, and evaluation with screening strategies. AFFs are rare but significant complications associated with prolonged bisphosphonate (BP) therapy for osteoporosis. Although the pathogenesis of AFFs has not been fully elucidated, its primary mechanism is thought to involve impaired bone remodeling, leading to unhealed microfractures that progress to stress fractures under repetitive loading. AFFs can occur in various regions of the femur, influenced by femoral geometry and the lower limb axis. Other risk factors include prolonged steroid use, arthroplasty, genetic predispositions, and metabolic bone disorders. The diagnosis of AFFs is based on criteria established by the American Society for Bone and Mineral Research. Key radiographic features include lateral cortical transverse fracture lines and localized cortical thickening, typically with minimal or no comminution on the medial cortex. Dual-energy X-ray absorptiometry for screening tests and magnetic resonance imaging as an advanced imaging modality enable the early detection of incomplete fractures. This multi-modal approach facilitates the prompt identification of prodromal cortical changes, reducing the risk of complete fractures in high-risk populations, particularly patients undergoing prolonged BP therapy.Level of Evidence: V