Epidemiology of atypical subtrochanteric and femoral shaft fractures

Abstract

Subtrochanteric or femoral shaft fractures represent a small subset (10–30 %) of all hip/femur fractures. There may be differences in the clinical characteristics between subtrochanteric and femoral shaft fractures. Atypical femoral fractures (AFFs) are located along the femoral diaphysis from just distal to the lesser trochanter to just proximal to the supracondylar flare and must meet certain criteria (four of five major criteria and minor criteria are not required) to be considered atypical. There may be important clinical differences between the AFF that have minor features present as compared to those that only meet the major features of AFF. AFFs are rare, and the absolute risk of these fractures ranges from 3.2 to 50 cases per 100,000 person-years. Risk factors include prodromal pain (70 %), Asian race, and several comorbid conditions and use of medications. AFFs appear to be more frequent among individuals who are being treated with bisphosphonates, and longer duration of use may further increase risk. However, the risk of AFF is reduced by up to 70 % per year after bisphosphonates are stopped. The benefit of bisphosphonates to prevent osteoporosis-related fractures has been estimated to be 100-fold greater than the risk of AFF.