Spaceflight and Fractures: 5-Year-Fracture Incidence Upon Return From Spaceflight

Introduction Exposure to spaceflight and microgravity environments has been implicated in large reductions in astronaut bone mineral density (BMD). While low BMD is a known risk factor for fracture, there have been no reported cases of in-flight fracture, and very little documentation of post-flight fracture. The present study sought to review the incidence of fractures within 5 years of return to spaceflight. Methods Using NASA's Lifetime Surveillance of Astronaut Health epidemiology database, a retrospective cohort study was conducted to identify the incidence of fracture in the 5-year post-flight period. All astronauts who participated in spaceflight with 5-year post-flight medical data were included. Demographics were compared between the fracture and nonfracture cohorts. Results Of the 242 astronauts who met the inclusion criteria, 7 (2.9%) sustained fractures within 5 years post-flight. Three post-flight fractures occurred in the hip or spine. Six of the 7 fractures occurred within 2 years of return from spaceflight. Spaceflight length, age, and time from spaceflight were not statistically significantly associated with increased risk of fracture. Conclusion Fracture upon return to the gravitational environment is a serious risk for astronauts that can significantly jeopardize astronaut health and mission success. Fractures of the hip and spine, specifically, are associated with decreased BMD. While the incidence of these fractures is roughly 1%, the negative implications, including high 1-year mortality rates and functional implications, emphasize the need to optimize bone health and fracture treatment protocols.