Increased Rates of Hip Fractures Associated With Longer Spaceflight Durations

To analyze a recent survey of all astronaut fractures to assess whether the rate of postflight fractures is associated with durations of spaceflight missions.

Follow-up group comparisons of fracture incidence data (surveyed between 2018 and 2022) were analyzed within the astronaut cohort. Analyzing within the astronaut cohort addressed biases associated with the perception of greater physical activity in astronauts as a discriminating risk factor for fractures. The number of fractures was modeled using count regression adjusting for (1) repeated measures within individuals across the follow-up groups, (2) differing lengths of surveillance for each individual, and (3) average age for members of the follow-up groups.

Analysis of hip fractures revealed an increased rate of hip fractures during the surveillance period after exposure to a long-duration spaceflight (LD-SF) vs non-LD-SF [posterior probability (relative rate >1)] = 0.9929; Bayes factor [where >3 is considered significant] = 140) or no spaceflight (posterior probability [relative rate >1] = 0.9988; Bayes factor = 832). Compared with terrestrial hip fracture rates, fracture rates in the LD-SF timeframe were similar to non-astronaut persons who were 8 to 16.5 years older (mean age 62.5 vs 70 to 79-year-old persons). For all other skeletal sites, rates of fracture were similar for long-duration (LD) and non-LD exposures.

This analysis is the first to report an increased hip fracture rate in astronauts (1) at an earlier age than in non-astronauts and (2) with astronaut fracture surveillance conducted during the period following an LD-SF mission (greater than 90 days) rather than during the period before or with no exposure to long-duration mission.