Forecasting Postflight Hip Fracture Probability Using Probabilistic Modeling

Abstract

A probabilistic model predicts hip fracture probability for postflight male astronauts during lateral fall scenarios from various heights. A biomechanical representation of the hip provides impact load. Correlations relate spaceflight bone mineral density (BMD) loss and postflight BMD recovery to bone strength (BS). Translations convert fracture risk index (FRI), the ratio of applied load (AL) to BS, to fracture probability. Parameter distributions capture uncertainty and Monte Carlo simulations provide probability outcomes. The fracture probability for a 1 m fall 0 days postflight is 15% greater than preflight and remains 6% greater than pre-flight at 365 days postflight. Probability quantification provides insight into how spaceflight induced BMD loss affects fracture probability. A bone loss rate reflecting improved exercise countermeasures and dietary intake further reduces the postflight fracture probability to 6% greater than preflight at 0 days postflight and 2% greater at 365 days postflight. Quantification informs assessments of countermeasure effectiveness. When preflight BMD is one standard deviation below mean astronaut preflight BMD, fracture probability at 0 days postflight is 34% greater than the preflight fracture probability calculated with mean BMD and 28% greater at 365 days postflight. Quantification aids review of astronaut BMD fitness for duty standards. Increases in postflight fracture probability are associated with an estimated 18% reduction in postflight BS. Therefore, a 0.82 deconditioning coefficient modifies force application limits for crew vehicles.