Development and Validation of a Predictive Bone Fracture Risk Model for Astronauts

Abstract

There are still many unknowns in the physiological response of human beings to space, but compelling evidence indicates that accelerated bone loss will be a consequence of long-duration spaceflight. Lacking phenomenological data on fracture risk in space, we have developed a predictive tool based on biomechanical and bone loading models at any gravitational level of interest. The tool is a statistical model that forecasts fracture risk, bounds the associated uncertainties, and performs sensitivity analysis. In this paper, we focused on events that represent severe consequences for an exploration mission, specifically that of spinal fracture resulting from a routine task (lifting a heavy object up to 60 kg), or a spinal, femoral or wrist fracture due to an accidental fall or an intentional jump from 1 to 2 m. We validated the biomechanical and bone fracture models against terrestrial studies of ground reaction forces, skeletal loading, fracture risk, and fracture incidence. Finally, we predicted fracture risk associated with reference missions to the moon and Mars that represented crew activities on the surface. Fracture was much more likely on Mars due to compromised bone integrity. No statistically significant gender-dependent differences emerged. Wrist fracture was the most likely type of fracture, followed by spinal and hip fracture.

Ergonomic Challenges for Astronauts during Space Travel and the Need for Space Medicine

“…This allows mission planners to propose and agree mitigation risks, some of which will include the development and refinement of countermeasures. There are many reviews which summarise the potential and actual countermeasures which are in put in place and a representative set is cited for further interest [2, 7,10,34,50,53,57,71,72,74,[76][77][78][79][80][81]. In Table 2, countermeasures in operation today are described for each of the physiological and psychological effects of spaceflight described in the preceding sections.…”

“…vertical treadmills, nutrition and pharmacological regimes. Development of tools to predict muscle and bone loss [76,78,79] Healing capacity Risk-based monitoring to reduce injury, pharmacological intervention [7,77] Limited data available on healing rates in humans in space. Translation of animal model to human healing rates in microgravity requires further exploration N/A Evaluation of medications used in-flight in 79 space shuttle missions showed that the majority of medications provided for and taken were for motion sickness, sleep disturbance and as analgesics or anticongestants [100].…”

Assessing the likelihood of rare medical events in astronauts

“…The team at NASA GRC has been particularly successful in addressing injury modalities such as bone fracture [2] on planetary missions. Here we present two examples of how our general approach was applied to specific medical event analyses.…”

“…Previous efforts at NASA GRC to quantify bone fracture risk on moon and Mars missions have illustrated that, while substantial bone mineral can be lost at load bearing locations, it is the wrist which has the highest probability of fracture due to forceful impacts such as falls [2]. The likelihood of wrist fracture during an ISS mission was also assessed.…”

“…Differential equations of motion, described in detail in [2], were solved to determine the load on the wrist during an impact with an ISS wall. The velocity of impact was determined from four studies of the force resulting from a push-off of a space craft wall in a microgravity environment [9][10][11][12][13].The peak forces reported in these studies, along with the subjects' masses were used with a derived force pulse width (1.1 ± 20%, based on the average push-off force duration in [9]) to estimate impact velocity.…”