Astronaut Bone Medical Standards Derived from Finite Element [FE] Modeling of QCT Scans from Populations Studies (FEMQCT)
Bone and calcium physiology
Scientific Name: Homo sapiens Species: Human
This study was a follow-up to the recommendations from two advisory panels – the Bone Summit in June 2010 and the Finite Element (FE) Task Group in October 2011. Both concurred that improved medical standards for bone are required for astronauts. In a previous flight study, Quantitative computed tomography (QCT) hip scans of astronauts who served on the International Space Station (ISS) were performed before and after missions and analyzed by finite element modeling (FEM) to characterize space flight effects on hip bone strength. The compelling data generated by this computational tool led these clinical experts in areal bone mineral density (aBMD) and osteoporosis to acknowledge that FEM of QCT data provides an improved detection of space flight-induced changes to hip bone strength, over DXA measurement of areal BMD.
This study had the following specific aims:
- Develop a dataset of FE hip strengths for subjects a) with ages covering the age range of the astronauts, and b) for which fractures outcome data have been collected.
- Review and evaluate dataset by FE Task Group members to suggest methods by which FE strength cutoffs from this dataset could supplement current areal BMD-based standards for the following:
a) a non-permissible outcome (POL) for hip bone strength after space flight to establish level of countermeasure efficacy, b) an additional metric for screening bone healthy in applicants to the astronaut corps who fail to meet the bone medical standard of hip T-score>-1.0, c) a fitness-for-flight standard in astronauts for a second long-duration mission, and d) an index for assessing an astronaut’s risk for overloading the hip due to certain post-mission physical activities.
- A manuscript of FE Task Group opinions.
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QCT-FE models of eight astronaut were analyzed using nonlinear single-limb stance (NLS) and posterolateral fall (NLF) loading configurations. QCT data from the Age Gene/Environment Susceptibility (AGES) Reykjavik cohort and the Rochester Epidemiology Project, referred to as the Mayo cohort (ages 27–55 years), were analyzed using identical modeling procedures. All eight crewmembers received pre and postflight DXA scans of the hip. Scans were acquired on average 95 ± 34 days prior to flight and 8 ± 2 days after returning from flight. Both the left and right hips were scanned; however, only left hip data are reported here, as the left hip was used in the analysis across all components of this study. All DXA scans for an individual crewmember were acquired on the same scanner and analyzed by the same operator to ensure consistency.
For the stance loading configuration, the preflight and postflight data of astronauts both exceeded the FE load capacity POL. For the fall loading configuration, the hip load capacity of one astronaut fell below this POL cut-point before space flight and hip load capacities for three astronauts fell below the POL cut-point after space flight. On average, the data indicates that astronaut preflight and postflight hip load capacities are significantly greater than the population mean for a subset of the AGES cohort depicts correlations between the DXA T-Scores and FE outcomes for the AGES cohort and the astronaut cohorts. The population DXA data are moderately correlated and statistically significant with the FE estimated NLS and NLF hip load capacities. The astronaut DXA data are poorly correlated with the NLS and NLF load capacities, where the NLS correlation is not statistically significant.
Michalski AS, Amin S, Cheung AM, Cody DD, Keyak JH, Lang TF, Nicolella DP, Orwoll ES, Boyd SK, and Sibonga JD. Hip load capacity cut-points for Astronaut Skeletal Health NASA Finite Element Strength Task Group Recommendations. NPJ Microgravity.
2019. March; 5(1):6. [DOI]
Finite element analysis
Bone and bones
Bone mineral density
DXA scan time, days
Non-linear fall load
Non-linear stance load
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QCT scan time, days
Total hip areal bone mineral density (aBMD)
Total hip T-score
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Project Manager: Eric Gallagher
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