Hip load capacity cut-points for Astronaut Skeletal Health NASA Finite Element Strength Task Group Recommendations.

Area of Science:

• Space medicine
• Biomechanics
• Skeletal health

Background:

• Astronaut skeletal health standards rely on areal bone mineral density (aBMD) from DXA scans.
• Concerns from a 2010 Bone Summit highlighted the need for improved hip fracture prediction in astronauts.
• Current standards may not fully capture the risk of hip fractures in spaceflight environments.

Purpose of the Study:

• To propose incorporating hip load capacity into astronaut skeletal health standards.
• To evaluate the utility of finite element (FE) modeling for assessing hip fracture risk in astronauts.
• To recommend methods for screening astronaut candidates and assessing post-mission fracture risks.

Main Methods:

• Developed and analyzed quantitative CT-based finite element (QCT-FE) models for eight astronauts.
• Utilized nonlinear single-limb stance (NLS) and posterolateral fall (NLF) loading configurations.
• Analyzed QCT data from the AGES Reykjavik cohort and Rochester Epidemiology Project using identical FE modeling procedures.

Main Results:

• Established a post-mission hip bone load capacity permissible outcome limit (POL) using the 75th percentile of NLS hip load capacity from the AGES cohort (9537N).
• The NLF model and Probabilistic Risk Assessment tool were used to evaluate hip load capacity during post-flight activities.
• FE estimation of hip load capacity was found to be more meaningful for younger, physically active astronauts.

Conclusions:

• Finite element (FE) hip load capacity is recommended to supplement current aBMD measurements for astronaut skeletal health.
• FE analysis can be used for screening astronaut corps applicants and assessing fracture risk after space missions.
• No replacement of current DXA-based standards was recommended, but FE analysis offers a valuable complementary tool.