Predicting Bone Adaptation in Astronauts during and after Spaceflight.

Area of Science:

• Biomedical Engineering
• Skeletal Biology
• Space Medicine

Background:

• Trabecular bone adaptation is crucial for skeletal health.
• Previous methods allowed participant-specific modeling of bone adaptation from CT imaging.
• Spaceflight significantly impacts bone health, necessitating accurate monitoring.

Purpose of the Study:

• To estimate changes in astronaut bone health during spaceflight and recovery using a computational model.
• To assess the model's accuracy in predicting bone structure and adaptation.
• To apply a versatile computational framework for testing bone adaptation models.

Main Methods:

• Longitudinal high-resolution peripheral quantitative CT (HR-pQCT) scans of astronaut tibias (N=16) were acquired before launch, and at 0, 6, and 12 months post-flight.
• Participant-specific parameters were determined for a trabecular bone adaptation model.
• Model predictions were compared to observed static and dynamic bone morphometry, and geometric measures (Dice coefficient, symmetric distance).

Main Results:

• Modeled and observed static bone morphometry showed high correlation (R² > 0.94) with errors near HR-pQCT precision limits.
• Dynamic bone morphometry, reflecting adaptation rates, was poorly estimated by the model (p < 0.0001).
• Dice coefficient and symmetric distance indicated a reasonable local fit between observed and predicted bone volumes.

Conclusions:

• The computational framework provides a versatile approach for testing bone adaptation models on a participant-specific basis.
• The model accurately predicts static bone structure but struggles with dynamic adaptation rates.
• Future research should incorporate load or physiological factors into more sophisticated bone adaptation models.