Forces associated with launch into space do not impact bone fracture healing.

Area of Science:

• Biomedical Engineering
• Orthopedics
• Space Medicine

Background:

• Segmental bone defects (SBDs) from trauma require prolonged recovery with limited weight bearing, often exceeding six months.
• Current small animal models for SBDs do not adequately simulate disuse conditions, as rodents typically resume ambulation quickly post-surgery.
• Simulating disuse is crucial for accurately testing novel bone healing strategies.

Purpose of the Study:

• To develop and validate a rodent model for studying segmental bone defect (SBD) healing under simulated disuse conditions.
• To assess the impact of launch-associated forces and vibrations on bone healing in a rodent model.
• To evaluate the feasibility of using the International Space Station (ISS) microgravity environment for SBD research.

Main Methods:

• A 2mm femoral defect was surgically created in mice.
• Mice underwent simulated launch conditions (vibration, centrifugation) and/or hindlimb unloading (HLU) to mimic disuse.
• Bone healing was assessed 28 days post-simulation using micro-Computed Tomography (µCT).

Main Results:

• Mice tolerated launch simulation conditions, and launch forces/vibrations did not significantly impact bone healing.
• Hindlimb unloading (HLU) resulted in a significant 52.5% reduction in total callus volume compared to controls (p=0.0003).
• These findings confirm that disuse, not launch simulation, negatively affects bone healing.

Conclusions:

• Rodent models can tolerate launch conditions, and launch simulation does not impede bone healing.
• Prolonged disuse, as simulated by HLU, significantly impairs bone healing in segmental bone defects.
• The spaceflight environment offers a unique platform for studying SBD therapies under unloading conditions.