Reduction in proximal femoral strength due to long-duration spaceflight.
Level 4 - case-series / case-control
Pre-post observational study without an independent control group.
PubMed 19100348 · doi:10.1016/j.bone.2008.11.014
What was done
Pre- and post-flight CT scans of the left proximal femur were obtained from 13 astronauts who spent 4.3 to 6.5 months on the International Space Station. Subject-specific finite element models were created to simulate proximal femoral strength under two mechanical conditions: single-limb stance and a fall onto the posterolateral aspect of the greater trochanter.
What was found
Mean proximal femoral strength decreased from 18.2 times body weight (BW) pre-flight to 15.6 BW post-flight for stance loading, and from 3.5 BW to 3.1 BW for fall loading. Normalized for flight duration, estimated strength decreased at mean rates of 2.6% (0.6% to 5.0%) per month for stance loading and 2.0% (0.6% to 3.9%) per month for fall loading. These reductions were greater than previously reported DXA total femoral bone mineral density decreases of 0.4% to 1.8% per month.
Why it matters
Bone strength declines during microgravity at a faster rate than suggested by conventional DXA bone mineral density measurements alone, potentially reducing safety margins against fracture in some crew members.
Limits
The study had a small sample size (n = 13) and lacked a terrestrial control group. Outcomes were based on computational finite element simulations rather than direct clinical fracture endpoints, and long-term post-flight recovery was not assessed in the abstract.
Cited by
- supports Spending six months to a year in space results in the equivalent of 10 to 15 years of skeletal and muscle aging.