Gap Osteo 3: We need a validated clinically relevant method for assessing the effect of spaceflight on osteoporosis or fracture risk in long-duration astronauts.
Last Published:  07/30/21 01:05:31 PM (Central)
Responsible Element: Human Health Countermeasures (HHC)
Status: Open

Initial/Present State:


The Bone Summit Panel (June 2010) had identified a clinical trigger for the hip which Space Medicine shall monitor in order to prevent early onset osteoporosis. The trigger is based upon the reported absence of recovery in trabecular hip volumetric  Bone Mineral Density (BMD) of ISS astronauts at approximately two years after return and the validation of decreased Quantitative Computed Tomography (QCT)-measured parameters of the hip as independent predictors of fracture in elderly men (Carpenter, Acta Astronautica, 2010; Black, JBMR, 2008). Specifically, the Panel identified the trabecular bone compartment of the hip (which includes total hip, trochanter and femoral neck) as a skeletal site to evaluate for recovery. However, the panel did not make a recommendation for how the spine, particularly the lumbar spine, should be monitored. The decline in Dual-energy X-ray absorptiometry (DXA) areal (Bone Mineral Density) aBMD among astronauts is highly variable and the degeneration of the spine with aging increases the data heterogeneity.  There is no clear advantage of using QCT over DXA modality for the spine BMD (which is predominantly composed of trabecular bone). Still, the losses in lumbar spine aBMD are rapid and there is a concern for the presence of stress risers in trabecular bone induced by aggressive, resorptive activity. The Clinical Advisory panel emphasized that surveillance at this site should not be ignored but would require further research.

Intermediate Stages/Metrics (Sequential):
  1. Determine best methods for surveillance of bone health to mitigate risk of early onset osteoporosis (30%)
  2. Convene Research and Clinical Advisory Panel (RCAP) to refine the surveillance method, following interim data reviews (at intervals of n=3-6 complete sets of pre, post- and R+1 year hip Quantitative Computed Tomography (QCT) data). (10%)
  3. Submit surveillance method for clinical trigger at R+2 years in astronauts for Transition to Operations (TTO) upon completion of Hip QCT study (5%)
  4. Modify medical standard, if required, with additional Finite Element (FE) data from astronauts (at completion of Hip QCT study).(5%)
  5. Develop surveillance method for spine deconditioning based upon RCAP recommendation. (10%)
  6. Implement pilot validation of spine deconditioning surveillance. (20%)
  7. Convene RCAP to evaluate spine data (#6) acquired by surveillance method (#5) for spine and solicit recommendation. (10%)
  8. Submit recommendation for surveillance method(s) for spine for TTO process. (10%)
  1. Prior to FE strength standards being available, the index for recovery is restoration of hip Trabecular BMD to within the measurement error (Least Significant Change, LSC %) of QCT baseline measurement (preflight).   The precision (LSC %) for an automated analysis of QCT scans of hip trabecular BMD is:  Femoral Neck - (12.5%); Trochanter (1.7%); Total Hip -(2.3%). 
  2. After the FE cut-points for bone standards are accepted (Gap Osteo 1), establish that hip strength is recovered in ISS astronaut at R+1 year according to the permissible outcome limit determined for FE strength (Gap Osteo 1).  If not, then re-evaluate at R+ 2 years. If recovery is not detected, then a clinical response is required, as dictated by clinical advisory panel. 
Target for Closure
Surveillance method for identifying astronauts who reached “red zone” identified in Gap Osteo 1 for a) hip bone integrity and b) spine integrity.
Risk Risk of Bone Fracture due to Spaceflight-induced Changes to Bone
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Multi-Disciplinary Research Plans

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