Gap Fracture 3: We need a validated method to estimate the the risk of fracture by evaluating the ratio of applied loads to bone fracture loads for expected mechanically-loaded activities during a mission.
Last Published:  07/30/21 01:05:31 PM (Central)
Responsible Element: Exploration Medical Capability (ExMC)
Status: Closed
Closure Rationale
Sufficient knowledge exists with respect to estimating the risk of fracture during standard nominal spaceflight operations. Computational models that predict the likelihood of bone fracture during spaceflight have been developed and validated ( ExMC has no plans for new research or work on this gap. 
Closure Documentation:
No Closure Documentation Available
Initial  State:

Calculating a fracture Factor of Risk [FOR] will describe, for a given scenario, the relationship between the applied load vector to a bone and the bone failure loads such that if the ratio is >1 then fracture will occur. Osteoporosis (severely reduced bone strength) is not required for an astronaut to have a FOR > 1. For example, a high FOR during spaceflight may be the result of an astronaut overloading his bones mechanical loads by large masses during a mission (e.g., crush fractures).  In addition, an increased fracture risk may stem from the asymptomatic nature of bone loss, the physical activities of astronauts during a mission and the uncertainties and “unknowns” of exploration-class missions. The accuracy of a FOR is contingent upon the accuracy behind estimating or quantifying the force and orientation of a mechanical load to bone, and the ability to quantify the determinants of bone strength for bones subjected to that load. A FOR calculation can inform astronauts and flight surgeons of fracture probability based upon measures of bone strength and the biomechanical loads of typical physical activities (for the individual astronaut). Moreover, the Bone Fracture Risk Module [BFxRM] of the Integrated Medical Model [IMM] has estimated fracture probability, using Monte Carlo simulations for given mission architecture, specific mission activities and scenarios, and specific biomedical data ([Bone Mineral Density] BMD, age, height, [Body Mass Index [BMI]) obtained from crewmembers. However, the understanding of bone changes has expanded with modalities, such as Quantitative Computed Tomography (QCT) and computational tools like Finite Element Modeling [FEM]. QCT has been used to characterize the effects of spaceflight on sub-regional distributions of bone mass –and FEM translated QCT data to changes in bone failure loads (i.e., estimates of hip bone strength) for the specific (axial and posterolateral)  loading scenarios (Lang et al. JBMR, 2004, 2006; Keyak Bone 2009). Furthermore, changes in Dual-energy X-ray absorptiometry  (DXA) hip areal BMD (a widely-applied surrogate for bone strength and fracture risk) do not appear to correlate with changes in  FEM estimated hip strength (for given load vectors) in ISS astronauts (Keyak, 2009). This disconnect suggests that DXA modality is not capturing all the changes in bone strength due to spaceflight. Hence, inclusion of these more sensitive data and analyses in modeling could improve fracture prediction in astronauts.

Interim Stages (Sequential):
  1. Provide inputs from Gap Fracture 2 to Fracture Probability Model(s). (25%)
  2. Provide bone parameter inputs (example:  DXA BMD, QCT BMD, geometry) to Fracture Probability Model(s). (30%)
  3. Submit model inputs to IMM for calculation of Fracture Risk Index (FRI) or like index to assess the probability of fracture (Factor of Risk). (40%)
  4. Convene Fracture Research and Clinical Advisory Panel (RCAP) to review and assess data and relevance of Fracture Prediction Module. (2.5%)
  5. Submit recommendation to Human System Risk Board (HSRB) for disposition. (2.5%)

Application of surveillance data of the astronaut corps (short- and long-duration) to a current, validated fracture prediction model (BFxRM module) with additional verification of sensitivity and specificity to population data.
Target for Closure
An updated Fracture Prediction module to the Integrated Medical Model (IMM).
Risk Risk of Bone Fracture due to Spaceflight-induced Changes to Bone
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Multi-Disciplinary Research Plans

No Documentation Available