CPMS TSR Example: Predictive Bone Fracture Risk Model for Astronauts

Investigators
Dr. Emily Nelson, Dr. Beth Lewandowski, Dr. Jerry Myers
Contact info (email)
jerry.g.myers@nasa.gov
1. Define context(s)
other
Current Conformance Level / Target Conformance Level
Extensive
Primary goal of the model/tool/database

Lacking phenomenological data on fracture risk in space, we have developed a predictive tool based on biomechanical and bone loading models at any gravitational level of interest. The tool is a statistical model that forecasts fracture risk, bounds the associated uncertainties, and performs sensitivity analysis.  The model is intended to be extensible to all genders, all races and all age groups applicable to astronaut demographics.  The model is intended to addresses, in-flight and post-flight risks based on assumptions regarding astronaut mission and personal activities utilizing the best available information for space flight induced bone loss and return from flight recovery in bone :gravity load bearing regions (hips, lumbar spine) and areas endangered from falls (wrist, hips).  To make the model tractable with current space flight planning, the model uses a series of characteristic loading scenarios to characterize the risk.   Characterization of this risks allows for mission trades with other medical conditions, as well as defining mission parameters and engineering requirements.

Biological domain of the model
Skeletal fracture
Structure(s) of interest in the model
Lumbar spine, Hip (all aspects), Calcaneous, Wrist
Spatial scales included in the model
10^-2 to 10^1 meters
Time scales included in the model
10^-1 to 10^7 seconds
Other uses for the model (optional)

The model can be used to evaluate the protective nature of space suit designs, to characterize future studies in bone fracture prevention and to predict the fracture resistive changes at load bearing regions important for spacecraft off-nominal design requirements.

Additional comments about the model’s context (optional)

The model context is exclusively for the astronaut corp, a group considered to be in good health, under frequent medical surveillance, yet operating in an extremely stressful environment where true risks are not adequately characterized.  Further application and assessment of this model should bear those criteria in mind.

2. Data for building and validating the model
Data for building the model Published? Private? How is credibility checked? Current Conformance Level / Target Conformance Level
in vitro (primary cells cell, lines, etc.)
ex vivo (excised tissues)
in vivo pre-clinical (lower-level organism or small animal)
in vivo pre-clinical (large animal)
Human subjects/clinical Yes Specific individuals are private, Averaged data is available Individuals are scanned multiple times at different locations Adequate
Other: ________________________
Data for validating the model Published? Private? How is credibility checked? Current Conformance Level / Target Conformance Level
in vitro (primary cells cell, lines, etc.)
ex vivo (excised tissues)
in vivo pre-clinical (lower-level organism or small animal)
in vivo pre-clinical (large animal)
Human subjects/clinical Yes Data was obtained from published data - averaged values are not private the source data is confirmed to meet detailed data requirements for consistency and source description Adequate
Other: ________________________
3. Validate within context(s)
Who does it? When does it happen? How is it done? Current Conformance Level / Target Conformance Level
Verification NASA Software QA throughout development of the software with an independent review prior to release There is an assessment of software risk and line by line review, regression testing and global testing to insure code meets conceptual implementation Extensive
Validation Developers and users have done independent validations throughout development and prior to SME reviews of modeling products model is used to reproduce experimental scenarios, primarily loading conditions at specific locations, then population predictions are quantitatively and qualitatively compared to observed fracture risk index values in analog populations Extensive
Uncertainty quantification the model is designed to propagate uncertainty, so this requirement is met by virtue of the model development and application Every time the model is run for a new scenario Monte Carlo Sampling of ALL parameters with known uncertainty Extensive
Sensitivity analysis User performs sensitivity analysis on influential parameters at each new scenario A post-processing tool that implements Partial Rank Correlation Coefficient algorithm to address sensitivity of model parameters Adequate
Other:__________
Additional Comments
4. Limitations
Disclaimer statement (explain key limitations) Who needs to know about this disclaimer? How is this disclaimer shared with that audience? Current Conformance Level / Target Conformance Level
In a fall to the side, we assumed that the astronaut was initially standing on solid ground and impacted the ground with the hip. The natural response to such a fall is to extend a hand toward the ground to absorb some of the impact. Clinicians/ risk custodians A list of limitations is provided with each report from each model run and stated in the accompanying documentation. Extensive
In the space flight dynamic fall scenarios, we assumed that the crew was situated on the reduced-gravity surface of the moon or Mars. The probabilities are therefore based only on the portion of the mission that occurred on the surface. Mission planners A list of limitations is provided with each report from each model run and stated in the accompanying documentation. Extensive
In simulations of extra-vehicular activity (EVA), we assumed that the stiff 82-kg spacesuit would add to the mass of the astronaut, improve the padding to the hip, and limit the torso’s bending angle to 45 degrees EVA suit developers, clinicians A list of limitations is provided with each report from each model run and stated in the accompanying documentation. Extensive
5. Version control
Current Conformance Level / Target Conformance Level
Extensive
Naming Conventions? Repository? Code Review?
individual modeler Yes Subversion (off site) Yes
within the lab NA
collaborators NA Yes
6. Documentation
Current Conformance Level / Target Conformance Level
Code commented? Extensive: Code commenting follows NASA standard 7150.2a
Scope and intended use described? Extensive: Yes - in both internal NASA documentation and supporting material in publications
User’s guide? Adequate
Developer’s guide? Partial: No, there is a concept document and a software design document
7. Dissemination
Current Conformance Level / Target Conformance Level
Adequate
Target Audience(s): “Inner circle” Scientific community Public
Simulations
Models DOI:10.3357/asem.2855.2011
Software
Results DOI: 10.1007/s10439-009-9779-x
Implications of results DOI:10.1115/1.4041164
8. Independent reviews
Current Conformance Level / Target Conformance Level
Extensive
Reviewer(s) name & affiliation: Robinovitch (Simon Fraser University), Peter Cavanagh (CCF), David Burr (Indiana University School of Medicine), Tom Lang (University of California, San Francisco)
When was review performed? 2/7/2008
How was review performed and outcomes of the review? Presentation of concepts, data providence, results, live demo of software, software provided to panel, updated simulations
9. Test competing implementations
Current Conformance Level / Target Conformance Level
Adequate
Yes or No (briefly summarize)
Were competing implementations tested? yes - predictive capability tested against FEM analysis and analog populations, included recreation of code by independent researchers
Did this lead to model refinement or improvement? Yes - improvements on data passing and model performance. No changes to the underlying concepts or overall results.
10. Conform to standards
Current Conformance Level / Target Conformance Level
Extensive
Yes or No (briefly summarize)
Are there operating procedures, guidelines, or standards for this type of multiscale modeling? Yes - NASA STD 7150.2 Software quality assurance standards and NASA 7009 Model and Simulation Credibility standards
How do your modeling efforts conform? We meet all documentation, programming and credibility standards as confirmed by independent assessment by users and management customers
11. (optional) Additional information to support items 1-10

This model has been in use by NASA for >10 years.  Applications have included assessment of space flight contribution to a post flight fracture event and acceptance of the space flight, in-flight, fracture risk, as well as the characterization of commercial crew risk.  Work on this model has garnered Paper of the year awards at NASA GRC, and the developers have been awarded 3 silver snoopy awards (highest award astronaut office can award for contributions to space flight safety),  NASA exceptional service medals (Nelson ad Myers, each) and the NASA exceptional science medal (Lewandowski) all for the application of physics-based modeling to enhance our understanding and characterization of space flight health and performance risk.