Sponsors : National Aeronautics and Space Administration (NASA)

1. Interactions of Musculoskeletal Tissues During Disuse Introduction Methods Results Mice from the BALB and C3H strains were chosen and then crossbred. The child population was then inbred to create a population with a highly diverse genotype. They were then scanned at for the first time at week 0. These mice were then subjected to hind limb suspension for 3 weeks and scanned a second time (week 3). They were then let down and permitted to move for another 3 weeks before being scanned a third and final time (week 6). The scans were then reconstructed, evaluated, and output to a spreadsheet. The data for the left and right bones is then segregated so it can be evaluated separately. Trends were then evaluated in several categories including Bone Volume, Bone/Tissue Volume, and SMI. Bone loss is an increasing problem that affects all demographics. This loss occurs when a load bearing bone is not used for a prolonged periods of time. Such an example of disuse would be an astronaut on a mission or a sick person undergoing bed rest. Currently, methods are being developed to help prevent this loss as it poses a serious problem to long duration space missions or critically ill patients. Ways of recovering bone mass such as running or lifting weights will not work for these people due to a zero-g environment or they would be already too weak to do such activities. The experimental methods focus on various speeds and magnitudes of vibrations which can induce strain even in a zero-g environment or on a weakened patient. Some of these methods have been rather successful in increasing overall bone mass but the amount it affects bones sections relative to each other is largely unexamined. To induce disuse in mice a hind limb suspension apparatus is utilized. This lift’s the mice’s tail up causing no pressure to be exerted on the rear limbs. The mice still maintain mobility via their front limbs. To examine the effects a VivaCT scanner is employed. This generates images of the bone cross-sections while not harming the mouse. These images can later be reconstructed into a 3D model. There were no major differences between the left and the right leg’s data. The trabecular bone suffered more of a percent bone volume loss with 35.7% compared to cortical’s 3.1% loss during the suspension period. Cortical bone also was able to recover its loss with a 4.1% increase in total bone volume while trabecular bone only had a 7.6% increase. The trabecular bone also had a greater decrease in its bone volume fraction with a 36.8% decrease compared to cortical’s 4.7% decrease. Once again cortical bone had a greater recovery compared to loss with a 2.8% regain compared to trabecular’s 6.44%. The cortical bone lost its shape more quickly with a 72.1% change in SMI compared to trabecular’s 38.9% but it also regained its original shape more easily with a 25.2% regain to trabecular’s 4.4%. Discussion Overall trabecular bone is much more susceptible to disuse and less responsive to any recovery then cortical bone. This is evident in the greater total volume loss and less of the lost amount being recovered. The same trend is also evident in the bone volume fraction which measures the amount of bone to total tissue. This data can shows us that we will have to monitor someone’s trabecular bone much more then their cortical bone. As expected neither of the legs showed any significant amount difference over the other with only very small percent differences. This however could not be carried over to humans because mice have no favorite side while humans do. Future Work Sponsors: National Aeronautics and Space Administration (NASA) NASA Goddard Space Flight Center (GSFC) NASA Goddard Institute for Space Studies (GISS) NASA New York City Research Initiative (NYCRI) Contributors: Dr. Stefan Judex Engin Ozcivici Further work would be done pertaining to muscle and moment of inertia values. The moment of inertial values is close to being completed and will probably be included in any later versions of this report. Work into specific frequencies or treatments that focus on the trabecular bone in particular should be developed over a cortical specific treatment. References Hawkey, A. (2005) Physiological and biomechanical considerations for a human mars mission. Journal of the British Interplanetary Society,58 117-30 Judex, S., Boyd, S., Yi-Xian, Q., Simon, T., Kenny, Y., Ralph, M., & Rubin, C. (2003). Adaptations of trabecular bone to low magnitude vibrations result in more uniform stress and strain under load. Annals of Biomedical Engineering, 31, 12-20. Judex, S., Monaghan, M., Dhundale, A., & Rubin, C. (2006a). Disuse and low-level whole body vibrations produce broad transcriptional changes across the genome. Presented at the American Society of Bone Mineral Research. Judex, S., & Zernicke, R. (2000). High-impact exercise and growing bone: relation between high strain rates and enhanced bone formation. Journal of Applied Physiology, 88, 2183-2191.