Astronauts exposed to microgravity for extended periods have incurred damage to their musculoskeletal systems. There is concern that the changes observed may lead to reduced performance and an increased risk of injury, including fractures, when dynamic loads are experienced. This experiment is a flight definition investigation in which the investigators hypothesize that crewmembers exposed to long-duration microgravity will exhibit profound degradation in cervical, thoracic, and lumbar vertebrae and spinal musculature. It is further hypothesized that spaceflight-induced changes to crewmember vertebrae and spinal musculature will result in reduced vertebral strength and increased fracture risk from dynamic loading.
The central objective of this investigation is to quantify the dynamic strength changes in the cervical, thoracic, and lumbar vertebrae incurred following long-duration microgravity exposure. Specific objectives are to:
APPROACH:
In this study, a unique engineering approach will be used for determining musculoskeletal strength and injury risk under dynamic loading conditions. Quantitative computed tomography (qCT) scans will be used to measure bone morphology, vBMD, and cortical thickness of the spine. Magnetic resonance imaging (MRI) will be used to measure the volume of spinal musculature. Results derived from pre- and postflight scans will be integrated and applied in dynamic simulations.
Subjects for this study will be ISS crewmembers who have previously flown as well as nine crewmembers who have yet to fly.
Retrospective data will include pre- and postflight qCT scans and MRI scans archived with NASA’s Life Sciences Data Archive. The lumbar spine (L1 and L2) were the focus of the qCT scans. MRIs focused on the cervical and lumbar areas.
Data collection from prospective subjects is planned to occur once preflight between L-180 and L-45 days and once postflight between R+0 and R+14 days. Each data collection will include a qCT scan of the C3, T3, and L1 vertebrae. Each data collection will also include MRI scans of the cervical, thoracic, and lumbar spine regions. qCT scanning and MRI scanning need not occur on the same day, but must occur within 30 days of each other. There will be no inflight data collection.
Tissue degradation will be measured from retrospective and prospective qCT and MRI pre- and postflight scans. Image segmentation, registration, cortical thickness, and vBMD analysis techniques will be applied to quantify morphological and material property changes that occur in the vertebrae (cervical, thoracic, and lumbar) and spinal musculature when exposed to long-duration microgravity.
Geometric, volumetric, cortical thickness, and vBMD data will be used to morph and scale a finite element (FE) HBM to represent the pre- versus postflight spinal anatomy of individual crewmembers. Dynamic loads representing launch, pad or launch abort, and landing will be simulated with each altered HBM to assess individual and group strength decrement and injury risk with stress, strain, force, moment, and acceleration-based metrics.
RESULTS:
This investigation is in progress and results are not yet available. However, this study is expected to provide a greater understanding of spaceflight-induced bone and muscle degradation of the vertebral column and the resulting risk of vertebral fracture. Knowledge gained will inform the development and evaluation of countermeasures to prevent or reduce the effects of microgravity.