QCT images have been used successfully to demonstrate negative effects of spaceflight on bone density and strength of the proximal femur. However, a similar examination of the effects of spaceflight on vertebral strength has not been performed, despite reports of significant trabecular bone loss in the spine in long-duration astronauts. Moreover, no prior studies have examined whether spinal loading, a key aspect of vertebral fracture risk, is affected by long duration spaceflight. Thus the degree of spinal deconditioning and subsequent risk of vertebral fracture following long-duration spaceflight remains unknown.
Our central objective is to address the gap in knowledge regarding effects of spaceflight on vertebral bone strength and spine fracture risk by assessing changes in volumetric bone density and strength of lumbar vertebrae using previously collected QCT scans from long duration ISS crewmembers. In addition, since bone fractures occur when the forces applied to the bone exceed its strength, we will also estimate the risk of spine fracture by computing a load-to-strength ratio in each astronaut for different activities of daily living. Vertebral strength will be measured using an FDA-approved method that employs finite element analyses of QCT scans, and has been validated against in vitro bone strength testing as well as in large, population-based studies of spine fracture. We will estimate loads applied to the spine using a musculoskeletal model of the lumbar and thoracic spine that can be adjusted to reflect the astronaut’s height, weight, spinal shape and specific trunk muscle anatomy — all factors that are important contributors to spinal loading.
This work is funded by NIH-NIAMS RC1-AR058389.