Use of Quantitative Computed Tomography to Assess for Clinically-relevant Skeletal Effects of Prolonged Spaceflight on Astronaut Hips

ABSTRACT Introduction In 2010, experts in osteoporosis and bone densitometry were convened by the Space Life Sciences Directorate at NASA Johnson Space Center to identify a skeletal outcome in astronauts after spaceflight that would require a clinical response to address fracture risk. After reviewing astronaut data, experts expressed concern over discordant patterns in loss and recovery of bone mineral density (BMD) after spaceflight as monitored by dual-energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT). The pilot study described herein demonstrates the use of QCT to evaluate absence of recovery in hip trabecular BMD by QCT as an indicator of a clinically actionable response. Methodology QCT and DXA scans of both hips were performed on 10 astronauts: once preflight and twice postflight about 1 week and 1 year after return. If trabecular BMD had not returned to baseline (i.e., within QCT measurement error) in one or both hips 1 yr after flightt, then another QCT hip scan was obtained at 2 years after flight. Results Areal BMD by DXA recovered in 9 of 10 astronauts at 1 year postflight while incomplete recovery of trabecular BMD by QCT was evident in 5 of 10 astronauts and persisted in 4 of the 5 astronauts 2 years postflight. Conclusion As an adjunct to DXA, QCT is needed to detect changes to hip trabecular BMD after spaceflight and to confirm complete recovery. Incomplete recovery at 2 years should trigger the need for further evaluation and possible intervention to mitigate premature fragility and fractures in astronauts following long-duration spaceflight.