Risk of intervertebral disc damage after prolonged space flight.

BACKGROUND: Back pain and intervertbral disc (IVD) damage are common problems experienced by astronauts. We hypothesize this is from paraspinal muscle deconditioning, ∼5 cm body lengthening from spinal swelling and straightening, and biochemical tissue changes.

OBJECTIVE: Examine morphological changes in the lumbar spine induced by spaceflight.

DESIGN: Prospective, case series clinical study.

SETTING: We studied crewmembers from the National Aeronautics and Space Administration (NASA).

PARTICIPANTS: Recruitment from International Space Station NASA/European Space Agency/Canadian Space Agency crewmembers, starting 2011. We enrolled 8 NASA crewmembers. One crewmember completed the study. The others are in various stages of testing.

RISK FACTORS ASSESSMENT: Crew members were studied before and after a ∼180 day mission in the International Space Station.

MAIN OUTCOME MEASUREMENTS: In pre-flight and post-flight studies of the lumbar spine, evaluate: 1) degenerative changes using MRI, 2) compressibility using an upright MRI backpack loading protocol, 3) spinal kinematics with X-ray videography, 4) visual analog scale pain.

RESULTS: Comparing pre-flight and post- flight data, there were 1) increased lumbar IVD heights in the supine position, 2) increased lumbar IVD compressibility in the upright position, 3) decreased flexibility, and 4) increased low back pain post-flight. Figure 1Spinal kinematics (angles in degrees) during flexion/extension. Pre-flight degenerate disks had less motion. Post-flight, all disks had less motion.

CONCLUSIONS: The data support the idea that decreased gravitational forces on the IVDs, during prolonged microgravity, increases their water content but decreases proteoglycan. This increases disk degeneration risk on Earth. We have a sample size of one for complete Pre- and Post-Flight testing. It's difficult to make conclusions with this preliminary data. However, the acquired images are very high quality and provide confidence for future tests. The next crewmember returns to Earth for final testing November, 2013. Testing of 4 crewmembers and ongoing recruitment are underway.