Study of astronauts reveals new clues for low back pain mechanisms

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An astronaut outside the International Space StationWinner of the 2017 Outstanding Paper Award for Medical/Interventional Science at the 2017 North American Spine Society (NASS) annual meeting (25–28 October, Orlando, USA), new research into astronauts returning from the International Space Station (ISS) is likely to have implications on Earth for the role of muscular stability in chronic low back pain and disc injuries.

The consequences of prolonged space flight on astronauts’ backs has been well studied, with time in microgravity environments causing increased height, low back pain and increased risk of disc herniation upon their return to Earth. The mechanisms for these effects remain unclear, though it is thought to be related to the swelling of intervertebral discs with fluid, making them more vulnerable to herniation.

Now, researchers from the University of California (San Fran­cisco, USA) and the Ola Grimsby Institute (Bellevue, USA) have used MRI and fluoroscopy imaging of astronauts who have spent at least six months in space to conclude that the likely mechanism is multifidus atrophy, rather than disc swelling.

The discovery of changes in the multifidus functional cross-sectional area (FCSA) in all six astronaut subjects may have important implications for deconditioned spines in patients on Earth.

Volunteer astronauts from the National Aeronautics and Space Administration (NASA) who spent six-month missions aboard the ISS received 3T magnetic resonance imaging (MRI) and fluoroscopy imaging 30 days pre-spaceflight and then again after their return from space.

Five of the six astronaut patients experienced an average 20% decrease for FCSA and 8–9% for cross-sectional area (CSA) in both multifidus and erector spinea, and in all subjects, multifidus FCSA “strongly correlated” with changes in lordosis (p=0.008) and active flexion-extension range of motion (p=0.007).

The authors, led by Jeannie F. Bailey (Orthopaedic Surgery, University of California, San Francisco, USA), also observed that “whilst multifidus-associated changes in lordosis and range of motion were present amongst all subjects, only those with severe, preflight endplate irregularities (two of six subjects) had postflight lumbar symptoms (including low back pain or disc herniation).”

The authors anticipate that their results will “inform new astronaut countermeasures” in preventing low back pain and lowering disc herniation risk upon their return to the gravity of Earth by targeting the multifidus muscles in maintaining in-flight spine health.

The paper, “From the International Space Station to the Clinic: How Prolonged Unloading May Disrupt Lumbar Stability”, was presented at the NASS 32nd annual meeting in Orlando, USA, on Thursday 28 October.

 

This article was originally published in issue 45 of Spinal News International

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