Microgravity-Induced Back Pain and Intervertebral Disc Herniation: International Space Station Results

摘要

There are yet unresolved spinal changes during and after microgravity exposure. Crewmembers frequently report moderate to severe back pain in space and upon return to Earth a high incidence of intervertebral disc (IVD) herniations within regions of the cervical and lumbar spines. In response to NASA's Critical Path Roadmap Risks and Questions regarding disc injury and higher incidence of HNPs after space flight (IRP Gap-B4), we are performing state-of-the art imaging analyses of crewmembers to investigate the mechanisms of in-flight back pain and IVD herniations post-flight. Twelve International Space Station crewmembers are approved for participation in this study. To date, six crew members have consented to our protocol and five have completed all pre-flight and post-flight testing. Crewmembers complete a battery of six tests before and after a 6 month mission to determine how the discs and other spinal structures change and whether anatomical alterations correlate with reported back pain. Pre-flight and post-flight baseline data are derived from six tests: 1. Supine MRI lumbar and cervical spines (morphology/water content), 2. MR Spectroscopy (IVD metabolites), 3. Upright MRI (axial load with 10% bodyweight), 4. Spinal Kinematics with the KineGraph Vertebral Motion Analyzer (lumbar spine stiffness and stability), 5. Biering-Sorensen test (isometric endurance strength test of the back muscles), and 6. Back pain and disability questionnaires. Comparative analyses of post-flight to pre-flight data indicate: 1) Variable water content changes variable in lumbar and cervical IVD heights observed in supine MRI scans, 2) increased axial compressibility of lumbar IVDs during upright MRI scans, 3) increased lumbar bending stiffness using Spinal Kinematics tests, 4) Paraspinal muscle atrophy from MRI, 4) Decreased isometric endurance of the back extensors, and 5) Increased low back pain scores post-flight. Countermeasures development for lumbar back pain on future spaceflights may include in-flight use of an axial compression device or spine compression maneuvers to prevent spinal straightening and stiffening, and exercises to provide Earth-like biomechanical stress with low-load, repetitive spine rotations. Crewmembers reported that a knee-to-chest position relieves in-flight lumbar back. This manual compressive loading of the IVDs may counteract increase fluid transfer across IVD endplates and back into the vertebral body circulation. This project will define spine maladaptive effects from prolonged spaceflight that will help develop countermeasures and perhaps reduce pain and dysfunction in order to enhance astronauts' performance of complex mission tasks. Supported by NASA grants NNX10AM18G and NNX13AM89G.