NASA Human Research Program Investigators' Workshop (2012)
4002.pdf
Mechanism of Post-Flight Herniation of Intervertebral Discs
AR Hargens1, SB Chiang2, JV Sayson1, SE Parazynski2, DG Chang1, SR Garfin1
and JC Lotz3
1
Department of Orthopaedic Surgery, UC-San Diego and San Francisco, CA 92103-8894 and
3
Methodist Hospital Research Institute, Houston, TX 77030, USA ahargens@ucsd.edu
During spaceflight many astronauts experience moderate to severe lumbar pain and
deconditioning of the spinal musculature. There is also a significant incidence of herniated
intervertebral disc (IVD) in astronauts after return to Earth. Relief of in-flight lumbar back pain
is facilitated by a knee-to-chest position. The pathogenesis of lumbar back pain during
spaceflight is most likely discogenic due to supra-physiologic swelling of the lumbar IVDs from
removal of gravitational compressive loads in microgravity. The knee-to-chest position may
reduce lumbar back pain by redistributing stresses by compressive loading of the IVDs, thus
reducing disc volume by fluid transfer across IVD endplates and into the circulation of the
vertebral body. IVD stress redistribution may reduce Type IV mechanoreceptor nerve-impulse
propagation in the annulus fibrosus and vertebral endplate, thus reducing centrally-mediated pain
during spinal flexion. Countermeasures for lumbar back pain may include in-flight use of axial
compression to prevent excessive IVD expansion and spinal column elongation, and exercises
with low-load repetitive spine rotations to provide Earth-like annular stress. The overall
objective of these countermeasures is to promote IVD health and to prevent degenerative
changes that may lead to herniated IVDs post-flight. Our investigation is a response to “NASA’s
Critical Path Roadmap Risks and Questions” regarding IVD injury and higher incidence of
herniated IVDs after space flight. Planned studies will incorporate pre- and post-flight imaging,
functional testing, pain questionnaires of International Space Station crew members to ascertain
mechanisms of lumbar back pain as well as degeneration and injury to spinal structures.
Quantitative results for morphological, biochemical, metabolic, and kinematic spinal changes in
the spine may optimize rehabilitation and aid development of countermeasures to reduce lumbar
back pain in microgravity and reduce the incidence of herniated IVDs post-flight.
Supported by NASA grant NNX10AM18G.