Disc herniations in astronauts: What causes them, and what does it tell us about herniation on earth?

Abstract

Purpose Recent work showed an increased risk of cervical and lumbar intervertebral disc (IVD) herniations in astronauts. The European Space Agency asked the authors to advise on the underlying pathophysiology of this increased risk, to identify predisposing factors and possible interventions and to suggest research priorities. Methods The authors performed a narrative literature review of the possible mechanisms, and conducted a survey within the team to prioritize research and prevention approaches.Results and conclusions Based on literature review the most likely cause for lumbar IVD herniations was concluded to be swelling of the IVD in the unloaded condition during spaceflight. For the cervical IVDs, the knowledge base is too limited to postulate a likely mechanism or recommend approaches for prevention. Basic research on the impact of (un)loading on the cervical IVD and translational research is needed. The highest priority prevention approach for the lumbar spine was post-flight care avoiding activities involving spinal flexion, followed by passive

Systematic review of countermeasures to minimise physiological changes and risk of injury to the lumbopelvic area following long-term microgravity

“…Prolonged and maintained increased spinal length may be particularly relevant to injury and pain risk, having been linked to disc degeneration through interuption of the diurnal cycle of disc compression and expansion [4]. A diurnal disc cycle is needed for normal fluid and nutrition turnover observed during typical terrestrial sleep-wake/loading-unloading cycles, which become disrupted in bed-rest and spaceflight [4,8,9]. Decreased lordosis angle may also be a key outcome, as prolonged periods of flexed lumbar postures have been linked to tissue creep changes in disc and posterior spinal ligaments and disc prolapse on subsequent axial loading [42].…”

“…Belavy et al [9] argued that the increased lumbar intervertebral disc herniation risk in astronauts was most likely caused by long term disc tissue deconditioning which results from swelling of the discs due to unloading during spaceflight.…”

The role of physiotherapy in the European Space Agency strategy for preparation and reconditioning of astronauts before and after long duration space flight

“…In the spine, primarily lumbar, intervertebral discs absorb more water (hyperhydration) than on Earth (Belavy et al 2016), which can be associated with low back pain (LBP) inflight but is short-lived and has been reported in 70% of astronauts without a history of LBP and 100% of those with a history of LBP (Pool-Goodzwaard et al 2015). The effects of microgravity on the intervertebral disc must be considered to allow safe re-loading of the spine postflight, as the astronaut must readapt abruptly to gravity on return to Earth.…”

Postflight reconditioning for European Astronauts – A case report of recovery after six months in space

“…Reductions of muscle strength and stability are associated with lower physical performance capacity and have a number of health implications [1,5]. There are alterations in muscle activity, proprioception and posture [5], disc hyperhydration associated with fluid shifts [6] and cardiovascular changes [7]. This is not a "sick" but an "adapted" status, which may negatively affect physical performance and capacity, especially on return into Earth's gravity.…”