Sayson Jojo V, Hargens Alan R
The Ola Grimsby Institute , San Diego, CA, USA.
Aviat Space Environ Med. 2008 Apr;79(4):365-73. doi: 10.3357/asem.1994.2008.
Astronauts exposed to microgravity frequently report low back pain. This pain is described as moderate to severe in intensity. This condition warrants investigation as low back pain may hinder an astronaut's ability to perform challenging tasks by virtue of disruption of sleep and, subsequently, mental concentration. It is reported by astronauts that a "fetal tuck position" described as knees to chest position relieves back pain. It is possible that the pathogenesis of back pain in microgravity is discogenic (or mechanical) and somatic, referred from the sinuvertebral nerves due to excessive expansion of the lumbar intervertebral discs associated with reduction of gravitational compressive loads in space. The fetal tuck position may increase lumbar intervertebral disc hydrostatic pressure by flexion and transfer of spinal compressive forces toward the anterior region of the lumbar discs, subsequently reducing disc volume. Moreover, this position may reduce Type IV mechanoreceptor facilitation and nerve impulse propagation from the sinuvertebral nerves of the annulus fibrosus, and thus diminish low back pain perception. Elongated posterior soft tissues (apophyseal joint capsules and ligaments) with spinal flexion may potentially stimulate Type I and II mechanoreceptors. This neutralizes substance P in the spinal cord dorsal horn by increasing naturally occurring opioids such as enkephalins. Separately, other investigators have reported a higher incidence of herniated discs (HNP) in astronauts postflight. Further studies of countermeasures are recommended to prevent excessive spinal elongation and disc expansion, reduce low back pain in microgravity, and simulate 1-G disc homeostasis, which may also help prevent HNPs postflight.
暴露于微重力环境下的宇航员经常报告有下背痛。这种疼痛的强度被描述为中度至重度。这种情况值得研究，因为下背痛可能会因睡眠中断以及随之而来的精神注意力分散而妨碍宇航员执行具有挑战性任务的能力。宇航员报告称，一种被描述为膝盖靠近胸部的“胎儿蜷缩姿势”可以缓解背痛。微重力环境下背痛的发病机制可能是椎间盘源性（或机械性）和躯体性的，是由于腰椎间盘过度扩张以及太空引力压缩负荷降低，由窦椎神经传导所致。胎儿蜷缩姿势可能通过屈曲并将脊柱压缩力转移至腰椎间盘前部区域来增加腰椎间盘的静水压力，从而减小椎间盘体积。此外，这个姿势可能会减少IV型机械感受器的易化作用以及来自纤维环窦椎神经的神经冲动传导，进而减轻下背痛的感觉。脊柱屈曲时拉长的后部软组织（关节突关节囊和韧带）可能会刺激I型和II型机械感受器。这会通过增加内啡肽等天然存在的阿片类物质来中和脊髓背角中的P物质。另外，其他研究人员报告称，宇航员飞行后椎间盘突出症（HNP）的发病率较高。建议进一步研究应对措施，以防止脊柱过度伸长和椎间盘扩张，减轻微重力环境下的下背痛，并模拟1-G环境下的椎间盘内环境稳定，这也可能有助于预防飞行后的椎间盘突出症。
