The effect of spaceflight on tissues of the spinal column

The unique mechanical unloading induced by spaceflight is associated with a very high incidence rate of chronic back pain and general degradation of tissues associated with the spinal column (i.e., bone, skeletal muscle, intervertebral disc, and cartilage). Despite the well documented phenomena of spinal damage following microgravity conditions, there is not a clear timeline of the pathways that leads to bulk tissue damage and back pain. This is both due to the majority of work in the field focusing on assessing the impact of microgravity on a single component or tissue, as well as in doing so at a narrow scale (e.g., genetic, cellular, morphologic, etc.). This review paper surveyed the literature to assemble a multiscale timeline for the pathway of degeneration due to mechanical unloading for key tissues of the spinal column. In doing so, we aim to clarify the cascading, multiscale, degenerative pathway caused by spaceflight conditions that manifest into bulk tissue atrophy and pain. This work also covers potential avenues of investigation to mitigate the deleterious effects of prolonged mechanical unloading on the spine.