Disc Degeneration in Military Personnel: A Systematic Review and Meta-Analysis for NASA Astronaut Preflight Imaging

Study Design: Systematic review and meta-analysis. Objective: To systematically review and meta-analyze spine magnetic resonance imaging (MRI) data from military personnel to characterize occupational risk factors for disc degeneration before spaceflight. Summary of Background Data: Approximately 60% of NASA astronauts have military backgrounds, potentially predisposing them to higher risk of spinal pathology. We evaluated data on disc degeneration in military personnel compared with an asymptomatic civilian population to estimate spinal pathology prevalence among NASA astronauts with military backgrounds. Methods: PubMed, Scopus, and Google Scholar databases were systematically queried in April 2024 using the MeSH terms: military personnel, spine, and MRI. Studies involving asymptomatic civilians from a prior systematic review served as a control population. A mixed-effects meta-analysis and linear regression were conducted to compare disc degeneration and average age between military and civilian populations. Results: There was a significant group effect, with military personnel showing higher overall prevalence of disc degeneration compared with civilians ( =0.999; 95% CI: 0.588, 1.4110; P <0.001). Age was also a significant predictor, with each additional year associated with an increase in the prevalence of disc degeneration [ =0.108; 95% CI: 0.075, 0.140; P <0.001]. Linear regression estimated that nearly all military personnel (∼100%) at the average age of first spaceflight (∼40 years old) exhibited at least one level of disc degeneration compared with ∼71% of civilians. Conclusions: Military personnel have a higher prevalence of disc degeneration compared with civilians, likely associated to their relative increased physical demands of military service. The extent of disc degeneration may even be underestimated, because our analyses included only young military personnel with a relatively short service duration. The current findings inform baseline expectations for disc degeneration in asymptomatic civilians and military personnel for more accurate interpretation of spine imaging before spaceflight. Level of Evidence: Level 3—systematic review of level 3 evidence