Lower Extremity Injury Increases Risk of First-time Low Back Pain in the U.S. Army

ABSTRACTLow back pain (LBP) and lower extremity injuries (LEI) are primary reasons for lost duty days and disability among military populations.PURPOSEThis study examined acute LEI as a risk factor for developing LBP and examined the time to incident LBP between individuals with and without a history of LEI.METHODSThis retrospective cohort study examined U.S. Army medical and personnel data from the Total Army Injury and Health Outcomes Database (TAIHOD) for the years 2007-2011. Anderson-Gill Cox Regression methods were used to examine the change in LEI status over time and changes in demographic covariates. Adjusted hazard ratios (HR) for LBP following LEI were calculated from the Cox regression model for each calendar year. An accelerated failure time (AFT) model was used to describe time to LBP, and mean time to event and adjusted time ratios (TR) following LEI were calculated from the AFT model for each year. Overall HR and TR for LBP following LEI were calculated over the 5 calendar years using variance-based weighted averages.RESULTSEach yearly analysis included an average of 213,307 Soldiers; on average for each year 8.44% of Soldiers developed LBP and 11.54% had previous LEI. The pooled time ratio showed Soldiers with a LEI had a 10% decrease in mean survival times to LBP compared to those without a LEI [TR=0.901, 95%CI (0.897, 0.905)]. The weighted average HR showed that Soldiers with a LEI had 1.7 times the hazard of LBP compared to those without LEI [HR=1.70, 95%CI (1.66, 1.74)].CONCLUSIONThese findings suggest that a potential second order effect of LEI is an increased short-term risk for developing LBP, which should be considered during rehabilitation planning. Low back pain (LBP) and lower extremity injuries (LEI) are primary reasons for lost duty days and disability among military populations. PURPOSE This study examined acute LEI as a risk factor for developing LBP and examined the time to incident LBP between individuals with and without a history of LEI. METHODS This retrospective cohort study examined U.S. Army medical and personnel data from the Total Army Injury and Health Outcomes Database (TAIHOD) for the years 2007-2011. Anderson-Gill Cox Regression methods were used to examine the change in LEI status over time and changes in demographic covariates. Adjusted hazard ratios (HR) for LBP following LEI were calculated from the Cox regression model for each calendar year. An accelerated failure time (AFT) model was used to describe time to LBP, and mean time to event and adjusted time ratios (TR) following LEI were calculated from the AFT model for each year. Overall HR and TR for LBP following LEI were calculated over the 5 calendar years using variance-based weighted averages. RESULTS Each yearly analysis included an average of 213,307 Soldiers; on average for each year 8.44% of Soldiers developed LBP and 11.54% had previous LEI. The pooled time ratio showed Soldiers with a LEI had a 10% decrease in mean survival times to LBP compared to those without a LEI [TR=0.901, 95%CI (0.897, 0.905)]. The weighted average HR showed that Soldiers with a LEI had 1.7 times the hazard of LBP compared to those without LEI [HR=1.70, 95%CI (1.66, 1.74)]. CONCLUSION These findings suggest that a potential second order effect of LEI is an increased short-term risk for developing LBP, which should be considered during rehabilitation planning. Corresponding Author: Joseph F. Seay, Ph.D., Military Performance Division, United States Army Research Institute of Environmental Medicine, 10 General Greene Avenue, Building 42, Natick, MA 01760, 508.233.4888 (Phone), joseph.f.seay.civ@mail.mil The opinions or assertions contained herein are the private views of the author(s) and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. The investigators have adhered to the policies for protection of human subjects as prescribed in Army Regulation 70-25, and the research was conducted in adherence with the provisions of 32 CFR Part 219. The authors have no conflicts of interest or financial disclosures to report. Results and conclusions of the study do not constitute endorsement of the American College of Sports Medicine. Accepted for Publication: 6 December 2017 © 2017 American College of Sports Medicine

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