Dose of Exercise Therapy Among Active Duty Soldiers With Chronic Pain Is Associated With Lower Risk of Long-Term Adverse Outcomes After Linking to the Veterans Health Administration
Authors: Meerwijk Esther L , Sayko Adams Rachel , Larson Mary Jo , Highland Krista B , Harris Alex H S 
Published: March 2022

ABSTRACT

Introduction
Research in soldiers who had been deployed to Iraq or Afghanistan suggests that nonpharmacological treatments may be protective against adverse outcomes. However, the degree to which exercise therapy received in the U.S. Military Health System (MHS) among soldiers with chronic pain is associated with adverse outcomes after soldiers transition to the Veterans Health Administration (VHA) is unclear. The objective of this study was to determine if exercise therapy received in the MHS among soldiers with chronic pain is associated with long-term adverse outcomes after military separation and enrollment into the VHA and whether this association is moderated by prescription opioid use before starting exercise therapy.

Materials and Methods
We conducted a longitudinal cohort study of electronic medical records of active duty Army soldiers with documented chronic pain after an index deployment to Iraq or Afghanistan (years 2008-2014) who subsequently enrolled in the VHA (N = 93,967). Coarsened exact matching matched 37,310 soldiers who received exercise therapy and 28,947 soldiers who did not receive exercise therapy in the MHS. Weighted multivariable Cox proportional hazard models tested for differences in adverse outcomes between groups with different exercise therapy exposure vs. no exercise therapy.
Exercise therapy was identified by procedure codes on ambulatory records in the MHS and expressed as the number of exercise therapy visits in 1 year after the first diagnosis with a chronic pain condition. The number of visits was then stratified into seven dose groups.
The primary outcomes were weighted proportional hazards for: (1) alcohol and drug disorders, (2) suicide ideation, (3) intentional self-injury, and (4) all-cause mortality. Outcomes were determined based on ICD-9 and ICD-10 diagnoses recorded in VHA healthcare records from enrollment till September 30, 2020.

Results
Our main analysis indicated significantly lower hazard ratios (HRs) for all adverse outcomes except intentional self-injury, for soldiers with at least eight visits for exercise therapy, compared to soldiers who received no exercise therapy. In the proportional hazard model for any adverse outcome, the HR was 0.91 (95% CI 0.84-0.99) for soldiers with eight or nine exercise therapy visits and 0.91 (95% CI 0.86-0.96) for soldiers with more than nine visits. Significant exercise therapy × prior opioid prescription interactions were observed. In the group that was prescribed opioids before starting exercise therapy, significantly lower HRs were observed for soldiers with more than nine exercise therapy visits, compared to soldiers who received no exercise therapy, for alcohol and drug disorders (HR = 0.85, 95% CI 0.77-0.92), suicide ideation (HR = 0.77, 95% CI 0.66-0.91), and for self-injury (HR = 0.58, 95% CI 0.41-0.83).

Conclusions
Exercise therapy should be considered in the multimodal treatment of chronic pain, especially when pain is being managed with opioids, as it may lower the risk of serious adverse outcomes associated with chronic pain and opioid use. Our findings may generalize only to those active duty soldiers with chronic pain who enroll into VHA after separating from the military.