Background

The post-9/11 U.S. military conflicts in Iraq and Afghanistan lasted over a decade and yielded the most combat casualties since the Vietnam War.¹ While patient survivability increased to the high­est level in history, a changing epidemiology of combat injuries emerged whereby focus shifted to addressing an array of long-term sequelae, including physical, psychologi­cal, and neurological issues.^2,3 The long-term effects of combat injury can adversely impact well-being and exact a significant burden on the health care system.^4–6
Physical pain is common among mili­tary personnel returning from deployment, particularly those injured in combat,^7–9 and is associated with detrimental effects such as medical discharge¹⁰ and sub­stance use disorders.¹¹ Pain has also been linked to post-traumatic stress disorder (PTSD), which is common in veterans of the Iraq and Afghanistan conflicts.¹² The mutual maintenance model posits that PTSD symptoms may exacerbate chronic pain and, in turn, pain may contribute to or enhance existing PTSD symptoms.¹³ PTSD is associated with negative outcomes among veterans with chronic pain, includ­ing disability, decreased functioning, and sleep disturbances,¹⁴ making the study of pain and PTSD essential for improved patient care and rehabilitation. 
Previous research on the co-occur­rence of pain and PTSD in wounded ser­vice members has been limited by small sample sizes, specific injuries, or short follow-up periods.^15–17 The present study adds to the existing literature by examin­ing the association between pain and PTSD screening outcomes nearly a decade after combat injury among a large, national sam­ple of service members and veterans who were injured during deployment and expe­rienced a wide range of injuries.

Methods

Data were collected from the Wounded Warrior Recovery Project (WWRP).⁴ Par­ticipants are identified from the Expedition­ary Medical Encounter Database (EMED), a deployment health repository maintained by the Naval Health Research Center that includes clinical records of service mem­bers injured in overseas contingency oper­ations since 2001.¹⁸ Individuals whose data are in the EMED are approached via postal mail and email to provide informed con­sent for participation in the WWRP and to complete biannual assessments of patient-reported outcomes for 15 years. Enrollment is conducted on a rolling basis, and data collection is ongoing. 

The present study utilized cross-sec­tional data from the seventh wave of the WWRP (i.e., 36 months post-baseline survey), when participants were asked to report on their pain during the past 6 months using the Chronic Pain Grading Scale.¹⁹ The measure was introduced into the WWRP in 2015 and was asked of all participants only at the seventh wave. Stan­dardized scoring procedures were used to calculate (1) pain intensity (a composite variable derived from current pain, worst pain in the past 6 months, and average pain in the past 6 months), (2) frequency of pain interference (number of days in the past 6 months that the respondent has been kept from their usual activities such as work, school, or housework because of pain), and (3) level of pain interference (a composite variable of how much pain has interfered with daily activities; recreational, social, and family activities; and ability to work, including housework).
PTSD screening status was measured using the PTSD Checklist–Civilian ver­sion (PCL-C) and PTSD Checklist for the DSM-5 (PCL-5). Both versions of the PCL are comparable in military personnel and veterans.²⁰ WWRP measures and proce­dures were updated in late 2018 to remain consistent with current standards of mea­surement of PTSD symptoms. Scores were summed for each PCL-related measure. Standard cutoffs of 44 and 33 indicated positive screens for PTSD using the PCL-C and PCL-5, respectively.^21,22 

Data from 2,649 combat-injured ser­vice members and veterans who partici­pated in the WWRP between 1 December 2015 and 30 September 2021 were included in the analysis. Injury date, Injury Sever­ity Scores (ISS), and demographics were obtained from the EMED. The ISS is a scor­ing system that accounts for multiple inju­ries in a patient and provides an overall measure of injury severity that ranges from 0 (no injury) to 75 (fatal injury). ISS was categorized as mild (1–3), moderate (4–8), and serious/severe (ISS 9+). Indepen­dent sample t-tests were used to examine mean differences in pain variables by PTSD screening status. An alpha level of .05 was considered statistically significant. Analy­ses were performed using SPSS Statistics, version 25 (IBM Corp., Armonk, NY).

Results

Participants were mostly enlisted, non-Hispanic White males in the Army (Table). At the time of the WWRP assess­ment, mean age was 37.2 years (standard deviation [SD]=7.6) and average time since injury was 9.4 years (SD=3.7). A majority of participants (86.9%) were injured in a blast and over one-half (54.1%) sustained mild injuries overall. Injury severity was not associated with PTSD screening sta­tus (p=.212). Participants who screened positive for PTSD had higher average pain intensity (60.6 vs. 37.5, p<.001, d=1.10), days of pain interference (42.7 vs. 9.8, p<.001, d=0.80), and level of pain interfer­ence (50.7 vs. 20.3, p<.001, d=1.29) than those who screened negative.

Editorial Comment

This study describes a significant association between PTSD screening out­comes and pain following combat injury. These results are consistent with previous literature and reaffirm that psychological and physical health issues can overlap and potentially complicate patient manage­ment.³ In a report by Shipherd et al.,23 66% of veterans who sought treatment for PTSD had comorbid chronic pain. Another study found that diagnosis of PTSD yielded 5 times greater odds of persistent pain com­plaints,²⁴ and other research suggests a link between greater pain severity after combat injury and PTSD risk.²⁵ Further, the poly­trauma clinical triad (co-occurrence of concussion, pain, and PTSD) was found in 42% of military polytrauma patients.⁸ Sharp and Harvey¹³ highlighted several possible pathways whereby pain and PTSD could be mutually maintaining, including pain acting as a reminder of the trauma, reduced activity levels, and increased pain perception due to elevated anxiety. Nota­bly, injury severity in the present study was not associated with PTSD screening sta­tus. This finding is consistent with previ­ous research¹⁷ and can be explained by ISS being a measure of mortality risk, which may not be directly related to other out­comes, such as mental health. Future stud­ies are needed to elucidate the etiological pathways of comorbid pain and PTSD after combat injury. Because pain and PTSD can co-occur many years after injury, the early recog­nition and identification of these condi­tions in primary care settings and through periodical health assessments may be important to refine clinical practice and, ultimately, improve the overall public health of the military.

Furthermore, the use of multidisciplinary health care teams should be examined and considered for use in future military conflicts to address co-occurring physical and psychological issues, which negatively impact long-term quality of life.³ A similar model was suc­cessfully employed to increase return-to-duty rates following concussion and could be adapted to address other injuries.²⁶ Such interventions should be considered for veterans in long-term care and also during the early phase following combat injury, as recent research demonstrated that symptom complaints in the initial year post-injury predicted mental and physical health years later.²⁷ 

This analysis has several limitations that should be considered when interpret­ing the results. A key limitation is due to the cross-sectional design of this study; because PTSD and pain were measured at a single point in time, their temporal­ity could not be assessed. Elucidating this relationship could be useful in developing targeted intervention and treatment strat­egies. Further, measures were obtained on average 9 years after injury, and other factors unaccounted for in the present study (e.g., depression, sleep problems, concussion) may influence the relation­ship between pain and PTSD. Additional research is needed to examine this relation­ship over time and include an assessment of confounders. Nevertheless, the findings suggest that pain is associated with PTSD years after injury and could inform medi­cal providers involved in the treatment and rehabilitation of military personnel after combat injury.

Author Affiliations

Naval Health Research Center, San Diego, CA (Dr. Mac­Gregor, Dr. Jurick, Dr. McCabe, Dr. Harb­ertson, Ms. Dougherty, and Mr. Galarneau); Leidos, Inc., San Diego, CA (Dr. Jurick, Dr. McCabe, Dr. Harbertson, Ms. Dougherty); Axiom Resource Management, Inc., San Diego, CA (Dr. MacGregor).

Disclaimer

The authors are military service members or employees of the U.S. Government. This work was prepared as part of their official duties. Title 17, U.S.C. §105 provides that copyright protection under this title is not available for any work of the U.S. Government. Title 17, U.S.C. §101 defines a U.S. Government work as work prepared by a military service member or employee of the U.S. Government as part of that per­son’s official duties. Report No. 22-19 was supported by the U.S. Navy Bureau of Medi­cine and Surgery under work unit no. 60808. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Depart­ment of the Navy, Department of Defense, nor the U.S. Government. The study protocol was approved by the Naval Health Research Center Institutional Review Board in com­pliance with all applicable Federal regula­tions governing the protection of human subjects. Research data were derived from an approved Naval Health Research Center Institutional Review Board protocol, number NHRC.2009.0014.

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