Neck Pain During Combat Operations:
An Epidemiological Study Analyzing
Clinical and Prognostic Factors

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

FROM:   Spine (Phila Pa 1976). 2010 (Apr 1); 35 (7): 758–763 ~ FULL TEXT

Steven P. Cohen, MD, Shruti G. Kapoor, MD, MPH, Cuong Nguyen, MD, Victoria C. Anderson-Barnes, BA, Charlie Brown, MD, Dominique Schiffer, MD, Ali Turabi, MD, and Anthony Plunkett, MD

Department of Anesthesiology,
Johns Hopkins School of Medicine,
Baltimore, MD 21029, USA.
scohen40@jhmi.edu

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STUDY DESIGN.   Prospective observational study among soldiers medically evacuated out of theaters of combat operations for neck pain, with retrospective analysis of variables associated with return-to-duty.

OBJECTIVES:   To provide an epidemiological overview of the burden of neck pain in deployed soldiers involved in combat operations and to identify factors associated with return-to-duty.

SUMMARY OF BACKGROUND DATA:   Neck pain represents one of the leading causes of medical evacuation out of theaters of combat operations. Yet when compared to other diagnostic categories, treatment outcomes, militarily defined as returning a soldier to duty, remain appallingly low.

METHODS:   Demographic, military-specific, and outcome data were prospectively collected over a 2–week period at the Deployed Warrior Medical Management Center in Germany on 374 consecutive soldiers medically evacuated out of theaters of combat operations for a primary diagnosis pertaining to neck pain between 2004 and 2007. The 2–week period represents the maximal allowable time an evacuated soldier can spend in treatment before disposition (i.e., return to theater or evacuate to United States) is rendered. Electronic medical records were reviewed to examine the effect the following variables had on the categorical outcome measure, return-to-unit: age, gender, service-affiliation, rank and seniority, smoking history, coexisting psychiatric diagnosis, prior neck pain, mechanism of injury, whether or not the injury was combat-related, presence of headache, quality of symptoms, correlation with radiologic imaging, and referral to pain specialist.

RESULTS:   Only 14% of service members returned to their units. Significant correlations were found between female gender and non-army service affiliation, and a service member returning to their unit. Weak trends toward returning to duty were noted for nonsmokers, absence of prior neck pain, concomitant psychiatric diagnosis, corresponding complaints of headache, and referral to a pain specialist.

CONCLUSION:   The treatment of service members medically evacuated for neck pain at the main receiving center, the level IV military treatment facility in Landstuhl, Germany, is associated with a low return-to-unit rate. Future studies should consider whether treating personnel predisposed towards a positive outcome with the limited resources available can improve return-to-duty rates.

Key words:   combat, military, neck pain, outcome predictor, war.

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The FULL TEXT Article

Introduction

Battle injuries have never been the major cause of soldier attrition in modern warfare. In World Wars I and II and the Korean War, respiratory and infectious illnesses represented the leading causes of morbidity and mortality. [1] But by Vietnam, the nature of warfare had begun to change such that the physical boundaries separating adversaries had blurred considerably. As tactics shifted from large-scale engagements to surgical strikes and counter-insurgency operations, the types of injuries suffered by soldiers changed in parallel. Since the Vietnam War, non-battle-related injuries have been the principal cause of unit degradation, with musculoskeletal disorders accounting for the majority of cases. [2]

Neck pain represents a significant cause of disability in the world, with the 12–month prevalence ranging between 30% and 50%. [3–5] Similar to back pain and other musculoskeletal conditions, numerous investigators have attempted to identify risk factors for the development and persistence of cervical pain. [5, 6] Predisposing factors that have been shown to predict acute neck pain episodes, and the persistence of pain include middle age, female gender, smoking, poor psychological health, poor general health, and participation in certain sports. [6] However, all of these studies have been conducted in civilian cohorts, who are subject to less physical and psychosocial stressors than in soldiers deployed to combat zones. These unique “stressors” can include wearing Kevlar and heavy rucksacks, prolonged separation from social support systems, poorly developed coping skills in younger soldiers, and a high incidence of combat stress.

In a series of epidemiological studies conducted in medically evacuated soldiers, Cohen et al determined that spinal pain represents the fifth leading cause of medical evacuation from theaters of operation, and the most common reason redeployed soldiers seek pain management services.7,8 Considering their propensity for neck injuries and the austere treatment environment, identifying soldiers at risk for poor neck pain outcomes is critical for military physicians, since the preservation of unit strength is the cornerstone of military medicine. The purpose of this study is to determine which factors are associated with return-to-unit among soldiers medically evacuated from combat areas to a fourth-level treatment facility with a primary complaint of neck pain.

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Materials and Methods

Permission to conduct this study was granted by the US Army Medical Command and the Department of Clinical Investigation at Walter Reed Army Medical Center. The lists of soldiers medically evacuated out of forward-deployed units for Operations Iraqi (OIF) and Enduring Freedom (OEF), and “other” operations between 2004, when military medical records became computerized, and 2007 were obtained from a prospective database actively maintained in Landstuhl, Germany by the Deployed Warrior Medical Management Center (DWMMC). The DWMMC was set up in November 2002 to coordinate medical evacuations from forward deployed areas overseas to Ramstein Air Base in Germany, and optimize the case management of evacuees. This database is conservatively estimated to contain identifying information on over 97% of evacuated service members. A single diagnosis for each patient included in this database corresponding to the primary reason the service member left theater was conferred by the evacuating physician, and recorded based on the International Statistical Classification of Diseases, 9th revision, clinical modification (ICD-9-CM codes).

Table 1

Thus, duplicate diagnoses are systematically excluded. Evacuated service members can usually remain in the DWMMC for up to 2 weeks before final disposition, at which time their demographic and clinical information are recorded. This study includes data on those patients with a primary diagnosis related to “neck pain” (Table 1). Other information prospectively collected in this database included age, gender, rank, date of evacuation, whether the injury was incurred during battle, deployment mission (i.e., OIF or OEF), and disposition (i.e., return-to-unit or transfer to a military treatment facility in the continental United States). The rare discrepancies between information contained in the database and a service member’s medical record were adjudicated on a case-to-case basis, usually in favor of the electronic record.

Electronic medical records were subsequently reviewed to obtain data on variables suspected of influencing return-to-duty and confirm the correct outcome. The data garnered from medical records included whether the presenting symptoms were primarily axial or radicular, corresponding MRI pathology, presence of headache, mechanism of injury, coexisting psychopathology, smoking history, treatment modality, and whether or not the soldier was treated by a pain specialist before outcome designation.

Battle- or non-battle-related injuries designation was recorded prospectively and conferred based on whether the injury occurred during a combat mission. Rank was divided into senior and junior levels based on pay grade. For enlisted personnel, senior level was designated as a noncommissioned officer in the pay grade of E5 and above (e.g., sergeant in the army or marines, and petty officer-second class in the navy). For officers, senior level was designated as a field grade or general officer (e.g., major or above in army or marines, and lieutenant commander and above in the navy).

The operation in which the injury occurred (e.g., OIF or OEF) was prospectively recorded from the DWMMC database, whose source was the soldier’s deployment orders. In addition to the principal operation in Afghanistan, OEF included subordinate missions in Kyrgyzstan, Horn of Africa, Trans-Sahara, Philippines, Europe, and Pankisi Gorge. OIF orders included not only deployments to Iraq proper, but support missions involving the Arabian Peninsula (e.g., Saudi Arabia, Kuwait, Qatar, etc.), Djibouti, Turkey, and the Republic of Georgia. The category “others” included soldiers deployed to Southeast Asia, Diego Garcia, and Eastern Europe.

The designation of neck pain as “axial” or “radicular/ myelopathic” pain was made from electronic record review based on the pain referral pattern, ancillary tests such as magnetic resonance imaging (MRI) and electromyography/nerve conduction studies, and the presence of physical examination signs and associated symptoms such as sensory or motor dysfunction. Guidelines used for diagnosing a “radicular” component included pain extending into the arm, sensory changes, neurologic motor deficits, or any combination thereof. In patients with radicular pain, corresponding MRI pathology was designated as concordant when there was a protruding or herniated disc noted on MRI that could reasonably account for the patient’s symptoms. For axial pain, MRI pathology was classified as concordant only if “moderate to severe” degenerative changes were found in spinal levels consistent with the patient’s presenting complaints. Information regarding treatment by a pain management specialist was garnered from electronic records.

Coexisting psychiatric symptoms were deemed positive when a patient was found to have a specific psychiatric diagnosis on record review that either preceded or was related to their deployment. The most frequent psychiatric diagnoses were “anxiety-related,” “depression,” and “combat stress/ posttraumatic stress disorder,” but the category included others as well (e.g., pain disorder).

      Outcome Measures and Statistical Analysis

A positive outcome was predefined as “return-to-unit in full or limited capacity,” as prospectively recorded in the DWMMC database. In rare cases (
2%) when a soldier was determined to have redeployed to their unit from a military treatment center in the United States, their outcome was changed from negative to positive.

Statistical analyses were performed using STATA 9.1 (Stata- Corp, College Station, TX). The age variable was categorized in order to achieve a normal distribution. Potential correlates to be studied were identified a priori.
2 and logistic regression analysis were used to quantify the significance of various potential predictors of outcome. As the outcome variable was binary (either positive or negative), a logistic statistical model was chosen. A P < 0.05 was considered statistically significant. Unadjusted univariate analyses were performed, followed by multivariate logistic regression. Those variables defined a priori as potential confounders (P < 0.25) were included in the multivariate logistic regression analysis.

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Results

      Demographic and Epidemiological Data

Table 2

A total of 392 subjects with an ICD-9 diagnosis pertaining to neck pain were processed in the DWMMC and evaluated, which represented 1.0% of the total evacuees. Eighteen were excluded for the following reasons: no outcome data/never reported to duty (n = 4); record review revealed the primary diagnosis to be a noncervical- related medical condition (n =13); and 1 subject was a dog, leaving 374 patients for data analysis. The demographic characteristics of these subjects are presented in Table 2. The mean age was 37.2 years (SD: 8.0; range: 18–56 years). Ninety-four percent of patients were men. Of the medically evacuated subjects 85% were in the army, with 6% being in the marines, 3% in the navy, and 5% serving in the air force. Eighty-eight percent of service members were enlisted. Thirty-eight percent were smokers, one-quarter had a concurrent psychiatric diagnosis, and 41% had a documented history of prior neck pain.

The mechanism of injury in most patients was unknown. Approximately 8% of the patients sustained injury while lifting objects, 9% attributed their pain to a fall, 10.4% were injured while driving, 2.4% cited “road marches” as their main source of injury, and 5% of injuries were related to wearing Kevlar (helmets) and carrying equipment. Few injuries (3.5%) were sustained during combat operations. Because of limited resources, only about a quarter of patients were referred to an interventional pain specialist.

      Correlates With Return-to-Duty

Table 3 Table 4

Fifty-two service members (14%) returned to their forward deployed units, 88% of whom were released without any physical limitations. Factors associated with return- to-duty are detailed in Tables 3 and 4. Females were approximately 80% more likely to return-to-duty after injury. This association was maintained even after controlling for all other covariates (P = 0.01). Marines and Air Force personnel were over 4 times more likely to return to their units compared to soldiers (P < 0.01). But analogous for females and gender analysis, only a small percentage of service members were marines or airmen.

Nonsignificant trends towards higher return-to-duty rates were seen among patients with concomitant headache (P = 0.10), those with no prior history of neck pain (P = 0.21), subjects with no psychiatric comorbidities (P =0.16), patients who were treated by a pain specialist in Germany (P = 0.15), and nonsmokers (P = 0.19 in univariate analysis). Patients with prior healthcare provider visits for neck pain and those with psychiatric comorbidities were 44% and 56% less likely, respectively, to return-to-theater based on multivariate analysis. No specific psychiatric diagnosis was more strongly associated with negative outcome than any other. Soldiers with longer service tenures, which was gauged via rank, were more than twice as likely to return to work when compared to their less senior counterparts (P = 0.25). Fifty-two percent of patients referred for pain management services received interventional treatment, which was most often interlaminar epidural steroid injections (data not shown).

Differences in conflict location were not related to return- to-duty in univariate analysis. Eighty-five percent of soldiers who developed neck pain were deployed in support of OIF, versus 15% who sustained their injury in Afghanistan. Neither age, quality of symptoms, nor MRI correlation, were found to be related to the primary outcomemeasure. The mean age of patients that returned to their workplace was 36.3 years (SD: 8.6) versus 37.2 years (SD: 7.8) for soldiers who did not return-to-theater (P > 0.3).

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Discussion

The only statistically significant predictors of outcome found in this study were being in the army, which was negatively associated with return-to-unit, and being female, which was positively correlated with a good outcome. Whereas trends for a positive correlation were noted for absence of prior history of neck pain, and coexisting psychiatric illness; treatment in a pain clinic; and presence of headache, these fell shy of statistical significance. Although this study is one of the largest epidemiological studies evaluating neck pain outcomes in any population, the results may not be generalizable to a nonmilitary cohort. The physical and psychosocial stressors servicemen deployed to a combat zone face probably far exceed that of most nonmilitary pain patients, and the potential confounding factors (e.g., secondary gain) are fundamentally different.

One of the more striking observations was the low return-to-unit rate found across the entire sample. Stratified by treatment location, the return-to-unit rate for spinal pain more closely resembles that of psychiatric illnesses than those conditions associated with more distinct findings and unambiguous pathophysiological mechanisms, such as urolithiasis, infectious disease, and battle injuries. [9, 10] Return-to-duty for spine pain and psychiatric illnesses seems to be profoundly affected by the proximity of the treatment location to the combat zone, with exponentially better outcomes noted when treatment is administered in a forward-deployed area. [7, 8, 11] For example, when combat stress symptoms are treated in forward-deployed mental health clinics, 95% of service members return to their units. When similar symptoms are treated in a combat support hospital or a transition location in Kuwait or Qatar, 75% and 50% return-to-unit rates are observed, respectively. From Landstuhl, Germany, only 10% of soldiers with combat stress return to theater. And if an evacuated service member with combat stress is treated in a military medical center within the continental United States, the likelihood of that person returning to their combat unit approaches 0%. [11]

In contrast, outcomes for conditions with more discrete pathology such as kidney stones, missile injuries, and neurologic disorders are relatively immune to the location of treatment. The parallels between neck pain and psychiatric outcomes in deployed soldiers might be due to the fact that the strongest risk factors for the development and persistence of neck pain tend to be psychosocial in nature. [12, 13] This suggests that the outcome ceiling for return-to-unit after neck pain episodes may be a function of treatment site, not treatment per se. Similar to the treatment of combat stress, the best way to improve outcomes might be to institute forward-deployed treatment. In a prospective cohort study evaluating return-to-duty rates in a forwarddeployed pain clinic, White and Cohen reported 95% positive outcomes in a cohort of servicemen whose predominant complaints were spine pain. [8]

The other principal finding in this study was that army affiliation was associated with a lower likelihood of returning to duty than that of other services. The current conflicts are often characterized by terms such as “nation building,” “conflict resolution,” “training mission,” and “boots on the ground.” In mature theaters of operation whereby a large occupational force is needed to achieve strategic goals, the brunt of the burden tends to be borne by infantry and support troops, which disproportionately affect the army. Soldiers are more likely to be injured in combat, suffer from combat stress, and face longer deployments than airmen and sailors. Their missions are also more likely to involve operations whereby wearing Kevlar helmets, and carrying heavy rucksacks are a necessity, which may predispose them to neck pain. Although the use of protective helmets for sports such as hockey and skiing is not generally associated with a higher risk of injury, protective sports gear tends to be lighter and used more sporadically than the Kevlar soldiers must wear. [14, 15] The higher return-to-duty rate for female personnel is likely attributable to several factors, including the low absolute numbers involved, and a greater relative representation in occupation specialties not associated with combat (e.g., healthcare and public relations) where they may be more able to return to work in a limited capacity.

Nonstatistically significant trends were found whereby psychiatric comorbidity, prior history of neck pain, and not being seen by a pain specialist, were negatively correlated with return-to-duty. The lack of significance for one or more of these variables may be partially due to a statistical anomaly, in that a significant impact is harder to prove for outcome measures associated with either very high or very low rates of occurrence (i.e., greater numbers of patients are required to detect a statistically significant difference). Nevertheless, in light of previous studies demonstrating that psychological comorbidities such as coexisting depression, anxiety, and somatization disorder are major risk factors for the persistence of back and neck pain, [12, 13, 16, 17] the lack of a stronger association between a psychiatric diagnosis and outcome is somewhat unexpected. However, the military has a very masculine identity, and visits to mental healthcare professionals may be misconstrued as a sign of “weakness,” or carrying the potential to negatively impact career advancement. Consequently, the true relationship between spinal pain outcome and coexisting psychopathology may not be accurately reflected here.

A weak association was found between a history of previous neck pain and not returning to theater. This is consistent with previous studies demonstrating prior neck pain episodes to be associated with future episodes,18 and the observation that previous back and other pain complaints are strong predictors for missed workdays from back pain.19 The correlation between treatment by a pain specialist and a positive outcome is not surprising, given that many causes of cervical pain such as radiculopathy and facet joint pathology are amenable to rapid resolution with simple interventions. [20, 21] Eighty-four percent of soldiers in this study were identified as having a radicular component to their pain, which is higher than prospective prevalence studies for both chronic cervical and low back pain. [22, 23] Since categorization was done retrospectively based on loose guidelines and often erratic medical records, it is likely that the true incidence of neuropathic pain in this population is somewhat lower. Although one might conjecture that treatment closer to a combat zone would result in even higher return-to-unit rates, this inference needs to be scientifically examined.

There are several shortcomings to this study that need to be examined in order to put the results in context. First, these results were obtained in a very select group of individuals faced with unique circumstances. Hence, generalizing them to civilians, nondeployed soldiers, or even deployed soldiers treated in different environments should be done with caution. Second, whereas outcomes and diagnoses were recorded prospectively, no specific set of inclusion and exclusion criteria were used. Thus, this was essentially a heterogeneous population who may have had secondary diagnoses that affected outcome. Third, since only one diagnosis is annotated in the database, the figures presented here may under-represent the burden of neck pain during wartime. Finally, since amajority of the clinical variables were examined post hoc, the potential flaws must include those inherent in any retrospective analysis.

In summary, the treatment of medically evacuated soldiers with neck pain at a level III military treatment facility is associated with low return-to-unit rates. Weak associations with a positive outcome were observed for female gender and non-army service affiliation. However, because of the unique circumstances faced by deployed service members and the nature of this study, these results should be interpreted with caution and may not be applicable to other populations with neck pain. Future studies should focus on whether the identification and early treatment of vulnerable personnel can improve return-to-duty rates, and if forward-deployed pain management capabilities enhance overall success rates.

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Key Points

• Neck pain is one of the leading causes of medical evacuation from
  theaters of combat operations.

• Three hundred seventy-four soldiers were identified who were medically
  evacuated out of Operations Iraqi and Enduring Freedom for neck pain,
  representing 1% of the total evacuees.

• Only 14% of soldiers returned to their units.

• The only factors associated with a positive outcome
  (i.e., return-to-unit) were female gender and non-army affiliation.

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