PREDICTORS OF SHORT-TERM WORK-RELATED DISABILITY AMONG ACTIVE DUTY US NAVY PERSONNEL: A COHORT STUDY IN PATIENTS WITH ACUTE AND SUBACUTE LOW BACK PAIN
 
   

Predictors of Short-term Work-related Disability Among Active Duty
US Navy Personnel: A Cohort Study in Patients with
Acute and Subacute Low Back Pain

This section is compiled by Frank M. Painter, D.C.
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   Frankp@chiro.org
 
   

FROM:   Spine J. 2012 (Sep);   12 (9):   806–816 ~ FULL TEXT

Carol Cancelliere, Deborah Sutton, Pierre Côté, Simon D. French, Anne Taylor-Vaisey & Silvano A. Mior

Occupational and Industrial Orthopedics Center (OIOC),
Department of Orthopedics, NYU Hospital for Joint Diseases,
NYU Langone Medical Center,
New York, NY 10014, USA.
rudi.hiebert@nyumc.org


BACKGROUND CONTEXT:   Musculoskeletal disorders of the spine in the US military account for the single largest proportion of the absence of sickness causes leading to early termination. We explored if selected psychological and physical factors were associated with poor outcome after episodes of low back pain (LBP).

PURPOSE:   To identify clinical, demographic, and psychological factors predictive of work duty status after a complaint of LBP.

STUDY DESIGN:   A prospective clinical cohort of US Navy personnel treated for LBP.

PATIENT SAMPLE:   Eligible cases were active duty US Navy or Marine Corps personnel presenting to an emergency clinic or primary care clinic with a complaint of LBP, where the index episode of LBP was no more than 12 weeks duration before enrollment.

OUTCOME MEASURES:   The subject's work status (full duty, light duty, sick in quarters [SIQ], limited duty, or medically released to full duty) was abstracted from the subject's electronic medical record at approximately 4 weeks and then again 12 weeks after study enrollment. Work status in this study population is assigned by a Navy health-care provider at the time of a clinical visit and based on the health-care provider's determination of medical fitness for duty. This study collapsed work status into two groups, "full duty" (consisting of "full duty" and "medically released to full duty") and "not at full duty" (consisting of "light duty," "SIQ," and "limited duty").

METHODS:   Volunteers completed a baseline questionnaire consisting of recommended well-validated measures, including attitudes and beliefs about LBP and work (Fear-Avoidance Beliefs Questionnaire [FABQ] and the Tampa Scale of Kinesiophobia), distress (the Pain Catastrophizing Scale), clinical depression (The Center for Epidemiologic Studies Depression scale), a numeric pain intensity scale, self-perceived disability (Oswestry Disability Index), and general health status (12-Item Short Form Health Survey). Navy health-care providers conducted a back pain-specific medical evaluation. Associations are expressed as multivariate-adjusted prevalence ratios (PRs) estimated using Poisson regression.

RESULTS:   Two hundred fifty-three participants were enrolled. Work status outcome was collected for 239 participants. Predictors of "not at full duty" at 4 weeks after enrollment included having back pain for 4 weeks or less before study enrollment (PR, 2.69; 95% CI, 1.21-5.97) and increased FABQ Work subscale score (PR, 1.05; 95% CI, 1.01-1.08). The sole predictor of work status at 12 weeks after enrollment was increased FABQ Physical Activity (FABQ Physical) subscale score (PR=1.14; 95% CI, 1.00-1.30).

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CONCLUSION:   The findings that fear-avoidance beliefs were predictive of subsequent work status among active duty service personnel in this study population (after adjusting for clinical, demographic, and psychological covariates) suggest the clinical utility of addressing these factors during treatment of back pain episodes in the military. These findings reflect the important role that psychological factors may play in the return to work process in an active duty military population.

KEYWORDS:   Low back pain; Disability; Cohort; Psychosocial; Military personnel



From the FULL TEXT :

Introduction

There is ongoing interest in identifying predictors of outcome for episodes of work-disabling low back pain (LBP). Psychological factors have shown consistent independent associations with poor outcome. [1–6] Assessment of psychological and psychosocial risk factors early in a treatment episode may result in health-care providers addressing these factors during the course of treatment and possibly result in decreased risk of chronicity. Assessment of psychosocial and psychological risk factors is consistent with recommendations from best evidence clinical practice guidelines. [7] This study evaluates the relationship between selected psychological factors, selected clinical variables, and work duty status among active duty US Navy and Marine Corps personnel presenting with LBP who are stationed at a large base located in the United States. This topic is important because musculoskeletal complaints involving the spine account for the single largest proportion of work-disabling injuries in this population (29%). [8] There is limited information on return to duty after shortterm disability. In theater, Cohen et al. [9] found that Navy and Marine Corps personnel were less likely to return to duty compared with Army personnel within 2 weeks of an out of theater evacuation event (Operation Iraqi Freedom) after adjusting for type of injury, gender, commission, or rank (adjusted odds ratio, 0.59; 95% CI, 0.45–0.78 for Navy and adjusted odds ratio, 0.86 and 95% CI, 0.77– 0.96 for Marine Corps personnel).

It is not known at present whether factors predictive of short-term work-related disability in civilian occupational populations are the same or different in a military population. There can be profound differences in attitudes toward work and disability between a military and civilian occupational population although some of the work that is done in the military (eg, shipyard work, administrative, and hospital) can be similar to that in the civilian sector. Unlike the civilian occupational population, enlisted and career personnel are always considered "on duty," blurring the lines between professional and private life.We conducted this study to understand better the role of demographic, physical, and psychological factors and short-term work-related disability after episodes of LBP in active duty US Navy and Marine Corps personnel.



Materials and methods

      Study design

The study design is a prospective cohort of active duty military personnel presenting to a branch medical clinic (BMC) with a complaint of LBP. At the time of presentation, all the candidate subjects were on full duty. The study evaluated the probability of work disability assessed at 4 weeks and again 12 weeks after enrollment. The focus of this study was to evaluate for factors predictive of work disability status after a relatively brief follow-up period relevant to clinical management. We chose 4 weeks as this is considered by some as the beginning of the subacute stage where specialized or coordinated multidisciplinary care programs have evidence of treatment efficacy. [7] We chose 12 weeks (considered by some as the chronic stage of LBP) for similar reasons. Identification of predictor factors may lead to changes in early management to reduce risk of subsequent back pain–related work disability.

      Recruitment and enrollment procedures

Potential candidates were drawn from those seeking care from a BMC for a complaint of LBP. All potential candidates were evaluated by trained Navy health-care providers who conducted a back pain–specific standardized medical evaluation. [10] Health-care provider training consisted of instructions for documenting the findings of a back pain– specific examination. The training did not include any instructions on patient management, messages to the patient, or any changes to the current manner of practice.

Once the health-care provider had established that the primary reason for the visit was LBP, the health-care provider would contact the research assistants to speak with the potential candidate. The research assistants explained the study and conducted the informed consent process. Enrollment into the study was voluntary. Once the potential candidate agreed to participate in the study, he/she completed a paper and pencil questionnaire to document baseline measures of pain intensity, alcohol use, symptoms of posttraumatic stress disorder, depression, self-perceived disability, as well as feelings and beliefs about physical activity, work, and back pain. Completion of the entire questionnaire battery took about 20 minutes of the patient’s time. The study procedures were approved by a US Navy Institutional Review Board (approval: CIP# NMCP.2009.008 reducing attrition of military personnel because of LBP).

      Screening for enrollment

Patients were considered eligible for enrollment if back pain was the primary reason for seeking care and the duration of back pain before enrollment was less than 12 weeks. Subjects were excluded from the cohort if "red flags" (ie, clinical signs or symptoms indicating a specific cause of LBP requiring emergency care) [11, 12] were found at enrollment or if the candidate was pregnant (confirmed with a urine pregnancy test). These determinations were made by the US Navy health-care provider seeing the patient.

Subjects were also given an Audit-C questionnaire [13] to screen for alcohol abuse, the Center for Epidemiologic Studies Depression scale [14] (CES-D) to screen for clinical depression, and the military version of the posttraumatic symptom disorder checklist. [15] The Audit-C consists of three items, where each item is scaled from 0 to 4. The summary score of the Audit-C is the sum of the three items, with a minimum score of 0 (indicating no alcohol use) up to 12. We used the author’s recommended cutoff of 8 or greater (suggesting alcohol dependence) as a cutoff for referral to specialty care. [13] The CES-D consists of 20 items, each scaled from 0 to 3. The CES-D summary score is calculated as the sum total of the items, where the minimum value (no depression) is 0 and the maximum 60. We used the author’s criteria of 16 points (suggesting clinical depression) as the one for referral to specialty care. [14] Finally, the military version of posttraumatic symptom disorder checklist consists of 17 items, each item scored from 1 to 5. The summary score has a minimum value of 17 and a maximum of 50. Higher scores indicate greater likelihood of posttraumatic stress disorder. We used the recommended cutoff of 50 or greater for referral to specialty treatment. [15] Individuals who scored above threshold values for any of the three screening instruments were referred for specialized treatment. These subjects were not, however, excluded from follow-up from the cohort.

      Follow-up

Primary outcome   The primary outcome of interest was work duty status at the time of a clinical encounter closest to 4 weeks and at 12 weeks after enrollment. To collect these data, we assembled the medical records of the participants at two points in time: at 4 weeks duration after enrollment, and again at 12 weeks after enrollment.We selected the medical visit that was the closest to the target date of 4 and 12 weeks and used that encounter as the date for determining duty status.

Duty status was abstracted from the "Administrative Disposition" field of the subject’s electronic medical record. In the US Navy, the health-care provider assigns work duty status. Work status is recorded at the time of a clinical encounter, and it represents the health-care provider’s assessment of medical fitness for duty. Navy health-care providers are guided in their assessment of work readiness by taking into consideration their informal knowledge of the person’s job requirements, their awareness of the person’s state of mind, the patient’s desires and needs, and their own clinical evaluation. In the Navy, there are four classifications of duty status of interest for this study: full duty, light duty, sick in quarters, and limited duty. The assignment of work duty status is a routine administrative function. The procedures for this study did not modify how the health-care provider determined or assigned work duty status for the subject.

Full duty means that participants can function in their regular job without restriction and are available to perform any task that the job may require without medical restriction. They also are fit for worldwide assignment and deployment; all other classifications mentioned in this discussion are not fit for worldwide assignment or deployment. A light duty work designation means that the individual cannot execute normal work duties but still keeps his/her normal duty assignment. Alternative tasks, such as clerical work, may be found for the individual; exposure to certain activities (such as lifting and climbing ladders) may be limited on advice from the health-care provider. Light duty is usually used for short periods of disability (30–90 days). Sick in quarters is assigned when the individual is not able to perform any duty at all but remains on board ship or another assigned location. Sick in quarters is given for a short period (1–2 days). Limited duty is reserved for work-disabled individuals requiring full-time convalescence. Limited duty is assigned for up to a 6–month period. Active duty personnel have two limited duty assignments before the Navy considers discharging the person because of a permanent medical disability. In this study, duty status was recorded into the subject’s electronic medical record by the health-care provider and then abstracted by the researchers. For purposes of this study, outcome was dichotomized into "at full duty" and "not at full duty." This article analyzes factors predictive of "not at full duty" status.

      Predictors of outcome

Predictors consisted of demographic, clinical, and subject self-reported variables. The authors were guided in their selection of specific instruments using work done by the Multinational Musculoskeletal Inception Cohort Study, which proposed a common set of established predictors and important outcomes for patients with LBP and validated measures for both. [5]

      Demographic factors

Demographic characteristics included age, gender, pay grade (expressed as seniority, either enlisted or commissioned), race/ethnicity, and smoking. Pay grade is categorized according to whether the person is an enlisted, a commissioned, or a warrant officer, and rank. For purposes of this study, enlisted and commissioned personnel with a pay grade greater than 4 were categorized as senior-level personnel, whereas enlisted and commissioned personnel with a pay grade of 4 or less were categorized as junior-level personnel. Warrant officers were collapsed together into a single group. Pay gradewas abstracted fromthe subject’s electronic medical records.

Smoking was self-reported by the subject and specific to cigarette use. Smoking was dichotomized if the subject responded to "no cigarette use" and categorized as "cigarette use" if the subject indicated that they smoked occasionally or more.

Race/ethnicity was dichotomized in "white not of Hispanic origin" and "nonwhite." Race/ethnicity information was abstracted from the subject’s electronic medical records.

      Clinical factors

Description of LBP at study enrollment.   The health-care providers were trained in the use of a standardized LBP examination form. The examination records "red flags," that is, findings on the history and clinical examination that raise concern of serious underlying medical condition. [11] The form recorded a history of recent trauma, a history of constant progressive nonmechanical pain, previous history of cancer, a recent unexplained weight loss, a history of long-term steroid use, a history of substance abuse, recent widespread neurologic changes, or progressive neurologic deficit or sphincter disturbance. The clinical examination assessed for gait (heel walk and toe walk), lower extremity voluntary motor control reflexes, seated and supine straight leg raising, and hip flexion, extension, and rotation.

Back pain was categorized by the health-care provider in two ways. The health-care provider recorded the subject’s self-report of the duration of LBP symptoms before the clinical encounter serving as the index clinical visit for study. Three choices were available: less than 4 weeks duration, from 4 weeks to 12 weeks duration, and greater than 12 weeks duration.

The second categorization was a pain description adapted from the classification developed by Spitzer et al. [16] This classification characterizes back pain symptoms along two dimensions: whether the pain extends below the knee; and whether neurologic impairment is observed. Pain extending below the knee is reported by the subject, and the presence of neurologic impairment is established by evaluating for gait pattern (heel and toe walk), muscle strength of the lower extremities, reflexes, sensation, as well as seated and supine straight leg raising. For purposes of statistical analysis, we report these findings as whether radiculopathy is present; subjects who exhibit a positive seated or supine straight leg raising test are categorized as exhibiting radiculopathy.

      Subject self-reported data

Pain intensity   Pain intensity was measured using the Numeric Pain Rating Scale and represents self-perceived intensity of LBP on a 10–point scale, where 0 is no pain and 10 the worst pain imaginable. [17] A two-point change is considered significant for patients with acute or subacute LBP. [18]

Fear of activity   Fear of movement was measured using two instruments, the Tampa Scale for Kinesiophobia (TSK) [19] and the Waddell Fear-Avoidance Beliefs Questionnaire (FABQ). [20] We used both questionnaires initially because the Tampa Scale and the Waddell FABQ measure related but different constructs. The Tampa Scale measures fear of movement in general, whereas theWaddell FABQmeasures maladaptive beliefs about work and physical activity specific to LBP.

The TSK is a 17–item questionnaire developed to identify fear of reinjury because of movement or activities. Test-retest reliability is estimated to be 0.77. Items are scored on a four-point Likert scale with scoring possibilities ranging from "strongly disagree" (score51) to "strongly agree" (score54). Total scores range from 17 to 68, with a higher score indicating greater fear of reinjury. [19] The FABQ has two subscales: the Work (FABQ) subscale and the Physical Activity (FABQ Physical) subscale. Fear- Avoidance Beliefs Questionnaire Work subscale assesses patient beliefs with regard to the effect of their own specific work activities on their LBP. It consists of seven questions on a seven-point Likert scale (0–6) with a maximum score of 42, with a higher score indicating greater concern that work will effect LBP. Fear-Avoidance Beliefs Questionnaire Physical subscale assesses patient beliefs with regard to the effect of general physical activity on their LBP. Like the FABQ Work subscale, it is scored on a seven-point Likert scale (0–6), it consists of about four questions, with a maximum score of 24. Again, a higher score indicates greater concerns about the adverse effect of physical activity on LBP. [20]

Perceived disability   The Oswestry Disability Index [21, 22] (ODI) was developed to measure perceived disability in patients with back pain. The questionnaire consists of 10 items addressing different aspects of function, such as personal care, work, walking, sitting, standing, lifting, sleeping ability, sex life, social life, and pain intensity. Each item is scored from 0 to 5. The scale is scored from 0% to 100%, where 0 to 20 is considered low perceived disability and 80 to 100 severe disability. [22]

Depression   The CES-D is a 20–item self-administered scale. It measures the major components of depressive symptomatology, including depressive mood, feelings of guilt and worthlessness, psychomotor retardation, loss of appetite, and sleep disturbance using a four-point Likert scale. The item scores are summed to obtain the total scale score between 0 and 60. [14]

Catastrophizing   The Pain Catastrophizing Scale assesses three components of catastrophizing: rumination, magnification, and helplessness using 13 items on a five-point Likert scale. Total scores range from 0 to 65 with a higher score indicating greater catastrophizing. [23] This study used the total score for statistical analysis.

General health status   The SF-12 is a multipurpose short-form generic measure of general health status. [24] It is subdivided into two scales that measure physical and mental health. It has a general question about health, such as "would you say your health is excellent, very good, good, fair and poor". [25] These scores are population-based normalized values, where the minimum value 0 represents the lowest level of health and 100 represents the highest level of health. For context, Baldwin et al. found that SF-12 physical subscale scores in a sample of civilian workers ranged from 40.62 (standard deviation [SD], 10.65) for those whose back pain did not involve the absence of sickness from work to 32.62 among those whose back pain resulted in the continued absence of sickness from work and that SF-12 mental subscale scores ranged from 49.88 (SD, 10.92) to 41.75 (SD, 11.99), respectively. [26]

      Statistical analysis

The analysis consisted of computing estimated prevalence ratios (PRs) of duty status at 4 and 12 weeks after enrollment using Poisson regression. We chose Poisson regression because this regression technique produces beta coefficients that can be interpreted as rate ratios. We use the term "PR" as opposed to "relative risk" to reflect the cross-sectional nature of the way that outcome information was assembled for the analysis.

First, descriptive analyses were conducted to identify possible predictors from the baseline data. Factors showing a univariate Wald statistic with p#.15 were retained for multivariable analysis. For multivariate modeling, we forced the terms age, gender, radiculopathy, and duration of current episode before cohort enrollment into the model to control for the effect of these demographic and clinical factors. Multivariable analysis retained those prevalence factors that showed a Wald statistic associated with a p value less than or equal to .05.



Results

One thousand three hundred twelve individuals presented to the BMC with clinical visit reason of "LBP" between May 18, 2009, and November 30, 2009. Of the 1,312 candidates, the researchers were able to contact 454 potential candidates (35% contact rate). Of the 454 contacts, 286 agreed to be screened for the study and 260 met criteria for participation. Of the 260 candidates, 253 enrolled in the study. The 253 study participants did not differ from the 1,312 potential candidates on age, gender, service branch, or pay grade (Table 1). Table 2 shows the demographic and medical characteristics of the cohort as recorded at enrollment.

      Duty status at 4 and 12 weeks

Duty status at 4 weeks after enrollment was available for 239 individuals (94% of the participants enrolling), and duty status at 12 weeks after enrollment was available for 236 participants (93%). At 4 weeks, 200 were at "full duty" status (84% of the 239); and at 12 weeks, 225 were at full duty (95% of the 236). Of the demographic and medical characteristics, only the duration of the current LBP before study enrollment was associated with work duty status. Those having a duration of back pain greater than 4 weeks but less than 12 weeks duration at the time of enrollment were more likely to be "at full duty" as compared with those with 4 weeks or lesser duration of pain. No clinical evaluation factors (heel walk, toe walk, loss of motor control, diminished reflexes, seated or supine straight leg raising tests, or hip abduction/ flexion/external rotation) were predictive of work duty status at 4 or 12 weeks after enrollment. Individuals reporting a previous history of LBP were more likely to be on full duty. No other factors were associated with work duty status.

Table 3 shows unadjusted estimates of PRs for the cohort for selected demographic, clinical, and psychological factors measured at enrollment into the study. A PR greater than 1 indicates an elevated prevalence of poor outcome (ie, "other than full duty") for the exposure level as compared with a reference group. Findings indicate that participants having less than 4 weeks pain before enrollment ("acute" presentation) were 2.73 times more likely to be given a work duty status of "other than full duty" 4 weeks after enrollment compared with those having a prior history of LBP. For each one-point increase on the ODI, the prevalence of being on light duty at 4 weeks increased by 4% (PR, 1.04; 95% CI, 1.01– 1.06). For each one-point increase on the FABQ Work subscale, the prevalence of being placed on light duty increased by 5% (PR, 1.05; 95% CI, 1.01–1.08). The only factor associated with outcome at 12 weeks was the FABQ Physical activity subscale (PR, 1.14; 95% CI, 1.00–1.30).

Univariate analysis showed that the age, gender, cigarette use, race/ethnicity, pay grade, and the SF-12 were not associated with duty status at 4 or 12 weeks after cohort enrollment. These factors (except for age and gender) were dropped from subsequent multivariate modeling.

      Factors associated with "not at full duty status" 4 weeks after enrolling into the cohort

Multivariate-adjusted analysis showed that individuals enrolling in the cohort early in their back pain episode (#4 weeks duration of the current episode of LBP before enrollment) were 2.69 times more likely to be "not at full duty" 4 weeks after enrollment as compared with those whose duration of the current episode before enrollment was greater than 4 weeks (PR, 2.69; 95% CI, 1.21–5.97). In addition, the PR for the association between the FABQ Work subscale and "not at full duty" status was estimated at 1.05 (PR, 1.05; 95% CI, 1.01–1.08). This model was simultaneously adjusted for age, gender, FABQ Physical Activity subscale, ODI, pain intensity, presence of radiculopathy, and duration of current episode before enrollment.

      Factors associated with "not at full duty status" 12 weeks after enrolling into the cohort

Multivariate-adjusted analysis showed only one factor to be predictive of "not at full duty" status at 12 weeks after enrollment. The predictor factor was the FABQ Physical subscale (PR, 1.14; 95% CI, 1.00–1.30). This model was simultaneously adjusted for age, gender, FABQ Work subscale, ODI, pain intensity, presence of radiculopathy, and duration of current episode before enrollment.

In both models, the TSK and FABQ scales exhibited some colinearity, and the Tampa Scale was dropped because the fit of the data was marginally better using the FABQ scales as compared with the Tampa Scale.

The utility of the regression model is to estimate likelihood of duty status given a predictor value. Fig. 1 shows the likelihood of a duty status of "other than full duty" for participants enrolled in the cohort. The y-axis shows the estimated prevalence or likelihood of being "not at full duty," and the x-axis shows the value of the FABQ Work subscale. For an individual entering the study with 4 weeks or less back pain before enrolling the cohort and scoring 30 on a FABQ Work subscale, the estimated likelihood of being "not at full duty" at 4 weeks is approximately 40%. The value is half of that if the person had experienced more than 4 weeks of back pain before enrolling in the cohort.

Fig. 2 shows the relationship between work duty status and FABQ Physical activity subscale for outcome at 12 weeks. The structure and interpretation of the graph is similar to that of Fig. 1. The x-axis represents the FABQ Physical activity subscale score. Fig. 2 shows that the estimated likelihood of being "not at full duty" at 12 weeks after enrollment into the cohort increases with an increase of the physical activity subscale measured at study enrollment. For example, the likelihood was estimated to be 2% of being "not at full duty" at 12 weeks for those scoring an 8 or lower on the FABQ Physical activity subscale at cohort enrollment. The estimated likelihood of being "not at full duty" rose to 13% for those scoring 24 on the physical activities subscale at cohort enrollment.



Discussion

We found that duration of the current episode before cohort enrollment and the FABQ Work subscale predicted subsequent duty status at 4 weeks, and only the FABQ Physical subscale predicted duty status at 12 weeks after initial intake. No other demographic, clinical, or psychological factors predicted outcome at follow-up in multivariate-adjusted analysis.

      The role of fear and perceived disability

Our results are consistent with fear-avoidance theory. Fear-avoidance theory suggests negative emotional responses to nociception leading to short-term avoidance of physical activity. [20, 27, 28] Lack of activity reduces pain in the short term and reinforces this behavior. Over time, generalized avoidance of activity can lead to physical deconditioning. Resumption of physical activity leads once again to discomfort and provides negative reinforcement for activity as well as an increased perception of disability.

Subject beliefs about the effect of physical activity in general and LBP, and not beliefs about specific work activities, were predictive of "not at full duty" 12 weeks after study enrollment. This suggests some independence of the two fear-avoidance belief subscales. It is possible that more generalized maladaptive beliefs about physical activity have implications for long-term work disability than maladaptive beliefs about immediate and specific workrelated physical activities.

Perceived disability (ODI) was not found to be statistically significantly associated with probability of "not at full duty" at 4 or 12 weeks after multivariate-adjusted analysis. The ODI was statistically significantly associated with outcome at 4 weeks in univariate analysis, but the association disappeared after multivariate adjustment. For comparison, Fairbanks and Pendent calculated weighted means for studies collecting ODI information. They found that studies reporting on what they term "normal" populations were approximately 10 (SD ranging from 2.2 to 12), the weighted ODI for what they term "primary back pain" was 27 (SD ranging from 5.8 to 23.6), and for "chronic low back pain" the weighted ODI was 43 (SD ranging from 10 to 21). [21] Carragee [29] found that the average ODI score was 12.9 (standard error, 2.5) and a mean visual analog pain scale score of 5 among military personnel with what was termed "chronic low back pain." The failure to observe a statistically significant association does not necessarily rule out ODI as a predictive factor for short-term disability in this population, just that the strength of the association observed in this study is not detectable as statistically significant with the study’s sample size of 253.

      The role of duration of back pain

Those who reported to their health-care provider that they had back pain for less than 4 weeks duration before enrollment were more likely to be assigned "not at full duty status" as compared with those reporting back pain for a period longer than 4 weeks before enrollment. One might have expected the opposite finding as studies of civilian populations have reported poorer recovery in those struggling with back pain. [10, 27, 30, 31] These findings may reflect the unique culture of the military, expressed through a combination of health-care provider and patient preferences. US Navy health-care providers may initially prescribe work limitations (light duty) through the use of sick chits for service personnel in the acute phase to give patient the time to recover from their acute onset of pain. However, as the episode of pain (and disability) continues, prolonged or continued absence from their command can have significant negative implications. US Navy policy requires that work-disabled personnel be evaluated for placement in a limited duty status. When placed on limited duty, the individual is removed from his/her command for convalescence, and if disability persists may eventually be discharged. Navy policy allows for three limited duty periods during a person’s Navy career before the individual is administratively reviewed for fitness for continued service. Therefore, in addition to all other factors specific to the military that motivate return to duty, there can be a strong career-related incentives for military members with back pain to return to full duty, despite ongoing pain, rather than risk not being able to remain at their command.

Strengths and limitations of the study

The longitudinal nature of this study is a strength that contributes to the validity of the findings. A second strength of the study was that fear of movement was measured using two different validated instruments. Both instruments showed association with work duty status in univariate analysis and modestly correlated with each other. The FABQ was chosen to be retained in multivariate modeling as this instrument contained questions related to work. A second strength of the study is the use of widely used clinically relevant predictor instruments. For example, the study protocol called for administering the questionnaire package during the time the subject was waiting for their clinical examination. The questionnaire took approximately 5 minutes to be completed by the subject. The practical experience of the study suggests the practicality of routine collection of the FABQ for purposes of screening for maladaptive beliefs about physical activity, work, and LBP early in a patient’s LBP episode.

An important consideration of this study is the way in which work duty status is operationalized. In this study, duty status was the assignment of the primary care manager at the time of the clinical visit, subject to the health-care provider’s clinical examination and understanding of the patient’s own particular circumstances. Recent research suggests that psychosocial factors relevant to return to work can be affected by an individual’s "community culture" (eg, beliefs about pain that derive from a person’s community and workplace) and the "way in which compensation, health care, and workplace systems function and delay the return to work process". [32] In other words, return to work is a complex multidetermined outcome. [33] Our study captured data on relevant psychosocial factors but did not capture data on possibly important workplace environmental or cultural issues that may further explain the return to duty decision. Additional research into the process of return to duty after back pain, specific to the military, is warranted.

Finally, this study captured 253 subjects of 1,312 persons possibly eligible for the study. In this study, the approved protocol required potential subjects to actively volunteer after the evaluating health-care provider determined that the individual’s primary medical complaint was for LBP. A significant proportion of potentially eligible cases were lost between the conclusion of the health-care provider’s evaluation and the subsequent administration of informed consent by the study research assistants. In some cases, BMC health-care providers did not notify the researchers of a possible study candidate. In other cases, during the course of the medical encounter, it was found that LBP was not the primary medical complaint. Finally, many possible candidates went back to their duty post immediately after their medical encounter without contacting the research assistants. When candidates did approach the research assistants, the research assistants were able to enroll a high percentage of patients.

The implications for possible selection bias are not entirely clear. For example, if patients were leaving the clinic early to return back to their duty post, this would suggest, possibly, that these cases were perhaps less severe as compared with those enrolling in the cohort. More likely, those individuals who ended up enrolling in the cohort had the time, interest, and motivation to participate in the research study. However, a comparison between participants and nonparticipants did not reveal any significant systematic differences in demographic characteristics or duration of the back pain episode before enrollment.

It is important to note that this is the first longitudinal study of LBP in the US Military Health System that includes data on psychological factors associated with return to duty. The study fostered excellent collaborative research relationship between the US Navy Orthopedics and Public Health services and a major USuniversity. This first study of psychological factors and back pain disability is consistent with the military’s increased attention to psychological effects of service by military personnel and health outcomes.



Conclusion

This study provides evidence for the utility of evaluating for maladaptive beliefs in the clinical setting for military personnel presenting with complaints of LBP. The doctorpatient interaction has been shown to have a strong impact on patient’s attitudes and behaviors related to LBP. Fearavoidance beliefs are modifiable psychological factors that respond to clinical intervention. Primary care physicians, aware of the findings of this study, may use these findings as a justification to modify their interactions with patients to emphasize a good prognosis and the importance of maintaining normal activity levels despite pain during the initial stages of a treatment for LBP. Doing so may interrupt a possible negative cycle of fear and disability as articulated by the fear-avoidance models and may enhance, in the long run, force readiness. Our results lend additional evidence to the importance of psychological factors in the progression and maintenance of disability across populations.


Acknowledgments

Mary Brinkmeyer, PhD, Linda Carroll, PhD, David Collins, CDR MC USN, Jessica Dail, MPH, Denise Davis, MD, Ivan Hinnant, MD, Jessica Hohman, MPH, James Need, PhD, Chris Rennix, ScD, Damita Turner, RN, and the Backs to Work Research Team.



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