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.
Nahin ~ Pain 2017
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).
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 :
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.  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%). 
There is limited information on return to duty after shortterm
disability. In theater, Cohen et al.  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
Materials and methods
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.  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.  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
Subjects were also given an Audit-C questionnaire 
to screen for alcohol abuse, the Center for Epidemiologic
Studies Depression scale  (CES-D) to screen for clinical
depression, and the military version of the posttraumatic
symptom disorder checklist.  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.  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.  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.  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.
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. 
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
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
Race/ethnicity was dichotomized in "white not of Hispanic
origin" and "nonwhite." Race/ethnicity information
was abstracted from the subject’s electronic medical records.
Description of LBP at study enrollment.
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.  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. 
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
Subject self-reported data
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.  A two-point change is considered significant
for patients with acute or subacute LBP. 
Fear of activity
Fear of movement was measured using two instruments,
the Tampa Scale for Kinesiophobia (TSK)  and the
Waddell Fear-Avoidance Beliefs Questionnaire (FABQ).  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. 
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. 
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. 
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
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.  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.  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".  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),
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.
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,
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
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
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.
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
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
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).  Carragee  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".  In other words, return to work
is a complex multidetermined outcome.  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.
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.
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