European Spine Journal 2017 (Apr 8) [Epub]
Paul S. Nolet, Vicki L. Kristman, Pierre Côté,
Linda J. Carroll, J. David Cassidy
Department of Graduate Education and Research,
Canadian Memorial Chiropractic College,
Toronto, ON, Canada.
PURPOSE: This population-based cohort study investigated the association between a lifetime history of a low back injury in a motor vehicle collision (MVC) and future troublesome low back pain. Participants with a history of a low back injury in a motor vehicle collision who had recovered (no or mild low back pain) were compared to those without a history of injury. Current evidence from two cross-sectional and one prospective study suggests that individuals with a history of a low back injury in a MVC are more likely to experience future LBP. There is a need to test this association prospectively in population-based cohorts with adequate control of known confounders.
METHODS: We formed a cohort of 789 randomly sampled Saskatchewan adults with no or mild LBP. At baseline, participants were asked if they had ever injured their low back in a MVC. Six and 12 months later, participants were asked about the presence of troublesome LBP (grade II-IV) on the Chronic Pain Grade Questionnaire. Multivariable Cox proportional hazards regression analysis was used to estimate the association while controlling for known confounders.
RESULTS: The follow-up rate was 74.8% (590/789) at 6 months and 64.5% (509/789) at 12 months. There was a positive crude association between a history of low back injury in a MVC and the development of troublesome LBP over a 12-month period (HRR = 2.76; 95% CI 1.42-5.39). Controlling for arthritis reduced this association (HRR = 2.25; 95% CI 1.11-4.56). Adding confounders that may be on the casual pathway (baseline LBP, depression and HRQoL) to the multivariable model further reduced the association (HRR = 2.20; 95% CI 1.04-4.68).
CONCLUSION: Our analysis suggests that a history of low back injury in a MVC is a risk factor for developing future troublesome LBP. The consequences of a low back injury in a MVC can predispose individuals to experience recurrent episodes of low back pain.
KEYWORDS: Low back pain, Traffic accidents, Whiplash injuries, Risk factors, Cohort studies
From the FULL TEXT Article:
Globally, low back pain (LBP) is the leading cause of
years lived with disability  and as a cause of disability
adjusted life years (DALY) has gone from a rank of
eleventh in 2000 to sixth place in 2010 . LBP has a
substantial economic burden with both direct and indirect
costs . In the general population, LBP is marked by a
recurrent or persistent course . Most LBP is mild and
does not result in visits to primary care . In those
seeking primary care for LBP, one third had recovered by
12 weeks, and 65% reported LBP 1 year later . Troublesome
LBP can impact physical health related quality
of life . LBP has a point prevalence of 18.3%, 1-month
period prevalence of 30.8% and 1-year period prevalence
of 38% .
LBP is common after a motor vehicle collision (MVC).
In patients reporting to emergency departments after a
MVC, 37% reported moderate to severe low back pain
6 weeks later . In a population-based cohort of Saskatchewan
residents who reported being injured in a traffic
accident, where they were treated or filed an auto insurance
claim within 30 days, 60.4% reported LBP . Subjects
with LBP in this cohort were followed for 6 months. High
pain intensity, female gender, full-time employment, concentration
problems and early lawyer involvement delayed
claim closure .
A question of importance to clinicians, insurers and
governments is whether a history of a low back injury in a
MVC will predispose subjects to experience future LBP
and disability. Two cross-sectional studies found a positive
association between a prior low back injury and current
LBP [12, 13]. Cross-sectional studies are susceptible to
issues of temporality, including prevalence/incidence bias
and recall bias. A prospective study of insured drivers by
Berglund et al. , found an increased risk of low back
pain 7 years later in subjects with an injury in a rear-end
collision compared to controls. They found no association
7 years later between those with no injury after a rear-end
collision compared to controls. No prospective study of the
general population has investigated the risk of future LBP
due to a history of low back injury in a MVC. The purpose
of this analysis was to test the association between a history
of a low back injury in a MVC and future troublesome LBP
in a general population sample while controlling for
potential confounding factors.
Study design and source population
The Saskatchewan Health and Back Pain Survey (SHBPS),
was a population-based 21-page mailed survey, on the
distribution, determinants and risks of spinal disorders .
The Canadian province of Saskatchewan, during the time
of the survey, had approximately one million inhabitants
with universal health care coverage. Eligible for the study
were Saskatchewan residents between the ages of 20 and
69 with a valid Health Services card on August 31, 1995.
Excluded from the survey were inmates of correctional
facilities, residents under the Office of the Public Trustee,
foreign students and workers holding employment or
immigration visas, and residents of special care homes
Residents were selected from an age-stratified random
sample from the Saskatchewan Health Insurance Registration
File. The Health Insurance Registration File included
more than 99% of the Saskatchewan residents.
Subjects were randomly selected and sent the survey by
Saskatchewan Health to protect the confidentiality of the
participants. Participation in the survey was voluntary. The
University of Saskatchewan Advisory Committee on Ethics
in Human Experimentation approved the SHBPS and the
current analysis was approved by the Lakehead University
Research Ethics Board.
Eligible for the survey were 593,464 individuals of which
2,184 were randomly selected to receive the survey. One
hundred and twenty-nine baseline questionnaires were
returned due to mailing errors, ‘health reasons’, immigrated
or died. Of the remaining 2,055 participants, 1,133
(55.1%) completed the baseline questionnaire. Twenty-one
subjects did not complete the low back pain questionnaire
and two subjects were outside of the pre-determined age
range. Therefore, 1,110 subjects were eligible for this
analysis (Figure 1). There were no important differences in
age or gender between the eligible population and the
randomly selected sample. However, a comparison of
participants and nonparticipants found slightly more
participation in older individuals, women and those who
were married .
The baseline survey was mailed in September 1995. The
6-month follow-up survey was sent to respondents of the
baseline survey. The 12-month survey was sent to
respondents of the 6-month survey.
Population at risk
The population at risk in this analysis consisted of individuals
at baseline with no or mild low back pain (Grade 0
or Grade I) on the Chronic Pain Grade Questionnaire
(CPQ)  (Table 1). Given that most individuals experience
mild episodes of LBP annually, we included Grade I
LBP in our population at risk of developing troublesome
The main exposure was measured by asking participants:
"Have you ever injured your low back in a motor vehicle
Troublesome LBP was measured with the CPQ at 6 and
12 months. The questionnaire measures the 6-month period
prevalence of LBP, LBP grades, and related disability,
grading LBP into five ordered categories (Table 1). The
questionnaire has good psychometric properties . Participants
with grades II, III or IV LBP were classified as
having troublesome LBP.
The CPQ includes seven questions to grade LBP. Three
questions used a numerical rating scale (0–10/10) to measure
current, average (past 6 months), and worst LBP (past
6 months). One question asked about the number of days in
the last 6 months that activity was limited due to LBP.
Three questions asked about how much LBP has limited
the ability to take part in recreational, social, and family
activities; has limited daily activities; and the ability to
Baseline grade 1 LBP may lie on the casual pathway
between a history of low back injury in a MVC and the
development of troublesome LBP (making it an intermediate
variable). Alternatively, grade 1 LBP may increase
the risk of troublesome LBP (potential confounding
effects). The same may be true for HRQoL and depressive
symptomatology. Misclassifying a factor as a confounder
when it is in fact a mediator can introduce bias into the
results. Thus, we developed two sets of potential confounders
and analyzed the two sets separately. One set of
potential confounders included the three factors that could
be mediators, and the other set excluded these three factors.
The following variables were considered as potential confounders
of the association of interest.
Baseline gender, age, marital status, education level,
income, employment status and location of residence.
The Medical Outcomes Study SF-36 standard English-
Canadian version 1.0 was used to measure self-perceived
general health status . The questionnaire assesses
physical and mental HRQoL in eight domains. This analysis
used the physical component summary (PCS) and
mental component summary (MCS) of the SF-36. The
physical component summary (PCS) includes physical
functioning, bodily pain, role limitations due to physical
health problems and general health domains. The mental
component summary (MCS) includes role limitations due
to emotional health, mental health, social functioning and
vitality domains. The SF-36 has high internal consistency
 and test–retest reliability . It has a reliability
estimate that usually exceeds 0.90 [21, 22].
Comorbidities and their self-perceived impact on health
were measured with the Comorbidity Questionnaire. The
questionnaire included questions about allergies, arthritis,
cancer, digestive disorders, headaches, heart/circulation,
high blood pressure, and kidney disorders. The self-perceived
health impact of each comorbidity was rated on a
four-point ordinal scale as: (1) not at all, (2) mild, (3)
moderate and (4) severe. The Comorbidity Questionnaire
has good test–retest reliability (ICC = 0.93) and adequate
face, concurrent and convergent validity [23, 24].
The Center for Epidemiological Studies Depression Scale
(CES-D) was used to measure depressive symptomatology
. The 20-item questionnaire asks about how often in the
past week they have experienced symptoms of depression.
Responses include 0 for rarely or none; 1 for some or little
of the time; 2 for moderately or much of the time and 3 for
most or almost all the time. The questionnaire is scored out
of a possible score of 60 with 16 as the cut-off score for
depression in the general population which has a sensitivity
of 100% for major depression and a specificity of 88%
. The questionnaire has been shown to be reliable and
valid in various populations with good internal consistency
(alpha coefficients [0.85) [25, 27, 28]. The CES-D was
used as a continuous variable in this analysis.
Baseline characteristics of the sample were described
stratified by exposure status. Loss to follow-up was
examined for attrition bias by comparing baseline characteristics
between responders and non-responders at 6- and
12-month follow-up using the Chi-square and t test.
Cox proportional hazards models were used to measure
the association between a history of low back injury in a
MVC and troublesome LBP. The modeling included three
steps. First, a univariate model was built to estimate the
crude association between our exposure and outcome.
Second, a series of bivariate models were built to determine
which variables led to a 10% change in the exposure
regression coefficient. These variables were deemed to be
confounders and included in the final model. Third, the
final model included the exposure and all confounders
identified in the second step . IBM-SPSS version 22
was used for the analysis .
Variables deemed to be possible mediators on the causal
pathway (depressive symptomatology, HRQoL and baseline
LBP) were excluded in the first Cox model and
included in a separate model if there was a 10% change in
the exposure regression coefficient in the bivariate model.
Our population at risk included 789 participants with
baseline Grade 0 or I LBP. A history of a low back injury
in a MVC was reported by 48 subjects (6.1%). Forty-five
subjects reported troublesome LBP at 6 months and 39 at
Participants with a history of low back injury in a MVC
were younger, more likely to have grade I LBP and were
less likely to have allergies that moderately to severely
impacted their health (all at p\0.05) compared to those
without a history of low back injury at baseline. Baseline
HRQoL was similar between both groups (Table 2).
The follow-up rate was 74.8% (590/789) at 6 months and
64.5% (509/789) at 12 months. Those completing the
survey at 6 months were older and more likely to have
higher levels of education and income (all at p\0.05)
compared to those lost to follow-up at 6 months. Those
followed at the 12-month survey were older and less likely
to have cardiovascular problems that impacted their health,
and more likely to have a higher income and higher education
(all at p\0.05) than those lost to follow-up at
12 months. There was no statistically significant difference
in baseline HRQoL scores grade between those followed
and those lost to follow-up at either 6 or 12 months.
Association between a history of low back injury
in a motor vehicle collision and troublesome LBP
We found a positive crude association between a history of
low back injury in a MVC and the development of troublesome
LBP over a 12-month period (HRR = 2.76; 95%
CI 1.42–5.39). Adjusting for arthritis reduced the association
(HRR = 2.25; 95% CI 1.11–4.56). Adjusting for
covariates that may be mediators on the causal pathway
(depressive symptomatology, HRQoL PCS and baseline
graded LBP) along with arthritis further reduced this
association (HRR = 2.20; 95% CI 1.04–4.68) (Table 3).
| Table 2.
Frequency distribution of the baseline demographic, socioeconomic, comorbidities |
and health-related characteristics by exposure category
Table 2. Part A
Table 2. Part B
Table 2. Part C
Table 2. Part D
Our survey was the first North American cohort study from
the general population to prospectively investigate the
association between a self-reported low back injury in a
MVC (in those who had recovered to have no or mild low
back pain) and the development of future troublesome
LBP. Our results suggest that the incidence of troublesome
LBP is higher in individuals who have had a past low back
injury in a MVC compared to those who have not had a low
back injury in a MVC.
Our findings confirmed the associations of prior crosssectional
and prospective studies. A cross-sectional internet
survey in Japan on 65,496 adults found a positive association
between a traffic injury and chronic disabling low
back pain (adjusted OR 2.81; 95% CI 2.07–3.81) . In a
cross-sectional study from the general population of Norway,
59,104 subjects responded to the whiplash question of
the survey and of those 79.3% answered the questions on
musculoskeletal symptoms . After controlling for
confounding factors there was a positive association
between a history of a whiplash injury and low back pain in
both males (adjusted OR 3.1; 95% CI 2.4–3.9) and females
(adjusted OR 4.8; 95% CI 3.8–6.3) . Cross-sectional
studies cannot address the issue of causality, as LBP may
have been present prior to the low back injury. Further,
those with prevalent LBP may be more likely to recall a
low back injury in a MVC. In a prospective study from a
large insurance company in Sweden, subjects having had
an injury in a rear-end collision (n = 242) were more
likely to have LBP 7 years later compared to a group in
similar collisions that did not complain of injury (age and
gender adjusted RR 1.7; 95% CI 1.3–2.4). Subjects
exposed to a rear-end collision without an injury were no
more likely than an unexposed comparison group to have
LBP 7 years later (age and gender adjusted RR 0.9; 95% CI
Baseline LBP, depressive symptomatology and HRQoL
were analyzed in a separate Cox proportional hazards
model. Controlling for these covariates separately was to
avoid over-adjustment by including covariates that may
also be mediators on the casual pathway between a history
of a low back injury in a MVC and the outcome, troublesome
low back pain . If these variables are on the
casual pathway they should not be controlled for as confounders.
In that case, including these variables as confounding
variables would cause an under-estimation of the
true association. In fact, controlling for these variables had
little impact on the observed association. This had not been
the case in a similar analysis from the SHBPS testing the
association between a history of work-related low back
injury and future troublesome low back pain gender
(arthritis adjusted HRR = 2.24; 95% CI 1.05–2.77). When
covariates that may also be mediators of the association
(baseline LBP, depressive symptomatology and HRQoL)
were added to the model, the effect estimate was attenuated
(adjusted HRR = 1.37; 95% CI 0.82–2.29) .
The strengths to our study were the use of a large
prospective, population-based random sample of Saskatchewan
adults. Second, we used a valid and reliable
questionnaire to measure LBP. Third, Cox proportional
hazards modeling was used to control for confounding.
Our study also has limitations. The risk factors for future
incident LBP, such as a low back injury in a MVC, may
have a mediating effect on future pain and disability in
those with a prior history of LBP. The population followed
in this study excluded those with prevalent troublesome
LBP which could reduce this risk of bias, but future studies
need to test this hypothesis. Second, our analysis excluded
those with troublesome LBP at baseline. This may have
caused us to underestimate the true association as some of
these subjects may have recovered from their LBP after a
MVC, but may have developed a new incident episode of
troublesome LBP prior to the baseline survey. Third, the
exposure, a history of low back injury in a MVC could
suffer from general misclassification although this is
probably a minor issue as two previous studies have found
that participants have a good recollection of a history of
self-reported injury [33, 34]. Further, if misclassification of
the exposure occurred, it would be non-differential in
nature given the prospective study design. This would bias
estimates towards the null, meaning the estimates of
association calculated in this study were most likely conservative.
Fourth, the attrition analysis suggested that
estimates of the association were underestimated. Those
lost to follow-up were younger and have lower levels of
income and education than those continuing in the study,
but did not differ in their baseline HRQoL. Finally, the
baseline survey of the SHBPS had a 55% response rate.
This may result in selection bias, but this was unlikely as
the target population was similar to the actual population
with respect to age group, gender and geographic location
. Further, in the wave analysis of the baseline survey
the differences between response waves suggest no selective
response bias due to LBP .
Our results inform the debate surrounding the etiology
of LBP in the general population. Few studies have identified
risk factors for recurrent episodes of LBP. This study
supports prior research on the hypothesis that a past history
of a low back injury in a MVC may be a determinant of
future LBP. Our analysis provides the public, clinicians,
government and insurers with evidence that a low back
injury in a MVC may have a role in the development of
future low back pain. The causal mechanisms linking a past
history of low back injury in a MVC and future low back
pain remains unknown, although it likely involves complex
biopsychosocial relationships. These associations need to
be examined in large cohort studies with careful attention
The authors would like to acknowledge the
Chiropractors’ Association of Saskatchewan for funding the Saskatchewan
Health and Back Pain Survey and the assistance of Saskatchewan
Health in sampling the Saskatchewan population. Dr.
Kristman is supported by the Canadian Institutes of Health Research
through a New Investigator Award in Community-based Primary
Conflict of interest
The authors declare that they have no competing
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