PM R. 2019 (Apr 25) [Epub] ~ FULL TEXT
Paul S. Nolet, DC, MS, MPH, Peter C. Emary, DC, MSc, Vicki L. Kristman, PhD, Kent Murnaghan, MA MISt,
Maurice P. Zeegers, PhD, Michael D. Freeman, MedDr, PhD,
Care and Public Health Research Institute,
OBJECTIVE: To summarize the literature that has examined the association between a motor vehicle collision (MVC) related neck injury and future neck pain (NP) in comparison with the population that has not been exposed to neck injury from an MVC.
LITERATURE SURVEY: Neck injury resulting from a MVC is associated with a high rate of chronicity. Prognosis studies indicate 50% of injured continue to experience NP a year after the collision. This is difficult to interpret due to the high prevalence of NP in the general population.
METHODOLOGY: We performed a systematic review of the literature using five electronic databases, searching for risk studies on exposure to a MVC and future NP published from 1998 to 2018. The outcome of interest was future NP. Eligible risk studies were critically appraised using the modified Quality in Prognosis Studies (QUIPS) instrument. The results were summarized using best-evidence synthesis principles, a random effects meta-analysis, meta-regression and testing for publication bias was performed with the pooled data.
SYNTHESIS: Eight articles were identified of which seven were of lower risk of bias. Six studies reported a positive association between a neck injury in an MVC and future NP compared to those without a neck injury in a MVC. Pooled analysis of the six studies indicated an unadjusted relative risk of future NP in the MVC exposed population with neck injury of 2.3 (95% CI [1.8, 3.1]), which equates to a 57% attributable risk under the exposed. In two studies where exposed subjects were either not injured or injury status was unknown, there was no increased risk of future NP.
CONCLUSIONS: There was a consistent positive association among studies that have examined the association between MVC-related neck injury and future NP. These findings are of potential interest to clinicians, insurers, patients, governmental agencies, and the courts.
KEYWORDS: motor vehicle collision; neck pain; risk; systematic review; whiplash trauma
From the FULL TEXT Article:
Neck pain (NP) is a common finding in the general population and the fourth leading cause of
years lived with disability globally.  Out of the 291 diseases examined in the Global Burden of Disease study in 2010, NP ranked 21st in terms of total burden of health as measured by
disability adjusted life years.  In 2010, the average point prevalence of activity limiting NP
over all age groups was 4.9%, and was higher in women (5.8%) than in men (4.0%).  NP is
often a chronic or recurrent condition  and results in a significant economic burden on health
care systems  as well as impacts on health-related quality of life. 
NP pain is a common complaint after involvement in a motor vehicle collision (MVC) with
86% of injured occupants reporting NP pain.  In Ontario 17.6% of those exposed to a MVC
report a personal injury.  The question of whether injury in an MVC can lead to ongoing or
future episodes of NP is important to patients, health care providers, governments, insurers
and courts. The prognosis after neck injury in a MVC can be prolonged with 50% still
reporting NP a year later.  However, there is a high prevalence of NP in the general
population (12 month prevalence of 30% to 50%), where many were not injured in a MVC. 
Given the fact that prognosis studies indicate a high rate of persisting pain a year or more after
traffic crash-related injury, prevalence studies indicate a high rate of NP regardless of history
and injury status at the time of the crash appears to be an important predictor of risk, we find
that the literature is missing a reliable estimate of NP risk following a crash-related neck
injury. Such an estimate is important both for understanding public health risks among the
population with acute injury, as well as for medicolegal applications for the individual
with ongoing NP after acute injury in order to quantify the probability that the persisting
symptoms are attributable to the crash-related injury versus background rate. Therefore, the
objective of the present review and meta-analysis is to estimate the risk for an association
between the exposure to a MVC and future NP, in comparison with the population that has not
been exposed to a MVC.
We included studies of participants aged 16 years of age and older who were
involved in a previous road traffic collision and included an appropriate comparison group
without neck injury. NP was defined as pain located in the anatomic region of the neck below the
superior nuchal line, external occipital protuberance and above the spine of the scapula, superior
border of the clavicle and suprasternal notch.  This systematic review included papers
including subjects with non-radicular NP, radicular NP and neck and shoulder pain.
The exposure was defined as subjects that had been exposed to a MVC or a neck
injury in a MVC. Exposure to a MVC included collisions reported to police where not everyone
may have been injured or collisions where no injury occurred. Neck injury in a MVC included
self-reported injury, primary care or emergency room physician diagnosed injury or an injury
that had been filed with an automobile insurance company.
To be included in the systematic review, studies had to fulfill the
following inclusion criteria: 1) written in the English language; 2) published from January 1,
1998 to May 17, 2018; 3) published in a peer-reviewed journal; 4) examined the association
between neck injury in a MVC (or involvement in a MVC) compared to individuals not injured
in a MVC and future NP; 5) used a case-control or cohort design; 6) Studies that included
a mixed population with individuals less than 16 years of age, must have stratified for adults 16
years of age and older.
Studies fulfilling any of the following characteristics were excluded: 1) studies with less than 20
human participants with NP, or less than 20 participants at risk of NP; and 2) NP related to
fracture or dislocation, systematic disease, tumors, infections, fractures or dislocations,
myelopathy or inflammatory joint disease.
Data Sources and Searches
The search strategy was developed in consultation with a health sciences librarian. To ensure
accuracy and completeness a second librarian was consulted. The following electronic databases
were systematically searched from January 1st, 1998 to May 17, 2018: PUBMED, EMBASE,
Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL, SPORTDISCUS and
MEDLINE (EBSCO). The search strategy was reviewed using the Peer Review of Electronic
Search Strategies (PRESS) checklist.  Search terms consisted of subject headings specific to
each database (e.g. MeSH in MEDLINE) and free text words relevant to neck pain/neck injuries,
motor vehicle accidents, incidence, prevalence, and risk factors (Appendix I).
Screening of articles occurred in two stages by pairs of independent reviewers (PN and PE).
First, titles and abstracts were screened for relevant, possibly relevant or irrelevant citations
based on the inclusion and exclusion criteria. Second, we screened full text articles of all
possibly relevant citations from stage 1. Disagreements at each stage were discussed
between reviewers to reach consensus. A third reviewer independently screened the citation
when consensus could not be reached to help the reviewers reach consensus or where a reviewer
was an author on a study (MF).
Assessment of Risk of Bias
Two reviewers (PN and PE) critically appraised all relevant studies using the Quality in
Prognosis Studies (QUIPS) appraisal tool modified for risk studies (12). A third reviewer
critically appraised any studies where the first two reviewers could not reach consensus or where
a reviewer was an author on a study (MF). Studies were included if they had adequate internal
validity and limited risk of bias. The QUIPS appraisal tool has moderate to substantial inter-rater
reliability (0.56≤k≤0.82) and assesses studies for risk of bias in 6 domains: 1) participation; 2)
attrition; 3) exposure measurement; 4) confounding measurement and account; 5) outcome
measurement; and 6) analysis and reporting. 
Studies with limited risk of bias were classified
according to methodology. Hypothesis generating studies are exploratory in nature describing
crude (unadjusted) associations between a history of neck injury in a MVC (or exposure to a
MVC) and future NP. Exploratory studies use multivariable techniques or stratification to
identify risk factors related to the onset of NP and a history of neck injury in a MVC (or
exposure to a MVC) while adjusting for other factors. Confirmatory studies have a priori
hypotheses which confirm one or more independent risk factors for incident NP after adjusting
for confounding. 
Data Extraction and Synthesis of Results
One reviewer (PN) created evidence tables from data from studies screened with the QUIPS tool
and a second reviewer (PE) reviewed the tables for accuracy. The studies were
stratified according to whether the exposure was to a MVC or to an injury in a MVC. A metaanalysis
was performed on the exposure of a neck injury in a MVC and future NP in the
studies. We used the QUIPS tool to report on a best evidence synthesis using qualitative
synthesis with evidence statements.  Summary statements were formulated using the
evidence in the summary table to make comparisons and outline the best available evidence.
Inter-rater reliability for the screening of articles was calculated using the kappa coefficient (k)
and 95% confidence intervals (CI). Percentage agreement was calculated between reviewers for
classifying studies into high or low risk of bias following independent critical appraisal. Random
effects meta-analysis for relative risk of the pooled studies, test for heterogeneity (Cochran’s
Q and I²) and absolute risk difference used MedCalc Statistical Software version 18.6 and metaregression.
Publication bias (Funnel plot and Egger regression) used Comprehensive Meta
Analysis v3.3.070 software (2014). Attributable risk (AR) was calculated using the pooled
relative risk (RR) value from the review in the following formula: AR = RR–1/RR*100%. 
The present review complies with the Reporting Items for Systematic Reviews and Meta-
Analyses (PRISMA) statement , and has been registered with the PROSPERO registry
We identified 9,667 citations, removed 672 duplicates, and screened 8,955 articles for eligibility
(Figure 1). In stage 1 screening, 8,942 citations were deemed ineligible. In stage 2 screening, 13
full text papers were reviewed, and 5 articles were excluded as ineligible: unspecified age range
(n=1) , ineligible age range (n=1) , ineligible outcome measures (n=2) [18, 19] and
ineligible exposure definition (n=1).  The inter-rater agreement for screening articles had a
Cohen’s Kappa of 0.87.
We critically appraised 8 articles and 7 articles had low to moderate risk of bias and were
included in our evidence synthesis. [21–27] The reviewers had perfect agreement on the
admissibility of studies (8 agreements over 8 articles appraised).
The studies had varied source populations:
primary care and emergency department patients (3/7 articles) [23–25],
insurance and injury databases (2/7 articles) [22, 27],
police records (1/7 articles) ,
and the general population (1/7 articles)  (Table 1).
The duration of time
between the MVC and the outcome varied across studies:
unknown (3/7 articles) [24–26], and
one or more years (4/7 articles) (Table 2). [21–23, 27]
Exposure to a MVC was determined by:
a question on self-reported neck injury in a MVC (3/7 articles) [24–26],
physician diagnosed neck injury in an emergency room of a hospital (2/7 articles) [23–27],
collision reported in police records (1/7 articles) , and
collision reported in insurance records (1/7 articles). 
Exposure was defined as:
exposure to a rear-end collision without injury and exposure to a rear-end collision with neck/shoulder injury (1/7 articles) ,
exposure to a rear-end collision where it is not known if all subjects were injured (1/7 articles) , and
exposure to a MVC with a neck injury (5/7 articles). [23–27]
groups were defined as:
no prior self-reported neck injury in a MVC ,
randomly selected subjects from the general population which included some with prior exposure to a MVC ,
randomly selected insured drivers with no recorded prior MVC in the insurance database ,
other recorded injuries (not neck injuries) in a MVC ,
consecutive sample of chronic LBP patients  and
other self-reported causes of NP (not MVC related). 
The outcome of NP was measured with:
a self-reported question (4/7 articles) [21, 22, 24, 27] or
a validated questionnaire (3/7 articles). [23, 25, 26]
Studies that controlled for confounding
included: age, gender and other confounders (5/7 articles) [21, 22, 24, 26] and no control for
confounding (2/7 articles). [22, 27]
The country the studies were conducted in were:
the Netherlands ,
Sweden [22, 23] and
the USA. 
Studies were classified according to phases of explanatory analysis for observational studies for
risk of exposure to a MVC and future NP.  The seven risk studies included two hypothesis
generating studies (2/7 articles) [23, 27], four exploratory studies (4/7 articles) [21, 22, 24, 25] and
one confirmatory study (1/7 articles)  (Table 1).
Assessment of Risk of Bias
Low to moderate risk of bias studies met the following criteria in six bias domains: study
participation, study attrition, MVC exposure, NP measurement, study confounding and statistical
analysis and reporting. One study was low risk of bias in all six domains.  However,
the following limitations were noted from the risk assessment:
1) two studies (2/7 articles) had moderate risk of bias in the study participation domain [23, 25];
2) one study (1/7 articles) had moderate risk of bias in the study attrition domain ;
3) four studies (4/7 articles) had moderate risk of bias in NP measurement [21, 22, 24, 27];
4) four studies had moderate risk of bias when controlling for confounding (4/7 studies) [21, 22, 24, 25], and two studies (2/7 articles) had high risk of bias as they did not control for confounding [22, 27]; and
5) one study (1/7 articles) had moderate risk of bias in their statistical analysis and reporting  (Table 3).
One study (1/8 articles) was excluded after critical appraisal that had high risk of bias in the
attrition and confounding domains and moderate risk of bias in the study participation and
statistical analysis and reporting domains. 
Summary of the Evidence
Exposure to a neck injury in a MVC compared to no neck injury in a MVC
Six studies investigated the association between a neck injury in a MVC and future NP. [22–27]
Two hypothesis generating studies found a positive association between a neck injury in a MVC
and future NP: odds ratio (OR) = 2.95 (95% CI [1.97–4.42])  and OR= 9.2 (95% [CI 4.2–
20.1]).  Three exploratory studies found a positive association between a neck injury in a
MVC and future NP: adjusted relative risk (RR)= 2.7 (95% CI [2.1–3.5]) , adjusted OR
(males)= 4.0 (95% CI [2.1–7.5]) and adjusted OR (females)= 2.1 (95% CI [1.3–3.3])  and
adjusted OR= 5.34 (95% CI [1.9–15.0]). 
One confirmatory study found a positive
association between a neck injury in a MVC and future incident NP: Adjusted Hazard Rate Ratio
(HRR) = 2.14 (95% CI [1.12–4.10]).  Random effects meta-analysis of these studies found
a positive association between neck injury in a MVC on future NP across studies (RR=2.3, 95%
CI [1.8–3.1], p=0.001) (Figure 2). Tests for heterogeneity resulted in a Q of 20.4 (DF 5, p=0.001)
and I² of 75.5% (95% CI [44.6%–89.1%]) indicating substantial heterogeneity among the
reviewed studies. A sensitivity analysis was performed and removing each study from the model
one at a time to see if any reduced the heterogeneity.
Removing the study by Tournier et al., (2016)  which had a higher RR than the other studies, slightly reduced the RR=2.1 (95%
CI [1.7–2.5]) while reducing heterogeneity (I²=55.3%, 95% CI [0.0%–83.5%] and
Q=9.4, p=0.06). The RR of 2.3 (95% CI [1.8–3.1]) was used to calculate an AR under the
exposed of 57% for individuals with ongoing NP who have a previous history of neck injury in a
Meta-regression compared the reference studies from hospital and primary care
population [23–25] to studies from insurance and injury databases [22, 27] (coefficient 0.602, SE
0.219 95% CI [0.173–1.0316], Z=2.75, p=0.006). The reference group was also compared to
the study from the general population  coefficient 0.497, SE 0.419 95% CI [0.325–
1.318], Z=1.18, p=0.236).
Meta-regression examined follow-up time from baseline to the
outcome measure (coefficient –0.0037, SE 0.0269 95% CI [–0.057–0.049], Z= –0.14,
p=0.8907). Absolute risk difference between the exposure and control groups in the prevalence
studies was between 21.1% to 25.6% [22–25, 27] and 8.2% in the incidence study. 
Publication bias was tested in a funnel plot (Figure 3) and using Eggers regression (Intercept
2.598, SE 1.805, 95% CI [–2.414–7.609], t-value 1.439, df 4, p=0.223).
Exposure to a MVC compared to no exposure to a MVC
Two exploratory studies examined the association between an exposure to a MVC and future NP. [21, 22] Both of these studies did not find an association between exposure to a rear-end
collision where it is not known if the subjects were all injured, OR= 0.62 (95% CI [0.41–0.94])  or where the subjects did not claim a neck injury to the insurance company, RR= 1.3 (95%
CI [0.8–2.0]). 
The present study is the first systematic review and meta-analysis to estimate the pooled RR
and AR of latent NP etiology in the population of patients who have sustained an acute neck
injury in a MVC. Overall, the evidence suggests that exposure to neck injury in a MVC more
than doubles the risk for developing future NP. Pooling of the data in a random effects metaanalysis
further confirmed a positive association (RR= 2.3, 95% CI [1.8, 3.1]), although subanalysis
found that removing one study from the meta-analysis reduced the heterogeneity. 
The AR under the exposed was determined to be 57% across the studies examining exposure to a
neck injury in a MVC. The AR under the exposed meets the legal standard of “more likely true
than not” where at least ≥ 50% of ongoing NP in those patients previously injured in a past MVC
was attributable to the MVC.  Studies examining exposure to a rear-end collision where it
was not known if the included subjects were injured or where no claim for a neck injury was
made to an insurance company, found no increased risk of future NP.
The reviewed studies were from different source populations, which is important to note due to
the potential for misclassification bias of the exposure. We reviewed three studies from primary
care/emergency rooms [23–25], two studies from injury database/insurance claims [22, 27], one
study from police records  and one study from the general population  (Table 1). Studies
from the general population can capture injured participants, who were missed in other
data sources. For example, participants who did not seek care or report their injury to an insurer
may nonetheless report a history of neck injury in a general population survey. Alternatively,
participants responding to a general population survey may not remember an injury they
sustained in the past. Subjects from police records may have been involved in a MVC but may or
may not have sustained a neck injury. In the studies where individuals were injured in the
MVC there was significant heterogeneity seen in the pooled meta-analysis. In the metaregression
analysis, some of the observed heterogeneity was evident with the studies from source
populations from injury and insurance databases. [22, 27]
Studies can have less than optimal response rates and still be at low risk of selection bias if in
comparing responders to non-responders there is no differential enrollment into the study that
would influence the outcome.  The paper by Nolet et al., (2010)  had a 55% response
rate in the baseline survey, which was not deemed to have resulted in selection bias as there was
low levels of differential response reported.  Berglund et al., (2000) had a low risk of
selection bias as they selected participants from the same population of persons covered by
traffic insurance at Folksam.  They had an acceptable response rate and non-responders did
not differ with regard to age and gender. Other papers at low risk of selection bias recruited
consecutive participants from their target populations. [21, 24]
The studies with low risk of bias from attrition all had good follow-up rates. [21–23, 25, 26] Four
of those five studies compared responders to non-responders for non-differential exposure to a
MVC which made them less likely to suffer from attrition bias. [22, 23, 25, 26] One of the
studies did not compare responders to non-responders at follow-up but had a high follow-up
response rate in the exposure group (95%) and the control group (92%).  One study had a
moderate risk of bias, as only 64.5% responded to the 5–year questionnaire; yet, response rates in
the whiplash and non-whiplash groups were similar and responders in the whiplash group had
similar response rates for both grade I and grade II injuries.  Therefore, it is unlikely that
attrition biased the findings in the studies presented in our review.
Our study selected articles where those exposed to a MVC or neck injury in a MVC were
compared to a comparison group of non-exposed individuals. Having an appropriate comparison
group allows for a determination of excess risk of future prevalent or incident NP associated with
a MVC. The randomly selected control group from the general population in the study
by Bunketorp et al (2005) may have led to an underestimation of risk because the control group
included subjects exposed to a prior MVC (34%) of which 31% of those exposed to a MVC also
reported being injured. 
The measure of neck injury in a MVC varied between studies. Three studies used a question
asking about a prior neck injury [24–26] and two studies used hospital emergency room
diagnosed neck injury. [23, 27] Two other studies relied on injuries in a rear-end collision being
reported to an insurance company  and rear-end collisions reported to the police where it is
not known if everyone was injured.  Self-reported injuries could be more prone to
misclassification bias although we classified this as a low risk of bias. Recall of an event such as
a neck injury in a MVC is likely high. Three studies examined the test-retest reliability of selfreported
questions on the history of injury in a MVC, reporting moderate to substantial reliability
(0.55≤k≤0.80). [32, 34] Further, in a study by Begg et al., (1999) participants were able to recall
injuries 3 years earlier compared to a health system database and police traffic crash records:
86% (95% CI 68%–96%) for unintentional injury; 100% for the type of car involved; 84% for
number of years since the crash.  More importantly, the longitudinal nature of prospective
cohort studies eliminates the possibility of differential exposure recall, meaning exposure
misclassification in the included cohort studies would result in conservative estimates of risk.
The one case-control study we included also had a low chance of recall bias because the authors
selected a chronic back pain control group. These individuals would be just as likely to recall a
MVC as the case group with chronic NP. 
It is important to examine the effects of confounding in cohort and case-control studies as the
association between the exposure and the outcome can be due to confounding factors. Studies
that controlled for confounding did not have a marked effect on the association between the
exposure and the outcome of NP. In the study by Nolet et al. (2010), controlling for a
priori confounding by sociodemographic, general health, comorbidities, depression, cigarette
smoking, body mass index and exercise only slightly reduced the risk of neck injury in a MVC
on future NP.  In a study of primary care patients, when controlling for confounding in a
multivariable regression model, there was an increased risk of NP in patients who reported the
cause of their NP as a MVC.  Finally, one study controlling for age and gender using a
Mantel-Haenszel technique found no change from the crude results on neck injury in a rear-end
collision with NP 7 years later. 
The measurement of various parameters of NP varied between studies, with some studies asking
about the frequency of NP, while others used a binary measure of whether the subject had NP
(yes or no). [21, 22, 24, 27] These studies did not account for the intensity or duration of NP. Other
studies asked a similar question but also compared NP between the exposure group and the
control group with a valid and reliable questionnaire or pain scale (neck disability index (NDI) or
NP numerical rating scale). [23, 25] The NDI has been found to have good to excellent internal
consistency and moderate to excellent test-retest reliability.  Another study from the general
population measured NP with the Chronic Pain Grade Questionnaire  which has been
recommended as an outcome measure for NP in survey research due to its established
psychometric properties. 
There was a wide variation in the timelines between the exposure to a MVC and the outcome of
future neck pain in the studies. Three studies had fixed follow-up times between the exposure
and measure of future neck pain of one year , five years , 7 years  and 17 years. 
Two studies examined a past history of neck injury in a MVC of an unknown duration prior to
the baseline of the studies, following subjects for one year. [25, 26] Finally, a case-control study
examined a past history of a neck injury in a MVC.  Controlling for the follow-up timelines
in the meta-regression did not account for any of the heterogeneity between studies. We did not
find a trend with the timelines between studies.
Five studies compared prevalent, as opposed to incident, NP at follow-up between the group
exposed to a neck injury in a MVC and the comparison group. The risk differences for NP after a
MVC between the injured and uninjured groups were similar across the prevalence studies,
ranging from 21.1% to 25.6%.. [22–25, 27] Although, in prevalence studies it is difficult to
determine whether the outcome is a manifestation of the original neck injury in the MVC or if it
is a new incident case of future NP. The episodic nature of NP also makes it difficult to establish
a new, incident case.  Only one study in our review examined incident troublesome NP in a
population at risk with no or mild NP.  The population at risk excluded those at baseline with
prevalent troublesome NP, resulting in a more accurate estimate of the risk for a new episode of
NP. Further, this study provides more evidence for the causal nature of a neck injury in a MVC,
as the new incident episode of troublesome NP occurred sometime after the MVC. 
It was important to differentiate between studies examining an exposure to a MVC versus
studies examining neck injury in a MVC. Involvement in a MVC is only a meaningful exposure
to the question of causation of future NP if the majority of this group has had an acute neck
injury. Not everyone involved in a rear-end collision sustains an injury as demonstrated in the
Ontario Road Safety Annual Report (2014). There were 63,732 reported rear-end collisions in
Ontario, Canada in 2014 of which 82.5% reported no injuries and 17.5% sustained a personal
injury.  In our review we examined both studies where individuals were exposed to a neck
injury in a MVC and studies where the exposure was being in a rear-end collision where we
don’t know who was injured or where no injury was reported.
In the study by Obelieniene et al.,
(1999) only 10% had NP alone and 18% had NP and headache shortly after the rear-end
collision, so it is apparent that not everyone was injured in the exposure group of this study. 
The comparison group, who were not in a MVC, self-reported more NP one year later than the
MVC-exposed group (OR= 0.62, 95% CI [0.41–0.94]). Further, the study by Berglund et al.,
(2000) found an increased risk of NP seven years later only in the group reporting neck injury in
a rear-end collision and not the group reporting a rear-end collision without neck injury. 
Therefore, we cannot rely on studies where the exposure group was only exposure to a MVC
(where not everyone was injured) to inform on causation of future NP in individuals injured in a
Comparison with other Systematic Reviews
The 2000–2010 Bone and Joint Task Force on NP and Its Associated Disorders reviewed the
scientific literature from 1980 to early 2007 for risk factors for NP.  The authors reported one
study by Berglund et al., (2000) , that was also included in our systematic review, which
reported approximately a three times higher risk of neck and shoulder pain seven years after
a neck injury in a rear-end collision compared to a random sample of drivers not in a MVC. The
Task Force on NP and Its Associated Disorders differed from our review in that we reviewed
only papers which included a comparison group. Although the NP Task Force examined studies
for risk of bias, our study used the QUIPS assessment tool and included a more recent search of
the scientific literature.
Strengths and Limitations
Our systematic review had several strengths. First, we used a comprehensive search strategy that
was developed by a health sciences librarian in conjunction with a content expert and reviewed
by an independent health sciences librarian using the PRESS Checklist.  Second, several
databases were searched with predefined inclusion and exclusion criteria. Third, independent
reviewers were used to screen and critically appraise citations to reduce bias and error. Finally,
the critical appraisal incorporated trained reviewers using a QUIPS assessment tool previously
used in the evaluation of risk studies. 
This review also had limitations. First, our search was limited to studies published in English
which may have excluded relevant studies in other languages, although we are not aware of any
relevant studies that were excluded. Second, our search was limited to studies published in 1998
or later but we do not feel this biased our results. There were no other studies identified on this
topic in a prior review.  Thirdly, it is possible that reviewers had differences in scientific
judgement during the critical appraisal of the studies. We feel that this was minimized by the
consensus process used to determine the internal validity of the studies along with our high interrater
agreement (k=0.87). Finally, our meta-analysis tested for publication bias and used metaregression
to account for heterogeneity between pooled studies. We did not find any publication
bias but we found some heterogeneity that was partially accounted for in the meta-regression
when comparing the different source populations.
We synthesized the evidence from studies on the association between a MVC and future NP (1,
5, 7 and 17 years after injury and a prior history of injury). The evidence from a meta-analysis of
all low to moderate risk of bias studies supports an increased risk of future NP in individuals
who have been acutely injured in a prior MVC (RR=2.3, 95% CI [1.8, 3.1]). Based on the
estimate of the AR risk from the pooled analysis, for the patient who presents with chronic NP
after a past history of an acute MVC-related neck injury and with no intervening injury, 57% of
the cause of the ongoing NP is attributable to the crash in which the injury occurred. There was
no significant association between exposure to a rear-end collision (in which study subjects were
not injured or where it is unknown if there was an injury) and future NP. These results should
help inform patients, clinicians, insurers, governments and the courts on the association between
motor vehicle collisions on future NP, as well as the contribution of a prior MVC-related neck
injury to ongoing NP. The results of this study will need to be updated as further risk studies are
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