Abstract
The objective of this population-based cohort study was to investigate the association between a lifetime history of neck injury from a motor vehicle collision and the development of troublesome neck pain. The current evidence suggests that individuals with a history of neck injury in a traffic collision are more likely to experience future neck pain. However, these results may suffer from residual confounding. Therefore, there is a need to test this association in a large population-based cohort with adequate control of known confounders. We formed a cohort of 919 randomly sampled Saskatchewan adults with no or mild neck pain in September 1995. At baseline, participants were asked if they ever injured their neck in a motor vehicle collision. Six and twelve months later, we asked about the presence of troublesome neck pain (grade II–IV) on the chronic pain grade questionnaire. Multivariable Cox regression was used to estimate the association between a lifetime history of neck injury in a motor vehicle collision and the onset of troublesome neck pain while controlling for known confounders. The follow-up rate was 73.5% (676/919) at 6 months and 63.1% (580/919) at 1 year. We found a positive association between a history of neck injury in a motor vehicle collision and the onset of troublesome neck pain after controlling for bodily pain and body mass index (adjusted HRR = 2.14; 95% CI 1.12–4.10). Our analysis suggests that a history of neck injury in a motor vehicle collision is a risk factor for developing future troublesome neck pain. The consequences of a neck injury in a motor vehicle collision can have long lasting effects and predispose individuals to experience recurrent episodes of neck pain.
Keywords: Neck pain, Whiplash, Epidemiology, Risk, Cohort
Introduction
Whiplash is an acceleration–deceleration mechanism of energy transfer to the neck that occurs in motor vehicle collisions [10, 24]. The trauma can lead to whiplash-associated disorders (WAD), which includes neck pain and other symptoms such as headache, dizziness, and upper extremity numbness [24]. As many as 83% of individuals involved in traffic collisions suffer from whiplash injuries [10, 24, 26]. Consequently, WAD is a common source of pain, disability, and health care utilization in the Western world.
The recently published report of the Bone and Joint Decade 2000–2010 Task Force on Neck Pain and its Associated Disorders found that a significant proportion of patients with WAD develop persistent or recurrent neck pain. Specifically, more than 50% of patients report neck pain 1 year after their injury [9]. Recovery from WAD is negatively associated with initial symptom severity, post-injury psychological distress, passive coping, and the intense initial health care utilization [9].
It has been proposed that individuals with a history of whiplash injuries are more likely to suffer from future episodes of musculoskeletal pain, including neck pain, than those without a history of whiplash injuries. This association is supported by five studies conducted in various source populations [4, 7, 11, 15, 16]. However, two Lithuanian studies of individuals sampled from police records did not support this association [18, 23]. The varying evidence reported in the literature is likely attributable to the differences in study samples, exposure and outcome definition and measurement, and to inadequate control of confounding. Therefore, there is a need for a rigorous, population-based cohort study where the association between a lifetime history of neck injury in a motor vehicle collision and future neck pain can be tested with good control of confounding factors. The objective of this study was to determine whether a lifetime history of neck injury in a motor vehicle collision is associated with an incident episode of troublesome neck pain.
Methods
Study design and source population
We used data from the Saskatchewan Health and Back Pain Survey, a population-based mailed survey of the distribution, determinants, and risks of spinal disorders in the province of Saskatchewan [11]. Saskatchewan is a Canadian province of approximately one million inhabitants that provides universal health care coverage. Eligible for the study were Saskatchewan residents between the ages of 20 and 69 who held a valid Health Services card on August 31, 1995. Excluded 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 [8].
An age-stratified random sample of residents was selected from the Saskatchewan Health Insurance Registration File. The Health Insurance Registration File is a representative and complete list of Saskatchewan residents that includes more than 99% of the population. Saskatchewan Health randomly selected the participants and mailed all surveys to protect the confidentiality of the participants. Participation was voluntary. The University of Saskatchewan Advisory Committee on Ethics in Human Experimentation approved the Saskatchewan Health and Back Pain Survey, and the analysis presented in this paper was approved by the University Health Network Research Ethics Board, Toronto, Canada.
Study sample and population at risk
Of the eligible 593,464 individuals, 2,184 were randomly selected. One-hundred nineteen baseline questionnaires were returned due to mailing errors, five because of ‘health reasons’, four individuals had emigrated and one had died. Of the 2,055 remaining participants, 1,133 (55.1%) returned baseline questionnaires. Two questionnaires were completed by participants outside of the pre-determined age range, and 30 participants did not complete the neck pain questionnaire. Therefore, the eligible sample for this analysis includes 1,101 participants. A comparison of the eligible population and the randomly selected sample revealed no important differences in age, gender, and geographic location of residence. However, a comparison of participants and non-participants suggested that older individuals, women, those married, and those with intense non-disabling neck pain were slightly more likely to participate [8].
The population at risk for this analysis includes individuals who reported grade 0 or I neck pain on the chronic pain grade questionnaire (Table 1). This information was collected in the baseline questionnaire. Given that most individuals suffer from mild (trivial) neck pain annually, we were interested in determining whether neck injury in a motor vehicle collision was a risk factor for significant neck problems.
Table 1.
Classification of neck pain grade (as reproduced from Côté et al. [11])
| Grade | Scoring | Interpretation |
|---|---|---|
| 0 | No pain, no disability | No chronic pain |
| I | PI < 50; DP < 3 | Low pain intensity/low disability |
| II | PI ≥ 50; DP < 3 | High pain intensity/low disability |
| III | DP = 3–4 | High disability/moderately limiting |
| IV | DP = 5–6 | High disability/severely limiting |
PI pain intensity; DP disability points
Data collection
The baseline data were collected in September 1995, and the follow-up data collected 6 and 12 months later. The 6-month follow-up questionnaire was sent to respondents of the baseline questionnaire, and the 12-month follow-up to respondents of the 6-month follow-up.
Exposure
The exposure was measured by asking participants: “Have you ever injured your neck in a motor vehicle accident?”
Outcome
Neck pain was measured with the chronic pain questionnaire at baseline, and 6 and 12 months later. The questionnaire measures the 6-month period prevalence of neck pain, and grades neck pain and its related disability into five ordered categories, based on seven questions and has been described elsewhere [11, 28]. The instrument has good psychometric properties [14]. Participants reporting grade II, III or IV neck pain in the previous 6 months were classified as having troublesome neck pain.
Potential confounders
The following potential confounders were identified a priori: demographic characteristics (age, gender, marital status, and location of residence), socioeconomic variable (education, income, and employment status), general health (SF36), comorbidities, depression, cigarette smoking, BMI, and exercise. We did not test the confounding effect of baseline neck pain grade (grade 0 or I) because it lies on the casual pathway between our exposure of a neck injury in a motor vehicle collision and outcome of troublesome neck pain. As such, it is an intermediate variable and does not meet the definition of a confounder.
Socio-demographics
Gender, age, marital status, education level, income, employment status, and location of residence (city, town, village, rural municipality, and Indian Reserve) were included in the analysis.
Health-related quality of life (SF36)
The Medical Outcomes Study SF-36 standard English-Canadian version 1.0 was used to measure self-perceived general health status [30]. The questionnaire assesses health-related quality of life in eight domains: physical functioning, bodily pain, role limitations due to physical health problems, role limitations due to emotional health, mental health, social functioning, vitality, and general health. The SF-36 has been shown to have high internal consistency [6] and test–retest reliability [1]. The SF-36 has been shown to have good validity in studies involving physical and mental health criteria when compared to the longer questionnaire used in the Medical Outcomes Study [29].
Comorbidities
The presence of comorbidities and their self-perceived impact on health were measured with the comorbidity questionnaire. The questionnaire includes questions about allergies, arthritis, high blood pressure, heart/circulation, digestive disorders, headache, and mental/emotional disorders. The self-perceived impact of each comorbidity on one’s health is rated on a 4-point ordinal scale as: (1) not at all, (2) mild, (3) moderate, and (4) severe. The questionnaire has been shown to have good test–retest reliability (ICC = 0.93) and adequate face, concurrent, and convergent validity [20, 27].
Depressive symptomatology
The Center for Epidemiological Studies Depression scale (CES-D) was used to measure depressive symptomatology [19]. This questionnaire has a possible score of 60 with 16 as the cutoff score for depression in the general population. The 16-point cutoff for depressive symptomatology had a sensitivity of 100% for major depression and 88% for the specificity [2]. The questionnaire has been shown to be reliable and valid in various populations with good internal consistency (alpha coefficients >0.85) [5, 13, 19, 20].
Exercise
Exercise frequency was measured with a question asking the average number of days per week participating in a minimum of 30 min of exercise. The question asked about the frequency of exercise during the previous 6 months.
Cigarette smoking
Self-report of smoking status was obtained and categorized as non-smoker, ex-smoker or current smoker.
Body mass index
Self-reported height and weight were used to calculate the body mass index (BMI, kg/m2).
Analysis
We described the baseline characteristics of the sample stratified by exposure status. We aimed to determine whether loss to follow-up led to attrition bias by comparing responders and non-responders to the 6 and 12-month follow-ups by comparing the baseline characteristics of exposed and non-exposed participants.
Our objective was to determine whether a history of neck injury in a motor vehicle collision is independently associated with the development of troublesome neck pain. However, identifying confounders of the association between a lifetime history of neck injury in a traffic collision and troublesome neck pain is challenging. The difficulty lies in insuring that the variables considered as potential confounders are indeed confounders and not mediators of the association of interest. A mediator is an intermediate effect of the exposure, and lies on the causal pathway between the exposure and the outcome.
We built Cox proportional hazard models to measure the association between a history of neck injury in a motor vehicle collision and troublesome neck pain. Our modeling included three steps. First, we built a univariate model to estimate the crude association between our exposure and outcome. Second, we built as series of bivariate models to determine which variables were confounders of the association of interest. Variables that led to a 10% change in the exposure regression coefficient were deemed to be confounders and included in the final model. Finally, our final model included the exposure and all confounders identified in the second step [22]. SPSS version 15 was used for the analysis [25].
Results
Sample characteristics
Our population at risk included 919 participants. The follow-up rate was 73.5% (676/919) at 6 months and 63.1% (580/919) at 12 months.
Of the 919 eligible adults with grade 0 or I neck pain at baseline, 122 (13.3%) reported a history of neck injury in a motor vehicle collision. Fewer participants with a history of neck injury in a motor vehicle collision were married and a higher percentage lived in urban Saskatchewan. A higher proportion of exposed than unexposed individuals reported a household income of less than $20,000 and fewer reported incomes over $60,000. Further, more participant with a history of neck injury worked part time or were unemployed, but fewer were retired. With the exception of hypertension and low back pain, all comorbidities were more common among participants with a history of neck injury in a motor vehicle collision. Further, the self-perceived impact of comorbidities was more pronounced in individuals who had a neck injury in a motor vehicle collision. Exposed subjects (70.5%) were more likely to suffer from grade I neck pain than unexposed (41.4%). The proportion of current smokers was higher in the exposed group (Table 2).
Table 2.
Frequency distribution of the demographic socioeconomic characteristics, comorbidities, and health-related characteristics by exposure category at baseline
| Characteristic | History of neck injury in motor vehicle collision | |
|---|---|---|
| Yes (%) | No (%) | |
| Age (years) [mean (SD)] | 42.0 (12.3) | 44.9 (14.4) |
| Gender (no., %) | ||
| Male | 45 (36.8) | 406 (50.9) |
| Female | 77 (63.2) | 391 (49.1) |
| Marital status (no., %) | ||
| Married | 86 (71.7) | 605 (76.6) |
| Divorced | 14 (11.6) | 49 (6.2) |
| Widowed | 3 (2.5) | 20 (2.5) |
| Single | 18 (14.9) | 116 (14.7) |
| Location of residence (no., %) | ||
| Urban | 65 (53.3) | 278 (35.0) |
| Rural | 57 (46.7) | 517 (65.0) |
| Annual household income (no., %) | ||
| $0–20,000 | 27 (23.7) | 140 (19.1) |
| $20,001–40,000 | 38 (33.3) | 263 (35.8) |
| $40,001–60,000 | 28 (24.6) | 171 (23.3) |
| Over $60,000 | 21 (18.4) | 160 (21.8) |
| Education (no., %) | ||
| Less than grade 8 | 7 (5.8) | 44 (5.6) |
| High school | 29 (24.0) | 171 (21.6) |
| High-school grade | 36 (29.8) | 207 (26.2) |
| Post-secondary | 36 (29.8) | 248 (31.4) |
| University grade | 13 (10.7) | 120 (15.2) |
| Full time worker (no., %) | ||
| Yes | 60 (50.0) | 408 (51.8) |
| No | 60 (50.0) | 380 (48.2) |
| Part time worker (no., %) | ||
| Yes | 22 (18.3) | 118 (15.0) |
| No | 98 (81.7) | 669 (85.0) |
| Unemployed (no., %) | ||
| Yes | 11 (9.2) | 38 (4.8) |
| No | 109 (90.8) | 750 (95.2) |
| Retired (no., %) | ||
| Yes | 3 (2.5) | 106 (13.5) |
| No | 117 (97.5) | 682 (86.5) |
| Homemaker (no., %) | ||
| Yes | 23 (19.2) | 134 (17.0) |
| No | 97 (80.8) | 654 (83.0) |
| Student (no., %) | ||
| Yes | 7 (5.8) | 30 (3.8) |
| No | 113 (94.2) | 758 (96.2) |
| Comorbidities | ||
| Allergy | ||
| Absent | 57 (47.1) | 472 (60.8) |
| No/Min impact on health | 45 (37.2) | 227 (29.3) |
| Mod./Sev. impact on health | 19 (15.7) | 77 (9.9) |
| Arthritis | ||
| Absent | 85 (71.4) | 579 (75.1) |
| No/Min impact on health | 17 (14.3) | 129 (16.7) |
| Mod./Sev. impact on health | 17 (14.3) | 63 (8.2) |
| Breathing disorders | ||
| Absent | 80 (66.7) | 565 (72.4) |
| No/Min impact on health | 29 (24.2) | 169 (21.7) |
| Mod./Sev. impact on health | 11 (9.2) | 46 (5.9) |
| Cardiovascular disorders | ||
| Absent | 98 (80.3) | 687 (87.9) |
| No/Min impact on health | 19 (15.6) | 74 (9.5) |
| Mod./Sev. impact on health | 5 (4.1) | 21 (2.7) |
| Hypertension | ||
| Absent | 103 (85.1) | 666 (85.4) |
| No/Min impact on health | 13 (10.7) | 84 (10.8) |
| Mod./Sev. impact on health | 5 (4.1) | 30 (3.8) |
| Digestive disorders | ||
| Absent | 88 (73.9) | 596 (76.0) |
| No/Min impact on health | 18 (15.1) | 141 (18.0) |
| Mod./Sev. impact on health | 13 (10.9) | 47 (6.0) |
| Low back pain | ||
| Absent | 31 (25.8) | 254 (32.3) |
| Low intensity/low disability | 68 (56.7) | 394 (50.1) |
| High intensity/low disability | 8 (6.7) | 81 (10.3) |
| High disability | 13 (10.8) | 57 (7.3) |
| Depressive symptomatology | ||
| Absent | 90 (75.6) | 628 (83.0) |
| Present | 29 (24.4) | 129 (17.0) |
| Cigarette smoking | ||
| Never smoked | 53 (44.9) | 417 (54.0) |
| Past smoker | 31 (26.3) | 191 (24.7) |
| Current smoker | 34 (28.8) | 164 (21.2) |
| Body mass index (kg/m2)—quartiles | ||
| >28.71 | 31 (26.1) | 196 (25.2) |
| 25.77–28.71 | 28 (23.5) | 203 (26.1) |
| 23.42–25.76 | 32 (26.9) | 186 (23.9) |
| ≤23.41 | 28 (23.5) | 193 (24.8) |
| General health [Mean (SD)] | 63.7 (14.5) | 65.3 (12.6) |
| No. of days of exercise/week [Mean (SD)] | 2.93 (2.07) | 2.83 (2.16) |
| Graded neck pain | ||
| Grade 0 | 36 (29.5) | 467 (58.6) |
| Grade 1 | 86 (70.5) | 330 (41.4) |
Min minimal; Mod moderate; Sev severe
Attrition
In the group not exposed to a neck injury in a motor vehicle collision, response to the follow-up survey was positively associated with female gender. In the exposed group, non-response to the follow-up survey was positively associated with increased depression and headaches that moderately to severely impact their health (Tables 3, 4).
Table 3.
Comparison of responders and non-responders at 6 months for frequency distribution of the demographic socioeconomic characteristics and comorbidities by exposure category at baseline
| Characteristic | Exposed to neck injury in a MVC | Not exposed to neck injury in MVC | ||
|---|---|---|---|---|
| Responder | Non-responder | Responder | Non-responder | |
| Age (years) [Mean (SD)] | 43.5 (12.38) | 39.3 (11.67) | 46.1 (13.30) | 40.8 (14.04) |
| Gender (no., %) | ||||
| Male | 28 (36.4) | 17 (37.8) | 304 (49.0) | 102 (58.0) |
| Female | 49 (63.6) | 28 (62.2) | 317 (51.0) | 74 (42.0) |
| Marital status (no., %) | ||||
| Married | 54 (70.1) | 32 (72.7) | 480 (77.8) | 125 (72.3) |
| Divorced | 8 (10.4) | 6 (13.6) | 39 (6.3) | 10 (5.8) |
| Widowed | 2 (2.6) | 1 (2.3) | 20 (3.2) | 0 (0.0) |
| Single | 13 (16.9) | 5 (11.4) | 78 (12.6) | 38 (22.0) |
| Location of residence (no., %) | ||||
| Urban | 41 (53.2) | 24 (53.3) | 224 (36.1) | 54 (30.9) |
| Rural | 36 (46.8) | 21 (46.7) | 396 (63.9) | 121 (69.1) |
| Annual household income (no., %) | ||||
| $0–20,000 | 13 (17.3) | 14 (35.9) | 102 (17.6) | 38 (24.4) |
| $20,001–40,000 | 29 (38.7) | 9 (23.1) | 208 (36.0) | 55 (35.3) |
| $40,001–60,000 | 19 (25.3) | 9 (23.1) | 134 (23.2) | 37 (23.7) |
| Over $60,000 | 14 (18.7) | 7 (17.9) | 134 (23.2) | 26 (16.7) |
| Education (no., %) | ||||
| Less than grade 8 | 4 (5.2) | 3 (6.8) | 32 (5.2) | 12 (6.9) |
| High school | 16 (20.8) | 13 (29.5) | 128 (20.7) | 43 (24.9) |
| High school grade | 26 (33.8) | 10 (22.7) | 154 (25.0) | 53 (30.6) |
| Post-secondary | 21 (27.3) | 15 (35.1) | 199 (32.3) | 49 (28.3) |
| University grade | 10 (13.0) | 3 (6.8) | 104 (16.9) | 16 (9.2) |
| Full time worker (no., %) | ||||
| Yes | 39 (51.3) | 21 (47.7) | 306 (49.8) | 102 (58.6) |
| No | 37 (48.7) | 23 (52.3) | 308 (50.2) | 72 (41.4) |
| Part time worker (no., %) | ||||
| Yes | 16 (21.1) | 6 (13.6) | 94 (15.3) | 24 (13.8) |
| No | 60 (78.9) | 38 (86.4) | 519 (84.7) | 150 (86.2) |
| Unemployed (no., %) | ||||
| Yes | 4 (5.3) | 7 (15.9) | 25 (4.1) | 13 (7.5) |
| No | 72 (94.7) | 37 (84.1) | 589 (95.9) | 161 (92.5) |
| Retired (no., %) | ||||
| Yes | 2 (4.0) | 1 (2.3) | 98 (16.0) | 8 (4.6) |
| No | 74 (97.4) | 43 (97.7) | 516 (84.0) | 166 (95.4) |
| Homemaker (no., %) | ||||
| Yes | 14 (18.4) | 9 (20.5) | 111 (18.1) | 23 (13.2) |
| No | 62 (81.6) | 35 (79.5) | 503 (81.9) | 151 (86.8) |
| Student (no., %) | ||||
| Yes | 4 (5.3) | 3 (6.8) | 21 (3.4) | 9 (5.2) |
| No | 72 (94.7) | 41 (93.2) | 593 (96.6) | 165 (94.8) |
| Comorbidities (no., %) | ||||
| Allergy | ||||
| Absent | 36 (46.8) | 21 (47.7) | 361 (59.3) | 111 (66.5) |
| No/Min impact on health | 29 (37.7) | 16 (36.4) | 185 (30.4) | 42 (25.1) |
| Mod./Sev. impact on health | 12 (15.6) | 7 (15.9) | 63 (10.3) | 14 (8.4) |
| Arthritis | ||||
| Absent | 53 (69.7) | 32 (74.4) | 445 (73.7) | 134 (80.2) |
| No/Min impact on health | 10 (13.2) | 7 (16.3) | 106 (17.5) | 23 (13.8) |
| Mod./Sev. impact on health | 13 (17.1) | 4 (9.3) | 53 (8.8) | 10 (6.0) |
| Breathing disorders | ||||
| Absent | 56 (73.7) | 24 (54.5) | 444 (72.8) | 121 (71.2) |
| No/Min impact on health | 14 (18.4) | 15 (34.1) | 129 (21.1) | 40 (23.5) |
| Mod./Sev. impact on health | 6 (7.9) | 5 (11.4) | 37 (6.1) | 9 (5.3) |
| Hypertension | ||||
| Absent | 68 (88.3) | 35 (79.5) | 517 (84.5) | 149 (88.7) |
| No/Min impact on health | 7 (9.1) | 6 (13.6) | 69 (11.3) | 15 (8.9) |
| Mod./Sev. impact on health | 2 (2.6) | 3 (6.8) | 26 (4.2) | 4 (2.4) |
| Cardiovascular disorders | ||||
| Absent | 62 (80.5) | 36 (80.0) | 534 (87.3) | 153 (90.0) |
| No/Min impact on health | 12 (15.6) | 7 (15.6) | 61 (10.0) | 13 (7.6) |
| Mod./Sev. impact on health | 3 (3.9) | 2 (4.4) | 17 (2.8) | 4 (2.4) |
| Digestive disorders | ||||
| Absent | 57 (75.0) | 31 (72.1) | 456 (74.3) | 140 (82.4) |
| No/Min impact on health | 12 (15.8) | 6 (14.0) | 121 (19.7) | 20 (11.8) |
| Mod./Sev. impact on health | 7 (9.2) | 6 (14.0) | 37 (6.0) | 10 (5.9) |
| Low back pain | ||||
| Absent | 21 (27.6) | 10 (22.7) | 196 (31.9) | 58 (33.7) |
| Low intensity/low disability | 43 (56.6) | 25 (56.8) | 308 (50.2) | 86 (50.0) |
| High intensity/low disability | 3 (3.9) | 5 (11.4) | 66 (10.7) | 15 (8.7) |
| High disability | 9 (11.9) | 4 (9.1) | 44 (7.2) | 13 (7.5) |
| Headache | ||||
| Absent | 32 (42.1) | 14 (31.8) | 303 (49.5) | 88 (51.5) |
| No/min. impact on health | 32 (42.1) | 16 (36.4) | 235 (38.4) | 63 (36.8) |
| Mod./Sev. impact on health | 12 (15.8) | 14 (31.8) | 74 (12.1) | 20 (11.7) |
| Depressive symptomatology | ||||
| Absent | 59 (77.6) | 31 (72.1) | 493 (83.4) | 135 (81.3) |
| Present | 17 (22.4) | 12 (27.9) | 98 (16.6) | 31 (18.7) |
Table 4.
Comparison of responders and non-responders at 12 months for frequency distribution of the demographic socioeconomic characteristics and comorbidities by exposure category at baseline
| Characteristic | Exposed to neck injury in a MVC | Not exposed to neck injury in MVC | ||
|---|---|---|---|---|
| Responder | Non-responder | Responder | Non-responder | |
| Age (years) [mean (SD)] | 45.1 (12.62) | 38.8 (11.14) | 46.9 (12.96) | 40.8 (13.40) |
| Gender (no., %) | ||||
| Male | 23 (37.7) | 22 (36.1) | 259 (48.5) | 147 (55.9) |
| Female | 38 (62.3) | 39 (63.9) | 275 (51.5) | 116 (44.1) |
| Marital status (no., %) | ||||
| Married | 42 (68.9) | 44 (73.3) | 417 (78.7) | 188 (72.3) |
| Divorced | 7 (11.5) | 7 (11.7) | 32 (6.0) | 17 (6.5) |
| Widowed | 3 (4.9) | 0 (0.0) | 20 (3.8) | 0 (0) |
| Single | 9 (14.8) | 9 (15.0) | 61 (11.5) | 55 (21.2) |
| Location of residence (no., %) | ||||
| Urban | 33 (54.1) | 32 (52.5) | 188 (35.2) | 90 (34.5) |
| Rural | 28 (45.9) | 29 (47.5) | 346 (64.8) | 171 (65.5) |
| Annual household income (no., %) | ||||
| $0–20,000 | 9 (15.3) | 18 (32.7) | 75 (15.2) | 65 (27.2) |
| $20,001–40,000 | 22 (37.3) | 16 (29.1) | 185 (37.4) | 78 (32.6) |
| $40,001–60,000 | 16 (27.1) | 12 (21.8) | 120 (24.2) | 51 (21.3) |
| Over $60,000 | 12 (16.4) | 9 (16.4) | 115 (23.2) | 45 (18.8) |
| Education (no., %) | ||||
| Less than grade 8 | 3 (4.9) | 4 (6.7) | 27 (5.1) | 17 (6.5) |
| High school | 12 (19.7) | 17 (23.3) | 112 (21.1) | 59 (22.7) |
| High school grade | 22 (36.1) | 14 (27.0) | 129 (24.3) | 78 (30.0) |
| Post-secondary | 16 (26.2) | 20 (33.3) | 172 (32.5) | 76 (29.2) |
| University grade | 8 (13.1) | 5 (8.3) | 90 (17.0) | 30 (11.5) |
| Full time worker (no., %) | ||||
| Yes | 36 (59.0) | 24 (40.7) | 261 (49.4) | 147 (56.5) |
| No | 25 (41.0) | 35 (59.3) | 267 (50.6) | 113 (43.5) |
| Part time worker (no., %) | ||||
| Yes | 14 (23.0) | 8 (13.6) | 82 (15.6) | 36 (13.8) |
| No | 47 (77.0) | 51 (86.4) | 445 (84.4) | 224 (86.2) |
| Unemployed (no., %) | ||||
| Yes | 1 (1.6) | 10 (16.9) | 16 (3.0) | 22 (8.5) |
| No | 60 (98.4) | 49 (83.1) | 512 (97.0) | 238 (91.5) |
| Retired (no., %) | ||||
| Yes | 2 (3.3) | 1 (1.7) | 90 (17.0) | 16 (6.2) |
| No | 59 (96.7) | 58 (98.3) | 438 (83.0) | 244 (93.8) |
| Homemaker (no., %) | ||||
| Yes | 10 (16.4) | 13 (22.0) | 95 (18.0) | 39 (15.0) |
| No | 51 (83.6) | 46 (78.0) | 433 (82.0) | 221 (85.0) |
| Student (no., %) | ||||
| Yes | 1 (1.6) | 6 (10.2) | 14 (2.7) | 16 (6.2) |
| No | 60 (98.4) | 53 (89.8) | 514 (97.3) | 244 (93.8) |
| Comorbidities (no., %) | ||||
| Allergy | ||||
| Absent | 28 (45.9) | 29 (48.3) | 312 (59.5) | 160 (63.5) |
| No/Min impact on health | 24 (39.3) | 21 (35.0) | 158 (30.2) | 69 (27.4) |
| Mod./Sev. impact on health | 9 (14.8) | 10 (16.7) | 54 (10.3) | 23 (9.1) |
| Arthritis | ||||
| Absent | 41 (68.3) | 44 (74.6) | 383 (73.5) | 196 (78.4) |
| No/Min impact on health | 10 (16.7) | 7 (11.9) | 91 (17.5) | 38 (15.2) |
| Mod./Sev. impact on health | 9 (15.0) | 8 (13.6) | 47 (9.0) | 16 (6.4) |
| Breathing disorders | ||||
| Absent | 44 (73.3) | 36 (60.0) | 386 (73.5) | 179 (70.2) |
| No/Min impact on health | 11 (18.3) | 18 (30.0) | 108 (20.6) | 61 (23.9) |
| Mod./Sev. impact on health | 5 (8.3) | 6 (10.0) | 31 (5.9) | 15 (5.9) |
| Hypertension | ||||
| Absent | 54 (88.5) | 49 (81.7) | 444 (84.3) | 222 (87.7) |
| No/Min impact on health | 5 (8.2) | 8 (13.3) | 60 (11.4) | 24 (9.5) |
| Mod./Sev. impact on health | 2 (3.3) | 3 (5.0) | 23 (4.4) | 7 (2.8) |
| Cardiovascular disorders | ||||
| Absent | 50 (82.0) | 48 (78.7) | 465 (88.4) | 222 (86.7) |
| No/Min impact on health | 8 (13.1) | 11 (18.0) | 49 (9.3) | 25 (9.8) |
| Mod./Sev. impact on health | 3 (4.9) | 2 (3.3) | 12 (2.3) | 9 (3.5) |
| Digestive disorders | ||||
| Absent | 46 (76.7) | 42 (71.2) | 394 (74.6) | 202 (78.9) |
| No/Min impact on health | 10 (16.7) | 8 (13.6) | 101 (19.1) | 40 (15.6) |
| Mod./Sev. impact on health | 4 (6.7) | 9 (15.3) | 33 (6.3) | 14 (5.5) |
| Low back pain | ||||
| Absent | 14 (23.0) | 17 (28.8) | 172 (32.6) | 82 (31.8) |
| Low intensity/low disability | 39 (63.9) | 29 (49.2) | 263 (49.8) | 131 (50.8) |
| High intensity/low disability | 2 (3.3) | 6 (10.2) | 52 (9.8) | 29 (11.2) |
| High disability | 6 (9.8) | 7 (11.9) | 41 (7.7) | 16 (6.2) |
| Headache | ||||
| Absent | 25 (42.4) | 21 (34.4) | 262 (49.8) | 129 (50.2) |
| No/min. impact on health | 27 (45.8) | 21 (34.4) | 204 (38.8) | 94 (36.6) |
| Mod./Sev. impact on health | 7 (11.9) | 19 (31.1) | 60 (11.4) | 34 (13.2) |
| Depressive symptomatology | ||||
| Absent | 47 (78.3) | 43 (72.9) | 433 (84.7) | 195 (79.3) |
| Present | 13 (21.7) | 16 (27.1) | 78 (15.3) | 51 (20.7) |
Association between history of neck injury in a motor vehicle collision and troublesome neck pain
We found a positive crude association between a history of neck injury in a motor vehicle collision and the development of troublesome neck pain at 6 and/or 12 months (HRR = 2.43; 95% CI 1.28–4.60). Age and gender did not alter this association. However, scores on the bodily pain scale of the SF-36 and BMI mildly reduced the strength of the crude association (HRR = 2.14; 95% CI 1.12–4.10).
Discussion
Our survey was the first North American cohort study to investigate the association between a lifetime history of neck injury resulting from a motor vehicle collision and the development of troublesome neck pain. Our results suggest that the incidence of troublesome neck pain is higher in individuals who have a history of neck injury in a motor vehicle collision.
Our study has limitations. Neck pain follows a recurrent course and that risk factors for future episodes, such as motor vehicle collisions, may have a mediating effect on the incidence of pain and disability in those with a prior history of neck pain. Future studies need to test this hypothesis.
Our exposure, neck injury in a motor vehicle collision, could suffer from differential misclassification. It is possible that participants with recurrent neck pain were more likely to remember an injury in a traffic collision than those who remained free of neck pain. However, we believe that this bias had minimal impact on our results because it is likely that all participants would remember an event such as being injured in a motor vehicle collision. Data from two studies support the view that individuals can recall injuries sustained in a recent motor vehicle collision. Self-reported motor vehicle collision injuries 12 months earlier in the Canadian National Population Health Survey were not significantly different from the police reported data from Transport Canada [21]. Moreover, in a small sample of young adults, self-reported injury over the previous 3 years was comparable to hospital discharge file data and police motor vehicle collision reports [3].
Our analysis of attrition suggests that the hazard rate ratio of this study could have been underestimated. A higher percentage of females responded to the follow-up surveys in the non-exposed group, and females are more likely to report neck pain than males [17].
There were a lower percentage of responders in the exposed group with depression at 6 months, and depression is a risk factor for the development of neck pain [17]. Finally, in the exposed group, participants with headaches that had a moderate to severe impact on health were less likely to respond to the survey at both 6 and 12 months. Attrition varied across employment status, education, and income, but there was no clear trend in attrition to suggest that the results were biased.
Our analysis may have underestimated the true effect of neck injury in a motor vehicle collision on the development of a future episode of troublesome neck pain. It is likely that in excluding subjects with prevalent troublesome neck pain from our cohort, we excluded some subjects that had developed a new episode of troublesome neck pain (incident cases) after exposure to a motor vehicle collision but prior to the baseline survey. Excluding these cases would likely cause an underestimation of the true incidence of troublesome neck pain after a motor vehicle collision.
Our study augments the evidence of a positive association between neck injury in a motor vehicle collision and future neck pain. The strength of our study is in our ability to test for the confounding effect of more variables than prior studies, which mostly controlled for age and gender [4, 7, 15, 16, 18]. In our final model, we controlled for the effects of baseline bodily pain and the BMI. It is possible that bodily pain was in fact a mediating variable that lies on the causal pathway between the exposure to neck injury in a motor vehicle collision and the outcome of troublesome neck pain.
Our results inform the debate surrounding the etiology of neck pain in the population. Neck pain is a recurrent disorder characterized by the periods of the fluctuating pain and disability [12]. To date, few studies have identified risk factors for the recurrent episodes of the neck pain. Our study raises the hypothesis that a past history of a neck injury in a MVC is one of the determinants of recurrent neck pain. Our analysis provides the public, clinicians, and insurers with evidence that a past neck injury in a motor vehicle collision may have a significant role in the development of future episodes of pain and disability. While the causal mechanisms linking a past history of neck injury following a motor vehicle collision and future neck pain remain unknown, it likely involves complex relationships between biological, psychological, and social factors. Future research needs to focus on elucidating these mechanisms within the biopsychosocial model of health.
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