Section 2. The Quebec Whiplash-Associated Disorders Cohort Study

CHAIRPERSON'S NOTE: This section is a discrete report of original research conducted by Samy Suissa, Susan Harder, and Martin Veilleux under the auspices of the Task Force in fulfillment of its mandate. Thus, he and his coauthors, with the agreement of the Editor of Spine, will also cite this report as a peer-reviewed article, when appropriate in support of further research. Two previous reports produced by the SAAQ have presented analyses of data from subjects compensated for whiplash, indicating the growing importance of this problem in Quebec since 1978.16,29 Close to 20% of claimants to the SAAQ are recognized as having whiplash, making it the most common type of injury for which claims are submitted.34,35 In British Columbia and Saskatchewan, two other Canadian provinces with single-payer motor vehicle insurance programs, staggering proportions of 68% and 85% of the claims paid out, respectively, in these two provinces are for whiplash.35,98 Finally, the cost of whiplash injuries sustained in motor vehicle collisions represents a substantial financial burden to the SAAQ.58 In this study, using the claims database of the SAAQ, we estimate the incidence of compensated whiplash injury in Quebec and describe its variation by age, gender, and geographic region. We identify the sociodemographic and collision-related prognostic factors associated with the duration of compensation and the risk of recurrence of whiplash injury, using a large, population-based cohort. The direct medical and compensation cost of whiplash injury is assessed, along with its association with duration of compensation. ▪ Methods Design. The source population for this epidemiologic study is made up of all persons who sustained a whiplash injury in a motor vehicle collision in 1987 in Quebec and who submitted a claim for compensation to the SAAQ. The study subjects were identified from the SAAQ's computerized information systems by searching for individuals with an international classification of diseases-version 9 diagnostic code of 847.0 (sprains and strains of the neck, including whiplash injury). The year 1987 was selected because in that year the SAAQ achieved virtually complete coding of claimant-injury data by professional medical archivists. A historical cohort design was used. The primary source cohort was defined as all subjects for whom some form of compensation was received from the SAAQ (i.e., reimbursement for one or more collision-related expenses or compensation to replace regular income), rather than simply as those who submitted a claim to the SAAQ. This source cohort was used in all analyses not involving collision-related data, such as the analyses of costs. A source subcohort was formed of all subjects in the primary cohort for whom collision-related data from a police accident report were available in the SAAQ's computerized databases. This subcohort was used as the source in all analyses involving. collision-related data, such as the analyses of duration of absence and of recurrence. The date of entry into the cohort was defined as the date of the collision. The exit date from the cohort was the earliest of either the date on which the whiplash subject's file was closed by the SAAQ or the date on which the data were extracted from the SAAQ's computerized databases (May 1993) for the purposes of this study. The cohort was followed for approximately 6 years. Factors Under Study. The potential prognostic factors that were available in the SAAQ's computerized databases for all members were sociodemographic (gender, age, area of residence, marital status, employment status, net income, and number of dependents of the whiplash subject). For the subcohort for whom collision-related data from a police accident report were available, collision-related factors (severity, type of vehicle occupied by the subject, position of subject in the vehicle, type of collision, seatbelt use, direction of collision, number of vehicles involved, and the authorized speed limit at the collision location) were used. In addition, the presence of multiple injuries was indicated. Outcome Variables. The first outcome of interest was the duration of absence from usual activities for which some financial compensation was given. This was defined as the number of days between the date of the collision and the last date for which compensation.to replace regular income was made by the SAAQ. This outcome corresponded roughly to the amount of time taken off work by the whiplash subject (if the subject was employed) or the length of time during which the whiplash subject could not carry out his or her usual activities (if the subject was a student, homemaker, retiree, or unemployed). SAAQ policy dictates that motor vehicle collision subjects who can return to work or to their usual activities within 7 days of the collision are ineligible to receive compensation to replace regular income, but may receive reimbursements for expenses. Such subjects, whose injuries were presumably minor, were assigned a mean duration of 3.5 days, or one half of the 7-day waiting period required by the SAAQ. For all others, the absence was taken as the duration of compensation plus 7 days. Because the duration of compensation is measured cumulatively by the SAAQ and does not allow successive intervals of compensation to be distinguished in cases of recurrence, the study cohort for this first outcome excluded all subjects who experienced a recurrence. The second outcome of interest was whether or not the subject experienced a recurrence or relapse of the injury. For the purpose of this study, recurrence was defined as the return of apparently resolved symptoms after a single motor vehicle collision in which the subject was involved in 1987. It did not include "reoccurrences" of whiplash resulting from subsequent motor vehicle collisions. The study cohort for this second outcome included only those individuals diagnosed with whiplash as their sole injury. This was necessary to ensure that the recurrence was related only to the whiplash injury and not to another injury sustained during the collision. The third outcome under study was the financial cost of whiplash injury to the SAAQ. For descriptive purposes, the distribution of costs according to the type of reimbursement or compensation was determined for all subjects who submitted a claim to the SAAQ for a whiplash injury sustained in 1987. The medical cost associated with whiplash injury (besides those costs covered by Quebec's universal health insurance plan or other private insurance plans) comprised the fees and expenses that are routinely reimbursed by the SAAQ, such as expenses for medical apparatus necessary for the social and professional integration of whiplash patients undergoing rehabilitation; expenses for professional services used in the development of a rehabilitation plan (e.g, psychologists, psychiatrists); expenses for medical and paramedical care not covered by the provincial or other health insurance plans; hospital expenses not covered by the provincial or other health insurance plans; medical expenses (prescriptions); ambulance fees; expenses for orthoses, prostheses; physiotherapy fees; and fees for medical examinations or expert medical consultations and evaluations not covered by the provincial or other health insurance plans. The study cohort for this cost outcome was the entire cohort of subjects who received some compensation from the SAAQ in 1987 for a whiplash injury. Analysis. Using all whiplash patients who received some compensation from the SAAQ in 1987, the age- and gender-specific incidence rates for whiplash injury in Quebec were calculated using the 1987 stratum-specific Quebec population figures in the denominator99. The resulting rates are thus of the incidence of compensated whiplash injury. Region-specific incidence rates were also calculated for the 16 administrative regions in the province. These rates were based on the region of residence of the whiplash subjects rather than the region in which the collision occurred because the collision location information was frequently unavailable from the computerized databases. Driver-specific incidence rates using the number of licensed drivers in the province as the denominator99 could only be calculated by extrapolation because of the lack of collision-related data on many of the whiplash cases. It was therefore assumed thatthe proportion of drivers among whiplash cases for whom collision-related data were available was equal to the proportion of drivers among whiplash cases whose collision data were missing from the databases. Duration of absence and costs were analyzed using simple methods for continuous data. Comparisons were based on the Wilcoxon two-sample nonparametric test. Distributions of the duration of absence were described using standard techniques for survival data, such as Kaplan-Meier curves. Methods for proportions were used to analyze the rate of relapse or recurrence of whiplash symptoms. ▪ Results Study Cohorts A total of 4766 subjects submitted claims for compensation to the SAAQ after whiplash injury in a motor vehicle collision in 1987. Nine of these 4766 individuals were found to have received no compensation or reimbursement of any sort from the SAAQ and were therefore deemed ineligible for inclusion in the study cohort. The remaining 4757 individuals formed the primary source cohort. Of these, 1743 did not have police collision report data entered in the computerized databases and were therefore excluded, leaving a total of 3014 whiplash subjects in the source subcohort aimed at assessing the role of collision-related factors. Reasons for the lack of police report data for 1743 individuals may include the possibility that police may not have been called to the scene of the collision or that the SAAQ may have been unable to link the police report with the subject's claim for compensation. The study cohort for the analysis of the duration of absence had 2810 members because it excluded the 204 subjects with a recurrence from the 3014 members. The study cohort for the analysis of the rate of recurrence had 1666 members because it excluded the 1348 subjects with multiple injuries along with whiplash from the 3014 members to ensure that the recurrence was related only to the whiplash injury and not to another injury sustained during the collision. The study cohort for the analysis of costs comprised all 4757 members. Incidence Based on the Quebec population figures from 1987 and considering that the 4757 claimants represented the total number of compensated whiplash cases in the province in that year, the annual incidence of compensated whiplash in Quebec in 1987 was 70 per 100,000 inhabitants. The age- and gender-specific incidence rates of whiplash in Quebec in 1987 are shown in Figure 1A. The annual incidence of whiplash among female sufferers (86 per 100,000) was more than 1.5 times greater than among males sufferers (54 per 100,000). This difference in incidence was less marked in very young and in older age groups. For the 5-9 and the 65-year age groups, the incidence rate of whiplash among male patients exceeded the observed rate among female patients. The highest incidence of whiplash for both genders occurred in the 20-24 age group. For comparative purposes, the age- and gender-specific population-based incidence of all injuries combined that were reported by police in Quebec in 1987 is shown in Figure 1B.Figure 1: (A) Incidence rate of compensated whiplash injury by age and gender in Quebec (1987). (B) Incidence rate of all motor vehicle injuries by age and gender in Quebec (1987).The driver-specific annual incidence rate of whiplash, calculated by extrapolating from the data, showed that among those whiplash cases for whom collision-related data were available (3014 of 4757 cases), the percentage who were driving the vehicle at the time of their injury was 76.3 (2300 of 3014 cases). Assuming that an equal proportion and distribution of the whiplash subjects with missing collision data were also driving their vehicles at the time of the event, the total number of whiplash subjects who were drivers was 3613 of 4757. Therefore, using the total number of licensed drivers in Quebec as the denominator,99 the driver-specific incidence rate of whiplash in 1987 was 96 per 100,000 licensed drivers per year. Among male and female drivers, the incidence rates were 73 and 126 per 100,000 licensed drivers per year, respectively. The incidence of whiplash can be alternatively expressed in terms of the number of registered motor vehicles rather than in terms of population. Because there were 3.65 million registered vehicles in Quebec in 1987 and 4757 compensated claims for whiplash paid by the SAAQ, there were approximately 131 whiplash injuries per 100,000 vehicles per year in 1987. Region-specific incidence rates for the 16 administrative regions in the province are shown in Figure These rates are based on the region of residence of the whiplash subjects rather than the region in which the collision occurred because the collision location information was frequently unavailable from the computerized databases. The highest incidence per 100,000 was observed in the which is on the of the between and regions with whiplash incidence rates were the per 100,000 per 100,000 and per 100,000 The incidence rates occurred in the regions of the per 100,000 and per 100,000 It be that for out of the for whom the region of residence and the region of the collision were the occurred in the region the subject Incidence rate of compensated whiplash injury by geographic region of Quebec and Factors A of the sociodemographic of the 3014 subcohort members with the 1743 members of the cohort who were excluded because of the lack of collision-related data is in also a of the sociodemographic according to whether the cohort members sustained only a whiplash injury or other injuries in to whiplash on employment was available for only of the study cohort information for the study cohort is in along with a according to whether the cohort members sustained only a whiplash injury or other injuries in to Among the members of the study only were involved in collisions in which at one was of the cohort members as a of the motor vehicle collision. of the 3014 cohort members were reported to have been involved in a collision in which there were no injuries when the police were at the For subjects with whiplash of the collisions were as having no injuries at the scene with of collisions in which subjects sustained other injuries in to also the distribution of vehicle for the whiplash subjects in the study cohort. A or of 3014 were of and or at the time of the collision. were the second most frequently occupied vehicle type at than of the whiplash subjects were using other such as and at the time of the of the subjects were of the or of sustained other injuries in to whiplash, only of and sustained multiple The of whiplash subjects were driving a vehicle at the time of the collision. of the whiplash subjects or of 3014 were involved in in which a motor vehicle with another another motor with other such as and were for only of 3014 of collisions. of included collisions with such as and or of 3014 cases), and not involving such as and leaving the or of 3014 cases). A total of that in whiplash injury in 1987 involved only one vehicle, and the were with the number of vehicles involved from two to The collisions to be the most as in a number of whiplash subjects with multiple for of whiplash subjects with multiple injuries with only of subjects with whiplash Of the of involved two The direction of collision was not very by the police who were called to the scene of the For 16 whiplash subjects, the direction of collision was not on the police Among those was on the collision the direction of collision was as indicating an direction of collision in of were as and were collisions. with those who were in whiplash subjects involved in collisions were more to have sustained multiple information seatbelt was missing for of 3014 of the among those for whom this information was available, of were at the time of the collision. Of those most were using a or of cases), rather than a Based on the shown in there to be a greater for multiple injuries at speed than half of the whiplash injuries or of 3014 occurred on the speed limit was less than Duration of For the analysis of absence the study cohort 2810 members because it from the 3014 members the 204 subjects with a recurrence. Among these study cohort more than one within of the collision more than to from their year after the event, were from usual activities or Among those who sustained only a whiplash injury, had an absence of than year. The absence among those study cohort members who did not a recurrence was days. This corresponded to an exit date from the cohort of Kaplan-Meier return to for the 2810 whiplash subjects in the study cohort who did not a recurrence of symptoms is shown in Figure at of 2810 were because the on these whiplash subjects were not closed at the time when the data were extracted from the SAAQ's computerized databases. The return to which is a of the data in that approximately of the 2810 whiplash subjects within of the collision, and within days. 6 and year after the collision the proportion of subjects who had was and respectively. to by gender and age are shown in and return to for cohort of whiplash return to by return to by of and of the mean duration of absence and rate of recurrence are shown in for sociodemographic factors and in for the collision-related factors. Thus, female gender, older age, number of status, multiple greater collision vehicle other than or collisions other than and of seatbelt are associated with a defined as the recurrence of symptoms of collision-related were found to have occurred in or of the study those cohort members who sustained injuries in to whiplash were excluded from the the rate of recurrence was with collisions and the presence of dependents at information on seatbelt was missing for of the subjects, these individuals were included in the to which were most with to time to return to were to the that was using a seatbelt at the time of the collision, thus resulting in a seatbelt to of the collision-related expenses compensated by the SAAQ to the 4757 whiplash claimants is shown in with all in Canadian This cohort cost the SAAQ a total of million in reimbursements and compensation or an of more than per whiplash subject, was paid to subjects for the of their regular income were unable to work or carry out their usual The total amount of made to with whiplash as their only injury of 4757 was more than 9 with of regular income for million of the The cost per subject with whiplash was mean amount of reimbursement for at a by whiplash subjects in the cohort was of the 4757 whiplash or were assigned to a rehabilitation by the SAAQ. These individuals received an of in compensation and reimbursements from the SAAQ, This amount represented of the total amount of paid out by the SAAQ to members of the cohort. and Duration of Of the 4757 subjects who sustained a whiplash injury in Quebec in 1987, individuals experienced at one recurrence related to the injuries sustained in the motor vehicle collision and cost the SAAQ This amount the costs both and after the recurrence because it was not to between these time from the computerized data from the SAAQ. These who represented of the study for of the total costs paid out by the SAAQ to members of the study cohort. Of the cohort of patients who sustained only a whiplash injury, whose absence or less for only of the total costs paid out by the SAAQ for all patients in this cohort. The whose absence between and 6 for of the the whose absence between 6 and for of the and the remaining of patients compensated after the collision for of the total costs paid by the SAAQ. For the cohort of patients who sustained a whiplash injury along with other the proportions are that the whose absence between 6 and for only of the were compensated after the collision, and for of the total costs paid by the SAAQ. ▪ The variation in the incidence of whiplash in of the is For we found that the population-based incidence of compensated whiplash injury in Quebec was 70 per 100,000 in the incidence rates of whiplash in and of were and per 100,000 respectively, during a period from the incidence very in the rate of compensated whiplash injury in that region was only per 100,000 not all of the whiplash claimants in received compensation for their in and Quebec there were or no between the number of claimants and the number of individuals who received some form of compensation. This that of the Quebec had the highest population-based incidence of compensated whiplash injury. because the incidence rates for whiplash injury reported in this study the incidence of compensated claims made to the SAAQ by whiplash subjects, the rates are of the incidence of whiplash injury in subjects with injuries of this not claims for compensation to the SAAQ, to an of the incidence of in British Columbia and Saskatchewan, two other Canadian provinces with single-payer motor vehicle insurance programs, 68% and 85% of the claims paid out, respectively, for motor vehicle injuries are for with 20% for For Saskatchewan, with its one million and approximately claims paid per year, this proportion to a staggering incidence rate of compensated whiplash of per 100,000 times the rate in A for this may their in the insurance systems of these two Canadian the in Quebec the in The incidence of whiplash claims was among female subjects than among male subjects in most age to the that the of whiplash subjects are is that the have more than making less to whiplash possibility is that may be more than to file an insurance claim for The age- and gender-specific incidence of whiplash injury was found not to to the age- and gender-specific incidence of all injuries combined that were reported by police in Quebec in 1987. This distribution that male subjects have a incidence of all injuries combined than female subjects in age and the incidence of injuries to those years. The incidence of whiplash injuries to those 20-24 years. The variation in the incidence of claims for whiplash to be on population and the number of in region. For the regions to the of and to the of Quebec were found to have a incidence of whiplash This that many who in these regions a of time to the for work or the amount of time and the of involved in a collision and a whiplash injury The regions of Quebec had a very incidence of whiplash because these regions are and there is less on the resulting in a number of collisions. The that of the whiplash subjects did not to be at the scene of the collision with the reported by who found that the of in of collision subjects with injuries did not or more after the collision. The data showed that time to return to after whiplash injury was found in subjects with injuries whiplash, female gender, older age, greater number of status, in a collision involving or injury, in a collision other than and in a vehicle other than a or at the time of the collision. was found to in a absence from in with a previous study by The that whiplash subjects who were of vehicles other than or had a than those in or at the time of the collision may that and other vehicles lack into the design and of and The and total costs of whiplash injury paid by the SAAQ calculated in this study have been reported total costs to duration of the of subjects with only a whiplash injury whose absence or less for only of the total the whose absence between and 6 for of the and the of patients compensated 6 after the collision for of the total costs paid out by the SAAQ. and The population-based annual incidence rate of compensated insurance claims for whiplash injury in Quebec in 1987 was 70 per 100,000 inhabitants. The incidence rate was among female subjects and 20-24 years. The incidence rate was with that of other but than that found in the rate may be as as per A for this difference between the two provinces may be because of the insurance in Quebec and in gender, older age, status, and a greater number of dependents were the factors associated with a time of absence for in a collision, in a vehicle other than a or in a collision other than and not using a seatbelt were the collision-related factors associated with a time of The presence of multiple injuries was also an prognostic collisions and having one or more dependents were associated with a rate of relapse or recurrence of symptoms of whiplash Of the more than million Canadian paid out by the SAAQ to the 1987 cohort of 4757 whiplash subjects, was paid for the of regular Thus, the of the total cost by the SAAQ for whiplash is related to the duration of compensation. The of subjects with only a whiplash injury whose absence between and 6 for of the the remaining of patients compensated 6 after the collision for of the total costs paid out by the SAAQ. For the patients with multiple injuries whiplash, of patients were compensated 6 after the event, and for of the total costs. Therefore, the financial burden of whiplash injury to the SAAQ from the number of persons who