Early Aggressive Care and Delayed Recovery From Whiplash: Isolated Finding or Reproducible Result?

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1 Arthritis & Rheumatism (Arthritis Care & Research) Vol. 57, No. 5, June 15, 2007, pp DOI /art , American College of Rheumatology ORIGINAL ARTICLE Early Aggressive Care and Delayed Recovery From Whiplash: Isolated Finding or Reproducible Result? PIERRE CÔTÉ, 1 SHEILAH HOGG-JOHNSON, 2 J. DAVID CASSIDY, 3 LINDA CARROLL, 4 JOHN W. FRANK, 5 AND CLAIRE BOMBARDIER 6 Objective. To test the reproducibility of the finding that early intensive care for whiplash injuries is associated with delayed recovery. Methods. We analyzed data from a cohort study of 1,693 Saskatchewan adults who sustained whiplash injuries between July 1, 1994 and December 31, We investigated 8 initial patterns of care that integrated type of provider (general practitioners, chiropractors, and specialists) and number of visits (low versus high utilization). Cox models were used to estimate the association between patterns of care and time to recovery while controlling for injury severity and other confounders. Results. Patients in the low-utilization general practitioner group and those in the general medical group had the fastest recovery even after controlling for important prognostic factors. Compared with the low-utilization general practitioner group, the 1-year rate of recovery in the high-utilization chiropractic group was 25% slower (adjusted hazard rate ratio [HRR] 0.75, 95% confidence interval [95% CI] ), in the low-utilization general practitioner plus chiropractic group the rate was 26% slower (HRR 0.74, 95% CI ), and in the high-utilization general practitioner plus chiropractic combined group the rate was 36% slower (HRR 0.64, 95% CI ). Conclusion. The observation that intensive health care utilization early after a whiplash injury is associated with slower recovery was reproduced in an independent cohort of patients. The results add to the body of evidence suggesting that early aggressive treatment of whiplash injuries does not promote faster recovery. In particular, the combination of chiropractic and general practitioner care significantly reduces the rate of recovery. KEY WORDS. Whiplash injuries; Neck pain; Health services research; Episode of care; Primary health care; Prognosis; Recovery of function. INTRODUCTION Whiplash is the most common traffic injury, affecting 83% of individuals involved in motor vehicle collisions (1,2). It leads to neck pain, headache, and other symptoms such as dizziness (1). Whiplash injuries result in a significant burden of disability and health care utilization. In 1994, in Saskatchewan, Canada, the incidence of whiplash was 834 This study is based in part on nonidentifiable data provided by the Saskatchewan Department of Health. The interpretations and conclusions contained herein do not necessarily represent those of the Government of Saskatchewan or the Saskatchewan Department of Health. Supported by Health Canada through the National Health Research and Development Program (grant ) and the Canadian Institutes for Health Research. Dr. Côté s work was supported by a Doctoral Fellowship Training award from the National Health Research and Development Program, a New Investigator award from the Canadian Institutes of Health Research, and by the Workplace Safety and Insurance Board of Ontario through the Institute for Work & Health. Dr. Carroll s work was supported by a Health Scholar award from the Alberta Heritage Foundation for Medical Research. 1 Pierre Côté, DC, PhD: Institute for Work & Health, the University of Toronto, and the Toronto Western Research Institute and Rehabilitations Solutions, Toronto, Ontario, Canada; 2 Sheilah Hogg-Johnson, PhD: Institute for Work & Health, the University of Toronto, and Mt. Sinai Hospital, Toronto, Ontario, Canada; 3 J. David Cassidy, PhD, Dr Med Sc: the University of Toronto, and the Toronto Western Research Institute and Rehabilitations Solutions, Toronto, Ontario, Canada; 4 Linda Carroll, PhD: Alberta Centre for Injury Control and Research, Edmonton, Canada; 5 John W. Frank, MD, MSc: Institute for Work & Health, the University of Toronto, and the Institute of Population and Public Health, Toronto, Ontario, Canada; 6 Claire Bombardier, MD: Institute for Work & Health, the University of Toronto, the Toronto General Hospital Research Institute, and Mt. Sinai Hospital, Toronto, Ontario, Canada. Dr. Cassidy has received consulting fees (less than $10,000) from the Insurance Bureau of Canada. Address correspondence to Pierre Côté, DC, PhD, Toronto Western Hospital, Fell Pavilion 4-124, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8. pierre.cote@ uhnresearch.ca. Submitted for publication June 29, 2006; accepted in revised form October 31,

2 862 Côté etal per 100,000 inhabitants and 80% were still receiving insurance benefits 6 months after the injury (2). In 2000, whiplash was the most common emergency department treated motor vehicle injury in the US, with an incidence of 328 visits per 100,000 in the general population (3). Whiplash injuries are responsible for long-term disability and increase the risk of future neck pain and other health problems (1,2,4 6). Although there are few effective treatments for whiplash, a growing body of evidence suggests that the delivery of intensive health care shortly after the injury may lead to iatrogenic disability (7 9). Specifically, Côté et al found that patients who visited general practitioners more than 2 times, visited chiropractors more than 6 times, received combined care from general practitioners and chiropractors, and consulted general practitioners and specialists had a longer recovery than patients who visited general practitioners once or twice (7). In another study, Cassidy et al documented that patients who attended fitness training or an outpatient rehabilitation program within the first 3 months after their injury had slower recovery than those who received usual care (8). A recent randomized trial comparing education and advice by general practitioners (mean number of treatments 3.9, mean duration of care 18.8 weeks) with education and exercises by physiotherapists (mean number of treatments 12.7, mean duration of care 19.9 weeks) supports these results. One year after the injury, patients in the general practitioner group reported clinically significant lower levels of neck pain and headache than those treated by physiotherapists (9). This evidence suggests that the type and intensity of clinical care received in the first few weeks after a traffic collision have a long-lasting influence on the prognosis of whiplash injuries. The objective of our analysis was to test whether the association between early patterns of care and time to recovery reported by Côté et al (7) in a cohort of patients compensated under no-fault insurance is reproducible in an independent cohort of patients with whiplash compensated under tort insurance. We hypothesized that the intensity of health care utilization during the first month after the injury is positively associated with time to recovery. Testing the reproducibility of results is important for 2 main reasons. First, it assists researchers in ruling out that chance contributed to the earlier findings. Second, it provides information about the effect of differences in population characteristics on the associations of interest. The main difference between our earlier report and the present analysis is the nature of the insurance system in place to compensate individuals with traffic injuries. PATIENTS AND METHODS We reproduced the methodology used in our previous analysis. There were no deviations from the methods reported by Côté et al (7). The study methodology is described in detail elsewhere (2,7,10). The context. Saskatchewan is a Canadian province of 1 million inhabitants with a universal health care system and a single, provincially administered automobile insurer. Routine medical visits are fully covered by the provincial health care system. Reimbursement of chiropractic services includes an insured and an uninsured portion. Chiropractic fees are fully covered for individuals receiving supplementary benefits. There are no limits to the annual number of medical or insured chiropractic visits. Until December 31, 1994, Saskatchewan residents were covered under a tort automobile insurance system. All injured claimants were eligible to receive benefits, regardless of fault. The benefits included a maximum of $10,000 (Canadian) in rehabilitation and medical benefits, up to $200 (Canadian) per week in income replacement benefits (for 104 weeks), and up to $10,000 (Canadian) for permanent impairment. Claimants who were not at fault for the collision had the right to sue the other party for pain and suffering. Study design and source population. We formed a cohort of Saskatchewan residents ages 18 years who experienced whiplash injuries between July 1, 1994 and December 31, 1994 and reported the injury to Saskatchewan Government Insurance (7). Individuals who were injured at work and filed a workers compensation claim, those who did not speak English, those who made multiple insurance claims during the study period, and those who sustained severe injuries or had pathologic conditions were not eligible for the study. Inclusion and exclusion criteria. We included claimants who reported their injury to Saskatchewan Government Insurance within 30 days of the collision and answered yes to 2 questions: Did the accident cause neck/ shoulder pain? and Have you felt neck/shoulder pain, or reduced or painful neck movement since the accident? We excluded claimants with neck fractures or dislocations, skull fractures, spinal cord injury, and those with patterns of care that did not fit into one of the 8 predefined patterns. We also excluded claimants whose claim was closed and then reopened because Saskatchewan Government Insurance overwrites the first closure date with the second one when a claim is reopened. Entry into the cohort was the date of injury, and claimants exited the study on the date of claim closure, date of death, or on November 1, 1997 when we censored the remaining observations. Data sources. We used 2 sources of data. First, Saskatchewan Government Insurance data were used to collect potential confounders and our outcome measure. Second, administrative health services data from Saskatchewan Health were used to collect potential confounders and information to measure initial patterns of care. These data included information on all health care visits to medical doctors and chiropractors for a period of 1 year before and 1 year after injury. Diagnoses (International Classification of Diseases, Ninth Revision [ICD-9] codes), number of services, service dates, provider types, and date of death were extracted from the medical services, hospital services, and registration files (Table 1)

3 Delayed Whiplash Recovery With Early Care 863 Table 1. Patterns of care derived from the type and intensity of care received in the first 30 days following a traffic collision Pattern of care General practitioner Low utilization High utilization Chiropractic Low utilization High utilization Combined general practitioner plus chiropractic Low utilization High utilization Combined general practitioner plus specialist General medical group 1 2 visits 2 visits 1 6 visits 6 visits Description General practitioners (any number of visits) and chiropractor (1 6 visits) General practitioners (any number of visits) and chiropractor ( 6 visits) General practitioner (any number of visits) and specialist (any number of visits) Any number of visits to medical doctors, but the submitted diagnosis was not whiplash (11 13). All Saskatchewan Health databases are subjected to a routine data validation process that includes computer checks for illogical entries, cross checking between databases to verify eligibility, verification of claimants demographic information, and manual verification of invalid claims (11 13). The insurance data were linked to administrative health services data by Saskatchewan Health. Saskatchewan Health compiled the data using the Health Services Number, a unique identifier assigned to each registered beneficiary. To protect confidentiality, Saskatchewan Health removed all identifiers from the study files. The University of Saskatchewan s Advisory Committee on Ethics in Human Experimentation approved the study. Patterns of care. We defined 8 patterns of care by combining data on the type and intensity of health care each patient received within 30 days of sustaining whiplash injury (Table 1). We studied 3 types of health care providers: general practitioners, chiropractors, and specialists (all specialties except radiology). The intensity of health care corresponded to the number of visits made to each type of provider. We ensured that the visits were for whiplash by restricting services to ICD-9 codes related to whiplash-associated disorders (ICD-9 codes 721, 722, 723, 724, 729, 784, 840, and 847) (14). In Saskatchewan, chiropractors do not use ICD-9 codes. We assumed that all chiropractic visits were for whiplash because most chiropractic treatments are for neck pain, headache, back pain, and other musculoskeletal pain (15). The eighth pattern included patients who consulted medical doctors who submitted diagnoses other than whiplash. We refer to this group as the general medical group (Table 1). Outcomes. We measured time to recovery as the number of days between the date of injury and the date corresponding to the closure of the insurance claim (1,2,7, 10,16). Time to recovery corresponds to the end of treatment, the attainment of maximal medical improvement, or the termination of income replacement benefits. We validated claim closure as a marker of health recovery in our population by studying its relationship with clinically important levels of improvement in self-reported neck pain intensity, physical functioning, and depressive symptoms (10). These indices were assessed by mailed questionnaires at 6 weeks and 4, 8, and 12 months postinjury. Our analysis demonstrated that claimants who closed their claims had significantly lower levels of neck pain, better physical functioning, and no depression compared with claimants who did not close their claim (10). This finding supports the use of claim duration as a valid marker of health recovery. Potential confounders. We recognized the threat of confounding by indication and collected information on known confounders: injury severity, comorbidities, precollision health status, and previous health care utilization (17). Potential confounders related to injury severity included current and usual pain intensity in the neck, head, and other body locations using mm visual analog scales (18,19); percentage of body in pain (20,21); work absenteeism; postcollision symptoms (headache; dizziness; nausea; vomiting; vision, memory, or concentration problems; ringing in ears; difficulty swallowing; reduced/ painful jaw movement; low back pain; numbness/pain in arm[s] or leg[s]; and loss of consciousness); and postcollision medical diagnoses (ICD-9 codes) made during the first 30 days after the collision. We classified all preinjury diagnoses (ICD-9 codes) made during the year prior to the collision into 16 categories of comorbidities: neoplasm; mental disorders; disorders of the endocrine system, nervous system, circulatory system, digestive system, or genitourinary system; chronic bronchitis, emphysema, or asthma; migraines; arthropathies and rheumatism; dorsopathies; acquired deformities; symptoms of the head and neck; fractures; sprains and strain; and chiropractic diagnoses. We used administrative data from Saskatchewan Health to compute and control for the number of visits made to general practitioners, specialists, and chiropractors, and the number of hospitalizations during the year prior to the collision. Patients were asked to rate their general health (excellent to poor) during the month prior to the collision. They were also asked to report whether they experienced any of

4 864 Côté etal Figure 1. Study population. the following symptoms prior to the collision: neck pain, headache, jaw pain, low back pain, anger, depression, anxiety, fearfulness, tiredness, frustration, concentration or memory problems, body discomfort, and sleeping problems. Patients were asked to report a previous neck injury from a motor vehicle collision. Finally, self-reported height and weight were used to compute body mass index (in kg/m 2 ). Finally, we controlled for the following demographic, collision, and legal variables: age, sex, marital status, education, annual family income, number of dependants, employment status, main work activity, direction of impact, seating position in vehicle, seat belt use, head rest use, head position at impact, hit head during impact, vehicle stopped or in movement, vehicle rollover, vehicle drivable after the collision, collision time, type of road and road surface, lawyer involvement, and fault for the collision. Statistical analysis. We computed median time to recovery and 95% confidence intervals (95% CIs) using the Kaplan-Meier method (22). We used multivariable Cox regression models to measure the associations between patterns of care and time to recovery (22 24). In these models, the low-utilization general practitioner group served as the reference category. Hazard rate ratios (HRRs) and 95% CI described the strength and direction of association, with ratios 1 suggesting slower recovery. We first built a univariate model to measure the crude associations between patterns of care and time to recovery. Exploratory analyses demonstrated that the hazards of the various patterns of care were nonproportional. Therefore, our Cox regression models included interaction terms between the patterns of care and the logarithm of time (22,23). To identify confounders, we built a set of bivariate models that tested whether the inclusion of each potential confounder produced a 5% change in any of the patterns of care HRRs (25). The variables producing a 5% change were considered to be confounders and were retained in the final model to control for aggregate confounding. The final model included age, sex, and all confounders meeting the criteria described above. All analyses were conducted using SAS software (26). RESULTS Study population. A total of 2,217 acute whiplash injuries were reported to Saskatchewan Government Insurance during the study period (Figure 1). We excluded 477 claimants because of reopened claims, 2 because of neck or skull fractures, 6 because of spinal cord injuries, and 39 because their pattern of care did not correspond to one of the 8 predefined patterns. We found no systematic differences in injury severity between claimants who reopened a claim and those who did not reopen a claim (27). Our cohort included 1,693 patients (76.3% of all claimants). There was no loss to followup because we had outcome information on all patients. Baseline characteristics. The baseline characteristics of patients by pattern of care are presented in Table 2. The mean age ranged from 34.4 years in the high-utilization general practitioner group to 40.2 years in the general medical group. The chiropractic groups included more patients with postsecondary education. Data on the prevalence of postcollision symptoms, pain intensity, and postcollision work absenteeism suggest that compared with patients in the low-utilization general practitioner group, those in the high-utilization general practitioner group and in the high-utilization general practitioner plus chiropractic group had more serious whiplash injuries (Table 2). However, patients in the lowutilization chiropractic group had less serious injuries. Moreover, the prevalence of severe and superficial injuries was higher in the general medical group. Time to recovery. Patients in the general medical group (median time to recovery 323 days; 95% CI ) had the fastest recovery (Table 3). Patients in the high-utilization general practitioner group (median time to recovery 517 days; 95% CI ), those in the low-utilization general practitioner plus chiropractic group (median time to recovery 516 days; 95% CI ), and those in the high-utilization general practitioner plus chiropractic group (median time to recovery 689 days; 95% CI ) had the slowest recovery.

5 Delayed Whiplash Recovery With Early Care 865 Table 2. Baseline characteristics of 1,693 patients with whiplash injuries stratified by patterns of care* Patterns of care to providers Characteristics GP, 1 2 visits (n 650) GP, >2 visits (n 295) DC, 1 6 visits (n 47) DC, >6 visits (n 60) GP and DC, 1 6 visits (n 127) GP and DC, >6 visits (n 120) GP and specialist (n 108) General medical group (n 286) Age, mean SD years Women 380 (58.5) 168 (57.0) 30 (63.8) 35 (58.3) 82 (64.6) 69 (57.5) 65 (60.2) 160 (55.9) Education Postsecondary 300 (46.2) 120 (40.6) 28 (59.6) 31 (51.7) 63 (49.6) 52 (43.3) 48 (44.4) 119 (41.6) High school graduate 182 (40.2) 88 (29.8) 11 (23.4) 13 (21.7) 33 (26.0) 42 (35.0) 26 (24.1) 58 (20.3) High school or less 168 (25.9) 87 (18.2) 8 (17.0) 16 (26.7) 31 (24.4) 26 (21.7) 34 (31.5) 109 (38.1) Precollision symptom Headache 215 (33.1) 90 (30.6) 22 (46.8) 20 (33.3) 41 (32.3) 47 (39.2) 27 (25.0) 71 (24.8) Neck pain 126 (19.4) 53 (18.0) 19 (40.4) 21 (35.0) 32 (25.2) 37 (30.8) 10 (9.3) 54 (18.9) General health in last month Excellent 304 (46.7) 118 (40.1) 25 (53.2) 29 (48.3) 62 (48.8) 51 (42.5) 51 (46.4) 116 (40.0) Very good 206 (31.6) 112 (38.1) 11 (23.4) 20 (33.3) 37 (29.1) 44 (36.7) 25 (22.7) 96 (33.1) Good/fair/poor 140 (21.5) 64 (16.5) 11 (23.4) 11 (18.3) 28 (22.1) 25 (20.8) 32 (29.6) 78 (27.3) Mental disorders comorbidity 91 (14.0) 61 (20.7) 8 (17.0) 12 (20.0) 26 (20.5) 19 (15.8) 17 (15.7) 42 (14.7) Vehicle drivable after collision 362 (55.8) 164 (55.6) 28 (59.6) 38 (63.3) 75 (59.1) 66 (55.0) 51 (47.2) 111 (38.8) Postcollision symptom Headache 532 (81.9) 265 (90.1) 33 (70.2) 53 (88.3) 105 (83.3) 103 (85.8) 94 (87.0) 207 (72.9) Jaw pain 99 (15.3) 72 (24.4) 2 (4.3) 10 (16.7) 14 (11.1) 25 (20.8) 22 (20.6) 34 (11.9) Low back pain 401 (61.8) 202 (68.7) 27 (57.5) 41 (68.3) 85 (66.9) 84 (70.0) 58 (53.7) 137 (48.2) Arm numbness/pain 240 (36.9) 134 (45.4) 15 (31.9) 18 (30.0) 51 (40.2) 54 (45.0) 53 (49.1) 108 (37.8) Pain intensity, mean SD Headache (current) Headache (usual) Neck pain (current) Neck pain (usual) Other pain (current) Other pain (usual) Off work because of injury 252 (39.6) 188 (64.4) 16 (34.0) 19 (32.2) 52 (41.9) 71 (59.7) 69 (64.5) 147 (52.3) Severe injury 18 (2.8) 7 (2.4) 2 (4.3) 2 (3.3) 6 (4.7) 6 (5.0) 7 (6.5) 50 (17.5) Superficial injury 151 (23.2) 47 (15.9) 11 (23.4) 12 (20.0) 26 (20.5) 24 (20.0) 27 (25.0) 159 (55.6) Health care utilization in previous year General practitioner Mean SD Median Chiropractor Mean SD Median Lawyer involved with claim 81 (12.5) 79 (26.8) 1 (2.1) 6 (10.0) 26 (20.5) 31 (26.1) 26 (24.1) 37 (13.0) * Values are the number (percentage) unless otherwise indicated. GP general practitioner; DC chiropractor. Measured on a visual analog scale from 0 (no pain) to 100 (pain as bad as could be). Fractures, dislocations, intracranial injury, internal injuries, open wounds of the head and neck, and nerve injury diagnosed within the first month after the collision. Superficial injury and contusion with intact skin diagnosed within the first month after the collision.

6 866 Côté etal Table 3. Median time to recovery in days and 95% confidence interval for 2,486 patients with whiplash injuries stratified by patterns of care* Pattern of care Time to recovery GP (1 2 visits) 362 ( ) General medical group 323 ( ) GP and specialist 405 ( ) DC (1 6 visits) 375 ( ) GP ( 2 visits) 517 ( ) DC ( 6 visits) 363 ( ) GP and DC (1 6 visits) 516 ( ) GP and DC ( 6 visits) 689 ( ) * Values are the median (95% confidence interval). GP general practitioner; DC chiropractor. The crude analysis indicated that the intensity of care received during the first 30 days after the collision was negatively associated with the rate of recovery (Table 4). Our multivariable analysis demonstrated that our results were minimally confounded by injury severity and other variables. Compared with the low-utilization general practitioner group, the high-utilization chiropractic group was 33% less likely to have recovered 6 months after the collision (HRR 0.67, 95% CI ) and the high-utilization general practitioner group was 20% less likely to have recovered (HRR 0.80, 95% CI ) (Table 5). The largest and most persistent delays in recovery occurred in the general practitioner plus chiropractic groups. Compared with patients in the low-utilization general practitioner group 1 year after the collision, patients in the low-utilization general practitioner plus chiropractic group had a 26% slower rate of recovery (HRR 0.74, 95% CI ) and those in the high-utilization general practitioner plus chiropractic groups had a 36% slower rate of recovery (HRR 0.64, 95% CI ). Initially, patients in the general medical group had a more favorable prognosis than those who visited general practitioners once or twice (HRR 1.31, 95% CI ) (Table 5). However, the effect was short lived and patients who had not recovered within the 3 months had a prognosis similar to those in the reference category. Finally, the rate of recovery for patients in the general practitioner plus specialist group was similar to the reference category and remained constant throughout the followup (Table 5). DISCUSSION We analyzed a large cohort of patients compensated under a tort insurance provision and found that increasing the intensity of care to 2 visits to a general practitioner, 6 visits to a chiropractor, or adding chiropractic care to general practitioner care was associated with slower recovery. The results agree with our previous analysis in a cohort of patients compensated under a no-fault insurance scheme and support the hypothesis that the prognosis of whiplash injuries is influenced by the type and intensity of care received within the first month after the injury (7). As stated by Harrell et al, the most stringent test of the validity of a prognostic model is its reproduction in an external population (28). Results that are reproduced in an independent cohort are less likely to be due to chance, or to overfitting of the regression model (28). The care delivered to whiplash patients aims to restore health and prevent the development of chronic pain and disability. If medically needed, effective care improves the prognosis of patients. Practice guidelines recommend that, shortly after the injury, the treatment of whiplash should include pain control and activation (1). However, Spitzer at al warned that dependency on clinical care should be avoided (1). Because patient pressure is a known predictor of physician behavior, doctors may use treatments, schedule followup visits, and refer patients when not medically needed (29). This in turn may lead to adverse outcomes and even prolong recovery by legitimizing patients fears and creating unnecessary anxiety. It is also plausible that early aggressive clinical care delays recovery by promoting the use of passive coping strategies. Reliance on frequent clinical care, a form of passive coping strategy, may have a negative effect on recovery by reinforcing patients beliefs that whiplash injuries often lead to disability (30 32). Carroll et al have shown that independent of injury severity, whiplash patients who use coping strategies such as wishing for better pain medication or thinking I can t do anything to lessen this pain have a slower recovery than those who do not use these strategies (30). Table 4. Crude hazard rate ratios and 95% confidence intervals for the association between patterns of care and time to recovery under the tort insurance system (n 1,693)* Time since collision Pattern of care 3 months 6 months 1 year 2 years GP, 1 2 visits (n 650) 577; ; ; ; 1.00 General medical group (n 286) 241; 1.30 ( ) 191; 1.12 ( ) 123; 0.96 ( ) 61; 0.82 ( ) GP and specialist (n 108) 101; 0.85 ( ) 80; 0.83 ( ) 58; 0.81 ( ) 33; 0.79 ( ) DC, 1 6 visits (n 47) 43; 0.91 ( ) 33; 0.88 ( ) 24; 0.85 ( ) 14; 0.82 ( ) GP, 2 visits (n 295) 269; 0.63 ( ) 246; 0.68 ( ) 181; 0.75 ( ) 109; 0.81 ( ) DC, 6 visits (n 60) 58; 0.64 ( ) 54; 0.70 ( ) 29; 0.77 ( ) 19; 0.85 ( ) GP and DC, 1 6 visits (n 127) 122; 0.46 ( ) 107; 0.58 ( ) 82; 0.74 ( ) 43; 0.94 ( ) GP and DC, 6 visits (n 120) 119; 0.20 ( ) 115; 0.32 ( ) 92; 0.52 ( ) 56; 0.84 ( ) * Values are the number; hazard rate ratio (95% confidence interval). GP general practitioner; DC chiropractor.

7 Delayed Whiplash Recovery With Early Care 867 Table 5. Adjusted hazard rate ratios and 95% confidence intervals for the association between patterns of care and time to recovery under the tort insurance system (n 1,693)* Time since collision Pattern of care 3 months 6 months 1 year 2 years GP, 1 2 visits (n 650) 577; ; ; ; 1.00 General medical group (n 286) 241; 1.31 ( ) 191; 1.14 ( ) 123; 0.98 ( ) 61; 0.85 ( ) GP and specialist (n 108) 101; 1.02 ( ) 80; 1.03 ( ) 58; 1.03 ( ) 33; 1.03 ( ) DC, 1 6 visits (n 47) 43; 0.79 ( ) 33; 0.80 ( ) 24; 0.81 ( ) 14; 0.81 ( ) GP, 2 visits (n 295) 269; 0.71 ( ) 246; 0.80 ( ) 181; 0.89 ( ) 109; 1.00 ( ) DC, 6 visits (n 60) 58; 0.60 ( ) 54; 0.67 ( ) 29; 0.75 ( ) 19; 0.84 ( ) GP and DC, 1 6 visits (n 127) 122; 0.49 ( ) 107; 0.60 ( ) 82; 0.74 ( ) 43; 0.91 ( ) GP and DC, 6 visits (n 120) 119; 0.25 ( ) 115; 0.40 ( ) 92; 0.64 ( ) 56; 1.02 ( ) * Values are the number; hazard rate ratio (95% confidence interval). Model is adjusted for age; sex; employment status; neck pain before the injury; neoplasm, circulatory disorder, and genitourinary disorder diagnosed before the collision; chiropractic diagnosis during the year prior to the collision; number of visits to general practitioner and chiropractor during the year prior to the collision; lawyer involvement; headache, dizziness, visual problems, concentration problems, reduced/painful jaw, and arm pain/numbness experienced during the first 4 days after the collision; off work because of injury; current headache intensity; current neck pain intensity; percentage of body in pain; superficial injury resulting from the collision. GP general practitioner; DC chiropractor. We cannot rule out that residual confounding influenced our results. However, we are confident that our analysis is valid because we controlled for known prognostic factors of delayed recovery (1,3). A comparison of the crude and adjusted results demonstrates the stability of the effect sizes for patterns of care even when known confounders were included in our multivariate model. We recognize that confounding by indication is a serious risk to the internal validity of cohort studies investigating health care. However, it has been demonstrated that confounding by indication can be alleviated through careful selection and control of key confounders (33,34). To minimize this risk, we extensively and judiciously controlled for injury severity. These adjustments had little effect on our results. For example, data in Table 2 clearly show that on average, patients in the high-utilization general practitioner group or those in the combined general practitioner plus chiropractic group had more severe injuries than those in the low-utilization general practitioner group. Specifically, they had more severe pain ratings and a higher proportion of postinjury symptoms. A comparison of the crude and adjusted results demonstrates that controlling for these differences in injury severity had little impact on the associations. Moreover, the argument that the type and intensity of care is associated with recovery is augmented by the observation that patients in the lowutilization chiropractic group had slower recovery rates even though their initial injuries were, on average, less severe. Our study has several strengths. First, selection bias due to nonparticipation and attrition was unlikely because we had complete ascertainment of eligible patients and complete outcome data on all patients. Second, information bias due to misclassification of the pattern of care was minimized by using Saskatchewan Health data, which provide a complete and accurate registry of all patients visits to general practitioners, chiropractors, and specialists. We validated our outcome measure and demonstrated that time to claim closure is a valid marker of health recovery (10). Finally, we extensively controlled for important confounders including a large number of measures of initial injury severity, precollision comorbidities, and precollision health care utilization. We previously reported that under no-fault insurance, patients who consulted a general practitioner and a specialist had a slower recovery than those who consulted a general practitioner once or twice. This association was not reproduced in patients compensated under a tort scheme, which suggests that the insurance system is an effect modifier of the association between certain patterns of care and recovery. The effect modification of insurance system may be related to the legal and economic realities of tort insurance and may influence how patients perceive their medical needs, the pressure they put on clinicians to be referred, and how insurers require them to legitimize their injury. In conclusion, our study augments the evidence that too much health care too early after a soft tissue injury negatively influences the prognosis of whiplash patients. Specifically, combining chiropractic and general practitioner care appears to confer no benefit to patients. Our research complements the findings of randomized clinical trials suggesting that early minimal care that promotes activation improves prognosis (9,35). Future research should include the design of pragmatic randomized trials to test the effectiveness of various patterns of care in the community. These trials are essential to understand the influence of health care provision in preventing or facilitating disability. ACKNOWLEDGMENT We thank Mrs. Diana Fedesoff for her help with the management of the insurance data. AUTHOR CONTRIBUTIONS Dr. Côté had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study design. Côté, Hogg-Johnson, Cassidy, Carroll, Frank, Bombardier. Acquisition of data. Côté, Cassidy, Carroll.

8 868 Côté etal Analysis and interpretation of data. Côté, Hogg-Johnson, Cassidy, Carroll, Frank, Bombardier. Manuscript preparation. Côté, Carroll, Frank, Bombardier. Statistical analysis. Côté, Hogg-Johnson, Frank. REFERENCES 1. Spitzer WO, Skovron ML, Salmi LR, Cassidy JD, Duranceau J, Suissa S, et al. Scientific monograph of the Quebec Task Force on Whiplash Associated Disorders: redefining whiplash and its management [published erratum appears in Spine 1995;20:2372]. Spine 1995;20:1S 73S. 2. Cassidy JD, Carroll L, Cote P, Lemstra M, Berglund A, Nygren A. Effect of eliminating compensation for pain and suffering on the outcome of insurance claims for whiplash injury. N Engl J Med 2000;342: Quinlan KP, Annest JL, Myers B, Ryan G, Hill H. Neck strains and sprains among motor vehicle occupants: United States, Accid Anal Prev 2004;36: Holm L, Cassidy JD, Sjogren Y, Nygren A. 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