HEALTH CARE CONSULTATION AND SICK LEAVE BEFORE AND AFTER NECK INJURY: A COHORT STUDY WITH MATCHED POPULATION-BASED REFERENCES For peer review only

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1 HEALTH CARE CONSULTATION AND SICK LEAVE BEFORE AND AFTER NECK INJURY: A COHORT STUDY WITH MATCHED POPULATION-BASED REFERENCES Journal: Manuscript ID: bmjopen-0-00 Article Type: Research Date Submitted by the Author: 0-May-0 Complete List of Authors: Jöud, Anna; Clinical Sciences Lund, Department of Orthopedics, Lund University; Epi-centre Skåne, Skåne University Hospital Stjerna, Johanna; Department of Rehabilitation, Skåne University Hospital Malmström, Eva-Maj; Department of Rehabilitation, Skåne University Hospital; Department of Otorhinolaryngology, Clinical Sciences Lund, Lund University Westergren, Hans; Department of Rehabilitation, Skåne University Hospital; Department of Health Sciences, Lund University Petersson, Ingemar; Clinical Sciences Lund, Department of Orthopedics, Lund University; Epi-centre Skåne, Skåne University Hospital Englund, Martin; Clinical Sciences Lund, Department of Orthopedics, Lund University; Epi-centre Skåne, Skåne University Hospital <b>primary Subject Heading</b>: Epidemiology Secondary Subject Heading: Public health, Rehabilitation medicine Keywords: EPIDEMIOLOGY, Musculoskeletal disorders < ORTHOPAEDIC & TRAUMA SURGERY, Whiplash injury, Register, Treatment : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright. -

2 Page of HEALTH CARE CONSULTATION AND SICK LEAVE BEFORE AND AFTER NECK INJURY: A COHORT STUDY WITH MATCHED POPULATION-BASED REFERENCES Anna Jöud, MPH,, Johanna Stjerna, MD RPT, Eva-Maj Malmström, RPT PhD,, Hans Westergren, MD PhD,, Ingemar F. Petersson, MD PhD, Martin Englund, MD PhD,,*. Department of Orthopedics, Clinical Sciences Lund, Lund University, Lund, Sweden. Epi-centre Skåne, Skåne University Hospital, Lund, Sweden. Department of Rehabilitation, Skåne University Hospital, Lund, Sweden Department of Otorhinolaryngology, Clinical Sciences Lund, Lund University, Lund, Sweden Department of Health Sciences, Lund University, Lund, Sweden Clinical Epidemiology Research & Training Unit, Boston University School of Medicine, Boston, MA, USA. * Corresponding author, to whom requests for reprints should be sent: Martin Englund Epi-centre Skåne, Medicon Village Tunavägen, SE- Lund, Sweden Phone: + 0 (PA) martin.englunded.lu.se The authors have no conflict of interest to declare. Key words: whiplash injuries; epidemiology; register; treatment; health care Word count: - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

3 Page of ABSTRACT Objectives: To study health care consultation and sick leave patterns before and after neck injury (whiplash). Design: Cohort study with matched references studied both prospectively and retrospectively via regional health care registers. Setting: Population-based study in Region Skåne, Sweden (population=. million) including all levels of health care (primary, secondary care and hospitalisations). Participants:, subjects (% women) with acute sprain or strain of cervical spine (ICD- 0 code S.) in 00 or 00 and no such diagnosis since. Each neck injured subject was assigned four randomly selected population references matched for age, sex and area of residence (% of the patients and % of the references were followed the whole study period). Primary and secondary outcome measures: We studied changes in health care consultations three years before to three years after diagnosis as well as sick leave episodes. Analyses were also stratified by pre-injury frequency of consultation (low-frequent, frequent or high-frequent). Results: Before the injury, the mean number of total consultations over months among the neck injured (n=,) and references (n=,) was. vs.. (P<0.000) and post-neck injury. vs.. (P<0.000). Especially consultations to physiotherapists increased among neck injured. In the group of high-frequent consulters there were more women compared to frequent and low-frequent consulters (0.% vs..%; P< 0.000). This group was also older (mean age vs. years; P<0.000). Among low-frequent and frequent consulters preinjury (n=,.0% of the cohort),.0% became high-frequent consulters attributable to - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

4 Page of the injury. Number of days of sick leave was associated with the number of pre-injury consultations (p<0.00). Conclusions: Neck-injured individuals constitute a heterogeneous group. Pre-injury level of health care consultation is associated with post-injury level of consultation. Consultation history should be taken into account when tailoring individual treatment and rehabilitation after a neck sprain or strain. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

5 Page of ARTICLE SUMMARY Article focus Recent studies, based on self-assessed data both on exposure and outcome, suggest a negative association between poor health before neck injury and recovery. Using observational data in a population setting, our aim was to study actual health care consultation before and after neck injury to establish the potential connection between the two. Key message Neck injured individuals constitute a heterogeneous group, including e.g., both lowfrequent consulters and high-frequent consulters before the injury. Pre-injury level of health care consultation is associated with post-injury level of consultation. Consultation history should be taken into account when tailoring individual treatment and rehabilitation after a neck sprain or strain. Strengths and limitations of this study We performed a large scale population-based cohort study with matched references drawn from the general population of. million people followed for six years Our use of register-based data enabled us to study outcome and exposure without influence of recall-bias in both injured cases and references. A limitation of the study is potential misclassification of injury which is expected to bias the study to find less difference in consultation frequency between cases and references. Also, although the injury code used to identify cases primarily is connected to the whiplash injury mechanism, other trauma mechanisms may be included as well. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

6 Page of INTRODUCTION One common cause for trauma resulting in pain and dysfunction of the neck is still the rearimpact car crash.[] The so called whiplash trauma mechanism may result in tearing of several structures present in the neck e.g. facet joints [, ], stabilizing muscles [] and intervertebral discs.[, ] The symptoms after such trauma are heterogeneous as well as the recovery rate.[] In the post trauma treatment, pain sensitization, can be present or not, but if present it may have a substantial influence on the effect of different treatment strategies.[, ] Up to 0% report an incomplete recovery [0] and about 0% remain moderately or severely disabled.[, ] Long lasting musculoskeletal symptoms and consequences such as neck pain, arm-shoulder pain and reduced mobility are frequently reported after the trauma.[] Common psychological symptoms after whiplash trauma are depression, anxiety and posttraumatic stress syndrome.[ ] Additionally headache, dizziness and tinnitus are frequently reported.[ ] The post whiplash trauma course is difficult to predict due to the wide range of traumatic event types, individual symptom presentations, progress in recovery and the heterogeneous health care and follow-up systems.[, 0] The prognostic factors involve both pre-trauma risk factors [0, ] and trauma related factors.[, ]. Previous pain experiences, psychological distress as well as socioeconomic situation and education have been reported to negatively influence recovery to various degrees.[0 ] Recent studies have reported links between pre- and post-injury self-reported health care consultation and health status.[ ] The trauma related factors include the level of initial neck-pain and cervical range of motion directly after the trauma.[0,, ] Most collision variables reported have been shown to not be associated with the prognosis.[0,, 0] - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

7 Page of From the perspective of the society, health care consumption and return to work are important outcomes.[, ] In Region Skåne, located in southern Sweden, there is a possibility to study patients actual health care consultations and sick leave episodes using longitudinal data from independent sources both before and after neck injury diagnosis. Comparing the actual consultation pattern before and after injury diagnosis may provide insights and better understanding of the course and of the prognostic factors. Hence, the objective was to study health care consultation and sick leave patterns before and after diagnosis. MATERIAL AND METHODS Data sources Health care consultations We used data from the Skåne Health Care Register (SHCR) that contains routinely prospectively ascertained information from computerized medical records, as well as from administrative application sources, on all health care in Region Skåne, the southernmost part of Sweden (total population 00 =,,, ages years =,). The SHCR includes data on type of consultation (e.g., public/private, primary, specialist or hospitalizations), type of health care professional (physician, nurse, physiotherapist etc.), date of consultation, diagnostic codes, and surgical and /or injury codes where relevant. The physicians diagnostic codes are automatically transferred from the medical records. Since diagnoses are classified according to the Swedish translation of International Classification of Diseases and Related Health Problems (ICD) 0 system available online from Diagnoses from private practitioners are not automatically transferred to the SHCR and therefore only cases receiving a diagnosis within the public care is included in this study. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

8 Page of Sick leave and disability pension The Swedish social insurance is administered by the Swedish Social Insurance Agency (SSIA) and covers everyone who lives and/or works in Sweden. All sick leave periods exceeding days and all disability pension payments are administered and registered by the SSIA. The SSIA register includes dates, type and amount of sick leave and disability pension as well as diagnostic codes. Sick leave and disability pension can be full or part time. Sick leave data was available three years before up until two years after the neck injury. Educational level Data on educational level was drawn from the Longitudinal Integration Database for Health Insurance and Labour Market Studies (LISA). LISA includes data on e.g. occupation and educational level for the Swedish population. Here educational level is divided into three groups based on the number of years of formal education that an individual has had: Lower (up to years), medium (0- years) and higher education (more than years). We linked data from the SHCR, SSIA and LISA with the Swedish population register using the personal identification number, a unique 0-digit number assigned to all Swedish residents, in order to only include residents of Region Skåne. Study cohorts Neck injury cohort We identified all adult ( years or older) residents of Region Skåne who had been diagnosed with sprain or strain of the cervical spine (ICD-0 code S.) by a physician in an acute setting (emergency ward, acute non planned visit to physician in either specialist or primary care) between January 00 and December 00 with no previous record of an S. diagnosis since. We excluded all cases with any record of an injury involving the head and or neck (ICD-0 chapter S00-S) since up until the month before the identified - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

9 Page of neck injury diagnosis (Figure ). We refer to this month as the screening month to reduce the possibility of excluding subjects with acute neck injuries that were initially labelled differently, i.e., had a somewhat delayed S. diagnosis. The subjects were followed for six years; from three years prior to the screening month until three years after the neck injury (Figure ) or until relocation or death. Reference cohorts To be able to compare the health care pattern and sick leave pattern of cases with the general population, we also assigned each case with four reference subjects randomly sampled from the Swedish population register matched for birth year, sex, area of residence, and study period (figure, table ). We considered this reference group to be our primary references (References ). As part of sensitivity analyses, we also sampled two alternative reference cohorts. First, we hypothesized that educational level would affect the health care consultation frequency. Hence, we created a second reference cohort which was additionally matched for educational level (References ). Second, for the third reference cohort (References ), we additionally required all subjects to have had at least one health care consultation the same year as the case had its neck sprain or strain diagnosis (table ). The reason for this was to evaluate the effect on outcomes using a reference cohort with a propensity to consult health care (similar to our cases). If not stated otherwise, all comparative analyses are with the primary reference cohort. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

10 Page of Table. Matching variables for the three reference groups and characteristics of the study groups Number of matched references per case Matched on: Cases n= References (primary) n= References n= References n=0 a Sex Age (± years) Area of residence Observation time Educational level Health care consultation the year of case inclusion Women, n (%) () () () () Age, mean (SD) (.) (.) (.) (.) Educational level, n (%) Low ( years) (.0) (.0) Medium (0- years) (.) (0.) High (> years) (.) (.0) Missing (.0) (.) a For one case only two references were identified Outcomes Health care consultations We studied the number of consultations overall and the number of consultations to physicians and physiotherapists, respectively. Based on the median (quartile [Q]; quartile [Q]) number of consultations in the reference group (References ) two years prior to the neck injury, we specified cut-offs to define low-frequent ( consultation), frequent (= to consultations) and high-frequent consulters ( consultations). We used this categorization to perform stratified analyses. We also assessed the absolute portion of those neck injured who went from being a low-frequent to a high-frequent consulter due to the injury (attributable risk). - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

11 Page 0 of Further, we aimed to study physician consultations specifically associated with musculoskeletal disorders (ICD-0 chapter XIX), headache (ICD-0 codes M., G.0, G., F., G., R, G.) dizziness (ICD-0 codes H.0, H., H., H., H., H., H., R., F0.0) and tinnitus (ICD-0 code H.). Finally selected mental conditions here defined as psychological distress; depression (ICD-0 code F), anxiety (ICD-0 code F) and stress (ICD-0 code F) were studied. These conditions have all been associated with the disability period after neck injury.[, ] The proportion of subjects assigned diagnoses from the different disease groups, as well as mean number of consultations, are presented. Sick leave We studied the sick leave and disability pension patterns according to the data from SSIA. We compared the mean net sick leave days between cases and references as well as between the different sub groups. One net sick day is one full working day of sick leave and/or disability pension, i.e., two days with 0% sick leave correspond to one full net day of sick leave. Statistical analysis We present mean numbers with their % confidence intervals (% CI) of consultations and sick leave days. For median values (Q;Q), please see supplemental data provided online (table S-S). Differences between cohorts and subgroups (cases/references and lowfrequent/frequent/high-frequent consulters) were analysed by Students t-test and Mann- Whitney U-test as appropriate for parametric and non-parametric variables. Changes over time within groups were analysed by paired Students t-test, and Wilcoxon signed rang sum test. To test the differences in proportions we used the Chi- test. Pearson correlation coefficient were computed for the association between mean sick leave days and number of consultations A two-tailed p-value of 0.0 or less was considered to be statistically : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

12 Page of significant. All analyses were performed using SAS software version. (SAS Institute Inc, Cary, North Carolina). Ethics Statement The study was approved by the Regional Ethical Review Board in Lund (0-). Only register-data made anonymous was used for analyses. The individuals in the cohort were informed of the study and offered opt-out via regional news press, a process sanctioned by the Ethical Review Board. RESULTS Cohort characteristics Between January 00 and December 00, adult residents (% women) were diagnosed with sprain or strain of cervical spine (ICD-0 code S.) by a physician and fulfilled our eligibility criterion (no registered head/neck injury since up until the screening month) (figure, ). The mean (SD) age at diagnosis was (.) years (table). In the neck injury group % of the patients had been diagnosed at an emergency department and % at an acute visit in primary care and % at an acute visit in specialist care. During the follow-up period,.% had consulted a specialist at a rehabilitation clinic and.% had seen a neurologist or a neurosurgeon. Health care consultations Over the six-year study period, the neck injury cohort had significantly more health care consultations than each of the three different reference groups (p<0.000). After adding education as a matching variable (Reference ), the difference between neck injured and references remained significant but decreased slightly as did adding the criterion of having - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

13 Page of had at least one health care consultation to be an eligible reference subject (Reference ) (figure ). The mean age was higher in the neck injured and primary references of highfrequent consulters compared to their corresponding low-frequent consulters ( vs. years in cases, p<0.000). Women were overrepresented in the group of high-frequent consulters and underrepresented in low-frequent consulters (p<0.000) (table ). Of the neck injured defined as low-frequent consulters before neck injury (n=),.% switched to become high-frequent consulters the year after neck injury diagnosis. The corresponding risk for the references was.%. Hence, the attributable risk, i.e., the proportion of low-frequent consulters switching explained by the neck injury was 0.% (n=). Of the neck injured defined as low-frequent or frequent consulter consulters before neck injury (n=),.% switched to become high-frequent consulters the year after neck injury diagnosis. The corresponding risk for the references was.%. Hence, the attributable risk, i.e., the proportion of low-frequent or frequent consulters switching explained by the neck injury was.0% (n=). The increase in consultations in this subgroup was largely explained by an increased number of consultations to physiotherapists. In the stratified analyses, the three subgroups (pre-injury; low-frequent, frequent, and highfrequent consulters) had similar shape of their consultation frequency curves and they remained clearly separated from each other also after the injury (figure ). The level of education did not differ between these three subgroups (p=0.) (table ). - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

14 Page of Table. Characteristics for the neck injured and primary reference (reference ) cohort by their pre-injury consultation level. Cases n= Low-frequent Frequent High-frequent References n=00 Cases n= References n= Cases n= References n= Women, n (%) (.) (.) (.) (.0) (0.) 0 (.0) Age, mean (SD) (.) a (.) a (.) (.) (.) a (.) a Educational level, n (%) Low ( years) (.) (.) (.) (.) (.) (.) Medium (0- years) (.) b 0 (0.0) b (.) (.) (.) c (.) c High (> years) 0 (.) (.) (.) (.) (.) 0 (.) Missing (.0) (.) (0.) (.) (0.) (0.) a significant difference between low and high frequent consulter,( p<0.000, Students t-test) b Significant difference between case and reference (p<0.0, χ ) c Significant difference between case and reference (p<0.0, χ ) on 0 April 0 by guest. Protected by copyright. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from

15 Page of The neck injured consulted on average more than the references did, both before and after the neck injury diagnosis p<0.000 (table ). The proportion of subjects who were classified as low-frequent consulters among neck injured vs. reference subjects prior to the neck injury was vs. %, (p<0.000). Especially the diagnoses headache, dizziness and tinnitus became more frequent after the neck injury, particularly among the low-frequent consulters, both in numbers of cases diagnosed, but also in mean number of consultations post-neck injury (both p<0.000). The proportion of cases diagnosed with psychological distress or musculoskeletal disorders also increased (table, p<0.000). The low and frequent consulters were the group that changed the most both in terms of proportion of cases diagnosed with the particular disease but also the mean number of consultations per patient, while the high-frequent consulters changed the least in both aspects. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

16 Page of Table. Proportion of cases and primary references (reference ) who have consulted a physician due to different diagnostic chapters (ICD-0) before and after neck injury diagnosis and mean numbers of consultation per subject consulting. Year a Cases n= Low-frequent Frequent High-frequent References n= 00 Cases n= References n= Cases n= References n= % mean % mean % mean % mean % mean % mean Diseases of the musculoskeletal system and connective tissue b Year Year Year Year Year Year Psychological distress Year Year Year Year Year Year Headache, dizziness and tinnitus d Year Year Year Year Year Year a Year -= three years until two years before the washout month, Year - = two years until one year before the washout month, Year -= one year before the washout month, Year = one day after until one year after the neck trauma diagnosis, Year = one year to two years after neck trauma diagnosis, Year = two to three years after the neck trauma diagnosis b ICD-0 chapter XII, c ICD-0 block F, F, F, d ICD-0 M. G.0 G.0 G. F. G. R G. H.0 H. H. H. H. H. H. R. F 0.0 H. on 0 April 0 by guest. Protected by copyright. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from

17 Page of Sick leave At the day of the neck injury diagnosis, subjects of the case cohort (.%) were on disability pension, primarily connected to the two ICD-0 chapters musculoskeletal disorders (%) and mental disorders (0%) (table ). Among the reference cohort,.% were on disability pension, most typically due to mental disorders (%) and musculoskeletal disorders (%). Among the cases and references eligible for sick leave (not on full time disability pension), the mean number of sick days were higher in the cases than in the references both before and after the neck sprain and strain diagnosis (figure ). The number of mean sick leave days before neck injury were correlated to the number of health care consultations before neck injury (ρ=0., p<0.000). The number of mean total sick leave days before neck injury were different in the low-frequent, frequent and high-frequent group of consulter (p<0.000). Among the low-frequent cases, the patients becoming frequent or high-frequent consulters after injury diagnosis increased their mean annual number of sick days the most, from days (three years before diagnosis) to sick leave days (two years after) (p<0.000) (data not shown). - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

18 Page of Table. Number (%) of neck injured and references on sick leave or disability pension at the time of the neck injury diagnosis, by total and stratified by lowfrequent, frequent and high-frequent consulters before neck-injury diagnosis All Low-frequent Frequent High-frequent Cases References Cases References Cases References Cases References Disability pension* (.) (.) (.) 0 (.) (.) 0 (.) (.) 0 (.) Sick leave* (.0) (.) (.) (.) (.) (.) 0 (.) (.) *All differences between case and references within groups (within all, no, moderate and high) statistically significant p< : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

19 Page of DISCUSSION Neck injured individuals constitute a heterogeneous group. We found increased health care consultation frequency and sick leave associated with acute sprain or strain of the neck regardless of pre-injury consultation rates. Noteworthy, about % developed a high-frequent consultation pattern that could be attributed to the injury, and this pattern persisted up to at least years. However, in a subgroup of patients, high levels of health care consultations were noted already long before the neck injury diagnosis. This implies that individually tailored multimodal rehabilitation is an important tool in the care and recovery process of a subset of patients after neck injury.[, ] Our goal was to study the actual health care consultation before and after neck injury and to, based on the expected heterogeneity of this patient category, sub-group the patients depending on their pre-injury health care consultation frequency. In a recent study Kasch et al. have presented a way of early stratification of acute neck injured patients based on a risk score in relation to chronicity and work disability.[] Prior consultation frequency may serve as an additional variable for risk assessment of patients diagnosed with neck injury. The overall health care pattern before and after injury was similar for a majority of the cases, i.e., high-frequent consulters pre-injury also had high consultation frequency after the injury diagnosis. We noted a distinct change among a subset of the low-frequent consulters. Consultations for musculoskeletal diseases but also to some extent mental disorders were particularly common post-injury in this group. This group will be a special challenge for health care providers to pay particular attention to prevent development of chronicity. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

20 Page of Previous reports have suggested that depression is a risk factor for neck pain.[, ] However, neck pain may also be a risk factor for depression.[] Recently concerns have been raised that poor health in general could be a risk factor for neck injury.[, ] The explanation would be that poor health, especially mental conditions in combination with pharmaceuticals, would increase the risk of a car accident.[] Our results indicate that psychological distress are common reasons for physician health care consultations already before an acute neck injury diagnosis and that this tendency was maintained and even increased after injury. In our study we also made sensitivity analyses to separately evaluate the effects of educational level and propensity to seek health care, respectively. Also, after this process we found increased health care utilization among the neck injured already before the injury. One may speculate about this increase, which can be driven by a subgroup of individuals with a great need for health care due to specific characteristics before the injury and thus more vulnerable. It might also be individuals with high propensity to consult for a wide variety of symptoms for other reasons. The persons diagnosed with acute sprain or strain of the neck is thus a heterogeneous group of patients, and it is important to recognize the different subsets within these patients. Among the neck injured who were low-frequent consulters, the proportion which was diagnosed by a physician with psychological distress or dizziness before the neck injury was in line with their reference individuals. However, post-neck injury this subgroup increased their consultation rates due to these conditions, corroborating prior reports.[] The proportion of patients with a physician diagnosis with psychological distress, rose relatively - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

21 Page 0 of more post-injury than musculoskeletal disorders did. This should be taken into account in treatment and rehabilitation based on the bio-psychosocial model.[] Interestingly, in the high-frequent group, the mean number of consultations due to mental disorders decreased while the mean number of consultations due to musculoskeletal disorders increased. One hypothesis would be that the former underlying cause of stress, anxiety or depression could be diverted to consultations regarding musculoskeletal symptoms after the injury. Sick leave was associated with the consultation pattern; high-frequent consulters had higher mean number of sick days than the low-frequent consulters had. A relationship between sick leave and consultation frequency is expected. The findings in our study emphasize the importance to highlight and incorporate the early work and workplace interventions in the rehabilitation process to increase work ability in patients after neck injury.[,,, ] Our study has some methodological limitations. The ICD-0 injury diagnosis S. is recommended to be used for acute sprain or strain of the cervical spine, nevertheless the way physicians choose to diagnose may vary. It is however unlikely that these variations should follow any systematic direction, i.e. any misclassification of exposure is likely nondifferential with respect to outcomes. Further, the validity of this diagnostic code has not been tested, and the severity of the acute injury and its cause (car crash, sports injury, unclear cause etc.) is likely to vary greatly. Still, the validity of other musculoskeletal diagnoses in the SHCR has been proven to be high and the diagnostic codes are derived directly from the electronic medical records as noted by the physicians.[, 0] : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

22 Page of In our study, our aim was to compare neck injured subjects with population-based references. Although the overall pattern remained essentially the same, the exact differences between these groups changed slightly depending on how the references were sampled. The advantage of using population-based reference subjects is that it allows us to take more general changes, e.g., systematic changes in the health care system over time, into account. Further we could estimate the increase in consultation frequency that could be considered to be attributable to the neck injury, e.g., taking into account for the regression to the mean phenomenon. In summary, our study provides novel population-based evidence on the consultation patterns pre- and post-injury for patients diagnosed with acute sprain or strain of the cervical spine. If studying post-neck injury health care consultation level, without stratifying for pre-neck injury consultation level, one would miss the clear association between pre-injury and postinjury consultation frequency illustrating the heterogeneity of the patients. Our study also raises the importance of a subset of patients, the low-frequent consulters before, but highfrequent after a neck injury episode, where the neck injury is the likely explanation. We suggest that it is important to consider prior consultation history and pre-existing conditions in the rehabilitation process for the individual neck-injured patient. COMPETING INTEREST The authors declare no conflict interest. FUNDING The study was supported by grants from the regional health service authorities in Region Skåne, The Swedish Research Council (Vetenskapsrådet) (Grant number K00- X-0-0), The Swedish Association for Survivors of Accident and Injury (RTP) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

23 Page of and the Faculty of Medicine at Lund University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. CONTRIBUTION Original idea: AJ, EMM, HM and ME, Planned the study: AJ, JS, EMM, HW, IFP and ME. Data acquisition and data management: AJ. Had access to the data: AJ, IFP and ME. Conducted the statistical calculations: AJ. Interpreted results: AJ, JS, EMM, HW, IFP and ME. Drafted the manuscript with input from ME: AJ. Participated in manuscript revision, and approved the final version for submission: AJ, SJ, MEE, HW, IFP and ME. Guarantors: IFP ME. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

24 Page of FIGURE LEGENDS Figure. Flowchart of study inclusion. Figure. Schematic figure over the six-year study period; three years before until three years after neck injury diagnosis. Figure. Mean number of health care consultations, for all types of health care, physican care and physiotheraphist care by neck injured and three different reference cohorts (see methods). Figure. Annual post-injury consultation level stratified by pre-injury consultation level; lowfrequent consultation, frequent = to consultations, and high-frequent consultations per year pre neck injury. Interpretation; Panel A, Proportion of neck injured defined as lowfrequent consulter pre neck injury that was defined as low-frequent, frequent and highfrequent consulters year, and post neck injury. Figure. Mean number of health care consultations for all types of health care, physican care and physiotheraphist care by neck injured stratified by their pre-injury consultation level; lowfrequent (n=), frequent (n=) and high-frequent (n=). Figure. Mean number of sick days (sick leave and disability pension) per neck injured and references (panel A) and by pre-injury consultation level for cases; low-frequent (n=), frequent (n=) and high-frequent (n=) (panel B). - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

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26 Page of Carroll LJ, Holm LW, Hogg-Johnson S, et al. Course and prognostic factors for neck pain in whiplash-associated disorders (WAD): results of the Bone and Joint Decade Task Force on Neck Pain and Its Associated Disorders. J Manipulative Physiol Ther 00;:S S0. Rebbeck T, Sindhusake D, Cameron ID, et al. A prospective cohort study of health outcomes following whiplash associated disorders in an Australian population. Inj Prev 00;:. Sterling M, Jull G, Kenardy J. Physical and psychological factors maintain long-term predictive capacity post-whiplash injury. Pain 00;:0. Sterling M. Whiplash-associated disorder: musculoskeletal pain and related clinical findings. J Man Manip Ther 0;: 00. Sullivan MJL, Adams H, Martel M-O, et al. Catastrophizing and perceived injustice: risk factors for the transition to chronicity after whiplash injury. Spine 0;:S. Sullivan MJL, Scott W, Trost Z. Perceived injustice: a risk factor for problematic pain outcomes. Clin J Pain 0;:. Andersen TE, Elklit A, Vase L. The relationship between chronic whiplash-associated disorder and post-traumatic stress: attachment-anxiety may be a vulnerability factor. Eur J Psychotraumatol 0;. doi:0.0/ejpt.vi0. Sterling M, Kenardy J, Jull G, et al. The development of psychological changes following whiplash injury. Pain 00;0:. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

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28 Page of Walton DM, Pretty J, MacDermid JC, et al. Risk factors for persistent problems following whiplash injury: results of a systematic review and meta-analysis. J Orthop Sports Phys Ther 00;: 0. Crutebo S, Nilsson C, Skillgate E, et al. The course of symptoms for whiplash-associated disorders in Sweden: -month followup study. J Rheumatol 00;:. Holm LW, Carroll LJ, David Cassidy J, et al. Factors influencing neck pain intensity in whiplash-associated disorders in Sweden. Clin J Pain 00;:. Kasch H, Qerama E, Kongsted A, et al. Clinical assessment of prognostic factors for long-term pain and handicap after whiplash injury: a -year prospective study. Eur J Neurol 00;: 0. 0 Scholten-Peeters GGM, Verhagen AP, Bekkering GE, et al. Prognostic factors of whiplash-associated disorders: a systematic review of prospective cohort studies. Pain 00;0:0. Buitenhuis J, de Jong PJ, Jaspers JPC, et al. Work disability after whiplash: a prospective cohort study. Spine 00;:. Ozegovic D, Carroll LJ, Cassidy JD. What influences positive return to work expectation? Examining associated factors in a population-based cohort of whiplash-associated disorders. Spine 00;:E0. Kasch H, Qerama E, Kongsted A, et al. The risk assessment score in acute whiplash injury predicts outcome and reflects biopsychosocial factors. Spine (Phila Pa );:S. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

29 Page of Carroll LJ, Cassidy JD, Côté P. Depression as a risk factor for onset of an episode of troublesome neck and low back pain. Pain 00;0:. Linton SJ. A review of psychological risk factors in back and neck pain. Spine 000;:. Engel GL. The Need for a New Medical Model: A Challenge for Biomedicine. Science ;:. Reme SE, Shaw WS, Steenstra IA, et al. Distressed, immobilized, or lacking employer support? A sub-classification of acute work-related low back pain. J Occup Rehabil 0;:. Scott W, Trost Z, Milioto M, et al. Further Validation of a Measure of Injury-Related Injustice Perceptions to Identify Risk for Occupational Disability: A Prospective Study of Individuals with Whiplash Injury. J Occup Rehabil Published Online First: January 0. doi:0.00/s0-0-- Englund M, Jöud A, Geborek P, et al. Prevalence and incidence of rheumatoid arthritis in southern Sweden 00 and their relation to prescribed biologics. Rheumatology (Oxford) Published Online First: May 00. doi:0.0/rheumatology/keq 0 Haglund E, Bremander AB, Petersson IF, et al. Prevalence of spondyloarthritis and its subtypes in southern Sweden. Ann Rheum Dis;0:. - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

30 Page of Figure. Flowchart of study inclusion. 00xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

31 Page 0 of Figure. Schematic figure over the six-year study period; three years before until three years after neck injury diagnosis. xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

32 Page of Figure. Mean number of health care consultations, for all types of health care, physican care and physiotheraphist care by neck injured and three different reference cohorts (see methods). xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

33 Page of Figure. Annual post-injury consultation level stratified by pre-injury consultation level; low-frequent consultation, frequent = to consultations, and high-frequent consultations per year pre neck injury. Interpretation; Panel A, Proportion of neck injured defined as low-frequent consulter pre neck injury that was defined as low-frequent, frequent and high-frequent consulters year, and post neck injury. xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

34 Page of Figure. Mean number of health care consultations for all types of health care, physican care and physiotheraphist care by neck injured stratified by their pre-injury consultation level; low-frequent (n=), frequent (n=) and high-frequent (n=). xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

35 Page of Figure. Mean number of sick days (sick leave and disability pension) per neck injured and references (panel A) and by pre-injury consultation level for cases; low-frequent (n=), frequent (n=) and highfrequent (n=) (panel B). xmm (00 x 00 DPI) - : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright.

36 : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright. Page of Section/Topic Item # STROBE 00 (v) Statement Checklist of items that should be included in reports of cohort studies Recommendation Reported on page # Title and abstract (a) Indicate the study s design with a commonly used term in the title or the abstract Introduction (b) Provide in the abstract an informative and balanced summary of what was done and what was found Background/rationale Explain the scientific background and rationale for the investigation being reported Objectives State specific objectives, including any prespecified hypotheses Methods Study design Present key elements of study design early in the paper,, Setting Describe the setting, locations, and relevant dates, including periods of recruitment, exposure, follow-up, and data collection Participants (a) Give the eligibility criteria, and the sources and methods of selection of participants. Describe methods of follow-up,, (b) For matched studies, give matching criteria and number of exposed and unexposed, Variables Clearly define all outcomes, exposures, predictors, potential confounders, and effect modifiers. Give diagnostic criteria, if Data sources/ measurement applicable * For each variable of interest, give sources of data and details of methods of assessment (measurement). Describe comparability of assessment methods if there is more than one group Bias Describe any efforts to address potential sources of bias Study size 0 Explain how the study size was arrived at, Quantitative variables Explain how quantitative variables were handled in the analyses. If applicable, describe which groupings were chosen and why Statistical methods (a) Describe all statistical methods, including those used to control for confounding 0, (b) Describe any methods used to examine subgroups and interactions,0 (c) Explain how missing data were addressed - (d) If applicable, explain how loss to follow-up was addressed (e) Describe any sensitivity analyses Results 0, - NA

37 Page of Participants * (a) Report numbers of individuals at each stage of study eg numbers potentially eligible, examined for eligibility, confirmed, eligible, included in the study, completing follow-up, and analysed (b) Give reasons for non-participation at each stage, (c) Consider use of a flow diagram Fig Descriptive data * (a) Give characteristics of study participants (eg demographic, clinical, social) and information on exposures and potential confounders Table (b) Indicate number of participants with missing data for each variable of interest Table - (c) Summarise follow-up time (eg, average and total amount) Outcome data * Report numbers of outcome events or summary measures over time Main results (a) Give unadjusted estimates and, if applicable, confounder-adjusted estimates and their precision (eg, % confidence interval). Make clear which confounders were adjusted for and why they were included (b) Report category boundaries when continuous variables were categorized (c) If relevant, consider translating estimates of relative risk into absolute risk for a meaningful time period Other analyses Report other analyses done eg analyses of subgroups and interactions, and sensitivity analyses, Discussion Key results Summarise key results with reference to study objectives Limitations Interpretation 0 Give a cautious overall interpretation of results considering objectives, limitations, multiplicity of analyses, results from - similar studies, and other relevant evidence Generalisability Discuss the generalisability (external validity) of the study results 0 Other information Funding Give the source of funding and the role of the funders for the present study and, if applicable, for the original study on which the present article is based *Give information separately for cases and controls in case-control studies and, if applicable, for exposed and unexposed groups in cohort and cross-sectional studies. Note: An Explanation and Elaboration article discusses each checklist item and gives methodological background and published examples of transparent reporting. The STROBE checklist is best used in conjunction with this article (freely available on the Web sites of PLoS Medicine at Annals of Internal Medicine at and Epidemiology at Information on the STROBE Initiative is available at : first published as 0./bmjopen-0-00 on 0 August 0. Downloaded from on 0 April 0 by guest. Protected by copyright. Fig,