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European Journal of Pain xxx (2007) xxx–xxx

Acute stress response and recovery after whiplash injuries.A one-year prospective study

Alice Kongsted a,*, Tom Bendix b, Erisela Qerama c,d, Helge Kasch c,d,Flemming W. Bach c,d, Lars Korsholm e, Troels S. Jensen c,d

a The Back Research Center Part of Clinical Locomotion Science, Backcenter Funen, University of Southern Denmark,

Funen Hospital Ringe, Lindevej 5, DK-5750 Ringe, Denmarkb Institutes of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark

c Danish Pain Research Center, Aarhus University Hospital, Aarhus, Denmarkd Department of Neurology, Aarhus University Hospital, Aarhus, Denmark

e Department of Statistics, University of Southern Denmark, Odense, Denmark

Received 3 October 2006; received in revised form 29 June 2007; accepted 9 July 2007

Abstract

Chronic whiplash-associated disorder (WAD) represents a major medical and psycho-social problem. The typical symptomatol-ogy presented in WAD is to some extent similar to symptoms of post traumatic stress disorder. In this study we examined if the acutestress reaction following a whiplash injury predicted long-term sequelae. Participants with acute whiplash-associated symptoms aftera motor vehicle accident were recruited from emergency units and general practitioners. The predictor variable was the sum score ofthe impact of event scale (IES) completed within 10 days after the accident. The main outcome-measures were neck pain and head-ache, neck disability, general health, and working ability one year after the accident. A total of 737 participants were included andcompleted the IES, and 668 (91%) participated in the 1-year follow-up. A baseline IES-score denoting a moderate to severe stressresponse was obtained by 13% of the participants. This was associated with increased risk of considerable persistent pain(OR = 3.3; 1.8–5.9), neck disability (OR = 3.2; 1.7–6.0), reduced working ability (OR = 2.8; 1.6–4.9), and lowered self-reported gen-eral health one year after the accident. These associations were modified by baseline neck pain intensity. It was not possible to dis-tinguish between participants who recovered and those who did not by means of the IES (AUC = 0.6). In conclusion, the associationbetween the acute stress reaction and persistent WAD suggests that post traumatic stress reaction may be important to consider in theearly management of whiplash injury. However, the emotional response did not predict chronicity in individuals.� 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. Allrights reserved.

Keywords: Neck pain; Post-Traumatic stress disorder; Prognosis; Psychology; Whiplash injuries

1. Introduction

Persistent symptoms after an acute whiplash injuryknown as chronic whiplash-associated disorders

1090-3801/$32 � 2007 European Federation of Chapters of the International

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doi:10.1016/j.ejpain.2007.07.008

* Corresponding author. Tel.: +45 6362 1848; fax: +45 6362 1839.E-mail address: Alice.Kongsted@shf.regionsyddanmark.dk (A.

Kongsted).

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(WAD) are characterized by pain in the neck and sur-rounding areas together with a series of cognitive com-plaints. The mechanisms underlying WAD are notclear, but a bio-mechanical as well as a psycho-socialgenesis have been proposed. Injury to cervical facetjoints (Lord et al., 1996; McDonald et al., 1999), pro-prioceptors (Gimse et al., 1996; Treleaven et al., 2005)and upper cervical ligaments (Krakenes et al., 2002;

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Krakenes et al., 2004) have been suggested as causes ofchronic WAD. Other trials point towards the impor-tance of psychological factors, such as coping strategies(Carroll et al., 2006; Soderlund and Lindberg, 2003) andthe emotional reaction to being involved in a traffic acci-dent (Drottning et al., 1995; Sterling et al., 2003; Sterlinget al., 2006). Moreover, cultural factors seem to beimportant since the risk of chronicity is observed to beminimal or absent in cultures in which there are onlyfew factors that potentially accelerate sickness impact,such as focus on disability, access to a wide variety ofineffective treatment options (Cote et al., 2005; Kong-sted et al., 2007) and compensation systems (Cassidyet al., 2000). Lithuania and Greece represent such a cul-ture, and studies from these countries have shown nolong-term disability due to whiplash (Obelienieneet al., 1999; Partheni et al., 2000; Schrader et al., 1996;Schrader et al., 2000). This contrasts observations incountries with great awareness of chronic consequencesdue to whiplash in the general public. In Scandinavia, asmany as 40–50% of whiplash exposed are reported todevelop chronic symptoms (Borchgrevink et al., 1997;Hildingsson and Toolanen, 1990; Karlsborg et al.,1997; Kasch et al., 2001). Studies from Lithuaniaincluded participants from police records and these pop-ulations are therefore not directly comparable to theScandinavian populations recruited in emergency units.The latter studies included persons who sought carebecause of acute symptoms, whereas the former coveredcohorts that were included because of the exposure to acar collision without any selection in relation to reportedearly symptoms. Still it is striking that chronicity ratesdiffer to such great extent.

Musculoskeletal pain, headache and difficulties withshort time memory and concentration are described inboth WAD and in post-traumatic stress disorder (PTSD)(Norman et al., 2007; Ouimette et al., 2004; Rodriquezet al., 2004; Sterner and Gerdle, 2004), and an overlapbetween these conditions has been suggested (Kuchet al., 1996; McLean et al., 2005b; McLean et al.,2005a). The diagnosis PTSD is established through a clin-ical interview, but self-report instruments have beendeveloped as a practical tool to assess the degree of posttraumatic stress response. The impact of event scale (IES)(Horowitz et al., 1979; Sundin and Horowitz, 2002) is themost widely used instrument. It has been validated andfound to be a useful measure of stress reactions in a largenumber of populations exposed to various traumaticexperiences, including road traffic accidents (Sundinand Horowitz, 2002; Sundin and Horowitz, 2003), andhas been used in previous trials regarding whiplash inju-ries (Drottning et al., 1995; Sterling et al., 2003).

Acute post traumatic stress symptoms were observedto be associated with an increased risk of persistent neckpain and neck disability following a whiplash injury intwo trials (Drottning et al., 1995; Sterling et al., 2003;

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Sterling et al., 2006). However, one of these trials hada follow-up of only 4 weeks (Drottning et al., 1995)and the other studied a relatively small populationresulting in only 17 cases with significant long-lastingsymptoms (Sterling et al., 2003; Sterling et al., 2006).If it holds true, also from larger trials that an intensepost traumatic stress reaction is related to increased riskof chronic WAD, this problem should be specificallydealt with, rather than solely focusing on the neckinjury. Since results of conservative interventions afterwhiplash injury have been discouraging (Kongstedet al., 2007; Verhagen et al., 2004), it is of major impor-tance to identify patients in whom other mechanismsbehind the development of chronicity are relevant.

The objective of this study was to investigate whetherthe acute emotional stress reaction, as assessed by theIES, predicted the development of long-term pain anddisability after a whiplash injury.

2. Methods

2.1. Study design

This prospective trial was performed as a two-centerstudy. Part of the study population was allocated to arandomized clinical trial and received one of three inter-ventions: (1) Immobilization in a semi-rigid collar fol-lowed by exercises, (2) active mobilization, or (3)advice to act as usual. None of these interventions weredirected towards post traumatic stress, acute stressscores did not differ between groups, and there was nosignificant difference in outcome after 1-year in thesethree treatment groups (Kongsted et al., 2007). Otherparticipants were randomized to either written or oraladvice to act as usual in another randomized trial(Fig. 1). Follow-up was performed 3, 6 and 12 monthsafter the injury. The present study included data onlyfrom the 1-year follow-up, since the long-term prognosiswas the object of interest. Other prognostic evaluationswill be published elsewhere. The trial was approved bythe local ethical committee and was carried out in accor-dance with the Helsinki II declaration. Data collectionwas permitted by the Danish Data Protection Agency.Recruitment took place between May 2001 and June2003 and follow-up was completed in October 2004.

Participants were recruited from emergency units andgeneral practitioners in four Danish counties coveringapproximately 1.7 million inhabitants. Persons whohad acute symptoms after a rear-end or frontal car col-lision were considered potential participants. All eligibleparticipants received a visit by a project nurse in theirhome. If inclusion criteria were met, written consent toparticipate was obtained at this visit after verbal andwritten information about the study. Inclusion criteriawere: Age 18–70 years, debut of symptoms within 3 days

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From emergency units and GPsn=1495 [898/597]

Excluded during the follow-upperiod due to other illness oraccident N = 14 [8/6]

Drop out N = 55 [34/21]:Denied further participation n=23Unknown address n=22No response to contact n=8Unknown n=21-year follow-up

n = 668 [430/238]:511 questionnaires

157 interviews

IES availablen= 737 [472/265]

Baseline evaluationn= 740 [474/266]:

3-armed RCT n = 4582-armed information trial n = 282

Ineligible n= 540 [311/229]

Declined participation n= 200[102/98]

Excluded due to protocol violationn= 15 [11/4]

Fig. 1. Flow of participant in the trial [females/males]. IES = Impact of event scale.

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after the motor vehicle accident (MVA) and a maximumof 10 days should pass from the MVA to inclusion.Exclusion criteria were: Fractures or dislocations ofthe cervical spine visualized on X-ray, amnesia con-nected to the accident, unconsciousness in relation tothe accident, injuries other than the whiplash injury,self-reported average neck pain during the preceding 6months exceeding 5 on a box scale 0–10, where 0 = nopain and 10 = worst possible pain, significant pre-exist-ing somatic or psychiatric disease, and known alcohol-or drug abuse. Subjects were also excluded if they couldnot read or understand Danish. These criteria resulted ininclusion of WAD grades I–III (Spitzer et al., 1995).

2.2. Variables of interest

2.2.1. Baseline variables

A post traumatic stress score was obtained by theIES. A total sum-score was calculated from all 15 itemsof the scale (0–8 = subclinical; 9–25 = mild; 26–43 = moderate; 44–75 = severe stress reaction). In addi-tion, an intrusion score (sum of 7 items) and an avoidancescore (sum of 8 items) were calculated (Horowitz et al.,1979). Intrusion is symptoms related to reexperiencingthe traumatic event. The items covering avoidance dis-close whether situations, which remind the subject aboutthe event, are avoided. The total sum-score was theexplaining variable of interest. Other questionnairesincluded assessment of general health by the SF-36(Bjorner et al., 1998a; Bjorner et al., 1998b), neck painand headache intensity rated on 11-point box scales

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(0 = no pain and 10 = worst possible pain) (Jensenet al., 1989), sociodemographic factors, and crashrelated data. Two summary scores, a physical healthscore and a mental health score, are obtained from theSF-36 scale. The SF-36 was directed at self-experiencedhealth four weeks prior to the car accident. In addition,participants scored their average neck pain and head-ache 6 months prior to the accident on 11-point boxscales.

2.2.2. Measures of non-recovery

Outcome parameters were chosen so that aspects ofself-reported pain, neck disability, general health andwork-related consequences one year after the MVA werecovered. Follow-up data were collected from a mailedquestionnaire. Participants were contacted by phone ifthe questionnaires were not returned. In case subjectsdeclined to fill in the 1-year questionnaire, they wereasked to participate in a short telephone interview. Thisincluded whether symptoms related to the accident werestill present and information about their working abilitythe preceding month. The main outcome parameterswere self-reported average neck pain and headacheintensity the preceding week (11 point box scales;0 = no pain, 10 = worst imaginable pain), neck disabil-ity (15-item Copenhagen Neck Functional DisabilityScale; 0 = no neck disability, 30 = extremely disabled)(Jordan et al., 1998), general health (SF-36), andreduced ability to work during the 12th month afterthe injury (‘‘unaffected workability’’, ‘‘reduced workinghours’’, ‘‘off sick’’) marked day by day in a calendar.

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2.2.3. Validity

The IES has been widely used (Sundin and Horowitz,2003) and found to be a valid measure of post traumaticstress reactions (Joseph, 2000; Sundin and Horowitz,2002), but its reproducibility has been evaluated onlyin one small trial (Horowitz et al., 1979). The scalesfor measuring pain and neck disability have been vali-dated in other spinal pain populations (Bolton and Wil-kinson, 1998; Jordan et al., 1998). The short-form healthsurvey, SF-36, is considered a valid instrument measur-ing self-reported general health (Bjorner et al., 1998a;Brazier et al., 1992), but there is a risk that pre-existinghealth problems reported at baseline are underreportedwhen using the scale retrospectively as in this study.Crash-related data including impact direction (frontal/rear end) and car damage were self-reported and thevalidity of this information is unknown. Informationregarding car damage should be considered a rough esti-mate only. Working ability during the 12th month afterthe injury was registered by marking days with sick list-ing and reduced working hours in a calendar con-structed for this trial. The answers of the calendarswere controlled on a spot sample basis by a secretarywho checked that participants understood how to fill itin.

2.3. Statistical methods

The IES-score was dichotomized into ‘‘mild stressresponse’’ (IES < 26) and ‘‘distinct stress response’’(IES 26–75) (Horowitz et al., 1979) in the analyses. Incase of incomplete IES-scores, missing items werereplaced by the mean-value of the completed questionsto calculate the total IES-score. The variables neck painintensity and headache intensity were merged into onepain measure by using the higher of the two scores asthe pain outcome in the analyses. Pain scores from 0to 3 and disability scores from 0 to 6 were defined as‘‘minimal’’ based on previously suggested categories(Jordan et al., 1998) and the distribution of the vari-ables. Missing items in the neck disability scale werereplaced by worst case scores if a maximum of 2/15items were missing, and no disability-score was calcu-lated if more items were missing. Working ability wasdefined as ‘‘affected’’ if any days with reduced workinghours or days off sick were present during the 12thmonth after the accident, and ‘‘unaffected’’ when a per-son had not been sick listed or worked reduced hoursdue to the accident during that month.

Associations between the IES-score and outcomemeasures were evaluated by means of linear and logisticregression using robust variance estimation (Royall,1986; White, 1980). Two models were tested: In modelI the regression was adjusted for gender. In model IIthe regression models were furthermore adjusted forbaseline pain intensity, since an association between

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baseline pain intensity and the IES was observed, andinitial pain is known to be associated with prognosis(Scholten-Peeters et al., 2003). Self-reported car damageand impact direction were tested as modifiers, but werenot associated with outcome and hence not included inthe regression model. Results are presented as oddsratios (OR) and regression coefficients with 95% confi-dence intervals (95% CI). In case of positive associa-tions, the ability of the IES to distinguish betweenpatients with good and poor outcome was tested bymeans of receiver operant curves (ROC) and presentedas area under the curve (AUC) (Metz, 1978). All analy-ses were performed using STATA 8 (release 8.2, StataCorp., TX).

3. Results

3.1. Study sample and baseline characteristics

A total of 740 participants were included in the study,and 737 (265 males/472 females), median age 33 years(IQR 26–43), filled in the baseline IES. One year fol-low-up data were analyzed for 668 participants; 511who completed the follow-up questionnaires and 157who did not respond to the mailed questionnaire butparticipated in a short telephone interview. These 157were included only in the analysis concerning workingability (Fig. 1).

Baseline data were obtained a median of five daysafter the accident (IQR 3–6). All participants reportedneck discomfort. Neck pain was reported by 99% ofthe population and headache by 86%. Neck pain orheadache intensity of at least 4 was reported by 65%of the population. Baseline characteristics are shownin Table 2.

All items of the IES were completed by 721 partici-pants and 1–4 items were missing in 16 IES-question-naires. A mild stress response was observed in 87% ofthe participants and distinct stress was present in 13%(8% males, 15% females) (Fig. 2). Data on the IES areshown in Table 1. A distinct stress response was associ-ated with female gender (OR 1.9; 95% CI 1.2–3.2), andhigher initial pain intensities (Fig. 3). An increasedIES-score was also associated with self-reported cardamage of more than 50% (OR 2.6; 95% CI 1.5–4.6),and with the accident described as severe (OR 5.0;95% CI 3.0–8.4). Self-reported general health (SF-36),neck pain and headache intensities prior to the accidentdid not differ significantly between participants withmild and distinct stress responses.

3.2. Measures of non-recovery

At the 1-year follow-up, 43% (95% CI: 39–48) of 510participants reported considerable neck pain and/or

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0

10

20

30

40

50

60

subclinical mild moderate severe

male

female

”Distinct”

Fig. 2. Percentage of participants within each stress-reaction category.Percentage of females and males with an IES-score corresponding tothe illustrated categories. Moderate and severe were considered a‘‘distinct stress reaction’’ in the analyses.

Table 1Impact of event score at baseline

All subjects Females Male

Total IES n = 737 9 (3–18) 10 (5–21) 6 (2–15)Intrusive items n = 727 5 (2–11) 6 (3–12) 3 (1–8)Avoidance items n = 730 3 (0–7) 4 (1–8) 2 (0–6)

IES = Impact of event score. Median scores (interquartile range).

0

2

4

6

8

10

Neck Pain Headache

IES < 26 IES ≥ 26 IES < 26 IES ≥ 26

Fig. 3. Baseline pain intensity in relation to stress response. Baselineneck pain and headache intensity by IES. IES = Impact of event score.

Table 2Baseline data and outcome measures at the 1-year follow-up

Baseline 1-year

n

Rear end collision (direct or oblique), % 70Neck pain (0–10), median (IQR) 4 (3–6) 2 (0–6) 508Neck pain >3, % (CI) 59 (56–63) 36 (32–40) 508Headache (0–10), median (IQR) 3 (2–6) 2 (0–6) 508Headache >3, % (CI) 49 (46–53) 38 (33–42) 508Neck disability (0–30), median (IQR) 2 (0–11) 466Neck disability >6, % (CI) 34 (29–38) 466Physical health (SF-36), median (IQR) 56 (52–58)a 52 (40–57) 495Mental health (SF-36), median (IQR) 57 (53–60)a 56 (48–58) 495Sicklisted, % (CI) 43 (39–46)Reduced working ability during the12th month, % (CI)

16 (13–19) 631

Concentration difficulties, % (CI) 41 (40–47) 33 (29–37) 614Memory difficulties, % (CI) 23 (20–26) 31 (28–35) 616Sleeping disturbances, % (CI) 35 (31–38) 26 (23–29) 615Any lasting trouble due to the MVA, %

(CI)54 (50–58) 633

a Baseline scores of SF-36 denotes general health prior to the acci-dent IQR = interquartile range. CI = 95% confidence interval.

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headache and 34% (95% CI: 29–38) considerable neckdisability. In the 12th month after the MVA, 9% (95%CI 7–11) were sick listed the entire month and 16%(95% CI: 13–19) had some extent of affected workingability. The average SF-36 scores were slightly lower,denoting worse health, at the 1-year follow-up com-pared to four weeks preceding baseline (Table 2).

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3.3. Prediction of outcome by IES

The baseline IES-score was significantly associatedwith all outcome measures in the primary analysis (Table3, model I) (Fig. 4). Significant pain at 1-year follow-upwas reported by 68% of the participants with a distinctstress response and by 40% of those with a mild stressresponse at baseline (OR 3.3; 95% CI 1.8–5.9). Signifi-cant disability was reported by 58% (distinct stress)and 31% (mild stress) (OR 3.2; 95% CI 1.7–6.0). In thegroup with mild stress response, 14% reported reducedworking ability in the 12th month after the car collision,whereas this was the case for 31% of participants with adistinct stress response (OR 2.8; 95% CI 1.6–4.9). Whenbaseline pain intensity was taken into account, the asso-ciation between IES-scores and outcome measures werelowered, and the association with working ability wasno longer statistically significant (Table 3, model II).The observed associations were insufficient to distinguishbetween the patients with considerable pain or reducedworking ability from those recovering since ROC analy-sis revealed quite low AUC for the IES-score (pain = 0.6,work = 0.6, disability = 0.7).

Since baseline pain and gender modified the effect ofthe early stress reaction, data were analyzed separatelyin groups with low and high initial pain intensities andwithin each gender. Regarding initial pain, data wereanalyzed separately in the 189 participants with lowintensity baseline pain (0–3) and those 173 with high ini-tial pain intensity (6–10). In participants with low pain asevenfold risk of persistent considerable pain in case of adistinct stress response was estimated (OR 7.1; 95% CI2.3–21.8). In participants with high initial pain, thestress score was not significantly associated with

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Table 3Associations between total baseline IES and outcome measures

Outcome variables at 1-year Odds ratio [Robust 95% CI]Explaining variables at baseline

Crude Model I Model II

Pain >3

IES (distinct stress vs. othersa) 3.3 [1.8; 5.9]*** 3.0 [1.6; 5.5]*** 2.1 [1.1; 4.1]*

Gender (female vs. malea) 2.1 [1.4; 3.1]*** 1.9 [1.3; 2.9]**

Baseline pain intensity (0a–10) 1.4 [1.3; 1.6]***

Reduced working ability

IES (distinct stress vs. othersa) 2.8 [1.6; 4.9]*** 2.7 [1.5; 4.7]** 1.8 [1.0; 3.4]NS

Gender (female vs. malea) 1.6 [1.0; 2.6]NS 1.5 [0.9; 2.4]NS

Baseline pain intensity (0a–10) 1.3 [1.2; 1.5]***

Disability >6

IES (distinct stress vs. othersa) 3.2 [1.7; 6.0]*** 3.1 [1.6; 5.8]** 2.1 [1.1; 4.2]*

Gender (female vs. malea) 1.5 [1.0; 2.2]NS 1.3 [0.8; 2.0]NS

Baseline pain intensity (0a–10) 1.4 [1.2; 1.5]***

Regression coefficient [Robust 95% CI]

Pain (0–10)

IES (distinct stress vs. othersa) 2.4 [1.4; 3.4]*** 2.3 [1.3; 3.3]*** 1.5 [0.5; 2.4]**

Gender (female vs. malea) 0.9 [0.3; 1.4]** 0.6 [0.1; 1.2]*

Baseline pain intensity (0a–10) 0.6 [0.5; 0.7]***

Disability (0–30)

IES (distinct stress vs. othersa) 3.2 [1.7; 6.0]*** 3.1 [1.6; 5.8]** 2.1 [1.1; 4.2]*

Gender (female vs. malea) 1.5 [0.9; 2.2]NS 1.3 [0.9; 2.0]NS

Baseline pain intensity (0a–10) 1.4 [1.2; 1.5]***

SF-36 physical health

IES (distinct stress vs. othersa) �7.7 [�11.0; �4.3]*** �7.3 [�10.7; �4.0]*** �5.1 [�8.3; �1.9]**

Gender (female vs. malea) �2.4 [�4.2; �0.6]* �1.8 [�3.5; �0.1]*

Baseline pain intensity (0a–10) �1.6 [�2.0; �1.2]***

SF-36 mental health

IES (distinct stress vs. othersa) �7.6 [�10.9; �4.2]*** �7.5 [�10.9; �4.1]*** �6.1 [�9.5; �2.8]***

Gender (female vs. malea) �0.7 [�2.5; 1.0]NS �0.4 [�2.1; 1.4]NS

Baseline pain intensity (0a–10) �0.9 [�1.4; �0.5]***

Effect of the IES score on pain, working ability and general health after one year.Model I was adjusted for gender. Model II was adjusted for gender and baseline pain intensity (the higher of neck pain and headache).NS = non-significant, *p < 0.05, **p < 0.01, ***p < 0.001.

a = Reference.

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long-lasting pain (OR 2.0; 95% CI 0.8–4.8). Participantswith low baseline pain also had an increased risk ofreduced working ability in case of distinct stress,whereas the stress score was not significantly associatedwith working ability in case of high initial pain (Table4). When this stratified analysis is interpreted, oneshould note that high initial pain is in itself a relativelystrong predictor of poor prognosis (Table 3).

With regard to gender, it appeared that the IES wasmore strongly related to outcome in males, who had amore than fourfold risk of long-lasting pain in case ofa distinct stress response (OR 4.4; 95% CI 1.2–15.9) ascompared to females’ threefold risk (OR 2.7, 95% CI1.4–5.2). The associations with working ability (Table4), neck disability and general health (data not shown)were slightly stronger in males than females. Note thatsome results of the stratified analyses had wide confi-dence intervals and no firm conclusions should hencebe based upon these.

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4. Discussion

This prospective study on emotional reactions to awhiplash injury demonstrated an association between apost traumatic stress reaction and development ofchronic WAD. While this observation is consistent withtwo previous prospective studies (Drottning et al., 1995;Sterling et al., 2006), this study is by far the largest pro-spective study with a long-term follow up. In one earliertrial the follow-up was only four weeks (Drottning et al.,1995) and in another trial with long-term follow-up only65 participants were enrolled (Sterling et al., 2006). Thepresent study represents a verification of the linkbetween psychological response to a car collision andlong-lasting physical symptoms which is in demand(Williamson et al., 2007).

Even though the association between the early stressreaction and chronic WAD was statistically significant itwas not sufficiently strong to predict prognosis in indi-

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0

20

40

60

80

100

mild stress mild stressdistinct stress distinct stress

mild stress distinct stress

pain > 3

pain ≤ 3

0

20

40

60

80

100

neck disability ≥ 6neck disability < 6

0

20

40

60

80

100

reduced workingability

unaltered workingability

Fig. 4. Pain, neck disability and working ability at the 1-year follow-up in relation to baseline IES-scores. Percentage of participants withconsiderable: ( ) pain/disability versus mild; (n) lasting symptoms by baseline IES score.

Table 4Risk of reduced working ability considering gender and separategroups with mild and severe initial pain

Mild PTSRIES < 26

Distinct PTSRIES P 26

OR

Reduced working ability

Mild initial pain 8% 38% 7.2 [1.6; 32.8]Severe initial pain 18% 31% 1.6 [0.8; 3.3]Female 16% 32% 2.4 [1.2; 4.7]Male 10% 29% 3.7 [1.1; 11.4]

Risk of reduced working ability during the 12th month after a whip-lash injury.Percentage of the population defined in the cell.

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viduals. Thus, the acute stress response to a car accidentis related to the prognosis, but it is clear that the acutestress response is not the only determining factor.Patients with a severe acute stress response have anincreased risk of developing chronicity after whiplashinjuries, but still it is unknown whether ‘‘correction’’of the stress response would improve outcome. Further-more, this study did not attempt to investigate why thestress response differed between subjects. In theory, astronger stress response could be related to accidentsinvolving more severe impact but also to greater fearof injury. We observed that heavier car damage wasassociated with higher IES-scores, which can indicate

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that the link between post traumatic stress and chronicpain is a car collision with higher impact. Another pos-sible link is that a high expectancy of long-lasting painafter whiplash seems to relate to higher incidence ofchronic WAD (Ferrari et al., 2002), and severe stressmight be caused by fear of lasting pain itself. It maybe too that a marked post traumatic stress is an elementof the ‘‘cultural factor’’ playing a part in the develop-ment of chronic sequelae following whiplash injury.

Stratification by baseline pain indicated that the IES-score was more strongly related to outcome in partici-pants with lower baseline pain scores. Thus, baselinepain had an effect-modifying influence on IES, whichwas partly driven by a relatively high risk of chronicWAD in participants with severe baseline pain alsowithout signs of a post traumatic stress reaction. Strati-fication also showed that the IES was somewhat stron-ger associated to outcome in men than in women.

The observed frequency of severe post traumaticstress response was lower than previously reported ratesof post traumatic stress disorders (PTSD) in traffic acci-dent victims (Blanchard et al., 1996; Drottning et al.,1995; Jaspers, 1998). This might be due to the fact thatthis cohort consisted solely of relatively mildly injuredtraffic victims, and that it was not primarily includedwith the purpose of studying psychological distress.

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We believe that this reduced the risk of selection bias.The present study population was recruited consecu-tively from emergency units and general practitioners,and we consider it to be representative for persons seek-ing acute care after whiplash-type accidents. Therefore itis of importance that a considerable number of the par-ticipants showed signs of a clinically important acutestress response. Moreover, this population was includedwithin a mean of 5 days after the injury, indicating thatan undesirable stress reaction can be depicted early aftera whiplash injury. Earlier results from longitudinalobservations were reported from a population includedfrom emergency units, a number of primary care prac-tices and advertisements within a mean of about 3 weeksafter the accident (Sterling et al., 2003).

Participants in the present study were randomized toconservative treatment or information. Since the scopeof this study was to illuminate whether post traumaticstress was generally a predictor of poor recovery it wasnot analyzed whether the association between early posttraumatic stress and recovery was related to early treat-ment. Hence it is undisclosed whether intervention inter-feres with post-traumatic stress. This will be evaluated ina future sub-group analysis.

A classification system for WAD, which includes theacute stress response in addition to physical risk factors,has previously been suggested (Sterling, 2004). This trialconfirmed the importance of considering the acute stressresponse as one of more risk factors. It also pointedtowards it being questionable whether diagnostic cate-gories should be defined by merely adding predictorsof the prognosis as in some classification systems (Spit-zer et al., 1995; Sterling, 2004). Instead of looking forgeneral risk factors for developing chronic WAD byconsidering the number of present risk factors, it maybe relevant to look for specific risk factors in subgroupsof patients. This way the handling of a patient can betailored towards the individual ‘‘main risk factor’’.

5. Conclusion

The acute stress response was significantly related tothe development of chronic WAD, particularly clear inthose with low baseline pain. However, the associationwas not sufficiently strong to predict chronicity on anindividual level.

Acknowledgements

This study has been made possible by an unrestrictedgrant from Danish Insurance Association. Support wasalso received from PTU, Karen Elise Jensens Founda-tion and the IMK Foundation. We would like to thanknurses Lene Kiertzner, Ove Nielsen, Ingrid Gejl, secre-

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taries Ann-Christina Just Pedersen, Jytte Frandsen,Helle Andersen and physiotherapists Eva Hauge andJette Spottag for their skilful participation in this study.Further, we want to thank Professor Werner Vach,department of statistics, University of Southern Den-mark for statistical advice regarding the design of thestudy.

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