Risk Factors Associated With the Transition From Acute to Chronic Occupational Back Pain

Risk Factors Associated With the Transition From Acute to Chronic Occupational Back Pain SPINE Volume 27, Number 1, pp 92 98 2002, Lippincott Williams & Wilkins, Inc. Marlene Fransen, PhD,* Mark Woodward, PhD,* Robyn Norton, PhD,* Carolyn Coggan, PhD, Martin Dawe, BA, and Nicolette Sheridan, MPH Study Design. A prospective cohort study was conducted on workers claiming earnings-related compensation for low back pain. Information obtained at the time of the initial claim was linked to compensation status (still claiming or not claiming) 3 months later. Objective. To identify individual, psychosocial, and workplace risk factors associated with the transition from acute to chronic occupational back pain. Summary of Background Data. Despite the magnitude of the economic and social costs associated with chronic occupational back pain, few prospective studies have investigated risk factors identifiable in the acute stage. Methods. At the time of the initial compensation claim, a self-administered questionnaire was used to gather information on a wide range of risk factors. Then 3 months later, chronicity was determined from claimants computerized records. Results. The findings showed that 3 months after the initial assessment, 204 of the recruited 854 claimants (23.9%) still were receiving compensation payments. A combined multiple regression model of individual, psychosocial, and workplace risk factors demonstrated that severe leg pain (odds ratio [OR], 1.9), obesity (OR, 1.7), all three Oswestry Disability Index categories above minimal disability (OR, 3.1 4), a General Health Questionnaire score of at least 6 (OR, 1.9), unavailability of light duties on return to work (OR, 1.7), and a job requirement of lifting for three fourths of the day or more all were significant, independent determinants of chronicity (P 0.05). Conclusions. Simple self-report measures of individual, psychosocial, and workplace factors administered when earnings-related compensation for back pain is claimed initially can identify individuals with increased odds for development of chronic occupational disability. [Key words: chronic back pain, occupational back injury, risk factors] Spine 2002;27:92 98 Low back pain is recognized as the leading cause of occupational injury in developed countries. 1,25 There is strong evidence, however, that approximately 10% of the cases cause more than 80% of the cost for low back pain because of their chronicity. 26,36,41 At this writing, most research efforts have been directed at investigating From the *Institute for International Health, University of Sydney, Australia, and the Injury Prevention Research Centre, University of Auckland, New Zealand. Supported by the Accident Rehabilitation and Compensation Insurance Corporation (ACC). The Injury Prevention Research Centre is jointly funded by the Health Research Council of New Zealand and the ACC. Acknowledgment date: February 6, 2001. First revision date: May 10, 2001. Acceptance date: May 17, 2001. Device status category: 1. Conflict of interest category: 14. risk factors for the incidence or reporting of acute back pain. 9,16,19,31,33,40,42 Unfortunately, the findings have not been consistent, probably because of difficulties dissociating occupational back pain from the underlying high incidence of low back pain found in any general community. Inconsistency in the findings also can be attributed to differences in the range of risk factors or occupational groups chosen for investigation. Primary prevention of occupational back pain injury remains elusive and possibly unattainable to any significant degree. 8 Risk factors associated with the transition from acute to chronic back pain differ from those associated with the incidence or reporting of back pain. 6,8,18,21,28,29,36,38 In contrast to acute back pain, individual 41 and psychosocial factors 9,21 are hypothesized to be more highly associated with chronic back pain than objective physical or biomechanical measures. 32 However, only a few prospective studies have investigated risk factors for the transition to chronic occupational low back pain. 11,12,21,22,30,39 Apart from the small number of cases in each of these studies, differences in recruitment timing, definition of chronicity, applicable compensation systems, and range of risk areas assessed may explain the lack of agreement in the conclusions reached. Recent extensive reviews on occupational low back pain have emphasized that individual, psychosocial, and workplace risk factors are closely related and have predicted spurious associations without simultaneous evaluation. 7,14,18,34 The Second International Forum for Primary Care Research on Low Back Pain held in 1997 designated predictors, determinants, and risk factors for low back pain disability and chronicity as second highest in terms of research priority. 4 The aim of the current prospective study was to investigate whether simple self-report measures of individual, psychosocial, and workplace factors administered when earnings-related compensation for back pain is claimed initially can identify claimants at high risk of chronicity. Risk factors for low back pain work disability and chronicity can be divided broadly into the factors potentially amenable to interventions directed at the individual and those related to employer systems. Appropriate and timely intervention to facilitate an expedient return to work directed at high-risk claimants or high-risk employer systems would have great potential to reduce the community burden associated with chronic occupational back pain. 20,27 Methods Between May 1994 and December 1995, individual claimants for earnings-related compensation resulting from new cases of 92

Predictors of Chronic Occupational Back Pain Fransen et al 93 work-related back injury were identified from the claims files of the Accident Rehabilitation and Compensation Insurance Corporation (ACC) in the greater Auckland region of New Zealand. New Zealand has a no-fault compensation system for work-related injuries administered through the ACC. To achieve sufficient cases for a meaningful evaluation of risk factors, three occupational groups identified by the ACC as having a higher than average proportion of chronic occupational back pain claims were targeted: nurses and nurses aids, heavy manual workers, and drivers. A letter of introduction, an information sheet, and a consent form were sent to eligible new claimants, who were invited to participate in the study. Those who did not respond were contacted by telephone 1 week later, and again by mail, if necessary, 2 weeks later. Claimants agreeing to participate in the study were sent a self-administered questionnaire and a stamped return-addressed envelope. Those not returning the questionnaire within 2 weeks were contacted and encouraged to reply. In addition to basic demographic information, participants were asked to provide information on any history of back pain in the preceding 12 months, episodes of prior ACC claims for back pain, perceived fitness before current back pain, and level of current pain in the back or lower limbs. Information was sought on workplace factors such as available employer systems for the reporting and management of back-injured employees and the perceived amount of manual handling and prolonged postures the job required. Six validated instruments of physical or psychosocial status were incorporated into the questionnaire 35 : 1. Oswestry Disability Index: The Oswestry Disability Index questionnaire assesses general functional disability associated with back pain. 17 Scores range from 0 to 100: 0 to 20 (minimal disability), 20 to 40 (moderate disability), 40 to 60 (severe disability), and 60 to 100 (extremely severe to crippling disability). 2. General Health Questionnaire (GHQ-28): The GHQ- 28 23 identifies personality disorders or patterns of adjustment where these are associated with distress 35 and would reflect the influence both of injury severity and psychological coping skills. The questions are grouped into four areas: somatic symptoms (hypochondriasis), anxiety and insomnia, social dysfunction, and severe depression. Scores for each of the four GHQ-28 subscales range from 0 (better or same as usual symptoms for all questions) to 7 or (worse or much worse than usual symptoms for all questions). From a possible score of 28, an aggregate score of 6 or more is considered indicative of case or psychological distress. 24 3. Modified Work APGAR (Appendix 1): The modified work APGAR 3 assesses the claimant s perception of support from fellow workers. The seven questions result in a score ranging from 7 to 21, with higher scores representing greater dissatisfaction with workplace relations. 4. Overall Job Satisfaction Scale (Appendix 1): For overall job satisfaction, each of three statements allows responses ranging from 1 (strongly disagree) to 7 (strongly agree). A mean score is extrapolated from the three responses, resulting in a score range of 1 to 7, with higher scores demonstrating greater job satisfaction. 5. Life Events: Claimants were questioned on whether any of 10 specific major life events had occurred in the preceding 12 months: death of someone close, beginning of a serious illness in self or a family member, involvement in an accident by self or a family member, new family member gained, breaking off of a close relationship, a particular financial crisis, job or business loss as a result of retiring or resigning, beginning of a different job, acceptance of income support, or change of duties at work. 37 6. Loci of Control of Behavior Scale (Appendix 1): Locusof-control scales measure a persons perception of control over his or her behavior and life circumstances. 13 To limit the participant burden, four questions were extrapolated from the original 17 questionnaire questions on advice from the originators of the scale (personal communication). Scores from the modified locus of control of behavior scale ranged from 4 to 16, with higher scores indicating less personal control or more externality. The outcome, compensation status 3 months after the initial claim, was obtained from the claimant s files at the ACC. Statistical analysis was by logistic regression analysis using SAS Version 8 (SAS Institute, Cary, NC). All regression models included adjustment for age and gender. Where factors were assessed using a scoring scheme, cut points described in the literature were used to determine groups for comparison (validated criteria). Where no such literature was obtained, ranges were split into roughly equal-size groups (distribution criteria). The University of Auckland Human Subjects Ethics Committee approved the study. Results Over the 20-month recruitment period, 1440 claimants initially agreed to be contacted by the research team. Of the 854 claimants (59.3%) who completed the selfadministered questionnaire, 617 (72.3%) belonged to the targeted high-risk occupational groupings: nurses and nurses aids, heavy manual workers, and drivers. As reported, 3 months after the initial claim, 204 (23.9%) claimants were still receiving compensation payments. The age and gender-adjusted odds ratios (OR) and 95% confidence intervals (95% CI) for the variables grouped as individual, psychosocial, and workplace risk factors for the development of chronic occupational back pain are outlined in Tables 1 to 3. All the logistic regression models were age and gender adjusted. Individual Factors For the individual factors, increasing age (OR, 1.5 1.6), the presence of a severe radiating pain in the legs (OR, 2.3), a higher than normal body mass index (OR, 1.6 1.9) and an Oswestry Disability score indicating at least moderate disability (OR, 3.5 5.9) were significant predictors of chronicity with dose response relationships (P 0.05) (Table 1). When these significant predictors were entered into a multiple regression model, a body mass index representing obesity relative to normal weight (OR, 1.8; 95% CI, 1.2 3), severe radiating leg pain (OR, 2.1; 95% CI, 1.3 3.5), and Oswestry Disability Index scores indicating moderate (OR, 3.3; 95% CI, 1.5 7), severe (OR, 5.1; 95% CI, 2.4 10.6), or extremely severe disability (OR, 4.6; 95% CI, 2.2 9.7) relative to minimal disability retained significance (Table 4).

94 Spine Volume 27 Number 1 2002 Table 1. Individual Characteristics of Workers Compensation Claimants* Characteristic Claiming at 3mo n (%) OR (95% CI) P Males (n 636) 149 (23.4) 1.0 0.59 Females (n 218) 55 (25.2) 1.10 (0.77 1.58) Age group (y) 15 30 (n 252) 47 (18.7) 1.0 0.06 31 45 (n 361) 92 (25.5) 1.49 (1.00 2.22) 46 (n 241) 65 (27.0) 1.61 (1.05 2.47) Living alone (n 307) 64 (20.9) 1.0 0.31 Cohabiting (n 541) 137 (25.3) 1.21 (0.84 1.73) Education 4 y secondary (n 350) 90 (25.7) 1.0 0.31 Secondary/trade (n 384) 92 (24.0) 0.95 (0.68 1.34) Diploma/degree (n 110) 21 (19.1) 0.66 (0.37 1.15) Current smoking status None (n 517) 122 (23.6) 1.0 0.37 1 19 per day (n 197) 44 (22.3) 0.96 (0.65 1.43) 20 per day (n 122) 36 (29.5) 1.35 (0.87 2.10) Back pain in past 12 months No (n 553) 135 (24.4) 1.0 0.39 Yes (n 280) 61 (21.8) 0.86 (0.61 1.21) Prior ACC claim for back pain No (n 471) 110 (23.4) 1.0 0.63 Yes (n 361) 90 (24.9) 1.08 (0.78 1.50) Pain in back Mild (1 3) (n 57) 11 (19.3) 1.0 0.19 Moderate (4 6) (n 223) 45 (20.2) 1.08 (0.52 2.27) Severe (7 10) (n 573) 148 (25.8) 1.47 (0.74 2.91) Pain in legs None (n 320) 53 (16.6) 1.0 0.0001 Mild (1 3) (n 188) 39 (20.7) 0.76 (0.48 1.20) Moderate (4 6) (n 173) 48 (27.7) 1.45 (0.89 2.35) Severe (7 10) (n 166) 64 (38.5) 2.33 (1.44 3.76) BMI (kg/m 2 ) 0.01 Normal ( 25) (n 396) 75 (18.9) 1.0 Overweight (25.1 30) (n 305) 81 (26.6) 1.56 (1.08 2.25) Obese (30 ) (n 130) 39 (30.0) 1.85 (1.17 2.90) Physical fitness 0.57 Unfit (1 3) (n 60) 12 (20.0) 1.0 Medium (4 6) (n 394) 92 (23.4) 1.22 (0.62 2.40) Very fit (7 10) (n 392) 99 (25.3) 1.38 (0.70 2.70) Oswestry Disability Index 0.0001 0 20 (n 130) 9 (6.9) 1.0 21 40 (n 237) 49 (20.7) 3.48 (1.65 7.35) 41 59 (n 247) 76 (30.8) 5.89 (2.84 12.20) 60 (n 229) 70 (30.6) 5.69 (2.73 11.89) * Odds ratios (age- and gender-adjusted) for chronicity. OR odds ratio; CI confidence interval; ACC Accident Rehabilitation and Compensation Insurance Corporation; BMI body mass index. Psychosocial Factors Of the psychosocial assessment measures (Table 2), only poor GHQ-28 scores (anxiety or insomnia, social dysfunction, and severe depression) demonstrated significant age and gender-adjusted associations with chronicity. Individuals with a total GHQ-28 score of 6 or more had significantly greater odds of chronic disability developing (OR 2.8) than those scoring less than 6. Workplace Factors Among the many workplace factors assessed in this study, significant age and gender-adjusted associations were found for the following: perception that reporting to the ACC was actively discouraged (OR, 2), unavailability of light duties on return to work (OR, 2), need to lift objects for about one half (OR, 1.5) or for at least three fourths of the working day (OR, 2), need to lift (OR, 1.4) or maneuver (OR, 1.5) extremely heavy items regularly, need to spend at least three fourths of the working day driving (OR, 1.8) (Table 3). Borderline significance (P 0.05) was achieved for the need to work shifts of longer than 8 hours regularly (OR, 1.4) and for noticing vibration while driving (OR, 1.6). When these significant workplace risk factors and those of borderline significance were put into a multiple regression model, only the unavailability of light duties on return to work (OR 1.8; 95% CI 1.3, 2.7) and the job requirement to lift for at least three fourths of the day, as compared with only lifting as long as one fourth of the day, (OR 1.9; 95% CI 1.3, 2.8) retained significance (Table 4). Combined Model Radiating pain in the lower limb, the Oswestry Disability Index, and the GHQ-28 all were similarly and signifi- Table 2. Psychosocial Characteristics of Workers Compensation Claimants* Characteristic Claiming at 3mo n (%) OR (95% CI) P General Health Questionnaire (GHQ) Somatic 0(n 402) 87 (21.6) 1.0 0.10 1 (n 448) 116 (25.9) 1.31 (0.95 1.81) Anxiety/insomnia 0(n 426) 75 (17.6) 1.0 0.0001 1 (n 424) 128 (30.2) 2.08 (1.50 2.89) Social dysfunction 0(n 394) 58 (14.7) 1.0 0.0001 1 (n 456) 145 (31.8) 2.79 (1.98 3.93) Severe depression 0(n 716) 151 (21.1) 1.0 0.0001 1 (n 134) 52 (38.8) 2.47 (1.66 3.67) GHQ-28 total 6 (n 537) 89 (17.5) 1.0 0.0001 6 (n 313) 107 (34.2) 2.78 (2.00 3.87) Work APGAR Score 7 9 (n 202) 49 (24.3) 1.0 0.19 Score 10 12 (n 178) 49 (27.5) 1.24 (0.78 1.97) Score 13 21 (n 214) 42 (19.6) 0.80 (0.50 1.28) Job satisfaction At least slightly agree ( 5) 146 (23.6) 1 0.53 (n 619) Mostly disagree ( 5) (n 223) 56 (25.1) 1.14 (0.80 1.64) Life events (yes) Death (n 284) 59 (20.8) 0.77 (0.54 1.08) 0.13 Illness (n 194) 50 (25.8) 1.12 (0.77 1.62) 0.55 Accident (n 149) 41 (27.5) 1.29 (0.86 1.94) 0.21 New family member (n 186) 32 (17.2) 0.60 (0.39 0.91) 0.02 Relationship broken (n 133) 31 (23.3) 1.03 (0.66 1.62) 0.88 Financial crisis (n 231) 60 (26.0) 1.23 (0.86 1.75) 0.26 Retired, resigned, lost job 37 (30.3) 1.47 (0.96 2.24) 0.08 (n 122) Started different job (n 192) 35 (18.2) 0.68 (0.45 1.03) 0.07 Went on income support (n 76) 24 (31.6) 1.61 (0.96 2.71) 0.07 Changes in work duties (n 211) 49 (23.2) 0.98 (0.68 1.43) 0.93 External locus of control Score 4 7 (n 213) 48 (22.5) 1.0 0.84 Score 8 9 (n 413) 100 (24.2) 1.10 (0.74 1.63) Score 10 16 (n 216) 54 (25.0) 1.13 (0.72 1.77) * Odds ratios (age- and gender-adjusted) for chronicity. OR odds ratio; CI confidence interval.

Predictors of Chronic Occupational Back Pain Fransen et al 95 Table 3. Workplace Factors of Workers Compensation Claimants* Workplace factor Claiming at 3mo n (%) OR (95% CI) P System for identifying potentially harmful materials and situations No (n 289) 67 (23.2) 1 0.68 Yes (n 397) 98 (24.7) 1.08 (0.76 1.54) System for reporting injuries No (n 157) 42 (26.8) 1 0.23 Yes (n 610) 138 (22.6) 0.77 (0.52 1.17) Response to reporting to ACC Actively encouraged (n 170) 35 (20.6) 1 0.14 Routine (n 394) 95 (24.1) 1.22 (0.79 1.89) Actively discouraged (n 65) 21 (32.3) 1.95 (1.02 3.72) Availability of light duties Yes (n 307) 51 (16.6) 1 0.0002 No (n 468) 133 (28.4) 1.99 (1.39 2.86) Regularly work more than 8-h shifts No (n 372) 80 (21.5) 1 0.08 Yes (n 481) 124 (25.8) 1.36 (0.97 1.92) Work unsociable hours No (n 382) 87 (22.8) 1 0.46 Yes (n 471) 117 (24.8) 1.13 (0.82 1.56) How much lifting time per day Up to one fourth (n 420) 80 (19.1) 1 0.0007 About half (n 189) 48 (25.4) 1.52 (1.01 2.24) About three fourths or more 75 (31.0) 2.04 (1.41 2.96) (n 242) Regularly lift extremely heavy items No (n 516) 113 (21.9) 1 0.05 Yes (n 286) 79 (27.6) 1.41 (1.01 1.98) Regularly maneuver extremely heavy items No (n 467) 99 (21.2) 1 0.02 Yes (n 380) 105 (27.6) 1.48 (1.08 2.04) Time spent sitting each day None (n 376) 89 (23.7) 1 0.56 Up to about one half (n 392) 90 (23.0) 0.96 (0.68 1.34) About three fourths or more 24 (28.9) 1.28 (0.75 2.19) (n 83) Time spent walking each day None (n 47) 16 (34.0) 1 0.26 Up to about half (n 432) 104 (24.1) 0.61 (0.32 1.17) About three fourths or more 84 (22.4) 0.57 (0.30 1.09) (n 375) Time spent driving each day None (n 430) 104 (24.2) 1 0.04 Up to about one half (n 361) 77 (21.3) 0.85 (0.60 1.21) About three fourths or more 23 (36.5) 1.82 (1.03 3.22) (n 63) If driving, notice vibration No (n 121) 23 (19.0) 1 0.07 Yes (n 293) 76 (25.9) 1.61 (0.96 2.70) * Odds ratios (age- and gender-adjusted) for chronicity. Sample size not always complete because several questions allowed a not applicable response and were therefore not included in the analysis. OR odds ratio; CI confidence interval; ACC Accident Rehabilitation and Compensation Insurance Corporation. cantly intercorrelated (r 0.21 0.23). When the significant risk factors in the individual, psychosocial, and workplace risk factor areas were combined into one model, although all demonstrated slightly decreased odds ratios (apart from the workplace requirement to lift for at least three fourths of the day), all maintained significance as predictors of chronic occupational back pain (Table 4). Even after adjusting for age, gender, severity of leg pain, body mass index, level of psychological distress (GHQ-28), availability of light duties on return to work, or workplace lifting requirement, the most strongly significant predictor for chronicity was an Oswestry Disability Index score above minimal disability: moderate disability (OR, 3.1; 95% CI, 1.4 6.8), severe disability (OR, 4; 95% CI, 1.8 8.6), and very severe disability (OR, 3.4; 95% CI, 1.6 7.5). Discussion The results of this study demonstrate that individual, psychosocial, and workplace factors all are associated with the transition from acute to chronic occupational back pain. If workers at the time they make their initial claim for earnings-related compensation report severe radiating lower limb pain, at least moderate physical disability or psychological distress, the need to lift for at least three fourths of the day, or a workplace unable to provide light duties on return to work, the odds that they still will be receiving compensation 3 months later will be significantly increased. Importantly, these determinants each retained significant associations with chronic occupational back pain, even when statistical adjustments were made for age, gender, and the other significant individual, psychosocial, or workplace risk factors (Table 4). In fact, reporting severe radiating leg pain, psychological distress as measured by the GHQ-28, or the requirement to lift for at least three fourths of the day at the time of the initial compensation claim almost doubled a claimant s odds, whereas reporting at least moderate disability associated with back pain, as measured by an Oswestry Disability Index score of at least 20, increased a claimant s odds of still receiving three- to fourfold for work disability 3 months later. The strength of the current prospective cohort is that the participants were recruited from a diversity of occupational groups and assessed on a wide range of validated self-report measures at the time of their initial claim for earnings-related compensation. Furthermore, there were no losses to follow-up assessment 3 months Table 4. Significant Risk Factors in Multiple Regression Models Models* Separate Models OR (95% CI) Combined Model OR (95% CI) Individual Severe leg pain (7 10) 2.09 (1.26 3.46) 1.92 (1.11 3.33) BMI (30 ) 1.84 (1.15 2.96) 1.68 (1.01 2.81) Oswestry Disability Index 21 40 3.29 (1.53 7.02) 3.10 (1.41 6.80) 41 59 5.05 (2.40 10.60) 3.98 (1.84 8.62) 60 4.58 (2.16 9.71) 3.43 (1.57 7.51) Psychosocial GHQ-28 (6 ) 2.78 (2.00 3.87) 1.87 (1.29 2.71) Workplace Unavailability of light duties 1.84 (1.28 2.66) 1.66 (1.12 2.46) Lifting about 3 4 day or more 1.85 (1.25 2.75) 1.98 (1.30 3.04) * Age- and gender-adjusted with base groups as per Tables 1 to 3. OR odds ratio; CI confidence interval.

96 Spine Volume 27 Number 1 2002 later when compensation status was ascertained. Sufficient cases were identified to make meaningful evaluations. However, the generalizability of the current study results probably are restricted to workers covered by similar no-fault, nonadversarial workers compensation systems. 10 Although the importance of acute disease severity, as measured by individual factors such as radiating pain and physical disability, for determining back pain chronicity was not unexpected, there were some unexpected results among the many psychosocial and workplace factors assessed in the current study. In contrast to the current study, several previous large epidemiologic studies investigating psychosocial factors in occupational groups have shown significant associations between job dissatisfaction or poor workplace relations and the incidence of work-related back pain. 7,14 The current study, however, specifically investigated the transition from acute to chronic occupational back pain, and this difference may explain the lack of an independent significant association (Table 2). On the other hand, in an attempt to limit participant burden, the current study assessed work satisfaction and locus of control with only a limited number of questions, and threshold scores again were chosen on the basis of distribution (Appendix 1). Measurement imprecision may have caused the insignificant effect of work satisfaction and locus of control on occupational back pain disability. Workplace systems such as those for reporting back injuries or identifying potentially harmful materials or situations did not independently demonstrate significant protection against chronicity (Table 3). On reflection, it seems probable that these systems provide protection against incidence, and that a negative response simply indicates a low-risk working environment. The results of the current study therefore should not be interpreted as providing evidence for the ineffectiveness of such management systems. The loss of significance for the need to regularly lift extremely heavy items or regularly maneuver extremely heavy items in the multiple regression workplace factors model also was unexpected. The accuracy and validity of self-reported workplace physical or postural load relating to occupational low back pain often has been discussed in the literature. 5 Several authors have argued the need for objective load measurement through the use of various instruments or observational assessments. Apart from practical difficulties covering various occupational groups in large studies or symptomatic samples, it can be debated whether even very sophisticated instruments can allow for all the differences and interactions in influential anatomic, biomechanical, physiologic, and psychosocial components between, and even within, individuals. 34 The accuracy of the observational gold standard is further questioned when most often only instances of the working week are observed. In fact, an individual s perception of physical load may more readily incorporate all these variations, and thereby constitute a more valid measure. The cohort in the current study covered a wide range of occupational groups, and therefore did not experience a lack of contrast within the workplace variables. The use of the nebulous term regularly may have resulted in substantial random measurement error, leading to nondifferential misclassification of this dichotomous exposure variable and attenuation of the odds ratio. Quantification of frequency or duration is likely to reduce differences in interpretation. 43 In addition, it is likely that the job requirement to work regularly with extremely heavy objects will, in fact, self-select out the people prone to low back pain. However, the effect of the need to lift or maneuver extremely heavy objects regularly simply may have been absorbed by the stronger effects of the availability of light duties on return to work or the need to lift for at least three fourths of the day (Table 2) in the multiple regression workplace factors model (Table 4). Interestingly, all the significant factors in the individual, psychosocial, and workplace models retained their significance in the combined model (Table 4). Previous studies have suggested that much of the effect from workplace physical load may be absorbed by individual or psychosocial variables in any combined model. 15 In the current study, whereas unavailability of light duties on return to work had a reduced effect in the combined model, the need to lift for at least three fourths of the day was mostly unaffected by adjustment for significant individual and psychosocial factors. Among the psychosocial characteristics assessed (Table 2), only the GHQ-28 retained significance in the multiple regression models (Table 4). A total GHQ-28 threshold score of 6, which demonstrated a screening sensitivity and specificity of approximately 80% for case detection in a large World Health Organization study of psychological disorders in general health care, was used in the current analysis. 24 A tendency for a high falsepositive rate in people with substantial physical illness has, however, been suggested. 35 Using a higher cutoff point did not appreciably change the odds ratio for chronicity. However, disregarding the somatic section but keeping the threshold score of 6 increased the predictive value of this questionnaire in a population with acute back pain (OR, 3.20; 95% CI, 2.25 4.54). The Oswestry questionnaire rates pain intensity and the degree to which an individual s functional ability in personal care, lifting, walking, sitting, standing, sleeping, sex life, social life, and traveling is affected by back pain. The Oswestry questionnaire has demonstrated construct validity through significant positive correlation with physical tests and signs indicative of disease severity. 2 Not unexpectedly, therefore, of all the factors analyzed in the current study, the Oswestry questionnaire provided scores that were the most highly predictive of occupational back pain chronicity. However, if, for example, an Oswestry Disability Index score of 41 or more had been used as the criteria for identifying claimants at

Predictors of Chronic Occupational Back Pain Fransen et al 97 Modified Work APGAR Appendix 1 1. I am satisfied that I can turn to a fellow worker when something is troubling me. 2. I am satisfied with the way my fellow workers talk over things and share problems with me. 3. I am satisfied that my fellow workers accept and support my new ideas or thoughts. 4. I am satisfied with the way my fellow workers respond to my emotions, such as anger, sorrow, or laughter. 5. I am satisfied with the way my fellow workers and I share time together. 6. I enjoy the tasks involved in my job. 7. Please write the number that indicates how well you get along with your closest or immediate supervisor. Response 1 almost always 2 some of the time 3 hardly ever 4 does not apply Overall Job Satisfaction 1. All in all, I am satisfied with my job. 2. In general, I do not like my job.* 3. In general, I like working here. Response 1 strongly disagree 2 disagree 3 slightly disagree 4 neither agree nor disagree 5 slightly agree 6 agree 7 strongly agree * Reverse scored Locus of Control Over Behavior 1. A great deal of what happens to me is probably just a matter of chance. 2. Everyone knows that luck or chance determines one s future. 3. When I make plans, I am almost certain that I can make them work.* 4. I am confident of being able to deal successfully with future problems.* Response 1 strongly disagree 2 disagree 3 agree 4 strongly agree * Reverse scored high risk for chronicity, more than half of the sample would have been targeted for early intervention. Yet only approximately 30% of this identified group were still claiming compensation after 3 months. More work is required to determine optimal cut points for this score. The current study demonstrates that it is possible to identify, at a very early stage, many claimants at increased odds for the development of chronic occupational back pain. For claimants who report the unavailability of light duties on return to work or a job requirement to lift for at least three fourths of the day, the provision of modified work by employers has demonstrated cost effectiveness. 27 However, whether the early identification of claimants with significant individual or psychosocial risk factors would reduce occupational low back pain disability in a cost-effective manner still requires further investigation into both screening sensitivity and specificity as well as intervention cost effectiveness. Conclusion Simple self-report measures of individual, psychosocial, and workplace factors at the time the initial earningsrelated compensation claim is made for back pain can identify individuals with increased odds for development of chronic occupational disability. Key Points The current prospective study examines a cohort of workers from a variety of occupations, but all covered by a no-fault nonadversarial workers compensation system. Simple self-report questionnaires administered at the time of initial back pain can identify those workers with increased odds for developing chronic occupational disability. Various individual, psychosocial, and workplace factors retain significant association with the transition from acute to chronic occupational back pain in a combined model. The current study did not find that job dissatisfaction or poor workplace relations significantly identified those workers who develop occupational back pain. Acknowledgments The authors acknowledge the assistance of Niurangi Taua, Judith Rudd, Robin Brian, Elizabeth Robinson and Trevor Lee-Joe in data collection and management of the study. References 1. Battie MC, Bigos SJ. Industrial back pain complaints: A broader perspective. Orthop Clin North Am 1991;22:273 82. 2. Beurskens AJ, de Vet HC, Koke AJ, et al. Measuring the functional status of patients with low back pain: Assessment of the quality of four disease-specific questionnaires. 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