MEDICALLY CERTIFIED WORK LOSS, RECURRENCE AND COSTS OF WAGE COMPENSATION FOR BACK PAIN: A FOLLOW-UP STUDY OF THE WORKING POPULATION OF JERSEY

British Journal of Rheumatology 1998;37:82±86 MEDICALLY CERTIFIED WORK LOSS, RECURRENCE AND COSTS OF WAGE COMPENSATION FOR BACK PAIN: A FOLLOW-UP STUDY OF THE WORKING POPULATION OF JERSEY P. J. WATSON,* C. J. MAIN,*$ G. WADDELL,% T. F. GALES} and G. PURCELL-JONES} *Rheumatic Diseases Centre, University of Manchester, $Department of Behavioural Medicine, Hope Hospital, Salford, %Department of Orthopaedic Surgery, Glasgow Nu eld Hospital, Glasgow, }Department of Social Security, States of Jersey and }St Helier Hospital, St Helier, Jersey SUMMARY The 1 yr incidence, prevalence and wages compensation costs of work loss due to medically certi ed back pain in the working population of Jersey were identi ed by analysis of the Social Security database for the year 1994. A total of 2291 subjects absenting due to back pain during this period were followed for up to 3 yr to identify return to work rates and subsequent absences. Incidence and prevalence rates were 5.6 and 6.3%, respectively. The cost of wages compensation was 1.29 million or 10.5% of such bene ts paid. Work loss was greater for the second absence. The rate of return to work was broadly in line with that suggested by the Clinical Standards Advisory Group (CSAG), but the number still absent at 1 yr was less, suggesting that the CSAG gures for long-term absence may have been overestimated. The in uence of compensation systems and unemployment on work-related absence due to back pain is highlighted. KEY WORDS: Back pain, Epidemiology, Wages compensation, Work loss. LOW back pain (LBP) is one of the most common medical reasons for work loss in the UK and most Western countries [1]. The duration of work loss is of particular importance to the individual, their medical management and to the total impact on society. Yet it is surprisingly di cult to obtain accurate data. The Clinical Standards Advisory Group (CSAG) [1] tried to estimate the rate of return to work based on the best data available at that time, but clearly acknowledged the limitations of their gures. Consequently, the duration of work loss and rate of return to work following back pain in the UK are not known. Detailed analysis of duration of work loss and rate of return to work following an acute attack of back pain has been reported by Andersson et al. [2], Choler et al. [3], the Quebec task force [4, 5] and the Workmen's Compensation Board of British Columbia [6]. Although large series, they are all either Scandinavian or North American, are mainly from Workmen's Compensation Board or work-related situations, and the data are now at least 10 yr old. There are no comparable large-series data for the UK. Department of Social Security (DSS) data on the incidence of back pain are about bene ts paid, which is quite di erent from work loss. Walsh et al. [7] investigated the incidence of back pain and associated work loss in eight selected general practitioner (GP) practices in di erent areas of the UK based on a self-report questionnaire. They Submitted 5 March 1997; revised version accepted 16 June 1997. Correspondence to: P. J. Watson, Rheumatic Diseases Centre, Clinical Sciences Building, Hope Hospital, Eccles Old Road, Salford M6 8HD. identi ed a rate of between 6.5 and 10% with wide variations between regions. A response rate of only 59% may have led to over- or under-reporting in this study. UK data on short-term work loss are available from the O ce of Population and Census Surveys (OPCS) [8], but this is a very small sample. There are no reliable or recent UK data on the number who remain o work after 1 yr. Accurate and up-to-date data are available in Jersey. The Social Security and Healthcare system in the island of Jersey di ers from the UK in a number of important ways. Firstly, there is no self sickness certi cation facility and sickness bene t is only payable on receipt of sickness certi cation by a medical practitioner. Sick pay is not payable for a single days absence. Secondly, there is no Statutory Sick Pay (SSP) system. In the UK, up to 28 weeks of sick pay are paid by the employer. In Jersey, all claims for wages compensation for sickness-related absences are paid by the Social Security fund. Compensation is paid at a at rate with an enhancement for persons with dependants, but it is not related to the claimant's normal earnings. In the island population of 082 000 in 1994, the working population derived from manpower returns for 1994 was 40 771. There is no unemployment bene t payable in Jersey. Unemployment during the period of the study was <3% and so in economic terms the island can be seen as having virtually full employment. The purpose of this study is to quantify work loss by analysis of medical certi cation of absence, diagnosed by a medical practitioner, in the working population during 1994; to gain accurate data on the 82 # 1998 British Society for Rheumatology

WATSON ET AL.: BACK PAIN, WORK LOSS AND BENEFIT COSTS 83 cost of sickness bene ts paid to LBP su erers; to ascertain the cost of LBP-associated absences as a proportion of the total cost of wages compensation; and to investigate the length of initial and second absences. METHOD Jersey records all sickness, incapacity and accident bene ts on a computer database which enables analysis of the data by individual claimant, GP, ailment code and bene ts paid. Each claimant is identi ed by a unique Social Security number. Ailments are diagnosed on the coding system speci cally developed for the purposes of the DSS in Jersey by one of the authors (TFG). All medical practitioners use this method of coding reasons for absence from work on medical certi cates. Input error rates monitored internally by auditors and externally by States of Jersey Treasury auditors are currently <2%. The frequencies of the diagnoses recorded for rst absences during the study year were gathered and these are shown in Table I. Diagnoses were grouped into speci c LBP (sciatica and intervertebral disc pathology), non-speci c (backache and lumbago) and back injuries. Di erences in length of absence and the rate of return to work for the rst episode were investigated. Each new claim for back pain was identi ed from the beginning of 1994. Those claims current from 1993 were also identi ed. The incidence of back pain in the population was calculated by the number of persons ling rst claims in 1994. This group formed the baseline cohort for the study. The period prevalence was calculated by including those subjects already absent from work at the beginning of 1994 in this gure. The costs of bene ts paid for all days lost due to chronic LBP were calculated by summing the bene ts paid for work days lost by all new claims and old claims still current during 1994. The baseline cohort was followed until they returned to work (ceased the claim) and the return to work rates were monitored. Data from the OPCS suggest that 35% of those absenting from work due to back pain do so for only 1 day and return by the second day, and TABLE I Certi ed absences from work for back pain by diagnosis for all subjects newly absent from work in 1994 Diagnosis Number of cases Percentage Sciatica 170 7.4 Lumbago 116 5.1 Prolapsed intervertebral disc 119 5.2 Disc problem 59 2.6 Injury to the back 261 11.4 Injury to the back at work 209 9.1 Backache 1357 59.4 Total number of cases 2291 therefore these cases may not appear in the current data set. Two sets of gures for the incidence and the rate of return to work were calculated: the measured incidence for the period concerned and an estimated number based on the assumption of a return to work of 35% of subjects by day two. Subjects in the baseline cohort were followed until the end of 1996 to detect second absences and the recurrence of back pain-related work absence within 1 yr of ceasing the rst claim. Second absences were followed until the end of 1996 to identify the duration and calculate the cost of second absences. RESULTS Incidence and prevalence of work loss due to back pain A total of 2822 new claims for back pain were registered in 1994 by 2291 individuals. The incidence of new absences for back pain was therefore 5.62% per annum for the working population or 0.47% per month. There was no seasonal pattern to the claims. There were 270 persons who were already absent at the beginning of the study period, giving a total of 2561 people absent from work, an annual prevalence of 6.28%. Recalculation of the data assuming a return to work of 35% after the rst day give an adjusted annual incidence of 7.60%, a monthly incidence of 0.63% and an annual prevalence of 8.25%. Cost of bene ts The total cost for the bene ts paid for back trouble during 1994 was 1 287 204, equivalent to a cost of 3.16 million/100 000 working population. The total cost of all sickness and invalidity payments for all claims of >1 day in Jersey for 1994/95 was 12.2 million [9]. The cost of wages replacement compensation was therefore 10.5% of the total paid for all claimed absences during the same period. Subjects absent from work for more than 6 months (182 days) were only 3% of the total number. However, this group accounted for 33% of the bene- t paid during the period of this study. This highlights the high cost of developing chronicity. Return to work Table II shows the duration of work loss and hence the rate of return to work (RTW) for those who submitted new claims for back pain in Jersey in 1994. The gures are given for all rst claims in 1994 and all second claims as de ned in the protocol above. The CSAG [1] estimates are shown for comparison. Assuming that 35% of subjects returned to work after only 1 day, as suggested in the OPCS study [8], then the gures look lower than the CSAG estimate. Figure 1 gives the return to work curves. These have been adjusted in line with the data from the OPCS to assume a return to work of 35% of sufferers by day 2, although it was not possible to verify this gure in this study, so the non-adjusted gures are given for comparison. A total of 422 persons absented from work due to back trouble for a second time within one calendar

84 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 37 NO. 1 TABLE II Return to work following claimed absence from work with back pain 1. 4. 5. 6. 7. % Still o work % Still o workð Adjusted for % Still o workð Adjusted for CSAG 1st absence Jersey 35% RTW 2nd absence Jersey 35% RTW Days o work (n = 2291) by day 2 (n = 422) by day 2 2 65 96.8 63 98.8 64.3 7 33 56.3 36.6 67.8 44.1 14 25 29.3 19 4.1 28.7 28 16 15 9.8 28 18.2 60 95 8 5.2 18.7 12.2 91 6.5 5.8 3.8 15.4 10 182 4.3 3 1.9 12.1 7.9 365 3 1 0.65 6.9 4.5 year of returning to work. This represents a recurrence rate of 18.4%. The lengths of the rst and second absences were compared by ANOVA. The results demonstrate a signi cant di erence between the two absences [ rst absence mean work loss 20.73 days (S.D. 38.9); second absence mean work loss 36.8 days (S.D. 61.4), F = 49.4, signi cance of F = <0.001]. The e ect of diagnostic grouping (speci c, nonspeci c and injury) on return to work was investigated by means of one-way analysis of variance with a post hoc Sche e test at a signi cance level of P < 0.05. Those with speci c LBP had a mean absence of 45.1 days, which was signi cantly greater than that of those with non-speci c back pain (mean absence 35.8 days) and both of these groups had signi cantly longer periods of absence than those who were diagnosed with back injuries (mean absence 23.1 days). There was no signi cant di erence between those diagnosed as sustaining injuries at work and those who were injured elsewhere. The proportion remaining absent at 1 yr Rates of return to work have been recalculated to allow for a return to work of 35% after only 1 day; these are also given in Table II and represented graphically in Fig. 1. The rates of return to work di er depending on whether the claims are rst or second claims. The rate of return to work for all the rst episodes in the year is substantially faster than for the second episode. The RTW gures from CSAG [1] are given for comparison. The RTW rates in the CSAG gures lag behind those for the rst episode of back-related absence in 1994. Only 0.65% (adjusted gure) of those absent on the rst claim in 1994 remained so for 12 months or longer. This increases to 4.5% (adjusted gure) for those who went on to have a second period of absence within 1 yr of returning to work. The rate of return to work by diagnostic group for the rst episode only is given in Fig. 2. Those given a speci c diagnosis demonstrate a slower RTW than non-speci c back pain or injury-related back pain. Incidence of injury at work There are no accurate records for work-related back injuries in the UK. The CSAG [1] suggests that 5% of work loss due to LBP was related to an injury at work. Injuries sustained at work in Jersey are recorded by the GPs; this generates an automatic computer code to allow investigation by the Health and Safety Inspectorate. The total number of work- FIG. 1.ÐReturn to work following absence from work (Jersey data adjusted to 35% returned by day 2). FIG. 2.ÐReturn to work by diagnosis for rst episode of back pain (adjusted for 35% RTW by day 2).

WATSON ET AL.: BACK PAIN, WORK LOSS AND BENEFIT COSTS 85 related back injuries was 209, accounting for 9.1% of the total number of absences from work. Data from the Health and Safety Department of Jersey show that during the period October 1993±September 1994, there were 1588 certi ed work-related injuries in Jersey, 387 of these involved injury to the back; this accounted for 24.3% of the total number of workplace injuries reported. DISCUSSION This study is the rst in the UK clearly to identify the incidence of work loss due to back pain that has been medically veri ed in a large working population. All previous reported data have been from self-report or have been extrapolated from other studies. This study lends support to the best estimates for the rate of return to work calculated in the CSAG report. It must be remembered that the CSAG gures were an attempt to synthesize previous data and were not based on an investigation of a speci c population. The 1 yr adult prevalence of LBP back symptoms lasting >24 h has been suggested to be 38% [7]. Taking the yearly prevalence in Jersey as a guide, a gure of nearly 7.5% for employed people yields an estimate of 2.03 million people in the UK losing some time from work each year due to back pain. Since many will have more than one attack and will be o work more than once, this is certainly an underestimate of the number of attacks. DSS gures from 1990/91 [1] show that 286 000 employed people started invalidity bene t for back pain in that year, i.e. were o work for >28 weeks. That suggests that >2% of those who lose any time o work are o for >6 months. Allowing for the proportion who return to work between 6 and 12 months, that would mean <1% are still o work at 1 yr, which is nearer to the Jersey gure of 0.65% (1% unadjusted gure) for all rst absences. This seems more accurate than the CSAG [1] estimate of 3%. The observation that those with a diagnosis of speci c LBP (sciatica and disc disorders) have longer periods of absence than those with non-speci c back pain is in agreement with other studies [10]. Frank et al. [11] have suggested that doctors `overtreat' patients with sciatic symptoms, and this may account for the increased disability and prolonged absence from work in this group. However, in this study there was no attempt to verify the accuracy of the GPs' diagnosis. The recurrence of back pain-related absence has received little attention in the UK. Anderson [12] showed that 8.9% of dock workers had a recurrence of back pain-related absence within 2 yr of the initial study period. The results from the present study give a higher incidence of recurrence of absence. It must be pointed out that some of the initial cohort in the study may have had previous back pain-related absences and therefore may not be strictly rst absences from work. The gures in this study are nevertheless representative of the more recent data from Canada of 20% in 1 yr and 36% within 2 yr [13, 14], but are considerably less than the gures reported in Sweden of 44% [15] within 1 yr, and higher than those reported in a study of health and veterinary professionals by van Doorn of 8.6% [16]. The concordance with the results reported by the Canadian group may be due to the similarity of reporting, the requirement for payment of wages compensation to be veri ed by a medical practitioner and the entry criteria for the study: the rst episode of back pain in the initial study year. Those subjects in the van Doorn study were initial episodes in subjects who had not previously claimed wages compensation for back pain. It was not possible to screen out those who had previously been compensated for LBP in this study. Van Doorn's study represents a select patient group of self-employed dentists, veterinarians and physical therapists, and so cannot be seen as representative of the diverse population in this study. According to the most recently available statistics [9], 48% of male workers and 14% of female workers in the present study were in manual occupations (e.g. agriculture and shing, distribution services, craft occupations, construction and labouring). Von Kor [17] points out that back pain is often a recurrent problem. Pain and disability are often disproportionate. The majority of patients may continue to have some pain after 1 yr, but a very much smaller number have any disability. The present gure relates purely to work loss and not to symptoms. Moreover, because many patients have recurrent symptoms, it may be misleading to consider return to work from a `single attack'. The DSS gures may more truly re ect the chances of an individual developing chronic disability over a period of 1 yr rather than the outcome of a single attack, but symptoms are not the same as sickness or work loss. In the UK, 9.2% of adults consult their GP each year with back pain as their main complaint [18]. Only 22% of those who consult with back pain receive a sick certi cate [8]. Sick certi cation is basic to both work loss and sickness bene ts, but the CSAG [1] found that most people who were o work with back pain did not receive DSS bene t, while most of those on DSS bene ts were not employed. There was <10% overlap between these two groups. There are major interactions between job availability and unemployment, sickness and sick certi cation and sickness and unemployment bene ts. The employment situation, unemployment bene ts and sickness bene ts are all di erent in Jersey. The present gures suggest that the prevalence of work loss attributed to back pain is lower in Jersey. The duration of work loss and rate of recovery are similar. The proportion of people who remain o work for >1 yr may also be lower. The unemployment situation and bene ts entitlement are likely to in uence all of these. The CSAG [1] suggests that physical, psychological and social e ects of unemployment may interact to aggravate pain and disability. In addition, there may

86 BRITISH JOURNAL OF RHEUMATOLOGY VOL. 37 NO. 1 be both social and nancial bene ts to sickness certi- cation and Invalidity Bene t. The latter explanation has recently been o ered as an explanation of the increasing chronic incapacity by the Back Pain in the Workplace report by Fordyce [19]. Where the Jersey data di er from the UK estimates, it is not possible to say whether they are simply more accurate, if there is a regional variation throughout the UK, or if Jersey is di erent because of the e ect of full employment and a less generous wages compensation system than on the mainland. The Jersey data certainly illustrate the lack of accurate information on sick certi cation, work loss and sickness bene ts for back pain on the mainland UK. Planning for health care and social bene ts, and measuring the e ects of any intervention, depend on creating a comprehensive database which integrates sick certi cation, work loss and bene ts paid. ACKNOWLEDGEMENT The authors would like to acknowledge the contribution of Professor Malcolm Jayson, Rheumatic Diseases Centre, University of Manchester, in supporting this study. REFERENCES 1. Clinical Standards Advisory Group. In: Waddell G, ed. Epidemiology review: The epidemiology and cost of back pain. London: HMSO, 1994. 2. Andersson GBJ, Svensson HO, Oden A. The intensity of work recovery in low back pain. Spine 1983;8:880±4. 3. Choler U, Larsson R, Nachemson A, Paterson L-E. Ont y ryggenðfarsok med vardsdprogram for patienter med lumbarla smattillstrand. Stockholm SPRI Report 188/85, 1985. 4. Abenhaim L et al. The social burden of occupational back pain: a study of 3000 cases representative of Quebec. Montreal: Ecole de relations industrielles, University of Montreal, 1985. 5. Spitzer WO et al. Scienti c approach to the assessment and management of activity related spinal disorders. A monograph for clinicians. Report to the Quebec Task Force on spinal disorders. Spine 1987;12(suppl.):S1±59. 6. Hrudey WP 1986 (unpublished data) Workman's Compensation Board of British Columbia. In: Waddell G, ed. A new clinical model for the treatment of low back pain. Spine 1987;12:632±44. 7. Walsh K, Cruddas M, Coggon D. Low back pain in eight areas of Britain. J Epidemiol Community Health 1992;46:227±30. 8. O ce of Population and Census Surveys. Report to the Department of Health by the OPCS. Published as Mason V. The prevalence of back pain in Great Britain. London: HMSO, 1993. 9. States of Jersey, Department of Social Security. Abstract of statistics 94/95. Jersey: States Printers, 1995. 10. Hadler N, Carey TS, Garrett J. The in uence of indemni cation by workers compensation insurance on recovery from acute backache. Spine 1995;20:2710±5. 11. Frank JW, Booker A-S, DeMaio SE, Kerr MA, Maetzel A, Shannon HS et al. Disability resulting from occupational low back pain part I: What do we know about primary prevention? A review of the scienti c evidence on prevention after disability begins. Spine 1996;21:2918±29. 12. Anderson JAD. Epidemiological aspects of back pain. J Social Occup Med 1986;36:90±4. 13. Abenhaim L, Suissa S, Rossignol M. Risk of recurrence of occupational back pain over three years follow-up. Br J Ind Med 1988;45:829±33. 14. Rossignol M, Suissa S, Abenhaim L. The evolution of compensated occupational spinal injuries: A three year follow up study. Spine 1992;17:1043±7. 15. Nachemson A. Ont y ryggen. Orsaker, diagnostic och behandling. Sweden: The Swedish Council of Technology Assessment in Health Care, Stockholm, 1991. 16. Van Doorn JWC. Low back disability among selfemployed dentists, veterinarians, physicians and physical therapists in the Netherlands. Acta Orthopaed Scand 1995;263(suppl.):66. 17. Von Kor M. Studying the natural history of back pain. Spine 1994;19(suppl.):2041±6. 18. Royal College of General Practitioners. Morbidity statistics from general practice: Fourth national morbidity survey 1991/92. London: HMSO. 19. Fordyce WE. Back pain in the workplace: management of disability in non-speci c low back pain. Seattle: IASP Press, 1995.