Incidence and suspected cause of work-related musculoskeletal disorders, United Kingdom, 1996–2001

Abstract

Background Musculoskeletal conditions are the most common self-reported work-related disease, with high costs incurred from long-term disability. In the United Kingdom, occupational physicians and rheumatologists have been reporting new cases of work-related musculoskeletal disorders to voluntary surveillance schemes since 1996.

Aims To estimate population incidence rates for work-related musculoskeletal disorders reported by rheumatologists and occupational physicians by occupation and industry, in relation to tasks and movements suspected as causal.

Methods Estimated average annual incidence rates were calculated for nine main job categories and eight industrial groups; Labour Force Survey figures were used as the denominator for rheumatologists, and a special survey for the occupational physicians. These were then related to tasks and movements reported as causal.

Results Between October 1997 and the end of 2001, an estimated 2599 new cases/year were reported by rheumatologists, and from January 1996, 5278 cases/year by occupational physicians. Average annual rates overall were 94 per million for rheumatologists and 1643 per million for occupational physicians (a 17-fold difference). Jobs at highest risk for the upper limb were primarily clerical, craft-related and machine work. Tasks associated with upper limb disorders and with neck and back problems were predominantly keyboard work and heavy lifting, and in craft-related occupations with gripping or holding tools.

Conclusions Jobs at risk and the associate tasks were identified which should assist prevention, but the extent to which these factors were causal or aggravating previous injury requires further study. The much higher rates reported by occupational physicians reflect, in part, the type of industries they served.

Introduction

A clinically based voluntary reporting scheme for occupational disease was started in the United Kingdom in 1989, first for respiratory illnesses [1], and then in turn for dermatoses [2], infectious disease [3], audiological disorders [4], musculoskeletal problems [5], and mental ill-health [6]. These six schemes, together with one for occupational physicians for all types of work-related illness [7], were brought together under the umbrella of Occupational Disease Intelligence Network (ODIN) in 1998, coordinated from the Centre for Occupational and Environmental Health at the University of Manchester. Numerous reports have been published on these schemes over the years but, when ODIN was superseded by The Health and Occupation Reporting network in 2002, it was considered useful to summarize the main information provided by ODIN; this paper has this objective for the musculoskeletal group. An initial report published in 2001 [5] described the evolution and methods of the scheme, which became known as Musculoskeletal Occupational Surveillance Scheme (MOSS), launched in late 1997, with the full support of the British Society of Rheumatology. That report dealt only with some 8000 new cases reported by rheumatologists in the first 3 years of the scheme, and excluded cases reported by occupational physicians. Of the total, two-thirds related to injury to the upper limb, the remainder about equally to the lumbar spine, shoulder and cervical spine. The current analysis will cover all cases reported 1997–2001 by rheumatologists and 1996–2001 by occupational physicians, and will in particular examine incidence rates by occupation and industry. It will also examine the association between disorders reported by rheumatologists and those physical risk factors (tasks and movements) thought to have been responsible [8].

Methods

Some 330 participating consultant rheumatologists (∼80% of the Society's membership) were enrolled in MOSS in 1997. Initially, these physicians were allocated at random to one of 3 months, October–December 1997. From January 1998, the scheme continued with rheumatologists randomly allocated to 1 month during each year and asked to report all new cases of work-related musculoskeletal disorders seen during the assigned month [5]. Occupational physicians began systematically to report all kinds of work-related ill-health, including work-related musculoskeletal disorders in 1996. Initially ∼800 occupational physicians agreed to take part in the surveillance scheme (the Occupational Physicians Reporting Activity—OPRA). This amounted to ∼75% of occupational physicians who were in active practice in the United Kingdom and who were on the Specialist Register [7]. Between 1996 and 2001, participating occupational physicians had been reporting for one randomly allocated month in each calendar year. The estimated number of cases that would have been reported within each 12 months was calculated by multiplying the number of cases per month by 12 (or by 3 for MOSS reporters in 1997). The estimated annual average numbers have been used throughout this analysis. Cases reported to OPRA by Health & Safety Executive medical inspectors were excluded. In both schemes, physicians were asked to report cases that they considered caused or made substantially worse by work. A pre-existing disease in which work exposure made a substantial difference in severity could also be included. The decision on work-relatedness was based essentially on whether the disease would have occurred in the absence of occupational factors.

The reported occupation is coded to three digits and industry to two digits using the Standard Occupational Classification and the Standard Industrial Classification schemes developed by the Office of Population Censuses and Surveys and the Central Statistical Office (now jointly the Office for National Statistics) [9,10]. Denominators for the reports from rheumatologists were obtained from the Labour Force Survey [11], which estimates UK employment figures for occupation and industry by age, sex and region. Employment data from 1999 were used in calculating the rates presented here. For the purpose of this report, distributions by occupation are presented in nine main job categories and by industry in the eight main groups used in analyses of cases reported by occupational physicians [12]. However, as only about 12% of the working population were served by the participating occupational physicians, results of a special survey conducted in 2001 were used as the denominator for the latter [13].

Coding of risk factor

Between October 1997 and December 1999, 667 new cases of musculoskeletal disease were reported by >300 consultant rheumatologists in the United Kingdom, together with a short description of the tasks and activities they considered to have been causal [8]. Almost all these descriptions were related to exposures of physical risk factors. By summarizing physicians' descriptions, a coding scheme of physical risk factors was developed comprising 16 categories of task codes and another 16 categories of movement codes. The reliability of this scheme has been discussed elsewhere [8] but briefly, four reviewers coded the work activities independently for 576 cases, in which a specific diagnosis had been attributed to repeated exposure. The fourth rater coded the cases twice. With the use of a single summary kappa statistic and a matrix of kappa coefficients [14], both inter-rater reliability and intra-rater reliability were assessed. The overall inter-rater agreement on the task (κ = 0.73) and movement (κ = 0.79) was good. The intra-rater agreement was somewhat better than the inter-rater agreement on both dimensions. The results suggest that the coding scheme was, on the whole, reliable for classifying the physical risk factors reported, and coding of rheumatologists reports was continued to December 2001.

Confidence intervals

Exact 95% confidence intervals (CIs) were calculated for incidence rates taking into account the number of reported cases (numerator) and the number of employed persons in the denominator. The number of reported cases was assumed to be Poisson distributed.

Ethical approval was considered not to be required as physician reports were anonymous. This position had later been confirmed by the North West Multi-centre Research Ethics Committee for the continuation of the data collection.

Results

The estimated annual number of cases reported by rheumatologists and occupational physicians, together with rates per million employees at risk, are shown in Table 1. The overall rates, based on occupational physician reports (annual average rate/million = 1643, 95% CI: 1599–1688), were much higher than those reported by rheumatologists (94, 95% CI: 91–98). The latter rate was higher for women (104, 95% CI: 99–110) than for men (84, 95% CI: 79–88), particularly for hand/wrist/arm. The opposite can be seen for cases reported by occupational physicians where men had higher overall rates (1745, 95% CI: 1681–1810) than women (1530, 95% CI: 1469–1592), with a higher rate at all sites except shoulder and neck/thoracic spine and with a nearly three times higher rate of hip/knee disorders.

In Table 2, the same data were analysed in more detail by anatomical site. As noted previously [5], the upper limb was most often affected, followed by neck or back; there were relatively few cases of the lower limb. For cases reported by occupational physicians, a frequent problem was pain of ill-defined pathology, particularly at the hand, wrist, arm or shoulder.

The distribution of average annual rates is examined in Table 3 in nine main categories of occupation at the three main anatomical sites. Similar analyses in eight broad categories of industry are presented in Table 4. Again the rates were all much higher when based on reports from occupational physicians than rheumatologists. Overall, however, it is evident from Table 3 that the jobs at highest risk were similar, whether reported by rheumatologists or by occupational physicians. For upper limb, these were primarily clerical, craft-related and machine work. Within the craft-related category, builders, decorators, fitters, welders and textile machinists were frequently mentioned (data not shown). For neck and back disorders, craft-related and machine work were again prominent, though workers in personal and protective services were also at high risk, together with associated professional workers (mainly nursing staff) in reports of occupational physicians. Craft-related and machine workers were also at risk for lower limb disorders. The overall rates for any musculoskeletal disorder were highest for craft-related workers in each of the schemes (MOSS 173, 95% CI: 159–189; OPRA 4513, 95% CI: 4206–4837).

Industries at high risk (Table 4) were also fairly similar, with disorders at all three anatomical sites being increased in mining and in food and organic product manufacture, and of the upper and lower limbs in utilities and construction. The overall rates for any musculoskeletal disorder were highest for mining and quarrying in both schemes (MOSS 604, 95% CI: 458–775; OPRA 9375, 95% CI: 7876–11077). Frequently reported conditions in mining included hand–arm vibration syndrome (HAVS), mechanical back pain and disorders of hip and knee (data not shown). Employees in metallic and automotive products manufacturing were also at high risk for upper limb disorders. Production workers in car manufacturing, aircraft fitters and welders in shipbuilding were frequently reported jobs of this group. Among reports for those in ‘other industries’, the highest numbers were for workers in public administration and defence and the retail trade in both MOSS and OPRA but in MOSS, where risks for these subgroups could be calculated, the risks/million were below the mean for all sites except for neck/back disorders (38) in public administration and defence.

Information reported by rheumatologists on factors they considered causal is shown for each anatomical region by task in Table 5, and movement in Table 6. Tasks associated with upper limb disorders were predominantly ‘keyboard work’, ‘guiding/holding building tools’ and, to a lesser extent, ‘heavy lifting’; those associated with neck and back disorders were predominantly heavy lifting but also keyboard work. For lower limb problems, coordinated whole body movement was most frequently reported, but also heavy lifting. The associated movements (Table 6) show that upper limb disorders were overwhelmingly associated with ‘fine hand work’ and ‘forceful grip’, neck/back with ‘lifting’ and lower limb with ‘standing and walking’.

The tasks and movements suspected to be causal were studied by occupation and industry. The disorders associated with craft-related occupations were most frequently attributed to guiding or holding tools (tasks) and forceful upper limb grip (movements), whereas the problems experienced by clerical workers were predominantly related to keyboard work (tasks) and fine handwork (movement). Many disorders in personal and protective services, where, for example, care assistants were often reported, were attributed to lifting tasks. Heavy lifting/carrying is a potential hazard in most industries, and the guiding or holding of tools in many. Forceful upper limb work was implicated in most industries but few other movements, except fine handwork and lifting, were mentioned frequently.

Discussion

The results presented in this paper raise two main questions, the first on the very large difference between rates based on the two groups of reporting physicians and the second on the causal interpretation of the analyses of tasks and movements. The close correlation between the pattern of illness from the two sets of rates—although one is some 17 times higher than the other—suggests that both groups of reporters were observing essentially the same types of work-related disease, but that rheumatologists were seeing only the tip of the iceberg. This may well be so, as most musculoskeletal problems do not require referral to a hospital specialist; a worker may simply be treated by a general practitioner. It may also be that, in companies with an occupational physician, early detection and management obviate the need for specialist referral. These hypotheses could be tested to see whether there is any difference in outcome from the various referral routes. Since only about 12% of employees are served by an occupational physician, a comparison of outcomes in those with and without this resource might help to elucidate the question.

Correct interpretation of both incidence and reported cause of work-related musculoskeletal disorders is clearly affected by the inconsistencies or potential bias in the reporting procedure. Cases reported by rheumatologists and even by occupational physicians can only capture a small proportion of the more severe cases in the working population from which they draw their patients, a proportion that may vary from industry to industry: the high rates of occupational disease reported from the mining industry, for example, probably reflect both the rapidly shrinking denominator and the high coverage of work-related illness by the occupational health services. In other industries, particularly those without occupational health provision, many employees with musculoskeletal conditions may not seek medical care; or if seen by a general practitioner, not be referred to a rheumatologist, only 70–80% of whom participate in MOSS. Even so, this should not seriously affect a comparison of risks between industries and occupations, providing that appropriate denominators are used.

Although there have been a number of studies of factors associated with musculoskeletal pain within industry [15–17], no similar analyses have been made, so far as we are aware, of the suspected role of tasks and movements in the causation of new cases of musculoskeletal disorders in the general working population. Psychosocial risk factors, although their roles in the aetiology are still inconclusive, may also contribute to the development of work-related musculoskeletal disorders [18]. As almost all cases reported by physicians were related to physical risk factors and only in very few cases psychosocial factors were also mentioned, this analysis of causes was limited to physical risk factors. The extent to which the factors reported caused the disorder, exacerbated an existing condition or reflected changes in work methods resulting from the disability might well be different if based on reports from rheumatologists or physicians in occupational health. Thus, it is clear that we need comparable data on tasks and movements from the occupational physicians, as their cases would probably have been much closer to the causal event. Taking the analyses in Tables 5–8 at face value, however, we are left with the question of the extent to which the opinion of the reporting physician was largely that of the patient (please note that Tables 7 and 8 are available as Supplementary data at Occupational Medicine Online).

Two recent studies [19,20] of physicians' beliefs and habits in reporting musculoskeletal disorders suggest that they are generally cautious in attributing these to occupational factors. This may lead to underestimation of disease incidence; nevertheless, the findings on task and movement are in line with those from cross-sectional and prospective studies carried out in industry [15–17] and suggest that heavy lifting and the forceful use of hand tools should continue to be priorities for prevention.

Conflicts of interest

None declared.

We are grateful to the Health & Safety Executive (United Kingdom) for providing funding for the ODIN reporting schemes, to the professional bodies (the British Society for Rheumatology and Society of Occupational Medicine) whose support made the schemes possible and to the reporting physicians.

References