The results of this population-based study suggest that there is an important relationship between occupation and epicondylitis. After adjustment for age, gender and psychological distress, lateral and medial epicondylitis were highly significantly associated with repetitive bending/straightening of the elbow for greater than one hour/day (OR 2.5, 95%CI 1.2-5.3 and OR 5.1, 95%CI 1.8-14.3 respectively). This study also allows an estimation of the impact of epicondylitis on the workplace such that 5% of those diagnosed with epicondylitis reported having taken sickness absence in consequence and the median estimated duration of sickness absence was 29 days out of the last 12 months.
The demonstration of an association between physical workplace factors and epicondylitis is not new having been shown in several manually intensive occupations, such as butchers and meat cutters [3
] construction workers [16
] and automobile assembly workers [17
]. However, workplace based studies can be subject to bias, not least the healthy worker effect. The strength of the current study is that it includes information from more than 6000 working-aged adults across the age range 25-64 years, in or out of work. The outcomes of both medial and lateral epicondylitis have been verified by a clinical examination algorithm which has been shown to be reliable and valid and, if anything, to be specific rather than sensitive. This suggests that the cases of epicondylitis diagnosed by the examination algorithm are highly unlikely to be overturned by clinicians. Uniquely, this study separates lateral from medial epicondylitis and demonstrates that the relationship between manual occupations and epicondylitis holds true in both types of epicondylitis.
In the past, occupational epidemiological studies have focussed on physical workplace exposures and taken little account of psychosocial factors. Our finding of strong associations (OR 3.9 and 4.9) of lateral and medial epicondylitis with psychological distress are of course cross-sectional and therefore cannot be interpreted as cause or effect. However, these findings together with those of another recent small study, which showed that sufferers of lateral epicondylitis were significantly more anxious and depressed than controls [18
], suggest that prevention and treatment of epicondylitis should focus not only on physical and ergonomic measures but also that psychological factors and the Karasek [19
] model (demand/control/support) of psychosocial workplace factors need to be considered within any intervention.
The findings of this study need to be considered alongside several limitations. An important consideration when interpreting our observations is the potential for bias from incomplete participation of subjects who were eligible for study. The 62% response rate and 65% response rate at each of the sampling stages were comparable to that in other recent UK population studies. Furthermore, subjects who attended for examination had a similar symptom profile and demography to that of those invited who did not attend and in each case, closely resembled the demography of the UK population. Our sampling frame was the register of two large general practice surgeries purposively sampled so as to represent two widely different socio-economic profiles. In the UK, GP registers are recognised to be 98-99% complete for all the population and as such, are considered highly representative of the local population of any area.
The area of assessment of mechanical (workplace) exposure is fraught with controversy [20
]. For a survey on this scale, we opted to use self-defined exposure according to a carefully validated list of exposures ranging from working with the neck bent/twisted; working with arms raised above shoulder height; through to keyboard use. However it is widely believed that self-reported exposure may result in relative over estimates of exposure [20
]. This might clearly apply selectively in individuals who believe themselves to have been harmed by their workplace exposure. However, in this study which recorded details of pain at multiple sites in the neck and upper limb and included questions about exposure to different anatomical sites, it seems unlikely that such a selective bias would have applied.
In conclusion, we found that epicondylitis affects approximately 1% of working-aged adults at any point in time. We have produced one of the first ever population estimates of the occurrence of medial epicondylitis and find it to be only marginally less prevalent than lateral epicondylitis. Both medial and lateral epicondylitis were strongly cross-sectionally associated with psychological distress and independently with exposure to bending/straightening the elbow > 1 hour/day. Our findings support those of others in suggesting a role for physical workplace factors in the aetiology of epicondylitis and add new data on the importance of epicondylitis as a cause of sickness absence.