Primary Care Sciences Research Centre, Keele University, Staffordshire, UK.
Correspondence to: J. Sim, Primary Care Sciences Research Centre, Keele University, Staffordshire ST5 5BG, UK. E-mail: j.sim{at}keele.ac.uk
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Abstract |
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Methods. A questionnaire was mailed to an age-stratified random sample of 9596 adults. All subjects were asked about hand paraesthesia in the past 4 weeks. Information was obtained on respondents' main job (the job held for the longest time), whether this job involved any of six neck or upper limb activities on most or all days of the working week, and questions on the psychosocial aspects of the work environment. The questionnaire also asked about NULP according to a preshaded manikin.
Results. A total of 5133 people replied to the survey (adjusted response 53.5%). Of these, 1592 reported abnormal feelings in the hands (prevalence of 31.9%). Prolonged gripping, prolonged bending of the neck forwards, working with arms at/above shoulder height, low job control, many changes in tasks and low job support were independently associated with hand paraesthesia. Among responders also reporting NULP, working with arms at/above shoulder height and many changes in tasks were independently associated with hand paraesthesia; prolonged gripping was linked to hand paraesthesia in the absence of NULP.
Conclusions. Hand paraesthesia is associated with physical and psychosocial workplace factors, although different work-related factors were associated with hand paraesthesia according to the concurrent presence of NULP, suggesting that these symptoms may not always be mediated in the same way.
KEY WORDS: Hand, Occupation, Paraesthesia, Psychosocial factors, Questionnaire, Upper limb
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Introduction |
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There have been few population studies exploring the association of occupational factors with hand paraesthesia, in contrast to the growing body of literature regarding work-related risk factors for carpal tunnel syndrome [1517]. In particular, little is known about the influence of psychosocial factors of the work environment, e.g. the perception of being able to control the way you work in your job, on hand paraesthesia. A population study of hand paraesthesia allows us to identify potential work-related risk factors for this problem in the community, and does not suffer from the bias associated with sampling from a workplace setting. By investigating the work-related physical and psychosocial factors associated with hand paraesthesia in the presence and absence of neck and upper limb pain (NULP), we can also gain insight into the possibility that symptoms of numbness and tingling in the hand may be mediated differently, depending on the occupational factors involved.
The primary aim of this study was to investigate the association between hand paraesthesia and (i) specific work activities involving the neck and upper limbs, and (ii) psychosocial factors of the work environment, in a general adult population. A secondary aim was to determine the independent work-related factors associated with hand paraesthesia alone, and those associated with symptoms in the presence of NULP, in this population.
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Methods |
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Approximately 98% of the UK population are registered with a general practitioner (GP) [18]; thus the GP register is regarded as being representative of the general population in the UK [19]. The study population was adults aged 1875 yr on the general practice database of the North Staffordshire District Health Authority, UK. From this population, we randomly sampled 10 000 adults in equal numbers from four age groups: 1844, 4554, 5564, 6575 yr. This sample size would provide at least 99% power to detect a 5% difference in prevalence of hand paraesthesia at a two-tailed 5% significance level.
Following initial mailing of the questionnaire, a reminder postcard was sent to all non-responders 2 weeks later. We sent all remaining non-responders another questionnaire after a further 2 weeks.
Questionnaire
Outcome measures
The main outcome measure was the presence of hand paraesthesia. All respondents were asked to answer this question: In the past 4 weeks, have you had any abnormal feelings in your hands (for example tingling, pins and needles, loss of sensation)? Those responding positively to this question were asked to report in which hand(s) the symptoms occurred (both; right; left), and the time since initial onset of abnormal feelings (less than 4 weeks ago; one to 6 months ago; more than 6 months but less than 12 months ago; 15 yr ago; more than 5 yr ago).
Our study design did not permit us to classify respondents according to clinical criteria [5], and so we did not collect information on the precise distribution of paraesthesia in the hand.
Measurement of exposure
Participants were asked to complete a grid question, which asked for details of up to five most recent jobs (job title, area of work, start date, end date) held for at least 12 months. Within the grid question, respondents were asked to indicate whether or not their jobs involved any of six work activities on most or all days of the working week. The activities were chosen on the basis that they involved repetitive movements or sustained postures of the neck and upper limbs; similar descriptions of work activities have been used in other studies [2022]. The work activities were:
From the jobs recorded by the respondent, the one that had been held for the longest time was designated as the respondent's main job. We only identified a main job for those respondents who provided complete information in the grid question; those with two or more main jobs held for the same length of time were not included. Information on the psychosocial aspects of respondents' main job was collected using questions based on the Karasek model [23], similar to those of other studies [21, 24]. Scoring was based on a five-point adverbial scale (none of the time to all of the time). The questions were:
Other questions
Respondents were asked to answer a preshaded NULP manikin question [25], questions about spare time activities involving repeated movements of arms or hands, and demographics. The Townsend Deprivation Index was used as a measure of multiple deprivation [26]. The deprivation score is calculated from four 1991 Census variables (unemployment, overcrowding, non-car ownership and non-home ownership); high scores indicate high deprivation.
Statistical analysis
For the main outcome, we calculated the crude associations between the 1-month prevalence of hand paraesthesia and (i) specific work activities and (ii) psychosocial factors, in relation to the respondents' main job. Since data collection was cross-sectional, we used odds ratios (ORs) with 95% confidence intervals (CIs), rather than risk ratios, to estimate these associations. Associations were also tested using the 2 test. Multivariable analysis was carried out using logistic regression to investigate independent associations with hand paraesthesia. Two such analyses were carried out: (i) a partial model, in which the covariates were age, sex and Townsend category; and (ii) a full model, in which the covariates were all sociodemographic variables, work activities and psychosocial factors. The full regression analysis was carried out for all responders and also stratified according to the presence and absence of NULP.
Bias in the main associations was assessed in four ways. First, non-response bias was investigated by looking at the response to the three questionnaire mailings (this was done on the assumption that the factors underlying late response are similar to those underlying non-response, and that late responders are therefore most representative of non-responders); a similar strategy has been used in a previous study of neck pain [27]. Second, recall (information) bias was addressed by confining the analysis to responders who were still working and whose current job was their main job. Third, we assessed causeeffect by restricting the analysis to responders whose hand paraesthesia did not predate their main job. Lastly, we analysed the data to account for the possible confounding factor of leisure activities involving repetitive arm or hand movements.
Statistical significance was set at P 0.05 (two-tailed). Statistical analysis and random sampling were carried out using SPSS version 11.5 (2002; SPSS, Chicago, IL, USA).
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Results |
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Multivariable analysis of predictors of hand paraesthesia
The association of work activities and psychosocial factors with hand paraesthesia was independent of age, sex and Townsend category (Table 3). Prolonged gripping was still associated with twice the likelihood of having symptoms. All work tasks and psychosocial factors were significantly correlated, suggesting that they commonly occur together in the work place. Results of the full multivariable model investigating the independent effects of each of the work activities, psychosocial factors and sociodemographic characteristics are also shown in Table 3. The work activities independently associated with hand paraesthesia were prolonged gripping (P = 0.001), prolonged bending of the neck (P = 0.001) and working with arms at/above shoulder height (P = 0.015). Insufficient job control (P = 0.002) and management support (P = 0.003), and many changes in tasks (P = 0.002) were each independently associated with hand paraesthesia.
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Non-responders were more likely to be male and younger than responders [25]. However, the association between physical and psychosocial workplace factors and hand paraesthesia was similar across the three waves of mailing response. For example, in relation to repeated lifting of heavy objects the associations were OR = 1.74, 1.91 and 1.61 for wave responses 1, 2 and 3, respectively.
Recall bias and causeeffect
In order to address recall bias, we restricted the full regression analysis to responders who were still working and whose current job was their main job; there were significant, independent associations with gripping (OR = 1.51), bending neck (OR = 1.41), raised arms (OR = 1.48), change in tasks (OR = 1.54) and job support (OR = 1.49). To address causeeffect, we further restricted the above analysis to those with hand abnormalities for less than 12 months, revealing similar patterns of associations: gripping (OR = 1.30), bending neck (OR = 1.44), raised arms (OR = 1.28), change in tasks (OR = 1.46) and job support (OR = 1.13). These associations were not statistically significant due to the smaller size of this subgroup.
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Discussion |
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According to our findings, individuals are at least risk of hand paraesthesia if: (i) aged 1844 yr; (ii) not exposed to physical factors (particularly repeated lifting of heavy objects, prolonged gripping of objects, prolonged bending of the neck and working with arms at or above shoulder height); and (iii) not perceiving themselves to have a poor psychosocial work environment (particularly in relation to little job control, many changes in tasks and little supervisor support). In our data, on the basis of the UK Standard Occupational Classification [30], managerial/professional occupations (e.g. production, works and maintenance managers, teachers, chartered accountants and lawyers) have a high probability of fitting this work description. A young secretary who commonly does repeated finger movements as part of the job has no additional risk providing that the job does not entail those work activities or psychosocial factors that are significantly predictive of hand paraesthesia. In comparison, an older secretary (aged 5564 yr) is 1.65 times more likely to have hand paraesthesia. Furthermore, a person aged 5564 yr who has an occupation that involves prolonged gripping of objects, prolonged bending of the neck and perceives little job control (such as is commonly the case, according to our data, for a number of skilled trade workers, e.g. glass ceramic makers, decorators and finishers) has four times (i.e. 1.65 x 1.38 x 1.35 x 1.30) the estimated likelihood of hand paraesthesia compared with an adult aged 1844 yr with no physical/psychosocial risks, and nearly two-and-a-half times (i.e. 1.38 x 1.35 x 1.30) the estimated likelihood compared with an adult of the same age with no such risk factors.
The association of hand paraesthesia with work-related factors was influenced by the concurrent presence or absence of NULP, and provides support for a distinction in the mediation of symptoms of hand paraesthesia. In responders reporting NULP, working with arms at or above shoulder height was associated with symptoms of numbness and tingling; it is possible that this sustained posture may result in hand symptoms mediated by pathologies proximal to the hand, involving pain in the neck, shoulder or arm. Perception of many changes in tasks in the work environment was also linked with more hand symptoms in those with concurrent NULP. This might appear surprising, since work that is perceived to involve many changes in tasks, or to have variability, is likely to be ergonomically advantageous compared with monotonous work [24]. However, multiple changes in tasks, with consequent disruption of the individual's pattern of work, could also be perceived to exert an increased psychological demand on workers. Indeed, a review of several studies has shown that high job demands appear to be associated with upper limb problems [31]. The association of many changes in tasks with pain in the neck or the proximal part of the upper limb may, again, result in paraesthesia in the hand via, for example, nerve impingement or entrapment in the neck or arm.
By contrast, in those with no NULP, only prolonged gripping was associated with hand paraesthesia; this is not unexpected, since gripping involves sustained forceful use of the hand and finger joints, and not the nerve root at the neck level. Furthermore, in these cases, there was no significant association between hand paraesthesia and an adverse psychosocial working environment. This supports the suggestion of a purely mechanical problem localized to the hand.
Cases of hand paraesthesia may be transient. For example, in a study of workers pruning vines, 90% of cases began during the pruning period and ended after the season [32], suggesting that a relatively short exposure allowed the hand to recover. The authors concluded that the development of hand paraesthesia in vineyard workers was different from that observed in industrial workers since most recovered without medical treatment after the pruning season. In our general population, we found that in over 60% of cases, the symptoms started at least 12 months ago, indicating chronic conditions that were not of recent onset.
This study is susceptible to a number of possible biases. For example, we attempted to counter the healthy worker effect (workers who perceive they have work-related conditions leave their job, so only the healthy workers remain) by designing our study to include both current and past workers, sampled from a general population. Recall bias may occur if those who recall specific neck and upper limb activities at work, or perceive an adverse psychosocial work environment, are more likely to recall hand paraesthesia subsequently, leading to an overestimate of the association. Efforts to reduce this effect were made in two ways. First, we gathered all symptom information before that related to potential risk factors in the questionnaire. Second, we looked at the association between hand paraesthesia and work-related risk factors in responders whose main job was their current job; associations were still evident in this population subgroup. Although the direction of cause and effect cannot be determined from cross-sectional data, when we restricted the analysis to those respondents whose hand paraesthesia did not predate their main job, a significant association remained. The stability of the prevalence rates and statistical associations across the waves of mailing response also makes it reasonable to assume that our estimates are representative.
We realize that in this study there may have been alternative, non-occupational causes of hand paraesthesia for which we have not been able to account and which therefore may limit our conclusions. For example, it is possible that underlying conditions like diabetes, alcohol abuse, disorders of the central nervous system or rheumatoid arthritis could account for some cases of paraesthesia [2, 14], although there is no reason to suspect that such conditions act as confounders of any of the occupational associations reported. Leisure activities involving repetitive arm or hand movements could have also influenced our results; however, the pattern of associations persisted in our study after controlling for this potential confounder.
Although we cannot speculate on the associations of specific neck and upper limb disorders with occupational factors from our data, we have attempted to look at the reporting of distinct symptomshand paraesthesia and NULPand their interaction. Indeed, it has been proposed recently that an objective and descriptive approach to the grouping of symptoms may further the progress of classification of neck and upper limb disorders [8]. This population study provides evidence that the physical and psychosocial workplace factors associated with hand paraesthesia differ according to the concurrent presence of NULP. These results suggest that (i) symptoms of numbness and tingling may not always be mediated in the same way, and (ii) the nature, and possibly combination, of the occupational factors involved in a job may result in different patterns of hand paraesthesia and NULP. This information has potential use for assessing the risks involved in different neck and upper limb work activities, in order to develop preventative workplace strategies.
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Acknowledgments |
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The authors have declared no conflicts of interest.
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References |
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