Theoretical impact of simulated workplace-based primary prevention of carpal tunnel syndrome in a French region

In lack of controlled intervention studies comparing the effectiveness of workplace-based WI and GI [16, 26], information on AFE could be useful to estimate the theoretical preventive impact of workplace-based primary prevention interventions aiming to reduce exposure to work-related and/or personal risk factors for CTS. The aims of this pilot study were therefore to estimate the number of cases of surgically-treated CTS (CTS) attributable to work in jobs at high risk in the population of working age, and to simulate the impact of workplace-based mono-component WI and multi-component GI preventive primary interventions aiming to reduce the incidence of CTS.

The population included in this surveillance program was made up of residents of the Pays de la Loire region (Loire Valley area, west central France) in the 20–59 age group (914,999 women and 914,957 men), whether they were professionally active or not, in 2009. According to the 2009 census data, the region has 5.7% of the French population, with a diversified socioeconomic structure and high employment rate (70.0% for women and 76.4% for men) [28].

The hospital discharge database of the French National Medical Information Systems Program (PMSI) was analyzed to include all patients aged 20 to 59 years residing in the region and having undergone surgery for CTS (WHO ICD-10 code G 56.0) in 2009.

Due to a lack of information on employment status in the PMSI database, we used data collected by a pilot study conducted among 1500 persons (1053 women and 447 men) having undergone CTS surgery in the three largest hand surgery settings of the region in 2002–2003 (unpublished data). Employment status and jobs at the time of surgery were experimentally registered in the medical files of the hand clinics during the pilot study and were available for 1371 (91%) patients (975 (92.6%) women and 396 (88.6%) men): 1149 (83.8%) were professionally active (784 (80.4%) women and 365 (92.2%) men) and 222 (19.3.8%) were inactive (191 (19.6%) women and 31 (7.8%) men). Occupations were coded using the French version of the Classification of Economic Activities in the European Community (Nace codes) and the French classification of occupations (PCS codes). Jobs were identified by a combination of the occupational category and the industry sector using the 2-digit PCS and 2-digit Nace codes.

In absence of precise data in the literature, we arbitrarily hypothesized that interventions could reduce the incidence of CTS by 10% in high-risk jobs, and simulated three scenarios of workplace-based primary prevention, differing by their main target:

Incidence rates of CTS in the whole population (I _wp-cts ) were computed separately for each gender using the regional 2009 PMSI database and 2009 census data. Using the information from the 2002–2003 pilot study, three indicators were computed. 1) The age-adjusted standardized incidence ratios of CTS (SIR _job-cts ) were calculated for each job with all other jobs as reference. 2) The age-adjusted relative risks of CTS according to job (aRR _job-cts ) were computed using the Mantel-Haenszel method, with the whole sample of subjects included in the study as reference, whether they were employed at the time of diagnosis or not. 3) The contribution of the jobs to the occurrence of CTS was quantified with the age-adjusted attributable fraction of risk in exposed individuals (AFE) which estimates the proportion of surgical CTS attributable to work in the jobs at high risk of CTS [24, 29]: AFE _job-cts  = (aRR _job-cts -1) / aRR _job-cts .

These indicators were computed for each job when (i) more than 15 men or women were employed and (ii) aRR _job-cts was significantly higher than 1. Jobs at high risk of CTS in comparison with the whole population were thus detected and called “high-risk jobs”. Then, specific incidence rates (I _job-cts ) were computed according to high-risk jobs (the numerators were obtained by multiplying ‘I _wp-cts ’ by the SIR of CTS in the considered job, the denominators were the number of persons of the same gender in the job). The total number of CTS (N _job-cts ) in the job considered was computed by multiplying the number of workers employed in this job (N_e-job) by the incidence rate in this job (I _job-cts ):

N _job-cts  = N _e-job x I _job-cts .

The number of WR-CTS (N _job-wr-cts ) was calculated by multiplying the total number of CTS by the AFE in the job considered [29]:

N _job-wr-cts  = N _job-cts x AFE _job-cts(%) .

The preventive efficiency (PE) was estimated as the ratios of CTS hypothetically avoided / total number of CTS (%) in the job considered. A 95% confidence interval was computed only for SIR _job-cts and for aRR _job-cts . For other indicators, a range was calculated using the lower and upper limits of the considered indicator in the calculation formula.

A total of nine jobs were identified as being at high risk of CTS in women (7 jobs) and/or men (4 jobs) accounting for 15% of the region’s workforce (women, 23%; men, 9%) (Table 1). Five jobs were at risk only in women: government and public service personal care workers (e.g., aide-nurses) in the health sector (‘Healthcare jobs’), sales workers and cashiers in the trade and commerce sectors (‘Trade jobs’), personal service workers (e.g., home aides) in the health sector in women (‘Personal services health jobs’), personal service workers (e.g., housekeepers) and cleaners in the services to enterprises sectors (‘Cleaning jobs’) and machine operators and assemblers in the shoe industry sector (‘Shoe industry jobs’).

Two jobs were at risk for both genders: food and related products machine operators in the meat and food industry sector (‘Food industry jobs’) and skilled agricultural workers and laborers in the agricultural sector (‘Agriculture jobs’).

Two jobs were at risk only in men: building craft workers (e.g., painters) in the construction sector (‘Construction jobs’) and drivers and mobile plant operators in the transport sector (‘Transport jobs’).

A total of 1603 [1137–2212] surgical CTS were estimated to have occurred in this subpopulation at risk, accounting for 29% of all cases registered in the region. Gender effect was observed with a greater number of CTS in women than in men (1265 [922–1702] vs. 338 [215–510]), accounting for 32% vs. 21% of all cases, respectively. A total of 906 [450–1522] cases were considered as attributable to work (WR-CTS) accounting for 57% of CTS in high-risk jobs (17% of all cases). Greater numbers of WR-CTS were also observed in women (664 [329–1106] vs 242 [121–416]), but the proportion of WR-CTS in comparison to CTS was lower than in men (53% vs 72%).

Large variations in CTS incidence and AFEs were observed in different jobs (Table 1). The three top jobs according to the number of CTS were ‘Healthcare jobs’, with 381 CTS, followed by ‘Trade jobs’ (288) and ‘Personal service health jobs’ (267). The three top jobs according to WR-CTS were the ‘Food industry jobs’ (195 cases) followed by ‘Healthcare jobs’ (183) and ‘Trade jobs’ (158).

As shown in Table 1, six jobs were characterized by high proportions of WR-CTS (> 60%) and fewer cases of CTS: ‘Agriculture jobs’, ‘Food industry jobs’, ‘Shoe industry jobs’, ‘Construction jobs’ ‘Transport jobs’ and ‘Cleaning jobs’. These six jobs (group 1) employing approx. 98,000 workers were associated with 740 [447–1274] CTS, including 563 [280–1101] WR-CTS (76%).

Three other jobs were characterized by moderate to low proportions of WR-CTS (< 60%) and large numbers of CTS (> 250): ‘Healthcare jobs’, ‘Trade jobs’ and ‘Personal service health jobs’. These jobs (group 2) employing approx.154,000 workers were associated with 936 [696–1290] CTS but only 406 [173–749] WR-CTS (43%).

Greater numbers of CTS were preventable in women than men, in all the jobs and preventive scenarios considered. As shown in Table 2, the number of avoidable CTS varied between the different preventive scenarios and jobs.

Considering the jobs at risk overall (7 in women and 4 in men), the 10%-GI had the highest preventive efficiency, hypothetically preventing 159 [114–223] CTS out of 1603 [1137–2212] (PE =10.0% [5.2–19.4]). The 10%-WI prevented a lower number of cases than the 10%-GI (PE = 5.7% [2.0–13.4]), preventing at most 90 [46–153] cases, only slightly more than the 5%- GI, which avoided 81 [58–111] cases (PE = 5.0% [2.6–9.8]).

Considering the jobs targeted, the 10%-GI (PE = 10%) had maximum impact in the three jobs with the most cases of CTS: ‘Healthcare jobs’, ‘Trade jobs’ and ‘Personal service health jobs’, with 38, 28 and 27 cases prevented, respectively. The 10%-WI had maximum impact in the ‘Food industry jobs’ (20 cases avoided, PE = 8.7%), for which the preventive efficiency almost reached the level of the 10%-GI (23 cases avoided, PE = 10.0%). More generally, the 10%-WI was more efficient for jobs with high proportion of WR-CTS (PE = 7.7% for all the six jobs of group 1) than for jobs with moderate to low proportion of WR-CTS (PE = 4.4% for the three jobs of group 2) due to higher proportions of WR-CTS (76% vs 43%). Compared to the 5%-GI, the preventive efficiency of the 10%-WI was higher or at least equal for all jobs of group 1, but similar for ‘Healthcare jobs’ (PE = 4.8% vs. 5.0%) and ‘Trade jobs’ (PE = 5.5% vs. 5.1%), and even lower for ‘Personal services jobs’ (PE = 2.6% vs. 4.9%).

Surveillance data used for the computation of potentially preventable CTS included data from one of the largest and most complete surveillance programs for CTS, covering an entire region of France [1, 27].

The French PMSI database registering only surgical CTS underestimated cases potentially preventable since CTS requiring only medical treatment (e.g., corticosteroid injection) were not counted. The proportion of CTS requiring surgery is unknown in France. The surveillance of electrophysiologically confirmed CTS in the same region in 2002–2004 showed that about 66% of CTS did not undergo surgery (unpublished data). Analysis of compensation data in the Pays de la Loire region between 2008 and 2014 gave similar estimates: 63% (64% in men and 63% in women) of CTS compensated as occupational disease did not have undergone surgical treatment, without difference between the nine jobs at risk understudy (unpublished data). Surgical treatment is widely preferred to non-surgical or conservative therapies for overtly symptomatic patients, while mild cases are usually not treated, and therefore the surgical CTS included in the present study represented the most severe or most disabling cases of CTS in the regional population [30].

Given that the PMSI database lacked information relating to occupation and no more recent data were available, we used information on employment of patients undergoing surgery for CTS collected in 2002–2003 from the region’s three main hand surgery centers to estimate AFEs of CTS (unpublished data). No exhaustive job exposure data of the working population was available in the Pays de la Loire region, except the job titles collected by the 2009 Census. The use of job titles as surrogates variables for physical work exposure may result in significant exposure misclassification [31], but our estimates were in line with AFEs calculated in the only equivalent study comparing the incidence of surgical CTS in the Montreal region in 1995 [32]. Data from the pilot study described above revealed that the mean interval between the onset of the hand symptoms and the date of surgery was 3 to 4 years [1]. Therefore, AFE estimates probably reflected the working conditions in the late 90’s or early 00’s, and this may introduce bias in the calculation of the potential preventive efficiency of the preventive scenarios. Nevertheless, the SUMER French survey of working conditions conducted in 2003 and 2010 did not showed major changes of physical exposure in France, and it is unlikely that exposure to the main work-related risk factors for CTS drastically vary in the Pays de la Loire region [33].

Given that no more recent data were available that contained all needed variables, we analyzed surgical CTS registered in 2009 in the PMSI database and the 2009 census data to compute potentially avoidable surgical CTS according to different preventive scenarios. The incidence of surgical CTS was slightly higher in the Pays de la Loire region than in the whole France, but the region was characterized by a high employment rate. The incidence of surgical CTS had slightly decreased in the region since 2003 in men and above all in women, but we have no information indicating changes in surgeons’ practice and modification of the choice of surgical rather than conservative treatment of CTS in the region. French governmental action plans for improvement of occupational health were implemented in 2005–2009, but no clear conclusion can be drawn on the possible relationships between improved working conditions and decreasing trends in the incidence of CTS [1]. Finally, it is unlikely that higher decreasing incidence trends in women introduced major bias in the calculations of attributable fraction and potential preventive effectiveness, since our data were stratified according to gender.

The computation of AFEs took into consideration age and gender, which are the main unmodifiable personal risk factors for CTS, but not the possible joint effects of medical risk factors (e.g., obesity, rheumatoid arthritis and diabetes). Diabetes mellitus requiring pharmacological treatment (3.8% vs 4.2%) and obesity (13.3% vs 14.5%) were slightly less prevalent in the Pays de la Loire than in the whole France in 2009 [34, 35].

Certain very high-risk jobs involving few workers may not have been identified in the present study due to the lack of statistical power, and this might have led to underestimating the impact of work-centered prevention.

The computation of the preventable cases of CTS supposed several hypotheses [29], namely (i) causal relationships between the occurrence of CTS and work exposure and (ii) substantial impact of interventions reducing exposure to risk factors at the workplace [29]. Numerous biomechanical and epidemiological evidences argue in favor of causal relationships between biomechanical exposure at work and CTS [2, 8‐10], even if the relative proportion of cases attributable to work is still under debate [2]. However, although decreasing exposure to work-related and/or personal risk factors was assumed to reduce the incidence of CTS by 10% in our study, evidence of such impact for primary prevention of CTS remains sparse, regardless of whether interventions will focus on personal factors [12, 13] or work-related factors [15‐19, 22].

Information remains sparse on the impact of health promotion (such as weight loss) and/or specific exercises to prevent or reduce the incidence of CTS in the general working-age population [12, 13, 23]. We did not evaluate the hypothetical preventive efficiency of interventions that focus only on personal risk factors, expecting that changes in “personal risk factors” would be an essential component of multifaceted workplace interventions (10%-GI scenarios) [15]. Combining interventions on personal and work-related factors was assumed to have a higher impact than interventions targeting only on personal or work-related factors [15, 17]. To the best of our knowledge, we still lack data on the impact of multiple global interventions to estimate their joint effects. We have therefore adopted a simplistic additive model. We focused prevention only at the workplace level, although interventions to prevent CTS at the population level (e.g., media campaign of health promotion and prevention) might worth investigating.

Most preventive interventions included in systematic reviews involve non-specific symptoms and focus on certain industry sectors (e.g., construction, healthcare) or occupational groups (e.g., office workers). Their effectiveness to decrease the incidence of CTS is still under debate [15‐17, 22]. This hypothetical impact study conducted on surgical CTS at a regional population level showed that the potential preventive efficiency of workplace-based primary prevention of CTS will depend on (i) the theoretical efficiency of intervention, (ii) the targeting of jobs at the highest risk of CTS and (iii) the size of the population targeted. In practice, such interventions should be tailored by the professionals involved in the prevention and promotion of health at work.

Our study showed that the primary prevention of CTS had a greater impact on the number of preventable surgical CTS in women than men, regardless the jobs and scenarios of prevention considered. This was explained by the greater incidence of CTS in women leading to greater numbers of CTS [1], and concerned primarily PR-CTS rather than WR-CTS. Conversely, higher proportions of WR-CTS in men explained the slightly higher preventive efficiency of the 10%-WI in men. For ethical and legal reasons, workplace-based primary prevention should involve all workers exposed to occupational risks of CTS, regardless of gender.

Workplace-based interventions focusing on work-related risk factors had a greater impact on high-risk jobs and prevention efforts should focus on these jobs first. As expected, multiple global workplace-based interventions (10%-GI) were the most efficient strategy assuming additive effects on PR-CTS and WR-CTS. This is in line with systematic reviews reporting promising evidence for multifaceted interventions to prevent non-specific musculoskeletal disorders [15‐17, 23]. However, we still lack of guidelines to implement such global multi-component interventions in real prevention practices [20, 23]. The highest preventive impact in our study concerned the two largest occupational groups at moderate risk of CTS (nursing aides and cashiers) and an occupational group at very high risk of CTS (operators in the meat and food industry). Focusing interventions on these three occupational groups would have the greatest impact on avoiding the majority of the preventable cases in the region.