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Upper limb work-related musculoskeletal disorders (UL-WMSDs) are the most common after lower back pain and have been included in the list of occupational diseases by the International Labor Organization (ILO). In recent years, WMSDs have been widespread among the Chinese occupational populations, leading to job replacement and long-term sick leave. It is difficult to add UL-WMSDs to China’s List of Legal Occupational Diseases because data on the occurrence of UL-WMSDs and their relationship with specific works are lacking. Therefore, this study included a large sample to conduct an epidemiological investigation and research into the occurrence of UL-WMSDs in key industry populations in different regions of China. The results showed the standardized incidence of UL-WMSDs in crucial industries or occupational groups in China is 22.5%. The risk of UL-WMSDs changes with the length of service, type of work, work posture, work organization, and other factors. The results may provide data support for recommending the prevention and control of such diseases and their inclusion in China’s List of Legal Occupational Diseases.
The research data included in this study were obtained from seven China regions (North, East, Central, South, Southwest, Northwest, and Northeast China), and included data from 21 industries or operations, such as automobile manufacturing, furniture manufacturing, and the footwear industry. In this study, we used a stratified cluster sampling method; the workers on duty were the study participants. The inclusion criteria for subjects were employed for more than a year. The exclusion criteria were as follows: patients with congenital spinal deformity and those with non-WMSDs due to trauma, infectious diseases, and malignant tumors. This study has been reviewed by the Medical Ethical Review Committee of the Occupational Health and Poison Control at the Chinese Center for Disease Control and Prevention.
To conduct this survey, experts used the Ergonomic Evaluation and Analysis System of WMSDs provided by the Department of Occupational Protection and Ergonomics of the National Institute of Occupational Health and Poison Control of the Chinese Center for Disease Control and Prevention was used to investigate the incidence of WMSDs and its influencing factors in participants from key industries or occupational groups in different regions of China. The system includes four other sub-systems: an electronic ergonomics survey and evaluation tool for remote operation site, a real-time data monitoring system, a data transmission network, and a background data terminal. This study's survey tool (the Chinese electronic version of the musculoskeletal disorders questionnaire) was one of the built-in questionnaires in the system, namely. This electronic questionnaire system was based on the Nordic Musculoskeletal Disorders Questionnaire (NMQ) and Dutch Musculoskeletal Questionnaire (DMQ) (1-2). After appropriate modification, it was shown to have good reliability and validity, and can be used for Chinese occupational populations. After the survey data were exported from the backend database, they were statistically processed using SPSS 20.0 statistical software (version 20.0, SPSS Inc, Chicago, IL, USA). Based on China’s population composition data, the standardized incidence rate of upper-limb musculoskeletal disorders was calculated using the direct method. The single-factor analysis of WMSDs adopts the χ2 test method, multivariate analysis was performed using an unconditional logistic regression model.
Till date, 72,029 valid questionnaires have been received. Table 1 shows that the standardized rate of UL-WMSDs in key industries or occupational groups in China was 22.5%, and the standardized rates differed significantly between different industries (P<0.05). The standardized incidence rates (ranked from the highest to the lowest) in the top five industries were animal husbandry (40.8%), biopharmaceutical product manufacturing (36.8%), civil aviation (32.5%), healthcare industry (31.5%), ferrous metal smelting and rolling processing industry (29.9%).
Industry/working group Number Upper-limb musculoskeletal disorders n pi (%) p' (%) Total 72,029 18,193 25.3 22.5 Animal husbandry 246 62 25.2 40.8 Biopharmaceutical manufacturing 285 115 40.4 36.8 Civil aviation 1,356 420 31.0 32.5 Healthcare industry 6,961 2,520 36.2 31.5 Ferrous metal smelting and rolling 1,921 444 23.1 29.9 Cement, lime, and gypsum manufacturing 193 22 11.4 25.4 Nonferrous metal smelting and rolling processing industry 2,364 696 29.4 25.0 Computer, communication industry, and other electronic equipment manufacturing 8,910 2,229 25.0 23.3 Automobile manufacturing 21,598 5,730 26.5 22.0 Toy manufacturing 333 141 42.3 20.4 Automobile repair and maintenance 802 145 18.1 19.2 Footwear industry 7,123 1,844 25.9 18.2 Coal mining, and washing 3,461 804 23.2 17.3 Shipping and related device manufacturing 3,493 886 25.4 16.7 Railway transportation equipment manufacturing 965 186 19.3 16.7 Agriculture 243 52 21.4 16.5 Road transportation 1,317 228 17.3 16.1 Construction 1,476 206 14.0 15.2 Power, heat, gas, water production, and supply 591 82 13.9 13.5 Furniture manufacturing 8,241 1,371 16.6 12.0 Petrochemical industry 150 10 6.7 4.0 Chi-square test 1203.6 P value 0 Note: pi: actual age-specific prevalence rate, p': standardized prevalence rate. Table 1. Prevalence of upper-limb musculoskeletal disorders in key industries or occupational groups in China, 2018–2021 (n=72,029).
The influencing factors of UL-WMSDs were divided into individual, work type, and work organization factors. The univariate analysis results (Table 2) show that gender, age, length of service, educational level, smoking status, sports, and other individual-level factors were significantly associated with the occurrence of UL-WMSDs (P<0.05). The incidence of UL-WMSDs in women was higher than that in men. The risk of UL-WMSDs increased with the length of service and educational level. The risk of UL-WMSDs in smoking and physical exercise groups was significantly lower than in the control group. Maintaining the same posture at a high frequency, always making the same movement with the trunk, always pinching/grasping some objects/tools, wrist is in a bent posture for a prolonged time, and other factors such as work type correlated significantly with the occurrence of UL-WMSDs (P<0.05). Frequent overtime work, staff shortages, and doing the same job nearly every day are positively correlated with the occurrence of UL-WMSDs, and the difference is statistically significant (P<0.05).
Variable Upper-limb musculoskeletal disorders Number of workers Case Percentage (%) OR (95% CI) Individual risk factors Gender Men 49,079 11,050 22.5 1 Women 22,950 7,143 31.1 1.555 (1.502–1.611)* Age (years) <25 7,909 1,858 23.5 1 25– 29,582 7,495 25.3 1.105 (1.043–1.171)* 35– 19,768 5,269 26.7 1.184 (1.114–1.258)* 45– 11,385 2,857 25.1 1.091 (1.020–1.167)* 55– 3,385 714 21.1 0.871 (0.790–0.960)* Length of service (years) <2 19,138 4,143 21.6 1 2– 14,549 3,617 24.9 1.198 (1.138–1.260)* 4– 9,179 2,332 25.4 1.233 (1.163–1.307)* 6– 6,790 1,781 26.2 1.287 (1.207–1.372)* 8– 22,373 6,320 28.2 1.425 (1.362–1.491)* Educational level Junior high school 21,365 4,810 22.5 1 Senior high school 26,632 6,586 24.7 1.131 (1.084–1.180)* University degree 14,365 3,776 26.3 1.227 (1.169–1.289)* Graduate degree 9,667 3,021 31.3 1.564 (1.483–1.651)* Body mass index (BMI) <18.5 6,681 1,725 25.8 1 18.5– 48,323 12,284 25.4 0.979 (0.924–1.038) 25– 17,025 4,184 24.6 0.936 (0.877–0.999) Smoking No 43,743 11,600 26.5 1 Occasionally 13,034 2,800 21.5 0.758 (0.723–0.795)* Frequently 15,252 3,793 24.9 0.917 (0.879–0.957)* Physical exercise No 21,619 5,877 27.2 1 Occasionally 38,073 9,443 24.8 0.883 (0.851–0.918)* Frequently 12,337 2,873 23.3 0.813 (0.772–0.856)* Workplace risk factor Standing often at work No 11,038 2,816 25.5 1 Yes 60,991 15,377 25.2 0.984 (0.940–1.031) Sitting often at work No 30,850 7,792 25.3 1 Yes 41,179 10,401 25.3 1 (0.967–1.035) Squatting or kneeling often at work No 41,776 9,828 23.5 1 Yes 30,253 8,365 27.7 1.242 (1.201–1.285)* Lifting heavy loads (more than 5 kg) No 25,091 5,764 23.0 1 Yes 46,938 12,429 26.5 1.208 (1.165–1.252)* Lifting heavy loads (more than 20 kg) No 38,885 9,189 23.6 1 Yes 33,144 9,004 27.2 1.205 (1.165–1.247)* Exerting great force on the upper limbs or hands No 11,908 2,186 18.4 1 Yes 60,121 16,007 26.6 1.614 (1.535–1.696)* Use of vibration tools at work No 43,855 10,087 23.0 1 Yes 28,174 8,106 28.8 1.352 (1.307–1.399)* Maintaining the same posture at a high frequency No 13,728 1,927 14.0 1 Yes 58,301 16,266 27.9 2.370 (2.251–2.495)* Trunk posture Trunk straight 24,051 4,441 18.5 1 Bending slightly at the trunk 38,398 10,502 27.4 1.662 (1.598–1.729)* Bending heavily at the trunk 9,580 3,250 33.9 2.267 (2.149–2.391)* Always turning around with the trunk No 25,512 5,327 20.9 1 Yes 46,517 12,866 27.7 1.449 (1.397–1.502)* Always bending and twisting with the trunk No 40,670 8,313 20.4 1 Yes 31,359 9,880 31.5 1.790 (1.731–1.852)* Always making the same movement with the trunk No 28,488 5,031 17.7 1 Yes 43,541 13,162 30.2 2.020 (1.947–2.096)* Always bending the wrist up and down No 25,344 4,431 17.5 1 Yes 46,685 13,762 29.5 1.973 (1.899–2.049)* Wrist is in a bent posture for a prolonged time No 40,455 7,503 18.5 1 Yes 31,574 10,690 33.9 2.248 (2.172–2.326)* Wrist is often placed on the edge of hard and angular objects No 45,945 9,733 21.2 1 Yes 26,084 8,460 32.4 1.786 (1.726–1.848)* Always pinching/grasping some objects/tools No 16,396 2,643 16.1 1 Yes 55,633 15,550 28.0 2.019 (1.929–2.113)* Working above the shoulder level No 59,211 14,804 25.0 1 Yes 12,818 3,389 26.4 1.078 (1.032–1.126)* Work organization factors Often working overtime 34,078 7,492 22.0 1 No 37,951 10,701 28.2 1.394 (1.347–1.442)* Yes Abundant resting time No 38,303 12,579 32.8 1 Yes 33,726 5,614 16.6 0.408 (0.394–0.423)* Deciding on an independent rest time No 57,741 15,346 26.6 1 Yes 14,288 2,847 19.9 0.687 (0.657–0.719)* Staff shortage No 38,967 8,003 20.5 1 Yes 33,062 10,190 30.8 1.724 (1.666–1.783)* Doing the same job nearly every day No 8,579 1,415 16.5 1 Yes 63,450 16,778 26.4 1.820 (1.715–1.932)* Job rotation No 34,642 9,457 27.3 1 Yes 37,387 8,736 23.4 0.812 (0.785–0.840)* Abbreviation: COR=Crude odds ratio; CI=confidence interval.
* P<0.05.Table 2. Univariate analysis of factors of upper-limb musculoskeletal disorders among occupational groups in key industries in China, 2018–2021.
Abundant resting time, deciding on an independent rest time and job rotation are the protective factor of UL-WMSDs. The results of the multiple logistic regression showed that the influencing factors of UL-WMSDs were maintaining the same postures at a high frequency, use of vibration tools at work, working above shoulder level, length of service (in years), exerting great force on the upper limbs or hands, lifting of heavy loads (more than 20 kg) and job rotation, according to the odds ratio (OR). The last item, job rotation, is a protective factor (Table 3).
Variable Coefficient Wald χ2 aOR 95% CI P value Maintaining the same posture at a high frequency 0.270 418.798 1.310 1.277–1.345 0.000 Use of vibration tools at work 0.148 53.134 1.160 1.114–1.207 0.000 Working above the shoulder level 0.076 10.515 1.079 1.030–1.130 0.001 Length of service 0.071 117.284 1.073 1.060–1.087 0.000 Exerting great force on the upper limbs or hands 0.066 4.675 1.068 1.006–1.134 0.031 Lifting heavy loads (more than 20 kg) 0.056 7.430 1.058 1.016–1.102 0.006 Job rotation −0.105 17.066 0.900 0.857–0.946 0.000 Note: North China: Beijing, Tianjin; East China: Shanghai, Jiangsu, Zhejiang, Fujian, Shandong, Jiangxi; Central China: Hubei; South China: Guangdong; Southwest China: Sichuan, Chongqing, Guizhou, Yunnan, Northwest China: Shanxi, Ningxia; Northeast China: Liaoning.
Abbreviation: aOR=adjusted odds ratio; CI=confidence interval.Table 3. Multivariate logistic regression model predicting the risk factors of upper-limb musculoskeletal disorders among occupational groups in key industries in China, 2018–2021.
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This study was an occupational health risk assessment investigation established by the Chinese Center for Disease Control and Prevention from January 2018 to December 2023. It is the largest population survey on WMSDs in China so far. It aimed to include a large sample to conduct an epidemiological survey and research into the occurrence of UL-WMSDs in critical industries or occupational groups in different regions of China. This aim was to determine the occurrence and distribution characteristics of WMSDs in key sectors in China. Furthermore, we explored the epidemic rule and identified the influencing factors of WMSDs.
Moreover, our study provided big data to support the inclusion of WMSDs in crucial industries in China’s List of Legal Occupational Diseases. The study published relevant reports in China CDC Weekly in 2020 and 2021, respectively (3-4). The data reported in this paper were those collected until 2021. Hence, they only described the occurrence of UL-WMSDs and analyzed the relevant influencing factors.
The survey results show that the standardized rate of UL-WMSDs in key industries or occupational groups in China was 22.5%. A survey (5) on musculoskeletal diseases related to work during the second industrial revolution in the 21st century in Europe shows a prevalence of upper limb musculoskeletal diseases between 4% and 26%, similar to our survey results. The survey found a significantly different incidence of WMSDs among different industries and showed that WMSDs were related to the work type and work organization factors, with prominent occupational characteristics. This study found that animal husbandry and biopharmaceutical product manufacturing had the highest upper limb musculoskeletal diseases among the industries, with an incidence of more than 35%. The survey found that the operation mode in the above two industries occurred during the assembly line operation, and workers’ hands, wrists, and elbows needed quick and repetitive activity. At the end of each operation cycle, there was little or very short rest time. Research shows that (6) prolonged, repeated exertion may lead to local muscle fatigue and, if left unrecovered for a long time, causes musculoskeletal disorders easily. The risk factors of UL-WMSDs can be divided into individual-level, work type, and work organization factors. The results of this study showed that, in terms of individual-level factors, gender, age, length of service, educational level, smoking status, and sports were all related to the occurrence of UL-WMSDs (P<0.05). Of these, length of service remained a significant variable in univariate and multivariate logistic regression analyses. In terms of the work type factors, repetitive work in the same posture at a high frequency, use of vibration tools at work, working above shoulder level, exerting great force on the upper limbs or hands, lifting of heavy loads (more than 20 kg) are all risk factors of UL-WMSDs. A large number of scholarly articles have confirmed the above results. A population-based case-control study found (7) a dose-response relationship between the cumulative duration of work with highly elevated arms (positioned above shoulder level) and ruptures of the supraspinatus tendon.
The results of this study show that the risk of UL-WMSDs will increase when handling objects that weigh over 20 kg. Some studies have also confirmed (8) that the occurrence of UL-WMSDs is positively correlated with the weight of the object being carried (load mass). This may be related to manual handling without the use of auxiliary tools. The heavier the load of moving objects, the harder it is for workers to carry them, resulting in increased hand pain. In terms of work organization factors, the results of this study show that job rotation is a protective factor of UL-WMSDs. Previous studies also support this view. A study showed that (9) the implementation of job rotation can help increase the variability of muscle activities, particularly in upper extreme muscles and can reduce the burden of occupational injury.
Although this study is a population survey with a large sample used to clarify the epidemiological characteristics and risk factors of UL-WMSDs in critical sectors or occupational groups in China, the following limitations still exist. First, the current study’s design makes it difficult to determine the temporal relationship between the antecedents and consequences and infer the causal relationship between the risk factors and the occurrence of UL-WMSDs. Second, this study used questionnaires to obtain information about the respondents’ illnesses in the past year. Since it is easy to forget the past, report and recall bias could have occurred.
In conclusion, the standardized incidence of UL-WMSDs in key industries or occupational groups in China is 22.5%. UL-WMSDs have recognized occupation-related characteristics, and their risk factors change with the length of service, type of work, work posture, work organization, and other factors. Given this, it is suggested to continue to carry out special epidemiological investigation and research on a large sample of the occupational population in key industries nationwideand establish a database of factors related to musculoskeletal disorders among occupational population in key industries in China, to provide extensive data support for listing UL-WMSDs to relevant regions in China’s List of Legal Occupational Diseases.
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All the participants involved in this study, from Chongqing, Shanghai, Jiangsu, Zhejiang, Tianjin, Beijing, Hubei, Ningxia Hui Autonomous Region, Sichuan, Shaanxi and Yunnan Provincial Centers for Disease Prevention and Control, Hubei Provincial Hospital of Integrated Chinese and Western Medicine, Guangzhou Twelfth People’s Hospital Affiliated to Guangzhou Medical University, Liaoning Provincial Health Supervision Center, Shenyang, Liaoning, China, Guizhou Province Occupational Disease Prevention and Control Hospital, Shandong Academy of Occupational Health and Occupational Medicine, Civil Aviation Medical Center of China Civil Aviation Administration, Tianjin Occupational Disease Prevention and Control Hospital, Fujian Province Occupational Disease and Chemical Poisoning Prevention and Control Center, Guangdong Province Hospital for Occupational Disease Prevention and Treatment, and Institute of Occupational Medicine of Jiangxi.
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