Objectives To examine the association of education and physical work load factors on the occupational differences in disability retirement due to knee osteoarthritis (OA).
Design Longitudinal study.
Setting Linkage of several nationwide registers and a job exposure matrix in Finland.
Participants A total of 1 135 654 Finns aged 30–60 years in gainful employment were followed from 2005 to 2013 for full disability retirement due to knee OA.
Primary and secondary outcome measures We calculated age-adjusted incidence rates and examined the association of occupation, education and physical work load factors with disability retirement using competing risk regression model. Disability retirement due to other causes than knee OA, old-age retirement and death were treated as competing risk.
Results A total of 6117 persons had disability retirement due to knee OA. Women had a higher age-adjusted incidence rate than men (72 vs 60 per 100 000 person-years, respectively). In men, a very high risk of disability retirement was found among construction workers, electricians and plumbers (HR 16.6, 95% CI 12.5 to 22.2), service workers (HR 12.7, 95% CI 9.2 to 17.4) and in women among building caretakers, cleaners, assistant nurses and kitchen workers (HR 15.5, 95% CI 11.7 to 20.6), as compared with professionals. The observed occupational differences were largely explained by educational level and noticeably mediated by physical work load factors in both genders.
Conclusion Our observational study suggests that the risk of disability retirement among manual workers is strongly attributed to the physically heavy work.
- public health
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Contributors EV-J obtained the data. All authors were involved in study conception and design, interpretation of results. SS conducted the statistical analyses. TK wrote the first drafts of the article. All authors discussed the drafts, revised them critically and prepared the final version to be submitted for publication. SS has full access to all data in the study and takes responsibility of the integrity of the data and the accuracy of the data analysis.
Funding This work was supported by NordForsk grant number 76659 (SS), the Finnish Work Environment Fund grant number 115105 (SS) and by the Academy of Finland grant number 267589 (EV-J).
Competing interests None declared.
Patient consent Not required.
Ethics approval The researchers used fully anonymous register data for which ethics committee approval is not needed according to Finnish legislation. Statistics Finland linked its data to those of the Social Insurance Institution of Finland and the Finnish Centre for Pensions, after which the data were anonymised and stored by Statistics Finland. The researchers analysed the anonymous data using a remote access system. All output extracted from the system was approved by Statistics Finland to ensure compliance with data protection regulations. The data can only be accessed by individual researchers who have obtained permission from each of the administrative sources providing the data.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Due to data protection regulations of the administrative sources providing the register data, the authors do not have the permission to share the data. Permissions to use the register data can be applied from the Social Insurance Institution of Finland (http://www. kela.fi/web/en/research-data-requests), the Finnish Centre for Pensions (http://www.etk.fi/en/statistics-2/statistics/producer-of-statistics/) and Statistics Finland (http://www.stat.fi/meta/tietosuoja/kayttolupa_en.html).
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