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BundesInzidenz von Rückenerkrankungen in einer Kohorte von Hauern und Elektrikern im Untertageerzbergbau der SDAG Wismut

Issue: Mining work is characterised by intense physical work in combination with high biomechanical strain on the lumbar spine. The epidemiological design of a longitudinal study is the best way to determine the relationship between such exposure at the workplace and the point in time when back complaints occur. Objectives: The aim of the study was to use the above mentioned epidemiological design in a pilot project to describe and compare the risk of developing complaints of the lower back in stope miners and mining electricians with respect to the length of exposure. Method: The contents of medical files of 55 miners and 55 electricians of a German mining company were analysed. Every disease of the lower back mentioned in the files was recorded. The period of time from the end of apprenticeship to the termination of underground activity was considered. The Kaplan-Meier method, the incidence density ratio and the Cox regression model were used for the statistical estimation. Results: The stope miners and electricians worked for the mining company in the period from 1955 to 1990. The duration of underground activities of the individuals varied from a few months up to 26 years. An exposure matrix showed that stope miners had a considerably higher physical work load and a higher biomechanical work load. Miners finished their underground activities on average after 8.3 ± 6.4 years (electricians: 12.8 ± 7.7 years). 62 % of the miners and 51 % of the electricians had to undergo medical treatment at least once due to complaints of the lower back. The first complaints occurred on average after 4.3 ± 3.2 years in the cohort of miners and after 10.2 ± 6.4 years in the cohort of electricians. The incidence was calculated to be 143 cases per 1000 person years for miners and 53 cases per 1000 person years for electricians (incidence density ratio: 2.72 (Cl: 1.65 ... 4.49)). The Cox regression model confirms that the assignment to a job (working as a miner or as a mining electrician) was the main risk factor compared with age, the year of birth, and anthropometric parameters (height, body weight). Conclusions: The study shows the strong time relationship between high physical demands at work and the risk of developing complaints of the lower back. Stope miners had a significantly increased risk a few years after beginning underground mining activities. The shorter period until termination of underground activity underlines the strong selection effect in the cohort of stope miners as a result of the high physical demands. The data from historical health archives are suitable for this type of risk analysis.