Case control study of the relations between risk of back pain sickness absence and the nature of tasks carried out by coalminers. Final report on CEC research contract 7280/04/022

This case control study investigated the differences between tasks performed by underground coalminers at two collieries in the United Kingdom and their history of back pain sickness absence during a six month period.Sickness absence data was provided by British Coal Medical Services and used for case selection. A case was defined as a miner with one or more spells of at least seven days absence due to a defined back complaint during the period 1.8.91 to 31.1.92. The control miners were selected in a random manner from colliery staff lists separated into ten year age bands in a ratio of two controls to one case.A questionnaire was developed as the method of identifying the tasks which each miner had performed. Ergonomists visited both collieries and observed the work performed underground. These observations were used to identify the tasks which occurred underground. These tasks were then incorporated into a questionnaire which asked about lifting, carrying, holding, pushing, pulling and use of transport systems underground. In addition, a shortened version of a back pain questionnaire previously used by the Institute in research on coalminers was included.The task component questionnaire was the subject of a small validation exercise at one colliery. This exercise indicated that cases reported completing tasks that they were observed performing more commonly than controls. In addition, the estimates of frequency of performing a task, total duration that a task was performed and the longest duration without a break that a task was performed were more accurate for cases than controls.A questionnaire administrator was trained in the method of administration of the questionnaire. The questionnaire administration took place in the medical centre at each colliery. The study recruited 104 cases and 215 controls. The mean age of the population was 37 years. The mean duration of employment in the coal industry was 17 years. Participants at Colliery 1 were older with more years experience than participants at Colliery 2. A large number of redundancies occurred at Colliery 2 during this study with the loss of older workers. The average length of back pain absence was 16.7 days. The most common reason for absence was back pain or strain, followed by back injury. A smaller number were certified as having lumbago or sciatica. Self-reported back pain in the preceding twelve months was experienced by all cases and 78% of controls. Eighty percent of cases and 72% of controls had had attacks of back pain in the period more than 12 months before the study. Chronic back ache or pain (occurring on most days of every month) was present in 46% of cases and 24% of controls. Forty one percent of cases had more than one attack of back pain in the preceding year compared to 42% of controls.The questionnaire responses were analysed by logistic regression techniques. Individual positive associations were found between increased risk of back-related sickness absence and increases in (1) lifting more than 50 kg with a frequency of more than 20 times in a shift; (2) holding weights above shoulder height more than 50 times in a shift; (3) carrying more than 50 kg; and (4) twisting the body while pushing more than 50 times in a shift. A negative association was found with time spent driving free steer vehicles underground. In statistically derived models fitted to assess the effect of multiple risk factors, the only risk factors which showed significant effects were driving free steer vehicles (negative) and lifting more than 50 kg (positive).This study has identified that frequency of heavy lifting by underground miners is associated with an increased risk of absence due to a back problem. A variety of risk reduction methods can be implemented to attempt to improve this situation. Research is recommended to validate the task questionnaire further and also to study a more active medical management of back pain among coalminers.