In a field survey of rheumatic complaints Lawrence and Aitken-Swan (1952) found that coal miners suffered more disability from pain in the back sciatic distribution and in the knees than the surrounding general population, and from the limited examination possible in the field it appeared that these disabilities were due to disc degeneration, osteo-arthritis, and rheumatic disorders of undetermined nature. To investigate this more fully it was decided to carry out a detailed clinical study and

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... radiological survey of small but carefully selected groups of coal miners and other workers from the populations covered most comprehensively by the field survey: that is to say, the underground workers at Bedford Colliery and the employees of the engineering yard and the administrative offices at Walkden. The study was confined to males in the fifth decade. This age group was chosen as most likely to show the effects of occupation upon the incidence and severity of degenerative joint changes, since at this age these changes begin to be radiologically demonstrable in a proportion of the general population. Consideration of the numbers available between the ages of 40 and 50 showed that there were 47 office workers (clerks and administrative staff), 89 manual workers (blacksmiths, machinists, carpenters, painters, and general labourers), and 259 miners. We decided to study all 47 office workers together with an equal number of manual workers, thus making a composite group of 94 non-miners who had never been underground, and to compare these with 94 underground workers. All manual and underground workers in the appropriate age group were therefore numbered consecutively and the samples for study were abstracted by random sampling of numbers. To avoid error due to increasing observer experience each of the three groups of workers was evenly distributed throughout the study; thus five office workers were seen at one session, five manual workers at the next, and five miners at the third and fourth, and so in sequence thereafter. This also secured complete impartiality on the part of those reading the radiographs to whom the order of calling was unknown. In spite of difficulties due to the long distance some of the miners had to travel to the clinic, there were only nine refusals amongst the miners and five amongst the non-miners. From the field survey it was known that three of the miners and two of the non-miners who refused had in fact suffered from rheumatic complaints so that these refusals did not appear to be associated with the presence or absence of complaints. In addition a number of men had left their employment and could not be traced, so that the groups finally studied were 84 miners, 45 manual workers, and 42 office workers. In addition 24 men who had worked both underground and on the surface were investigated, and the findings in these men have been included in those tables which do not deal with comparisons between miners, manual, and office workers. Method of Examination A detailed history was taken of both rheumatic and other symptoms and of past and family illnesses. Then a routine general clinical examination was carried out, a note being made of all deviations from the normal regardless of whether or not they were causing disability. Particular attention was naturally paid to the limb joints and the spine. In addition, height, stem height (from the seat to the top of the head in a sitting position), and body weight were recorded. The x-ray examination included lateral views of the cervical and lumbar spine in both flexion and extension, an anteroposterior view of the lumbar spine, and a lateral cone picture of the lumbo-sacral junction. In