The workers used an impact wrench to screw in or unscrew bolts in the processes of molding and unmolding at a factory manufacturing concrete electric light poles. Special medical examinations for vibration syndrome began at the factory in 1981. They consisted of a primary medical examination and a secondary medical examination (Japanese Labour Standards Bureau Notification, No. 609)16). Each subject was asked to complete a questionnaire regarding their work history, medical history and subjective symptoms, including Raynaud’s phenomenon. All subjects using a vibrating tool were scheduled to take
a special medical examination for vibration syndrome every year. However, some of them did not take a special medical examination in a year.