| Abstract
| - Dysbaric osteonecrosis is now the accepted term which applies to the skeletal lesions developing in tunnel or caisson workers and also in divers. Bone lesions require time tc become evident and it is 6 months at least before positive radiological changes become evident. Amongst a group of 4422 North Sea divers who have had radiographic skeletal survey, 194 men (4.4 per cent) were found to have 328 positive lesions of osteonecrosis. Lesions are multiple and bilateral, and the commonest site was the femoral shaft (66 per cent of all lesions). Other sites included the head of the humerus, tibial shaft and the head of the femur. Amongst a group of 2510 compressed air workers with skeletal surveys the prevalence of men with positive lesions was 17.7 per cent. The distribution was the same as in the divers, with the femoral shaft being the commonest site but only forming 28 per cent of all lesions. Relation to the occupational history suggests that in divers bone lesions increase with depth and are more prevalent in those who have had decompression sickness and have carried out saturation diving. Moreover, the prevalence also increases with age and experience. In the differential diagnosis one must consider other causes of the aseptic necrosis of bone—injury, high dose steroid therapy and calcified enchondroma. Particular attention should be paid to differentiating the earliest changes of dysbaric osteonecrosis from bone islands which is present in up to 40 per cent of normal individuals. The use of bone-seeking isotopes is giving encouraging results and it is possible that bone necrosis may be detected as early as 3 weeks after the ischaemic episode and several months before radiological changes become evident. For the present, early detection depends on reliable interpretation of good quality radiographs which should be interpreted by at least two radiologists experienced in this kind of work. A pre-diving chest radiograph is required as part of the initial and annual medical examination for commercial divers which should include lung function tests. All are agreed that a lung cyst or bulla is a totally disqualifying factor. Minor radiological changes should always be reported.
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