Dysbaric disorders: aseptic bone necrosis in tunnel workers and divers

Dysbaric osteonecrosis is a serious complication for those exposed to a hyperbaric environment, with prevalence of 17% amongst compressed air workers and 4.2% amongst divers. Bone lesions are characteristically multiple and bilateral, occurring frequently in the shafts of the femora or tibiae and the heads of the humeri or femora. A proportion of the lesions will lie next to the joint surface, the so called juxta-articular lesion, and these may progress to a structural failure and secondary osteoarthritis. These lesions can be severely disabling, especially in a young adult male. When related to the occupational history the prevalence of bone lesions, both in compressed air workers and divers, increases with age, experience and with greater pressures of air or at greater depths. Moreover, acute attacks of decompression sickness, the bends, are more liable to be associated with subsequent bone lesions. Current decompression schedules certainly reduce the bends rate but, no matter how strictly adhered to, will not prevent the development of dysbaric osteonecrosis. It is possible that bone necrosis could result solely from exposure to a high pressure of air, either from work in compressed air or diving. Those men with positive bone lesions should be advised to seek expert medical opinion and probably advised to discontinue work in compressed air or diving if a juxta-articular lesion is present. Detection of bone necrosis depends on good quality radiographs with reliable interpretation, preferably by double observation, especially in the early stages. Lesions, especially when early or doubtful, can be confirmed by CT or bone scintigraphy. MRI promises to detect osteonecrosis in the very early stages but is not yet readily available. To detect dysbaric osteonecrosis at an early stage it is important to monitor both compressed air workers and divers with regular radiological skeletal surveys or bone scintigraphy. In 1987, the Bone Necrosis Working Group of the Decompression Sickness Panel recommended that all divers should have a radiological survey on completion of their initial diving training and that bone scintigraphy should be used for subsequent surveillance for certain groups, including those diving deeper than 30 metres, where the time at depth exceeds 4 hours, when experimental decompression is used and in other situations.