Dysbaric osteonecrosis: a reassessment and hypothesis

Dysbaric osteonecrosis is associated with exposure to large ambient pressur e changes, and comprises necrotic lesions in the fatty marrow-containing sh afts of the long bones, and the ball and socket joints (hips and shoulders) . The fundamental causes are still in question and the illness remains a si gnificant health hazard. (C) 2000 Harcourt Publishers Ltd. Radiological and pathological features of both dysbaric and non-dysbaric os teonecrosis are indistinguishable and both are characterized by intramedull ary venous stasis, ischemia and necrosis of bone. It has been generally acc epted that gas bubbles (probably by initiating intramedullary venous stasis ) are the prime cause of dysbaric osteonecrosis, as well as being responsib le for Type 1 Decompression Sickness or 'the bends'. Importantly, however, not all series have found a correlation between dysbaric osteonecrosis and 'the bends'. Thus even though it is likely that gas bubbles remain the prim e cause of dysbaric osteonecrosis, workers have proposed that in some Gases there is another etiological factor which may exaggerate the pathologic ef fects of gas bubbles, making the bone more susceptible to necrosis. It is proposed that rapid compression by impeding venous drainage from bone initiates intramedullary venous stasis. In the presence of intramedullary gas bubbles, this may progress to thrombosis, ischemia and bone necrosis. T he review offers an explanation for total sparing of the knee joint in dysb aric osteonecrosis, and sole involvement of the hip and shoulder (in terms of sub-articular lesions and subsequent joint collapse). In addition to con tinued observance of proper decompression procedures, a slower rate of comp ression may further reduce the incidence of dysbaric osteonecrosis. Bone death or osteonecrosis is a concept which Hippocrates put forward in a ntiquity (1), but it was not until 1794 that James Russell of Edinburgh wro te the first modern-day descriptions. In these cases infection was the pred ominant etiology (1,2). In 1888 Konig described necrosis of the adult femor al head without infection (3) (aseptic necrosis of bone) and in the same ye ar Twynam reported a case of osteonecrosis in a caisson worker (4) in which there was still a significant infective component. In 1911 Bornstein and Plate, followed later and independently by Bassoe in 1913, presented radiological confirmation of aseptic necrosis of bone in co mpressed air workers (5). The first report of aseptic necrosis in an underw ater diver subsequently appeared in 1936 (6). The condition of aseptic necrosis of bone in association with exposure to r aised ambient pressure (previously referred to as caisson disease, pressure -induced osteoarthropathy (7), 'bone rot' (8) and other synonyms (6)) is no w generally known as dysbaric osteonecrosis (6). Despite detailed examinati on of this problem by many authorities, dysbaric osteonecrosis still remain s a significant occupational hazard with serious medico-legal consequences (5-13). This suggests that preventative measures are being based upon an in complete understanding of the pathophysiology of the disease, and that othe r etiological factors are perhaps being overlooked. (C) 2000 Harcourt Publi shers Ltd.