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Comprehensive information about diving and undersea medicine for the non-medical diver, the non-diving physician and the specialist.
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DYSBARIC OSTEONECROSIS History Osteonecrosis in divers is of two basic types: juxta-articular (subchondral), and shaft, a description that includes the neck and a portion of the long bone. The shaft lesions are predominately saponified fat. The juxta-articular lesions are of greater clinical significance. These lesions show areas of dead bone surrounded by a layer of collagen which forms a fibrous band and the formation of new bone. Beyond the area that can be detected radiologically is seen an area of creeping substitution and healing trabeculae (McCallum and Harrison, 1993). Perhaps the most important step towards proper assessment of the significance of bone necrosis to the diving population was the standardization of diagnostic techniques. With agreement on x-ray diagnosis in the late 1950s and 1960s it was possible to move away from purely clinical descriptions of the illness to surveys of the prevalence of pre-symptomatic lesionsin the apparently healthy population. The radiological diagnosis of bone necrosis depends on the quality of the x-rays that are taken and the experience of those who read them. The x-ray remains the gold standard of diagnosis and although the disabling complications affect only the shoulders and the hips, extensive views of the lower femur and upper tibia are included in knee x-rays in order to find as many shaft lesions as possible. MDP (99mTechnetium Methyl-dipolyphosphate) scans are very sensitive to local bone pathology. A ‘hot spot" indicates increased perfusion and metabolism and may be seen only hours after a dive. However,in a Royal Navy survey (Pearson et al, 1982) only four divers became radiologically positive some two to three years after 22 had demonstrated positive scans. Eleven still had abnormal scans and 7 had reverted to normalcy. Thus a positive scan is of little diagnostic significance, but may indicate a need for radiological follow-up. Magnetic resonance imaging (MRI) has a remarkable power to detect early lesions and is becoming more readily available for routine screening of large populations.
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