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Dysbaric osteonecrosis or DON is a form of avascular necrosis where there is death of a portion of the bone that is thought to be caused by nitrogen embolism (blockage of the blood vessels by a bubble of nitrogen coming out of solution) in divers. Although the definitive pathologic process is poorly understood, there are several hypotheses: *Intra- or extravascular nitrogen in bones, "nitrogen embolism". *Osmotic gas effects due to intramedullary pressure effects. *fat embolism *hemoconcentration and increased coagulability. ==Process== The diagnosis is made by x-ray/MRI appearance and has five juxta-articular classifications and forehead, neck, and shaft classifications indicating early radiological signs. Early on there is flattening of articular surfaces, thinning of cartilage with osteophyte (spur) formation. In juxta-articular lesions without symptoms, there is dead bone and marrow separated from living bone by a line of dense collagen. Microscopic cysts form, fill with necrotic material and there is massive necrosis with replacement by cancellous bone with collapse of the lesions. The lesion begins as a random finding on x-ray without symptoms. Symptomatic lesions usually involve joint surfaces and fracture with attempted healing occurs. This process takes place over months to years and eventually causes disabling arthritis, particularly of the femoral head (hip). The following staging system is sometimes useful when managing lesions.〔 * Stage 0 - Intravascular coagulation * Stage 1 - Dead Bone without repair * Stage 2 - Dead Bone with repair but without collapse * Stage 3 - Dead Bone with repair and with collapse * Stage 4 - Secondary degenerative arthritis In a study of bone lesions in 281 compressed air workers done by Walder in 1969, 29% of the lesions were in the humeral head (shoulder), 16% in the femoral head (hip), 40% in the lower end of the femur (lower thigh at the knee) and 15% in the upper tibia (knee below the knee cap). Worsening of the condition from continued decompression in an asymptomatic x-ray finding may occur. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dysbaric osteonecrosis」の詳細全文を読む スポンサード リンク
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