Histopathological Study on Dysbaric Osteonecrosis (DON) in Tibiae of Sheep with a Hyperbaric Exposure

Previously we proposed a hypothesis that activation of blood coagulability in the intraosseous blood vessels contr ibutes impor tantly to produce decompression sickness (DCS) including dysbaric osteonecrosis (DON) after a hyperbar ic exposure. This paper presents evidence suppor ting this hypothesis. Crossbred, adult, female sheep were exposed to a three-hour exposure at 2.8-3.2 atm abs, using an exper imental hyperbar ic chamber . They showed signs of bends in various legs soon after the exposure. Eight weeks after decompression insult, more or less marked and extensive pathologic findings of the bone mar row tissue wer e noted at the time of autopsy in their tibiae. In thr ee tibiae of seven exper imental ・・sheep, a wide spread necrosis was found in the bone mar row, particular ly in the upper half of the shaft. ・・ In one of them, the large branches including the main ascending branch of the intraosseous nutr ient ar tery wer e obliter ated by organized thrombi at a little above the middle por tion of the shaft of the r ight tibia. This ar ter ial lesion seemed closely r elated to a widespr ead necrosis of the bone mar row of upper half of the shaft. Another conspicuous finding was formation of cutting cones, a repair process, observed in the cor tical compact bone. Through formation of cutting cones, blood supply of the cor tical bone recovered from the per iosteum resulting in an active organization of necrotic bone mar row, where active formation of woven bone was observed. These suggest that provocative hyperbar ic exposure can cause ar ter ial thrombosis to produce ear ly stage of necrosis of the bone tissues, and the subsequent repair processes can exagger ate the featur es of DON