Pathological study on the prevention of osteonecrosis of the femoral head in spontaneously hypertensive rats.

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Osteonecrosis of the femoral head which resembled Perthes'-disease occurs naturally in spontaneously hypertensive rats (SHRs). A similar lesion could be induced by standing in Wistar Kyoto rats (WKYs). Standing is one of major factors by which the femoral head suffers mechanical stress. To clarify the pathogenesis of the osteonecrosis in rats would contribute for prevention and treatment of Perthes' disease. The purpose of this study is to investigate the participation of the mechanical stress on the femoral head in the occurrence of osteonecrosis of the femoral head.In this experiment, custom-designed cages were prepared, which were 27 cm of height (high cage) and 10 cm of height (low cage). SHRs and WKYs at 5 weeks after birth were fed in these cages. In high cage group, a feed box and a drinking aperture were located high enough so that rats had to stand in feeding. To evaluate their activity, behavior was recorded on video tape using a camera with notovision. The rats were very act … More ive at night and stood up a total of around 2 hours each day in high cage group. The rats in low cages could not stand up. For pathological study, bilateral femurs were resected under ether anesthesia at 9, 12 and 15 weeks of age. After soft X-ray photos taken, thin paraffin-embedded sections of the femoral heads were stained with hematoxylin eosin.In SHRs, the incidence of the osteonecrosis of high cage group was slightly higher than that of low cage group. The difference between both groups was significant in WKYs. The osteonecrosis rarely occurred in low cage group, however, it appeared frequently at 15 weeks in high cage group. WKYs at 15 weeks in high cage group showed localized cartilaginous abnormalities of the growth plate like SHRs. The abnormalities were remarkable in the lateral of the femoral head where the mechanical stress centered and the feeding vessels penetrated into. These results suggest that the repeated mechanical stress playd an important role in the occurrence of osteonecrosis of the femoral head. Less