Femoral head necrosis and osteopenia in stroke-prone spontaneously hypertensive rats (SHRSPs)

Necrosis of the femoral head and osteopenia were examined histopathologically in stroke-prone spontaneously hypertensive rats (SHRSPs) aged 6 to 36 weeks and compared with that of spontaneously hypertensive rats (SHRs) and Wistar-Kyoto rats (WKYs). Avascular necrosis of the femoral head was frequently observed, mainly in the young SHRSPs and SHRs (about 8 to 15 weeks of age). SHRSPs had the highest incidence of femoral head necrosis among the three strains. This necrotic change in the femoral head was considered to be secondary ischemia induced by angiospasm or arteriosclerosis, similar to the disorders observed in the brain, kidney, and heart in SHRSPs. However, the complication occurred in spite of treatment with antihypertensive agents (ACE inhibitor: enalapril, spirapril) even though other ischemic disorders such as brain hemorrhage and renal infarction were prevented, indicating that the femoral head necrosis in SHRSPs was not due to hypertensive complications induced by angiospasm or arteriosclerosis. Bone mineral density (BMD) of the femoral bone was significantly lower in SHRSPs, and the femoral heads in this strain were the most easily deformed by loads applied during compression tests. Histopathologically, the infarctions were encountered on the lateral side of the epiphysis, but no thrombi were observed. The lateral side of the epiphysis is the anatomic site where the weight load is greatest and the site where the nutritive artery enters. Our results strongly suggest that the coexistence of vulnerable bone matrix and physical weight load to the nutritive artery plays a crucial role in the occurrence of femoral head necrosis in SHRSPs, whether based on generalized or localized osteopenia.