Objective To investigate the histomorphometric features of the necrotic femoral head of rabbits induced by methylprednisolone combined with lipopolysaccharide. Methods Thirty-two male adult New Zealand white rabbits were used. Among them, 16 were injected with lipopolysaccharide and methylprednisolone (osteonecrosis group), and another 16 were sham-injected with saline (control group). Magnetic resonance (MR) imaging was taken for femoral heads of the rabbits in both groups at the end of 2, 4 and 6 weeks after the injection. All the rabbits were then killed 6 weeks later. The femoral heads of the rabbits were collected and processed for histological and histomorphometric analysis. Results Femoral head necrosis occurred in 14 rabbits of the osteonecrosis group which were confirmed by histological evaluation and MR imaging. Osteonecrotic femoral heads, compared to controls, were characterized by lower values of bone volume/tissue volume (P<0.01), tabecular thichness (P<0.01), osteoid surface/bone surface (P<0.05), mineralizing apposition rate (P<0.05), and bone formation rate/bone surface (P<0.05). However, tabecular separation and eroded surface/bone surface were higher in osteonecrotic femoral heads than in controls (P<0.01). Trabecular number and osteoclast surface/bone surface did not differ significantly. Conclusion The results demonstrated that osteoporosis was apparent in osteonecrotic femoral heads induced by methylprednisolone and lipopolysaccharide, due mainly to trabecular thinning rather than reduction of trabecular number. This might be due to reduced bone formation combined with increased bone resorption.
