Femoral head osteonecrosis can be caused by disruption of the systemic immune response via the toll-like receptor 4 signalling pathway.

OBJECTIVES: Osteonecrosis of the femoral head is observed in patients treated with steroids. However, the pathogenesis of femoral head osteonecrosis remains unclear. We established a rat model with femoral head osteonecrosis by injecting lipopolysaccharide (LPS) and steroid, and assessed the consequences of this on femoral head histology, the systemic immune response and lipid synthesis.
METHODS: Male Wistar rats were injected intravenously on days 0 and 1 with 2 mg/kg LPS and intramuscularly with 20 mg/kg methylprednisolone on days 3, 4 and 5. The animals were sacrificed 1, 2, 3 or 4 weeks after the last methylprednisolone injection. Histopathological and biochemical analyses were performed every week.
RESULTS: Osteonecrosis of the femoral head was observed in the rats. The plasma triglyceride concentrations had decreased significantly by weeks 2 and 3. The total plasma cholesterol concentrations had increased significantly by week 1 but then decreased significantly by week 4. The plasma concentrations of IL-1beta, IL-2, IL-4, IL-6, IL-10, GM-CSF, IFN-gamma and TNF-alpha had increased significantly by week 1. These cytokines can all be induced by toll-like receptor 4 (TLR4) signalling.
CONCLUSIONS: LPS and methylprednisolone induced osteonecrosis of the femoral head in rats and this was associated with a disruption of the innate immune system and lipid synthesis. These findings suggest that the TLR4 signalling pathway plays an important role in the pathogenesis of femoral head osteonecrosis.