Pathological and hemodynamic study in a new model of femoral head necrosis following traumatic dislocation.

The blood of the femoral head is thought to be supplied by vessels originating from the medial and lateral circumflex femoral arteries and via the marrow cavity of the neck. Therefore, it is difficult to induce osteonecrosis of the femoral head when the marrow cavity of the neck is preserved. In the present study, we established a new model of femoral head necrosis by dislocating the hip joint and ligating the medial and lateral circumflex femoral arteries and veins. Measurement of femoral head blood flow revealed that a marked decrease to 14.7% of the control value was achieved by both hip dislocation and ligation of blood vessels. Pathologic examination showed no necrosis with either dislocation or ligation alone, whereas at 2 and 4 weeks 80% of the animals subjected to both procedures showed widespread necrosis. These pathologic findings considered in the light of results of the blood flow measurements suggest that a decrease in femoral head blood flow below 20% of the control value is needed to cause osteonecrosis. In addition, magnetic resonance images (MRI) of the model were evaluated in the combined dislocation and ligation group at 4 weeks (n = 5). Changes on MRI were seen in 3 of 5 dogs. The necrotic changes of the femoral head are thought to be detectable on MRI within 4 weeks after ischemia without enhancement.