Early magnetic resonance imaging and histologic findings in a model of femoral head necrosis.

The authors examined early magnetic resonance images and histologic findings of avascular necrosis of the femoral head in a canine model. The avascular necrosis of the femoral head model was surgically induced. Animals were euthanized at 3 days, 1, 2, and 4 weeks, and the proximal femurs were retrieved. Magnetic resonance images and histologic sections were performed on each of the specimens obtained. Twenty-five mongrel dogs were studied, 4 dogs at 3 days and 7 dogs at each of the other intervals. Findings suggest that histologic changes may be seen as early as 3 days, with marrow edema and hemorrhage as early findings, and fibrous marrow transformation and appositional bone growth as later findings. Magnetic resonance imaging abnormalities did not occur until 1 week after injury and were seen in all animals by 4 weeks.