An in vivo model has been developed for chronic observation of the effects of
ischemia on cortical bone remodeling and perfused vascularity. Diaphragm occluders were implanted around the right common iliac artery of four rabbits and inflated to produce 10 h of
ischemia to the limb. Microcirculation was monitored with intravital microscopy of injected fluorescent
microspheres and
FITC-Dextran 70 through a bone window, the tibial bone chamber implant (
BCI).
Bone resorption and apposition in the
BCI were indicated with mineralization
dyes. Between 2 and 12 h following release of the occluder, secondary
ischemia/no-reflow and other evidence of
reperfusion injury were observed. Vessel damage was suggested by abnormally high leakage of FITC-D70 from the few vessels perfused during secondary
ischemia. In the weeks following occluder release perfused vasculature increased beyond pre-occlusion levels. Net
bone resorption reached a maximum when vascularity passed normal levels. In order to further validate the
arterial occlusion model for
osteonecrosis, techniques for (1) confirming bone death and (2) detecting increased leukocyte adherence to endothelial cells were added. The dead cell
stain Ethidium homodimer-1 was used to tag dead osteocytes immediately after occlusion and produced a measure designated "
osteonecrosis index." To detect leukocytes adhering to vessel walls,
carboxyfluorescein diacetate, succinimidyl ester was injected at occluder release. An increase in the number of adherent leukocytes was detected.