Evidence for reperfusion injury in cortical bone as a function of crush injury ischemia duration: a rabbit bone chamber study

A model for critical limb ischemia was produced by occluding femoral vessels in 24 rabbits with a pneumatic cuff for 0, 2, 4, or 6 hours. Immediate sequelae and subsequent creeping substitution of cortical bone were observed in vivo using an implanted tibial window, the optical bone chamber implant (with intravital microscopy), and then by light and fluorescence microscopy of fluorochrome-labeled and surface-stained ground sections of retrieved implants. Six rabbits were used as controls (0 h) for each ischemia treatment, and the animals were monitored for 5 weeks postocclusion. A subpopulation of 13 implants was retrieved after euthanization and then histologically assessed for bone necrosis and remodeling. The hypothesis tested was that reperfusion injury during the 24 h after occluder release (reperfusion phase), and vessel perfusion/caliber, angiogenesis, and net bone resorption during the 5 subsequent weeks (creeping substitution phase), would exhibit ischemia duration-dependent effects. All animals could bear weight on the affected limb to ambulate by 1 week posttreatment. Two-way analysis of variance (ANOVA) comparison of the resulting data confirmed a significant difference between control and ischemia-treated rabbits for: (1) vessel perfusion/reperfusion; (2) vessel caliber; and (3) net bone resorption. Vascular responses to 4 vs. 6 h of ischemia were not significantly different, but net bone resorption was strictly ischemia duration-dependent. The conclusion that reperfusion injury was the mechanism spreading ischemia to more vessels was supported by a decrease in reperfusion and caliber of vessels, and an increase in vascular permeability and leukocyte adherence during the reperfusion phase. It is postulated that reperfusion injury produces a secondary ischemia that amplifies the occlusion-created primary ischemia and, in the present work, may have been succeeded by progressive episodes of ischemia, similar to the infarction pattern of ischemic hearts.