Reperfusion injury in free bone grafts after tourniquet-induced ischemia

For successful revascularization, incorporation, and survival of fracture fragments or free non-pedicled bone grafts, the first days after surgery seem to be most critical. Using intravital fluorescence microscopy, the effects of 3 hours of tourniquet-induced ischemia were assessed on newly formed angiogenic microvessels 4, 8, and 12 days after isogeneic transplantation of metatarsal bones into dorsal skin fold chambers of adult inbred C57BL/6 mice. The microvascular perfusion index of newly formed microvessels was quantified 30 and 120 minutes after initiation of reperfusion. Four days after transplantation, a complete breakdown of the perfusion of all grafts was found accompanied by hemorrhage as a sign of microvascular damage. In contrast, at 8 and 12 days after transplantation a complete breakdown of graft perfusion rarely occurred. Therefore, the tourniquet-induced ischemia was most pronounced in early stages of development of angiogenic microvessels. These experimental data provide rationale for critical application of tourniquets in revision surgery shortly after initiation of fracture treatment or transplantation of free nonpedicled grafts so as not to compromise angiogenesis-induced tissue revascularization.