The connective-tissue envelope in revascularisation of patellar tendon grafts

Endoligamentous revascularization of an anterior cruciate ligament graft

After replacement of the anterior cruciate ligament with a free tendon graft, the substitute initially is avascular and without a synovial surface. To ensure long-term survival, the graft must become revascularized. Despite numerous studies on the topic, there still is discussion regarding revascularization. The goal of the current study was to investigate the endoligamentous microcapillary revascularization of the free tendon graft after anterior cruciate ligament replacement with time. Thirty-six mature sheep had an anterior cruciate ligament reconstruction with an ipsilateral flexor tendon split graft. Midsubstance tissue samples were immunostained for von Willebrand factor (Factor VIII) at 6, 9, 12, 24, 52, and 104 weeks to detect the endothelial cells of capillaries. Cross sections of vessels were determined in three zones (subsynovial, intermediate, and center of the graft) and were evaluated by means of histomorphometry using a digital imaging analysis system. The observations showed that capillary vessels, which originate from the synovial envelope, invaded the avascular graft tissue from the surface toward the center zone. The highest level of vascular density was found after 6 weeks, reaching the vascular status of the native anterior cruciate ligament after 24 weeks. These findings are in contrast to the findings of previous studies in animals. The current study showed, for the first time, the kinetics of an endoligamentous revascularization of a free tendon graft at the capillary level. In the current model, the process of revascularization terminated earlier than previously described.

Reperfusion injury in free bone grafts after tourniquet-induced ischemia

For successful revascularization, incorporation, and survival of fracture fragments or free nonpedicled 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.