[Early revascularization of the reconstructed anterior cruciate ligament using a patellar tendon autograft]

Early revascularization of the reconstructed anterior cruciate ligament (ACL) using a patellar tendon autograft was investigated microangiographically and electron microscopically. In sixteen skeletally mature mongrel dogs, the ACL of the right knee was completely excised and tunnels through the tibia and femur were created at the insertion sites using a 3 mm Steinmann pin. The central portion of the patellar tendon (3 mm wide) was pulled through the holes and secured with sutures and buttons. The leg was immobilized with a plaster cast at 90 degrees of knee flexion until sacrifice. Eight dogs divided into four groups (two dogs each) were examined microangiographically at 1, 2, 3 and 4 weeks after the operation. Other eight dogs divided into four groups (two dogs each) were examined with an electron microscope at 3, 5, 7 and 14 days after the operation. The microangiographic study showed capillary buds invaded the graft from the bone tunnels and ran along the graft-bone interface at one week. Newly-formed capillaries were observed near the fat pad, but only at the surface of the graft. At two and three weeks, vascular sprouts anastomosed with each other, forming a network which extended internally into the graft. Although vascularity was present throughout the graft at four weeks, there was little in the midsubstance. The transmission electron microscopy (TEM) demonstrated that mesenchymal cells (undifferentiated fibroblasts) were in the process of migration to the graft in the area of the bone tunnels at five days. At seven days, these cells formed new vascular lumina and differentiated endothelial cells. At fourteen days, the newly-formed vessels had developed basement membrane. Some of mesenchymal cells appeared to differentiate into fibroblast. These results suggest that bone marrow plays an important role in revascularization and remodelling of the reconstructed graft.