Vascularized Limb Transplantation in the Rat

Using the rat model for vascularized orthotopic limb transplantation described elsewhere in this issue, 55 allogeneic grafts were studied. Composite musculoos-seous grafts were taken from Brown-Norway rats (Rt-1n); Fisher 344 rats (Rt-11) served as recipients. A group of 10 avascular allogeneic hind-limb grafts were performed as controls, but all recipients died of overwhelming sepsis within three weeks of the operation. Accordingly 10 avascular knee allografts were performed to serve as controls for the effects of vascularization. Initial vascular anastomotic patency of the allografts was comparable to that of syngeneic grafts. However, as rejection occurred, detected clinically by limb edema, flow progressively declined in the transplanted limbs, with eventual occlusion and fibrosis of the large blood vessels. Venous patency declined more rapidly than arterial patency. Bone scanning using 99m technetium methylene diphosphonate was a valuable tool for monitoring rejection of the grafts. Scan activity declined with rejection prior to occlusion of the major vessels feeding the grafts, and probably reflected the cessation of new bone formation early in the rejection process. Histologic examination revealed evidence of severe rejection, culminating in death of the epiphyseal cells, osteocytes, and, later, of articular chondrocytes. Vigorous alloantibody responses were detected both to vascularized and to nonvascularized allografts, but no major difference was seen between these two groups. The results indicate that allogeneic vascularized limb grafts can be followed easily with bone scans; that the loss of scan activity probably reflected rejection; that rejection involves cessation of new bone formation and eventual death of osteocytes; and that, despite severe rejection, the bone healing and joint function in the vascularized grafts improved relative to that observed in the avascular controls.