Neovascularization of 2-mm Allograft Discs: A Preliminary Intravital Microscope Bone Chamber Study in the Rabbit

Autografts, because they are histocompatible, are the standard by which other bone grafts are judged. There is, however, increased morbidity for the patient from which large autografts, of limited supply in any case, must be obtained. In contrast, allografts are readily obtainable in large quantities and are used routinely in procedures for major limb salvage, trauma involving bone loss, and joint reconstruction. They have achieved sufficient success to warrant continued use, although a high incidence of nonunions, fatigue fractures, and occasional premature graft resorption suggest they are often poorly incorporated [3]. Of the two allograft materials, cancellous and cortical bone, the former shows a faster and more complete incorporation when donor and recipient are immuno- and histocompatible, as shown by Goldberg et al. [5]. Yet, they also display a higher incidence of histoincompatibility and cannot provide the immediate structural support required in some long bone procedures. Accordingly, cortical allografts with improved incorporability are viable alternatives to both autografts and cancellous allografts. The achievement of such improvement is enhanced with an understanding of cortical allograft incorporation in general and creeping substitution in particular. Because of the central role of neovascularization in all forms of healing, including that characteristic of graft incorporation, a study of neovascularization in cortical allografts was undertaken using the rabbit tibia implanted with an allograft-bearing bone chamber as its model. The goal of the subproject reported here was to test the hypothesis that the model yields data consistent with that of other cortical allograft models. An additional goal was to obtain the data in the form of quantitative measurements.