Allograft ligament transplantation. A morphological and biochemical evaluation of a medial collateral ligament complex in a rabbit model

Our purpose in this investigation was to describe and compare several morphological, histological, vascular, and biochemical healing processes of allograft and autograft bone-medial collateral ligament-bone complexes in a rabbit model. Forty-nine animals had their right medial collateral ligament complex replaced with a frozen allograft while 30 separate control animals each received a fresh autograft. Animals were sacrificed at 3, 6, 12, 24, or 48 weeks after transplantation for comparison of grafted with unoperated contralateral control complexes. Results demonstrate some recovery of both allografts and autografts over time. Allografts generally showed slower recovery than autografts with more persistent abnormalities in gross appearances, increased cellularity (corresponding to increased DNA content), and decreased collagen content. Allografts also showed aggressive remodeling of bone at insertions and they remained hypervascular throughout their substance as compared with contralateral controls. Autografts went through similar but less chronic increases in cellularity and DNA concentration with no changes in collagen content. While both types of grafts showed some signs of "healing" and some recovery of control ligament biology, results are also consistent with allograft encasement, infiltration, and at least partial replacement by host tissue. This was particularly true of insertions. Collectively, these results also demonstrate some differences between allografts and autografts in this extraarticular model. The causes, mechanisms, and longer-term consequences of these changes, including defining the qualities of these graft and host tissues, clearly requires further investigation.