Neo‐Angiogenesis, Transplant Viability, and Molecular Analyses of Vascularized Bone Allotransplantation Surgery in a Large Animal Model

Abstract

Vascularized composite allotransplantation of bone is a possible alternative treatment for large osseous defects but requires life-long immunosuppression. Surgical induction of autogenous neo-angiogenic circulation maintains transplant viability without this requirement, providing encouraging results in small animal models [1][2][3]. A preliminary feasibility study in a swine tibia model demonstrated similar findings [4,5]. This study in swine tibial allotransplantation tests its applicability in a pre-clinical large animal model. Previously, we have demonstrated bone vascularized composite allotransplantation (VCA) survival was not the result of induction of tolerance nor an incompetent immune system [1]. Fourteen tibia vascularized bone allotransplants were microsurgically transplanted orthotopically to reconstruct size-matched tibial defects in Yucatan miniature swine. Two weeks of immunosuppression was used to maintain allotransplant pedicle patency during angiogenesis from a simultaneously implanted autogenous arteriovenous bundle. The implanted arteriovenous bundle was patent in group 1 and ligated in group 2 (a neo-angiogenesis control). At twenty weeks, we quantified the neo-angiogenesis and correlated it with transplant viability, bone remodeling, and gene expression. All patent arteriovenous bundles maintained patency throughout the survival period. Micro-angiographic, osteocyte cell count and bone remodeling parameters were significantly higher than controls due to the formation of a neo-angiogenic autogenous circulation. Analysis of gene expression found maintained osteoblastic and osteoclastic activity as well as a significant increase in expression of endothelial growth factor-like 6 (EGFL-6) in the patent arteriovenous bundle group. Vascularized composite allotransplants of swine tibia maintained viability and actively remodeled over 20 weeks when short-term immunosuppression is combined with simultaneous autogenous neoangiogenesis.

Methods of ex vivo analysis of tissue status in vascularized composite allografts

“…MicroCT (µCT) is an application of X-ray imaging with miniaturized hardware and enhanced resolution. The technology is commonly used to visualize vasculature in high resolution and has been used in ex vivo VCA, namely to visualize tissue perfusion and pressure-induced damage and to inform perfusion regimens during preservation [ 155 ]. While µCT imaging can measure surrogates of transplantation success, such as neo-vascularization, its utility in ex vivo VCA has not been thoroughly established.…”

An Inexpensive 3D Printed Mouse Model of Successful, Complication-free Long Bone Distraction Osteogenesis

“…Options, such as bone allograft and autograft, are fraught with limitations. 2,3 Distraction osteogenesis (DO) is an alternative limb-preserving treatment, first described in humans by Codivilla in 1905 4 and which later gained notoriety following work by Ilizarov in World War II. 4,5 DO is divided into three key steps: a latency period for callus development, a distraction period of gradual lengthening, and a consolidation period that allows the regenerate to mineralize.…”