The effect of surgical revascularization on the mechanical properties of cryopreserved bone allograft in a porcine tibia model

Abstract

Cryopreserved bone allografts(CBA) are susceptible to infection, nonunion, and late stress fracture. Although surgical revascularization by intramedullary implantation of an arteriovenous bundle (AV bundle) generates a neoangiogenic blood supply, there is potential for vascular ingrowth‐mediated bone resorption to weaken the graft. For this reason, we have evaluated changes in CBA mechanical properties of structural tibial allografts with and without surgically induced angiogenesis. Cryopreserved tibia bone allografts were transplanted to reconstruct a 3.5 cm segmental tibial defect in 16 Yucatan mini pigs. Surgical revascularization was performed in half by implantation of a cranial tibial AV bundle, (revascularization group). A control group of identical size had a ligated AV bundle implanted, (ligated group). At 20 weeks micro‐computed tomography (CT) measured bone mineral density (BMD) as well as bone union. Reference point indentation (RPI) compared cortex material properties, and axial compression determined the allotransplant compressive modulus. Seven of eight tibiae in the angiogenesis group were healed at both junction points at 20 weeks. Only four of eight tibiae healed in the ligated control group. There was no significant difference between the revascularization and ligated control groups in BMD and axial compression test. Similarly, RPI parameters were statistically equal. In paired comparisons with contralateral tibias, however, some RPI values were significantly worse in the ligated control group tibiae. This study demonstrates no adverse effect of surgical angiogenesis on cryopreserved structural bone allograft biomechanical properties in a large animal orthotopic segmental tibial defect model. These data suggest the potential value of surgical angiogenesis in clinical limb‐sparing reconstructive surgery.

Delayed Union and Nonunion: Current Concepts, Prevention, and Correction: A Review

“…While extensive discussion of bone grafting is outside of the scope for this review, we aim to highlight current advances and discussions related to bone graft treatments of surgical nonunions. To start, the topic of graft vascularization stems from a long-standing limitation of bone grafts, particularly allografts, in that the grafted bone lacks blood supply in the implantation site [ 120 , 121 ]. The majority of grafted bone will necrose, serving more signaling and scaffold functions than direct incorporation, and impaired vascularity or diminished osteoprogenitor cell populations at the implant site predispose the patient to graft failure or rejection [ 120 , 121 ].…”

“…To start, the topic of graft vascularization stems from a long-standing limitation of bone grafts, particularly allografts, in that the grafted bone lacks blood supply in the implantation site [ 120 , 121 ]. The majority of grafted bone will necrose, serving more signaling and scaffold functions than direct incorporation, and impaired vascularity or diminished osteoprogenitor cell populations at the implant site predispose the patient to graft failure or rejection [ 120 , 121 ]. The use of vascularized autografts involves careful preservation of the graft’s nutrient, metaphyseal, or other perforating vessel for anastomosis at the implant site.…”

“…Currently, the use of vascularized bone grafts is limited by donor site availability and graft viability during auto- or allotransplantation [ 120 ]. However, recently, Visser et al described a technique for the revascularization of cryopreserved bone allografts involving the surgical placement of the host cranial tibial arteriovenous bundle within the intramedullary canal of the donor tissue (porcine tibia model) [ 121 ]. The goal was to supply and utilize the vascular channels already present within the graft tissue to encourage direct revascularization and incorporation of the graft.…”

“…The goal was to supply and utilize the vascular channels already present within the graft tissue to encourage direct revascularization and incorporation of the graft. Seven of eight tibial defects treated with revascularized cryopreserved grafts healed within the 20-week experimental period, as compared to four of eight control defects treated with traditional cryopreserved grafts [ 121 ]. However, no differences in the bone mineral density or biomechanical characteristics were noted between the experimental and control bones, suggesting that, while revascularization does not seem to impair bone healing, it cannot be proven to enhance bone density or strength from this study alone [ 121 ].…”

“…Seven of eight tibial defects treated with revascularized cryopreserved grafts healed within the 20-week experimental period, as compared to four of eight control defects treated with traditional cryopreserved grafts [ 121 ]. However, no differences in the bone mineral density or biomechanical characteristics were noted between the experimental and control bones, suggesting that, while revascularization does not seem to impair bone healing, it cannot be proven to enhance bone density or strength from this study alone [ 121 ]. This theory of graft revascularization is a promising subject for future research and refinement, and may address limitations such as donor site morbidity, graft availability, and graft rejection.…”