A new porcine vascularized tibial bone allotransplantation model. Anatomy and surgical technique.

INTRODUCTION: Vascularized bone allotransplantation may provide new options for reconstruction of segmental defects if problems of long-term immune modulation can be solved. The current literature lacks an orthotopic large animal model, limited to bone and without the confounding effects of other tissue types, permitting a multifaceted evaluation before new methods are used clinically. The purpose of this study was to develop a large animal model for vascularized bone allotransplantation.

MATERIALS AND METHODS: Eight porcine hind limbs were dissected. Length, diameter, and location of all hindlimb vessels were measured and a single nutrient vessel supplying the tibial diaphysis identified enabling its use as a vascularized bone allotransplant. Four Yucatan minipigs were divided into two pairs with a major swine leukocyte antigen mismatch. A 3.5 cm tibial segment including its nutrient pedicle was raised simultaneously from each pig and transplanted into the matched defect of the other animal. Microarterial anastomosis of the pedicle and 3-drug immunosuppression maintained VCA viability. Bone healing and limb function were followed for 16 weeks.

RESULTS: A consistent tibia diaphyseal nutrient artery arose from the caudal tibial artery to enter bone a mean 2.8 mm distal to the tibial tubercle with a pedicle length of 6.6 ± 3.3 mm and diameter of 1.6 ± 0.2 mm. Using this pedicle, we reconstructed a 3.5 cm tibial defect with a vascularized bone allotransplant in four animals. Immediate weightbearing as well as progressive bone healing was demonstrated.

CONCLUSION: We have developed a vascularized tibial bone allotranplantation large-animal model suitable for future bone-only allotranplantation research in mini-pigs.