Heterotopic Hindlimb-to-Neck Transplantation in the Mouse: A Supermicrosurgical Model of Vascularized Composite Allotransplantation

Vascularized composite allotransplantation (VCA) is increasingly recognized as a reconstructive option that offers substantial benefits for patients with severe tissue loss, including injuries affecting the face and hand. Despite its clinical promise, VCA remains limited by surgical complexity, the need for long-term immunosuppression, and associated morbidity. Preclinical models are therefore essential for refining surgical techniques, testing novel immunomodulatory approaches, and investigating ischemia/reperfusion injury. Compared with large-animal models, rodent models offer advantages in accessibility and cost while adhering more closely to the 3Rs principles of Replacement, Reduction, and Refinement. Among them, the mouse offers unique advantages, including the availability of humanized strains, a broad panel of well-characterized antibodies, and compatibility with advanced immunological assays. These features make the mouse particularly valuable for translational VCA research. Murine VCA, however, requires demanding supermicrosurgical skills, as vascular anastomoses are performed on vessels measuring approximately 0.3-0.5 mm in diameter. To enhance reproducibility, we provide technical tips that have proven critical to the success of these procedures. These include the insertion of a nylon filament into the vessel lumen to stabilize the anastomosis, careful separation of the artery and vein over a sufficient distance along the pedicle, precise anesthetic dosing, and specific maneuvers to prevent pedicle twisting. We also highlight common pitfalls and errors, offering practical guidance to improve outcomes. Here, we describe a comprehensive, stepwise protocol for mouse heterotopic hindlimb-to-neck transplantation, accompanied by instructional video material. This non-functional model minimizes postoperative morbidity compared with orthotopic transplantation while providing robust and reproducible results. It is ideally suited for training in supermicrosurgery and for addressing key experimental questions in VCA, including immune tolerance, graft preservation, and ischemia/reperfusion mechanisms. This methodology provides investigators with a reliable murine platform to advance translational VCA research and to develop innovative strategies aimed at improving outcomes in reconstructive transplantation.