Limb transplantation is divided into replantation and allotransplantation. Replantation is the direct or indirect in replantation of a severed limb, whereas allotransplantation refers to the transplantation of limbs between individuals of different genotypes of the same species. Static cold storage (SCS) remains the gold standard for in vitro limb preservation. This hypothermic (0–4°C) storage method using ice packs is simple, cost-effective, and easy to implement. However, it is limited by a short preservation window of 4–6 hours, after which tissue viability and functional integrity decline.1,2 SCS also fails to preserve muscle architecture and strength, and induces cold ischemic injury, compromising long-term graft survival.3,4 Mechanical perfusion, though capable of relieving vasospasm and maintaining basic metabolism, still can not fully preserve tissue function and requires specialized equipment and protocols.4,5 Temporary intravascular shunting (TIVS) and temporary ectopic implantation offer alternative approaches, but both present significant challenges.6,7 IVS may cause toxin reflux and worsen the spread of infection in severely damaged patients.8 Temporary ectopic implantation helps in limb salvage under special circumstances but poses challenges in the second-stage replantation due to the increased risk of infection.7 Xenogeneic cross-circulation can initiate the self-repair mechanism of the limb by connecting it to the host’s circulation, promoting physiological function and tissue recovery, thereby prolonging the preservation time. However, it faces the critical challenge of immunological rejection.9 To safely and effectively improve the preservation and repair of severed limbs, the Microsurgery Branch of the Chinese Medical Association and the National Clinical Research Center for Orthopedics, Sports Medicine too low and it can compromise the delivery of nutrients and oxygen. Since perfusion pressure and tissue temperature interact dynamically, both must be carefully balanced to maintain the metabolic needs of the amputated limb (Grade 2A). Selection of the preservation solution for mechanical perfusion. An ideal mechanical perfusion fluid should mimic the physiological environment by delivering oxygen and nutrients, removing waste, and providing cytoprotective, anti-inflammatory, and antibacterial effects to extend preservation time. Commonly used solutions include UW solution, a high-potassium, high viscosity fluid that minimizes edema; HTK solution, which has a strong histidine buffer to reduce edema; and hemoglobin-based fluids, which use oxygen carriers to mimic erythrocyte function without the risks associated with blood perfusion (Grade 2A). TIVS Technique Indications and contraindications for TIVS. TIVS rapidly restores the blood supply to severed limbs by bridging a temporary vascular pathway through damaged vessels and decreases limb ischemia time. This technology is particularly useful in specialized settings for incomplete limb amputations or vascular injuries, especially those involving major limb vessels such as the brachial and popliteal arteries. Contraindications include severe shock, prolonged ischemia, and severely contaminated or damaged limbs (Grade 2B). Critical techniques for TIVS. The efficacy of TIVS is contingent upon the successful execution of several pivotal technical aspects. These include the selection of an appropriate shunting device, the implementation of efficacious anticoagulation strategies, thrombus removal, and the assurance of secure vessel fixation. These factors are of paramount importance for optimizing treatment outcomes and minimizing complications (Grade 1B). Temporary Ectopic Implantation Indications and complications of temporary ectopic implantation. Temporary ectopic implantation of a severed limb is an innovative procedure for salvaging the limb under special circumstances. Although this procedure is very demanding, it does deserve special consideration in reconstructive microsurgery because it offers the possibility of salvaging severed limbs with extensive soft tissue loss by preserving their anatomy and function. It is indicated for the treatment of severe trauma, hemodynamic instability, and segmental destruction of the limb. Temporary ectopic implantation represents an optimal treatment option for children with traumatic amputation of the upper extremity. The most common complications include infection at the recipient site, sepsis, and vascular injury at the recipient site (Grade 2B). Recipient sites for temporary ectopic implantation. Temporary ectopic implantation before subsequent replantation is an innovative and valuable surgical technique for patients who would otherwise be poor candidates for replantation. The recipient sites are selected at a distance from the injured area, always considering the availability and size of appropriate recipient vessels, and the safety of the surgical procedure. A contralateral healthy extremity is an ideal recipient site. The selection is based on the anatomy of the amputated limb and the donor site. For amputation injuries of the forearm and lower leg, temporary ectopic implantation on the medial side of the healthy lower leg is often chosen. For upper extremity amputations, the contralateral medial tibia or palmar distal forearm is often selected (Grade 2B). Critical techniques for temporary ectopic implantation. Preoperative planning for temporary ectopic implantation is of great benefit to the patient in terms of their recovery. Critical techniques such as bone fixation, anastomotic vascularization of the recipient area, and soft tissue coverage are important. Motor or sensory nerve anastomosis can address severed nerves and facilitate the restoration of sensory and neuromuscular functions. Anastomosing as many blood vessels as possible, with an arteriovenous ratio greater than 1:2, and preventing limb swelling, thrombosis, and vascular crises are the basis for ensuring limb survival and functional recovery. It is desirable to preserve healthy soft tissues as much as possible to increase coverage and avoid anastomotic infection. The optimal timing for reimplantation surgery is when the patient’s general condition has recovered, the ectopic implanted limb is viable, the stump wound is free of contamination, and the severed limb can be shortened and reimplanted or undergo tissue flap transplantation to rebuild the limb’s shape and function (Grade 2B). Xenogeneic Cross-Circulation Technology Critical technique of xenogeneic cross-circulation. Xenogeneic cross-circulation is a method of connecting the major arteries and veins of the severed limb to the host circulatory system based on extracorporeal membrane oxygenation (ECMO) and mechanical perfusion techniques. With the severed limb connected to the host’s circulatory system, recovery of physiological function and tissue injury may occur. The cross-circulation technique fully uses the self-repair mechanism of the limb and might represent a new technology for limb preservation in the future. This method is in the preclinical stage and has demonstrated promising applications. Mechanical perfusion in combination with xenogeneic cross-circulation technology integrates recent advancements in ECMO, genetic engineering, and transplantation immunology, and will bring about a revolutionary change in limb reimplantation and transplantation. In the xenogeneic cross-circulation system, the host animal can support the nutrient metabolism of the parasite limb by removing metabolic wastes through the liver and kidneys. ECMO can provide oxygen metabolism to the severed limb, prolonging the preservation time and enabling the limb to be repaired (Grade 3C). Conflicts of interest None.
Zhang et al. (Tue,) studied this question.