Nerve regeneration in vascularized composite allotransplantation: current strategies and future directions

Vascularized composite allotransplantation (VCA) has emerged as a viable treatment option for limb and face reconstruction of severe tissue defects. Functional recovery after VCA requires not only effective immunosuppression, but also consideration of peripheral nerve regeneration to facilitate motor and sensory reinnervation of donor tissue. At the time of transplantation, the donor and recipient nerves are typically coapted in an end-to-end fashion. Following transplantation, there are no therapies available to enhance nerve regeneration and graft reinnervation, and functional outcomes are dependent on the recipients’ innate regenerative capacities. Functional outcomes to date have been promising, but there is still much room for improvement, studies have demonstrated reliable return of protective sensation (pain, thermal, gross tactile), while discriminative sensation and motor function show more inconsistent results. In order to maximize the benefit afforded to the by VCA, we must develop consistent and reliable procedures and therapies to ensure effective nerve regeneration and functional outcomes. New technologies, such as nerve guidance conduits and fibrin glues, and the use of stem cells to facilitate nerve regeneration remain untested in VCA but are proving worthwhile in the context of peripheral nerve repair. VCA presents a unique set of challenges with regards to surgical techniques, postoperative regimen, and health of donor tissue. In this review, we discuss current challenges underlying achievement of nerve regeneration in VCA and discuss novel technologies and approaches to translate nerve regeneration into functional restoration.