Novel technique for innervated abdominal wall vascularized composite allotransplantation: a separation of components approach.

Over the past 2 decades, vascularized composite tissue allotransplantation has been rapidly evolving. Successful reports of upper extremity,1 face,2 abdominal wall,3-6 trachea,7 larynx,8 and recently lower extremities9-10 indicate that vascularized composite tissue allotransplants (VCA) are both feasible and efficacious. The Abdominal Wall Vascularized Composite Allotransplant (AW-VCA) differs from the other VCAs in that it is currently only performed in conjunction with intestinal and/or multivisceral transplantation. In addition, it is the only nonfunctional composite tissue transplant routinely performed. Since the first description by Levi et al a decade ago, 2 groups (University of Miami and University of Bologna) have published their consecutive case series of abdominal wall transplantation. In total, they have published the results of 18 denervated AW-VCA in 17 patients.3-6 Despite overall good graft and patient survival, this intriguing technique does not seem to have gained widespread acceptance. We believe this is due to the paucity of intestinal transplantations performed (n = 129 in 2011 according to the Scientific Registry of Transplant Recipients database) and the lack of a broader indication for AW-VCA. We postulate the patient population that might benefit most from increased indications for abdominal wall transplantation without viscera or organ would be those people with massive “end-stage” hernias. Hernia disease burden in the United States is now epidemic and multifactorial in etiology. Patients with “end-stage” hernia disease, having total loss of domain with impaired biophysical and psychosocial function, represent a population with few viable options for the repair of the hernia and reconstruction of the abdominal wall. Because abdominal wall reconstruction is morbid, frequent, and often multirecurrent at initial presentation, there may finally be good reason and indication—in select patients—to consider a functional AW-VCA with immunosuppression for the reconstruction of massive composite defects. Expanding the indications for AW-VCA evokes the ethical questions of subjecting a patient to a lifetime of immunosuppression. To justify such a risk, the AW-VCA procedure must first improve the biomechanical function of the graft and also minimize the immunosuppressive needs. Abdominal wall surgeons have learned that bridged mesh repairs are less durable than primary closure with functional reconstruction of the anterior fascia. Primary closure is most commonly achieved through component separation technique (ie, external oblique layer fasciotomy with subsequent rectus abdominis muscle flap medial advancement). We note the rectus abdominis muscle flap is not simply vascularized but, more importantly, also remains innervated when returned to its midline position of function with physiologic tension. In the same sense, it stands to reason that any AW-VCA graft should also remain innervated after transplantation to improve its function. As studies look to improve the practicality of nerve transfers in other VCA models, the same must be continued for AW-VCA.11 The minimization of immunosuppression and induction of immune tolerance reported in VCA has made large strides in recent years. Directly transplanting hematopoietic stem cells has shown to decrease the immunosuppressive burden due to its chimeric effects on the recipient.12-13 Studies at our institution have shown that simply including vascularized bone marrow with a VCA also has a chimeric effect that may decrease the immunosuppression requirements otherwise needed.14 The presence of vascularized bone marrow has already shown promising results with single agent maintenance therapy in upper extremity reconstructions.15 This concept of marrow-derived chimerism and future immunosuppressive regimens could help expand the indication for all vascularized composite allotransplants including the idea of abdominal wall allotransplantation without simultaneous solid organ or multivisceral transplant. With the end-stage hernia patient in mind, drawing upon our large experience with component separation techniques, and improvement in VCA transplant biology, we now hypothesize that procurement of an innervated abdominal wall is technically feasible for allotransplantation. Our approach combines the concepts of functional hernia repair with the notion of innervated abdominal wall allotransplantation through preparation of the graft using a stepwise “multi-layered” component separation technique that carefully identifies individual segmental intercostal nerves beneath the internal oblique muscle. Secondarily, we hypothesize that an allograft can be designed with an osseous component to utilize the aforementioned immune-modulating chimerism effect.