Cadaveric Nerve Allotransplantation in the Treatment of Persistent Thoracic Neuralgia

Management of Neuropathic Pain with Neurectomy Combined with Dermal Sensory Regenerative Peripheral Nerve Interface (DS-RPNI)

Neuropathic pain affects a large percentage of the U.S. population and leads to tremendous morbidity. Numerous nonsurgical and surgical treatments have been utilized to try and manage neuropathic pain with varying degrees of success. Recent research investigating ways to improve prosthetic control have identified new mechanisms for preventing neuromas in both motor and sensory nerves with free muscle and dermal grafts, respectively. These procedures have been used to treat chronic neuropathic pain in nonamputees, as well, in order to reduce failure rates found with traditional neurectomy procedures. Herein, we focus our attention on Dermal Sensory-Regenerative Peripheral Nerve Interfaces (DS-RPNI, free dermal grafts) which can be used to physiologically "cap" sensory nerves following neurectomy and have been shown to significantly decrease neuropathic pain.

Typical and atypical properties of peripheral nerve allografts enable novel strategies to repair segmental-loss injuries

We review data showing that peripheral nerve injuries (PNIs) that involve the loss of a nerve segment are the most common type of traumatic injury to nervous systems. Segmental-loss PNIs have a poor prognosis compared to other injuries, especially when one or more mixed motor/sensory nerves are involved and are typically the major source of disability associated with extremities that have sustained other injuries. Relatively little progress has been made, since the treatment of segmental loss PNIs with cable autografts that are currently the gold standard for repair has slow and incomplete (often non-existent) functional recovery. Viable peripheral nerve allografts (PNAs) to repair segmental-loss PNIs have not been experimentally or clinically useful due to their immunological rejection, Wallerian degeneration (WD) of anucleate donor graft and distal host axons, and slow regeneration of host axons, leading to delayed re-innervation and producing atrophy or degeneration of distal target tissues. However, two significant advances have recently been made using viable PNAs to repair segmental-loss PNIs: (1) hydrogel release of Treg cells that reduce the immunological response and (2) PEG-fusion of donor PNAs that reduce the immune response, reduce and/or suppress much WD, immediately restore axonal conduction across the donor graft and re-innervate many target tissues, and restore much voluntary behavioral functions within weeks, sometimes to levels approaching that of uninjured nerves. We review the rather sparse cellular/biochemical data for rejection of conventional PNAs and their acceptance following Treg hydrogel and PEG-fusion of PNAs, as well as cellular and systemic data for their acceptance and remarkable behavioral recovery in the absence of tissue matching or immune suppression. We also review typical and atypical characteristics of PNAs compared with other types of tissue or organ allografts, problems and potential solutions for PNA use and storage, clinical implications and commercial availability of PNAs, and future possibilities for PNAs to repair segmental-loss PNIs.

Cadaver Nerve Grafts: Past, Present and Future

Nerve grafts represent an invaluable tool, when reconstructing nerve defects of more than 1 cm. Historically, the criterion standard use of autografts has relied on the premise of using nonessential sensory nerves to fulfill the principle of replacing "like with like," while simultaneously minimizing the infliction of undue morbidity on the patient. The reconstructive surgeon thus faces a dilemma when extensive nerve damage requires reconstruction, or when donor nerves are not available or limited such as in the pediatric population. Cadaver nerve grafts (CNG) uniquely allow for reconstruction of large nerve lesions without the presence of host morbidity. The following article reviews the use of CNG, its indications, advantages, and disadvantages, as well as provides some case studies of real-world application. In addition, an insight into the future perspectives of CNG is provided.

Current State of the Surgical Treatment of Terminal Neuromas

Painful terminal neuromas resulting from nerve injury following amputation are common. However, there is currently no universally accepted gold standard of treatment for this condition. A comprehensive literature review is presented on the treatment of terminal neuromas. Four categories of terminal neuroma surgical procedures are assessed: epineurial closure; nerve transposition with implantation; neurorrhaphy, and alternate target reinnervation. Significant patient and case studies are highlighted in each section, focusing on surgical technique and patient outcome metrics. Studies presented consisted of a PubMed search for "terminal neuromas," without year limitation. The current available research supports the use of implantation into muscle for the surgical treatment of terminal neuromas. However, this technique has several fundamental flaws that limit its utility, as it does not address the underlying physiology behind neuroma formation. Regenerative peripheral nerve interfaces and targeted muscle reinnervation are 2 techniques that seem to offer the most promise in preventing and treating terminal neuroma formation. Both techniques are also capable of generating control signals which can be used for both motor and sensory prosthetic control. Such technology has the potential to lead to the future restoration of lost limb function in amputees. Further clinical research employing larger patient groups with high-quality control groups and reproducible outcome measures is needed to determine the most effective and beneficial surgical treatment for terminal neuromas. Primary focus should be placed on investigating techniques that most closely approximate the theoretically ideal neuroma treatment, including targeted muscle reinnervation and regenerative peripheral nerve interfaces.

Novel Uses of Nerve Transfers

Nerve transfer surgery involves using a working, functional nerve with an expendable or duplicated function as a donor to supply axons and restore function to an injured recipient nerve. Nerve transfers were originally popularized for the restoration of motor function in patients with peripheral nerve injuries. However, more recently, novel uses of nerve transfers have been described, including nerve transfers for sensory reinnervation, nerve transfers for spinal cord injury and stroke patients, supercharge end-to-side nerve transfers, and targeted muscle reinnervation for the prevention and treatment of postamputation neuroma pain. The uses for nerve transfers and the patient populations that can benefit from nerve transfer surgery continue to expand. Awareness about these novel uses of nerve transfers among the medical community is important in order to facilitate evaluation and treatment of these patients by peripheral nerve specialists. A lack of knowledge of these techniques continues to be a major barrier to more widespread implementation.

Nerve grafting for peripheral nerve injuries with extended defect sizes

Artificial and non-artificial nerve grafts are the gold standard in peripheral nerve reconstruction in cases with extensive loss of nerve tissue, particularly where a direct end-to-end suture or an autologous nerve graft is inauspicious. Different materials are marketed and approved by the US Food and Drug Administration (FDA) for peripheral nerve graft reconstruction. The most frequently used materials are collagen and poly(DL-lactide-ε-caprolactone). Only one human nerve allograft is listed for peripheral nerve reconstruction by the FDA. All marketed nerve grafts are able to demonstrate sufficient nerve regeneration over small distances not exceeding 3.0 cm. A key question in the field is whether nerve reconstruction on large defect lengths extending 4.0 cm or more is possible. This review gives a summary of current clinical and experimental approaches in peripheral nerve surgery using artificial and non-artificial nerve grafts in short and long distance nerve defects. Strategies to extend nerve graft lengths for long nerve defects, such as enhancing axonal regeneration, include the additional application of Schwann cells, mesenchymal stem cells or supporting co-factors like growth factors on defect sizes between 4.0 and 8.0 cm.

Characterization and Schwann Cell Seeding of up to 15.0 cm Long Spider Silk Nerve Conduits for Reconstruction of Peripheral Nerve Defects

Nerve reconstruction of extended nerve defect injuries still remains challenging with respect to therapeutic options. The gold standard in nerve surgery is the autologous nerve graft. Due to the limitation of adequate donor nerves, surgical alternatives are needed. Nerve grafts made out of either natural or artificial materials represent this alternative. Several biomaterials are being explored and preclinical and clinical applications are ongoing. Unfortunately, nerve conduits with successful enhancement of axonal regeneration for nerve defects measuring over 4.0 cm are sparse and no conduits are available for nerve defects extending to 10.0 cm. In this study, spider silk nerve conduits seeded with Schwann cells were investigated for in vitro regeneration on defects measuring 4.0 cm, 10.0 cm and 15.0 cm in length. Schwann cells (SCs) were isolated, cultured and purified. Cell purity was determined by immunofluorescence. Nerve grafts were constructed out of spider silk from Nephila edulis and decellularized ovine vessels. Finally, spider silk implants were seeded with purified Schwann cells. Cell attachment was observed within the first hour. After 7 and 21 days of culture, immunofluorescence for viability and determination of Schwann cell proliferation and migration throughout the conduits was performed. Analyses revealed that SCs maintained viable (>95%) throughout the conduits independent of construct length. SC proliferation on the spider silk was determined from day 7 to day 21 with a proliferation index of 49.42% arithmetically averaged over all conduits. This indicates that spider silk nerve conduits represent a favorable environment for SC attachment, proliferation and distribution over a distance of least 15.0 cm in vitro. Thus spider silk nerve implants are a highly adequate biomaterial for nerve reconstruction.