Schwann cells seeded in acellular nerve grafts improve functional recovery.

INTRODUCTION: This study evaluated whether Schwann cells (SCs) from different nerve sources transplanted into cold-preserved acellular nerve grafts (CP-ANGs) would improve functional regeneration compared with nerve isografts. METHODS: SCs isolated and expanded from motor and sensory branches of rat femoral and sciatic nerves were seeded into 14mm CP-ANGs. Growth factor expression, axonal regeneration, and functional recovery were evaluated in a 14-mm rat sciatic injury model and compared with isografts. RESULTS: At 14 days, motor or sensory-derived SCs increased expression of growth factors in CP-ANGs versus isografts. After 42 days, histomorphometric analysis found CP-ANGs with SCs and isografts had similar numbers of regenerating nerve fibers. At 84 days, muscle force generation was similar for CP-ANGs with SCs and isografts. SC source did not affect nerve fiber counts or muscle force generation. CONCLUSIONS: SCs transplanted into CP-ANGs increase functional regeneration to isograft levels; however SC nerve source did not have an effect.

Costimulation blockade inhibits the indirect pathway of allorecognition in nerve allograft rejection.

Nerve allografts provide a temporary scaffold for host nerve regeneration. The need for systemic immunosuppression limits clinical application. Characterization of the immunological mechanisms that induce immune hyporesponsiveness may provide a basis for optimizing immunomodulating regimens. We utilized wild-type and MHC class II-deficient mice, as both recipients and donors. Host treatment consisted of triple costimulatory blockade. Quantitative assessment was made at 3 weeks using nerve histomorphometry, and muscle testing was performed on a subset of animals at 7 weeks. Nerve allograft rejection occurred as long as either the direct or indirect pathways were functional. Indirect antigen presentation appeared to be more important. Nerve allograft rejection occurs in the absence of a normal direct or indirect immune response but may be more dependent on indirect allorecognition. The indirect pathway is required to induce costimulatory blockade immune hyporesponsiveness.

Fibrin glue mitigates the learning curve of microneurosurgical repair.

Microneurosurgical technique has a steep learning curve. An alternative to microepineurial suture repair of peripheral nerves that circumvents this learning curve would be ideal. We investigated the effect of surgeon experience on suture versus fibrin glue coaptations in a mouse sciatic nerve graft model. Sixty-four mice received sciatic nerve grafts with either suture or fibrin glue repair by either a naïve surgeon (medical student) or a surgeon with extensive microsurgical experience. Grafts underwent quantitative histomorphometry at 3 weeks postoperatively. Suture repairs performed by the naïve surgeon demonstrated significantly poorer distal regeneration than all other repairs. Histomorphometric parameters of suture and glue repairs performed by the experienced surgeon were not significantly different from the glue coaptation by the naïve surgeon. Fibrin glue may be considered as an alternative to microepineurial suture repair, particularly in the setting of relative surgeon inexperience with microsurgical technique.

The motor nerve to the masseter muscle: an anatomic and histomorphometric study to facilitate its use in facial reanimation.

INTRODUCTION: The motor nerve to the masseter muscle is increasingly being used for facial reanimation procedures. However, many surgeons have been reluctant to use this versatile source of axons because of difficulty in locating it intraoperatively. In this study we conducted a detailed assessment of its gross and microscopic anatomy and develop a simple, reliable method for locating this nerve. METHODS: We defined the anatomy of the nerve to the masseter, in particular its relationship to common surgical landmarks such as the auricular tragus and the zygomatic arch, and determined its intramuscular anatomy. We also performed a histomorphometric analysis. RESULTS: The anatomy of the motor nerve to the masseter was consistent. A convenient starting point for its dissection was found 3.16 ± 0.30 cm anterior to the tragus at a level 1.08 ± 0.18 cm inferior to the zygomatic arch. The nerve was located 1.48 ± 0.19 cm deep to the superficial muscular aponeurotic system (SMAS) at this point. Relative to the zygomatic arch, the nerve formed an angle of 50 ± 7.6° as it coursed distally into the masseter muscle. The distance from the arch to the first branch of the motor nerve to the masseter was 1.33 ± 0.20 cm. The histomorphometric analysis demonstrated that the motor nerve to the masseter contained an average of 2775 ± 470 myelinated fibers. CONCLUSIONS: Successful intraoperative location of the motor nerve to the masseter is facilitated by knowledge of its anatomy relative to standard surgical landmarks. A consistent and convenient starting point for dissection of this nerve is found 3 cm anterior to the tragus and 1 cm inferior to the zygomatic arch. The nerve contains over 2700 myelinated fibers, demonstrating its usefulness as a source of motor innervation for facial reanimation.

A transgenic rat expressing green fluorescent protein (GFP) in peripheral nerves provides a new hindlimb model for the study of nerve injury and regeneration.

BACKGROUND: In order to evaluate nerve regeneration in clinically relevant hindlimb surgical paradigms not feasible in fluorescent mice models, we developed a rat that expresses green fluorescent protein (GFP) in neural tissue. METHODS: Transgenic Sprague-Dawley rat lines were created using pronuclear injection of a transgene expressing GFP under the control of the thy1 gene. Nerves were imaged under fluorescence microscopy and muscles were imaged with confocal microscopy to determine GFP expression following sciatic nerve crush, transection and direct suturing, and transection followed by repair with a nerve isograft from nonexpressing littermates. RESULTS: In each surgical paradigm, fluorescence microscopy demonstrated the loss and reappearance of fluorescence with regeneration of axons following injury. Nerve regeneration was confirmed with imaging of Wallerian degeneration followed by reinnervation of extensor digitorum longus (EDL) muscle motor endplates using confocal microscopy. CONCLUSION: The generation of a novel transgenic rat model expressing GFP in neural tissue allows in vivo imaging of nerve regeneration and visualization of motor endplate reinnervation. This rat provides a new model for studying peripheral nerve injury and regeneration over surgically relevant distances.

Imaging of Schwann cells in vivo.

The ability to examine cells tagged with fluorescent proteins in vivo has led to exciting advances in molecular neurobiology. The integral role of Schwann cells in nerve regeneration is well characterized, but not until recently has dynamic imaging of these critical cells been possible. Unlike many static techniques, in vivo imaging of Schwann cells tagged with green fluorescent protein (GFP) allows for serial imaging and may provide important insights into their role in peripheral nerve regeneration. In this chapter, we describe a protocol for in vivo imaging of SC migration into nonfluorescent nerve grafts using transgenic S100-GFP mice.

Effect of cold nerve allograft preservation on antigen presentation and rejection.

OBJECT: Nerve allotransplantation provides a temporary scaffold for host nerve regeneration and allows for the reconstruction of significant segmental nerve injuries. The need for systemic immunosuppression, however, limits the current clinical utilization of nerve allografts, although this need is reduced by the practice of cold nerve allograft preservation. Activation of T cells in response to alloantigen presentation occurs in the context of donor antigen presenting cells (direct pathway) or host antigen-presenting cells (indirect pathway). The relative role of each pathway in eliciting an alloimmune response and its potential for rejection of the nerve allograft model has not previously been investigated. The objective of this investigation was to study the effect of progressive periods of cold nerve allograft preservation on antigen presentation and the alloimmune response. METHODS: The authors used wild type C57Bl/6 (B6), BALB/c, and major histocompatibility Class II-deficient (MHC-/-) C57Bl/6 mice as both nerve allograft recipients and donors. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap. Progressive cold preservation of donor nerve allografts was used. Quantitative assessment was made after 3 weeks using nerve histomorphometry. RESULTS: The donor-recipient combination lacking a functional direct pathway (BALB/c host with MHC-/- graft) rejected nerve allografts as vigorously as wild-type animals. Without an intact indirect pathway (MHC-/- host with BALB/c graft), axonal regeneration was improved (p < 0.052). One week of cold allograft preservation did not improve regeneration to any significant degree in any of the donor-recipient combinations. Four weeks of cold preservation did improve regeneration significantly (p < 0.05) for all combinations compared with wild-type animals without pretreatment. However, only in the presence of an intact indirect pathway (no direct pathway) did 4 weeks of cold preservation improve regeneration significantly compared with 1 week and no preservation in the same donor-recipient combination. CONCLUSIONS: The indirect pathway may be the predominant route of antigen presentation in the unmodified host response to the nerve allograft. Prolonged duration of cold nerve allograft preservation is required to significantly attenuate the rejection response. Cold preservation for 4 weeks improves nerve regeneration with a significant effect on indirect allorecognition.

Simplified negative pressure wound therapy in pediatric hand wounds.

Negative pressure wound therapy (NPWT) is commonly used as a bolster for skin grafts. The technique offers the benefit of negative pressure as well as reduced dressing changes. Skin grafting of the hand provides a unique challenge, and currently, the only commercially available NPWT hand dressings are adult-sized, precluding their use in small children. We present our custom NPWT "mitten" technique for use with skin grafts on the pediatric hand.

Functional recovery following an end to side neurorrhaphy of the accessory nerve to the suprascapular nerve: case report.

UNLABELLED: The use of end-to-side neurrorhaphy remains a controversial topic in peripheral nerve surgery. The authors report the long-term functional outcome following a modified end-to-side motor reinnervation using the spinal accessory to innervate the suprascapular nerve following a C5 to C6 avulsion injury. Additionally, functional outcomes of an end-to-end neurotization of the triceps branch to the axillary nerve and double fascicular transfer of the ulnar and medial nerve to the biceps and brachialis are presented. Excellent functional recoveries are found in respect to shoulder abduction and flexion and elbow flexion. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11552-009-9242-3) contains supplementary material, which is available to authorized users.

Intraneural synovial sarcoma of the median nerve.

Synovial sarcomas are soft-tissue malignancies with a poor prognosis and propensity for distant metastases. Although originally believed to arise from the synovium, these tumors have been found to occur anywhere in the body. We report a rare case of synovial sarcoma arising from the median nerve. To our knowledge, this is the twelfth reported case of intraneural synovial sarcoma, and only the fourth arising from the median nerve. Because the diagnosis may not be apparent until after pathological examination of the surgical specimen, synovial sarcoma should be kept in mind when dealing with what may seem like a benign nerve tumor.

The role of T helper cell differentiation in promoting nerve allograft survival with costimulation blockade.

OBJECT: Peripheral nerve allografts provide a temporary scaffold for host nerve regeneration and allow for the repair of significant segmental nerve injuries. Despite this potential, nerve allograft transplantation requires temporary systemic immunosuppression. Characterization of the immunological mechanisms involved in the induction of immune hyporesponsiveness to prevent nerve allograft rejection will help provide a basis for optimizing immunomodulation regimens or manipulating donor nerve allografts to minimize or eliminate the need for global immunosuppression. METHODS: The authors used C57Bl/6 mice and STAT4 and STAT6 gene BALB/c knockout mice. A nonvascularized nerve allograft was used to reconstruct a 1-cm sciatic nerve gap in the murine model. A triple costimulatory blockade of the CD40, CD28/B7, and inducible costimulatory (ICOS) pathways was used. Quantitative assessment was performed at 3 weeks with nerve histomorphometry, walking track analysis, and the enzyme-linked immunospot assay. RESULTS: The STAT6 -/- mice received 3 doses of costimulation-blocking antibodies and had axonal regeneration equivalent to nerve isografts, while treated STAT4 -/- mice demonstrated moderate axonal regeneration but inferior to the T helper cell Type 2-deficient animals. Enzyme-linked immunospot assay analysis demonstrated a minimal immune response in both STAT4 -/- and STAT6 -/- mice treated with a costimulatory blockade. CONCLUSIONS: The authors' findings suggest that Type 1 T helper cells may play a more significant role in costimulatory blockade-induced immune hyporesponsiveness in the nerve allograft model, and that Type 2 T helper differentation may represent a potential target for directed immunosuppression.

Limitations of conduits in peripheral nerve repairs.

Nerve conduits have emerged as alternatives to autologous nerve grafts, but their use in large-diameter nerve deficits remains untested. We report four patients who underwent repair of large-diameter nerves using absorbable nerve conduits and discuss the failed clinical outcomes. The reported cases demonstrate the importance of evaluating the length, diameter, and function of nerves undergoing conduit repair. In large-diameter nerves, the use of conduits should be carefully considered.

Intramedullary capillary hemangioma of the thoracic spine: case report and review of the literature.

Capillary hemangiomas are benign vascular neoplasms. When associated with the spine, these growths frequently involve the vertebral body, but rarely have they been reported to occur as intradural lesions, while even more rarely occurring in a true intramedullary location. We report a rare case of an intramedullary capillary hemangioma of the thoracic spinal cord and a review of the literature.

Transcardial perfusion versus immersion fixation for assessment of peripheral nerve regeneration.

Accurate assessment of peripheral nerve regeneration requires fixation techniques that preserve tissue in a natural state with minimal artifact. While transcardial perfusion fixation is accepted as the gold standard for tissue fixation, the less cumbersome approach of immersion fixation has been criticized for introducing artifacts in brain tissue. We investigated whether immersion fixation increased artifact compared to perfusion fixation in the rat sciatic nerve. Eighteen Lewis rats were randomized into three groups: glutaraldehyde immersion fixation; glutaraldehyde transcardial perfusion; and paraformaldehyde transcardial perfusion. All animals underwent sciatic nerve transection and repair followed by tissue harvest and fixation at three weeks. Qualitative assessment of neural architecture and histological features was followed by quantitative analysis of nerve regeneration parameters. Outcome measures included quantitative histomorphometry, analysis of axon/myelin ratios, assessment of fiber distributions, and ultrastructural analysis. No qualitative or quantitative differences were observed with immersion fixation when compared to the transcardial perfusion fixation methods. Immersion fixation is a valid method for assessment of peripheral nerve regeneration in a rat model.