Wesley P. Thayer

Rapid, effective, and long‐lasting behavioral recovery produced by microsutures, methylene blue, and polyethylene glycol after completely cutting rat sciatic nerves

Behavioral function lost in mammals (including humans) after peripheral nerve severance is slowly (weeks to years) and often poorly restored by 1–2‐mm/day, nonspecifically directed outgrowths from proximal axonal stumps. To survive, proximal stumps must quickly repair (seal) plasmalemmal damage. We report that, after complete cut‐ or crush‐severance of rat sciatic nerves, morphological continuity, action potential conduction, and behavioral functions can be consistently (>98% of trials), rapidly (minutes to days), dramatically (70–85% recovery), and chronically restored and some Wallerian degeneration prevented. We assess axoplasmic and axolemmal continuity by intra‐axonal dye diffusion and action potential conduction across the lesion site and amount of behavioral recovery by Sciatic Functional Index and Foot Fault tests. We apply well‐specified sequences of solutions containing FDA‐approved chemicals. First, severed axonal ends are opened and resealing is prevented by hypotonic Ca2+‐free saline containing antioxidants (especially methylene blue) that inhibit plasmalemmal sealing in sciatic nerves in vivo, ex vivo, and in rat B104 hippocampal cells in vitro. Second, a hypotonic solution of polyethylene glycol (PEG) is applied to open closely apposed (by microsutures, if cut) axonal ends to induce their membranes to flow rapidly into each other (PEG‐fusion), consistent with data showing that PEG rapidly seals (PEG‐seals) transected neurites of B104 cells, independently of any known endogenous sealing mechanism. Third, Ca2+‐containing isotonic saline is applied to induce sealing of any remaining plasmalemmal holes by Ca2+‐induced accumulation and fusion of vesicles. These and other data suggest that PEG‐sealing is neuroprotective, and our PEG‐fusion protocols that repair cut‐ and crush‐severed rat nerves might rapidly translate to clinical procedures.

Hydrophilic polymers enhance early functional outcomes after nerve autografting.

BACKGROUND Approximately 12% of operations for traumatic neuropathy are for patients with segmental nerve loss, and less than 50% of these injuries obtain meaningful functional recovery. Polyethylene glycol (PEG) therapy has been shown to improve functional outcomes after nerve severance, and we hypothesized this therapy could also benefit nerve autografting. METHODS We used a segmental rat sciatic nerve injury model in which we repaired a 0.5-cm defect with an autograft using microsurgery. We treated experimental animals with solutions containing methylene blue (MB) and PEG; control animals did not receive PEG. We recorded compound action potentials (CAPs) before nerve transection, after solution therapy, and at 72 h postoperatively. The animals underwent behavioral testing at 24 and 72 h postoperatively. After we euthanized the animals, we fixed the nerves, sectioned and immunostained them to allow for quantitative morphometric analysis. RESULTS The introduction of hydrophilic polymers greatly improved morphological and functional recovery of rat sciatic axons at 1-3 d after nerve autografting. Polyethylene glycol therapy restored CAPs in all animals, and CAPs were still present 72 h postoperatively. No CAPS were detectable in control animals. Foot Fault asymmetry scores and sciatic functional index scores were significantly improved for PEG therapy group at all time points (P < 0.05 and P < 0.001; P < 0.001 and P < 0.01). Sensory and motor axon counts were increased distally in nerves treated with PEG compared with control (P = 0.019 and P = 0.003). CONCLUSIONS Polyethylene glycol therapy improves early physiologic function, behavioral outcomes, and distal axonal density after nerve autografting.

Polyethylene glycol‐fused allografts produce rapid behavioral recovery after ablation of sciatic nerve segments

Restoration of neuronal functions by outgrowths regenerating at ∼1 mm/day from the proximal stumps of severed peripheral nerves takes many weeks or months, if it occurs at all, especially after ablation of nerve segments. Distal segments of severed axons typically degenerate in 1–3 days. This study shows that Wallerian degeneration can be prevented or retarded, and lost behavioral function can be restored, following ablation of 0.5–1‐cm segments of rat sciatic nerves in host animals. This is achieved by using 0.8–1.1‐cm microsutured donor allografts treated with bioengineered solutions varying in ionic and polyethylene glycol (PEG) concentrations (modified PEG‐fusion procedure), being careful not to stretch any portion of donor or host sciatic nerves. The data show that PEG fusion permanently restores axonal continuity within minutes, as initially assessed by action potential conduction and intracellular diffusion of dye. Behavioral functions mediated by the sciatic nerve are largely restored within 2–4 weeks, as measured by the sciatic functional index. Increased restoration of sciatic behavioral functions after ablating 0.5–1‐cm segments is associated with greater numbers of viable myelinated axons within and distal to PEG‐fused allografts. Many such viable myelinated axons are almost certainly spared from Wallerian degeneration by PEG fusion. PEG fusion of donor allografts may produce a paradigm shift in the treatment of peripheral nerve injuries.

Lack of emergency hand surgery: discrepancy between elective and emergency hand care.

Wrist, hand, and finger trauma are the most common injuries presenting to emergency departments. Shortage of emergency hand care is an emerging problem, as on-call hand coverage declines. This study evaluates the availability of elective and emergency hand surgery services in Tennessee, with the use of telephone surveys administered to emergency department and operating facility management. One hundred eleven Tennessee hospitals completed the surveys (93% response rate). In all, 77% of hospitals offer elective hand surgery, 58% offer basic emergency hand services, 18% offer occasional hand specialist call coverage and only 7% of hospitals have 24/7 hand specialist call coverage. Hospitals with hand specialists have significantly more payer charges from commercial insurance than hospitals without hand specialists (26.1% vs. 16.1%, P < 0.001). Our results strongly support the need for increased emergency hand coverage. Solutions include creating multihospital coordinated call schedules, increasing incentives for call coverage, and training more hand specialists.

The curious ability of polyethylene glycol fusion technologies to restore lost behaviors after nerve severance

Traumatic injuries to PNS and CNS axons are not uncommon. Restoration of lost behaviors following severance of mammalian peripheral nerve axons (PNAs) relies on regeneration by slow outgrowths and is typically poor or nonexistent when after ablation or injuries close to the soma. Behavioral recovery after severing spinal tract axons (STAs) is poor because STAs do not naturally regenerate. Current techniques to enhance PNA and/or STA regeneration have had limited success and do not prevent the onset of Wallerian degeneration of severed distal segments. This Review describes the use of a recently developed polyethylene glycol (PEG) fusion technology combining concepts from biochemical engineering, cell biology, and clinical microsurgery. Within minutes after microsuturing carefully trimmed cut ends and applying a well‐specified sequence of solutions, PEG‐fused axons exhibit morphological continuity (assessed by intra‐axonal dye diffusion) and electrophysiological continuity (assessed by conduction of action potentials) across the lesion site. Wallerian degeneration of PEG‐fused PNAs is greatly reduced as measured by counts of sensory and/or motor axons and maintenance of axonal diameters and neuromuscular synapses. After PEG‐fusion repair, cut‐severed, crush‐severed, or ablated PNAs or crush‐severed STAs rapidly (within days to weeks), more completely, and permanently restore PNA‐ or STA‐mediated behaviors compared with nontreated or conventionally treated animals. PEG‐fusion success is enhanced or decreased by applying antioxidants or oxidants, trimming cut ends or stretching axons, and exposure to Ca2+‐free or Ca2+‐containing solutions, respectively. PEG‐fusion technology employs surgical techniques and chemicals already used by clinicians and has the potential to produce a paradigm shift in the treatment of traumatic injuries to PNAs and STAs.

4.7-T diffusion tensor imaging of acute traumatic peripheral nerve injury.

Diagnosis and management of peripheral nerve injury is complicated by the inability to assess microstructural features of injured nerve fibers via clinical examination and electrophysiology. Diffusion tensor imaging (DTI) has been shown to accurately detect nerve injury and regeneration in crush models of peripheral nerve injury, but no prior studies have been conducted on nerve transection, a surgical emergency that can lead to permanent weakness or paralysis. Acute sciatic nerve injuries were performed microsurgically to produce multiple grades of nerve transection in rats that were harvested 1 hour after surgery. High-resolution diffusion tensor images from ex vivo sciatic nerves were obtained using diffusion-weighted spin-echo acquisitions at 4.7 T. Fractional anisotropy was significantly reduced at the injury sites of transected rats compared with sham rats. Additionally, minor eigenvalues and radial diffusivity were profoundly elevated at all injury sites and were negatively correlated to the degree of injury. Diffusion tensor tractography showed discontinuities at all injury sites and significantly reduced continuous tract counts. These findings demonstrate that high-resolution DTI is a promising tool for acute diagnosis and grading of traumatic peripheral nerve injuries.

Outcomes of Short-Gap Sensory Nerve Injuries Reconstructed with Processed Nerve Allografts from a Multicenter Registry Study

BACKGROUND Short-gap digital nerve injuries are a common surgical problem, but the optimal treatment modality is unknown. A multicenter database was queried and analyzed to determine the outcomes of nerve gap reconstructions between 5 and 15 mm with processed nerve allograft. METHODS The current RANGER registry is designed to continuously monitor and compile injury, repair, safety, and outcomes data. Centers followed their own standard of care for treatment and follow-up. The database was queried for digital nerve injuries with a gap between 5 and 15 mm reporting sufficient follow-up data to complete outcomes analysis. Available quantitative outcome measures were reviewed and reported. Meaningful recovery was defined by the Medical Research Council Classification (MRCC) scale at S3-S4 for sensory function. RESULTS Sufficient follow-up data were available for 24 subjects (37 repairs) in the prescribed gap range. Mean age was 43 years (range, 23-81). Mean gap was 11 ± 3 (5-15) mm. Time to repair was 13 ± 42 (0-215) days. There were 25 lacerations, 8 avulsion/amputations, 2 gunshots, 1 crush injury, and 1 injury of unknown mechanism. Meaningful recovery, defined as S3-S4 on the MRCC scales, was reported in 92% of repairs. Sensory recovery of S3+ or S4 was observed in 84% of repairs. Static 2PD was 7.1 ± 2.9 mm (n = 19). Return to light touch was observed in 23 out of 32 repairs reporting Semmes-Weinstein monofilament outcomes (SWMF). There were no reported nerve adverse events. CONCLUSION Sensory outcomes for processed nerve allografts were equivalent to historical controls for nerve autograft and exceed those of conduit. Processed nerve allografts provide an effective solution for short-gap digital nerve reconstructions.

Effects of extracellular calcium and surgical techniques on restoration of axonal continuity by polyethylene glycol fusion following complete cut or crush severance of rat sciatic nerves.

Complete crush or cut severance of sciatic nerve axons in rats and other mammals produces immediate loss of axonal continuity. Loss of locomotor functions subserved by those axons is restored only after months, if ever, by outgrowths regenerating at ∼1 mm/day from the proximal stumps of severed axonal segments. The distal stump of a severed axon typically begins to degenerate in 1–3 days. We recently developed a polyethylene glycol (PEG) fusion technology, consisting of sequential exposure of severed axonal ends to hypotonic Ca2+‐free saline, methylene blue, PEG in distilled water, and finally Ca2+‐containing isotonic saline. This study examines factors that affect the PEG fusion restoration of axonal continuity within minutes, as measured by conduction of action potentials and diffusion of an intracellular fluorescent dye across the lesion site of rat sciatic nerves completely cut or crush severed in the midthigh. Also examined are factors that affect the longer‐term PEG fusion restoration of lost behavioral functions within days to weeks, as measured by the sciatic functional index. We report that exposure of cut‐severed axonal ends to Ca2+‐containing saline prior to PEG fusion and stretch/tension of proximal or distal axonal segments of cut‐severed axons decrease PEG fusion success. Conversely, trimming cut‐severed ends in Ca2+‐free saline just prior to PEG fusion increases PEG fusion success. PEG fusion prevents or retards the Wallerian degeneration of cut‐severed axons, as assessed by measures of axon diameter and G ratio. PEG fusion may produce a paradigm shift in the treatment of peripheral nerve injuries.

A novel technique using hydrophilic polymers to promote axonal fusion.

The management of traumatic peripheral nerve injury remains a considerable concern for clinicians. With minimal innovations in surgical technique and a limited number of specialists trained to treat peripheral nerve injury, outcomes of surgical intervention have been unpredictable. The inability to manipulate the pathophysiology of nerve injury (i.e., Wallerian degeneration) has left scientists and clinicians depending on the slow and lengthy process of axonal regeneration (~1 mm/day). When axons are severed, the endings undergo calcium-mediated plasmalemmal sealing, which limits the ability of the axon to be primarily repaired. Polythethylene glycol (PEG) in combination with a bioengineered process overcomes the inability to fuse axons. The mechanism for PEG axonal fusion is not clearly understood, but multiple studies have shown that a providing a calcium-free environment is essential to the process known as PEG fusion. The proposed mechanism is PEG-induced lipid bilayer fusion by removing the hydration barrier surrounding the axolemma and reducing the activation energy required for membrane fusion to occur. This review highlights PEG fusion, its past and current studies, and future directions in PEG fusion.

A novel therapy to promote axonal fusion in human digital nerves.

BACKGROUND Peripheral nerve injury can have a devastating impact on our military and veteran population. Current strategies for peripheral nerve repair include techniques such as nerve tubes, nerve grafts, tissue matrices, and nerve growth guides to enhance the number of regenerating axons. Even with such advanced techniques, it takes months to regain function. In animal models, polyethylene glycol (PEG) therapy has shown to improve both physiologic and behavioral outcomes after nerve transection by fusion of a portion of the proximal axons to the distal axon stumps. The objective of this study was to show the efficacy of PEG fusion in humans and to retrospectively compare PEG fusion to standard nerve repair. METHODS Patients with traumatic lacerations involving digital nerves were treated with PEG after standard microsurgical neurorrhaphy. Sensory assessment after injury was performed at 1 week, 2 weeks, 1 month, and 2 months using static two-point discrimination and Semmes-Weinstein monofilament testing. The Medical Research Council Classification (MRCC) for Sensory Recovery Scale was used to evaluate the level of injury. The PEG fusion group was compared to patient-matched controls whose data were retrospectively collected. RESULTS Four PEG fusions were performed on four nerve transections in two patients. Polyethylene glycol therapy improves functional outcomes and speed of nerve recovery in clinical setting assessed by average MRCC score in week 1 (2.8 vs 1.0, p = 0.03). At 4 weeks, MRCC remained superior in the PEG fusion group (3.8 vs 1.3, p = 0.01). At 8 weeks, there was improvement in both groups with the PEG fusion cohort remaining statistically better (4.0 vs 1.7, p = 0.01). CONCLUSION Polyethylene glycol fusion is a novel therapy for peripheral nerve repair with proven effectiveness in animal models. Clinical studies are still in early stages but have had encouraging results. Polyethylene glycol fusion is a potential revolutionary therapy in peripheral nerve repair but needs further investigation. LEVEL OF EVIDENCE Therapeutic study, level IV.