Polyethylene Glycol (PEG)-Assisted Axonal Fusion in the Surgical Management of Brachial Plexus Injury: A Novel Clinical Methodology

Abstract

Background

Traumatic brachial plexus injury (BPI) often results in severe functional impairment due to the extensive distance required for axonal regeneration and the limited regenerative rate (∼1–3 mm/day). Traditional surgical strategies, including nerve grafts and transfers, often fail to deliver optimal outcomes, especially in pan-plexus or proximal injuries, due to delayed reinnervation and irreversible muscle atrophy.

Objective

This article develops and describes a novel surgical protocol integrating polyethylene glycol (PEG)-assisted axonal fusion with conventional nerve transfer techniques for improved functional recovery in patients with traumatic BPI.

Materials and Methods

This single-center, prospective clinical study enrolled adult patients with partial or complete traumatic BPI. After detailed neurological and radiological assessment, patients underwent nerve transfer procedures (e.g., spinal accessory nerve [SAN]–suprascapular nerve, SAN to musculocutaneous nerve [MCN] using sural nerve Oberlin, intercostal nerve–MCN), during which 50% PEG solution was applied at the coaptation site following the Bittner fusion sequence. Intraoperative steps included hypotonic and calcium-free saline preparation, methylene blue staining of nerve ends, PEG application, and final calcium-enhanced saline rinse. Patients were followed for 6 months with regular assessments of motor and sensory recovery, electromyography/nerve conduction studies, and patient-reported outcomes.

Outcomes

PEG-assisted fusion is hypothesized to prevent Wallerian degeneration, promote immediate axonal continuity, accelerate muscle reinnervation, and enhance both motor and sensory recovery compared to conventional methods alone.

Conclusion

This study introduces the first PEG-fusion protocol adapted for BPI repair in humans. By combining established microsurgical techniques with a biophysical approach to nerve continuity restoration, this methodology holds promise for improving recovery timelines and functional outcomes in BPI patients.

 

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Keywords

brachial plexus injury - polyethylene glycol - nerve fusion - axonal regeneration - nerve transfer - peripheral nerve repair

Introduction

Traumatic brachial plexus injuries (BPIs), often resulting from high-velocity motor vehicle accidents, falls, or penetrating trauma, remain one of the most debilitating peripheral nerve injuries. These result in partial or complete paralysis of the upper limb, with pan-plexus injuries involving roots C5–T1 leading to profound functional deficits and reduced quality of life.

Traditionally, surgical management relies on nerve transfers and grafting—such as spinal accessory nerve to suprascapular nerve (SAN-to-SSN) or Oberlin transfers—to bridge injured segments. However, axonal regeneration in humans proceeds at only approximately 1 to 3 mm per day, frequently insufficient to prevent target muscle atrophy in proximal injuries, thereby resulting in suboptimal recovery—even with prompt and technically flawless repair.

Polyethylene glycol (PEG) has recently emerged as an innovative adjunct in peripheral nerve repair, based on its capacity to fuse severed axonal membranes, potentially bypassing the need for long-distance axonal growth. Preclinical studies have consistently demonstrated that PEG-mediated fusion restores electrophysiological continuity across nerve transections, prevents Wallerian degeneration, preserves neuromuscular junctions, and enhances both histological and behavioral outcomes in animal models of sensory and motor nerve injury—including sciatic and digital nerves in rodents.[1]

Seminal work by Bittner and colleagues established a rigorous fusion protocol involving hypotonic, calcium-free washes, antioxidant (methylene blue) application to prevent axolemmal sealing, PEG application at the coaptation junction, and final calcium-enriched irrigation to seal residual membrane defects. This protocol enabled immediate conduction recovery in up to 75% of experimental animals when applied within minutes to hours posttransection.[2] [3]

Translational evidence in humans, though limited, is promising. A small case series involving digital nerve lacerations treated with PEG showed markedly accelerated sensory recovery, with significantly higher Medical Research Council classification to test sensory recovery (MRCC) scores at 1, 4, and 8 weeks (mean MRCC 2.8 vs. 1.0 at week 1, and 3.8 vs. 1.3 at week 4; p  =  0.01) compared to historical controls, without any adverse effects.[3] [4]

A recent narrative review highlights PEG fusion as a groundbreaking adjunct to microsurgical nerve repair, summarizing its mechanistic basis and emerging clinical relevance, while acknowledging the need for standardized human protocols and safety data.[2] [5]

This study applies a standardized PEG fusion protocol—replicating core elements from preclinical best practices—during nerve transfer surgeries (e.g., SAN-to-SSN, Oberlin procedures), combining conventional microsurgery with PEG at the coaptation site. This approach aims to test whether PEG-assisted fusion can enhance motor and sensory recovery timelines in traumatic BPI, compared to standard repair methods.

 

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Materials and Methods

Study Design

This is a single-center, prospective cohort study involving patients diagnosed with traumatic BPI (partial or complete). Ethical approval was obtained from the institutional ethics committee with number AIIMSA3142/07.02.2025, and written informed consent was acquired from all participants prior to inclusion in the study.

 

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Patient Selection

Inclusion Criteria

1. Adults aged between 18 and 55 years

2. Diagnosis of traumatic partial or pan-BPI

3. No previous surgical intervention for the current injury

4. Minimum 3 months' interval from the time of injury

 

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Exclusion Criteria

1. Patients with systemic illness that may impair healing (e.g., uncontrolled diabetes, malignancy)

2. Prior brachial plexus surgery

3. Congenital or nontraumatic brachial plexus lesions

4. Refusal to provide informed consent

 

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Preoperative Evaluation

All patients underwent a comprehensive preoperative assessment, including:

1. Neurological examination (motor grading via Medical Research Council grading for muscle power [MRC] scale, sensory assessment)

2. Imaging studies (magnetic resonance imaging of the cervical spine)

3. Blood investigations to ensure surgical fitness

Patients were evaluated and documented one day prior to surgery for baseline comparison postoperatively.

 

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Preparation of Surgical Reagents

All chemical reagents used in the surgical procedure were prepared in a sterile laminar flow hood under aseptic conditions.

• (1) PEG 50% w/w solution

  1. Prepared using medical-grade PEG 3350 Sigma-Aldrich dissolved in sterile distilled water.

  2. Final concentration: 50% w/w (10 g PEG dissolved in 10 mL water).

  3. Filtered using 0.2 µm sterile filters and subjected to ultraviolet (UV) sterilization for 30 minutes.

  4. Solution sent for the culture to check any microbial growth.

  5. Stored at 4°C in sterile vials until used.

• (2) Isotonic calcium-enhanced saline solution

  1. 10 mL of calcium gluconate was added to 500 mL of sterile 0.9% sodium chloride.

  2. Used for immersion and rinsing during transection and final irrigation.

  3. Maintained at room temperature in sterile containers.

• (3) Hypotonic saline

  1. Prepared by diluting 0.9% NaCl with sterile water to obtain 0.45% NaCl.

  2. Used during axonal end trimming to promote axoplasmic extrusion.

  3. Sterilized and stored in UV-exposed bottles.

• (4) Methylene blue

  1. 0.1% solution prepared from commercial methylene blue diluted with sterile saline.

  2. Applied as 1 to 2 drops to stain axonal ends and improve visualization under microscope.

All solutions were prepared fresh within 24 hours prior to the surgical procedure.

 

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Surgical Procedure

All surgeries were performed under general anesthesia with endotracheal intubation in a sterile operating room.

 

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Positioning and Exposure

1. The patient was placed in the supine or lateral decubitus position depending on the nerve transfer planned.

2. Sterile draping was done, and microscopic magnification was used throughout the procedure.

For SSN

SAN – SSN (via anterior or posterior approach) or phrenic nerve – SSN.

 

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For MCN

1. SAN – MCN using sural nerve graft or intercostal nerve – MCN or double Oberlin procedure (ulnar and median fascicles to MCN).

2. Sural nerve graft (length 15–20 cm) was harvested from the lower limb using a small linear incision technique under sterile conditions.

3. Nerve was identified and mobilized adequately for tension-free coaptation.

 

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PEG-Assisted Coaptation Protocol

1. The recipient nerve was completely transected under isotonic calcium-enhanced saline to prevent calcium influx that could trigger axonal sealing.

2. Axonal ends were trimmed under hypotonic saline, which causes swelling and extrusion of axoplasm, facilitating a cleaner edge for fusion.

3. Methylene blue (1–2 drops) was applied to highlight the severed axonal ends, enhancing visibility during coaptation.

4. Nerve coaptation was performed using 9–0 or 10–0 nylon epineurial sutures under the operating microscope in the presence of hypotonic saline.

5. After suturing, PEG 50% solution was applied gently at the coaptation site for 1 to 2 minutes. Care was taken to keep the site moist without washing off the polymer prematurely.

6. The repair site was then irrigated with isotonic calcium-enhanced saline to stabilize the axonal membranes and remove excess PEG.

7. Hemostasis ensured, and the wound was closed in layers with subcuticular and skin sutures.

 

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Postoperative Protocol

1. Limb was immobilized in a shoulder immobilizer or splint based on the procedure.

2. Analgesia and prophylactic antibiotics were administered.

3. Early initiation of physiotherapy and electrical muscle stimulation was begun from postoperative day 3.

 

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Postoperative Evaluation and Follow-Up

Follow-up evaluations were scheduled at:

1. Day 14 (at time of suture removal)

2. 1 month

3. 3 months

4. 6 months

Parameters assessed:

1. Motor function: MRC muscle grading

2. Sensory function by checking the dermatomes using the format attached in the supplementary sheet ([Supplementary Fig. S1], available in the online version )

3. Electrophysiology: Repeat electromyography and nerve conduction studies to detect early reinnervation

4. Functional assessment: Range of motion, grip strength, dexterity, and patient-reported outcomes

5. Documentation of pain, complications, wound healing, and any adverse reactions

 

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Expected Outcomes

The primary expected outcome is early restoration of motor and sensory function (time and extent of improvement) in nerves treated with PEG-assisted coaptation. PEG is anticipated to:

1. Prevent Wallerian degeneration

2. Promote immediate axonal fusion and continuity

3. Accelerate onset of target muscle reinnervation

4. Improve functional recovery timelines compared to conventional repair

Secondary outcomes include:

1. Wound infection

2. Lower postoperative neuropathic pain

3. Enhanced patient satisfaction

 

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Discussion

Traumatic BPIs present one of the most formidable challenges in peripheral nerve surgery, due to the prolonged distances required for axonal regeneration and subsequent risk of irreversible muscle atrophy. The classical paradigm of nerve repair—comprising nerve transfers and grafts—is inherently constrained by the slow pace of axonal regrowth (approximately 1–3 mm/day), leading to delayed reinnervation and suboptimal functional outcomes, particularly in proximal injuries.

Our proposed technique integrates ([Fig. 1]) PEG-assisted axonal fusion with established nerve transfer protocols (e.g., SAN-to-SSN, Oberlin procedures), aiming to restore axonal continuity at the moment of coaptation. This builds upon strong foundational principles: the underlying mechanism of PEG-induced membrane fusion across severed axons prevents Wallerian degeneration, preserves neuromuscular junctions, and facilitates immediate electrophysiological conduction across the repair site.[3] [6] [7] [8] [9]

Extensive animal model research has demonstrated that PEG-fusion dramatically improves structural and functional outcomes following nerve injury. Bittner and colleagues pioneered a protocol involving calcium-free washes, antioxidant application (e.g., methylene blue) [3], PEG application, and a final calcium-containing rinse. This sequence resulted in immediate restoration of compound action potentials across the injury site, retention of neuromuscular junctions, prevention of muscle atrophy, and accelerated behavioral recovery compared to neurorrhaphy alone.[3]

According to Davis et al (2012), a total of 13 studies were done on peripheral nerve injury using the animal model out of which 12 studies were done on rats and one was on guinea pig. Out of these 13 studies, 11 studies used PEG for treatment of the nerve and they conclude that majority of study reported positive outcome of using the PEG, which tell us that it is an effective method to enhance peripheral nerve regeneration after injury.[3]

Clinical translation of PEG fusion remains nascent but promising. The first human case series, involving digital nerve transections in two patients (four nerves), showed significantly higher MRCC sensory scores at 1 and 4 weeks compared to historical controls (week 1 mean MRCC score of 2.8 vs. 1.0; week 4, 3.8 vs. 1.3; p-values < 0.05).[4] [10]

More recently, a cohort involving mixed sensory-motor nerves (median and ulnar)—6 PEG patients versus 12 controls—showed superior sensory recovery at all intervals up to 1 year, and ultimately superior motor recovery at 12 months in the PEG group (p  <  0.001).[10]

Our operative approach closely mirrors the validated Bittner sequence: calcium-free and hypotonic saline preparation, methylene blue staining, precise microsurgical coaptation, PEG-50% application, and a calcium-enhanced saline rinse to stabilize fused membranes. The use of hypotonic saline facilitates axoplasmic extrusion and promotes cleaner nerve ends for fusion, aligning with preclinical observations that optimize fusion success.[3] [8] All the procedures previously performed did not include any BPI so it would be a novel protocol for repairing BPI that will help to recover the nerve 200 days prior as compare to normal surgery without PEG.

 

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Challenges

1. Ensuring precise timing and handling during coaptation

2. Standardization of PEG preparation and application technique

3. Risk of improper fusion if protocol steps are not strictly followed

Future directions include randomized controlled trials, larger sample sizes, and long-term evaluation of neuroplasticity and functional recovery with neuroimaging and advanced electrophysiological metrics.

 

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Conclusion

This study presents a novel, reproducible methodology for integrating PEG-assisted axonal fusion into the surgical management of BPIs. By combining established nerve transfer techniques with a biophysical approach to restore axonal integrity, this method holds promise in improving the timeline and quality of functional recovery in BPI patients. With further validation, PEG-mediated axonal repair could redefine the surgical standard for peripheral nerve injuries.

Fig. 1 Schematic representation of the polyethylene glycol (PEG)-assisted axonal fusion technique following peripheral nerve transection. The procedure begins with recording compound action potentials (CAPs) across the intact nerve to confirm baseline conduction (A), followed by sharp transection of the nerve (B). Both proximal and distal stumps are trimmed in hypotonic, calcium-free saline to expose fresh axonal ends and prevent calcium-mediated degeneration (C). A 1% solution of methylene blue (MB) is applied to each stump to stabilize membranes and inhibit vesicle formation (D), then rinsed with additional calcium-free saline (E). PEG (50% w/w) is applied at the coaptation site for 1–2 minutes to facilitate axonal membrane fusion (F), after which the site is irrigated with isotonic, calcium-containing saline to reseal and stabilize the fused membranes (G). Successful axonal fusion is confirmed by the restoration of CAP conduction across the lesion site (H).

 

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Conflict of Interest

None declared.

• References

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• 2 Sarac BA, Wordsworth M, Schmucker RW. Polyethylene glycol fusion and nerve repair success: practical applications. J Hand Surg Glob Online 2024; 6 (05) 740-742
• 3 Rippee DB, Glassman GE, Chaker SC. et al. Polyethylene glycol treatment for peripheral nerve repair in preclinical models. J Neurol Neuromedicine 2021; 6 (01) 21-25
• 4 Bamba R, Waitayawinyu T, Nookala R. et al. A novel therapy to promote axonal fusion in human digital nerves. J Trauma Acute Care Surg 2016; 81 (5 Suppl 2 Proceedings of the 2015 Military Health System Research Symposium): S177-S183
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• 6 Ghergherehchi CL, Mikesh M, Sengelaub DR. et al. Polyethylene glycol (PEG) and other bioactive solutions with neurorrhaphy for rapid and dramatic repair of peripheral nerve lesions by PEG-fusion. J Neurosci Methods 2019; 314: 1-12
• 7 Nemani S, Chaker S, Ismail H. et al. Polyethylene glycol-mediated axonal fusion promotes early sensory recovery after digital nerve injury: a randomized clinical trial. Plast Reconstr Surg 2024; 154 (06) 1247-1256
• 8 Paskal AM, Paskal W, Pietruski P, Wlodarski PK. Polyethylene glycol: the future of posttraumatic nerve repair? Systemic review. Int J Mol Sci 2019; 20 (06) 1478
• 9 Bittner GD, Mikesh M, Ghergherehchi CL. Polyethylene glycol-fusion retards Wallerian degeneration and rapidly restores behaviors lost after nerve severance. Neural Regen Res 2016; 11 (02) 217-219
• 10 Nemani SV, James AJ, Chaker SC, Torres-Guzman R, Yao J, Ismail H, Thayer W. Polyethylene-glycol assisted neurorrhaphy promotes superior functional recovery following injury of mixed nerves in the upper extremities. Plast Reconstr Surg Glob Open 2024; 12 (suppl 6) 6
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Publication History

Article published online:
23 September 2025