Regenerative Peripheral Nerve Interfaces for the Treatment and Prevention of Neuromas and Neuroma Pain

Regenerative Peripheral Nerve Interface Surgery for the Management of Chronic Posttraumatic Neuropathic Pain

Chronic pain resulting from peripheral nerve injury remains a common issue in the United States and affects 7 to 10% of the population. Regenerative Peripheral Nerve Interface (RPNI) surgery is an innovative surgical procedure designed to treat posttraumatic neuropathic pain, particularly when a symptomatic neuroma is present on clinical exam. RPNI surgery involves implantation of a transected peripheral nerve into an autologous free muscle graft to provide denervated targets to regenerating axons. RPNI surgery has been found in animal and human studies to be highly effective in addressing postamputation pain. While most studies have reported its uses in the amputation patient population for the treatment of neuroma and phantom limb pain, RPNI surgery has recently been used to address refractory headache, postmastectomy pain, and painful donor sites from the harvest of neurotized flaps. This review summarizes the current understanding of RPNI surgery for the treatment of chronic neuropathic pain.

Regenerative Peripheral Nerve Interfaces (RPNIs) in Animal Models and Their Applications: A Systematic Review

Regenerative Peripheral Nerve Interfaces (RPNIs) encompass neurotized muscle grafts employed for the purpose of amplifying peripheral nerve electrical signaling. The aim of this investigation was to undertake an analysis of the extant literature concerning animal models utilized in the context of RPNIs. A systematic review of the literature of RPNI techniques in animal models was performed in line with the PRISMA statement using the MEDLINE/PubMed and Embase databases from January 1970 to September 2023. Within the compilation of one hundred and four articles employing the RPNI technique, a subset of thirty-five were conducted using animal models across six distinct institutions. The majority (91%) of these studies were performed on murine models, while the remaining (9%) were conducted employing macaque models. The most frequently employed anatomical components in the construction of the RPNIs were the common peroneal nerve and the extensor digitorum longus (EDL) muscle. Through various histological techniques, robust neoangiogenesis and axonal regeneration were evidenced. Functionally, the RPNIs demonstrated the capability to discern, record, and amplify action potentials, a competence that exhibited commendable long-term stability. Different RPNI animal models have been replicated across different studies. Histological, neurophysiological, and functional analyses are summarized to be used in future studies.

Regenerative Peripheral Nerve Interface (RPNI) Surgery for Mitigation of Neuroma and Postamputation Pain

Background

A neuroma occurs when a regenerating transected peripheral nerve has no distal target to reinnervate. Symptomatic neuromas are a common cause of postamputation pain that can lead to substantial disability1-3. Regenerative peripheral nerve interface (RPNI) surgery may benefit patients through the use of free nonvascularized muscle grafts as physiologic targets for peripheral nerve reinnervation for mitigation of neuroma and postamputation pain.

Description

An RPNI is constructed by implanting the distal end of a transected peripheral nerve into a free nonvascularized skeletal muscle graft. The neuroma or free end of the affected nerve is identified, transected, and skeletonized. A free muscle graft is then harvested from the donor thigh or from the existing amputation site, and the distal end of each transected nerve is implanted into the center of the free muscle graft with use of 6-0 nonabsorbable suture. This can be done acutely at the time of amputation or as an elective procedure at any time postoperatively.

Alternatives

Nonsurgical treatments of neuromas include desensitization, chemical or anesthetic injections, biofeedback, transcutaneous electrical nerve stimulation, topical lidocaine, and/or other medications (e.g., antidepressants, anticonvulsants, and opioids). Surgical treatment of neuromas includes neuroma excision, nerve capping, excision with transposition into bone or muscle, nerve grafting, and targeted muscle reinnervation.

Rationale

Creation of an RPNI is a simple and reproducible surgical option to prevent neuroma formation that leverages several biologic processes and addresses many limitations of existing neuroma-treatment strategies. Given the understanding that neuromas will form when regenerating axons are not presented with end organs for reinnervation, any strategy that reduces the number of aimless axons within a residual limb should serve to reduce symptomatic neuromas. The use of free muscle grafts offers a vast supply of denervated muscle targets for regenerating nerve axons and facilitates the reestablishment of neuromuscular junctions without sacrificing denervation of any residual muscles.

Expected Outcomes

Articles describing RPNI surgery for postamputation pain have shown favorable outcomes, with significant reduction in neuroma pain and phantom pain scores at approximately 7 months postoperatively4,5. Neuroma pain scores were reduced by 71% and phantom pain scores were reduced by 53%4. Prophylactic RPNI surgery is also associated with substantially lower incidence of symptomatic neuromas (0% versus 13.3%) and a lower rate of phantom limb pain (51.1% versus 91.1%)5 compared with the rates in patients who did not undergo RPNI surgery.

Important Tips

Ask the patient preoperatively to point at the site of maximal tenderness, as this can serve as a guide for where the symptomatic neuroma may be located. The incision can be made either through the previous site of the amputation or directly over the site of maximal tenderness longitudinally. The pitfall of incising directly over the site is creating another incision with its attendant risk of wound infection.Excise the terminal neuroma with a knife until healthy-appearing axons are visualized.The free nonvascularized skeletal muscle graft can be obtained from local muscle (preferred) or from a separate donor site. A separate donor site can introduce donor-site morbidity and complications, including hematoma and pain.The harvested skeletal muscle graft should ideally be approximately 35 mm long, 20 mm wide, and 5 mm thick in order to ensure survivability and to prevent central necrosis. The harvesting can be performed with curved Mayo scissors.The peripheral nerve should be implanted parallel to the direction of the muscle fibers, and the epineurium should be secured to the free muscle graft at 1 or 2 places. One suture should be utilized to tack the distal end of the epineurium to the middle of the bed of the muscle graft. Another suture should be utilized to start the wrapping of the muscle graft around the nerve using a bite through the muscle, a bite through the epineurium of the proximal end of the nerve, and another bite through the other muscle edge in order to form a cylindrical wrap around the nerve.Wrap the entire muscle graft by taking only bites of muscle graft around the nerve to secure the muscle graft in a cylindrical structure using 2 to 4 more sutures.Avoid locating the RPNI near weight-bearing surfaces of the residual limb when closing. The RPNI should be in the muscular tissue, deep to the subcutaneous tissue and dermis.Do perform intraneural dissection for large-caliber nerves to create several (normally 2 to 4) distinct RPNIs, to avoid too many regenerating axons in a single free muscle graft.

A Direct Comparison of Targeted Muscle Reinnervation and Regenerative Peripheral Nerve Interfaces to Prevent Neuroma Pain

BACKGROUND AND OBJECTIVES

Targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) surgeries manage neuroma pain; however, there remains considerable discord regarding the best treatment strategy. We provide a direct comparison of TMR and RPNI surgery using a rodent model for the treatment of neuroma pain.

METHODS

The tibial nerve of 36 Fischer rats was transected and secured to the dermis to promote neuroma formation. Pain was assessed using mechanical stimulation at the neuroma site (direct pain) and von Frey analysis at the footpad (to assess tactile allodynia from collateral innervation). Once painful neuromas were detected 6 weeks later, animals were randomized to experimental groups: (a) TMR to the motor branch to biceps femoris, (b) RPNI with an extensor digitorum longus graft, (c) neuroma excision, and (d) neuroma in situ. The TMR/RPNIs were harvested to confirm muscle reinnervation, and the sensory ganglia and nerves were harvested to assess markers of regeneration, pain, and inflammation.

RESULTS

Ten weeks post-TMR/RPNI surgery, animals had decreased pain scores compared with controls ( P < .001) and they both demonstrated neuromuscular junction reinnervation. Compared with neuroma controls, immunohistochemistry showed that sensory neuronal cell bodies of TMR and RPNI showed a decrease in regeneration markers phosphorylated cyclic AMP receptor binding protein and activation transcription factor 3 and pain markers transient receptor potential vanilloid 1 and neuropeptide Y ( P < .05). The nerve and dorsal root ganglion maintained elevated Iba-1 expression in all cohorts.

CONCLUSION

RPNI and TMR improved pain scores after neuroma resection suggesting both may be clinically feasible techniques for improving outcomes for patients with nerve injuries or those undergoing amputation.

Post-traumatic radial nerve neuroma: A case report

Introduction

Radial nerve neuromas (RNNs) are mostly post-traumatic conditions that occur after a complete or partial section of a nerve. Here we report a case of post-traumatic RNN with good functional progression after intense physical rehabilitation.

Case presentation

A 49 years old patient with a post-complete section of the radial nerve underwent intensive physical rehabilitation with two sessions of ultrasound-guided injections of 10 % glucose saline around the neuroma. 12 months later, the patient improved his wrist and hand finger extension functions.

Conclusion

Several surgical and non-surgical therapies have been proposed for the treatment of neuromas. However, no consensus currently exists, and management is frequently adapted to each patient.

Regenerative Peripheral Nerve Interface Surgery: Anatomic and Technical Guide

Regenerative peripheral nerve interface (RPNI) surgery has been demonstrated to be an effective tool as an interface for neuroprosthetics. Additionally, it has been shown to be a reproducible and reliable strategy for the active treatment and for prevention of neuromas. The purpose of this article is to provide a comprehensive review of RPNI surgery to demonstrate its simplicity and empower reconstructive surgeons to add this to their armamentarium. This article discusses the basic science of neuroma formation and prevention, as well as the theory of RPNI. An anatomic review and discussion of surgical technique for each level of amputation and considerations for other etiologies of traumatic neuromas are included. Lastly, the authors discuss the future of RPNI surgery and compare this with other active techniques for the treatment of neuromas.

Regenerative Peripheral Nerve Interfaces Effectively Prevent Neuroma Formation After Sciatic Nerve Transection in Rats

Objective

The disordered growth of nerve stumps after amputation leading to the formation of neuromas is an important cause of postoperative pain in amputees. This severely affects the patients' quality of life. Regenerative peripheral nerve interfaces (RPNIs) are an emerging method for neuroma prevention, but its postoperative nerve growth and pathological changes are yet to be studied.

Methods

The rat sciatic nerve transection model was used to study the effectiveness of RPNI in this experiment. The RPNI (experimental) group (n = 11) underwent RPNI implantation after sciatic nerve transection, while the control group (n = 11) only underwent sciatic nerve transection. Autotomy behavior, ultrasonography, and histopathology were observed for 2 months postoperatively.

Results

Compared to the control group, the incidence and size of the neuromas formed and the incidence and extent of autotomy were significantly reduced in the RPNI group. The axon density in the stump and degree of stump fibrosis were also significantly reduced in the RPNI group.

Conclusion

RPNI effectively prevented the formation of neuromas.

Use of Vascularized, Denervated Muscle Targets for Prevention and Treatment of Upper-Extremity Neuromas

Purpose

Neuroma formation following upper-extremity peripheral nerve injury often results in persistent, debilitating neuropathic pain with a limited response to medical management. Vascularized, denervated muscle targets (VDMTs) offer a newly described surgical approach to address this challenging problem. Like targeted muscle reinnervation and regenerative peripheral nerve targets, VDMTs are used to redirect regenerating axons from an injured nerve into denervated muscle to prevent neuroma formation. By providing a vascularized muscle target that is reinnervated via direct neurotization, VDMTs offer some theoretical advantages in comparison with the other contemporary surgical options. In this study, we followed the short-term pain outcomes of patients who underwent VDMT surgery for neuroma prevention or treatment.

Methods

We performed a retrospective chart review of 9 patients (2 pediatric and 7 adult) who underwent VDMTs either for symptomatic upper-extremity neuromas or as a prophylactic measure to prevent primary neuroma formation. In-person and/or telephone interviews were conducted to assess their postoperative clinical outcomes, including the visual analog pain scale simple pain score.

Results

Of the 9 patients included in this study, 7 underwent VDMT surgery as a prophylactic measure against neuroma formation, and 2 presented with symptomatic neuromas that were treated with VDMTs. The average follow-up was 5.6 ± 4.1 months (range, 0.5-13.2 months). The average postoperative pain score of the 7 adult patients was 1.1 (range, 0-8).

Conclusions

This study demonstrated favorable short-term outcomes in a small cohort of patients treated with VDMTs in the upper extremity. Larger, prospective, and comparative studies with validated patient-reported and objective outcome measures and longer-term follow-ups are needed to further evaluate the benefits of VDMTs in upper-extremity neuroma management and prevention.

Type of study/level of evidence

Therapeutic III.

Pilot feasibility study of a simple regenerative peripheral nerve interface designed to diminish cutaneous dysesthesia after supraclavicular operations

Supraclavicular operations can be associated with postoperative cutaneous dysesthesia and hypersensitivity. Regenerative peripheral nerve interfaces, created by attaching the proximal end of a divided peripheral nerve into a viable muscle target, can promote neurite regrowth and neuromuscular connections to help suppress painful nerve hyperactivity. During 40 consecutive operations for neurogenic thoracic outlet syndrome, we demonstrated that division of at least one of the superficial supraclavicular cutaneous sensory nerve branches was necessary in 98% of cases. We subsequently developed a novel regenerative peripheral nerve interface for supraclavicular operations using the adjacent omohyoid muscle and have described the technical steps involved in this procedure.

Prophylactic Regenerative Peripheral Nerve Interfaces in Elective Lower Limb Amputations

Regenerative peripheral nerve interface (RPNI) is a relatively new surgical technique to manage neuromas and phantom pain after limb amputation. This study evaluates prophylactic RPNI efficacy in managing post-amputation pain and neuroma formation in amputees compared with patients in which lower limb amputation was performed without this procedure. We included 28 patients who underwent above the knee amputation (AKA) or below the knee amputation (BKA) for severe soft tissue infection from July 2019 till December 2020. All patients had insulin-dependent diabetes. The patients were divided into two groups, 14 patients with primary RPNI and 14 patients without. We analyzed the demographic data, level of amputation, number of RPNIs, operative time, postoperative complications and functional outcome on the defined follow up period. The mean patient age was 68.6 years (range 49-85), 19 (67.9 %) male and 9 (32.1 %) female patients. In this study 11 (39.3 %) AKA and 17 (60.7 %) BKA were performed. Overall, 37 RPNIs were made. The mean follow-up period was 49 weeks. PROMIS T-score decreased by 15.9 points in favor for the patients with RPNI. The VAS score showed that, in the RPNI group, all 14 patients were without pain compared to the group of patients without RPNI, where the 11 (78.6 %) patients described their pain as severe. Patients with RPNI used prosthesis significantly more (p < 0.005). Data showed significant reduction in pain and high patient satisfaction after amputation with RPNIs. This technique is oriented as to prevent neuroma formation with RPNI surgery, performed at the time of amputation. RPNI surgery did not provoke complications or significant lengthening of operative time and it should be furthermore exploited as a surgical technique.

Gellan-Xanthan Hydrogel Conduits with Intraluminal Electrospun Nanofibers as Physical, Chemical and Therapeutic Cues for Peripheral Nerve Repair

Optimal levels of functional recovery in peripheral nerve injuries remain elusive due to the architectural complexity of the neuronal environment. Commercial nerve repair conduits lack essential guidance cues for the regenerating axons. In this study, the regenerative potential of a biosimulated nerve repair system providing three types of regenerative cues was evaluated in a 10 mm sciatic nerve-gap model over 4 weeks. A thermo-ionically crosslinked gellan-xanthan hydrogel conduit loaded with electrospun PHBV-magnesium oleate-N-acetyl-cysteine (PHBV-MgOl-NAC) nanofibers was assessed for mechanical properties, nerve growth factor (NGF) release kinetics and PC12 viability. In vivo functional recovery was based on walking track analysis, gastrocnemius muscle mass and histological analysis. As an intraluminal filler, PHBV-MgOl-NAC nanofibers improved matrix resilience, deformation and fracture of the hydrogel conduit. NGF release was sustained over 4 weeks, governed by Fickian diffusion and Case-II relaxational release for the hollow conduit and the nanofiber-loaded conduit, respectively. The intraluminal fibers supported PC12 proliferation by 49% compared to the control, preserved up to 43% muscle mass and gradually improved functional recovery. The combined elements of physical guidance (nanofibrous scaffolding), chemical cues (N-acetyl-cysteine and magnesium oleate) and therapeutic cues (NGF and diclofenac sodium) offers a promising strategy for the regeneration of severed peripheral nerves.