"Decreasing Postamputation Pain with the Regenerative Peripheral Nerve Interface (RPNI)"

Neuroma morphology: A macroscopic classification system

INTRODUCTION/AIMS

Neuromas come in different shapes and sizes; yet the correlation between neuroma morphology and symptomatology is unknown. Therefore, we aim to investigate macroscopic traits of excised human neuromas and assess the validity of a morphological classification system and its potential clinical implications.

METHODS

End-neuroma specimens were collected from prospectively enrolled patients undergoing symptomatic neuroma surgery. Protocolized images of the specimens were obtained intraoperatively. Pain data (Numeric rating scale, 0-10) were prospectively collected during preoperative interview, patient demographic and comorbidity factors were collected from chart review. A morphological classification is proposed, and the inter-rater reliability (IRR) was assessed. Distribution of neuroma morphology with patient factors, was described.

RESULTS

Forty-five terminal neuroma specimens from 27 patients were included. Residual limb patients comprised 93% of the population, of which 2 were upper (8.0%) and 23 (92.0%) were lower extremity residual limb patients. The proposed morphological classification, consisting of three groups (bulbous, fusiform, atypical), demonstrated a strong IRR (Cohen's kappa = 0.8). Atypical neuromas demonstrated higher preoperative pain, compared with bulbous and fusiform. Atypical morphology was more prevalent in patients with diabetes and peripheral vascular disease.

DISCUSSION

A validated morphological classification of neuroma is introduced. These findings may assist surgeons and researchers with better understanding of symptomatic neuroma development and their clinical implications. The potential relationship of neuroma morphology with the vascular and metabolic microenvironment requires further investigation.

Neuroma-to-Nerve Ratio: Does Size Matter?

BACKGROUND AND OBJECTIVES

Anatomic features of neuromas have been explored in imaging studies. However, there has been limited research into these features using resected, ex vivo human neuroma specimens. The aim of this study was to investigate the influence that time may have on neuroma growth and size, and the clinical significance of these parameters.

METHODS

Patients who underwent neuroma excision between 2022 through 2023 were prospectively included in this study. Neuroma specimens were obtained after operative resection. Standardized neuroma size measurements, expressed as a neuroma-to-nerve ratio (NNR), were conducted with ImageJ software. Pain data (numeric rating scale, 0-10) were prospectively recorded during preoperative evaluation, and patient factors were collected from chart reviews.

RESULTS

Fifty terminal neuroma specimens from 31 patients were included, with 94.0% of the neuromas obtained from individuals with amputations. Most neuromas were excised from the lower extremities (n = 44, 88.0%). The neuromas had a median NNR of 2.45, and the median injury to neuroma excision interval was 6.3 years. Larger NNRs were associated with a longer injury to neuroma excision interval and with a smaller native nerve diameter. In addition, sensory nerves were associated with a larger NNR compared with mixed nerves. NNR was not associated with preoperative pain or with anatomical nerve distribution.

CONCLUSION

This study suggests that neuromas seem to continue to grow over time and that smaller nerves may form relatively larger neuromas. In addition, sensory nerves develop relatively larger neuromas compared with mixed nerves. Neuroma size does not appear to correlate with pain severity. These findings may stimulate future research efforts and contribute to a better understanding of symptomatic neuroma development.

Comparison of 2 Regenerative Peripheral Nerve Interface Techniques for the Treatment of Rat Neuroma Pain

SUMMARY

Treatment of painful neuromas has long posed a significant challenge for peripheral nerve patients. The regenerative peripheral nerve interface (RPNI) provides the transected nerve with a muscle graft target to prevent neuroma formation. Discrepancies in RPNI surgical techniques between animal models ("inlay" RPNI) and clinical studies ("burrito" RPNI) preclude direct translation of results from bench to bedside and may account for variabilities in patient outcomes. The authors compared outcomes of these 2 surgical techniques in a rodent model. Animals treated with burrito RPNI after tibial nerve neuroma formation demonstrated no improvement in pain assessment, and tissue analysis revealed complete atrophy of the muscle graft with neuroma recurrence. By contrast, animals treated with inlay RPNI had significant improvement in pain with viable muscle grafts. The results suggest superiority of the inlay RPNI surgical technique for the management of painful neuroma in rodents.

CLINICAL RELEVANCE STATEMENT

RPNIs are currently being used to prevent and treat neuroma and phantom limb pain. This preclinical study suggests the superiority of one surgical technique over the other.

Biology and pathophysiology of symptomatic neuromas

ABSTRACT

Neuromas are a substantial cause of morbidity and reduction in quality of life. This is not only caused by a disruption in motor and sensory function from the underlying nerve injury but also by the debilitating effects of neuropathic pain resulting from symptomatic neuromas. A wide range of surgical and therapeutic modalities have been introduced to mitigate this pain. Nevertheless, no single treatment option has been successful in completely resolving the associated constellation of symptoms. While certain novel surgical techniques have shown promising results in reducing neuroma-derived and phantom limb pain, their effectiveness and the exact mechanism behind their pain-relieving capacities have not yet been defined. Furthermore, surgery has inherent risks, may not be suitable for many patients, and may yet still fail to relieve pain. Therefore, there remains a great clinical need for additional therapeutic modalities to further improve treatment for patients with devastating injuries that lead to symptomatic neuromas. However, the molecular mechanisms and genetic contributions behind the regulatory programs that drive neuroma formation-as well as the resulting neuropathic pain-remain incompletely understood. Here, we review the histopathological features of symptomatic neuromas, our current understanding of the mechanisms that favor neuroma formation, and the putative contributory signals and regulatory programs that facilitate somatic pain, including neurotrophic factors, neuroinflammatory peptides, cytokines, along with transient receptor potential, and ionotropic channels that suggest possible approaches and innovations to identify novel clinical therapeutics.

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.

Anatomic Anomalies of the Nerves Treated during Headache Surgery

Background

Headache surgery is a well-established, viable option for patients with chronic head pain/migraines refractory to conventional treatment modalities. These operations involve any number of seven primary nerves. In the occipital region, the surgical targets are the greater, lesser, and third occipital nerves. In the temporal region, they are the auriculotemporal and zygomaticotemporal nerves. In the forehead, the supraorbital and supratrochlear are targeted. The typical anatomic courses of these nerves are well established and documented in clinical and cadaveric studies. However, variations of this "typical" anatomy are quite common and relatively poorly understood. Headache surgeons should be aware of these common anomalies, as they may alter treatment in several meaningful ways.

Methods

In this article, we describe the experience of five established headache surgeons encompassing over 4000 cases with respect to the most common anomalies of the nerves typically addressed during headache surgery. Descriptions of anomalous nerve courses and suggestions for management are offered.

Results

Anomalies of all seven nerves addressed during headache operations occur with a frequency ranging from 2% to 50%, depending on anomaly type and nerve location. Variations of the temporal and occipital nerves are most common, whereas anomalies of the frontal nerves are relatively less common. Management includes broader dissection and/or transection of accessory injured nerves combined with strategies to reduce neuroma formation such as targeted reinnervation or regenerative peripheral nerve interfaces.

Conclusions

Understanding these myriad nerve anomalies is essential to any headache surgeon. Implications are relevant to preoperative planning, intraoperative dissection, and postoperative management.

Vascularized Denervated Muscle Targets for Headache Surgery-Presentation and Surgical Management

Patients with substantial trauma to their occipital nerves and those with recurrent or persistent chronic headaches after occipital nerve decompression surgery require transection of their greater occipital and/or lesser occipital nerves to control debilitating pain. Current techniques, such as burying the transected nerve stump in nearby muscle, do not prevent neuroma formation, and more advanced techniques, such as targeted muscle reinnervation and regenerative peripheral nerve interface, have demonstrated only short-term anecdotal success in the context of headache surgery. Vascularized denervated muscle targets (VDMTs) are a novel technique to address the proximal nerve stump after nerve transection that has shown promise to improve chronic nerve pain and prevent neuroma formation. However, VDMTs have not been described in the context of headache surgery. Here authors describe the etiology, workup, and surgical management of 2 patients with recurrent occipital neuralgia who developed vexing neuromas after previous surgery and were successfully treated with VDMTs, remaining pain-free at 3-year follow-up.

Forequarter Amputation: Reconstruction With Targeted Muscle Reinnervation to the Filet of Forearm Free Flap

Forequarter amputation is a rarely indicated operation that has the potential for delayed wound healing, chronic pain, and dysfunction. Reconstruction in cases of skin and soft tissue loss may be particularly challenging. Here we present a 79-year-old female with recurrent, previously radiated left shoulder chondrosarcoma who underwent forequarter amputation with a 'spare parts' filet of forearm flap and targeted muscle reinnervation to the flap. The patient healed without complication and achieved reinnervation with minimal pain.

The Use of Nerve Caps after Nerve Transection in Headache Surgery: Cadaver and Case Reports

Background

Nerve transection with nerve reconstruction is part of the treatment algorithm for patients with refractory pain after greater occipital nerve (GON) and lesser occipital nerve (LON) decompression or during primary decompression when severe nerve injury or neuroma formation is present. Importantly, the residual nerve stump is often best addressed via contemporary nerve reconstruction techniques to avoid recurrent pain. As a primary aim of this study, nerve capping is explored as a potential viable alternative that can be utilized in certain headache cases to mitigate pain.

Methods

The technical feasibility of nerve capping after GON/LON transection was evaluated in cadaver dissections and intraoperatively. Patient-reported outcomes in the 3- to 4-month period were compiled from clinic visits. At 1-year follow-up, subjective outcomes and Migraine Headache Index scores were tabulated.

Results

Two patients underwent nerve capping as a treatment for headaches refractory to medical therapy and surgical decompressions with significant improvement to total resolution of pain without postoperative complications. These improvements on pain frequency, intensity, and duration remained stable at a 1-year time point (Migraine Headache Index score reductions of -180 to -205).

Conclusions

Surgeons should be equipped to address the proximal nerve stump to prevent neuroma and neuropathic pain recurrence. Next to known contemporary nerve reconstruction techniques such as targeted muscle reinnervation/regenerative peripheral nerve interface and relocation nerve grafting, nerve capping is another viable method for surgeons to address the proximal nerve stump in settings of GON and LON pain. This option exhibits short operative time, requires only limited dissection, and yields significant clinical improvement in pain symptoms.

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.

The Peripheral Nerve Surgeon's Role in the Management of Neuropathic Pain

Neuropathic pain (NP) underlies significant morbidity and disability worldwide. Although pharmacologic and functional therapies attempt to address this issue, they remain incompletely effective for many patients. Peripheral nerve surgeons have a range of techniques for intervening on NP. The aim of this review is to enable practitioners to identify patients with NP who might benefit from surgical intervention. The workup for NP includes patient history and specific physical examination maneuvers, as well as imaging and diagnostic nerve blocks. Once diagnosed, there is a range of options surgeons can utilize based on specific causes of NP. These techniques include nerve decompression, nerve reconstruction, nerve ablative techniques, and implantable nerve-modulating devices. In addition, there is an emerging role for preoperative involvement of peripheral nerve surgeons for cases known to carry a high risk of inducing postoperative NP. Lastly, we describe the ongoing work that will enable surgeons to expand their armamentarium to better serve patients with NP.

Evolving techniques for reducing phantom limb pain

At least two million people in the United States of America live with lost limbs, and the number is expected to double by 2050, although the incidence of amputations is significantly greater in other parts of the world. Within days to weeks of the amputation, up to 90% of these individuals develop neuropathic pain, presenting as phantom limb pain (PLP). The pain level increases significantly within one year and remains chronic and severe for about 10%. Amputation-induced changes are considered to underlie the causation of PLP. Techniques applied to the central nervous system (CNS) and peripheral nervous system (PNS) are designed to reverse amputation-induced changes, thereby reducing/eliminating PLP. The primary treatment for PLP is the administration of pharmacological agents, some of which are considered but provide no more than short-term pain relief. Alternative techniques are also discussed, which provide only short-term pain relief. Changes induced by various cells and the factors they release are required to change neurons and their environment to reduce/eliminate PLP. It is concluded that novel techniques that utilize autologous platelet-rich plasma (PRP) may provide long-term PLP reduction/elimination.

A Technical Guide for Sciatic Nerve Targeted Muscle Reinnervation in a Transfemoral Amputee

There are approximately 2 million people living with the loss of a major limb in America. It is estimated that 95% of these will have some form of pain associated with their amputation. Phantom limb pain, related to symptomatic neuromas, contributes to amputation morbidity and can be difficult to treat. Studies have shown that targeted muscle reinnervation (TMR), by giving symptomatic neuromas “somewhere to go and something to do,” can be an effective therapy. However, a large proportion of surgeons still treat symptomatic neuromas by burying them in nearby tissue.

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.

RPNI, TMR, and Reset Neurectomy/Relocation Nerve Grafting after Nerve Transection in Headache Surgery

In the context of headache surgery, greater occipital nerve (GON) transection is performed when the nerve appears severely damaged, if symptoms are recurrent or persistent, and when neuromas are excised. Lesser occipital nerve (LON) excision is commonly performed during the primary decompression surgery. Advanced techniques to address the proximal nerve stump after nerve transection such as regenerative peripheral nerve interface (RPNI), targeted muscle reinnervation (TMR), relocation nerve grafting, and reset neurectomy have been shown to improve chronic pain and neuroma formation. These techniques have not been described in the head and neck region.