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Regenerative Peripheral Nerve Interface: Surgical Protocol for a Randomized Controlled Trial in Postamputation Pain

Emily Pettersen , Paolo Sassu , Francesca Alice Pedrini , Hannes Granberg , Carina Reinholdt , Juan Manuel Breyer , Aidan Roche , Andrew Hart , Adil Ladak , Hollie Power , Michael Leung , Michael Lo , Ian Valerio , Kyle R. Eberlin , Jason Ko , Gregory A. Dumanian , Theodore A. Kung , Paul S. Cederna , Max Ortiz-Catalan
Published: 2024

Surgical procedures, including nerve reconstruction and end-organ muscle reinnervation, have become more prominent in the prosthetic field over the past decade. Primarily developed to increase the functionality of prosthetic limbs, these surgical procedures have also been found to reduce postamputation neuropathic pain. Today, some of these procedures are performed more frequently for the management and prevention of postamputation pain than for prosthetic fitting, indicating a significant need for effective solutions to postamputation pain. One notable emerging procedure in this context is the Regenerative Peripheral Nerve Interface (RPNI). RPNI surgery involves an operative approach that entails splitting the nerve end longitudinally into its main fascicles and implanting these fascicles within free denervated and devascularized muscle grafts. The RPNI procedure takes a proactive stance in addressing freshly cut nerve endings, facilitating painful neuroma prevention and treatment by enabling the nerve to regenerate and innervate an end organ, i.e., the free muscle graft. Retrospective studies have shown RPNI’s effectiveness in alleviating postamputation pain and preventing the formation of painful neuromas. The increasing frequency of utilization of this approach has also given rise to variations in the technique. This article aims to provide a step-by-step description of the RPNI procedure, which will serve as the standardized procedure employed in an international, randomized controlled trial (, NCT05009394). In this trial, RPNI is compared to two other surgical procedures for postamputation pain management, specifically, Targeted Muscle Reinnervation (TMR) and neuroma excision coupled with intra-muscular transposition and burying.

Targeted Muscle Reinnervation: Surgical Protocol for a Randomized Controlled Trial in Postamputation Pain

Emily Pettersen , Paolo Sassu , Francesca Alice Pedrini , Hannes Granberg , Carina Reinholdt , Juan Manuel Breyer , Aidan Roche , Andrew Hart , Adil Ladak , Hollie Power , Michael Leung , Michael Lo , Ian Valerio , Kyle R. Eberlin , Theodore A. Kung , Paul S. Cederna , Jason M. Souza , Oskar Aszmann , Gregory A. Dumanian , Max Ortiz-Catalan
Published: 2024

Over the past decade, the field of prosthetics has witnessed significant progress, particularly in the development of surgical techniques to enhance the functionality of prosthetic limbs. Notably, novel surgical interventions have had an additional positive outcome, as individuals with amputations have reported neuropathic pain relief after undergoing such procedures. Subsequently, surgical techniques have gained increased prominence in the treatment of postamputation pain, including one such surgical advancement – targeted muscle reinnervation (TMR). TMR involves a surgical approach that reroutes severed nerves as a type of nerve transfer to “target” motor nerves and their accompanying motor end plates within nearby muscles. This technique originally aimed to create new myoelectric sites for amplified electromyography (EMG) signals to enhance prosthetic intuitive control. Subsequent work showed that TMR also could prevent the formation of painful neuromas as well as reduce postamputation neuropathic pain (e.g., Residual and Phantom Limb Pain). Indeed, multiple studies have demonstrated TMR’s effectiveness in mitigating postamputation pain as well as improving prosthetic functional outcomes. However, technical variations in the procedure have been identified as it is adopted by clinics worldwide. The purpose of this article is to provide a detailed step-by-step description of the TMR procedure, serving as the foundation for an international, randomized controlled trial (, NCT05009394), including nine clinics in seven countries. In this trial, TMR and two other surgical techniques for managing postamputation pain will be evaluated.

Improved control of a prosthetic limb by surgically creating electro-neuromuscular constructs with implanted electrodes

Jan Zbinden , Paolo Sassu , Enzo Mastinu , Eric J. Earley , Maria Munoz-Novoa , Rickard Brånemark , Max Ortiz-Catalan
Published: 2023

A prosthetic limb can restore some functionality after an amputation, and muscles remnant in the residual limb are often used to generate signals to control it. However, in high amputation levels, such as above-elbow, there are not enough muscles left to control all the many missing joints. In this study, we demonstrated that splitting the nerves severed by the amputation and rerouting them into remnant and free muscles grafts can increases the number of potential control signals. This surgical approach, in combination with our neuromusculoskeletal interface, allowed an individual with above-elbow amputation to control all five fingers of a prosthetic hand intuitively.

Surgical treatments for postamputation pain: study protocol for an international, double‑blind, randomised controlled trial

Emily Pettersen , Paolo Sassu , Carina Reinholdt , Peter Dahm , Ola Rolfson , Anders Björkman , Marco Innocenti , Francesca Alice Pedrini , Juan Manuel Breyer , Aidan Roche , Andrew Hart , Lorraine Harrington , Adil Ladak , Hollie Power , Jacqueline Hebert , Max Ortiz-Catalan
Published: 2023

Background: Painful conditions such as residual limb pain (RLP) and phantom limb pain (PLP) can manifest after amputation. The mechanisms underlying such postamputation pains are diverse and should be addressed accordingly. Different surgical treatment methods have shown potential for alleviating RLP due to neuroma formation — commonly known as neuroma pain — and to a lesser degree PLP. Two reconstructive surgical interventions, namely targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI), are gaining popularity in postamputation pain treatment with promising results. However, these two methods have not been directly compared in a randomised controlled trial (RCT). Here, we present a study protocol for an international, double-blind, RCT to assess the effectiveness of TMR, RPNI, and a non-reconstructive procedure called neuroma transposition (active control) in alleviating RLP, neuroma pain, and PLP. Methods: One hundred ten upper and lower limb amputees suffering from RLP will be recruited and assigned randomly to one of the surgical interventions (TMR, RPNI, or neuroma transposition) in an equal allocation ratio. Complete evaluations will be performed during a baseline period prior to the surgical intervention, and follow-ups will be conducted in short term (1, 3, 6, and 12 months post-surgery) and in long term (2 and 4 years post-surgery). After the 12-month follow-up, the study will be unblinded for the evaluator and the participants. If the participant is unsatisfied with the outcome of the treatment at that time, further treatment including one of the other procedures will be discussed in consultation with the clinical investigator at that site. Discussion: A double-blind RCT is necessary for the establishment of evidence-based procedures, hence the motivation for this work. In addition, studies on pain are challenging due to the subjectivity of the experience and the lack of objective evaluation methods. Here, we mitigate this problem by including different pain evaluation methods known to have clinical relevance. We plan to analyse the primary variable, mean change in NRS (0–10) between baseline and the 12-month follow-up, using the intention-to-treat (ITT) approach to minimise bias and keep the advantage of randomisation. The secondary outcomes will be analysed on both ITT and per-protocol (PP). An adherence protocol (PP population) analysis will be used for estimating a more realistic effect of treatment. Trial registration: NCT05009394.

Development and Validation of a Wearable Device to Provide Rich Somatosensory Stimulation for Rehabilitation After Sensorimotor Impairment

Mirka Buist , Shahrzad Damercheli , Minh Tat Nhat Truong , Alessio Sanna , Enzo Mastinu , Max Ortiz-Catalan
Published: 2023

We developed a medical sensory training device, the device can give a wide variaty of sensations to the skin. During validation tests, we showed that peoples’ capability to distinguish different sensations improved. This may allow us to reduce the pain and restore function in people with neurological diseases.

Non‑rectangular neurostimulation waveforms elicit varied sensation quality and perceptive fields on the hand

Riccardo Collu , Eric J. Earley , Massimo Barbaro , Max Ortiz-Catalan
Published: 2023

Electrical stimulation of the nerves is known to elicit distinct sensations perceived in distal parts of the body. The stimulation is typically modulated in current with charge-balanced rectangular shapes that, although easily generated by stimulators available on the market, are not able to cover the entire range of somatosensory experiences from daily life. In this regard, we have investigated the effect of electrical neurostimulation with four non-rectangular waveforms in an experiment involving 11 healthy able-bodied subjects. Weiss curves were estimated and rheobase and chronaxie values were obtained showing increases in stimulation time required to elicit sensations for some waveforms. The localization of the sensations reported in the hand also appeared to differ between waveforms, although the total area did not vary significantly. Finally, the possibility of distinguishing different charge- and amplitude-matched stimuli was demonstrated through a two-alternative-forced-choice (2AFC) match-to-sample task, showing the ability of participants to successfully distinguish between waveforms with similar electrical characteristics but different shapes and charge transfer rates. This study provides evidence that, by using different waveforms to stimulate nerves, it is possible to affect not only the required charge to elicit sensations but also the sensation quality and its localization.

Upper limb prostheses: bridging the sensory gap

Aidan D. Roche , Zachary K. Bailey , Michael Gonzalez , Philip P. Vu , Cynthia A. Chestek , Deanna H. Gates , Stephen W. P. Kemp , Paul S. Cederna , Max Ortiz-Catalan , Oskar Aszmann
Published: 2023

Replacing human hand function with prostheses goes far beyond only recreating muscle movement with feedforward motor control. Natural sensory feedback is pivotal for fine dexterous control and finding both engineering and surgical solutions to replace this complex biological function is imperative to achieve prosthetic hand function that matches the human hand. This review outlines the nature of the problems underlying sensory restitution, the engineering methods that attempt to address this deficit and the surgical techniques that have been developed to integrate advanced neural interfaces with biological systems. Currently, there is no single solution to restore sensory feedback. Rather, encouraging animal models and early human studies have demonstrated that some elements of sensation can be restored to improve prosthetic control. However, these techniques are limited to highly specialized institutions and much further work is required to reproduce the results achieved, with the goal of increasing availability of advanced closed loop prostheses that allow sensory feedback to inform more precise feedforward control movements and increase functionality.

Online Classification of Transient EMG Patterns for the Control of the Wrist and Hand in a Transradial Prosthesis

Daniele D’Accolti , Andrea Mannini , Enzo Mastinu , Max Ortiz-Catalan , Christian Cipriani
Published: 2023

Decoding human motor intentions by processing electrophysiological signals is a crucial, yet unsolved, challenge for the development of effective upper limb prostheses. Pattern recognition of continuous myoelectric (EMG) signals represents the state-of-art for multi-DoF prosthesis control. However, this approach relies on the unreliable assumption that repeatable muscular contractions produce repeatable patterns of steady-state EMGs. Here, we propose an approach for decoding wrist and hand movements by processing the signals associated with the onset of contraction (transient EMG). Specifically, we extend the concept of a transient EMG controller for the control of both wrist and hand, and tested it online. We assessed it with one transradial amputee and 15 non-amputees via the Target Achievement Control test. Non-amputees successfully completed 95% of the trials with a median completion time of 17 seconds, showing a significant learning trend (p < 0.001). The transradial amputee completed about the 80% of the trials with a median completion time of 26 seconds. Although the performance proved comparablewith earlier studies, the long completion times suggest that the current controller is not yet clinically viable. However, taken collectively, our outcomes reinforce earlier hypothesis that the transientEMGcould represent a viable alternative to steady-state pattern recognition approaches.

Mindful SensoriMotor Therapy combined with brain modulation for the treatment of pain in individuals with disarticulation or nerve injuries: a single-arm clinical trial

Shahrzad Damercheli , Mirka Buist , Max Ortiz-Catalan
Published: 2022

This article describes the protocol for Mindful SensoriMotor Therapy in combination with Brain Modulation. This therapy will be used for the treatment of pain in individuals with disarticulations or nerve injuries.

A multi‑dimensional framework for prosthetic embodiment: a perspective for translational research

Jan Zbinden , Eva Lendaro , Max Ortiz-Catalan
Published: 2022

Prosthetic embodiment is a complex phenomenon capturing how strongly a prosthesis is perceived to be part of our own body (ownership) and to what degree we are in control of the prosthesis (agency). We proposed a multi-dimensional framework to showcase that prosthetic embodiment depends heavily on which tasks a prosthesis is used for (degree of interaction with the environment) and which prosthetic technology is used to do so (more advanced prostheses offer more functionality and thus the basis for volition and multisensory input to be correctly integrated more frequently). This work provides the context required to better understand prosthetic embodiment research and thereby make its results more relevant and readily applicable to prosthetics outside the research laboratories.