Free Muscle Grafts Research Articles

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

Over 185,000 limb amputations are performed in the United States annually, many of which are due to the sequelae of peripheral vascular disease. Symptomatic neuromas remain a significant source of postamputation morbidity and contribute to both phantom limb (PLP) and residual limb pain (RLP). While many interventions have been proposed for the treatment of symptomatic neuromas, conventional methods lead to a high incidence of neuroma recurrence. Furthermore, these existing methods do not facilitate an ability to properly interface with myoelectric prosthetic devices. The Regenerative Peripheral Nerve Interface (RPNI) was developed to overcome these limitations. The RPNI consists of an autologous free muscle graft secured around the end of a transected nerve. The muscle graft provides regenerating axons with end organs to reinnervate, thereby preventing neuroma formation. We have shown that this simple, reproducible, and safe surgical technique successfully treats and prevents neuroma formation in major limb amputations. In this paper, we describe RPNI surgery in the setting of major limb amputation and highlight the promising results of RPNIs in our animal and clinical studies.

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

A neuroma occurs when a regenerating transected peripheral nerve has no distal target to reinnervate. This situation can result in a hypersensitive free nerve ending that causes debilitating pain to affected patients. No techniques to treat symptomatic neuromas have shown consistent results. One novel physiologic solution is the regenerative peripheral nerve interface (RPNI). RPNI consists of a transected peripheral nerve that is implanted into an autologous free skeletal muscle graft. Early clinical studies have shown promising results in the use of RPNIs to treat and prevent symptomatic neuromas. This review article describes the rationale behind the success of RPNIs and its clinical applications.

Physiologic signaling and viability of the muscle cuff regenerative peripheral nerve interface (MC-RPNI) for intact peripheral nerves

Background. Robotic exoskeleton devices have become a promising modality for restoration of extremity function in individuals with limb loss or functional weakness. However, there exists no consistent or reliable way to record efferent motor action potentials from intact peripheral nerves to control device movement. Peripheral nerve motor action potentials are similar in amplitude to that of background noise, producing an unfavorable signal-to-noise ratio (SNR) that makes these signals difficult to detect and interpret. To address this issue, we have developed the muscle cuff regenerative peripheral nerve interface (MC-RPNI), a construct consisting of a free skeletal muscle graft wrapped circumferentially around an intact peripheral nerve. Over time, the muscle graft regenerates, and the intact nerve undergoes collateral axonal sprouting to reinnervate the muscle. The MC-RPNI amplifies efferent motor action potentials by several magnitudes, thereby increasing the SNR, allowing for higher fidelity signaling and detection of motor intention. The goal of this study was to characterize the signaling capabilities and viability of the MC-RPNI over time. Methods. Thirty-seven rats were randomly assigned to one of five experimental groups (Groups A–E). For MC-RPNI animals, their contralateral extensor digitorum longus (EDL) muscle was harvested and trimmed to either 8 mm (Group A) or 13 mm (Group B) in length, wrapped circumferentially around the intact ipsilateral common peroneal (CP) nerve, secured, and allowed to heal for 3 months. Additionally, one 8 mm (Group C) and one 13 mm (Group D) length group had an epineurial window created in the CP nerve immediately preceding MC-RPNI creation. Group E consisted of sham surgery animals. At 3 months, electrophysiologic analyses were conducted to determine the signaling capabilities of the MC-RPNI. Additionally, electromyography and isometric force analyses were performed on the CP-innervated EDL to determine the effects of the MC-RPNI on end organ function. Following evaluation, the CP nerve, MC-RPNI, and ipsilateral EDL muscle were harvested for histomorphometric analysis. Results. Study endpoint analysis was performed at 3 months post-surgery. All rats displayed visible muscle contractions in both the MC-RPNI and EDL following proximal CP nerve stimulation. Compound muscle action potentials were recorded from the MC-RPNI following proximal CP nerve stimulation and ranged from 3.67 ± 0.58 mV to 6.04 ± 1.01 mV, providing efferent motor action potential amplification of 10–20 times that of a normal physiologic nerve action potential. Maximum tetanic isometric force (F o) testing of the distally-innervated EDL muscle in MC-RPNI groups produced F o (2341 ± 114 mN–2832 ± 102 mN) similar to controls (2497 ± 122 mN), thus demonstrating that creation of MC-RPNIs did not adversely impact the function of the distally-innervated EDL muscle. Overall, comparison between all MC-RPNI sub-groups did not reveal any statistically significant differences in signaling capabilities or negative effects on distal-innervated muscle function as compared to the control group. Conclusions. MC-RPNIs have the capability to provide efferent motor action potential amplification from intact nerves without adversely impacting distal muscle function. Neither the size of the muscle graft nor the presence of an epineurial window in the nerve had any significant impact on the ability of the MC-RPNI to amplify efferent motor action potentials from intact nerves. These results support the potential for the MC-RPNI to serve as a biologic nerve interface to control advanced exoskeleton devices.

2: Sensorimotor Myoelectric Control Using Surface Based Regenerative Peripheral Nerve Interface (RPNI)

Purpose:Although advanced prosthetic devices have the potential to allow fine-motor movements and extract somatosensory signals via sensitive pressure sensors, an ideal interface to integrate the human nervous system with the prosthetic doesn’t exist. Furthermore, the requirement for the implantation of indwelling electrodes and prohibitive costs limits the application of current technologies. The Regenerative Peripheral Nerve Interface (RPNI) was developed as a stable biologic interface on the notion of providing physiologic end-organ targets for regenerating axons by implantation of a residual nerve into an autogenous free muscle graft. Despite providing intuitive motor control, RPNI sensory feedback is limited and also relies on implantable electrodes for myoelectric signal transmission. To address these challenges, we investigated the placement of RPNIs underneath the defatted skin in rats to capture myoelectric signals using surface electrodes. This strategy simultaneously provides sensory feedback through the sensory reinnervation of the overlying skin.Methods:Utilizing six male F344 rats, the right tibial nerve was transected distally in the thigh before entering the leg’s posterior compartment. Subsequently, the left side extensor digitorum longus (EDL) muscle was harvested and co-apted with the proximal segment of the tibial nerve for RPNI fabrication. The RPNI was placed and secured in between the biceps femoris muscle near the skin while the side opposite to the nerve coaptation was facing the dermis. The overlying skin was defatted and fixed on top of the superficial RPNI (S-RPNI). At two months post-surgery, functional motor reinnervation was evaluated by electrical stimulation of the tibial nerve and compound muscle action potentials (CMAPs) were recorded using surface electrodes. Sensory feedback was assessed by electrical and mechanical stimulation of the skin to respectively record sensory nerve action potentials (SNAPs) and sensory afferent signals. The S-RPNI construct and its overlying skin were subsequently harvested and processed for immunohistochemistry and whole-mount immunostaining.Results:Recording muscle CMAPs from the skin was readily feasible in all animals, showing robust signals with minimal noise distortion (366 µV ± 86.3). Electrical stimulation of the skin on the lateral thigh, which is not innervated by the tibial nerve normally, resulted in classic tri-phasic SNAP generation in this nerve. Brushing the overlying skin using a cotton swab generated synchronized monomorphic afferent signals. Sensory reinnervation of the skin was shown using IHC. Whole-mount staining of the muscle component showed regenerated muscle with new neuromuscular junctions (NMJs) and spatial segregation of sensory fibers toward their end-target organ.Conclusion:Superficially placed RPNI is a viable and an alternate methodology that is simple to implicate and has the potential to transmit simultaneous, real-time, and independent sensory and motor signals between the residual nerve and the prostheses.

Transfer of the deep temporal nerve for eyelid reconstruction in Mobius syndrome – an anatomic feasibility study and proposed surgical approach

Facial paralysis may result in significant functional, esthetic, and psychological morbidity. Mobius syndrome is a form of bilateral congenital facial paralysis that is particularly difficult to treat owing to the lack of readily available donor nerves, particularly in the upper face. In this study, we evaluate the feasibility of using the deep temporal nerves as donors for the innervation of free muscle grafts in the periorbital region. Preserved and fresh cadaver facial halves are dissected, and the course of the deep temporal nerves delineated. We find the middle branch of the deep temporal nerve to be located consistently 4.6 cm from the posterior edge of the tragus along the zygomatic arch, giving an easily identifiable surface landmark for our donor. Finally, we outline a proposed surgical approach for using the middle deep temporal nerve to innervate a free muscle graft to the eyelids through an interpositional nerve graft.

Regenerative Peripheral Nerve Interfaces for Advanced Prosthetic Control and Mitigation of Postamputation Pain

While recent advances have occurred in the field of prosthetic technology, there is still a need for a neuroprosthetic interface that permits high-fidelity prosthetic control to accurately replicate extremity movements. Peripheral nerve interfaces offer more intuitive prosthetic control by harnessing neural signals at a fascicular level. The direct application of electrodes to peripheral nerves is limited by device encapsulation, micromotion, and inevitable neural damage. To overcome these challenges, the regenerative peripheral nerve interface (RPNI) has been developed as a promising solution to enhance prosthetic control. During RPNI surgery, the end of a transected peripheral nerve is implanted into an autologous free skeletal muscle graft. The RPNI has demonstrated feasibility in transducing peripheral nerve signals from patients with upper limb amputations to control an artificial hand. In addition, by leveraging the physiological processes of nerve regeneration, muscle regeneration, and reinnervation, RPNIs have been shown to reduce postamputation pain, including neuroma pain and phantom limb pain. It can be used as a treatment for symptomatic neuromas or performed prophylactically at the time of limb amputation to reduce or eliminate postamputation pain. RPNI surgery is a safe, reliable, and reproducible technique that can be easily adopted across a variety of surgical specialties. This article describes the development, validation, and clinical application of the RPNI and discusses the surgical technique.

The prevalence and distribution of the variants of pectoralis minor in cadaveric studies: A systematic review and meta-analysis of 32 observational studies

Introduction: Pectoralis minor (PMi) is used as a vascularized and innervated free-muscle graft in the reconstructive surgical procedure. The present review aims to provide insights to the surgeons regarding the variants of PMi in terms of costal attachment, insertion, nerve supply and arterial supply. Methodology: Three major databases (PubMed, EMBASE, and Google Scholar) were thoroughly searched along with the full text of journals. Results: Seven studies (n = 1787) were analysed for the evaluation of costal attachment. PMi arise from 3rd to 5th rib in 33% (95% confidence interval [CI], 30–37%), but the most common variants II-5 ribs was observed in 36%, which was higher than normal. Eighteen studies (n = 2424) reported details of insertion. The variant insertion of PMi was observed in 21% (15–28; 95% CI). Seven studies reported nerve supply. Both medial pectoral nerve (MPN) and lateral pectoral nerve (LPN) innervates PMi in 93% and MPN absent in 7%. Only two studies reported arterial supply. The PMi was vascularized by single dominant artery in 77% (68–85; 95% CI) or two arteries in 19% (13–29; 95% CI) or three arteries 2% (2–8; 95% CI) or even four arteries in 1% (0–7; 95% CI). Conclusion: PMi has a constant costal attachment to the 3rd and 4th ribs. Origin of PMi from 5th rib is reported with a pooled prevalence of 73.3% and from 2nd rib is reported in 61.5%. PMi inserts to the superomedial boundary of the coracoid process in 79% only.

Regenerative peripheral nerve interface free muscle graft mass and function.

Regenerative peripheral nerve interfaces (RPNIs) transduce neural signals to provide high-fidelity control of neuroprosthetic devices. Traditionally, rat RPNIs are constructed with ~150 mg of free skeletal muscle grafts. It is unknown whether larger free muscle grafts allow RPNIs to transduce greater signal. RPNIs were constructed by securing skeletal muscle grafts of various masses (150, 300, 600, or 1200 mg) to the divided peroneal nerve. In the control group, the peroneal nerve was transected without repair. Endpoint assessments were conducted 3 mo postoperatively. Compound muscle action potentials (CMAPs), maximum tetanic isometric force, and specific muscle force were significantly higher for both the 150 and 300 mg RPNI groups compared to the 600 and 1200 mg RPNIs. Larger RPNI muscle groups contained central areas lacking regenerated muscle fibers. Electrical signaling and tissue viability are optimal in smaller as opposed to larger RPNI constructs in a rat model.

TMRpni: Combining Two Peripheral Nerve Management Techniques.

Summary:Amputee patients suffer high rates of chronic neuropathic pain, residual limb dysfunction, and disability. Recently, targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) are 2 techniques that have been advocated for such patients, given their ability to maximize intuitive prosthetic function while also minimizing neuropathic pain, such as residual and phantom limb pain. However, there remains room to further improve outcomes for our residual limb patients and patients suffering from symptomatic end neuromas. “TMRpni” is a nerve management technique that leverages beneficial elements described for both TMR and RPNI. TMRpni involves coaptation of a sensory or mixed sensory/motor nerve to a nearby motor nerve branch (ie, a nerve transfer), as performed in traditional TMR surgeries. Additionally, the typically mismatched nerve coaptation is wrapped with an autologous free muscle graft that is akin to an RPNI. The authors herein describe the “TMRpni” technique and illustrate a case where this technique was employed.

Functioning Free Muscle Transfer for Brachial Plexus Injury: A Systematic Review and Pooled Analysis Comparing Functional Outcomes of Intercostal Nerve and Spinal Accessory Nerve Grafts.

The aim of this study was to compare postoperative elbow flexion outcomes in patients receiving functioning free muscle transplantation (FFMT) innervated by either intercostal nerve (ICN) or spinal accessory nerve (SAN) grafts. A comprehensive systematic review on FFMT for brachial plexus reconstruction was conducted utilizing Medline/PubMed database. Analysis was designed to compare functional outcomes between (1) nerve graft type (ICN vs. SAN) and (2) different free muscle graft types to biceps tendon (gracilis vs. rectus femoris vs. latissimus dorsi). A total of 312 FFMTs innervated by ICNs (169) or the SAN (143) are featured in 10 case series. The mean patient age was 28 years. Patients had a mean injury to surgery time of 31.5 months and an average follow-up time of 39.1 months with 18 patients lost to follow-up. Muscles utilized included the gracilis (275), rectus femoris (28), and latissimus dorsi (8). After excluding those lost to follow-up or failures due to vascular compromise, the mean success rates of FFMTs innervated by ICNs and SAN were 64.1 and 65.4%, respectively. This analysis did not identify any difference in outcomes between FFMTs via ICN grafts and those innervated by SAN grafts in restoring elbow flexion in traumatic brachial plexus injury patients.

Regenerative Peripheral Nerve Interfaces for the Management of Symptomatic Hand and Digital Neuromas.

Summary:Painful neuromas result from traumatic injuries of the hand and digits and cause substantial physical disability, psychological distress, and decreased quality of life among affected patients. The regenerative peripheral nerve interface (RPNI) is a novel surgical technique that involves implanting the divided end of a peripheral nerve into a free muscle graft for the purposes of mitigating neuroma formation and facilitating prosthetic limb control. The RPNI is effective in treating and preventing neuroma pain in major extremity amputations. The purpose of this study was to determine if RPNIs can be used to effectively treat neuroma pain following partial hand and digital amputations. We retrospectively reviewed the use of RPNI to treat symptomatic hand and digital neuromas at our institutions. Between November 2014 and July 2019, we performed 30 therapeutic RPNIs on 14 symptomatic neuroma patients. The average patient follow-up was 37 weeks (6–128 weeks); 85% of patients were pain-free or considerably improved at the last office visit. The RPNI can serve as a safe and effective surgical solution to treat symptomatic neuromas after hand trauma.

Abstract 100: Restoration Of Proprioceptive And Cutaneous Sensation Using Regenerative Peripheral Nerve Interfaces (RPNIs) In Humans With Upper-limb Amputations

Purpose: Without meaningful and intuitive sensory feedback, even the most advanced prosthetic devices remain insensate, burdensome, and are associated with enormous cognitive demand. To provide a bidirectional motor and sensory neural interface, we have developed the Regenerative Peripheral Nerve Interface (RPNI). An RPNI consists of a free muscle graft that is reinnervated by a transected peripheral nerve. In previous human studies, RPNI’s have demonstrated stable high amplitude motor EMG signals with high signal to noise ratio for prosthetic control, and have been used to treat and prevent neuroma pain. In this study, we investigate if applying electrical stimulation through the RPNIs can produce meaningful proprioceptive and/or tactile sensations in participants with upper-limb amputations. Materials and Methods: Two distal transradial participants underwent surgical implantation of RPNIs for treatment of neuroma pain. One RPNI was created on each of the median and ulnar nerve for participant 1, while participant 2 had two RPNIs created on the ulnar nerve and one on the median nerve. The RPNIs were stimulated with a monopolar, charge balanced, biphasic square wave using intramuscular bipolar electrodes. To determine the sensory perception threshold, a stepwise increment of 0.1 mA was used at a constant 20 Hz frequency and 200 µS pulse-width. Stimulation lasted for 1 to 2 seconds for each increment. After each increment, participants were asked to report the sensations they felt. Once a sensation was felt, the amplitude was decremented until the sensation stopped, and then increased until a sensation was felt again. Amplitudes were then marked as the perception threshold. After a threshold was determined, amplitudes were increased until participants could clearly perceive the sensation. Participants then reported the location of the sensation on their phantom limb using their contralateral intact hand, and a description of the invoked sensation. Results: Stimulation of the RPNIs resulted in both participants reporting proprioceptive sensations in their phantom limb. In particular, stimulation of the median nerve RPNI activated a flexing sensation in the thumb or index finger of participant 1, while stimulation of the ulnar nerve RPNI invoked a flexing sensation of the ring or small finger. Likewise, during stimulation of ulnar nerve RPNI 1, participant 2 felt a flexed sensation at the ring finger distal interphalangeal (DIP) joint, specifically describing that only the DIP joint was being flexed on the phantom ring finger. Stimulation of the ulnar nerve RPNI 2 and the median nerve RPNI resulted in cutaneous sensations that corresponded to the dermatome of their respective nerve. Sensory stimulation thresholds remained stable across 7 and 11 months with an average amplitude of 1.27 ± 0.52 mA for participant 2, and 0.98 ± 0.04 mA for participant 1, respectively. Conclusions: These results suggest that RPNIs have the potential to restore proprioceptive and skin-referred sensory feedback that could improve prosthesis motor performance, producing a stable bidirectional interface for advanced prosthesis control.

Fabrication of the Composite Regenerative Peripheral Nerve Interface (C-RPNI) in the Adult Rat.

Recent advances in neuroprosthetics have enabled those living with extremity loss to reproduce many functions native to the absent extremity, and this is often accomplished through integration with the peripheral nervous system. Unfortunately, methods currently employed are often associated with significant tissue damage which prevents prolonged use. Additionally, these devices often lack any meaningful degree of sensory feedback as their complex construction dampens any vibrations or other sensations a user may have previously depended on when using more simple prosthetics. The composite regenerative peripheral nerve interface (C-RPNI) was developed as a stable, biologic construct with the ability to amplify efferent motor nerve signals while providing simultaneous afferent sensory feedback. The C-RPNI consists of a segment of free dermal and muscle graft secured around a target mixed sensorimotor nerve, with preferential motor nerve reinnervation of the muscle graft and sensory nerve reinnervation of the dermal graft. In rats, this construct has demonstrated the generation of compound muscle action potentials (CMAPs), amplifying the target nerve's signal from the micro- to milli-volt level, with signal to noise ratios averaging approximately 30-50. Stimulation of the dermal component of the construct generates compound sensory nerve action potentials (CSNAPs) at the proximal nerve. As such, this construct has promising future utility towards the realization of the ideal, intuitive prosthetic.

Spontaneity Assessment in Dually Innervated Gracilis Smile Reanimation Surgery.

Surgeons have sought to optimize outcomes of smile reanimation surgery by combining inputs from nerve-to-masseter and cross-face nerve grafts. An objective assessment tool could help surgeons evaluate outcomes to determine the optimal neural sources for smile reanimation. To evaluate the use of a novel video time-stamping method and standard outcome measurement tools to assess outcomes of facial reanimation surgery using various innervation strategies. Cohort study assessing the outcomes of dually innervated gracilis free muscle transfers vs single-source innervated gracilis transfer performed at a tertiary care facial nerve center between 2007 and 2017 using a novel, video time-stamping spontaneity assessment method. The statistical analyses were performed in 2018. Dually innervated gracilis free muscle transfers or single-source innervated gracilis transfer. Spontaneous smiling was assessed by clinicians and quantified using blinded time-stamped video recordings of smiling elicited while viewing humorous video clips. This retrospective cohort study included 25 patients (12 men and 13 women; median [range] age, 38.4 [29.3-46.0] years) treated with dually innervated gracilis free functional muscle graft for unilateral facial palsy between 2007 and 2017. Smile spontaneity assessment was performed in 17 patients and was compared with assessment performed in 24 patients treated with single-source innervated gracilis transfer (ie, nerve-to-masseter-driven or cross-face nerve graft-driven gracilis [n = 13]) (demographic data not available for NTM and CFNG cohorts). The use of time-stamped video assessment revealed that spontaneous synchronous oral commissure movement in a median percentage of smiles was 33% in patients with dually innervated gracilis (interquartile range [IQR], 0%-71%), 20% of smiles in patients with nerve-to-masseter-driven gracilis (IQR, 0%-50%), and 75% of smiles in patients with cross-face nerve graft-driven gracilis (IQR, 0%-100%). Clinicians graded smile spontaneity in dually innervated cases as absent in 40% (n = 6 of 15), trace in 33% (n = 5 of 15) and present in 27% (n = 4 of 15). No association was demonstrated between clinician-reported spontaneity and objectively measured synchronicity. Dually innervated gracilis free muscle transfers may improve smile spontaneity compared with masseteric nerve-driven transfers but not to the level of cross-face nerve graft-driven gracilis transfers. Quantifying spontaneity is notoriously difficult, and most authors rely on clinical assessment. Our results suggest that clinicians may rate presence of spontaneity higher than objective measures, highlighting the importance of standardized assessment techniques. 4.

Prophylactic Regenerative Peripheral Nerve Interfaces to Prevent Postamputation Pain.

Postamputation pain affects a large number of individuals living with major limb loss. Regenerative peripheral nerve interfaces are constructs composed of a transected peripheral nerve implanted into an autologous free muscle graft. The authors have previously shown that regenerative peripheral nerve interfaces can be used to treat symptomatic end neuromas that develop after major limb amputation. In this study, they investigated the potential of prophylactic interfaces to prevent the formation of symptomatic neuromas and mitigate phantom limb pain. Patients who underwent limb amputation with and without prophylactic regenerative peripheral nerve interface implantation were identified. A retrospective review was performed to ascertain patient demographics, level of amputation, and postoperative complications. Documentation of symptomatic neuromas and phantom limb pain was noted. Postoperative outcomes were evaluated in a total of 90 patients. Forty-five patients underwent interface implantation at the time of primary amputation, and 45 control patients underwent amputation without interfaces. Six control patients (13.3 percent) developed symptomatic neuromas in the postoperative period compared with zero (0.0 percent) in the prophylactic interface group (p = 0.026). Twenty-three interface patients (51.1 percent) reported phantom limb pain, compared with 41 control patients (91.1 percent; p < 0.0001). Prophylactic regenerative peripheral nerve interfaces in major limb amputees resulted in a lower incidence of both symptomatic neuromas and phantom limb pain compared with control patients undergoing amputation without regenerative peripheral nerve interfaces, suggesting that prevention of peripheral neuromas following amputation may diminish the central pain mechanisms that lead to phantom limb pain. Therapeutic, III.

Abstract 36: Viability and Signal Transduction with the Composite Regenerative Peripheral Nerve Interface (C-RPNI)

PURPOSE: There have been many advancements in the field of neuroprosthetics for functional restoration following limb loss. However, devices that provide prosthetic users with intuitive, simultaneous motor control and somatosensory feedback have not yet been realized. Critical to the evolution of this ideal bioprosthetic device is the development of a reliable, biologic human-machine interface that facilitates transmission of both efferent motor signals for device control, and afferent somatosensory information. The Composite Regenerative Peripheral Nerve Interface (C-RPNI) is a novel biologic interface that demonstrates promise in this role. The C-RPNI is a surgical construct composed of a transected, mixed peripheral nerve implanted between a composite free graft consisting of de-epithelialized glaborous skin and skeletal muscle. The purpose of the present study was to investigate the viability and bidirectional signal transduction capabilities of the C-RPNI. METHODS: C-RPNIs were surgically implanted on the end of transected common peroneal nerves of thirty F344 rats using de-epithelialized dermal grafts harvested from glaborous skin of isogenic donor rat hindpaws and free skeletal muscle grafts from the animal’s contralateral limb. Thirty animals underwent endpoint testing at three months (n=15) and at six months (n=15). Electrophysiologic testing was performed to determine both the in vivo efferent and afferent signal transduction capabilities of C-RPNIs following electrical stimulation. C-RPNI constructs were also harvested for histologic evaluation at both three- and six-month study endpoints. RESULTS: C-RPNI constructs remained viable over the study period with regeneration and revascularization evident on histologic analysis. At both three and six months, electrical stimulation of proximal peroneal nerve evoked efferent signals (CMAPs) and muscle contractions that were measured from the free muscle graft component of the C-RPNI. The average CMAP amplitude recorded from the muscle was 6.3 ± 1.4 mV at three months and 6.1 ± 1.6 mV at six months. The average conduction velocity was 11.0 ± 2.7 m/sec at three months and 12.0 ± 2.0m/sec at six months. Electrical stimulation of the dermal side of the C-RPNI evoked afferent signals (CSNAPs) in the proximal peroneal nerve at both three and sixth months. The average peak-to-peak CSNAP amplitude was 391.6 ± 145.0 µV at three months and 267.1 ± 143.8 µV at six months. The average conduction velocity with an average conduction velocity was 11.6 ± 3.0 m/sec at three months and 9.6 ± 2.4 m/sec at six months. CONCLUSIONS: C-RPNI constructs remained viable with preserved innervation for six months following implantation. Recorded efferent motor signals and evoked afferent signals remained robust over time. The C-RPNI facilitates bidirectional signal transduction of both efferent motor signals and afferent sensory signals. This confirmation of bidirectional signal transduction in the C-RPNI validates the potential role of the C-RPNI in human-machine interfacing.

Polyimide Electrode-Based Electrical Stimulation Impedes Early Stage Muscle Graft Regeneration.

Given the increasing use of regenerative free muscle flaps for various reconstructive procedures and neuroprosthetic applications, there is great interest and value in their enhanced regeneration, revascularization, and reinnervation for improved functional recovery. Here, we implant polyimide-based mircroelectrodes on free flap grafts and perform electrical stimulation for 6 weeks in a murine model. Using electrophysiological and histological assessments, we compare outcomes of stimulated grafts with unstimulated control grafts. We find delayed reinnervation and abnormal electromyographic (EMG) signals, with significantly more polyphasia, lower compound muscle action potentials and higher fatigability in stimulated animals. These metrics are suggestive of myopathy in the free flap grafts stimulated with the electrode. Additionally, active inflammatory processes and partial necrosis are observed in grafts stimulated with the implanted electrode. The results suggest that under this treatment protocol, implanted epimysial electrodes and electrical stimulation to deinnervated, and devascularized flaps during the early recovery phase may be detrimental to regeneration. Future work should determine the optimal implantation and stimulation window for accelerating free muscle graft regeneration.

Cerebrospinal Fluid Leakage During Temporal Bone Surgery: Selecting Intra-operative Dural Closure with a Dumbbell-Shaped Muscle Graft as a Surgical Approach.

Cerebrospinal fluid (CSF) leakages of the temporal bone may arise during mastoid surgery. The leakages can have multiple potential etiologies, for instance, using a cutting burr near the bony tegmen or monopolar electrocautery on the surface of the dura mater. In this paper, we introduced an effective and simple technique for the management of CSF leakages of the temporal bone. In a prospective case series, 36 patients (16 males and 20 females) who have had an experience of incidental or inevitable CSF otorrhea or otorhinorrhea during temporal bone surgery were selected. All patients were treated using a muscle graft in a dumbbell-shaped design through the dura defect at the Amir-Alam University Hospital between April 2005 and November 2008. The mean size of the defects was 5mm (a range of 2-10mm). A dumbbell-shaped autologous muscle graft was immediately successful in sealing the leakage in all patients. Only five patients (13.8%) had some evidence of leakage remaining on the day after the operation, which was subsequently resolved by conservative management in four of them (11.1%). Only one patient (2.7%) was subjected to a second operation for a new defect. Recurrence of CSF leakage or other related complications were not observed during about 7years of follow up. A free autologous muscle graft, using the dumbbell technique through a small to moderate dura defect is an effective, easily performed, and safe method to seal iatrogenic leakages of the temporal bone.

Regenerative Peripheral Nerve Interfaces for the Treatment of Postamputation Neuroma Pain: A Pilot Study.

Background:Originally designed for prosthetic control, regenerative peripheral nerve interfaces (RPNIs) prevent neuroma formation by providing free muscle grafts as physiological targets for peripheral nerve ingrowth. We report the first series of patients undergoing RPNI implantation for treatment of symptomatic postamputation neuromas.Methods:A retrospective case series of all amputees undergoing RPNI implantation for treatment of symptomatic neuromas between November 2013 and June 2015 is presented. Data were obtained via chart review and phone interviews using questions derived from the Patient Reported Outcomes Measurement Information System instruments. Statistical analyses were performed using dependent sample t tests with a significance threshold of P < 0.01.Results:Forty-six RPNIs were implanted into 16 amputees for neuroma relief (3 upper extremities and 14 lower extremities). Mean age was 53.5 years (6 females and 10 males). All patients participated in postoperative phone interviews at 7.5 ± 3.4 (range: 3–15) months. Patients reported a 71% reduction in neuroma pain and a 53% reduction in phantom pain. Most patients felt satisfied or highly satisfied with RPNI surgery (75%), reporting decreased (56%) or stable (44%) levels of analgesic use. Most patients would strongly recommend RPNI surgery to a friend (88%) and would do it again if given the option (94%). Complications included delayed wound healing (n = 4) and neuroma pain at a different site (n = 2).Conclusions:RPNI implantation carries a reasonable complication profile while offering a simple, effective treatment for symptomatic neuromas. Most patients report a significant reduction in neuroma and phantom pain with a high level of satisfaction. The physiological basis for preventing neuroma recurrence is an intriguing benefit to this approach.

A Porcine Urinary Bladder Matrix Does Not Recapitulate the Spatiotemporal Macrophage Response of Muscle Regeneration after Volumetric Muscle Loss Injury

Volumetric muscle loss (VML) results in irrecoverable loss of muscle tissue making its repair challenging. VML repair with acellular extracellular matrix (ECM) scaffolds devoid of exogenous cells has shown improved muscle function, but limited de novo muscle fiber regeneration. On the other hand, studies using minced autologous and free autologous muscle grafts have reported appreciable muscle regeneration. This raises the fundamental question whether an acellular ECM scaffold can orchestrate the spatiotemporal cellular events necessary for appreciable muscle fiber regeneration. This study compares the macrophage and angiogenic responses including the remodeling outcomes of a commercially available porcine urinary bladder matrix, MatriStem™, and autologous muscle grafts. The early heightened and protracted M1 response of the scaffold indicates that the scaffold does not recapitulate the spatiotemporal macrophage response of the autograft tissue. Additionally, the scaffold only supports limited de novo muscle fiber formation and regressing vessel density. Furthermore, scaffold remodeling is accompanied by increased presence of transforming growth factor and α-smooth muscle actin, which is consistent with remodeling of the scaffold into a fibrotic scar-like tissue. The limited muscle formation and scaffold-mediated fibrosis noted in this study corroborates the findings of recent studies that investigated acellular ECM scaffolds (devoid of myogenic cells) for VML repair. Taken together, acellular ECM scaffolds when used for VML repair will likely remodel into a fibrotic scar-like tissue and support limited de novo muscle fiber regeneration primarily in the proximity of the injured musculature. This is a work of the US Government and is not subject to copyright protection in the USA. Foreign copyrights may apply. Published by S. Karger AG, Basel