Evaluation of multiple perceptual qualities of transcutaneous electrical nerve stimulation for evoked tactile sensation in forearm amputees.

Objective. Evoked tactile sensation (ETS) elicited by transcutaneous electrical nerve stimulation (TENS) is promising to convey digit-specific sensory information to amputees naturally and non-invasively. Fitting ETS-based sensory feedback to amputees entails customizing coding of multiple sensory information for each stimulation site. This study was to elucidate the consistency of percepts and qualities by TENS at multiple stimulation sites in amputees retaining ETS.Approach. Five transradial amputees with ETS and fourteen able-bodied subjects participated in this study. Surface electrodes with small size (10 mm in diameter) were adopted to fit the restricted projected finger map on the forearm stump of amputees. Effects of stimulus frequency on sensory types were assessed, and the map of perceptual threshold for each sensation was characterized. Sensitivity for vibration and buzz sensations was measured using distinguishable difference in stimulus pulse width. Rapid assessments for modulation ranges of pulse width at fixed amplitude and frequency were developed for coding sensory information. Buzz sensation was demonstrated for location discrimination relating to prosthetic fingers.Main results. Vibration and buzz sensations were consistently evoked at 20 Hz and 50 Hz as dominant sensation types in all amputees and able-bodied subjects. Perceptual thresholds of different sensations followed a similar strength-duration curve relating stimulus amplitude to pulse width. The averaged distinguishable difference in pulse width was 12.84 ± 7.23µs for vibration and 15.21 ± 6.47µs for buzz in able-bodied subjects, and 14.91 ± 10.54µs for vibration and 11.30 ± 3.42µs for buzz in amputees. Buzz coding strategy enabled five amputees to discriminate contact of individual fingers with an overall accuracy of 77.85%.Significance. The consistency in perceptual qualities of dominant sensations can be exploited for coding multi-modality sensory feedback. A fast protocol of sensory coding is possible for fitting ETS-based, non-invasive sensory feedback to amputees.

Safety and Performance of Bone-Anchored Prostheses in Persons with a Transfemoral Amputation: A 5-Year Follow-up Study.

BACKGROUND: For almost 30 years, bone-anchored prostheses have offered an alternative solution to prosthetic sockets by attaching the artificial limb directly to the femoral residuum by means of an osseointegration implant. Osseointegration implant surgery was introduced in our center in 2009. The aim of the present study is to report on safety, prosthesis-wearing time, and health-related quality-of-life (HRQoL) for patients with femoral bone-anchored prostheses during a 5-year follow-up period. METHODS: All patients who underwent implantation of a press-fit osseointegration implant between May 2009 and November 2013 were eligible for the present study. Implantation was performed in 2 stages. Adverse events included infectious complications (grade 1 to 4), aseptic loosening, breakage, stoma-redundant tissue, and stoma hypergranulation. Prosthesis-wearing time and HRQoL were measured with the Questionnaire for Persons with a Transfemoral Amputation (Q-TFA) prosthetic use score and global score, respectively. RESULTS: Thirty-nine of 42 eligible patients were included. Thirty patients (77%) presented with some kind of infection (156 events in total), with 148 (95%) events being classified as grade 1 or 2 and 8 events (5%) being classified as grade 3; the latter 8 events occurred in 4 patients. There were no instances of septic loosening. The intramedullary stem of the osseointegration implant broke in 2 patients. In total, soft-tissue refashioning had to be done 30 times in 14 patients. The Q-TFA median prosthetic use and global scores improved significantly from 71 to 100 and from 33 to 75, respectively (p < 0.001). CONCLUSIONS: Despite the adverse events, patient prosthetic use and HRQoL improved significantly. Grade-1 and 2 infections were frequent but could mostly be treated with nonoperative measures. Most infections seemed to occur in the first 2 years and did not lead to deep infections. Two broken intramedullary stems were revised successfully. Current developments focus on reduction of infectious complications and prevention of osseointegration implant breakage. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Perineural local anaesthetic catheter after major lower limb amputation trial (PLACEMENT): results from a randomised controlled feasibility trial.

OBJECTIVES: To determine the feasibility of undertaking a randomised controlled effectiveness trial evaluating the use of a perineural catheter (PNC) after major lower limb amputation with postoperative pain as the primary outcome. DESIGN: Randomised controlled feasibility trial. SETTING: Two vascular Centres in South Wales, UK. PARTICIPANTS: 50 patients scheduled for major lower limb amputation (below or above knee) for complications of peripheral vascular disease. INTERVENTIONS: The treatment arm received a PNC placed adjacent to the sciatic or tibial nerve at the time of surgery, with continuous infusion of levobupivacaine hydrochloride 0.125% for up to 5 days. The control arm received neither local anaesthetic nor PNC. Both arms received usual perioperative anaesthesia and postoperative analgesia. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcomes were the proportion of eligible patients who were randomised and the proportion of recruited patients who provided primary effectiveness outcome data. Secondary outcomes were: the proportion of recruited patients reaching 2 and 6 month follow-up and supplying pain data; identification of key cost drivers; development of an economic analysis framework for a future effectiveness trial; identification of barriers to recruitment and site set-up; and identification of the best way to measure postoperative pain. RESULTS: Seventy-six of 103 screened patients were deemed eligible over a 10 month period. Fifty (64.5%) of these patients were randomised, with one excluded in the perioperative period. Forty-five (91.3%) of 49 recruited patients provided enough pain scores on a 4-point verbal rating scale to allow primary effectiveness outcome evaluation. Attrition rates were high; 18 patients supplied data at 6 month follow-up. Costs were dominated by length of hospital stay. Patients and healthcare professionals reported that trial processes were acceptable. CONCLUSIONS: Recruitment of patients into a trial comparing PNC use to usual care after major lower limb amputation with postoperative pain measured on a 4-point verbal rating scale is feasible. Evaluation of longer-term symptoms is difficult. TRIAL REGISTRATION NUMBER: ISRCTN: 85 710 690. EudraCT: 2016-003544-37.

Electrical stimulation shifts healing/scarring towards regeneration in a rat limb amputation model.

Different species respond differently to severe injury, such as limb loss. In species that regenerate, limb loss is met with complete restoration of the limbs' form and function, whereas in mammals the amputated limb's stump heals and scars. In in vitro studies, electrical stimulation (EStim) has been shown to promote cell migration, and osteo- and chondrogenesis. In in vivo studies, after limb amputation, EStim causes significant new bone, cartilage and vessel growth. Here, in a rat model, the stumps of amputated rat limbs were exposed to EStim, and we measured extracellular matrix (ECM) deposition, macrophage distribution, cell proliferation and gene expression changes at early (3 and 7 days) and later stages (28 days). We found that EStim caused differences in ECM deposition, with less condensed collagen fibrils, and modified macrophage response by changing M1 to M2 macrophage ratio. The number of proliferating cells was increased in EStim treated stumps 7 days after amputation, and transcriptome data strongly supported our histological findings, with activated gene pathways known to play key roles in embryonic development and regeneration. In conclusion, our findings support the hypothesis that EStim shifts injury response from healing/scarring towards regeneration. A better understanding of if and how EStim controls these changes, could lead to strategies that replace scarring with regeneration.

Targeted muscle reinnervation in oncologic amputees: Early experience of a novel institutional protocol.

BACKGROUND: We describe a multidisciplinary approach for comprehensive care of amputees with concurrent targeted muscle reinnervation (TMR) at the time of amputation. METHODS: Our TMR cohort was compared to a cross-sectional sample of unselected oncologic amputees not treated at our institution (N = 58). Patient-Reported Outcomes Measurement Information System (NRS, PROMIS) were used to assess postamputation pain. RESULTS: Thirty-one patients underwent amputation with concurrent TMR during the study; 27 patients completed pain surveys; 15 had greater than 1 year follow-up (mean follow-up 14.7 months). Neuroma symptoms occurred significantly less frequently and with less intensity among the TMR cohort. Mean differences for PROMIS pain intensity, behavior, and interference for phantom limb pain (PLP) were 5.855 (95%CI 1.159-10.55; P = .015), 5.896 (95%CI 0.492-11.30; P = .033), and 7.435 (95%CI 1.797-13.07; P = .011) respectively, with lower scores for TMR cohort. For residual limb pain, PROMIS pain intensity, behavior, and interference mean differences were 5.477 (95%CI 0.528-10.42; P = .031), 6.195 (95%CI 0.705-11.69; P = .028), and 6.816 (95%CI 1.438-12.2; P = .014), respectively. Fifty-six percent took opioids before amputation compared to 22% at 1 year postoperatively. CONCLUSIONS: Multidisciplinary care of amputees including concurrent amputation and TMR, multimodal postoperative pain management, amputee-centered rehabilitation, and peer support demonstrates reduced incidence and severity of neuroma and PLP.

Dorsal Root Ganglion Stimulation for Complex Regional Pain Syndrome (CRPS) Recurrence after Amputation for CRPS, and Failure of Conventional Spinal Cord Stimulation.

BACKGROUND: Limb amputation is sometimes being performed in long-standing complex regional pain syndrome (CRPS), although little evidence is available guiding management decisions, including how CRPS recurrence should be managed. METHODS: This report details the management of a young soldier with CRPS recurrence 2 years after midtibial amputation for CRPS. RESULTS: Conventional spinal cord stimulation did not achieve paraesthetic coverage, or pain relief in the stump, whereas L4 dorsal root ganglion stimulation achieved both coverage and initially modest pain relief, and over time, substantial pain relief. CONCLUSIONS: Current evidence does not support the use of amputation to improve either pain or function in CRPS. Before a decision is made, in exceptional cases, about referral for amputation, dorsal root ganglion stimulation should be considered as a potentially effective treatment, even where conventional spinal cord stimulator treatment has failed to achieve reliable paraesthetic cover. Furthermore, this treatment may provide pain relief in those patients with CRPS recurrence in the stump after amputation.

Common Synaptic Input to Motor Neurons and Neural Drive to Targeted Reinnervated Muscles.

We compared the behavior of motor neurons innervating their physiological muscle targets with motor neurons from the same spinal segment whose axons were surgically redirected to remnant muscles (targeted muscle reinnervation). The objective was to assess whether motor neurons with nonphysiological innervation receive similar synaptic input and could be voluntary controlled as motor neurons with natural innervation. For this purpose, we acquired high-density EMG signals from the biceps brachii in 5 male transhumeral amputees who underwent targeted reinnervation of this muscle by the ulnar nerve and from the first dorsal interosseous muscle of 5 healthy individuals to investigate the natural innervation of the ulnar nerve. The same recordings were also performed from the biceps brachii muscle of additional 5 able-bodied individuals. The EMG signals were decomposed into discharges of motor unit action potentials. Motor neurons were progressively recruited for the full range of submaximal muscle activation in all conditions. Moreover, their discharge rate significantly increased from recruitment to target activation level in a similar way across the subject groups. Motor neurons across all subject groups received common synaptic input as identified by coherence analysis of their spike trains. However, the relative strength of common input in both the delta (0.5-5 Hz) and alpha (5-13 Hz) bands was significantly smaller for the surgically reinnervated motor neuron pool with respect to the corresponding physiologically innervated one. The results support the novel approach of motor neuron interfacing for prosthesis control and provide new insights into the role of afferent input on motor neuron activity.SIGNIFICANCE STATEMENT Targeted muscle reinnervation surgically redirects nerves that lost their target in the amputation into redundant muscles in the region of the stump. The study of the behavior of motor neurons following this surgery is needed for designing biologically inspired prosthetic control strategies. Moreover, targeted muscle reinnervation offers a human experimental framework for studying the control and behavior of motor neurons when changing their target innervated muscle fibers and sensory feedback. Here, we show that the control of motor neurons and their synaptic input, following reinnervation, was remarkably similar to that of the physiological innervation, although with reduced common drive at some frequencies. The results advance our knowledge on the role of sensory input in the generation of the neural drive to muscles and provide the basis for designing physiologically inspired methods for prosthesis control.

Non-pharmacological conservative therapy for phantom limb pain: A systematic review of randomized controlled trials.

The aim of this manuscript was to investigate the effectiveness of conservative therapy for phantom limb pain (PLP). In this systematic review, CINAHL, AMED, the Cochrane database of systematic reviews, PEDro, psychology and behavioral sciences collection, and MEDLINE were systematically searched for appropriate randomized controlled trials (RCTs). Selected papers were assessed for risk of bias, and evidence was graded using the GRADE approach. Twelve RCTs met initial inclusion/exclusion criteria, of which five were of sufficient quality for final inclusion. There is conflicting evidence from two RCTs for the effectiveness of electromagnetic shielding limb liners on pain in the short term. There is limited evidence supporting the effectiveness of both hypnosis in the short term and graded motor imagery (GMI) in the short-to-medium term. Additionally, there is limited evidence that a single session of mirror therapy has no immediate effect on PLP. Limb liner discomfort was the only adverse effect identified. This review identifies a range of conservative therapies, many of which demonstrate preliminary evidence of potential with respect to clinically worthwhile effects above control interventions and few, if any, adverse effects. However, there is a paucity of high-quality evidence upon which to make any firm clinical conclusions.

Developing Non-Somatotopic Phantom Finger Sensation to Comparable Levels of Somatotopic Sensation through User Training With Electrotactile Stimulation.

Cutaneous electrical stimulation can provide tactile feedback for upper-limb amputees through somatotopic feedback (SF) or non-somatotopic feedback (NF). The SF delivers electrotactile stimulus to projection finger maps (PFMs) on the stumps of amputees, which outperforms NF that transfers stimulus to other human intact skin areas in general. However, the SF areas on stumps are very limited and often occupied by electromyography (EMG) sensors in application of myoelectric prosthesis. This work aims at improving NF performance on human upper arms through user training with electrotactile stimulation. The experiments were conducted over seven consecutive days on nine able-bodied subjects and two forearm amputees. The performance measures of NF/SF included the correct identification rates (CIRs), the response time and the NASA-TLX questionnaire. The between-day CIR s on NF sites increased logarithmically with a mean course of 3-day rapid-improving phase and plateaued in the relative-steady phase. The response time and NASA-TLX scores could also rapidly reduce to the comparable levels of the SF areas during the same mean period of 3-day rapid-improving phase, respectively. These results indicated that the performance of NF could be highly improved to the equivalent level as that of SF through 3-day electrotactile training, which we named as "3-day effect". It provides important insights that intact skin areas without phantom sensations can effectively replace SF sites to transfer tactile feedback after continuous user training, which validates effectiveness of non-invasive interfaces of tactile feedback for upper-limb amputees in practice.

Effective local anesthesia for onabotulinumtoxin A injections to treat hyperhidrosis associated with traumatic amputation.

BACKGROUND: Botulinum toxin type A (BTX-A) injections are an effective treatment for controlling hyperhidrosis at sites of amputation. Hyperesthesia associated with amputated limbs is a major barrier to performing this procedure under local anesthesia. OBJECTIVE: To present a novel method for improving local anesthesia with BTX-A injections. Methods & RESULTS: A 29-year-old military veteran with a below-the-knee amputation of his right leg was suffering from amputation site hyperhidrosis, which was impeding his ability to comfortably wear a prosthesis. Prior to presenting to our clinic, the patient received one treatment of BTX-A injections to his amputation stump while under general anesthesia for surgical repair of trauma-related injuries. In our dermatology clinic, we repeated the procedure using topical lidocaine-prilocaine (30 gm total) for local anesthesia. This provided effective relief of hyperhidrosis for 6 months, but the procedure was very painful (9/10 intensity). We repeated the same procedure 6 months later, using ice in addition to topical lidocaine-prilocaine (30 gm) for local anesthesia; this resulted in reduced pain (3/10 intensity) for the patient. CONCLUSIONS: We suggest using ice in combination with a topical anesthetic as an effective method for pain control that avoids general anesthesia in treating amputation-associated hyperhidrosis.

Improving the Performance Against Force Variation of EMG Controlled Multifunctional Upper-Limb Prostheses for Transradial Amputees.

We investigate the problem of achieving robust control of hand prostheses by the electromyogram (EMG) of transradial amputees in the presence of variable force levels, as these variations can have a substantial impact on the robustness of the control of the prostheses. We also propose a novel set of features that aim at reducing the impact of force level variations on the prosthesis controlled by amputees. These features characterize the EMG activity by means of the orientation between a set of spectral moments descriptors extracted from the EMG signal and a nonlinearly mapped version of it. At the same time, our feature extraction method processes the EMG signals directly from the time-domain to reduce computational cost. The performance of the proposed features is tested on EMG data collected from nine transradial amputees performing six classes of movements each with three force levels. Our results indicate that the proposed features can achieve significant reductions in classification error rates in comparison to other well-known feature extraction methods, achieving improvements of ≈ 6% to 8% in the average classification performance across all subjects and force levels, when training with all forces.

The effect of electromagnetic shielding on phantom limb pain: A placebo-controlled double-blind crossover trial.

BACKGROUND: Environmental electromagnetic fields influence biological systems. Evidence suggests these have a role in the experience of phantom limb pain in patients with amputations. OBJECTIVES: This article followed a previous study to investigate the effect of electromagnetic field shielding with a specially designed prosthetic liner. STUDY DESIGN: Randomised placebo-controlled double-blind crossover trial. METHODS: Twenty suitable participants with transtibial amputations, phantom pain at least 1 year with no other treatable cause or pathology were requested to record daily pain, well-being, activity and hours of prosthetic use on pre-printed diary sheets. These were issued for three 2-week periods (baseline, electromagnetic shielding (verum) and visually identical placebo liners - randomly allocated). RESULTS: Thirty-three per cent of the recruited participants were unable to complete the trial. The resulting N was therefore smaller than was necessary for adequate power. The remaining data showed that maximum pain and well-being were improved from baseline under verum but not placebo. More participants improved on all variables with verum than placebo. CONCLUSION: Electromagnetic field shielding produced beneficial effects in those participants who could tolerate the liner. It is suggested that this might be due to protection of vulnerable nerve endings from nociceptive effects of environmental electromagnetic fields. CLINICAL RELEVANCE: Electromagnetic field shielding with a suitable limb/prosthesis interface can be considered a useful technique to improve pain and well-being in patients with phantom limb pain.

A histological analysis of human median and ulnar nerves following implantation of Utah slanted electrode arrays.

For decades, epineurial electrodes have been used in clinical therapies involving the stimulation of peripheral nerves. However, next generation peripheral nerve interfaces for applications such as neuroprosthetics would benefit from an increased ability to selectively stimulate and record from nerve tissue. This increased selectivity may require the use of more invasive devices, such as the Utah Slanted Electrode Array (USEA). Previous research with USEAs has described the histological response to the implantation of these devices in cats and rats; however, no such data has been presented in humans. Therefore, we describe here the degree of penetration and foreign body reaction to USEAs after a four-week implantation period in human median and ulnar nerves. We found that current array designs penetrate a relatively small percentage of the available endoneurial tissue in these large nerves. When electrode tips were located within the endoneurial tissue, labels for axons and myelin were found in close proximity to electrodes. Consistent with other reports, we found activated macrophages attached to explanted devices, as well as within the tissue surrounding the implantation site. Despite this inflammatory response, devices were able to successfully record single- or multi-unit action potentials and elicit sensory percepts. However, modifying device design to allow for greater nerve penetration, as well as mitigating the inflammatory response to such devices, would likely increase device performance and should be investigated in future research.

Peripheral Neuromodulation to Treat Postamputation Pain.

Some of the more common peripherally mediated pain disorders are postamputation stump pain and phantom pain. These disabling conditions have proven difficult to treat. Here we aim to illustrate an option to treat postamputation pain using peripheral neurostimulation techniques. Traditional peripheral neuromodulation techniques use standard stimulation parameters and work by stimulation of nerve tissues which are then felt by the patient as a tingling sensation or paresthesia. Recently introduced high-frequency (10 kHz) electrical nerve block [HFAC (high-frequency alternating current) block] via a surgically implanted peripheral nerve cuff electrode results in true conduction block which actually blocks action potentials emanating from the painful neuroma and thus suppresses pain without tingling or paresthesia felt by the patient. In a recently completed 10-patient pilot study, the average pain level decreased from a score of 5.7 to 1.4 (out of 10) after HFAC block therapy with 85% of all testing sessions yielding a >50% pain reduction; a very significant reduction in the use of opioid and other analgesics was also noted, with all tested patients either stopping or decreasing their analgesic intake significantly. Patients achieved meaningful and significant pain reduction throughout the study, and patients who had phantom pain (in addition to stump pain) that responded to local anesthetic injections also responded favorably with HFAC block, presumably because in these particular patients, the phantom symptoms were peripherally generated. Each of the tested patients reported that HFAC block provided the most significant amount of pain reduction they had ever experienced when compared to other pain modalities tried since their amputations. The high-frequency electric nerve block technique is currently investigational pending FDA clearance. The next step for this modality is a pivotal trial, with the goal of having this therapy available to the mass market upon FDA clearance.

Characterization of evoked tactile sensation in forearm amputees with transcutaneous electrical nerve stimulation.

OBJECTIVE: The goal of this study is to characterize the phenomenon of evoked tactile sensation (ETS) on the stump skin of forearm amputees using transcutaneous electrical nerve stimulation (TENS). APPROACH: We identified the projected finger map (PFM) of ETS on the stump skin in 11 forearm amputees, and compared perceptual attributes of the ETS in nine forearm amputees and eight able-bodied subjects using TENS. The profile of perceptual thresholds at the most sensitive points (MSPs) in each finger-projected area was obtained by modulating current amplitude, pulse width, and frequency of the biphasic, rectangular current stimulus. The long-term stability of the PFM and the perceptual threshold of the ETS were monitored in five forearm amputees for a period of 11 months. MAIN RESULTS: Five finger-specific projection areas can be independently identified on the stump skin of forearm amputees with a relatively long residual stump length. The shape of the PFM was progressively similar to that of the hand with more distal amputation. Similar sensory modalities of touch, pressure, buzz, vibration, and numb below pain sensation could be evoked both in the PFM of the stump skin of amputees and in the normal skin of able-bodied subjects. Sensory thresholds in the normal skin of able-bodied subjects were generally lower than those in the stump skin of forearm amputees, however, both were linearly modulated by current amplitude and pulse width. The variation of the MSPs in the PFM was confined to a small elliptical area with 95% confidence. The perceptual thresholds of thumb-projected areas were found to vary less than 0.99 × 10(-2) mA cm(-2). SIGNIFICANCE: The stable PFM and sensory thresholds of ETS are desirable for a non-invasive neural interface that can feed back finger-specific tactile information from the prosthetic hand to forearm amputees.

Transcutaneous electrical nerve stimulation (TENS) for phantom pain and stump pain following amputation in adults.

BACKGROUND: This is the first update of a Cochrane review published in Issue 5, 2010 on transcutaneous electrical nerve stimulation (TENS) for phantom pain and stump pain following amputation in adults. Pain may present in a body part that has been amputated (phantom pain) or at the site of amputation (stump pain), or both. Phantom pain and stump pain are complex and multidimensional and the underlying pathophysiology remains unclear. The condition remains a severe burden for those who are affected by it. The mainstay treatments are predominately pharmacological, with increasing acknowledgement of the need for non-drug interventions. TENS has been recommended as a treatment option but there has been no systematic review of available evidence. Hence, the effectiveness of TENS for phantom pain and stump pain is currently unknown. OBJECTIVES: To assess the analgesic effectiveness of TENS for the treatment of phantom pain and stump pain following amputation in adults. SEARCH METHODS: For the original version of the review we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, PsycINFO, AMED, CINAHL, PEDRO and SPORTDiscus (February 2010). For this update, we searched the same databases for relevant randomised controlled trials (RCTs) from 2010 to 25 March 2015. SELECTION CRITERIA: We only included RCTs investigating the use of TENS for the management of phantom pain and stump pain following an amputation in adults. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trial quality and extracted data. We planned that where available and appropriate, data from outcome measures were to be pooled and presented as an overall estimate of the effectiveness of TENS. MAIN RESULTS: In the original review there were no RCTs that examined the effectiveness of TENS for the treatment of phantom pain and stump pain in adults. For this update, we did not identify any additional RCTs for inclusion. AUTHORS' CONCLUSIONS: There were no RCTs to judge the effectiveness of TENS for the management of phantom pain and stump pain. The published literature on TENS for phantom pain and stump pain lacks the methodological rigour and robust reporting needed to confidently assess its effectiveness. Further RCT evidence is required before an assessment can be made. Since publication of the original version of this review, we have found no new studies and our conclusions remain unchanged.

Somatotopical feedback versus non-somatotopical feedback for phantom digit sensation on amputees using electrotactile stimulation.

BACKGROUND: Transcutaneous electrical stimulation can provide amputees with tactile feedback for better manipulating an advanced prosthesis. In general, there are two ways to transfer the stimulus to the skin: somatotopical feedback (SF) that stimulates the phantom digit somatotopy on the stump and non-somatotopical feedback (NF) that stimulates other positions on the human body. METHODS: To investigate the difference between SF and NF, electrotactile experiments were conducted on seven amputees. Electrical stimulation was applied via a complete phantom map to the residual limb (SF) and to the upper arm (NF) separately. The behavior results of discrimination accuracy and response time were used to examine: 1) performance differences between SF and NF for discriminating position, type and strength of tactile feedback; 2) performance differences between SF and NF for one channel (1C), three channels (3C), and five channels (5C). NASA-TLX standardized testing was used to determine differences in mental workload between SF and NF. RESULTS: The grand-averaged discrimination accuracy for SF was 6% higher than NF, and the average response time for SF was 600 ms faster than NF. SF is better than NF for position, type, strength, and the overall modality regarding both accuracy and response time except for 1C modality (p<0.001). Among the six modalities of stimulation channels, performance of 1C/SF was the best, which was similar to that of 1C/NF and 3C/SF; performance of 3C/NF was similar to that of 5C/SF; performance of 5C/NF was the worst. NASA-TLX scores indicated that mental workload increased as the number of stimulation channels increased. CONCLUSIONS: We quantified the difference between SF and NF, and the influence of different number of stimulation channels. SF was better than NF in general, but the practical issues such as the limited area of stumps could constrain the use of SF. We found that more channels increased the amount and richness of information to the amputee while fewer channels resulted in higher performance, and thus the 3C/SF modality was a good compromise. Based on this study, we provide possible solutions to the practical problems involving the implementation of tactile feedback for amputees. These results are expected to promote the application of SF and NF tactile feedback for amputees in the future.

High-frequency electrical nerve block for postamputation pain: a pilot study.

OBJECTIVES: This study aimed to assess the analgesic effect of kilohertz alternating current applied to the severed nerves in amputees afflicted by intractable limb pain. METHODS: Ten lower-limb amputees with chronic and severe residual limb pain or phantom limb pain who attained significant pain reduction after local nerve block injection were enrolled. A cuff electrode was wrapped around the sciatic or tibial nerve. An external waveform generator was used for the main part of the study, while an implantable generator was developed and implanted in the responders after 9 to 12 months. Sinusoidal waveforms of 10 kHz and up to 10 V were applied for 30 min during each subject-initiated treatment session. A diary was used to record pain intensities before and after each session. RESULTS: Among the seven subjects who received treatment, the average pain reduction was 75% at the three-month primary end point. These subjects were responders per predefined criterion of achieving ≥50% pain reduction in ≥50% of treatment sessions for the three-month end point. Pain medication use and interference of pain on functions was significantly reduced. The treatment efficacy was sustained through the follow-up period of up to 12 months. Besides dislodgement and loss of function for one electrode in one subject, all other devices functioned as intended. No changes of residual motor and sensory function were observed. CONCLUSION: This pilot study generated preliminary evidence on the efficacy and safety of kilohertz electrical nerve block for postamputation pain, justifying a pivotal study for regulatory approval.

A sensory feedback system for prosthetic hand based on evoked tactile sensation.

The lack of reliable sensory feedback has been one of the barriers in prosthetic hand development. Restoring sensory function from prosthetic hand to amputee remains a great challenge to neural engineering. In this paper, we present the development of a sensory feedback system based on the phenomenon of evoked tactile sensation (ETS) at the stump skin of residual limb induced by transcutaneous electrical nerve stimulation (TENS). The system could map a dynamic pattern of stimuli to an electrode placed on the corresponding projected finger areas on the stump skin. A pressure transducer placed at the tip of prosthetic fingers was used to sense contact pressure, and a high performance DSP processor sampled pressure signals, and calculated the amplitude of feedback stimulation in real-time. Biphasic and charge-balanced current pulses with amplitude modulation generated by a multi-channel laboratory stimulator were delivered to activate sensory nerves beneath the skin. We tested this sensory feedback system in amputee subjects. Preliminary results showed that the subjects could perceive different levels of pressure at the tip of prosthetic finger through evoked tactile sensation (ETS) with distinct grades and modalities. We demonstrated the feasibility to restore the perceptual sensation from prosthetic fingers to amputee based on the phenomenon of evoked tactile sensation (ETS) with TENS.