Outcomes, Challenges, and Pitfalls after Targeted Muscle Reinnervation in High-Level Amputees: Is It Worth the Effort?

BACKGROUND

Although the distal targets have been lost in proximal upper limb amputees, the neural signals for intuitive hand and arm function are still available and thus can be incorporated into more useful prosthetic function using targeted muscle reinnervation technique. In this article, the authors present their outcomes and range of indications in addition to experiences and pitfalls after 30 targeted muscle reinnervation cases at above-elbow and shoulder disarticulation level of amputation.

METHODS

Thirty patients with above-elbow or shoulder disarticulation amputations were enrolled between 2012 and 2017. Indications for targeted muscle reinnervation surgery differed between improvement of prosthetic function (n = 19) and/or pain (n = 11). Functional outcome was evaluated with the Action Research Arm Test, the Southampton Hand Assessment Procedure, and the Clothespin-Relocation Test. Functional evaluation was performed at least at 6 months after final prosthetic fitting.

RESULTS

All nerve transfers were successful and provided independent myoelectric signals. The 10 patients available for final functional evaluation showed Action Research Arm Test scores of 20.4 ± 1.9 and Southampton Hand Assessment Procedure scores of 40.5 ± 8.1. The Clothespin-Relocation Test showed a mean time of 34.3 ± 14.4 seconds.

CONCLUSIONS

Targeted muscle reinnervation has improved prosthetic control and revolutionized neuroma treatment in upper limb amputees. Still, the rate of abandonment even after targeted muscle reinnervation surgery has been shown high, and several advances within the biotechnological interface will be needed to improve prosthetic function and acceptance in these patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Surface Electromyographic Biofeedback as a Rehabilitation Tool for Patients with Global Brachial Plexus Injury Receiving Bionic Reconstruction

In patients with global brachial plexus injury and lack of biological treatment alternatives, bionic reconstruction, including the elective amputation of the functionless hand and its replacement with a prosthesis, has recently been described. Optimal prosthetic function depends on a structured rehabilitation protocol, as residual muscle activity in a patient's arm is later translated into prosthetic function. Surface electromyographic (sEMG) biofeedback has been used during rehabilitation after stroke, but has so far not been used in patients with complex peripheral nerve injuries. Here, we present our rehabilitation protocol implemented in patients with global brachial plexus injuries suitable for bionic reconstruction, starting from identification of sEMG signals to final prosthetic training. This structured rehabilitation program facilitates motor relearning, which may be a cognitively debilitating process after complex nerve root avulsion injuries, aberrant re-innervation and extra-anatomical reconstruction (as is the case with nerve transfer surgery). The rehabilitation protocol using sEMG biofeedback aids in the establishment of new motor patterns as patients are being made aware of the advancing re-innervation process of target muscles. Additionally, faint signals may also be trained and improved using sEMG biofeedback, rendering a clinically "useless" muscle (exhibiting muscle strength M1 on the British Medical Research Council [BMRC] scale) eligible for dexterous prosthetic hand control. Furthermore, functional outcome scores after successful bionic reconstruction are presented in this article.

Long-term implant of intramuscular sensors and nerve transfers for wireless control of robotic arms in above-elbow amputees

Targeted muscle reinnervation (TMR) amplifies the electrical activity of nerves at the stump of amputees by redirecting them in remnant muscles above the amputation. The electrical activity of the reinnervated muscles can be used to extract natural control signals. Nonetheless, current control systems, mainly based on noninvasive muscle recordings, fail to provide accurate and reliable control over time. This is one of the major reasons for prosthetic abandonment. This prospective interventional study includes three unilateral above-elbow amputees and reports the long-term (2.5 years) implant of wireless myoelectric sensors in the reinnervation sites after TMR and their use for control of robotic arms in daily life. It therefore demonstrates the clinical viability of chronically implanted myoelectric interfaces that amplify nerve activity through TMR. The patients showed substantial functional improvements using the implanted system compared with control based on surface electrodes. The combination of TMR and chronically implanted sensors may drastically improve robotic limb replacement in above-elbow amputees.

Bionic reconstruction : Restoration of extremity function with osseointegrated and mind-controlled prostheses

Background

Loss of an extremity at any level has a major impact on a patient’s life. Using bionic reconstruction, extremity function can be restored and the patient reintegrated into daily life. Surgical procedures including selective nerve transfer and anchoring of prostheses into bone are combined with structured rehabilitation and modern prosthetic fitting. The patient is thereby able to use the prostheses intuitively and with multiple degrees of freedom.

Methods

This article presents the concept and approach for modern bionic reconstruction in detail and the relevant literature. The nerve transfer matrices for targeted muscle reinnervation (TMR) and the concept of osseointegration to optimally fit a patient with a modern prosthesis are described in detail. As a clinical example, the case of a patient who suffered from traumatic amputation and subsequently received TMR in combination with an osseointegrated implant and structured rehabilitation is presented.

Results

Using bionic reconstruction, basic hand functions can be restored and bimanual dexterity can expand the range of daily activities. Besides this approach to bionic reconstruction, its advantages and disadvantages are compared to hand transplantation. The limitations and perspectives of modern bionic reconstruction are also discussed.

Conclusions

Bionic reconstruction is a sophisticated method for restoring extremity function and nowadays can be considered a standard of care for all levels of upper extremity amputations. An interdisciplinary approach and structured rehabilitation are necessary to master prosthetic function to ultimately reintegrate patients into daily life.

Bionic hand as artificial organ: Current status and future perspectives

Even though the hand comprises only 1% of our body weight, about 30% of our central nervous systems (CNS) capacity is related to its control. The loss of a hand thus presents not only the loss of the most important tool allowing us to interact with our environment, but also leaves a dramatic sensory-motor deficit that challenges our CNS. Reconstruction of hand function is therefore not only an essential part of restoring body integrity and functional wholeness but also closes the loop of our neural circuits diminishing phantom sensation and neural pain. If biology fails to restore meaningful function, today we can resort to complex mechatronic replacement that have functional capabilities that in some respects even outperform biological alternatives, such as hand transplantation. As with replantation and transplantations, the challenge of bionic replacement is connecting the target with the CNS to achieve natural and intuitive control. In recent years, we have developed a number of strategies to improve neural interfacing, signal extraction, interpretation and stable mechanical attachment that are important parts of our current research. This work gives an overview of recent advances in bionic reconstruction, surgical refinements over technological interfacing, skeletal fixation, and modern rehabilitation tools that allow quick integration of prosthetic replacement.

Predicting wrist kinematics from motor unit discharge timings for the control of active prostheses

BACKGROUND

Current myoelectric control algorithms for active prostheses map time- and frequency-domain features of the interference EMG signal into prosthesis commands. With this approach, only a fraction of the available information content of the EMG is used and the resulting control fails to satisfy the majority of users. In this study, we predict joint angles of the three degrees of freedom of the wrist from motor unit discharge timings identified by decomposition of high-density surface EMG.

METHODS

We recorded wrist kinematics and high-density surface EMG signals from six able-bodied individuals and one patient with limb deficiency while they performed movements of three degrees of freedom of the wrist at three different speeds. We compared the performance of linear regression to predict the observed individual wrist joint angles from, either traditional time domain features of the interference EMG or from motor unit discharge timings (which we termed neural features) obtained by EMG decomposition. In addition, we propose and test a simple model-based dimensionality reduction, based on the physiological notion that the discharge timings of motor units are partly correlated.

RESULTS

The regression approach using neural features outperformed regression on classic global EMG features (average R² for neural features 0.77 and 0.64, for able-bodied subjects and patients, respectively; for time-domain features 0.70 and 0.52).

CONCLUSIONS

These results indicate that the use of neural information extracted from EMG decomposition can advance man-machine interfacing for prosthesis control.

Reconstruction of the spinal accessory nerve with selective fascicular nerve transfer of the upper trunk

OBJECTIVE

Spinal accessory nerve palsy is frequently caused by iatrogenic damage during neck surgery in the posterior triangle of the neck. Due to late presentation, treatment regularly necessitates nerve grafts, which often results in a poor outcome of trapezius function due to long regeneration distances. Here, the authors report a distal nerve transfer using fascicles of the upper trunk related to axillary nerve function for reinnervation of the trapezius muscle.

METHODS

Five cases are presented in which accessory nerve lesions were reconstructed using selective fascicular nerve transfers from the upper trunk of the brachial plexus. Outcomes were assessed at 20 ± 6 months (mean ± SD) after surgery, and active range of motion and pain levels using the visual analog scale were documented.

RESULTS

All 5 patients regained good to excellent trapezius function (3 patients had grade M5, 2 patients had grade M4). The mean active range of motion in shoulder abduction improved from 55° ± 18° before to 151° ± 37° after nerve reconstruction. In all patients, unrestricted shoulder arm movement was restored with loss of scapular winging when abducting the arm. Average pain levels decreased from 6.8 to 0.8 on the visual analog scale and subsided in 4 of 5 patients.

CONCLUSIONS

Restoration of spinal accessory nerve function with selective fascicle transfers related to axillary nerve function from the upper trunk of the brachial plexus is a good and intuitive option for patients who do not qualify for primary nerve repair or present with a spontaneous idiopathic palsy. This concept circumvents the problem of long regeneration distances with direct nerve repair and has the advantage of cognitive synergy to the target function of shoulder movement.

Cutaneous angiosome of the chimeric SLGA perforator flap: Anatomical study and clinical considerations

BACKGROUND

The superior lateral genicular artery (SLGA) is the basis for a chimeric perforator flap in the lateral knee region, which may include bone, cartilage, fascia, and/or skin. To the best of our knowledge, a detailed description of the corresponding perforator-based skin area is missing in the literature. The aim of this study was to describe the extent and possible variations of the cutaneous angiosome of the SLGA.

METHODS

In an anatomical study on 21 fresh frozen lower limbs, the SLGA was injected with toluidine blue. The anatomy of the vessel and its perforators was explored, and the skin containing the cutaneous angiosome was harvested and photo-documented. Evaluation of the images was performed using ImageJ software. In addition, the versatility of the SLGA perforator flap is illustrated as both a pedicled local and a free tissue transfer.

RESULTS

For each vessel, there were 1.75 ± 0.9 (range 1-3) perforators at an average position of 47.3 ± 21.3 mm lateral to the superolateral patella and 42.5 ± 18.7 mm proximal to the knee joint. The angiosome area was 222.8 ± 57.6 cm² with a length of 20.9 ± 3.0 cm and a width of 15.4 ± 3.0 cm. At the longitudinal axis of the highest perforator density, the proximal end and the distal end of perfusion averaged 13.4 ± 4.1 cm proximal and 2.5 ± 2.0 cm distal to the knee joint, respectively.

CONCLUSION

Our results show that the SLGA supplies a constant angiosome over the anterolateral proximal knee joint. Its description and visualization will guide surgeons in preoperative planning and further extend the use of this versatile chimeric perforator flap.

Peripheral nerve transfers change target muscle structure and function

Selective nerve transfers surgically rewire motor neurons and are used in extremity reconstruction to restore muscle function or to facilitate intuitive prosthetic control. We investigated the neurophysiological effects of rewiring motor axons originating from spinal motor neuron pools into target muscles with lower innervation ratio in a rat model. Following reinnervation, the target muscle's force regenerated almost completely, with the motor unit population increasing to 116% in functional and 172% in histological assessments with subsequently smaller muscle units. Muscle fiber type populations transformed into the donor nerve's original muscles. We thus demonstrate that axons of alternative spinal origin can hyper-reinnervate target muscles without loss of muscle force regeneration, but with a donor-specific shift in muscle fiber type. These results explain the excellent clinical outcomes following nerve transfers in neuromuscular reconstruction. They indicate that reinnervated muscles can provide an accurate bioscreen to display neural information of lost body parts for high-fidelity prosthetic control.

Rehabilitation of Upper Extremity Nerve Injuries Using Surface EMG Biofeedback: Protocols for Clinical Application

Motor recovery following nerve transfer surgery depends on the successful re-innervation of the new target muscle by regenerating axons. Cortical plasticity and motor relearning also play a major role during functional recovery. Successful neuromuscular rehabilitation requires detailed afferent feedback. Surface electromyographic (sEMG) biofeedback has been widely used in the rehabilitation of stroke, however, has not been described for the rehabilitation of peripheral nerve injuries. The aim of this paper was to present structured rehabilitation protocols in two different patient groups with upper extremity nerve injuries using sEMG biofeedback. The principles of sEMG biofeedback were explained and its application in a rehabilitation setting was described. Patient group 1 included nerve injury patients who received nerve transfers to restore biological upper limb function (n = 5) while group 2 comprised patients where biological reconstruction was deemed impossible and hand function was restored by prosthetic hand replacement, a concept today known as bionic reconstruction (n = 6). The rehabilitation protocol for group 1 included guided sEMG training to facilitate initial movements, to increase awareness of the new target muscle, and later, to facilitate separation of muscular activities. In patient group 2 sEMG biofeedback helped identify EMG activity in biologically "functionless" limbs and improved separation of EMG signals upon training. Later, these sEMG signals translated into prosthetic function. Feasibility of the rehabilitation protocols for the two different patient populations was illustrated. Functional outcome measures were assessed with standardized upper extremity outcome measures [British Medical Research Council (BMRC) scale for group 1 and Action Research Arm Test (ARAT) for group 2] showing significant improvements in motor function after sEMG training. Before actual movements were possible, sEMG biofeedback could be used. Patients reported that this visualization of muscle activity helped them to stay motivated during rehabilitation and facilitated their understanding of the re-innervation process. sEMG biofeedback may help in the cognitively demanding process of establishing new motor patterns. After standard nerve transfers individually tailored sEMG biofeedback can facilitate early sensorimotor re-education by providing visual cues at a stage when muscle activation cannot be detected otherwise.

Decoding motor neuron activity from epimysial thin-film electrode recordings following targeted muscle reinnervation

OBJECTIVE

Surface electromyography (EMG) is currently used as a control signal for active prostheses in amputees who underwent targeted muscle reinnervation (TMR) surgery. Recent research has shown that it is possible to access the spiking activity of spinal motor neurons from multi-channel surface EMG. In this study, we propose the use of multi-channel epimysial EMG electrodes as an interface for decoding motor neurons activity following TMR.

APPROACH

We tested multi-channel epimysial electrodes (48 detection sites) built with thin-film technology in an animal model of TMR. Eight animals were tested 12 weeks after reinnervation of the biceps brachii lateral head by the ulnar nerve. We identified the position of the innervation zone and the muscle fiber conduction velocity of motor units decoded from the multi-channel epimysial recordings. Moreover, we characterized the pick-up volume by the distribution of the motor unit action potential amplitude over the epimysium surface.

MAIN RESULTS

The electrodes provided high quality signals with average signal-to-noise ratio  >30 dB across 95 identified motor units. The motor unit action potential amplitude decreased with increasing distance of the electrode from the muscle fibers (P [Formula: see text] 0.001). The decrease was more pronounced for bipolar compared to monopolar derivations. The average muscle fiber conduction velocity was 2.46  ±  0.83 m s^-1. Most of the neuromuscular junctions were close to the region where the nerve was neurotized, as observed from the EMG recordings and imaging data.

SIGNIFICANCE

These results show that epimysial electrodes can be used for selective recordings of motor unit activities with a pick-up volume that included the entire muscle in the rat hindlimb. Epimysial electrodes can thus be used for detecting motor unit activity in muscles with specific fascicular territories associated to different functions following TMR surgery.

Relieving phantom limb pain with multimodal sensory-motor training

OBJECTIVE

The causes for the disabling condition of phantom limb pain (PLP), affecting 85% of amputees, are so far unknown, with few effective treatments available. Sensory feedback based strategies to normalize the motor commands to control the phantom limb offer important targets for new effective treatments as the correlation between phantom limb motor control and sensory feedback from the motor intention has been identified as a possible mechanism for PLP development.

APPROACH

Ten upper-limb amputees, suffering from chronic PLP, underwent 16 days of intensive training on phantom-limb movement control. Visual and tactile feedback, driven by muscular activity at the stump, was provided with the aim of reducing PLP intensity.

MAIN RESULTS

A 32.1% reduction of PLP intensity was obtained at the follow-up (6 weeks after the end of the training, with an initial 21.6% reduction immediately at the end of the training) reaching clinical effectiveness for chronic pain reduction. Multimodal sensory-motor training on phantom-limb movements with visual and tactile feedback is a new method for PLP reduction.

SIGNIFICANCE

The study results revealed a substantial reduction in phantom limb pain intensity, obtained with a new training protocol focused on improving phantom limb motor output using visual and tactile feedback from the stump muscular activity executed to move the phantom limb.

Attachment of upper arm prostheses with a subcutaneous osseointegrated implant in transhumeral amputees

BACKGROUND

The stump-socket interface is of utmost importance for prosthetic function in transhumeral amputees. Stability of this connection may be improved using a newly designed subcutaneous implant.

OBJECTIVES

The purpose was to determine the effect of the implant together with customized socket designs on the range of motion of the shoulder and the prosthetic function compared to conventional fitting.

STUDY DESIGN

Case series.

METHODS

The range of motion was measured with scaled metrics and the prosthetic function evaluated with the Southampton Hand Assessment Procedure and the Box and Block Test. Maximal loading was measured in straight and 90° flexion of the elbow.

RESULTS

The restriction of range of motion after conventional fitting was decreased from 42.55% ± 6.56% to 9.23% ± 14.89% in Patient I and from 62.18% ± 15.19% to 2.51% ± 2.49% in Patient II using the implant with customized sockets compared to range of motion without prosthesis. Both patients showed improved prosthetic function with the new system compared to conventional fitting.

CONCLUSION

The presented subcutaneous humeral implant, together with customized socket designs without straps and harnesses to the contralateral shoulder, can maintain almost complete range of motion of the shoulder. This resulted in improved prosthetic function and comfort for the patient without constant risk of infection. Clinical relevance Discomfort and limited prosthetic function are the main reasons for abandonment especially in transhumeral amputees. Shoulder straps and harnesses within conventional socket designs may not only lead to pain and skin irritations at the contralateral shoulder but also limit the range of motion of the shoulder joint and therefore prosthetic function.

Home-Based Tactile Discrimination Training Reduces Phantom Limb Pain

BACKGROUND

Phantom limb pain (PLP) affects a high percentage of amputees. Since treatment options are limited, low quality of life and addiction to pain medication frequently occur. New treatments, such as mirror therapy or electrical sensory discrimination training, make use of the brain's plasticity to alleviate this centrally derived pain.

AIM

This pilot study assessed the question of whether home-based tactile discrimination training (TDT) leads to a stronger decrease in PLP levels compared to standard massage treatment.

DESIGN

Controlled study.

SETTING

Outpatient.

POPULATION

Amputees (upper/lower extremity) with a PLP score of 4 or higher out of a possible 10 points on the visual analog scale.

METHODS

Eight patients participated in the study. The treatment phase comprised 2 weeks (15 minutes daily). Subjects were examined at baseline, after treatment, 2 weeks after completing treatment, and 4 weeks after completing treatment. Pain was assessed using the West Haven-Yale Multidimensional Pain Inventory.

RESULTS

There was a significantly stronger reduction in PLP in the treatment group receiving TDT. PLP intensity ratings were significantly reduced at the end of therapy, and at 2 and 4 weeks after completing treatment compared to pretreatment.

CONCLUSIONS

TDT seems to be an easy, cheap, time-effective, and safe method to achieve sustained alleviation of PLP and also brings about a positive change in body image.

REHABILITATION IMPACT

Home-based TDT could achieve a sustained reduction in PLP and should be considered as a possible alternative to established treatment methods.

Fascicular shifting: a novel technique to overcome large nerve defects

OBJECTIVE Over the last decade, a number of authors have investigated the utility of different biological and synthetic matrices as alternatives to conventional nerve grafts. However, the autologous nerve graft remains the gold standard, even though it often involves using a pure sensory nerve to reconstruct a mixed or even a pure motor nerve. Furthermore, limited donor sites often necessitate a significant mismatch of needed nerve tissue, especially for large proximal nerve defects such as brachial plexus lesions. Here, the authors present a new technique that overcomes these problems: the fascicular shift procedure (FSP). A fascicular group of the nerve distal to the injury is harvested in a sufficient length to bridge the nerve defect. METHODS The method of fascicular shifting was tested at the sciatic nerve in 45 Lewis rats. In the experimental group, a 15-mm nerve defect was created and reconstructed with a fascicular group that was harvested directly distal to the gap. This group was compared with 1 negative control group (defect without reconstruction) and 3 positive control groups (sensory, motor, and mixed graft). After 12 weeks of nerve regeneration, outcome was evaluated using retrograde labeling, histomorphometric analysis, and muscle force analysis. RESULTS All reconstructed groups showed successful regeneration with various levels of function. The negative control group showed minimal force measurements that were of no functional value. The fascicular shift provided sufficient guidance to overcome nerve defects, had higher (p < 0.1) motor neuron counts (1958.75 ± 657.21) than the sensory graft (1263.50 ± 538.90), and was equal to motor grafts (1490.43 ± 794.80) and mixed grafts (1720.00 ± 866.421). This tendency of improved motor regeneration was confirmed in all analyses. The mixed graft group was compared with the experimental group to investigate the influence of the potential damage induced by the fascicular shift distal to the repair site. However, none of the analyses revealed an impairment of nerve regeneration for both the tibial and common peroneal index muscles. CONCLUSIONS This study demonstrates that harvesting a transplant from the nerve segment distal to the injury site offers a mixed graft without causing additional donor-site morbidity. These grafts perform statistically better than a standard sensory graft in terms of motor recovery. The fascicular shift presents a novel method to reconstruct large proximal nerve defects, making it immensely attractive in brachial plexus reconstruction.

Axonal components of nerves innervating the human arm

OBJECTIVE

Axons traveling within the brachial plexus are responsible for the dexterous control of human arm and hand movements. Despite comprehensive knowledge on the topographical anatomy of nerves innervating the human upper limbs, the definite quantity of sensory and motor axons within this neural network remains elusive. Our aim was to perform a quantitative analysis of the axonal components of human upper limb nerves based on highly specific molecular features from spinal cord level to the terminal nerves at wrist level.

METHODS

Nerve specimen harvest at predefined harvesting sites (plexus roots and cords as well as major nerves originating from the brachial plexus innervating the arm and hand) was performed in 9 human heart-beating organ donors. Double immunofluorescence staining using antibodies against choline-acetyltransferase and neurofilament was performed to differentiate motor and sensory axons on nerve cross sections.

RESULTS

Three hundred fifty thousand axons emerge from the spinal cord to innervate the human upper limb, of which 10% are motor neurons. In all nerves studied, sensory axons outnumber motor axons by a ratio of at least 9:1. The sensory axon contribution increases when moving distally, whereas only 1,700 motor axons reach the hand to innervate the intrinsic musculature.

INTERPRETATION

Our results suggest that upper limb motor execution, and particularly dexterous coordination of hand movement, require an unexpectedly low number of motor neurons, with a large convergence of afferent input for feedback control. Ann Neurol 2017;82:396-408.

Longitudinal high-density EMG classification: Case study in a glenohumeral TMR subject

Targeted muscle reinnervation (TMR) represents a breakthrough interface for prosthetic control in high-level upper-limb amputees. However, clinically, it is still limited to the direct motion-wise control restricted by the number of reinnervation sites. Pattern recognition may overcome this limitation. Previous studies on EMG classification in TMR patients experienced with myocontrol have shown greater accuracy when using high-density (HD) recordings compared to conventional single-channel derivations. This case study investigates the potential of HD-EMG classification longitudinally over a period of 17 months post-surgery in a glenohumeral amputee. Five experimental sessions, separated by approximately 3 months, were performed. They were timed during a standard rehabilitation protocol that included intensive physio- and occupational therapy, myosignal training, and routine use of the final myoprosthesis. The EMG signals recorded by HD-EMG grids were classified into 12 classes. The first sign of EMG activity was observed in the second experimental session. The classification accuracy over 12 classes was 76% in the third session and ∼95% in the last two sessions. When using training and testing sets that were acquired with a 1-h time interval in between, a much lower accuracy (32%, Session 4) was obtained, which improved upon prosthesis usage (Session 5, 67%). The results document the improvement in EMG classification accuracy throughout the TMR-rehabilitation process.

Broadband Prosthetic Interfaces: Combining Nerve Transfers and Implantable Multichannel EMG Technology to Decode Spinal Motor Neuron Activity

Modern robotic hands/upper limbs may replace multiple degrees of freedom of extremity function. However, their intuitive use requires a high number of control signals, which current man-machine interfaces do not provide. Here, we discuss a broadband control interface that combines targeted muscle reinnervation, implantable multichannel electromyographic sensors, and advanced decoding to address the increasing capabilities of modern robotic limbs. With targeted muscle reinnervation, nerves that have lost their targets due to an amputation are surgically transferred to residual stump muscles to increase the number of intuitive prosthetic control signals. This surgery re-establishes a nerve-muscle connection that is used for sensing nerve activity with myoelectric interfaces. Moreover, the nerve transfer determines neurophysiological effects, such as muscular hyper-reinnervation and cortical reafferentation that can be exploited by the myoelectric interface. Modern implantable multichannel EMG sensors provide signals from which it is possible to disentangle the behavior of single motor neurons. Recent studies have shown that the neural drive to muscles can be decoded from these signals and thereby the user's intention can be reliably estimated. By combining these concepts in chronic implants and embedded electronics, we believe that it is in principle possible to establish a broadband man-machine interface, with specific applications in prosthesis control. This perspective illustrates this concept, based on combining advanced surgical techniques with recording hardware and processing algorithms. Here we describe the scientific evidence for this concept, current state of investigations, challenges, and alternative approaches to improve current prosthetic interfaces.

A Rapid Automated Protocol for Muscle Fiber Population Analysis in Rat Muscle Cross Sections Using Myosin Heavy Chain Immunohistochemistry

Quantification of muscle fiber populations provides a deeper insight into the effects of disease, trauma, and various other influences on skeletal muscle composition. Various time-consuming methods have traditionally been used to study fiber populations in many fields of research. However, recently developed immunohistochemical methods based on myosin heavy chain protein expression provide a quick alternative to identify multiple fiber types in a single section. Here, we present a rapid, reliable and reproducible protocol for improved staining quality, allowing automatic acquisition of whole cross sections and automatic quantification of fiber populations with ImageJ. For this purpose, embedded skeletal muscles are cut in cross sections, stained using myosin heavy chains antibodies with secondary fluorescent antibodies and DAPI for cell nuclei staining. Whole cross sections are then scanned automatically using a slide scanner to obtain high-resolution composite pictures of the entire specimen. Fiber population analyses are subsequently performed to quantify slow, intermediate and fast fibers using an automated macro for ImageJ. We have previously shown that this method can identify fiber populations reliably to a degree of ±4%. In addition, this method reduces inter-user variability and time per analyses significantly using the open source platform ImageJ.

Nerve grafts bridging the thenar branch of the median nerve to the ulnar nerve to enhance nerve recovery: a report of three cases

We report a nerve graft procedure bridging the thenar branch of the median nerve to the ulnar nerve in three patients with ulnar nerve transection and defect at the mid-forearm. Ulnar nerve function was evaluated with electroneurography and quantitative sensory-motor testing before and after surgery, and at a 6-year follow-up. After surgery all patients showed electroneurographic evidence of median nerve innervation of the intrinsic muscles normally innervated by the ulnar nerve. The average strength was Grade 4 in the intrinsic muscles originally supplied by the ulnar nerve at the final follow-up. Our results indicate that the thenar branch of the median nerve may support ulnar nerve regeneration and so help prevent intrinsic muscles from irreversible atrophy, but our report is preliminary. This procedure should be validated by future clinical data, especially those with complete ulnar nerve transection at or above the elbow.

LEVEL OF EVIDENCE

IV.

Translating Research on Myoelectric Control into Clinics-Are the Performance Assessment Methods Adequate?

Missing an upper limb dramatically impairs daily-life activities. Efforts in overcoming the issues arising from this disability have been made in both academia and industry, although their clinical outcome is still limited. Translation of prosthetic research into clinics has been challenging because of the difficulties in meeting the necessary requirements of the market. In this perspective article, we suggest that one relevant factor determining the relatively small clinical impact of myocontrol algorithms for upper limb prostheses is the limit of commonly used laboratory performance metrics. The laboratory conditions, in which the majority of the solutions are being evaluated, fail to sufficiently replicate real-life challenges. We qualitatively support this argument with representative data from seven transradial amputees. Their ability to control a myoelectric prosthesis was tested by measuring the accuracy of offline EMG signal classification, as a typical laboratory performance metrics, as well as by clinical scores when performing standard tests of daily living. Despite all subjects reaching relatively high classification accuracy offline, their clinical scores varied greatly and were not strongly predicted by classification accuracy. We therefore support the suggestion to test myocontrol systems using clinical tests on amputees, fully fitted with sockets and prostheses highly resembling the systems they would use in daily living, as evaluation benchmark. Agreement on this level of testing for systems developed in research laboratories would facilitate clinically relevant progresses in this field.

Game-Based Rehabilitation for Myoelectric Prosthesis Control

Background

A high number of upper extremity myoelectric prosthesis users abandon their devices due to difficulties in prosthesis control and lack of motivation to train in absence of a physiotherapist. Virtual training systems, in the form of video games, provide patients with an entertaining and intuitive method for improved muscle coordination and improved overall control. Complementary to established rehabilitation protocols, it is highly beneficial for this virtual training process to start even before receiving the final prosthesis, and to be continued at home for as long as needed.

Objective

The aim of this study is to evaluate (1) the short-term effects of a commercially available electromyographic (EMG) system on controllability after a simple video game-based rehabilitation protocol, and (2) different input methods, control mechanisms, and games.

Methods

Eleven able-bodied participants with no prior experience in EMG control took part in this study. Participants were asked to perform a surface EMG test evaluating their provisional maximum muscle contraction, fine accuracy and isolation of electrode activation, and endurance control over at least 300 seconds. These assessments were carried out (1) in a Pregaming session before interacting with three EMG-controlled computer games, (2) in a Postgaming session after playing the games, and (3) in a Follow-Up session two days after the gaming protocol to evaluate short-term retention rate. After each game, participants were given a user evaluation survey for the assessment of the games and their input mechanisms. Participants also received a questionnaire regarding their intrinsic motivation (Intrinsic Motivation Inventory) at the end of the last game.

Results

Results showed a significant improvement in fine accuracy electrode activation (P<.01), electrode separation (P=.02), and endurance control (P<.01) from Pregaming EMG assessments to the Follow-Up measurement. The deviation around the EMG goal value diminished and the opposing electrode was activated less frequently. Participants had the most fun playing the games when collecting items and facing challenging game play.

Conclusions

Most upper limb amputees use a 2-channel myoelectric prosthesis control. This study demonstrates that this control can be effectively trained by employing a video game-based rehabilitation protocol.