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Extrapolation of Emerging Technologies and Their Long-Term Implications for Myoelectric versus Body-Powered Prostheses: An Engineering Perspective
Abstract
Extrapolation of Emerging Technologies and Their Long-Term Implications for Myoelectric versus Body-Powered Prostheses: An Engineering Perspective
Richard F. ff. Weir, PhD
ABSTRACT
The field of prosthetic rehabilitation is at the cusp of a revolution in upper-limb prosthetic techniques and treatment options. After 50 years of largely incremental developments in the design of both body-powered and myoelectric upper extremity prostheses, new technologies are coming of age that will provide sensory feedback to the user. This, in turn, will promote embodiment of the prosthesis, allowing users to believe the device is a true extension of themselves. This will facilitate the incorporation of the prosthesis into their body image and allow users to finally begin to think of the prosthesis as a true limb replacement rather than as a tool. This review surveys innovations in upper-limb prosthetic rehabilitation from an engineering perspective.
(J Prosthet Orthot. 2017;29:P63–P74)
KEY INDEXING TERMS: cable operated, EMG, external power, electric powered, extended physiological proprioception, osseointegration, neural interface, rapid prototyping, implantable sensors, sensors, cineplasty, kineplasty, sensory feedback, body-powered, externally-powered, limb transplantation, tissue printing, bio-printing, limb regrowth
... Although they were considered primitive, earlier prosthetics were very functional and incorporated many vital prosthetic principles upon which today's technological advancements are hinged [3]. The first true rehabilitation aids acknowledged as prostheses were made in Egypt, Greece and Rome [4]. ...
... Weight loss was calculated using Equation 3. ...
The desire to restore the quality of life to amputees has been on the front burner in
recent years. This study compares the functional properties of a home-grown
nanocomposite (NC) and multiflex dynamic response-2 artificial foot (M.DR2). The
inherent challenge of ensuring uniform distribution of multi-walled carbon nanotube
(MWCNT) in host matrices was addressed by the use of sodium dodecylbenzene
sulfonate (C18H29NaO3S). Carbon nanotubes (CNTs) were synthesised via catalytic
chemical vapour deposition (CCVD) technique and the NC was produced using an
electrically heated hydraulic press. While the initial decomposition temperature (Tonset)
showed that the newly developed material with 260.01 0C is more thermally stable than
M.DR2 artificial foot with the temperature of 238.17 oC, incorporation of MWCNTs
into the unfilled NR matrix proved a significant change in Tonset. MWCNT loading was
found to influence the moisture content of the reinforced matrix by about 7% with the
NC being 35% more thermally stable than M. DR2 artificial foot. SEM/EDS
micrographs indicated complete embedment of MWCNTs in NR matrix, thereby
making it more suitable than M. DR2 foot which was inundated with cavities, thereby
making it susceptible to early failure. While it took both materials 120 days to attain
saturation point NR/MWCNT-3 is 93% more dimensionally stable that M. DR2 and
also demonstrated better resistance to wear. The wear rate results revealed that M. DR2
wears faster than NR/MWCNT-3 by approximately 32%. It can, therefore, be
concluded from the foregoing that the home-grown material is to be preferred to its
foreign counterpart for anthropomorphic prosthetic foot application.
... However, even with these advanced myoelectric devices and controllers, end users find their operation cumbersome and time consuming (20). Motor control is also challenged by the lack of proprioceptive sensory feedback from prostheses (12,(21)(22)(23). Together, the limitations of the current amputation approaches significantly lower the quality of life for persons with amputation (24)(25)(26)(27). ...
Significance
Despite advancements in prosthetic technologies, persons with amputation today suffer great diminution in mobility and quality of life. This is largely due to an outdated amputation paradigm that precludes efficacious communication between the residual limb and prosthesis. An amputation method utilizing agonist–antagonist myoneural interfaces (AMIs) constructs neuromuscular substrates in the residual limb to avail enhanced sensorimotor signaling. In our study, subjects with AMI amputation demonstrate improved motor control, phantom sensations, range of motion, and decreased pain when compared to patients with traditional amputation. With the demonstrated increases in motor coordination and position differentiation, our results suggest that patients with AMI amputation will be able to more efficaciously control bionic prostheses.
The human hand is a complex integrated system with motor and sensory components that provides individuals with high functionality and elegant behaviour. In direct connection with the brain, the hand is capable of performing countless actions ranging from fine digit manipulation to the handling of heavy objects. However the question of which movements mostly contribute to the manipulation skills of the hand, and thus should be included in prosthetic hands, is yet to be answered. Building from our previous work, and assuming that a hand with independent long fingers allowed performance comparable to a hand with coupled fingers, here we explored the actual contribution of independent fingers while performing activities of daily living using custom built orthoses. Our findings show that, when an opposable thumb is present, independent long fingers provide a measureable advantage in performing activities of daily living only when precision grasps are involved. In addition, the results suggest that the remarkable grasping skills of the human hand rely more on the independent abduction/adduction of the fingers than on their independent flexion/extension. These findings are of interest to the designers of artificial hands, including biomimetic prostheses and exoskeletons.
Background. The purpose of this experiment was to develop a peripheral nerve interface using cultured myoblasts within a scaffold to provide a biologically stable interface while providing signal amplification for neuroprosthetic control and preventing neuroma formation. Methods. A Regenerative Peripheral Nerve Interface (RPNI) composed of a scaffold and cultured myoblasts was implanted on the end of a divided peroneal nerve in rats (
n
=
25
). The scaffold material consisted of either silicone mesh, acellular muscle, or acellular muscle with chemically polymerized poly(3,4-ethylenedioxythiophene) conductive polymer. Average implantation time was 93 days. Electrophysiological tests were performed at endpoint to determine RPNI viability and ability to transduce neural signals. Tissue samples were examined using both light microscopy and immunohistochemistry. Results. All implanted RPNIs, regardless of scaffold type, remained viable and displayed robust vascularity. Electromyographic activity and stimulated compound muscle action potentials were successfully recorded from all RPNIs. Physiologic efferent motor action potentials were detected from RPNIs in response to sensory foot stimulation. Histology and transmission electron microscopy revealed mature muscle fibers, axonal regeneration without neuroma formation, neovascularization, and synaptogenesis. Desmin staining confirmed the preservation and maturation of myoblasts within the RPNIs. Conclusions. RPNI demonstrates significant myoblast maturation, innervation, and vascularization without neuroma formation.
The amplitude of the surface EMG (sEMG) is commonly estimated by rectification or other non-linear transformations, followed by smoothing (low-pass linear filtering). Although computationally efficient, this approach leads to an estimation accuracy with a limited theoretical signal-to-noise ratio (SNR). Since sEMG amplitude is one of the most relevant features for myoelectric control, its estimate has become one of the limiting factors for the performance of myoelectric control applications, such as powered prostheses. In this study, we present a recursive nonlinear estimator of sEMG amplitude based on Bayesian filtering. Furthermore, we validate the advantage of the proposed Bayesian filter over the conventional linear filters through an online simultaneous and proportional control (SPC) task, performed by 8 able-bodied subjects and 3 below-elbow limb deficient subjects. The results demonstrated that the proposed Bayesian filter provides significantly more accurate SPC, particularly for the patients, when compared with conventional linear filters. This result presents a major step toward accurate prosthetic control for advanced multi-function prostheses.
A myoelectric controller should provide an intuitive and effective human-machine interface that deciphers user intent in real-time and is robust enough to operate in daily life. Many myoelectric control architectures have been developed, including pattern recognition systems, finite state machines, and more recently, postural control schemes. Here, we present a comparative study of two types of finite state machines and a postural control scheme using both virtual and physical assessment procedures with seven nondisabled subjects. The Southampton Hand Assessment Procedure (SHAP) was used in order to compare the effectiveness of the controllers during activities of daily living using a multigrasp artificial hand. Also, a virtual hand posture matching task was used to compare the controllers when reproducing six target postures. The performance when using the postural control scheme was significantly better (p < 0.05) than the finite state machines during the physical assessment when comparing within-subject averages using the SHAP percent difference metric. The virtual assessment results described significantly greater completion rates (97% and 99%) for the finite state machines, but the movement time tended to be faster (2.7 s) for the postural control scheme. Our results substantiate that postural control schemes rival other state-of-the-art myoelectric controllers.
A remaining barrier to the clinical accessibility of pattern recognition systems is the lack of practical methods to acquire the myoelectric signals required to train the system. Many current methods involve screen-guided training (SGT), where wearers connected to an external computer perform muscle contractions synchronized with a sequence of visual cues. The system complexity prevents easy retraining when signal conditions change. We have developed a method called prosthesis-guided training (PGT), where the prosthesis itself provides the cues by moving through a sequence of preprogrammed motions; screen prompting and external connections are eliminated. Five prosthesis wearers performed a repetitive clothespin placement task using pattern recognition control. Wearers demonstrated similar baseline functionality between systems trained with PGT (10 ± 4 clothespins) and SGT (12 ± 7 clothespins) (p = 0.56). To investigate the efficacy of PGT retraining, real-world issues (e.g. broken wires, external noise) were simulated to accelerate control degradation. Sessions ended when wearers indicated loss of functional control. On average, wearers maintained function through two malfunctioning inputs, placing 48 ± 17 clothespins in 31.6 ± 16.2 minutes when allowed to retrain using PGT. These results suggest that PGT acquires adequate training data and may enable longer-lasting functional use, potentially increasing prosthesis wear time and reducing device rejection.
The potential for pattern recognition to improve powered prosthesis control has been discussed for many years. One remaining barrier to at-home use of these techniques is that practical methods of user prompting during system training are lacking. Most research and development of pattern recognition systems for prosthesis control has relied on on-screen cues to prompt the prosthesis wearer during signal collection; therefore most systems require connection to a computer or external device. We have developed a method called Prosthesis-Guided Training (PGT) to address this issue. In PGT, the prosthesis itself moves through a pre-programmed sequence of motions to prompt the wearer to elicit the appropriate muscle contractions. PGT requires no extra hardware and allows wearers to retrain, refresh, or recalibrate the controller in many locations and situations. Training via PGT is self-initiated and requires only about 1 minute of the wearer's time. Furthermore, PGT provides a practical mechanism for overcoming malfunctioning or changing inputs, addresses differences in routine donning, and results in acquisition of myoelectric signals representative of those elicited during functional use. Qualitative and quantitative data acquired to investigate the efficacy of PGT suggest that it is an intuitive, effective, and clinically viable method of training pattern recognition–controlled prostheses.
Background: Direct skeletal attachment of limb prostheses is associated with high rate of transcutaneous infection and loosening of the fixture in the medullary canal prompting for careful assessment of various means for enhancing the skindevice and bone-device interface. The skin and bone integrated pylon system constitutes a technological platform for different modifications being evaluated previously. Objectives: The current study assessed the combination of nano-treatment skin and bone integrated pylon with its reseeding
with dermal fibroblasts. We hypothesized that this combination will enhance cell interaction with skin and bone integrated pylon compared to nano-treatment and the fibroblast seeding when done separately.
Study design: The feasibility and safety of in-bone implantation of the skin and bone integrated pylon with nanotubes was investigated in vitro and in vivo in the animal model. Methods: TiO2 nanotubes were fabricated on the skin and bone integrated pylon, and the fibroblasts taken from rabbit’s skin were cultured on the pylons before implantation. Results: The in vitro experiments demonstrated higher cellular density in the samples with a nanotubular surface than in the non-modified pylons used as control. There were no postoperative complications in any of the animals during the 6-month observation period. Subsequent scanning electron microscopy of the pylon extracted from the rabbit’s femur showed the stable contact between the pylon and soft tissues in comparison to control samples where the patchy fibrovascular ingrowth was detected. Conclusion: The promising results prompt further investigation of the integrative properties of the nanotextured skin and bone integrated pylon system seeded with dermal fibroblasts and its optimization for clinical application. Clinical relevance The study is devoted to the development of more safe and efficient technology of direct skeletal attachment of limb prostheses aimed in improving quality of life of people with amputations.
Touch perception on the fingers and hand is essential for fine motor control, contributes to our sense of self, allows for effective communication, and aids in our fundamental perception of the world. Despite increasingly sophisticated mechatronics, prosthetic devices still do not directly convey sensation back to their wearers. We show that implanted peripheral nerve interfaces in two human subjects with upper limb amputation provided stable, natural touch sensation in their hands for more than 1 year. Electrical stimulation using implanted peripheral nerve cuff electrodes that did not penetrate the nerve produced touch perceptions at many locations on the phantom hand with repeatable, stable responses in the two subjects for 16 and 24 months. Patterned stimulation intensity produced a sensation that the subjects described as natural and without "tingling," or paresthesia. Different patterns produced different types of sensory perception at the same location on the phantom hand. The two subjects reported tactile perceptions they described as natural tapping, constant pressure, light moving touch, and vibration. Changing average stimulation intensity controlled the size of the percept area; changing stimulation frequency controlled sensation strength. Artificial touch sensation improved the subjects' ability to control grasping strength of the prosthesis and enabled them to better manipulate delicate objects. Thus, electrical stimulation through peripheral nerve electrodes produced long-term sensory restoration after limb loss.
Electrical stimulation is a promising technology for the restoration of arm function in paralyzed individuals. Control of the paralyzed arm under electrical stimulation, however, is a challenging problem that requires advanced controllers and command interfaces for the user. A real-time model describing the complex dynamics of the arm would allow user-in-the-loop type experiments where the command interface and controller could be assessed. Real-time models of the arm previously described have not included the ability to model the independently controlled scapula and clavicle, limiting their utility for clinical applications of this nature. The goal of this study therefore was to evaluate the performance and mechanical behavior of a real-time, dynamic model of the arm and shoulder girdle. The model comprises seven segments linked by eleven degrees of freedom and actuated by 138 muscle elements. Polynomials were generated to describe the muscle lines of action to reduce computation time, and an implicit, first-order Rosenbrock formulation of the equations of motion was used to increase simulation step-size. The model simulated flexion of the arm faster than real time, simulation time being 92% of actual movement time on standard desktop hardware. Modeled maximum isometric torque values agreed well with values from the literature, showing that the model simulates the moment-generating behavior of a real human arm. The speed of the model enables experiments where the user controls the virtual arm and receives visual feedback in real time. The ability to optimize potential solutions in simulation greatly reduces the burden on the user during development.
Background:
Osseointegrated percutaneous implants provide direct anchorage of the limb prosthesis to the residual limb. These implants have been used for the rehabilitation of transhumeral amputees in Sweden since 1995 using a two-stage surgical approach with a 6-month interval between the stages, but results on implant survival, adverse events, and radiologic signs of osseointegration and adaptive bone remodeling in transhumeral amputees treated with this method are still lacking.
Questions/purposes:
This study reports on 2- and 5-year implant survival, adverse events, and radiologic signs of osseointegration and bone remodeling in transhumeral amputees treated with osseointegrated prostheses.
Methods:
Between 1995 and 2010, we performed 18 primary osseointegrated percutaneous implants and two implant revisions in 18 transhumeral amputees; of those, 16 patients were available for followup at a minimum of 2 years (median, 8 years; range, 2-19 years). These include all transhumeral amputees who have received osseointegrated prostheses and represented approximately 20% of the all transhumeral amputees we evaluated for potential osseointegration during that time; general indications for this approach included transhumeral amputation resulting from trauma or tumor, inability to wear or severe problems wearing a conventional socket prosthesis, eg, very short residual limb, and compliant patients. Medical charts and plain radiographs were retrospectively evaluated.
Results:
The 2- and 5-year implant survival rates were 83% and 80%, respectively. Two primary and one revised implant failed and were removed because of early loosening. A fourth implant was partially removed because of ipsilateral shoulder osteoarthritis and subsequent arthrodesis. The most common adverse event was superficial infection of the skin penetration site (15 infections in five patients) followed by skin reactions of the skin penetration site (eight), incomplete fracture at the first surgery (eight), defective bony canal at the second surgery (three), avascular skin flap necrosis (three), and one deep implant infection. The most common radiologic finding was proximal trabecular buttressing (10 of 20 implants) followed by endosteal bone resorption and cancellization (seven of 20), cortical thinning (five of 20), and distal bone resorption (three of 20).
Conclusions:
The implant system presented a survivorship of 83% at 5 years and a 38% 5-year incidence of infectious complications related to the skin penetration site that were easily managed with nonoperative treatment, which make it a potentially attractive alternative to conventional socket arm prostheses. Osseointegrated arm prostheses have so far only been used in transhumeral amputations resulting from either trauma or tumor. Their use has not been tested and is therefore not recommended in transhumeral amputations resulting from vascular disease. This method could theoretically be superior to socket prostheses, especially in transhumeral amputees with very short residual humerus in which the suspension of a conventional prosthesis is difficult. Comparative studies are needed to support its potential superiority. Moreover, the radiological findings in this study need to be followed over time because some of them are of uncertain long-term clinical relevance.
Myoelectrically powered prosthetic hands lack sensory feedback relating to the force exerted by the artificial hand on a grasped object. The degree of control is imprecise, and often much more force than necessary is applied. The aim of this study was to develop and evaluate a force feedback system considering design constraints, providing the user with closed-loop control. Different methods and design criteria for providing myoelectric prosthetic hands with force feedback were analyzed, with stimulation by vibration being preferred. A new feedback system was designed, consisting of a miniature vibration motor, a piezoresistive force sensor, and control electronics. Grasping forces with and without feedback were recorded and compared from five habitual myoelectric hand users when grasping a hand dynamometer with different weights attached to it. All five patients rapidly improved their ability to regulate the grasping force without the help of vision when feedback was applied. An average force reduction of 37% was found when vibration was applied indirectly to the hand, and a decrease of 54% was found when feedback was applied directly to the skin of the residual limb. Constraints for a prosthetic force feedback system such as low power consumption, compactness, and being imperceptible to others are included in the design. General acceptance of vibration as a feedback signal was good, especially when applied indirectly. The results indicate that the new system is of potential value for myoelectric prosthetic hand users. More precise control is possible, and redundant grasping force can be diminished with a feedback system. (J Prosthet Orthot. 2006;18:57–61.)
Publisher Summary
This chapter elaborates the sensory control of dexterous manipulation in humans. Successful manipulation requires the subject to select the appropriate pattern of motor commands based on the manipulative intent, on various constraints imposed by the task, and on the relevant physical properties of the manipulated object. The sensorimotor mechanisms employed in precision grip lifting to adapt force output to frictional condition and to object weight operate according to a predictive feed-forward sensory control policy running on at least two time scales. Contextual, cognitive, and movement phase-de pendent interpretations of multisensory input seem to be vital features of the underlying sensorimotor transformations. On an extended time scale, previous experience with the object at hand is used to adjust the motor commands parametrically in advance of the movement. This ability to parameterize default motor commands has been called anticipatory parameter control. It is found that while the task evolves, somatosensory as well as other sources of information may then modify the ongoing behavior. Force coordination across digits is partly an emergent property of these local control mechanisms.
Background
Porous tantalum trabecular metal has recently been incorporated in titanium dental implants as a new form of implant surface enhancement. However, there is little information on the applications of this material in implant dentistry. PurposeThe purpose of this article is to summarize the contemporary concept on the applications of porous tantalum trabecular metal in implant dentistry. Materials and Methods
We therefore review the current literature on the basic science and clinical uses of this material. ResultsPorous tantalum metal is used to improve the contact between osseous structure and dental implants and therefore presumably facilitate osseointegration. Success of porous tantalum metal in orthopedic implants led to the incorporation of porous tantalum metal in the design of root-form endosseous titanium implants. The porous tantalum three-dimensional enhancement of titanium dental implant surface allows for combining bone ongrowth together with bone ingrowth, or osseoincorporation. While little is known about the biological aspect of the porous tantalum in the oral cavity, there seems to be several possible advantages of this implant design. This article reviews the biological aspects of porous tantalum-enhanced titanium dental implants, in particular the effects of anatomical consideration and oral environment to implant designs. Conclusions
We propose here possible clinical situations and applications for this type of dental implant. Advantages and disadvantages of the implants as well as needed future clinical studies are discussed.
Reported studies on pattern recognition of electromyograms (EMG) for the control of prosthetic devices traditionally focus on classification accuracy of signals recorded in a laboratory. The difference between the constrained nature in which such data are often collected and the unpredictable nature of prosthetic use is an example of the semantic gap between research findings and a viable clinical implementation. In this paper, we demonstrate that the variations in limb position associated with normal use can have a substantial impact on the robustness of EMG pattern recognition, as illustrated by an increase in average classification error from 3.8% to 18%. We propose to solve this problem by: 1) collecting EMG data and training the classifier in multiple limb positions and by 2) measuring the limb position with accelerometers. Applying these two methods to data from ten normally limbed subjects, we reduce the average classification error from 18% to 5.7% and 5.0%, respectively. Our study shows how sensor fusion (using EMG and accelerometers) may be an efficient method to mitigate the effect of limb position and improve classification accuracy.
Functional electrical stimulation (FES), the coordinated electrical activation of multiple muscles, has been used to restore arm and hand function in people with paralysis. User interfaces for such systems typically derive commands from mechanically unrelated parts of the body with retained volitional control, and are unnatural and unable to simultaneously command the various joints of the arm. Neural interface systems, based on spiking intracortical signals recorded from the arm area of motor cortex, have shown the ability to control computer cursors, robotic arms and individual muscles in intact non-human primates. Such neural interface systems may thus offer a more natural source of commands for restoring dexterous movements via FES. However, the ability to use decoded neural signals to control the complex mechanical dynamics of a reanimated human limb, rather than the kinematics of a computer mouse, has not been demonstrated. This study demonstrates the ability of an individual with long-standing tetraplegia to use cortical neuron recordings to command the real-time movements of a simulated dynamic arm. This virtual arm replicates the dynamics associated with arm mass and muscle contractile properties, as well as those of an FES feedback controller that converts user commands into the required muscle activation patterns. An individual with long-standing tetraplegia was thus able to control a virtual, two-joint, dynamic arm in real time using commands derived from an existing human intracortical interface technology. These results show the feasibility of combining such an intracortical interface with existing FES systems to provide a high-performance, natural system for restoring arm and hand function in individuals with extensive paralysis.
Existing prosthetic limbs do not provide amputees with cutaneous feedback. Tactile feedback is essential to intuitive control of a prosthetic limb and it is now clear that the sense of body self-identification is also linked to cutaneous touch. Here we have created an artificial sense of touch for a prosthetic limb by coupling a pressure sensor on the hand through a robotic stimulator to surgically redirected cutaneous sensory nerves (targeted reinnervation) that once served the lost limb. We hypothesize that providing physiologically relevant cutaneous touch feedback may help an amputee incorporate an artificial limb into his or her self image. To investigate this we used a robotic touch interface coupled with a prosthetic limb and tested it with two targeted reinnervation amputees in a series of experiments fashioned after the Rubber Hand Illusion. Results from both subjective (self-reported) and objective (physiological) measures of embodiment (questionnaires, psychophysical temporal order judgements and residual limb temperature measurements) indicate that returning physiologically appropriate cutaneous feedback from a prosthetic limb drives a perceptual shift towards embodiment of the device for these amputees. Measurements provide evidence that the illusion created is vivid. We suggest that this may help amputees to more effectively incorporate an artificial limb into their self image, providing the possibility that a prosthesis becomes not only a tool, but also an integrated body part.
Functionality, controllability and cosmetics are the key issues to be addressed in order to accomplish a successful functional substitution of the human hand by means of a prosthesis. Not only the prosthesis should duplicate the human hand in shape, functionality, sensorization, perception and sense of body-belonging, but it should also be controlled as the natural one, in the most intuitive and undemanding way. At present, prosthetic hands are controlled by means of non-invasive interfaces based on electromyography (EMG). Driving a multi degrees of freedom (DoF) hand for achieving hand dexterity implies to selectively modulate many different EMG signals in order to make each joint move independently, and this could require significant cognitive effort to the user.
A Principal Components Analysis (PCA) based algorithm is used to drive a 16 DoFs underactuated prosthetic hand prototype (called CyberHand) with a two dimensional control input, in order to perform the three prehensile forms mostly used in Activities of Daily Living (ADLs). Such Principal Components set has been derived directly from the artificial hand by collecting its sensory data while performing 50 different grasps, and subsequently used for control.
Trials have shown that two independent input signals can be successfully used to control the posture of a real robotic hand and that correct grasps (in terms of involved fingers, stability and posture) may be achieved.
This work demonstrates the effectiveness of a bio-inspired system successfully conjugating the advantages of an underactuated, anthropomorphic hand with a PCA-based control strategy, and opens up promising possibilities for the development of an intuitively controllable hand prosthesis.
Treatment with osseointegrated transfemoral prostheses has been shown to improve quality of life. The treatment has been performed in Sweden since 1990 and consists of two surgical procedures followed by rehabilitation. During the first years, the rehabilitation process was not standardized. In 1999, a treatment protocol called OPRA (Osseointegrated Prostheses for the Rehabilitation of Amputees) was established. This article describes the current rehabilitation protocol and illustrates the overall results. The OPRA rehabilitation protocol is graded to stimulate the process of osseointegration and prepare the patient for unrestricted prosthetic use. It includes initial training with a short training prosthesis followed by gradually increased prosthetic activity. Between May 1990 and June 2008, we treated 100 patients with 106 implants (6 bilaterally; 61% males, 39% females; mean age 43 years; mean time since amputation 11.5 years.) The majority had amputations due to trauma (67%) or tumor (21%) (other = 12%). Currently, 68 patients are using their prostheses (follow-up: 3 months- 17.5 years) and 32 are not (4 are deceased, 7 are before second surgery, 6 are in initial training, 4 are not using prosthesis, and 11 had the implant removed). The majority of treatment failures occurred in patients before we established the OPRA protocol. The implementation of graded rehabilitation is considered to be of utmost importance for improved results.
Pattern recognition is a useful tool for deciphering movement intent from myoelectric signals. Recognition paradigms must adapt with the user in order to be clinically viable over time. Most existing paradigms are static, although two forms of adaptation have received limited attention. Supervised adaptation can achieve high accuracy since the intended class is known, but at the cost of repeated cumbersome training sessions. Unsupervised adaptation attempts to achieve high accuracy without knowledge of the intended class, thus achieving adaptation that is not cumbersome to the user, but at the cost of reduced accuracy. This study reports a novel adaptive experiment on eight subjects that allowed repeated measures post-hoc comparison of four supervised and three unsupervised adaptation paradigms. All supervised adaptation paradigms reduced error over time by at least 26% compared to the nonadapting classifier. Most unsupervised adaptation paradigms provided smaller reductions in error, due to frequent uncertainty of the correct class. One method that selected high-confidence samples showed the most practical implementation, although the other methods warrant future investigation. Supervised adaptation should be considered for incorporation into any clinically viable pattern recognition controller, and unsupervised adaptation should receive renewed interest in order to provide transparent adaptation.
A functional electrical stimulation controller is presented that uses a combination of feedforward and feedback for arm control in high-level injury. The feedforward controller generates the muscle activations nominally required for desired movements, and the feedback controller corrects for errors caused by muscle fatigue and external disturbances. The feedforward controller is an artificial neural network (ANN) which approximates the inverse dynamics of the arm. The feedback loop includes a PID controller in series with a second ANN representing the nonlinear properties and biomechanical interactions of muscles and joints. The controller was designed and tested using a two-joint musculoskeletal model of the arm that includes four mono-articular and two bi-articular muscles. Its performance during goal-oriented movements of varying amplitudes and durations showed a tracking error of less than 4 degrees in ideal conditions, and less than 10 degrees even in the case of considerable fatigue and external disturbances.
We have developed a multichannel electrogmyography sensor system capable of receiving and processing signals from up to 32 implanted myoelectric sensors (IMES). The appeal of implanted sensors for myoelectric control is that electromyography (EMG) signals can be measured at their source providing relatively cross-talk-free signals that can be treated as independent control sites. An external telemetry controller receives telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link provides power and commands to the implanted electrodes. Wireless telemetry of EMG signals from sensors implanted in the residual musculature eliminates the problems associated with percutaneous wires, such as infection, breakage, and marsupialization. Each implantable sensor consists of a custom-designed application-specified integrated circuit that is packaged into a biocompatible RF BION capsule from the Alfred E. Mann Foundation. Implants are designed for permanent long-term implantation with no servicing requirements. We have a fully operational system. The system has been tested in animals. Implants have been chronically implanted in the legs of three cats and are still completely operational four months after implantation.
Living systems exhibit remarkable abilities to self-assemble, regenerate, and remodel complex shapes. How cellular networks construct and repair specific anatomical outcomes is an open question at the heart of the next-generation science of bioengineering. Developmental bioelectricity is an exciting emerging discipline that exploits endogenous bioelectric signaling among many cell types to regulate pattern formation. We provide a brief overview of this field, review recent data in which bioelectricity is used to control patterning in a range of model systems, and describe the molecular tools being used to probe the role of bioelectrics in the dynamic control of complex anatomy. We suggest that quantitative strategies recently developed to infer semantic content and information processing from ionic activity in the brain might provide important clues to cracking the bioelectric code. Gaining control of the mechanisms by which large-scale shape is regulated in vivo will drive transformative advances in bioengineering, regenerative medicine, and synthetic morphology, and could be used to therapeutically address birth defects, traumatic injury, and cancer.
The functional assessment of myoelectric control algorithms by persons with amputation promotes the overarching goal of the field of prosthetic limb design: to replace what was lost. However, many studies use experimental paradigms with virtual interfaces and able-bodied subjects that do not capture the challenges of a clinical implementation with an amputee population. A myoelectric control system must be robust to variable physiology, loading effects of the prosthesis on the limb, and limb position effects during dynamic tasks. Here persons with transradial limb loss performed activities of daily living using a postural controller and multi-functional prosthetic hand in order to verify that the postural controller was robust to these clinical challenges. The Southampton Hand Assessment Procedure was performed by persons with limb loss and able-bodied subjects. The results indicate that persons with limb loss and able-limbed subjects achieved the same performance and therefore that the clinical challenges were overcome. Persons with limb loss achieved 55% of physiological hand function on average. Also, the postural controller is compared to other state of the art myoelectric controllers and prosthetic hands previously tested. This work confirms that the postural controller is potentially a clinically-viable method to control myoelectric multi-functional prosthetic hands.
A challenge for tissue engineering is producing three-dimensional (3D), vascularized cellular constructs of clinically relevant size, shape and structural integrity. We present an integrated tissue-organ printer (ITOP) that can fabricate stable, human-scale tissue constructs of any shape. Mechanical stability is achieved by printing cell-laden hydrogels together with biodegradable polymers in integrated patterns and anchored on sacrificial hydrogels. The correct shape of the tissue construct is achieved by representing clinical imaging data as a computer model of the anatomical defect and translating the model into a program that controls the motions of the printer nozzles, which dispense cells to discrete locations. The incorporation of microchannels into the tissue constructs facilitates diffusion of nutrients to printed cells, thereby overcoming the diffusion limit of 100-200 μm for cell survival in engineered tissues. We demonstrate capabilities of the ITOP by fabricating mandible and calvarial bone, cartilage and skeletal muscle. Future development of the ITOP is being directed to the production of tissues for human applications and to the building of more complex tissues and solid organs.
IT IS ESTIMATED THAT ABOUT ONE-THIRD OF THE UNILATERAL AMPUTEED PATIENTS INITIALLY PROVIDED WITH A PROSTHESIS NO LONGERUSE IT. THIS INDICATES THAT THE HUMAN PROSTHESIS INTERFACE OR THE DESIGN OF THE PROSTHESIS IS NOT AS SATISFACTORY AS MIGHT BE EXPECTED. IN CASES OF BILATERAL AMPUTATION ONE MAY SUPPOSE A MORE FREQUENT USE OF PROSTHESIS: THE PATIENT HAS NO OTHER POSSIBILITY, THEREFORE EVEN BADLY DESIGNED PROSTHESES WILL BE USED IN THESE CASES. BECAUSE OF THE FACT THAT EVEN THE IMPLEMENTATION OF MODERN MYO-ELECTRIC PROSTHESES SHOWS SIMILAR RESULTS, IT WAS THOUGHT THAT NOT NECESSARILY MORE SOPHISTICATED AND COMPLEX PROSTHESES SHOULD IMPROVE THIS SITUATION. A VERY THOROUGH AND FUNDAMENTAL APPROACH WAS THOUGHT TO BE NECESSARY TO TRACE THE UNDERLYING CAUSES OF LOW ACCEPTANCE OF THE PROSTHESES. THE PAPER STATES THE PROBLEM IS STATED FROM THE HUMAN FACTORS VIEWPOINT. A THEORETICAL MODEL IS GIVEN WHICH CONSTITUTES THE BASIS OF RESEARCH AND EXPERIMENTAL PROGRAMS.
Objective: to assess the intra-and inter-session reliability of estimates of motor unit behaviour and muscle fiber properties derived from high-density surface electromyography (HDEMG).
Methods: ten healthy subjects performed submaximal isometric knee extensions during three recording sessions (separate days) at 10, 30, 50 and 70% of their maximum voluntary effort. The discharge timings of motor units of the vastus lateralis and medialis muscles were automatically identified from HDEMG by a decomposition algorithm. We characterized the number of detected motor units, their discharge rates, the coefficient of variation of their inter-spike intervals (CoVisi), the action potential conduction velocity and peak-to-peak amplitude. Reliability was assessed for each motor unit characteristics by intra-class correlation coefficient (ICC). Additionally, a pulse-to-noise ratio (PNR) was calculated, to verify the accuracy of the decomposition.
Results: Good to excellent reliability within and between sessions was found for all motor unit characteristics at all force levels (ICCs > 0.8), with the exception of CoVisi that presented poor reliability (ICC < 0.6). PNR was high and similar for both muscles with values ranging between 45.1- 47.6 dB (accuracy >95%).
Conclusion: motor unit features can be assessed non-invasively and reliably within and across sessions over a wide range of force levels.
Significance: these results suggest that it is possible to characterize motor units in longitudinal intervention studies.
Objective:
Tactile feedback is critical to grip and object manipulation. Its absence results in reliance on visual and auditory cues. Our objective was to assess the effect of sensory feedback on task performance in individuals with limb loss.
Approach:
Stimulation of the peripheral nerves using implanted cuff electrodes provided two subjects with sensory feedback with intensity proportional to forces on the thumb, index, and middle fingers of their prosthetic hand during object manipulation. Both subjects perceived the sensation on their phantom hand at locations corresponding to the locations of the forces on the prosthetic hand. A bend sensor measured prosthetic hand span. Hand span modulated the intensity of sensory feedback perceived on the thenar eminence for subject 1 and the middle finger for subject 2. We performed three functional tests with the blindfolded subjects. First, the subject tried to determine whether or not a wooden block had been placed in his prosthetic hand. Second, the subject had to locate and remove magnetic blocks from a metal table. Third, the subject performed the Southampton Hand Assessment Procedure (SHAP). We also measured the subject's sense of embodiment with a survey and his self-confidence.
Main results:
Blindfolded performance with sensory feedback was similar to sighted performance in the wooden block and magnetic block tasks. Performance on the SHAP, a measure of hand mechanical function and control, was similar with and without sensory feedback. An embodiment survey showed an improved sense of integration of the prosthesis in self body image with sensory feedback.
Significance:
Sensory feedback by peripheral nerve stimulation improved object discrimination and manipulation, embodiment, and confidence. With both forms of feedback, the blindfolded subjects tended toward results obtained with visual feedback.
The myoelectric controller (MEC) remains a technological bottleneck in the development of multifunctional prosthetic hands. Current MECs require physiologically inappropriate commands to indicate intent and lack effectiveness in a clinical setting. Postural control schemes use surface electromyography signals to drive a cursor in a continuous two-dimensional domain that is then transformed into a hand posture. Here, we present a novel algorithm for a postural controller and test the efficacy of the system during two experiments with 11 total subjects. In the first experiment, we found that performance increased when a velocity cursor-control technique versus a position cursor-control technique was used. Also, performance did not change when using 3, 4, or 12 surface electrodes. In the second experiment, subjects commanded a six degree-of-freedom virtual hand into seven functional postures without training, with completion rates of 82 +/- 4%, movement times of 3.5 +/- 0.2 s, and path efficiencies of 45 +/- 3%. Subjects retained the ability to use the postural controller at a high level across days after a single 1 hr training session. Our results substantiate the novel algorithm for a postural controller as a robust and advantageous design for a MEC of multifunction prosthetic hands.
Currently, most externally powered prostheses are controlled using electromyography (or EMG), which is the measure of the electrical signals that are produced when voluntary muscle is contracted. One of the major problems is that there are a limited number of muscular control sites that can be used, which limits the complexity of the hands that are controllable. Many upper-limb prosthetics researchers are searching for methods to simply and effectively control complex prosthetic hands, and a significant number of these researchers have utilized virtual hands and other simulations to perform testing of these control algorithms (oftentimes on able bodied subjects). Thus, these control techniques remain firmly planted in the virtual realm, and the authors postulate that the development of a physical hand would help to validate results obtained through use of virtual hands and could help establish whether or not a given control scheme is realistically applicable for use by amputees. The development of such a hand would be beneficial for researchers in the field. A six degree-of-freedom hand was developed with such a purpose in mind, and two of the major goals of the project were that the hand be inexpensive and open source. The hand design is being shared on www.opensourcehand.wordpress.com.
A major challenge since the invention of implantable devices has been a reliable and long-term stable transcutaneous communication. In the case of prosthetic limbs, existing neuromuscular interfaces have been unable to address this challenge and provide direct and intuitive neural control. Although prosthetic hardware and decoding algorithms are readily available, there is still a lack of appropriate and stable physiological signals for controlling the devices. We developed a percutaneous osseointegrated (bone-anchored) interface that allows for permanent and unlimited bidirectional communication with the human body. With this interface, an artificial limb can be chronically driven by implanted electrodes in the peripheral nerves and muscles of an amputee, outside of controlled environments and during activities of daily living, thus reducing disability and improving quality of life. We demonstrate in one subject, for more than 1 year, that implanted electrodes provide a more precise and reliable control than surface electrodes, regardless of limb position and environmental conditions, and with less effort. Furthermore, long-term stable myoelectric pattern recognition and appropriate sensory feedback elicited via neurostimulation was demonstrated. The opportunity to chronically record and stimulate the neuromuscular system allows for the implementation of intuitive control and naturally perceived sensory feedback, as well as opportunities for the prediction of complex limb motions and better understanding of sensory perception. The permanent bidirectional interface presented here is a critical step toward more natural limb replacement, by combining stable attachment with permanent and reliable human-machine communication.
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Fine-wire intramuscular electrodes were used to obtain EMG signals from six extrinsic hand muscles associated with the thumb, index, and middle fingers. Subjects' EMG activity was used to control a virtual three-DOF hand as they conformed the hand to a sequence of hand postures testing two controllers: direct EMG control and pattern recognition control. Subjects tested two conditions using each controller: starting the hand from a pre-defined neutral posture before each new posture and starting the hand from the previous posture in the sequence. Subjects demonstrated their ability to simultaneously, yet individually, move all three DOFs during the direct EMG control trials, however results showed subjects did not often utilize this feature. Performance metrics such as failure rate and completion time showed no significant difference between the two controllers.
Providing functionally effective sensory feedback to users of prosthetics is a largely unsolved challenge. Traditional solutions require high band-widths for providing feedback for the control of manipulation and yet have been largely unsuccessful. In this study, we have explored a strategy that relies on temporally discrete sensory feedback that is technically simple to provide. According to the Discrete Event-driven Sensory feedback Control (DESC) policy, motor tasks in humans are organized in phases delimited by means of sensory encoded discrete mechanical events. To explore the applicability of DESC for control, we designed a paradigm in which healthy humans operated an artificial robot hand to lift and replace an instrumented object, a task that can readily be learned and mastered under visual control. Assuming that the central nervous system of humans naturally organizes motor tasks based on a strategy akin to DESC, we delivered short-lasting vibrotactile feedback related to events that are known to forcefully affect progression of the grasp-lift-and-hold task. After training, we determined whether the artificial feedback had been integrated with the sensorimotor control by introducing short delays and we indeed observed that the participants significantly delayed subsequent phases of the task. This study thus gives support to the DESC policy hypothesis. Moreover, it demonstrates that humans can integrate temporally discrete sensory feedback while controlling an artificial hand and invites further studies in which inexpensive, noninvasive technology could be used in clever ways to provide physiologically appropriate sensory feedback in upper limb prosthetics with much lower band-width requirements than with traditional solutions.
Postamputation neuroma pain can prevent comfortable prosthesis wear in patients with limb amputations, and currently available treatments are not consistently effective. Targeted muscle reinnervation (TMR) is a decade-old technique that employs a series of novel nerve transfers to permit intuitive control of upper-limb prostheses. Clinical experience suggests that it may also serve as an effective therapy for postamputation neuroma pain; however, this has not been explicitly studied.
We evaluated the effect of TMR on residual limb neuroma pain in upper-extremity amputees.
We conducted a retrospective medical record review of all 28 patients treated with TMR from 2002 to 2012 at Northwestern Memorial Hospital/Rehabilitation Institute of Chicago (Chicago, IL, USA) and San Antonio Military Medical Center (San Antonio, TX, USA). Twenty-six of 28 patients had sufficient (> 6 months) followup for study inclusion. The amputation levels were shoulder disarticulation (10 patients) and transhumeral (16 patients). All patients underwent TMR for the primary purpose of improved myoelectric control. Of the 26 patients included in the study, 15 patients had evidence of postamputation neuroma pain before undergoing TMR.
Of the 15 patients presenting with neuroma pain before TMR, 14 experienced complete resolution of pain in the transferred nerves, and the remaining patient's pain improved (though did not resolve). None of the patients who presented without evidence of postamputation neuroma pain developed neuroma pain after the TMR procedure. All 26 patients were fitted with a prosthesis, and 23 of the 26 patients were able to operate a TMR-controlled prosthesis.
None of the 26 patients who underwent TMR demonstrated evidence of new neuroma pain after the procedure, and all but one of the 15 patients who presented with preoperative neuroma pain experienced complete relief of pain in the distribution of the transferred nerves. TMR offers a novel and potentially more effective therapy for the management of neuroma pain after limb amputation.
Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
The clinical application of robotic technology to powered prosthetic knees and ankles is limited by the lack of a robust control strategy. We found that the use of electromyographic (EMG) signals from natively innervated and surgically reinnervated residual thigh muscles in a patient who had undergone knee amputation improved control of a robotic leg prosthesis. EMG signals were decoded with a pattern-recognition algorithm and combined with data from sensors on the prosthesis to interpret the patient's intended movements. This provided robust and intuitive control of ambulation--with seamless transitions between walking on level ground, stairs, and ramps--and of the ability to reposition the leg while the patient was seated.
Mechanical and neurological couplings exist between musculotendon units of the human hand and digits. Studies have begun to understand how these muscles interact when accomplishing everyday tasks, but there are still unanswered questions regarding the control limitations of individual muscles. Using intramuscular EMG electrodes, this study examined subjects' ability to individually initiate and sustain three levels of normalized muscular activity in the index and middle finger muscle compartments of EDC, FDP, and FDS as well as the extrinsic thumb muscles APL, EPB, EPL, and FPL. The index and middle finger compartments each sustained activations with significantly different levels of co-activity from the other finger muscle compartments. The middle finger compartment of EDC was the exception. Only two extrinsic thumb muscles, EPL and FPL, were capable of sustaining individual activations from the other thumb muscles, at all tested activity levels. Activation of APL was achieved at 20% and 30% MVC activity levels with significantly different levels of co-activity. Activation of EPB elicited co-activity from EPL and APL that were not significantly different. These results suggest that most finger muscle compartments receive unique motor commands, but of the four thumb muscles only EPL and FPL were capable of individually activating. This work is encouraging for the neural control of prosthetic limbs because these muscles and compartments may potentially serve as additional user inputs to command prostheses.
An ideal myoelectric prosthetic hand should have the ability to continuously morph between any posture like an anatomical hand. This paper describes the design and validation of a morphing myoelectric hand controller based on principal component analysis of human grasping. The controller commands continuously morphing hand postures including functional grasps using between two and four surface electromyography (EMG) electrodes pairs. Four unique maps were developed to transform the EMG control signals in the principal component domain. A preliminary validation experiment was performed by 10 non-amputee subjects to determine the map with highest performance. The subjects used the myoelectric controller to morph a virtual hand between functional grasps in a series of randomized trials. The number of joints controlled accurately was evaluated to characterize the performance of each map. Additional metrics were studied including completion rate, time to completion, and path efficiency. The highest performing map controlled over 13 out of 15 joints accurately.
In direct skeletal attachment (DSA) of limb prostheses, a construct is implanted into an amputee's residuum bone and protrudes out of the residuum's skin. This technology represents an alternative to traditional suspension of prostheses via various socket systems, with clear indications when the sockets cannot be properly fitted. Contemporary DSA was invented in the 1990s, and several implant systems have been introduced since then. The current review is intended to compare the design features of implants for DSA whose use in humans or in animal studies has been reported in the literature. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.
More than 6,600 one-page surveys were sent to individuals throughout the country with upper-limb loss or absence. Of those surveys, 2,477 were returned, and demographic information was recorded. A more comprehensive seven-page survey was then sent to the respondents who agreed to participate. A total of 1,575 of these surveys were returned: 1,020 by body-powered users, 438 by electric users and 117 by bilateral users of prostheses.
The results of the surveys indicate users of body-powered and electric prostheses identify surprisingly similar elements as necessary in the design of a better upper-limb prosthesis. These qualities include additional wrist movement, better control mechanisms that require less visual attention and the ability to make coordinated motions of two joints. Desired near-term improvements for body-powered prostheses include better cables and harness comfort, whereas those for electric prostheses include better gloving material, better batteries and charging units, and improved reliability for the hand and its electrodes. This article discusses the specific functions that various levels of upper-extremity amputees gain from their prostheses as well as the device features that aid or detract from their functions.
(C) 1996 American Academy of Orthotists & Prosthetists
Myoelectrically powered prosthetic hands lack sensory feedback relating to the force exerted by the artificial hand on a grasped object. The degree of control is imprecise, and often much more force than necessary is applied. The aim of this study was to develop and evaluate a force feedback system considering design constraints, providing the user with closed-loop control. Different methods and design criteria for providing myoelectric prosthetic hands with force feedback were analyzed, with stimulation by vibration being preferred. A new feedback system was designed, consisting of a miniature vibration motor, a piezoresistive force sensor, and control electronics. Grasping forces with and without feedback were recorded and compared from five habitual myoelectric hand users when grasping a hand dynamometer with different weights attached to it. All five patients rapidly improved their ability to regulate the grasping force without the help of vision when feedback was applied. An average force reduction of 37% was found when vibration was applied indirectly to the hand, and a decrease of 54% was found when feedback was applied directly to the skin of the residual limb. Constraints for a prosthetic force feedback system such as low power consumption, compactness, and being imperceptible to others are included in the design. General acceptance of vibration as a feedback signal was good, especially when applied indirectly. The results indicate that the new system is of potential value for myoelectric prosthetic hand users. More precise control is possible, and redundant grasping force can be diminished with a feedback system.
Surgical Principles Formation of a muscle tunnel (possible muscles: wrist flexors and — extensors, musculus biceps, musculus triceps, or musculus pectoralis), lined with the patient’s own skin, to be utilized by upper or forearm amputees for active and voluntary movements of an artificial hand. Transmission of power from the muscle tunnel to the prosthesis is achieved by cables connected to a plastic rod inserted into the tunnel (Plexiglass, previously ivory). © 1992, Urban & Vogel Medical Periodicals. All rights reserved.
Pattern recognition control systems have the potential to provide better, more reliable myoelectric prosthesis control for individuals with an upper-limb amputation. However, proper patient training is essential. We begin user training by teaching the concepts of pattern recognition control and progress to teaching how to control, use, and maintain prostheses with one or many degrees of freedom. Here we describe the training stages, with relevant case studies, and highlight several tools that can be used throughout the training process, including prosthesis-guided training (PGT)-a self-initiated, simple method of recalibrating a pattern recognition-controlled prosthesis. PGT may lengthen functional use times, potentially increasing prosthesis wear time. Using this training approach, we anticipate advancing pattern recognition control from the laboratory to the home environment and finally realizing the full potential of these control systems.
Using electromyogram (EMG) signals to control upper-limb prostheses is an important clinical option, offering a person with amputation autonomy of control by contracting residual muscles. The dexterity with which one may control a prosthesis has progressed very little, especially when controlling multiple degrees of freedom. Using pattern recognition to discriminate multiple degrees of freedom has shown great promise in the research literature, but it has yet to transition to a clinically viable option. This article describes the pertinent issues and best practices in EMG pattern recognition, identifies the major challenges in deploying robust control, and advocates research directions that may have an effect in the near future.
Many different concepts of peripheral nerve interfaces have been developed over the past few decades and transferred into neuroscientific or clinical applications with varying degrees of success. In this study, we present a novel electrode design that transversally penetrates the peripheral nerve and is intended to selectively activate subsets of axons in different fascicles within the nerve. The "transverse intrafascicular multichannel electrode" (TIME) has been designed and fabricated using the micromachining and patterning of a polyimide substrate and insulation material and platinum electrode sites. In vitro characterization of the electrodes were carried out to determine the electrochemical transfer characteristics during recording and stimulation. Acute implantations were performed in the sciatic nerves of rats and recruitment curves were determined. Results indicated selective stimulation of different fascicles with graded recruitment. Future studies will address chronic implantation to investigate the reactions on the material-tissue interface and the long-term behavior and recruitment properties of the TIMEs.
The principle underlying this project is that, despite nervous reorganization following upper limb amputation, original pathways and CNS relays partially maintain their function and can be exploited for interfacing prostheses. Aim of this study is to evaluate a novel peripheral intraneural multielectrode for multi-movement prosthesis control and for sensory feed-back, while assessing cortical reorganization following the re-acquired stream of data.
Four intrafascicular longitudinal flexible multielectrodes (tf-LIFE4) were implanted in the median and ulnar nerves of an amputee; they reliably recorded output signals for 4 weeks. Artificial intelligence classifiers were used off-line to analyse LIFE signals recorded during three distinct hand movements under voluntary order.
Real-time control of motor output was achieved for the three actions. When applied off-line artificial intelligence reached >85% real-time correct classification of trials. Moreover, different types of current stimulation were determined to allow reproducible and localized hand/fingers sensations. Cortical organization was observed via TMS in parallel with partial resolution of symptoms due to the phantom-limb syndrome (PLS).
tf-LIFE4s recorded output signals in human nerves for 4 weeks, though the efficacy of sensory stimulation decayed after 10 days. Recording from a number of fibres permitted a high percentage of distinct actions to be classified correctly. Reversal of plastic changes and alleviation of PLS represent corollary findings of potential therapeutic benefit.
This study represents a breakthrough in robotic hand use in amputees.
Improving the function of prosthetic arms remains a challenge, because access to the neural-control information for the arm is lost during amputation. A surgical technique called targeted muscle reinnervation (TMR) transfers residual arm nerves to alternative muscle sites. After reinnervation, these target muscles produce electromyogram (EMG) signals on the surface of the skin that can be measured and used to control prosthetic arms.
To assess the performance of patients with upper-limb amputation who had undergone TMR surgery, using a pattern-recognition algorithm to decode EMG signals and control prosthetic-arm motions.
Study conducted between January 2007 and January 2008 at the Rehabilitation Institute of Chicago among 5 patients with shoulder-disarticulation or transhumeral amputations who underwent TMR surgery between February 2002 and October 2006 and 5 control participants without amputation. Surface EMG signals were recorded from all participants and decoded using a pattern-recognition algorithm. The decoding program controlled the movement of a virtual prosthetic arm. All participants were instructed to perform various arm movements, and their abilities to control the virtual prosthetic arm were measured. In addition, TMR patients used the same control system to operate advanced arm prosthesis prototypes.
Performance metrics measured during virtual arm movements included motion selection time, motion completion time, and motion completion ("success") rate.
The TMR patients were able to repeatedly perform 10 different elbow, wrist, and hand motions with the virtual prosthetic arm. For these patients, the mean motion selection and motion completion times for elbow and wrist movements were 0.22 seconds (SD, 0.06) and 1.29 seconds (SD, 0.15), respectively. These times were 0.06 seconds and 0.21 seconds longer than the mean times for control participants. For TMR patients, the mean motion selection and motion completion times for hand-grasp patterns were 0.38 seconds (SD, 0.12) and 1.54 seconds (SD, 0.27), respectively. These patients successfully completed a mean of 96.3% (SD, 3.8) of elbow and wrist movements and 86.9% (SD, 13.9) of hand movements within 5 seconds, compared with 100% (SD, 0) and 96.7% (SD, 4.7) completed by controls. Three of the patients were able to demonstrate the use of this control system in advanced prostheses, including motorized shoulders, elbows, wrists, and hands.
These results suggest that reinnervated muscles can produce sufficient EMG information for real-time control of advanced artificial arms.