Prosthetic Elbow Research Articles

A Review of Myoelectric Prosthetic Arm Designs from 2011 to 2022

Prosthetic arms are worn by people whose arms have been amputated. Amputation involves surgical removal of the muscle, neurosensory system, and skeletal system. Myoelectric prosthetics make use of the signals generated by the intact muscles for the limb movement. Prosthetic limbs are designed using mechanical parts with suitable gear and motors. Users of prosthetic arms can carry out tasks associated with everyday living and their jobs almost exactly like they would with a natural arm. Prosthetic arms come in a variety of designs based on the needs of the user. The current research reviews the goals, plans, and trials conducted on prosthetic elbows, wrists, and hands between 2011 and 2022 from reputable conferences and journals. In this work, the design of two prosthetic hands with one degree of freedom and thirteen degrees of freedom, respectively, in the 3D simulation tool SolidWorks is described. Prosthetic elbow and a wrist with one degree of freedom were designed as well. The fine motor activities can be performed with the prosthetic fingers designed in this work.

Design, Characterization, and Validation of a Variable Stiffness Prosthetic Elbow

Design, Characterization, and Validation of a Variable Stiffness Prosthetic Elbow

Transhumeral Arm Reaching Motion Prediction through Deep Reinforcement Learning-Based Synthetic Motion Cloning.

The lack of intuitive controllability remains a primary challenge in enabling transhumeral amputees to control a prosthesis for arm reaching with residual limb kinematics. Recent advancements in prosthetic arm control have focused on leveraging the predictive capabilities of artificial neural networks (ANNs) to automate elbow joint motion and wrist pronation-supination during target reaching tasks. However, large quantities of human motion data collected from different subjects for various activities of daily living (ADL) tasks are required to train these ANNs. For example, the reaching motion can be altered when the height of the desk is changed; however, it is cumbersome to conduct human experiments for all conditions. This paper proposes a framework for cloning motion datasets using deep reinforcement learning (DRL) to cater to training data requirements. DRL algorithms have been demonstrated to create human-like synergistic motion in humanoid agents to handle redundancy and optimize movements. In our study, we collected real motion data from six individuals performing multi-directional arm reaching tasks in the horizontal plane. We generated synthetic motion data that mimicked similar arm reaching tasks by utilizing a physics simulation and DRL-based arm manipulation. We then trained a CNN-LSTM network with different configurations of training motion data, including DRL, real, and hybrid datasets, to test the efficacy of the cloned motion data. The results of our evaluation showcase the effectiveness of the cloned motion data in training the ANN to predict natural elbow motion accurately across multiple subjects. Furthermore, motion data augmentation through combining real and cloned motion datasets has demonstrated the enhanced robustness of the ANN by supplementing and diversifying the limited training data. These findings have significant implications for creating synthetic dataset resources for various arm movements and fostering strategies for automatized prosthetic elbow motion.

Prosthetic Elbow Flexion and Extension Sense rebuilt by Electrotactile Feedback: a Preliminary Study

The elbow position and movement (PM) feedback can help amputees control the prosthetic limbs more flexibly. This study attempts to explore whether electrotactile stimulation can help amputees identify the elbow PM information of prosthesis, due to valuable potential of electrotactile stimulation. This study designed an encoding scheme by relating the elbow PM information with amplitudes, and it tested the scheme on four able-bodied subjects and two transhumeral amputees. After two stimulation positions on the upper limb were determined using sensory sensitivity experiment, four sets of amplitudes (Am, An) were encoded four positions of prosthetic elbow (0°, 45°, 90°, and 135°) and changes in sets of amplitudes were encoded flexion and extension (FE) movements of prosthetic elbow. All subjects were required to identify the prosthetic elbow PM during the experiment, and the success rate and discrimination reaction time were recorded. The average success rates of the position and movement experiments among the four subjects were 76.25% and 91.17% respectively. For the two transhumeral amputees, the position feedback success rates were 86.38% and 75%, respectively, and the movement feedback success rates were 80.5% and 75%, respectively. These results indicate that subjects can learn the mapping relationship of this sensory feedback after training. This method potentially in future provides amputees with PM sensory information of elbow FE during the actual control of prosthetic elbows.

Evaluation of the Proximal Ulna Dorsal Angulation for Ulnar Component Sizing in Elbow Prosthetic Reconstruction After Distal Humeral Resection of Tumor.

Introduction:Elbow prosthetic reconstruction after distal humeral tumor resection is challenging. We identify the value of the proximal ulna dorsal angulation (PUDA) as an easily-measured radiographic parameter that can help inform ulnar component sizing in the Solar Elbow System (SES) and the Modular Universal Tumor and Revision System (MUTARS), two modular prosthetic systems that are commonly used after tumor resection in this anatomic location. We hypothesized that a larger PUDA measurement would require smaller ulnar stems.Methods:Demographic data and PUDA measurements were retrospectively reviewed for 514 patients. Multivariate regression was used to determine the effects of patient demographic data on the PUDA. PUDA measurements were collected by three independent reviewers on lateral elbow radiographs. MUTARS and SES templating software was then used to validate the relationship between the PUDA and ulnar stem sizing.Results:Regression analysis showed no substantial contribution of demographic variables to the PUDA measurement (adjusted R2 = 0.02, F(6, 508) = 2.704, P = 0.01). The MUTARS implant fit 97% of elbows with a PUDA <5° and 91.6% of elbows with PUDA ≥5° (P = 0.26). The largest SES combination fit 100% of elbows with a PUDA ≤10° versus 93% of elbows with a PUDA >10° (P = 0.029). Elbows accommodating the largest SES combination had a smaller median PUDA (5.4° versus 11.7°, P = 0.034); elbows accommodating the MUTARS implant had a smaller median PUDA (5.4° versus 5.8°, P = 0.34).Discussion:The PUDA is a valuable and easily used preoperative planning tool for prosthetic elbow reconstruction after tumor resection. The proximal ulna dorsal angulation can be easily measured to predict ulnar component fit and reduce intraoperative complications. In patients with a PUDA ≥5°, ulnar component stem fit for current systems may be more challenging.

Assessment of an Automatic Prosthetic Elbow Control Strategy Using Residual Limb Motion for Transhumeral Amputated Individuals With Socket or Osseointegrated Prostheses

Most transhumeral amputated individuals deplore the lack of functionality of their prosthesis due to control-related limitations. Commercialized prosthetic elbows are controlled via myoelectric signals, yielding complex control schemes when users have to control an entire prosthetic limb. Limited control causes the development of compensatory strategies. An alternative control strategy associates residual limb motions to automatize the prosthetic elbow motion using a model of physiological shoulder/elbow synergies. Preliminary studies have shown that elbow motion could be predicted from residual limb kinematic measurements, but results with transhumeral amputated individuals were lacking. This study focuses on the experimental assessment of automatic prosthetic elbow control during a reaching task, compared to conventional myoelectric control, with six transhumeral amputated individuals, among whom, three had an osseointegrated device. Part of the recruited participants had an osseointegrated prosthetic device. The task was achieved within physiological precision errors with both control modes. Automatic elbow control reduced trunk compensations, and restored a physiologically-like shoulder/elbow movement synchronization. However, the kinematic assessment showed that amputation and prosthesis wear modifies the shoulder movements in comparison with physiological shoulder kinematics. Overall, participants described the automatic elbow control strategy as intuitive, and this work highlights the interest of automatized prosthetic elbow motion.

Management of distal humerus fractures.

Distal humeral fractures represent approximately 2% of fractures in adults and are often treated operatively to restore stable humeral columns and allow early elbow motion. Diagnosis is made with orthogonal radiographs. The traction view radiograph and computed tomography with three-dimensional reconstruction can be helpful in preoperative planning. Treatment options include: (1) nonoperative management, which is reserved for lower-demand, medically unwell, elderly patients, (2) surgical osteosynthesis, which remains the treatment of choice for most fractures, and (3) prosthetic replacement with either hemiarthroplasty or total elbow arthroplasty, which is indicated for distal complex comminuted fracture patterns in elderly, low-demand patients with poor bone quality. A thorough understanding of the anatomy around the elbow is critical when planning surgical approach and reduction. Controversies exist in the following areas: (1) surgical approach, (2) management of the ulnar nerve, (3) plating technique-parallel versus orthogonal, and (4) whether osteosynthesis or prosthetic elbow replacement is superior in the elderly population.

Reference position estimation for prosthetic elbow and wrist using EMG signals

Progress in Bio robotics is opening several doors to mimic the system and purpose of human limbs, thus allowing better prostheses for amputees. This paper presents EMG based Human Machine Interface framework for estimate of reference positions of prosthetic arm for patients suffering from above elbow amputation. In the present study, a set of information about the four basic motions regarding elbow flexion/extension along with the twist of radius and ulna referred as pronation/supination has been acquired from bicep of human arm. Upon muscle activation, the numerical data set points representing the electromyographic intentions were recorded using the Thalamic Labs product i.e. Myo Armband. To analyze these acquired signals, feature selection followed with feature extraction was done in order to classify the input data extracted from human muscle. Afterwards, the performance of Artificial Neural Network (ANN) for motion classification was evaluated. Utilizing the Computer Aided design skills in SolidWorks®, a 2-DOF prosthetic arm model was developed. A mathematical model of its kinematics based on Denavit-Hardenberg convention was presented in Matlab®. Forward kinematics model were analytically verified using Matlab® with that of PeterCorke® Robotic toolbox. In order to check the physical significance of proposed work, the information of forward kinematics from Matlab® linked with that of Solid works and was simulated with reference to the EMG intentions that were captured and classified to generate the reference positions of above mentioned four motions. The classification accuracy obtained from ANN i.e. 91.9% is found significant (p<0.01) for a group of ten healthy subjects.

Upper Limb Prosthesis Control for High-Level Amputees via Myoelectric Recognition of Leg Gestures.

Recognition of motion intent via surface electromyography (EMG) has become increasingly practical for prosthesis control, but lacking residual muscle sites remains a major obstacle to its use by high-level amputees. Currently, there are few approaches to upper limb prosthesis control for individuals with amputations proximal to the elbow, all of which suffer from one or more of three primary problems: invasiveness, the need for intensive training, and lacking functionality. Using surface EMG sensors placed on the lower leg and a natural mapping between degrees of freedom of the leg and the arm, we tested a noninvasive control approach by which high-level amputees could control prosthetic elbow, wrist, and hand movements with minimal training. In this paper, we used able-bodied subjects to facilitate a direct comparison between control using intact arm and leg muscles. First, we found that foot gestures could be classified offline using time domain features and linear discriminant analysis with accuracy comparable to an equivalent system for recognizing arm movements. Second, we used the target achievement control test to evaluate real-time control performance in three and four degrees of freedom. After approximately 20 min of training, subjects tended to perform the task as well with the leg as with intact arm muscles, and performance overall was comparable to other control methods.

Can We Achieve Intuitive Prosthetic Elbow Control Based on Healthy Upper Limb Motor Strategies?

Most transhumeral amputees report that their prosthetic device lacks functionality, citing the control strategy as a major limitation. Indeed, they are required to control several degrees of freedom with muscle groups primarily used for elbow actuation. As a result, most of them choose to have a one-degree-of-freedom myoelectric hand for grasping objects, a myoelectric wrist for pronation/supination, and a body-powered elbow. Unlike healthy upper limb movements, the prosthetic elbow joint angle, adjusted prior to the motion, is not involved in the overall upper limb movements, causing the rest of the body to compensate for the lack of mobility of the prosthesis. A promising solution to improve upper limb prosthesis control exploits the residual limb mobility: like in healthy movements, shoulder and prosthetic elbow motions are coupled using inter-joint coordination models. The present study aims to test this approach. A transhumeral amputated individual used a prosthesis with a residual limb motion-driven elbow to point at targets. The prosthetic elbow motion was derived from IMU-based shoulder measurements and a generic model of inter-joint coordinations built from healthy individuals data. For comparison, the participant also performed the task while the prosthetic elbow was implemented with his own myoelectric control strategy. The results show that although the transhumeral amputated participant achieved the pointing task with a better precision when the elbow was myoelectrically-controlled, he had to develop large compensatory trunk movements. Automatic elbow control reduced trunk displacements, and enabled a more natural body behavior with synchronous shoulder and elbow motions. However, due to socket impairments, the residual limb amplitudes were not as large as those of healthy shoulder movements. Therefore, this work also investigates if a control strategy whereby prosthetic joints are automatized according to healthy individuals' coordination models can lead to an intuitive and natural prosthetic control.

Synergistic Elbow Control for a Myoelectric Transhumeral Prosthesis.

This paper presents a control approach for a myoelectric transhumeral prostheses that supplements a typical two-site electromyograms (EMG) input with the inertial measurement of arm motion. The inertial measurement is employed to: 1) provide synergistic movement between the prosthetic elbow joint and intact upper arm and 2) to switch control between the myoelectric elbow and hand. In order to assess the prospective efficacy of the control method, experiments were conducted on six healthy subjects who performed a series of pick-and-place tasks within a virtual environment. The assessments compared the time required to complete the pick-and-place tasks using the proposed coordinated control approach, with the time required using a sequential control approach (i.e., the conventional approach used in commercial devices). Subjects on average completed the pick-and-place tasks 34% faster with the coordinated control approach, relative to the conventional sequential EMG method, with no difference in compensatory torso motion.

Pre-clinical evaluation of a natural prosthetic elbow control strategy using residual limb motion and a model of healthy inter-joint coordinations

A gap has been growing between the mechanical features of newly commercialized prosthetic devices and the control strategies available to the users. The prosthetic joints are controlled sequentially via myoelectric control, and each actuation requires the user's attention. Because of a complex control scheme, transhumeral amputees are generally equipped with a 1-degree-of-freedom myoelectric hand, a myoelectric wrist rotator, and a manually locked elbow. The prosthetic forearm position, adjusted before the movement, is not involved in the overall upper limb movements, resulting in the development of compensatory strategies. A promising solution to improve prosthetic control utilizes the residual limb motions to control the elbow. Previous studies have shown that elbow motion could be predicted from measures of the residual limb movements and an inter-joint coordination model. This study is the first to report the utilization of an automatically driven prosthetic elbow by a transhumeral amputee. The participant pointed at targets with a prosthesis prototype including a modified motorized elbow. The prosthetic elbow motion was derived from a generic model of inter-joint coordinations, and IMU-based residual limb measurements. The participant performed also the task with the prosthetic elbow implemented with his own myoelectric control strategy. Body movements were assessed with the data recorded with a motion capture system. The patient achieved the pointing task with a better precision when the elbow was myoelectrically-driven. However, these movements required important trunk compensations. Trunk movements were smaller with residual limb motion-based elbow control, which enabled a more natural overall body behavior with synchronous shoulder and elbow motions. Due to socket impairment, but also to post-amputation body scheme modifications and discrepancies between healthy and artificial limbs, the participant's residual limb amplitudes were different of the ones of healthy shoulder movements for the same tasks. This work questions the paradigm whereby a prosthetic elbow can be intuitively and naturally used by an amputee while its motion is derived from healthy individual data. Although there is a need for novel modeling approaches to build an inter-joint coordination model adapted to each user, residual limb motion-driven prosthetic elbow enables simultaneous control of elbow and end-effector, and restores a more natural body behavior.

Pre-clinical assessment of an intuitive prosthetic elbow control strategy using residual limb motion with osseo-integrated patients

Most transhumeral amputees deplore that their prosthesis lacks functionality due to control-related limitations. Externally powered prosthetic devices are commonly controlled via myoelectric control whereby biceps and triceps contractions drive sequentially the prosthetic joints. Because of a complex control scheme, transhumeral amputees are generally equipped with a 1-degree-of-freedom myoelectric hand, a myoelectric wrist rotator, and a manually locked elbow, despite the commercialization of more advanced devices. This results in the development of compensatory strategies to overcome the prosthesis’ lack of mobility. An alternative control strategy relates the residual limb motions to the prosthetic elbow motion using the natural coordination between shoulder and elbow observed in healthy movements. However, conventional external sockets tend to prevent the residual limb mobility, limiting the potentiality of this novel control strategy. Osseo-integration enables a stable attachment of the prosthetic device and frees the residual limb. This study focuses on the performance of three osseo-integrated patients using an automatically driven prosthesis. A prosthesis prototype including a myoelectric hand, a wrist rotator, and a motorized elbow was mounted on the participants’ abutment from the osseo-integrated implant system. The subjects were asked to point at targets while the motorized elbow was controlled by residual limb movements based on a model of healthy shoulder/elbow coordination. For comparison purposes, the task was also performed with conventional sequential myoelectric control. Body movements were assessed with the data recorded with a motion capture system. Large trunk compensatory movements were measured during pointing gesture with a myoelectrically driven elbow. Automatic control of the elbow enabled a more natural body behavior whereby the trunk displacements were small, and the shoulder and the prosthetic elbow were moving synchronously. The study shows that osseo-integration made possible residual limb movements of large amplitudes, allowing the participants to achieve the pointing task with a prosthetic elbow driven by the residual limb motions. Moreover, simultaneous control of elbow and end-effector was achieved by one subject. Hence, this work highlights the interest of combining osseo-integration with an automatic control strategy for intermediate joints in terms of compensatory movement reduction and control intuitiveness gain.

Radial head, radiocapitellar and total elbow arthroplasties: A review of recent literature

The outcome of prosthetic elbow surgery is continually evolving. We thoroughly reviewed the literature on this issue to analyse the indications, outcomes and complications of the numerous types of implants currently in use. Radial head replacement is recommended in comminuted fractures of the radial head and in post-traumatic conditions. Medium- and long-term results prove to be satisfactory in the majority of cases, with no evidence to indicate that some prostheses (monopolar vs. bipolar; cemented vs. press-fit) are more effective than others; nonetheless, the bipolar-cemented implant was found to be associated with a lower revision rate than other prostheses. Unicompartmental arthroplasty has recently been used for the treatment of osteoarthritis and rheumatoid arthritis when the lateral compartment is prevalently involved; the results reported to date have been encouraging, although further studies are warranted to confirm the validity of these implants. Total elbow arthroplasty is performed in a range of conditions, including distal humerus fractures in the elderly and elbow arthritis. In the former condition, linked elbow replacement yields excellent results with few complications and a low revision rate. In elbow arthritis, total elbow arthroplasty is indicated when patients suffer from disabling pain, stiffness and/or instability that prevent them from performing daily activities. Unlinked elbow arthroplasty, which is used above all in rheumatoid arthritis, also yields satisfactory results, although the risk of instability persists. The use of linked elbow arthroplasty, which yields similar results but lower revision rates, has consequently increased. Lastly, the results yielded by linked elbow prosthesis in post-traumatic conditions are good, although not quite as good as those obtained in rheumatoid arthritis. Early mechanical failure may occur in younger and more active patients after elbow arthroplasty. However, the careful selection of patients who are prepared to accept functional limitations imposed by elbow implants will enable indications for elbow arthroplasty to be extended to young subjects, particularly when no other therapeutic options are available.

Implant sonication for the diagnosis of prosthetic elbow infection

Periprosthetic infection is a potentially devastating complication of elbow arthroplasty, associated with formation of microbial biofilm on the implant surface. The definitive microbiologic diagnosis of periprosthetic infection after elbow arthroplasty may be difficult to establish. Our study aim was to compare the diagnostic accuracy of conventional periprosthetic tissue culture and culture of fluid derived from vortexing and bath sonication of the explanted hardware (a biofilm-sampling strategy). Patients undergoing revision elbow arthroplasty at our institution between July 2007 and July 2010, from each of whom 2 or more periprosthetic tissue cultures and 1 implant sonicate culture were obtained, were studied. A standardized definition of orthopedic implant-associated infection was applied. We identified 27 subjects with aseptic failure and 9 with prosthetic elbow infection. Rheumatoid arthritis was the most common underlying disorder. The Coonrad-Morrey prosthesis was the most common type of implant used. The sensitivities of implant sonicate and periprosthetic tissue culture were 89% and 55%, respectively (P = .18), and the specificities were 100% and 93%, respectively (P = .16). Coagulase-negative staphylococci (n = 7) and Staphylococcus aureus (n = 2) were isolated in cases of infection. Culture of the implant by sonication is at least as sensitive as periprosthetic tissue culture to detect prosthetic elbow infection.

BIOMIMETIC DESIGN OF LOW STIFFNESS ACTUATOR SYSTEMS FOR PROSTHETIC LIMBS

The various relationships that are possible between the mechanical properties of single actuators and the overall mechanism (in this case a human arm with or without a prosthetic elbow) are discussed. Graphical and analytical techniques for describing the range of overall limb stiffnesses that are achievable and for characterizing the overall limb stiffness have been developed. Using a biomimetic approach and, considering energetic costs, stability and complexity, the implications of choosing passive or active implementations of stiffness are discussed. These techniques and approaches are particularly applicable with redundant (agonist - antagonist) actuators and multiple degrees of freedom. Finally, a novel biomimetic approach for control is proposed.

Total Elbow Arthroplasty in Patients Forty Years of Age or Less

It is generally accepted that prosthetic elbow replacement should be avoided in young patients because of an anticipated high rate of early failure. The purpose of this paper was to define the success, prosthetic survival rate, and problems encountered in patients who were treated with a semiconstrained total elbow arthroplasty when they were forty years of age or less. We retrospectively reviewed the records of 758 patients who had undergone primary arthroplasty with the Coonrad-Morrey total elbow prosthesis for any reason between 1982 and 2003. We identified fifty-five total elbow arthroplasties that had been performed in forty-nine patients (thirty-eight women and eleven men) who were forty years of age or less (mean, thirty-three years) at the time of the operation and that had been followed for a minimum of five years. Six patients had a bilateral procedure. The indication for the arthroplasty was inflammatory arthritis in thirty patients and posttraumatic arthritis in nineteen. Patients with hemophilia or a neoplasm were excluded. The medical record data were used to calculate the preoperative and postoperative Mayo Elbow Performance Score. The mean duration of follow-up was ninety-one months. During this period, twelve (22%) of the elbows had undergone a subsequent surgical procedure: four because of loosening, three because of triceps weakness, three because of wear, and two because of deep infection. On the basis of the Mayo Elbow Performance Score at the last review, thirty-six results (65%) were considered to be excellent; fifteen (27%), good; three (5%), fair; and one (2%), poor. Semiconstrained total elbow arthroplasty in young patients was associated with a 22% revision rate at a mean of ninety-one months, and the rate of revision was significantly higher for patients with posttraumatic arthritis. Despite this revision rate, fifty-one elbows (93%) had a good or excellent Mayo Elbow Performance Score.

User-modulated impedance control of a prosthetic elbow in unconstrained, perturbed motion.

Humans use the agonist-antagonist structure of their muscles to simultaneously determine both the motion and the stiffness of their joints. Designing this feature into an artificial limb may prove advantageous. To evaluate the performance of an artificial limb capable of modulating its impedance, we have created a compact series elastic actuator that has the same size and similar weight as commercially available electric prosthetic elbows. The inherent compliance in series elastic actuators ensure their safety to the user, even at high speeds, while creating a high-fidelity force actuator ideally suited for impedance control. This paper describes three serial studies that build on each other. The first study presents modeling of the actuator to ensure stability in the range of impedance modulation and empirically tests the actuator to validate its ability to modulate impedance. The actuator is found to be stable and accurate over a wide range of impedances. In the second study, four subjects are tested in a preliminary experiment to answer basic questions necessary to implement user-modulated impedance control. Findings include the superiority of velocity control over position control as the underlying motion paradigm and the preference for high stiffness and non-negative inertia. Based on the findings of the second study, the third study evaluates the performance of 15 able-bodied subjects for two tasks, using five different impedance paradigms. Impedance modulation, speed, and error were compared across paradigms. The results indicate that subjects do not actively modulate impedance if it is near a preferred baseline. Fixed impedance and viscosity modulation provide the most accurate control.

Targeted Reinnervation to Improve Prosthesis Control in Transhumeral Amputees

Controlling an upper-limb prosthesis is challenging for transhumeral amputees. A central problem is the inability to move multiple prosthetic joints at the same time. With a body-powered prosthesis, an amputee uses shoulder motion to sequentially move the prosthetic elbow and lock it in place before switching to operation of the wrist, hand, or hook. With a myoelectric prosthesis, surface electromyographic signals from the residual biceps and triceps are used to control a motorized arm. Again, sequential control is required, as the biceps and triceps can only operate one joint at a time. The use of these prostheses rarely becomes intuitive. The patient is forced to use chest, shoulder girdle, or upper-arm muscles to move the prosthetic elbow, wrist, and hand in a slow, complex, and burdensome manner. Often, expensive prostheses are left untouched in the patient's closet because the sequence of movements that is required to effectively use the prosthetic arm actions does not occur in a workable time frame for the patient. Use of a prosthetic arm will become more intuitive and facile if the nervous-system signals that formerly controlled arm movement can once again be used to direct the movement of the prosthesis. To date, most efforts at neural control have focused on brain-machine interface strategies in which electrodes implanted in the cerebral cortex1,2 and on peripheral nerve interfaces make use of electrode arrays placed in the amputated nerves of the arm3,4. These systems face the challenges of weak signals, signal instability over time, potential infections from implanted devices, implant-device failure, and difficulties with extracting the electrical signals to detectors outside the body. The ideal interface between patient and prosthesis would not break, become infected, need a power source, or require repeated trips to the operating room. Through the process of …

Improved Myoelectric Prosthesis Control Accomplished Using Multiple Nerve Transfers

The control of shoulder-level disarticulation prostheses is significantly more difficult than that of prostheses for more distal amputations. Amputees have significant difficulties coordinating the separate functions of prosthetic shoulder, elbow, wrist, and hand/hook components. The user must lock one joint at a particular position in space before subsequently moving a different joint. A patient with bilateral humeral disarticulations after an electrical injury underwent a novel nerve transfer procedure designed to improve the control of a myoelectric prosthesis. The median, radial, ulnar, and musculocutaneous nerves were transferred to the nerves of segments of the pectoralis major and minor muscles. Those muscles then act as bioamplifiers of peripheral nerve signals when the normal upper extremity nerves are activated by the patient's brain. Therefore, when the patient thinks "flex elbow," the transferred musculocutaneous nerve fires, and a segment of the pectoralis major contracts. An electromyographic signal is then detected transcutaneously and causes the prosthetic elbow to flex. Three of the four nerve transfers were successful. One of the nerve transfers unexpectedly yielded two separate controllable muscle segments. Standardized testing using a "box-and-blocks" apparatus was performed with the patient's previous myoelectric device and the current device after nerve transfers. The patient's performance improved by 246 percent. Nerve transfers to small muscle segments are capable of creating a novel neural interface for improved control of a myoelectric prosthesis. This is done using standard techniques of nerve and flap surgery, and without any implantable devices.