Advanced Upper Limb Prosthetic Devices: Implications for Upper Limb Prosthetic Rehabilitation

Extended physiological proprioception is affected by transhumeral Socket-Suspended prosthesis use

The objective of this study was to define targeted reaching performance without visual information for transhumeral (TH) prosthesis users, establishing baseline information about extended physiological proprioception (EPP) in this population. Subjects completed a seated proprioceptive targeting task under simultaneous motion capture, using their prosthesis and intact limb. Eight male subjects, median age of 58 years (range 29-77 years), were selected from an ongoing screening study to participate. Five subjects had a left-side TH amputation, and three a right-side TH amputation. Median time since amputation was 9 years (range 3-54 years). Four subjects used a body-powered prosthetic hook, three a myoelectric hand, and one a myoelectric hook. The outcome measures were precision and accuracy, motion of the targeting hand, and joint angular displacement. Subjects demonstrated better precision when targeting with their intact limb compared to targeting with their prosthesis, 1.9 cm2 (0.8-3.0) v. 7.1 cm2 (1.3-12.8), respectively, p = 0.008. Subjects achieved a more direct reach path ratio when targeting with the intact limb compared to with the prosthesis, 1.2 (1.1-1.3) v. 1.3 (1.3-1.4), respectively, p = 0.039 The acceleration, deceleration, and corrective phase durations were consistent between conditions. Trunk angular displacement increased in flexion, lateral flexion, and axial rotation while shoulder flexion decreased when subjects targeted with their prosthesis compared to the intact limb. The differences in targeting precision, reach patio ratio, and joint angular displacements while completing the targeting task indicate diminished EPP. These findings establish baseline information about EPP in TH prosthesis users for comparison as novel prosthesis suspension systems become more available to be tested.

Merging Humans and Neuroprosthetics through Regenerative Peripheral Nerve Interfaces

Limb amputations can be devastating and significantly affect an individual's independence, leading to functional and psychosocial challenges in nearly 2 million people in the United States alone. Over the past decade, robotic devices driven by neural signals such as neuroprostheses have shown great potential to restore the lost function of limbs, allowing amputees to regain movement and sensation. However, current neuroprosthetic interfaces have challenges in both signal quality and long-term stability. To overcome these limitations and work toward creating bionic limbs, the Neuromuscular Laboratory at University of Michigan Plastic Surgery has developed the Regenerative Peripheral Nerve Interface (RPNI). This surgical construct embeds a transected peripheral nerve into a free muscle graft, effectively amplifying small peripheral nerve signals to provide enhanced control signals for a neuroprosthetic limb. Furthermore, the RPNI has the potential to provide sensory feedback to the user and facilitate neuroprosthesis embodiment. This review focuses on the animal studies and clinical trials of the RPNI to recapitulate the promising trajectory toward neurobionics where the boundary between an artificial device and the human body becomes indistinct. This paper also sheds light on the prospects of the improvement and dissemination of the RPNI technology.

Advances in prosthetic technology: a perspective on ethical considerations for development and clinical translation

Technological advancements of prostheses in recent years, such as haptic feedback, active power, and machine learning for prosthetic control, have opened new doors for improved functioning, satisfaction, and overall quality of life. However, little attention has been paid to ethical considerations surrounding the development and translation of prosthetic technologies into clinical practice. This article, based on current literature, presents perspectives surrounding ethical considerations from the authors' multidisciplinary views as prosthetists (HG, AM, CLM, MGF), as well as combined research experience working directly with people using prostheses (AM, CLM, MGF), wearable technologies for rehabilitation (MGF, BN), machine learning and artificial intelligence (BN, KKQ), and ethics of advanced technologies (KKQ). The target audience for this article includes developers, manufacturers, and researchers of prosthetic devices and related technology. We present several ethical considerations for current advances in prosthetic technology, as well as topics for future research, that may inform product and policy decisions and positively influence the lives of those who can benefit from advances in prosthetic technology.

Current status and clinical perspectives of extended reality for myoelectric prostheses: review

Training with "Extended Reality" or X-Reality (XR) systems can undoubtedly enhance the control of the myoelectric prostheses. However, there is no consensus on which factors improve the efficiency of skill transfer from virtual training to actual prosthesis abilities. This review examines the current status and clinical applications of XR in the field of myoelectric prosthesis training and analyses possible influences on skill migration. We have conducted a thorough search on databases in the field of prostheses using keywords such as extended reality, virtual reality and serious gaming. Our scoping review encompassed relevant applications, control methods, performance evaluation and assessment metrics. Our findings indicate that the implementation of XR technology for myoelectric rehabilitative training on prostheses provides considerable benefits. Additionally, there are numerous standardised methods available for evaluating training effectiveness. Recently, there has been a surge in the number of XR-based training tools for myoelectric prostheses, with an emphasis on user engagement and virtual training evaluation. Insufficient attention has been paid to significant limitations in the behaviour, functionality, and usage patterns of XR and myoelectric prostheses, potentially obstructing the transfer of skills and prospects for clinical application. Improvements are recommended in four critical areas: activities of daily living, training strategies, feedback, and the alignment of the virtual environment with the physical devices.

Delivery of UK military upper limb prosthetics: current concepts and future directions

Upper limb prosthetics have a challenging task. A natural upper limb combines strength, coordination and dexterity to accomplish daily activities such as eating, writing, working and social interaction. Artificially replicating these functions requires a prosthetic with composite, synchronous motor function while maintaining sensory feedback and skeletal stability. Achieving these functions requires interfaces between biology and machine across nerve, muscle, bone and skin. This leads to issues related to infection, foreign material encapsulation and implant stability, and electrical signal transduction and interpretation. Over the last 20 years the advent of technologies such as osseointegration, targeted muscle reinnervation, implantable myoelectric sensors, peripheral nerve interfaces and pattern recognition technology has sought to address these problems.Due to many advances in prehospital care, truncated timelines to damage control surgery and improved combat personal protective equipment, the numbers of amputees have increased with more patients surviving injury. From October 2001 to March 2019 there were 333 amputees from Afghanistan and Iraq compared with 457 fatalities over a similar period. Over a third of these were significant multiple amputees. With a functional, robust upper limb prosthetic which mirrors or exceeds normal function, injured service personnel could be returned to an active combat role. This has benefits for their physical and mental health, improves employability prospects and allows Defence to retain some of its most highly motivated and skilled people who represent significant financial investment.

Force prediction in the cylindrical grip for a model of hand prosthesis

The aim of this paper is to present an analytical method of calculating forces acting on the thumb, index, middle finger, and metacarpal part of a hand prosthesis in a cylindrical grip. This prehension pattern represents a common operation of grabbing and manipulating everyday life objects. The design process assumed that such a prosthesis would have 5 fully operating fingers and 18 total degrees of freedom: three for each finger including the thumb, and another three for the wrist. The assumed load was 1 kg and the diameter equaled 70 mm, representing a water bottle. The method was based on analytical mechanics and as opposed to experiments or numerical methods does not require many resources. The calculations involved solving a system with seven unknown forces using an equilibrium equation for forces and moments in all three axes. The resulting equations were presented in a matrix form and solved using MATLAB software. The validation of the method with an experiment using FSR sensors and comparing it to other reports showed differences in index and middle finger involvement. However, the total sum of forces was similar, therefore it is reasoned that the grip can be performed and the prediction was accurate for the thumb and metacarpal. When using the model, the friction coefficient must be chosen with a safe margin as it influences the grip force. The presented method can be used for other models and designs by inserting their dimensions into the equations and solving them numerically to obtain forces useful in mechatronics design.

Measurement of Functional Use in Upper Extremity Prosthetic Devices Using Wearable Sensors and Machine Learning

Trials for therapies after an upper limb amputation (ULA) require a focus on the real-world use of the upper limb prosthesis. In this paper, we extend a novel method for identifying upper extremity functional and nonfunctional use to a new patient population: upper limb amputees. We videotaped five amputees and 10 controls performing a series of minimally structured activities while wearing sensors on both wrists that measured linear acceleration and angular velocity. The video data was annotated to provide ground truth for annotating the sensor data. Two different analysis methods were used: one that used fixed-size data chunks to create features to train a Random Forest classifier and one that used variable-size data chunks. For the amputees, the fixed-size data chunk method yielded good results, with 82.7% median accuracy (range of 79.3-85.8) on the 10-fold cross-validation intra-subject test and 69.8% in the leave-one-out inter-subject test (range of 61.4-72.8). The variable-size data method did not improve classifier accuracy compared to the fixed-size method. Our method shows promise for inexpensive and objective quantification of functional upper extremity (UE) use in amputees and furthers the case for use of this method in assessing the impact of UE rehabilitative treatments.

State-sponsored institute-based provision of advanced artificial limbs for rehabilitation of amputees

Introduction: Amputation is a painful functional experience and optimal rehabilitation of an amputee is a team effort. Functional restitution depends on many factors including the type of prosthesis available. We report our experience of providing advanced artificial limbs at free of cost to the underprivileged through a state-sponsored pilot initiative. Material and methods: This is a retrospective cohort study of amputees who have been rehabilitated with advanced artificial limbs through the Department of Orthopaedics at Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad, India from the years 2017 to 2021. Prostheses were procured through rate contract and monitory support was provided by the state. Evaluation, fitment and functional restitution were supervised by the orthopaedic surgeons to the utmost satisfaction of the amputees. Results: A total of 136 subjects received 142 advanced artificial limbs. Out of 136 subjects, 130 received unilateral and 6 subjects received bilateral prosthesis. Ninety-two percent (n  =  125) were men and 8% (n  =  11) were women. Eighty-eight (n  =  125) were lower limb prosthesis and 12% (n  =  17) were upper limb prosthesis. All the amputees fitted with advanced artificial limbs were highly satisfied at the end of the procedure and were confident of independent living. Conclusion: Appropriate rehabilitative measures are required for amputees to lead an independent life. Paucity of institutional support and monitory challenges preclude them from advanced prosthesis. State-sponsored, institute-based supply of advanced artificial limbs at free of cost to the beneficiaries is a replicable and feasible option for optimal rehabilitation of amputees with appropriate prosthesis.

Communicative capital: a key resource for human-machine shared agency and collaborative capacity

In this work, we present a perspective on the role machine intelligence can play in supporting human abilities. In particular, we consider research in rehabilitation technologies such as prosthetic devices, as this domain requires tight coupling between human and machine. Taking an agent-based view of such devices, we propose that human-machine collaborations have a capacity to perform tasks which is a result of the combined agency of the human and the machine. We introduce communicative capital as a resource developed by a human and a machine working together in ongoing interactions. Development of this resource enables the partnership to eventually perform tasks at a capacity greater than either individual could achieve alone. We then examine the benefits and challenges of increasing the agency of prostheses by surveying literature which demonstrates that building communicative resources enables more complex, task-directed interactions. The viewpoint developed in this article extends current thinking on how best to support the functional use of increasingly complex prostheses, and establishes insight toward creating more fruitful interactions between humans and supportive, assistive, and augmentative technologies.

[Update on prosthesis for partial hand and finger amputations]

Partial hand and finger amputations are relatively rare but devastating due to the consequences they provoque. In addition, they are more likely than lower limb amputations in car accidents, work accidents and by certain weapons of war. Men are going to have a much higher risk of traumatic amputation than women, with a rate 6.6 times higher. Fitting can be a complex process and a challenge for professionals. For this reason, it is important to know all the options available on the market that can meet the needs of patients, from cosmetic to myoelectric prostheses. Fitting requires the coordinated activity of a multiassistant clinical work team, the center of the team being the person who has suffered the amputation, who must have all the information possible to be able to actively participate in decision-making.

Testing Precision and Accuracy of an Upper Extremity Proprioceptive Targeting Task Assessment

Objective

To develop and test an assessment measuring extended physiological proprioception (EPP). EPP is a learned skill that allows one to extend proprioception to an external tool, which is important for controlling prosthetic devices. The current study examines the ability of this assessment to measure EPP in a nonamputee population for translation into the affected population.

Design

Measuring precision and accuracy of an upper extremity (UE) proprioceptive targeting task assessment. Participants completed 2 sessions of a targeting task while seated at a table. The targeting was completed with the dominant and nondominant hand and with eyes open and eyes closed during the task. Participants completed 2 sessions of the clinical test with a 1-week washout period to simulate reasonable time between clinical visits.

Setting

Research laboratory.

Participants

Twenty right-handed participants (N=20) with no neurologic or orthopedic deficits that would interfere with proprioception, median age of 25 years (range, 19-33 years), completed the assessment (10 men, 10 women).

Interventions

Not applicable.

Main Outcome Measures

Precision (consistency in targeting) and accuracy (distance between the intended target and participant result) in UE targeting task using EPP; test-retest repeatability between sessions.

Results

Both precision and accuracy were significantly decreased in the eyes-closed condition compared with the eyes-open condition regardless of targeting with dominant or nondominant hand (all P<.001). In the eyes-open condition, there was a dominance effect relating to the accuracy; however, in the eyes-closed condition, accuracy between dominant and nondominant hands was statistically equivalent. Based on minimum detectable change with 95% confidence, there was no change in either metric between the first and second sessions.

Conclusions

The results of this study support the feasibility of using this assessment to measure EPP-based on the definition of EPP as a learned skill that indicates control over an external, simple tool-because they demonstrate reliance on proprioception in the eyes-closed condition, symmetry in proprioceptive accuracy between hands for within-participant control, and test-retest reliability for longitudinal measurements. The results also establish normative values for this assessment in young, healthy adults. Further research is required in a clinical population to evaluate the UE proprioceptive targeting task assessment further and collect objective data on EPP.

Does Trans-radial Longitudinal Compression Influence Myoelectric Control?

BACKGROUND

Existing trans-radial prosthetic socket designs are not optimised to facilitate reliable myoelectric control. Many socket designs pre-date the introduction of myoelectric devices. However, socket designs featuring improved biomechanical stability, notably longitudinal compression sockets, have emerged in more recent years. Neither the subsequent effects, if any, of stabilising the limb on myoelectric control nor in which arrangement to apply the compression have been reported.

METHODOLOGY

Twelve able-bodied participants completed two tasks whilst wearing a longitudinal compression socket simulator in three different configurations: 1) compressed, where the compression strut was placed on top of the muscle of interest, 2) relief, where the compression struts were placed either side of the muscle being recorded and 3) uncompressed, with no external compression. The tasks were 1) a single-channel myoelectric target tracking exercise, followed by 2), a high-intensity grasping task. The wearers' accuracy during the tracking task, the pressure at opposing sides of the simulator during contractions and the rate at which the limb fatigued were observed.

FINDINGS

No significant difference between the tracking-task accuracy scores or rate of fatigue was observed for the different compression configurations. Pressure recordings from the compressed configuration showed that pressure was maintained at opposing sides of the simulator during muscle contractions.

CONCLUSION

Longitudinal compression does not inhibit single-channel EMG control, nor improve fatigue performance. Longitudinal compression sockets have the potential to improve the reliability of multi-channel EMG control due to the maintenance of pressure during muscle contractions.

Functional improvement by body-powered 3D-printed prosthesis in patients with finger amputation: Two case reports

RATIONALE

The most common upper limb amputations are finger amputations, resulting in functional limitations that lead to problems with activities of daily living or job loss. For many years, prosthetic options for finger amputations have been limited to passive prostheses. In many countries including South Korea, body-powered finger prostheses have rarely been prescribed due to high cost, lack of experience of physicians and prosthetists, low interest and no coverage by insurance benefits. We report 2 cases of work-related finger amputations in patients who received body-powered 3D-printed finger prostheses.

PATIENT CONCERNS AND DIAGNOSIS

Patient 1 was a 25-year-old woman with second and third finger amputations at the proximal interphalangeal level. Patient 2 was a 26-year-old man who sustained a second finger amputation at proximal interphalangeal level.

INTERVENTIONS

We created body-powered 3D-printed finger prostheses that mimicked distal interphalangeal joint motion through patient-driven metacarpophalangeal joint motion using a string connected to a wrist strap and a linkage system. The source code "Knick Finger" was downloaded from e-NABLE.

OUTCOMES

After 1 month of prosthesis training, both patients were satisfied with the prostheses and showed improved performance in patient-derived goals of cooking (patient 1) and typing on a computer (patient 2).

LESSONS

Over the past decade, significant advances have been made in 3D-printed prosthetics owing to their light weight, low cost, on-site fabrication, and easy customization. Although there are still several limitations in the general application of 3D-printed finger prostheses, our study suggests that for patients with finger amputations, body-powered 3D-printed finger prostheses have high potential as an additional prosthetic option to the existing passive cosmetic prostheses.

Extended Reality "X-Reality" for Prosthesis Training of Upper-Limb Amputees: A Review on Current and Future Clinical Potential

The rejection rates of upper-limb prosthetic devices in adults are high, currently averaging 26% and 23% for body-powered and electric devices, respectively. While many factors influence acceptance, prosthesis training methods relying on novel virtual reality systems have been cited as a critical factor capable of increasing the likelihood of long-term, full-time use. Despite that, these implementations have not yet garnered widespread traction in the clinical setting, and their use remains immaterial. This review aims to explore the reasons behind this situation by identifying trends in existing research that seek to advance Extended Reality "X-Reality" systems for the sake of upper-limb prosthesis rehabilitation and, secondly, analyzing barriers and presenting potential pathways to deployment for successful adoption in the future. The search yielded 42 research papers that were divided into two categories. The first category included articles that focused on the technical aspect of virtual prosthesis training. Articles in the second category utilize user evaluation procedures to ensure applicability in a clinical environment. The review showed that 75% of articles that conducted whole system testing experimented with non-immersive virtual systems. Furthermore, there is a shortage of experiments performed with amputee subjects. From the large-scale studies analyzed, 71% of those recruited solely able-bodied participants. This paper shows that X-Reality technologies for prosthesis rehabilitation of upper-limb amputees carry significant benefits. Nevertheless, much still must be done so that the technology reaches widespread clinical use.

Flexible Electronics and Devices as Human-Machine Interfaces for Medical Robotics

Medical robots are invaluable players in non-pharmaceutical treatment of disabilities. Particularly, using prosthetic and rehabilitation devices with human-machine interfaces can greatly improve the quality of life for impaired patients. In recent years, flexible electronic interfaces and soft robotics have attracted tremendous attention in this field due to their high biocompatibility, functionality, conformability, and low-cost. Flexible human-machine interfaces on soft robotics will make a promising alternative to conventional rigid devices, which can potentially revolutionize the paradigm and future direction of medical robotics in terms of rehabilitation feedback and user experience. In this review, the fundamental components of the materials, structures, and mechanisms in flexible human-machine interfaces are summarized by recent and renowned applications in five primary areas: physical and chemical sensing, physiological recording, information processing and communication, soft robotic actuation, and feedback stimulation. This review further concludes by discussing the outlook and current challenges of these technologies as a human-machine interface in medical robotics.

Advances in Upper Extremity Prosthetic Technology: Rehabilitation and the Interprofessional Team

Purpose of Review

The aim of this paper is to explore current trends and advancements that lead to improved practitioner knowledge and patient care resulting in better outcomes. It is common for the physiatrist to lead the team of interprofessional practitioners in the care of individuals with upper limb absence. The focus of the care is to understand and access prosthetic options, but there are often other health factors and relevant issues to consider.

Recent Findings

Some of the latest updates offer solutions to pain management, prosthetic control, access to relevant evidence, and outcomes-related data. An interesting finding was the influence of telehealth service delivery on multiple issues faced by this population. These issues include lack of information, pain management, monitoring skin breakdown and peripheral vascular disease, prosthetic training, and access to peers and specialized practitioners.

Summary

The diverse technology advancements in surgical techniques, materials, outcome measures, and data management, as well as telehealth, work together to assist the collaborative interprofessional team to provide contemporary and comprehensive care to this unique population.

Towards optimizing the non-invasive sensory feedback interfaces in a neural prosthetic control

Objective. The somatotopic interface (SI) and non-somatotopic interface (NI) are commonly used to provide non-invasive sensory feedback. Nevertheless, differences between SI and NI are rarely reported, and objective evaluations of the corresponding brain response are missing as well. Few studies have reported how to design the stimulation encoding based on the two interfaces. The objective of this study was to investigate the difference in sensory characteristics between SI and NI, and propose an optimal encoding method for non-invasive feedback interfaces. Approach. We recruited seven amputees and compared the tactile sensitivity to stimulated positions and intensities between SI (phantom finger area) and NI (upper arm) in a tactile discrimination task. Electroencephalography (EEG) evaluation task was subsequently conducted to objectively evaluate the stimulus-evoked brain response. Finally, the two kinds of tactile information (stimulated position and intensity) was applied to an object recognition task. Specifically, the object size was reflected by the prosthetic finger position through stimulated position encoding, and the object stiffness was reflected by the contact force of prosthetic fingers through stimulated intensity encoding. We compared the performance under four feedback conditions (combinations between two kinds of tactile information and two interfaces). Results. Behavioral results showed that NI was more sensitive to position information while SI was more sensitive to intensity information. EEG results were consistent with behavioral results, showing a higher sensitivity of sensory alpha ERD for NI in the position discrimination, while the trend was opposite in the intensity discrimination. The feedback encoding allowed amputees to discriminate the size and stiffness of nine objects with the best performance of 62% overall accuracy (84% for size discrimination, 71% for stiffness discrimination) when position and intensity information was delivered on the NI and SI, respectively. Signicance. Our results provided an instructive strategy for sensory feedback via non-invasive solutions.

Greater and More Natural Use of the Upper Limbs During Everyday Life by Former Amputees Versus Prosthesis Users

Hand loss profoundly impacts daily functioning. Reversal of amputation through hand replantation or transplantation offers an alternative to prosthetics for some. Whether recipients exhibit more extensive and natural limb use during everyday life than prosthesis users is, however, unknown.We asked unilateral, below-elbow amputees (N = 22), hand graft recipients (transplants N = 4; replants N = 2), and healthy matched controls (N = 20) to wear wireless accelerometers distally on their forearms/prostheses and proximally on their upper arms. These units captured limb activity over 3 days within participants' natural environments.Graft recipients exhibited heavier reliance on their affected hands compared to amputees' reliance on their prostheses, P < .001. Likewise, reliance on the injured side upper arm was also greater for hand graft recipients than amputees, regardless of whether they were wearing their prostheses, P < .05 in both cases. Hand graft recipients, like healthy controls, also relied more on forearm vs upper arm movements when controlling their limbs, P < .001.Compared with conventional prosthesis users, graft recipients exhibited more extensive and natural functioning of the upper limbs during everyday activities. This information is an important addition to other considerations when evaluating risk-benefit of these treatment alternatives.

Design of lower limb prosthetic sockets: a review

INTRODUCTION

The prosthetic socket is the connecting part between the stump and the prosthesis, which is the important basis for the function of the prosthesis. The current prosthetic socket is difficult in meeting the needs of amputees current, which is the main reason for amputees abandoning their prostheses. This paper reviews the design and use of prosthetic sockets for lower limb.

AREAS COVERED

The contribution of this publication is to review the skin problem, interface stress and volume fluctuations for prosthetic sockets, which are proposed as the key factors affecting the use of prosthetic sockets. Moreover, the lower limb prosthetic sockets are classified into the full-contact and the frame-type sockets according to the different contact type between stump and prosthetic socket, and their advantages and disadvantages are analyzed from different perspectives.

EXPERT OPINION

Aim to design the prosthetic socket with function transfer, suspension stability and comfort of socket, a design concept for prosthetic socket with self-adapt in real-time is proposed. It can be achieved by the smart materials with special mechanical properties.

Quantification of Upper Limb Isometric Force Control Abilities for Evaluating Upper Limb Functions Among Prosthetic Users

Force control abilities are essential to interact with objects in our environments. However, there is a lack of evaluation tools and methods to test the force control abilities of the upper limb in evaluating the upper limb functions of prosthetic users. This study aimed to quantify upper limb isometric force control abilities in healthy individuals and prosthetic users using a custom-built handle with a 6-axis force/torque sensor and visual cue, namely an Upper Limb End-effector type Force control test device (ULEF). Feasibilities of the test device were demonstrated through experiments by holding the ULEF with an intact hand among healthy subjects and transradial and wrist amputees with a myoelectric powered prosthetic hand, the bebionic hand. Compared to the healthy individuals, the prosthetic user group demonstrated poor isometric force control abilities in terms of higher control instability during the lateral direction task ( [Formula: see text]). Significantly higher variability in force-generating rates was also found in all task directions in the prosthetic user group ( [Formula: see text]). Compared to the healthy group, the prosthetic user group showed significant small peak biceps activities during the posterior task ( [Formula: see text]) and anterior task ( [Formula: see text]). Quantification of isometric upper limb force control abilities can potentially be beneficial to develop evaluation and research tools for investigating mechanisms underlying force control abilities of prosthetic users and provide guidelines for targeted isometric force control training and prosthesis development.

Deleterious Musculoskeletal Conditions Secondary to Lower Limb Loss: Considerations for Prosthesis-Related Factors

Significance: The intent of this work was to summarize the existing evidence of, and highlight knowledge gaps specific to, prosthetic devices/componentry and training regimes, particularly in the context of the human-device interaction and deleterious musculoskeletal conditions secondary to lower limb loss. Recent Advances: With the recent and evolving technological advancements in prostheses, there are numerous devices available to individuals with lower limb loss. Current literature demonstrates the importance of expanding the knowledge of all prosthetic device-specific factors and the significance of proper prescription, fit, and alignment, along with adequate device-/activity-specific training, to enhance human-device interaction, reduce gait abnormalities and compensatory motions, and as a result, mitigate risk for secondary musculoskeletal conditions. Critical Issues: Inadequate device prescription, fit, alignment, and training are evident owing to the lack of knowledge or awareness of the many device-specific properties and factors, leading to suboptimal use, as well as, biomechanical compensations, which collectively and adversely affect the function, activity level, and overall health of the prosthesis user. Future Directions: To maximize optimal outcomes after lower limb loss, it is essential to better appreciate the factors that affect both prosthesis use and satisfaction, particularly any modifiable factors that might be targeted in rehabilitation interventions such as device prescription, fit/alignment, and training regimes. A better understanding of such device-specific factors will help enhance the human-device interaction and resulting functional performance, thereby reducing secondary musculoskeletal conditions, allowing for the readiness of the fighting force (return-to-duty/redeployment) and/or improved reintegration into civilian society/work, and overall enhancing quality of life after lower limb loss.

Measuring mental workload in assistive wearable devices: a review

As wearable assistive devices, such as prostheses and exoskeletons, become increasingly sophisticated and effective, the mental workload associated with their use remains high and becomes a major challenge to their ecological use and long-term adoption. Numerous methods of measuring mental workload co-exist, making analysis of this research topic difficult. The aim of this review is to examine how mental workload resulting from the use of wearable assistive devices has been measured, in order to gain insight into the specific possibilities and limitations of this field. Literature searches were conducted in the main scientific databases and 60 articles measuring the mental workload induced by the use of a wearable assistive device were included in this study. Three main families of methods were identified, the most common being 'dual task' and 'subjective assessment' methods, followed by those based on 'physiological measures', which included a wide variety of methods. The variability of the measurements was particularly high, making comparison difficult. There is as yet no evidence that any particular method of measuring mental workload is more appropriate to the field of wearable assistive devices. Each method has intrinsic limitations such as subjectivity, imprecision, robustness or complexity of implementation or interpretation. A promising metric seems to be the measurement of brain activity, as it is the only method that is directly related to mental workload. Finally, regardless of the measurement method chosen, special attention should be paid to the measurement of mental workload in the context of wearable assistive devices. In particular, certain practical considerations, such as ecological situations and environments or the level of expertise of the participants tested, may be essential to ensure the validity of the mental workload assessed.

Training for users of myoelectric multigrip hand prostheses: a scoping review

BACKGROUND

Training is crucial to develop the ability to operate a myoelectric prosthetic hand and use it in daily life. Multigrip prostheses, with their wider repertoire of functions, require further training. Because studies show that prosthesis abandonment is an issue and the advanced functions are not used to the expected extent, the question of what training should be offered to patients arises. If the available training methods were synthesized, the training could be improved to the benefit of the people who are fitted with a multigrip prosthesis.

OBJECTIVE

To critically examine the content of published sources for training of users with myoelectric multigrip hand prostheses.

STUDY DESIGN

Scoping review.

METHODS

A literature search covering the period 2007-2020 in the databases PubMed, CINAHL, and Allied and Complementary Medicine Database, as well as gray literature from prosthesis manufacturers, identified 2,005 sources. After full-text review of 88 articles and four user manuals from manufacturers, nine sources were included and analyzed in their entirety.

RESULTS

We found few descriptions of multigrip prosthesis training, and no source described all training phases in detail. Integration of the prosthesis and training in daily activities was described least. Few sources actually described how to perform training in multigrip functions, and none described how to integrate these functions in daily life.

CONCLUSIONS

Existing training instructions for using multigrip prosthetic hands are inadequate, providing poor guidance to clinicians and insufficient training for patients. Further research is needed into the efficiency of various training methods.

Design, Construction and Tests of a Low-Cost Myoelectric Thumb

Myoelectric signals can be used to control prostheses or exoskeletons as well as robots, i.e., devices assisting the user or replacing a missing part of the body. A typical application of myoelectric prostheses is the human hand. Here, the development of a low-cost myoelectric thumb is described, which can either be used as an additional finger or as prosthesis. Combining 3D printing with inexpensive sensors, electrodes, and electronics, the recent project offers the possibility to produce an individualized myoelectric thumb at significantly lower costs than commercial myoelectric prostheses. Alternatively, a second thumb may be supportive for people with special manual tasks. These possibilities are discussed together with disadvantages of a second thumb and drawbacks of the low-cost solution in terms of mechanical properties and wearing comfort. The study shows that a low-cost customized myoelectric thumb can be produced in this way, but further research on controlling the thumb as well as improving motorization are necessarily to make it fully usable for daily tasks.

Modified Constraint-Induced Movement Therapy for persons with unilateral upper extremity amputation: A case report

STUDY DESIGN

Pretest/posttest case series design.

INTRODUCTION

Rates of prosthetic device abandonment are highest among persons with upper extremity (UE) amputation. Modified Constraint-Induced Movement Therapy (mCIMT), which has been extensively studied in patients with chronic, subacute, and acute stroke, is an under-utilized approach to treat persons with UE amputation.

PURPOSE OF THE STUDY

To present an mCIMT intervention for prosthetic device training after a unilateral UE amputation.

METHODS

The two cases from an advanced rehabilitation center herein described followed a standard UE amputation rehabilitation program used in conjunction with a home training program using mCIMT 3 hours a day, 5 days a week, for 3 weeks. Progress was evaluated weekly using the Activities Measure for Upper Limb Amputees (AM-ULA); Disabilities of the Arm, Shoulder, and Hand; Trinity Amputation and Prosthesis Experience Scales-Revised.

RESULTS

Both the cases exhibited an increase in observable and objective functional use with a UE prosthetic device, as indicated by the AM-ULA.

CONCLUSIONS

To our knowledge, this is the first description of mCIMT as part of a unilateral UE amputee rehabilitation program. The AM-ULA results show meaningful change, whereas Disabilities of the Arm, Shoulder, and Hand and Trinity Amputation and Prosthesis Experience Scales-Revised show mixed results.

Evaluation of Model-Based Biomimetic Control of Prosthetic Finger Force for Grasp

Restoring neuromuscular reflex properties in the control of a prosthetic hand may potentially approach human-level grasp functions in the prosthetic hand. Previous studies have confirmed the feasibility of real-time emulation of a monosynaptic spinal reflex loop for prosthetic control. This study continues to explore how well the biomimetic controller could enable the amputee to perform force-control tasks that required both strength and error-tolerance. The biomimetic controller was programmed on a neuromorphic chip for real-time emulation of reflex. The model-calculated force of finger flexor was used to drive a torque motor, which pulled a tendon that flexed prosthetic fingers. Force control ability was evaluated in a "press-without-break" task, which required participants to press a force transducer toward a target level, but never exceeding a breakage threshold. The same task was tested either with the index finger or the full hand; the performance of the biomimetic controller was compared to a proportional linear feedback (PLF) controller, and the contralateral normal hand. Data from finger pressing task in 5 amputees showed that the biomimetic controller and the PLF controller achieved 95.8% and 66.9% the performance of contralateral finger in success rate; 50.0% and 25.1% in stability of force control; 59.9% and 42.8% in information throughput; and 51.5% and 38.4% in completion time. The biomimetic controller outperformed the PLF controller in all performance indices. Similar trends were observed with full-hand grasp task. The biomimetic controller exhibited capacity and behavior closer to contralateral normal hand. Results suggest that incorporating neuromuscular reflex properties in the biomimetic controller may provide human-like capacity of force regulation, which may enhance motor performance of amputees operating a tendon-driven prosthetic hand.

Restoring Tactile Sensation Using a Triboelectric Nanogenerator

Loss of tactile sensation is a common occurrence in patients with traumatic peripheral nerve injury or soft tissue loss, but as yet, solutions for restoring such sensation are limited. Implanted neuro-prosthetics are a promising direction for tactile sensory restoration, but available technologies have substantial shortcomings, including complexity of use and of production and the need for an external power supply. In this work, we propose, fabricate, and demonstrate the use of a triboelectric nanogenerator (TENG) as a relatively simple, self-powered, biocompatible, sensitive, and flexible device for restoring tactile sensation. This integrated tactile TENG (TENG-IT) device is implanted under the skin and translates tactile pressure into electrical potential, which it relays via cuff electrodes to healthy sensory nerves, thereby stimulating them, to mimic tactile sensation. We show that the device elicits electrical activity in sensory neurons in vitro, and that the extent of this activity is dependent on the level of tactile pressure applied to the device. We subsequently demonstrate the TENG-IT in vivo, showing that it provides tactile sensation capabilities (as measured by a von Frey test) to rats in which sensation in the hindfoot was blocked through transection of the distal tibial nerve. These findings point to the substantial potential of self-powered TENG-based implanted devices as a means of restoring tactile sensation.

Development of overuse musculoskeletal conditions after combat-related upper limb amputation: a retrospective cohort study

STUDY DESIGN

Retrospective cohort study INTRODUCTION: Service members who have sustained traumatic amputations are typically young and otherwise healthy. Beyond standard care, these individuals desire long, highly active, and relatively pain-free lifestyle, whether that is returning to active duty or transitioning to civilian life. Development of overuse musculoskeletal conditions could have a significant influence on quality of life for Service members with traumatic upper limb amputation.

PURPOSE OF THE STUDY

Compare one-year incidence of overuse musculoskeletal injuries in Service members with different levels of combat-related upper limb amputation to Service members with minor combat-related upper limb injuries.

METHODS

Service members with deployment-related upper limb injury (N = 519), 148 major upper limb amputation (55 with amputation at or above elbow, 93 with amputation below elbow) and 371 minor upper limb injury were included in the study. Outcomes of interest clinical diagnosis codes associated with overuse conditions of the upper limb, neck and upper back, lower limb, low back pain, and all regions combined, one year before and one year after injury.

RESULTS

Overall, the one-year incidence of developing at least one musculoskeletal overuse condition after upper limb amputation was between 60% and 65%. Service members with upper limb amputations were 2.7 to 4.7 times more likely to develop an overuse upper limb condition, 3.6 to 3.8 times more likely to develop a neck and upper back condition, 2.8 to 4.4 times more likely to develop a lower limb condition, and 3.3 to 3.9 times more likely to develop low back pain as compared those who sustained minor combat-related injuries. No significant differences in the odds of developing a musculoskeletal condition was found between the above elbow and below elbow amputation groups.

CONCLUSIONS

Incidence of secondary overuse conditions is elevated in Service members with upper limb amputation and warrants focused research efforts toward preventative and rehabilitative interventions.

Clinic Use at the Departments of Defense and Veterans Affairs Following Combat Related Amputations

INTRODUCTION

Little population-based research has described the transition from Department of Defense (DoD) to Department of Veterans Affairs (VA) healthcare following combat related amputations. The objectives were to describe (1) to what extent patients used either DoD only facilities, both DoD and VA facilities, or VA only facilities during the first 5 years postinjury, (2) which specific clinics were used and (3) clinic use among patients with different levels of amputation (upper versus lower), and among patients with early or late amputation.

MATERIALS AND METHODS

This was a retrospective analysis of health data extracted from the expeditionary medical encounter database (EMED) and national DoD and VA databases. Patients were 649 US service members who sustained a single major limb amputation following injuries in the Iraq and Afghanistan conflicts, 2001-2008. We compared yearly DoD and VA clinic use by patient groups with different levels of amputation (upper limb: above versus below elbow or lower limb: above versus below knee), different timing of amputation (early: within 90 days postinjury versus late: more than 90 days postinjury), military component (Active Duty versus National Guard/Reserve) and race (White versus Black). For all groups, we calculated the percentage of patients using: (1) DoD only, (2) both DoD and VA or 3) VA only clinics during each of postinjury years 1 through 5. We also calculated the percentage of patients who used specific clinics (e.g., social work, prosthetics, mental health) during each postinjury year.

RESULTS

During postinjury year 1, over 98% of patients used DoD only or both DoD and VA clinics. Most individuals (70% to 78%) used both DoD and VA clinics during postinjury year 1. Use of VA only clinics increased gradually between postinjury year 2 (15% to 30% of patient groups) and year 5 (75% to 88%). This gradual transition to use of VA only clinics was seen consistently across patient groups with different anatomical levels or timing of amputation, military component or race. Patients with lower levels of amputation (versus higher levels) and individuals with early amputations (versus late) transitioned earlier to VA only care. Overall, clinic use was high as 91% to 100% of all patient groups used one or more clinics (DoD or VA) during each of the first 5 years. For specific clinics, most patients used DoD facilities related to rehabilitation (physical therapy, prosthetics) or transitional care (social work) particularly during postinjury year 1. Use of most VA clinics studied (social work, primary care, prosthetics, mental health) showed a modest increase primarily after postinjury year 1 and remained stable through postinjury year 5. The results indicated apparent underuse of psychiatric/mental health and prosthetics between postinjury year 1 and 2.

CONCLUSIONS

The present study indicated a gradual transition from DoD to VA only healthcare which extended across 5 years following combat related amputations. Patients with lower levels of amputation or early amputation generally transitioned earlier to VA only healthcare. These results can inform medical planning to support a timely and clinically effective transition from DoD to VA healthcare.

Brain lateralization in children with upper-limb reduction deficiency

Background

The purpose of the current study was to determine the influence of upper-limb prostheses on brain activity and gross dexterity in children with congenital unilateral upper-limb reduction deficiencies (ULD) compared to typically developing children (TD).

Methods

Five children with ULD (3 boys, 2 girls, 8.76 ± 3.37 years of age) and five age- and sex-matched TD children (3 boys, 2 girls, 8.96 ± 3.23 years of age) performed a gross manual dexterity task (Box and Block Test) while measuring brain activity (functional near-infrared spectroscopy; fNIRS).

Results

There were no significant differences (p = 0.948) in gross dexterity performance between the ULD group with prosthesis (7.23 ± 3.37 blocks per minute) and TD group with the prosthetic simulator (7.63 ± 5.61 blocks per minute). However, there was a significant (p = 0.001) difference in Laterality Index (LI) between the ULD group with prosthesis (LI = − 0.2888 ± 0.0205) and TD group with simulator (LI = 0.0504 ± 0.0296) showing in a significant ipsilateral control for the ULD group. Thus, the major finding of the present investigation was that children with ULD, unlike the control group, showed significant activation in the ipsilateral motor cortex on the non-preferred side using a prosthesis during a gross manual dexterity task.

Conclusions

This ipsilateral response may be a compensation strategy in which the existing cortical representations of the non-affected (preferred) side are been used by the affected (non-preferred) side to operate the prosthesis. This study is the first to report altered lateralization in children with ULD while using a prosthesis.

Trial registration The clinical trial (ClinicalTrial.gov ID: NCT04110730 and unique protocol ID: IRB # 614-16-FB) was registered on October 1, 2019 (https://clinicaltrials.gov/ct2/show/NCT04110730) and posted on October 1, 2019. The study start date was January 10, 2020. The first participant was enrolled on January 14, 2020, and the trial is scheduled to be completed by August 23, 2023. The trial was updated January 18, 2020 and is currently recruiting

A cutaneous mechanoneural interface for neuroprosthetic feedback

Amputation destroys sensory end organs and does not provide an anatomical interface for cutaneous neuroprosthetic feedback. Here, we report the design and a biomechanical and electrophysiological evaluation of the cutaneous mechanoneural interface consisting of an afferent neural system that comprises a muscle actuator coupled to a natively pedicled skin flap in a cuff-like architecture. Muscle is actuated through electrical stimulation to induce strains or oscillatory vibrations on the skin flap that are proportional to a desired contact duration or contact pressure. In rat hindlimbs, the mechanoneural interface elicited native dermal mechanotransducers to generate at least four levels of graded contact and eight distinct vibratory afferents that were not significantly different from analogous mechanical stimulation of intact skin. The application of different patterns of electrical stimulation independently engaged slowly adapting and rapidly adapting mechanotransducers, and recreated an array of cutaneous sensations. The cutaneous mechanoneural interface can be integrated with current prosthetic technologies for tactile feedback.

Telerehabilitation for Amputee Care

Patients with amputation have unique characteristics and needs that must be considered when services are being provided through a virtual platform. The types of amputation rehabilitation services that can be provided virtually are numerous and vary from a full clinical team evaluation to individual therapy services. Whether services are being provided in person or through a virtual platform, rehabilitation of the person with amputation ideally involves a collaborative interdisciplinary team. The potential benefits of providing amputation rehabilitation care through a virtual platform include enhanced access to specialized services, reduced travel burden, and improved continuity of care.

A review of technology, materials and R&D challenges of upper limb prosthesis for improved user suitability

Introduction

Hand amputation significantly challenges one's independence in carrying out daily activities. With the UK and Italy recoding circa 5200 and 3500 upper limb (UL) amputations (ULAs) yearly, respectively, and about 541,000 Americans losing ULs in 2005, incidence victims constitute a considerable proportion of our population and should be adequately supported. The use of upper limb prosthesis (ULP) offers amputees a new opportunity of living a quality life - but poses challenges on the physically and psychologically traumatised. With reports that up to 20% of adult UL amputees choose not to use a prosthesis, roughly 26% of adults and 45% of children and adolescents are dissatisfied with their devices and abandon them with reasons of poor solution to basic needs, a review of ULP for suitability has become crucial.

Objectives

These include, to review UL prosthetic technology (PT), the materials used in the manufacturing of ULP, challenges in research and development of ULP, and to advise on the suitability of different devices to the needs of amputees.

Methods

They involve an extensive review of relevant literature and application of statistics to analyse data obtained from literature.

Results

ULAs are characterised to show affected bones in seven types of amputations. The characterisation depicts key causes of incidences that lead to amputations while advising on device suitability. PT is classified in terms of cost, nature, functions/operations of each type of device while providing the design challenges. Users' opinions on PT materials are analysed and used to suggest new materials for the next generation of the devices. R&D challenges hindering future developments of PT is reviewed and results used to identify characteristics for the next generation of the technology.

Conclusions

To increase user satisfaction and reduce device abandonment, amputees need useful information on the trend in PT and engineers need information about device field performance for improvements. The use of better performing ULP will improve users' everyday lives.

Suitability of the Openly Accessible 3D Printed Prosthetic Hands for War-Wounded Children

The field of rehabilitation and assistive devices is being disrupted by innovations in desktop 3D printers and open-source designs. For upper limb prosthetics, those technologies have demonstrated a strong potential to aid those with missing hands. However, there are basic interfacing issues that need to be addressed for long term usage. The functionality, durability, and the price need to be considered especially for those in difficult living conditions. We evaluated the most popular designs of body-powered, 3D printed prosthetic hands. We selected a representative sample and evaluated its suitability for its grasping postures, durability, and cost. The prosthetic hand can perform three grasping postures out of the 33 grasps that a human hand can do. This corresponds to grasping objects similar to a coin, a golf ball, and a credit card. Results showed that the material used in the hand and the cables can withstand a 22 N normal grasping force, which is acceptable based on standards for accessibility design. The cost model showed that a 3D printed hand could be produced for as low as $19. For the benefit of children with congenital missing limbs and for the war-wounded, the results can serve as a baseline study to advance the development of prosthetic hands that are functional yet low-cost.

Using a 3D-Printed Prosthetic to Improve Participation in a Young Gymnast

BACKGROUND AND PURPOSE

The purpose of this case report was to investigate the application of a 3-dimensional (3D)-printed prosthetic hand to improve a child's participation, confidence, and satisfaction in gymnastic classes, specifically, horizontal bar-related skills.

SUMMARY OF KEY POINTS

A 9-year-old child was unable to participate in horizontal bar-related gymnastic skills due to a congenital hand deficiency. A prosthetic hand was designed, 3D printed, modified repeatedly, and incorporated into a program, which resulted in improvements in the child's ability to participate in gymnastics.

CONCLUSIONS

Using a 3D-printed upper limb prosthetic hand improved the child's participation, confidence, and satisfaction in her gymnastic classes permitting use of horizontal bar. To progress to higher-intensity activities, further safety measures and testing of the prosthetic hand are needed.

WHAT THIS CASE ADDS TO EVIDENCEBASED PRACTICE

A 3D-printed prosthetic hand was manufactured and customized allowing closely monitored, gradually increased, participation in horizontal bar gymnastics.

Recent Developments in Prosthesis Sensors, Texture Recognition, and Sensory Stimulation for Upper Limb Prostheses

Current developments being made in upper limb prostheses are focused on replacing lost sensory information to the amputees. Providing sensory stimulation from the prosthesis can directly improve control over the prosthetic and provide a sense of body ownership. The focus of this review article is on recent developments while including foundational knowledge for some of the critical concepts in neural prostheses. Reported concepts follow the flow of information from sensors to signal processing, with emphasis on texture recognition, and then to sensory stimulation strategies that reestablish the lost sensory feedback loop. Prosthetic sensors are used to detect the physical environment, converting pressure, force, and position into electrical signals. The electrical signals can then be processed in an effort to identify the surrounding environment using distinctive characteristics such as stiffness and texture. In order for the amputee to use this information in a natural manner, there must be real-time sensory stimulation, perception, and motor control of the prosthesis. Although truly complete sensory replacement has not yet been realized, some basic percepts can be partially restored, allowing progress towards a more realistic prosthesis with natural sensations.

Fully Implanted Prostheses for Musculoskeletal Limb Reconstruction After Amputation: An In Vivo Feasibility Study

Previous prostheses for replacing a missing limb following amputation must be worn externally on the body. This limits the extent to which prostheses could physically interface with biological tissues, such as muscles, to enhance functional recovery. The objectives of our study were to (1) test the feasibility of implanting a limb prosthesis, or endoprosthesis, entirely within living skin at the distal end of a residual limb, and (2) identify effective surgical and post-surgical care approaches for implanting endoprostheses in a rabbit model of hindlimb amputation. We iteratively designed, fabricated, and implanted unjointed endoprosthesis prototypes in six New Zealand White rabbits following amputation. In the first three rabbits, the skin failed to heal due to ishemia and dehiscence along the sutured incision. The skin of the final three subsequent rabbits successfully healed over the endoprotheses. Factors that contributed to successful outcomes included modifying the surgical incision to preserve vasculature; increasing the radii size on the endoprostheses to reduce skin stress; collecting radiographs pre-surgery to match the bone pin size to the medullary canal size; and ensuring post-operative bandage integrity. These results will support future work to test jointed endoprostheses that can be attached to muscles.

Ten-Year Outcomes of a Systems-Based Approach to Longitudinal Amputation Care in the US Department of Veteran Affairs

Background

The goal of the US Department of Veterans Affairs (VA) Amputation System of Care (ASoC) is to enhance the quality and consistency of amputation rehabilitation care for veterans with limb loss.

Objective

The ASoC provides specialized expertise in amputation rehabilitation incorporating the latest practices in medical management, rehabilitation, and artificial limbs in order to minimize disability and to enable the highest level of social, vocational, and recreational success for veterans with amputation.

Discussion

The ASoC serves veterans with limb amputation from any etiology. Between 2009 and 2019, the VA experienced a 34% increase in the number of veterans with amputation who received care. During the same 10-year period, the percentage of veterans with major limb amputation seen in an outpatient amputation specialty clinic each year increased from 4.8 to 26%. This article highlights how the mission of the ASoC has been accomplished over the past decade through prioritization and implementation of key strategic initiatives in learning organization creation, trust in VA care, modernization, and development of a high-performance network with enhanced access and customer service.

Conclusions

This synopsis of the VA amputation care program serves as a model of amputation care that can be utilized outside the federal sector and has the potential to serve as a systems-based example for providing longitudinal care to other populations within the VA.

Upper extremity prosthetic selection influences loading of transhumeral osseointegrated systems

Percutaneous osseointegrated (OI) implants are increasingly viable as an alternative to socket suspension of prosthetic limbs. Upper extremity prostheses have also become more complex to better replicate hand and arm function and attempt to recreate pre-amputation functional levels. With more functionality comes heavier devices that put more stress on the bone-implant interface, which could be an issue for implant stability. This study quantified transhumeral loading at defined amputation levels using four simulated prosthetic limb-types: (1) body powered hook, (2) myoelectric hook, (3) myoelectric hand, and (4) advanced prosthetic limb. Computational models were constructed to replicate the weight distribution of each prosthesis type, then applied to motion capture data collected during Advanced Activities of Daily Living (AADLs). For activities that did not include a handheld weight, the body powered prosthesis bending moments were 13–33% (range of means for each activity across amputation levels) of the intact arm moments (reference 100%), torsional moments were 12–15%, and axial pullout forces were 30–40% of the intact case (p≤0.001). The myoelectric hook and hand bending moments were 60–99%, torsional moments were 44–97%, and axial pullout forces were 62–101% of the intact case. The advanced prosthesis bending moments were 177–201%, torsional moments were 164–326%, and axial pullout forces were 133–185% of the intact case (p≤0.001). The addition of a handheld weight for briefcase carry and jug lift activities reduced the overall impact of the prosthetic model itself, where the body powered forces and moments were much closer to those of the intact model, and more complex prostheses further increased forces and moments beyond the intact arm levels. These results reveal a ranked order in loading magnitude according to complexity of the prosthetic device, and highlight the importance of considering the patient’s desired terminal device when planning post-operative percutaneous OI rehabilitation and training.

Performance among different types of myocontrolled tasks is not related

Studies on myocontrolled assistive technology (AT), such as myoelectric prostheses, as well as rehabilitation practice using myoelectric controlled interfaces, commonly assume the existence of a general myocontrol skill. This is the skill to control myosignals in such a way that they are employable in multiple tasks. If this skill exists, training any myocontrolled task using a certain set of muscles would improve the use of myocontrolled AT when the AT is controlled using these muscles. We examined whether a general myocontrol skill exists in myocontrolled tasks with and without a prosthesis. Unimpaired, right-handed adults used the sEMG of wrist flexors and extensors to perform several tasks in two experiments. In Experiment 1, twelve participants trained a myoelectric prosthesis-simulator task and a myocontrolled serious game for five consecutive days. Performance was compared between tasks and over the course of the training period. In Experiment 2, thirty-one participants performed five myocontrolled tasks consisting of two serious games, two prosthesis-simulator tasks and one digital signal matching task. All tasks were based on tasks currently used in clinical practice or research settings. Kendall rank correlation coefficients were computed to analyze correlations between the performance on different tasks. In Experiment 1 performance on the tasks showed no correlation for multiple outcome measures. Rankings within tasks did not change over the training period. In Experiment 2 performance did not correlate between any of the tasks. Since performance between different tasks did not correlate, results suggest that a general myocontrol skill does not exist and that each myocontrolled task requires a specific skill. Generalization of those findings to amputees using AT should be done with caution since in both experiments unimpaired participants were included. Moreover, training duration in Experiment 2 was short. Our findings indicate that training and assessment methods for myocontrolled AT use should focus on tasks frequently performed in daily life by the individual using the AT instead of merely focusing on training myosignals.

DARPA investment in peripheral nerve interfaces for prosthetics, prescriptions, and plasticity

BACKGROUND

Peripheral nerve interfaces have emerged as alternative solutions for a variety of therapeutic and performance improvement applications. The Defense Advanced Research Projects Agency (DARPA) has widely invested in these interfaces to provide motor control and sensory feedback to prosthetic limbs, identify non-pharmacological interventions to treat disease, and facilitate neuromodulation to accelerate learning or improve performance on cognitive, sensory, or motor tasks. In this commentary, we highlight some of the design considerations for optimizing peripheral nerve interfaces depending on the application space. We also discuss the ethical considerations that accompany these advances.

Design and Analysis of Flexible Joints for a Robust 3D Printed Prosthetic Hand

In war-affected regions in the world, limb loss is one of the leading injuries. The need for low-cost, low-maintenance prostheses arises. The rapid developments in 3D printing allows us to investigate robotic or prosthetic hand designs that can satisfy those basic requirements. 3D printed prosthetic hands are more affordable and lightweight alternatives for prostheses. In this paper, we investigate the flexibility of different designs of the soft joints of a low-cost 3D printed prosthetic hand with respect to the material type. We designed flexible joints from elastomeric materials instead of plastic joints. This modification can make the current 3D printed prosthesis designs more robust. As a drawback from these flexible joints, the prosthetic hand will not be in a full open palm position in its initial state, as compared to typical designs. We then converted this drawback to a beneficial feature by calculating the angles of the natural pose of the human hands and transfer those angles to the prosthetic hands with flexible joints. This work has implications in the design of 3D printed prosthetic hands that can be deployed for war-wounded refugees or for those in low-resource countries.

Exploring the Impact of Machine-Learned Predictions on Feedback from an Artificial Limb

Learning to get by without an arm or hand can be very challenging, and existing prostheses do not yet fill the needs of individuals with amputations. One promising solution is to improve the feedback from the device to the user. Towards this end, we present a simple machine learning interface to supplement the control of a robotic limb with feedback to the user about what the limb will be experiencing in the near future. A real-time prediction learner was implemented to predict impact-related electrical load experienced by a robot limb; the learning system's predictions were then communicated to the device's user to aid in their interactions with a workspace. We tested this system with five able-bodied subjects. Each subject manipulated the robot arm while receiving different forms of vibrotactile feedback regarding the arm's contact with its workspace. Our trials showed that using machine-learned predictions as a basis for feedback led to a statistically significant improvement in task performance when compared to purely reactive feedback from the device. Our study therefore contributes initial evidence that prediction learning and machine intelligence can benefit not just control, but also feedback from an artificial limb. We expect that a greater level of acceptance and ownership can be achieved if the prosthesis itself takes an active role in transmitting learned knowledge about its state and its situation of use.