Forskning

We show that tactile feedback is necessary for dexterous grasping with a prosthetic hand, and that the effectiveness of this feedback can be influenced by how the tactile information is encoded in the feedback. Three participants with a neuromusculoskeletal prosthesis repeatedly lifted an object which measured their grasping force and could randomly change weight, and we found that tactile feedback becomes more relevant when the expected wieght was more uncertain. Differences in participant preferences and performance also suggest that the effectiveness of sensory feedback may be partially dependent on their prior experiences. These insights into tactile sensory feedback may lead to improved control over prosthetic arms and reduce the need to closely watch the prosthesis while grasping objects.

Bone-anchored attachment of amputation limb prostheses is increasingly becoming a clinically accepted alternative to conventional socket suspension. The direct transfer of loads demands that the percutaneous implant system and the residual bone withstand all forces and moments transferred from the prosthesis. This study presents load measurements recorded at the bone-anchored attachment in 20 individuals with unilateral transfemoral amputation performing the everyday ambulatory activities: level ground walking, stairs ascent/descent and slope ascent/descent. Mean peak values for the sample populations across activities ranged from 498–684 N for the resultant force, 26.5–39.8 Nm for the bending moment, and 3.1–5.5 Nm for the longitudinal moment. Significant differences with respect to level walking were found for the resultant force during stairs ascent, (higher, p = 0.002), and stairs descent, (lower, p = 0.005). Using a crutch reduced the peak resultant forces and the peak bending moments with averages ranging from 5.5–12.6 % and 13.2–15.6 %, respectively. Large inter-participant variations were observed and no single activity resulted in consistently higher loading of the bone-anchored attachment across the participants. Results from this study can guide future development of percutaneous osseointegrated implant systems for limb prostheses and their rehabilitation protocols.

Conventional arm prosthesis used after above-elbow amputations are moved by non-intuitively contracting the biceps and triceps, lack sensory feedback, and are attached with a socket that compressed the stump. Here, we reported the long-time home use of a prosthetic system that is bone-anchored and connected to the human nervous system to allow for sensory feedback and intuitive control of a prosthesis. Thanks to the increased functionality and reliability of their new prosthetic systems, the patients could start working full-time and take up old hobbies again.

Wireless and leadless millimetre-scale implantable pulse generators, powered and controlled by ultrasonic links, enable the electrical stimulation of neural pathways in anaesthetized rats.

Prostheses are conventionally controlled via signals acquired from muscles. An amputation above the elbow leaves patient with a limited number of muscles and thus with few signal sources for controlling a prosthesis. Here we investigated an automatic elbow controller, leaving the muscle generated signals to open and close the hand. The automatic elbow controller reduced compensatory movements and was perceived as intuitive by the patients.

Myoelectric pattern recognition (MPR) to decode limb movements is an important advancement regarding the control of powered prostheses. However, this technology is not yet in wide clinical use. Improvements in MPR could potentially increase the functionality of powered prostheses. To this purpose, offline accuracy and processing time were measured over 44 features using six classifiers with the aim of determining new configurations of features and classifiers to improve the accuracy and response time of prosthetics control. An efficient feature set (FS: waveform length, correlation coefficient, Hjorth Parameters) was found to improve the motion recognition accuracy. Using the proposed FS significantly increased the performance of linear discriminant analysis, K-nearest neighbor, maximum likelihood estimation (MLE), and support vector machine by 5.5%, 5.7%, 6.3%, and 6.2%, respectively, when compared with the Hudgins’ set. Using the FS with MLE provided the largest improvement in offline accuracy over the Hudgins feature set, with minimal effect on the processing time. Among the 44 features tested, logarithmic root mean square and normalized logarithmic energy yielded the highest recognition rates (above 95%). We anticipate that this work will contribute to the development of more accurate surface EMG-based motor decoding systems for the control prosthetic hands.

A challenge when analysing electric signals from the muscles using artificial intelligence algorithms to control prosthetic limbs is to account for signal noise and faulty sensors. There is a class of processing that are wavelet based which usually cannot be used in real-time that can mitigate signal noise and faulty sensors. We tested wavelet-based processing on nine able-bodied participants with inconclusive results and on a dataset from 15 participants which showed improvements. These results suggest that wavelet-based processing can be used in real-time, but more research is needed to determine the trade-off between robustness and responsiveness.

Direct electrical stimulation of the peripheral nerves in individuals with amputations elicits sensations which are described as intuitive and natural with respect to where the sensation is felt on the missing hand, but not with respect to the subjective quality of the sensation. Three participants with a neuromusculoskeletal prosthesis were asked to describe the naturalness of sensations they felt when receiving nerve stimulation pulses that were slowly modulated. Sensations were generally perceived as artificial, citing “electric” or “tingling” characteristics. Our results indicate that this manner of patterned stimulation alone is not enough to transform sensations from artificial to natural quality, and thus novel developments and techniques are needed in the future.

Textile-based electrodes can be used to measure the electrical signals from muscles which can be used for diagnosis, monitoring and treatment. We reviewed articles describing applications of measuring the electrical signals from muscles using textile electrodes and summarised it. Based on the 41 articles we read, we introduce four textile integration levels to describe the various applications.

Replacement of a lost limb by an artificial substitute is not yet ideal. Resolution and coordination of motor control approximating that of a biological limb could dramatically improve the functionality of prosthetic devices, and thus reduce the gap towards a suitable limb replacement. In this study, we investigated the control resolution and coordination exhibited by subjects with transhumeral amputation who were implanted with epimysial electrodes and an osseointegrated interface that provides bidirectional communication in addition to skeletal attachment (e-OPRA Implant System). We assessed control resolution and coordination in the context of routine and delicate grasping using the Pick and Lift and the Virtual Eggs Tests. Performance when utilizing implanted electrodes was compared with the standard-of-care technology for myoelectric prostheses, namely surface electrodes. Results showed that implanted electrodes provide superior controllability over the prosthetic terminal device compared to conventional surface electrodes. Significant improvements were found in the control of the grip force and its reliability during object transfer. However, these improvements failed to increase motor coordination, and surprisingly decreased the temporal correlation between grip and load forces observed with surface electrodes. We found that despite being more functional and reliable, prosthetic control via implanted electrodes still depended highly on visual feedback. Our findings indicate that incidental sensory feedback (visual, auditory, and osseoperceptive in this case) is insufficient for restoring natural grasp behavior in amputees, and support the idea that supplemental tactile sensory feedback is needed to learn and maintain the motor tasks internal model, which could ultimately restore natural grasp behavior in subjects using prosthetic hands.