Assessment of an automatic prosthetic elbow control strategy using residual limb motion for transhumeral amputated individuals with socket or osseointegrated prostheses

International audienceMost 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 yields 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

Neuromuscular reorganization after arm amputation revealed by stump EMG evoked by different phantom movements

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Using the body kinematics to assess the utilization of transhumeral prostheses

International audienceBackground and aims: There is a gap between the technical capability of upper limb prostheses, and the control strategy (commonly sequential myoelectric control) used to actuate the motorized joints. Surprisingly, the control method is the same for prosthetic hands and hand/wrist/elbow systems, which leads to a complex utilization. Research groups are investigating new control strategies to make the prosthetic control easier. Most studies are focusing on the task achievement, but it is nonetheless essential to assess the achievement method, especially since high-level amputees are prone to develop compensation-related musculoskeletal disorders. The study aims to show that body kinematics can be used to compare different control strategies, or prosthetic equipments. Methods: Transhumeral amputees performed a reaching task with different prosthetic parameters (different sockets, different control strategies). They performed the task with a prosthesis prototype that could be adapted to any socket, and implemented with any control strategy. They were equipped with motion capture sensors in order to record their body kinematics. The body motion analysis included the trunk and shoulder displacements, as wellas the weight deviation.Results: We could observe that each transhumeral amputee had a unique utilization of their prosthesis, and that they had their own residual capabilities. All the participants performed the task with the two tested control strategies successfully. However, the kinematic analysis showed differences between the control strategies in terms of coordination restauration, that the participants described but that the task assessment (success or not) could not provide. Conclusions: Differences could be highlighted between control strategies that the standard assessment method could not show. Hence the whole body kinematics can be a substantial source of information, especially given the potential severity of compensatory strategies in upper limb prosthesis utilizatio

Improving the control of prostheses in arm amputees with approaches based on motor coordination

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Phantom hand and wrist movements in upper limb amputees are slow but naturally controlled movements

International audienceAfter limb amputation, patients often wake up with a vivid perception of the presence of the missing limb, called "phantom limb". Phantom limbs have mostly been studied with respect to pain sensation. But patients can experience many other phantom sensations, including voluntary movements. The goal of the present study was to quantify phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Six upper arm and two forearm amputees with various delays since amputation (6months to 32years) performed phantom finger, hand and wrist movements at self-chosen comfortable velocities. The kinematics of the phantom movements was indirectly obtained via the intact limb that synchronously mimicked the phantom limb movements, using a Cyberglove® for measuring finger movements and an inertial measurement unit for wrist movements. Results show that the execution of phantom movements is perceived as "natural" but effortful. The types of phantom movements that can be performed are variable between the patients but they could all perform thumb flexion/extension and global hand opening/closure. Finger extension movements appeared to be 24% faster than finger flexion movements. Neither the number of types of phantom movements that can be executed nor the kinematic characteristics were related to the elapsed time since amputation, highlighting the persistence of post-amputation neural adaptation. We hypothesize that the perceived slowness of phantom movements is related to altered proprioceptive feedback that cannot be recalibrated by lack of visual feedback during phantom movement execution

Classification of Phantom Finger, Hand, Wrist and Elbow Voluntary Gestures in Transhumeral Amputees with sEMG

International audienceDecoding finger and hand movements from sEMG electrodes placed on the forearm of transradial amputees has been commonly studied by many research groups. A few recent studies have shown an interesting phenomenon: simple correlations between distal phantom finger, hand and wrist voluntary movements and muscle activity in the residual upper arm in transhumeral amputees, i.e., of muscle groups that, prior to amputation, had no physical effect on the concerned hand and wrist joints. In this study, we are going further into the exploration of this phenomenon by setting up an evaluation study of phantom finger, hand, wrist and elbow (if present) movement classification based on the analysis of surface electromyographic (sEMG) signals measured by multiple electrodes placed on the residual upper arm of five transhumeral amputees with a controllable phantom limb who did not undergo any reinnervation surgery. We showed that with a state-of-the-art classification architecture, it is possible to correctly classify phantom limb activity (up to 14 movements) with a rather important average success (over 80% if considering basic sets of six hand, wrist and elbow movements) and to use this pattern recognition output to give online control of a device (here a graphical interface) to these transhumeral amputees. Beyond changing the way the phantom limb condition is apprehended by both patients and clinicians, such results could pave the road towards a new control approach for transhumeral amputated patients with a voluntary controllable phantom limb. This could ease and extend their control abilities of functional upper limb prosthetics with multiple active joints without undergoing muscular reinnervation surgery

Using the body kinematics to assess the utilization of transhumeral prostheses

International audienceBackground and aims: There is a gap between the technical capability of upper limb prostheses, and the control strategy (commonly sequential myoelectric control) used to actuate the motorized joints. Surprisingly, the control method is the same for prosthetic hands and hand/wrist/elbow systems, which leads to a complex utilization. Research groups are investigating new control strategies to make the prosthetic control easier. Most studies are focusing on the task achievement, but it is nonetheless essential to assess the achievement method, especially since high-level amputees are prone to develop compensation-related musculoskeletal disorders. The study aims to show that body kinematics can be used to compare different control strategies, or prosthetic equipments. Methods: Transhumeral amputees performed a reaching task with different prosthetic parameters (different sockets, different control strategies). They performed the task with a prosthesis prototype that could be adapted to any socket, and implemented with any control strategy. They were equipped with motion capture sensors in order to record their body kinematics. The body motion analysis included the trunk and shoulder displacements, as wellas the weight deviation.Results: We could observe that each transhumeral amputee had a unique utilization of their prosthesis, and that they had their own residual capabilities. All the participants performed the task with the two tested control strategies successfully. However, the kinematic analysis showed differences between the control strategies in terms of coordination restauration, that the participants described but that the task assessment (success or not) could not provide. Conclusions: Differences could be highlighted between control strategies that the standard assessment method could not show. Hence the whole body kinematics can be a substantial source of information, especially given the potential severity of compensatory strategies in upper limb prosthesis utilizatio