Motor learning in multijoint virtual arm movements with novel kinematics.

Humans move their hands toward precise positions, a skill supported by the coordination of multiple joint movements, even in the presence of inherent redundancy. However, it remains unclear how the central nervous system learns the relationship between redundant joint movements and hand positions when starting from scratch. To address this question, a virtual-arm reaching task was performed in which participants were required to move a cursor corresponding to the hand of a virtual arm to a target. The joint angles of the virtual arm were determined by the heights of the participants' fingers. The results demonstrated that the participants moved the cursor to the target straighter and faster in the late phase than they did in the initial phase of learning. This improvement was accompanied by a reduction in the amount of angular changes in the virtual limb joint, predominantly characterized by an increased reliance on the virtual shoulder joint as opposed to the virtual wrist joint. These findings suggest that the central nervous system selects a combination of multijoint movements that minimize motor effort while learning novel upper-limb kinematics.

Use it or lose it: The relationship between two image-based biomarkers in better understanding osteoarthritis progression in the wrist.

Bone tissue is influenced by its mechanical environment and adapts in response to its mechanical load. This is supported by studies analyzing bone adaptation in the knee and hip. Changes to the bone have also been found to precede cartilage degeneration in diseases such as osteoarthritis (OA). Our objective was to demonstrate the relationship between joint contact and bone density in the wrists of healthy adults. Static CT scans with a calibration phantom were taken to obtain measures of bone mineral density (vBMD) in 3 normalized depths; 0 - 2.5, 2.5 - 5, and 5 - 7.5 mm. Participants underwent a four-dimensional CT scan (4DCT) while performing maximum wrist extension to maximum wrist flexion. 3D bone models of the distal radius, scaphoid, and lunate were made, and analyzed vBMD and joint contact area (JCA) in the radiolunate (RL) and radioscaphoid (RS) joints separately. Correlation coefficients were calculated where vBMD was the dependent variable, and kinematic JCA throughout every 10 degrees of motion were the independent variables. Statistically significant independent variables associated with vBMD were assessed using a regression model and were entered in steps; (1) significant correlations, (2) sex, and (3) age.An increase in vBMD was significantly, positively associated with an increase in JCa. Notably, in the deeper regions (5 - 7.5 mm) of the radius that is primarily composed of trabecular bone. Sex contributed to the variance in vBMD, while age did not. Subchondral bone changes are influenced by wrist position, demonstrating that the wrist serves to bear load similar to the knee and hip.

Hybrid Rehabilitation System with Motion Estimation Based on EMG Signals.

Patients with upper limb paralysis undergo various types of rehabilitation to reconstruct upper limb functions necessary for their return to daily life and social activities. Therefore, it is necessary to develop an effective rehabilitation support system using robotic technologies. In this study, we propose an EMG-driven hybrid rehabilitation system based on the estimation of intended motion using a probabilistic neural network. In the proposed system, the developed robot and functional electrical stimulation are controlled by estimating the patient's intention, which enables the intuitive learning of the appropriate control abilities of joint motions and muscle contraction patterns. In the experiments, hybrid and visual feedback training were conducted for pointing movements of the wrist joint of the non-dominant hand. The results confirmed that the proposed method provides effective training and has great potential for use in rehabilitation.

Development of the Biomech-Wrist: A 3-DOF Exoskeleton for Rehabilitation and Training of Human Wrist.

This work describes a three-degrees-of-freedom rehabilitation exoskeleton robot for wrist articulation movement: the Biomech-Wrist. The proposed development includes the design requirements based on the biomechanics and anthropometric features of the upper limb, the mechanical design, electronic instrumentation, software design, manufacturing, control algorithm implementation, and the experimental setup to validate the functionality of the system. The design requirements were set to achieve human wrist-like movements: ulnar-radial deviation, flexion-extension, and pronation-supination. Then, the mechanical design considers the human range of motion with proper torques, velocities, and geometry. The manufacturing consists of 3D-printed elements and tubular aluminum sections resulting in lightweight components with modifiable distances. The central aspect of the instrumentation is the actuation system consisting of three brushless motors and a microcontroller for the control implementation. The proposed device was evaluated by considering two control schemes to regulate the trajectory tracking on each joint. The first scheme was the conventional proportional-derivative controller, whereas the second was proposed as a first-order sliding mode. The results show that the Biomech-Wrist exoskeleton can perform trajectory tracking with high precision ( RMSEmax = 0.0556 rad) when implementing the sliding mode controller.

Simultaneous and Proportional Control of Wrist and Hand Movements Based on a Neural-Driven Musculoskeletal Model.

Human-machine interfaces (HMIs) based on electromyography (EMG) signals have been developed for simultaneous and proportional control (SPC) of multiple degrees of freedom (DoFs). The EMG-driven musculoskeletal model (MM) has been used in HMIs to predict human movements in prosthetic and robotic control. However, the neural information extracted from surface EMG signals may be distorted due to their limitations. With the development of high density (HD) EMG decomposition, accurate neural drive signals can be extracted from surface EMG signals. In this study, a neural-driven MM was proposed to predict metacarpophalangeal (MCP) joint flexion/extension and wrist joint flexion/extension. Ten non-disabled subjects (male) were recruited and tested. Four 64-channel electrode grids were attached to four forearm muscles of each subject to record the HD EMG signals. The joint angles were recorded synchronously. The acquired HD EMG signals were decomposed to extract the motor unit (MU) discharge for estimating the neural drive, which was then used as the input to the MM to calculate the muscle activation and predict the joint movements. The Pearson's correlation coefficient (r) and the normalized root mean square error (NRMSE) between the predicted joint angles and the measured joint angles were calculated to quantify the estimation performance. Compared to the EMG-driven MM, the neural-driven MM attained higher r values and lower NRMSE values. Although the results were limited to an offline application and to a limited number of DoFs, they indicated that the neural-driven MM outperforms the EMG-driven MM in prediction accuracy and robustness. The proposed neural-driven MM for HMI can obtain more accurate neural commands and may have great potential for medical rehabilitation and robot control.

Characteristics of multi-channel intermuscular directional coupling based on time-varying partial directional coherence analysis.

The human body transmits directional information between muscles during upper limb movements, and this will be particularly evident when the dominant muscle changes during movement transitions. By capturing the electromyography (EMG) signals of wrist flexion and extension continuous transition movements, we investigated the characteristics of multichannel intermuscular directional coupling and directional information transmission, and consequently explored the control mechanism of Central nervous system (CNS) and the coordination mechanism of motor muscles. Multi-channel EMG was collected from 12 healthy subjects under continuous translational movements of wrist flexion and extension, and the time-varying biased directional coherence analysis (TVPDC) model was constructed using partial directional coherence analysis (PDC) frequency domain directionality to study the directional information transfer characteristics in the time-frequency domain, screen closely related muscle pairs and perform directional coupling significance analysis. Palmaris longus (PL) played a dominant role under wrist flexion movements(WF), Extensor Carpi Radialis (ECR) played a dominant role under wrist extension movements(WE), and the remaining muscles responded to them with information and Biceps Brachii (BB) played a responsive role throughout the movement; flexor pairs had the highest positive coupling values in the beta band during Conversion action1 (MC1) and WF phases, and extensor pairs had the highest positive coupling values in the gamma band during Conversion action2(MC2) phase and the highest coupling values in the beta band during WE phase. TVPDC can effectively analyze the multichannel intermuscular directional coupling and information transmission relationship of surface electromyography under wrist flexion and extension transition movements, providing a reference for exploring the control mechanism of CNS and abnormal control mechanism in patients with motor dysfunction in a new perspective.

Effects of wrist posture and stabilization on precision grip force production and muscle activation patterns.

Most of the power for generating forces in the fingers arises from muscles located in the forearm. This configuration maximizes finger joint range of motion while minimizing finger mass and inertia. The resulting multiarticular arrangement of the tendons, however, complicates independent control of the wrist and the digits. Actuating the wrist impacts sensorimotor control of the fingers and vice versa. The goal of this study was to systematically investigate interactions between isometric wrist and digit control. Specifically, we examined how the need to maintain a specified wrist posture influences precision grip. Fifteen healthy adults produced maximum precision grip force at 11 different wrist flexion/extension angles, with the arm supported, under two conditions: 1) the participant maintained the desired wrist angle while performing the precision grip and 2) a robot maintained the specified wrist angle. Wrist flexion/extension posture significantly impacted maximum precision grip force (P < 0.001), with the greatest grip force achieved when the wrist was extended 30° from neutral. External wrist stabilization by the robot led to a 20% increase in precision grip force across wrist postures. Increased force was accompanied by increased muscle activation but with an activation pattern similar to the one used when the participant had to stabilize their wrist. Thus, simultaneous wrist and finger requirements impacted performance of an isometric finger task. External wrist stabilization can promote increased precision grip force resulting from increased muscle activation. These findings have potential clinical significance for individuals with neurologically driven finger weakness, such as stroke survivors.NEW & NOTEWORTHY We explored the interdependence between wrist and fingers by assessing the influence of wrist posture and external stabilization on precision grip force generation. We found that maximum precision grip force occurred at an extended wrist posture and was 20% greater when the wrist was Externally Stabilized. The latter resulted from amplification of muscle activation patterns from the Self-Stabilized condition rather than adoption of new patterns exploiting external wrist stabilization.

Scaphoid, lunate and capitate kinematics in the normal and ligament deficient wrist: A bi-plane X-ray fluoroscopy study.

The ligamentous structures of the wrist stabilise and constrain the interactions of the carpal bones during active wrist motion; however, the three-dimensional translations and rotations of the scaphoid, lunate and capitate in the normal and ligament deficient wrist during planar and oblique wrist motions remain poorly understood. This study employed a computer-controlled simulator to replicate physiological wrist motion by dynamic muscle force application, while carpal kinematics were simultaneously measured using bi-plane x-ray fluoroscopy. The aim was to quantify carpal kinematics in the native wrist and after sequential sectioning of the scapholunate interosseous ligament (SLIL) and secondary scapholunate ligament structures. Seven fresh-frozen cadaveric wrist specimens were harvested, and cycles of flexion-extension, radial-ulnar deviation and dart-thrower's motion were simulated. The results showed significant rotational and translational changes to these carpal bones in all stages of disruptions to the supporting ligaments (p < 0.05). Specifically, following the disruption of the dorsal SLIL (Stage II), the scaphoid became significantly more flexed, ulnarly deviated, and pronated relative to the radius, whereas the lunate became more extended, supinated and volarly translated (p < 0.05). Sectioning of the dorsal intercarpal (DIC), dorsal radiocarpal (DRC), and scaphotrapeziotrapezoid (STT) ligaments (Stage IV) caused the scaphoid to collapse further into flexion, ulnar deviation, and pronation. These findings highlight the importance of all the ligamentous attachments that relate to the stability of the scapholunate joint, but more importantly, the dorsal SLIL in maintaining scapholunate stability, and the preservation of the attachments of the DIC and DRC ligaments during dorsal surgical approaches. The findings will be useful in diagnosing wrist pathology and in surgical planning.

Design and Performance Analysis of a Bioelectronic Controlled Hybrid Serial-Parallel Wrist Exoskeleton.

Wrist exoskeletons are increasingly being used in the rehabilitation of stroke and hand dysfunction because of its ability to assist patients in high intensity, repetitive, targeted and interactive rehabilitation training. However, the existing wrist exoskeletons cannot effectively replace the work of therapist and improve hand function, mainly because the existing exoskeletons cannot assist patients to perform natural hand movement covering the entire physiological motor space (PMS). Here, we present a bioelectronic controlled hybrid serial-parallel wrist exoskeleton HrWr-ExoSkeleton (HrWE) which is based on the PMS design guidance, the gear set can carry out forearm pronation/supination (P/S) and the 2-DoF parallel configuration fixed on the gear set can carry out wrist flexion/extension (F/E) and radial/ulnar deviation (R/U). This special configuration not only provides enough range of motion (RoM) for rehabilitation training (85F/85E, 55R/55U, and 90P/90S), but also makes it easier to provide the interface for finger exoskeletons and be adapted to upper limb exoskeletons. In addition, to further improve the rehabilitation effect, we propose a HrWE-assisted active rehabilitation training platform based on surface electromyography signals.

Stability of the distal radioulnar joint with and without activation of forearm muscles.

The purpose of this study was to quantify the effect of the flexor carpi ulnaris and the extensor carpi ulnaris muscles on distal radioulnar joint stability. The anteroposterior ulnar head translation in relation to the radius was measured sonographically when the forearm was in a neutral resting position and when the hand was actively pressed on to a surface, with and without intentional flexor carpi ulnaris and extensor carpi ulnaris activation, while also being monitored by an electromyogram. Data on 40 healthy participants indicated a mean anteroposterior translation in the distal radioulnar joint of 4.1 mm (SD 1.08) without and 1.2 mm (SD 0.54) with muscle activation. Our results indicate that intentional ulnar forearm muscle activation results in 70% less anteroposterior ulnar head translation and greater distal radioulnar joint stability. Therefore, the flexor carpi ulnaris and extensor carpi ulnaris muscles serve as dynamic stabilizers of the distal radioulnar joint. This finding may be clinically significant since ulnar forearm muscles strengthening may increase distal radioulnar joint stability.

Understanding the biomechanics of the forearm during the dart thrower's motion.

This study investigated the contribution of different forearm muscles, namely the flexor carpi ulnaris, extensor carpi radialis longus and brevis, extensor carpi ulnaris and flexor carpi radialis, during the dart thrower's motion. Thirteen healthy participants were recruited. The forearm muscle activation patterns during the dart thrower's motion were measured using surface electromyography. The average root mean square for the extensor carpi ulnaris was found to be the highest during the dart thrower's motion. Muscle activations during the dart thrower's motion were heterogeneous among the participants. The results suggest the rehabilitation protocol for patients with wrist injuries should be reconsidered.

Mapping Individual Motor Unit Activity to Continuous Three-DoF Wrist Torques: Perspectives for Myoelectric Control.

The surface electromyography (EMG) decomposition techniques provide access to motor neuron activities and have been applied to myoelectric control schemes. However, the current decomposition-based myoelectric control mainly focuses on discrete gestures or single-DoF continuous movements. In this study, we aimed to map the motor unit discharges, which were identified from high-density surface EMG, to the three degrees of freedom (DoFs) wrist movements. The 3-DoF wrist torques and high-density surface EMG signals were recorded concurrently from eight non-disabled subjects. The experimental protocol included single-DoF movements and their various combinations. We decoded the motor unit discharges from the EMG signals using a segment-wise decomposition algorithm. Then the neural features were extracted from motor unit discharges and projected to wrist torques with a multiple linear regression model. We compared the performance of two neural features (twitch model and spike counting) and two training schemes (single-DoF and multi-DoF training). On average, 145 ± 33 motor units were identified from each subject, with a pulse-to-noise ratio of 30.8 ± 4.2 dB. Both neural features exhibited high estimation accuracy of 3-DoF wrist torques, with an average [Formula: see text] of 0.76 ± 0.12 and normalized root mean square error of 11.4 ± 3.1%. These results demonstrated the efficiency of the proposed method in continuous estimation of 3-DoF wrist torques, which has the potential to advance dexterous myoelectric control based on neural information.

Tendon Transfer for Correction of the Radial Deviation Deformity of the Wrist and Centralization in Posterior Interosseous Nerve Palsy.

There are very few descriptions of tendon transfers designed specifically to address the reconstruction of posterior interosseous nerve palsy (PINP). Unlike a radial nerve palsy (RNP), a patient with a PINP is able to extend their wrist but in radial deviation, because of the preserved innervation of the extensor carpi radialis longus (ECRL). Tendon transfers to restore finger and thumb extension in PINP have been extrapolated from tendon transfers to restore these functions in RNP, specifically using flexor carpi radialis, not flexor carpi ulnaris, so as not to further exacerbate the distinctive radial deviation deformity of the wrist. However, the standard pronator teres to extensor carpi radialis brevis transfer for a RNP fails to address or correct the radial deviation deformity in PINP. We present a simple tendon transfer specifically to address this radial deviation deformity in a PINP, by performing a side-to-side tenorrhaphy of the ECRL tendon to the extensor carpi radialis brevis tendon, followed by transection of the ECRL insertion onto the base of the index finger metacarpal distal to the tenorrhaphy. This technique converts a functioning ECRL from a radially deforming force, transferring its vector of pull onto the base of the middle finger metacarpal and so producing centralization of wrist extension in axial alignment with the forearm.

Robot and ultrasound assisted needle insertion to the transverse carpal ligament.

BACKGROUND: A potential alternative treatment to surgery for carpal tunnel syndrome is to inject enzymes into the transverse carpal ligament to decrease its stiffness and alleviate pressure off the median nerve. An accurate injection is needed for delivery to achieve the effects of tissue degradation. The purposes of this study were to 1) determine injection sites using 3D reconstructed anatomy, and 2) insert the needle to the middle of the transverse carpal ligament thickness in situ. METHODS: Six fresh-frozen cadaveric hands were used in this study. Five injection sites were determined in the sagittal plane along the center of the transverse carpal ligament thickness ulnar to the thenar muscle attachment using 3D ultrasonographic reconstruction. Each injection was delivered by rigidly fixing a 27-gauge needle to a six degrees of freedom robot arm programmed to insert the needle tip to the intended target. Ultrasound images were taken of the needle after insertion to measure accuracy and precision of the needle placement. FINDINGS: The needle tip was successfully delivered to the middle region of the transverse carpal ligament thickness and visualized using ultrasound imaging. The accuracy and precision of the needle insertion were 0.83 and 0.31 mm, respectively. INTERPRETATION: Methodology was established for robot-assisted needle insertion to the transverse carpal ligament using 3D ultrasonographic reconstructed anatomy. This methodology can be used in the future to deliver enzymatic injections to the transverse carpal ligament as a potential treatment for carpal tunnel syndrome.

Does thermoplastics' thickness influence joint stabilization and movement coordination? An inferential study of wrist orthoses.

BACKGROUND: Given the existence of multiple low-temperature thermoplastics, clinicians fabricating can readily modify an orthoses' thickness, weight and flexibility, among other properties. However, there is limited evidence on the impact of such different materials on upper extremities' biomechanics. OBJECTIVE: Our study aimed to investigate differences in joint stabilization and movement coordination provided by upper extremity orthotics fabricated with low-temperature thermoplastics of different thicknesses. STUDY DESIGN: Inferential, cross-sectional study. METHOD: We conducted a kinematic analysis of a standardized task through a three-dimensional motion capture system. Ten participants (5 female) performed the same task under three circumstances: 1) wearing a volar wrist immobilization orthosis, made with a 3.2-mm thick low-temperature thermoplastic; 2) using the same orthotic fabricated with a 1.6-mm thick material; and (3) without orthoses. We divided the standardized task into five logical phases for data analysis, obtaining the active range of motion of the shoulder, elbow, forearm, and wrist joints as the primary outcome. Secondary outcomes included movement smoothness and coordination, measured by the number of motor units, time, and distance travelled by the upper extremity. RESULTS: Despite changes in thermoplastic thickness, both orthotics significantly restricted the wrist motion during task performance (F(2,16) = 14.32, P < .01, and η2p = 0.797), with no difference between the 2 devices and no significant changes to proximal joints' active range of motion. Although orthoses use increased the time required for task performance (F(2,16) = 23.05, P < .01, and η2p = 0.742), no significant differences in movement smoothness or coordination were noted. CONCLUSION: Our results indicate that wrist orthoses fabricated with a 1.6-mm thick low-temperature thermoplastic can provide joint stabilization similar to a device made from a 3.2-mm thickness material, suggesting thinner thermoplastics' efficacy to stabilize joints in the absence of contractures or preexisting chronic conditions.

Distal Nerve Transfer to Restore Wrist and Finger Extension - A Systematic Review.

Background: There are numerous options available for restoration of wrist and finger extension following radial nerve palsy. The aim of this study is to conduct a systematic review of the effectiveness of nerve transfer for radial nerve palsy. Methods: Electronic literature research of PubMed, Cochrane, Scopus and Lilacs database was conducted in June 2021 using the terms 'Distal nerve transfer' AND 'Radial nerve injury' 'Radial nerve palsy' OR 'Radial nerve paresis' OR 'Median nerve transfer' OR 'wrist extensor' OR 'finger extension' OR 'thumb extension' OR 'wrist motion'. The data extracted included the study details, demographic data, procedure performed and final functional outcome according to the muscle research council scale. Results: A total of 92.59% and 56.52% had satisfactory outcome following distal nerve transfer of median nerve to restore wrist and finger extension respectively. No significant correlation was found between time to injury duration and satisfactory outcomes. Conclusions: Outcomes of nerve transfers are comparable to tendon transfers. Multi-centric studies are needed to compare the results amongst various surgical procedures described. Level of Evidence: Level III (Therapeutic).

Design of magnetorheological brake for forearm rotation of a wrist prosthesis.

A wrist joint in upper limb prostheses significantly increases its handling capacity. However, current prostheses cannot reproduce the ability of torque combined with the volume and weight of the human wrist. Consequently, they do not provide high efficiency in handling and generate user dissatisfaction. In this context, this study aims to optimal design a wrist supination and pronation brake to improve the handling capacity of an upper limb prosthesis. The wrist actuator consists of an EC motor and harmonic drive parallel with a magnetorheological brake. The brake guarantees a fast response time, low energy consumption, controllability, and small dimensions. A particle swarm algorithm is applied to optimize design variables to minimize mass and energy consumption. As a result, the brake provided resistive torque of 7.4 N.m with dimensions close to a healthy member and weighing 0.1972 kg. Finally, a finite element analysis confirmed a satisfactory magnetic flux for the magnetorheological brake operating conditions. The designed brake addressed all the desired characteristics and is suitable to integrate the forearm prosthesis with wrist rotation.

Sensitivity analysis guided improvement of an electromyogram-driven lumped parameter musculoskeletal hand model.

EMG-driven neuromusculoskeletal models have been used to study many impairments and hold great potential to facilitate human-machine interactions for rehabilitation. A challenge to successful clinical application is the need to optimize the model parameters to produce accurate kinematic predictions. In order to identify the key parameters, we used Monte-Carlo simulations to evaluate the sensitivities of wrist and metacarpophalangeal (MCP) flexion/extension prediction accuracies for an EMG-driven, lumped-parameter musculoskeletal model. Four muscles were modeled with 22 total optimizable parameters. Model predictions from EMG were compared with measured joint angles from 11 able-bodied subjects. While sensitivities varied by muscle, we determined muscle moment arms, maximum isometric force, and tendon slack length were highly influential, while passive stiffness and optimal fiber length were less influential. Removing the two least influential parameters from each muscle reduced the optimization search space from 22 to 14 parameters without significantly impacting prediction correlation (wrist: 0.90 ± 0.05 vs 0.90 ± 0.05, p = 0.96; MCP: 0.74 ± 0.20 vs 0.70 ± 0.23, p = 0.51) and normalized root mean square error (wrist: 0.18 ± 0.03 vs 0.19 ± 0.03, p = 0.16; MCP: 0.18 ± 0.06 vs 0.19 ± 0.06, p = 0.60). Additionally, we showed that wrist kinematic predictions were insensitive to parameters of the modeled MCP muscles. This allowed us to develop a novel optimization strategy that more reliably identified the optimal set of parameters for each subject (27.3 ± 19.5%) compared to the baseline optimization strategy (6.4 ± 8.1%; p = 0.004). This study demonstrated how sensitivity analyses can be used to guide model refinement and inform novel and improved optimization strategies, facilitating implementation of musculoskeletal models for clinical applications.

The effects of isometric hand grip force on wrist kinematics and forearm muscle activity during radial and ulnar wrist joint perturbations.

The purpose of this work was to investigate forearm muscle activity and wrist angular displacement during radial and ulnar wrist perturbations across various isometric hand grip demands. Surface electromyography (EMG) was recorded from eight muscles of the upper extremity. A robotic device delivered perturbations to the hand in the radial and ulnar directions across four pre-perturbation grip magnitudes. Angular displacement and time to peak displacement following perturbations were evaluated. Muscle activity was evaluated pre- and post-perturbation. Results showed an inverse relationship between grip force and angular displacement (p ≤ 0.001). Time to peak displacement decreased as grip force increased (p ≤ 0.001). There was an increase in muscle activity with higher grip forces across all muscles both pre-and post-perturbation (p ≤ 0.001) and a greater average muscle activity in ulnar as compared to radial deviation (p = 0.02). This work contributes to the wrist joint stiffness literature by relating wrist angular displacement to grip demands during novel radial/ulnar perturbations and provides insight into neuromuscular control strategies.