Effects of carpal tunnel syndrome on reach-to-pinch performance

Association between three-dimensional motion analysis of the thumb and clinical parameters in patients with carpal tunnel syndrome

We analysed the relationship between motor dysfunction of the thumb and the clinical parameters of carpal tunnel syndrome using three-dimensional motion analysis. This single-centred, prospective study included 65 hands in 51 patients with idiopathic carpal tunnel syndrome and 30 healthy hands. Three-dimensional thumb kinematics were acquired using a motion capture system with a retroreflective surface-based marker method. The trajectory area of thumb tip, adduction and abduction of the trapeziometacarpal joints and metacarpophalangeal joints were correlated with the clinical parameters. There was no significant correlation between the results of motion analysis values and patient-reported outcomes measures. Thumb movement disorder associated with carpal tunnel syndrome affected specific activities of daily living based on the pinching movements, such as 'writing' and 'buttoning clothes' among the patient-reported outcome measure items.Level of evidence: III.

The Effect of Proprioceptive Training on Hand Function and Activity Limitation After Open Carpal Tunnel Release Surgery: A Randomized Controlled Study

OBJECTIVE

To investigate the effect of proprioceptive training on hand function and activity limitation in patients undergoing open carpal tunnel release surgery.

DESIGN

Randomized controlled study.

SETTING

A university hospital.

PARTICIPANTS

Thirty patients were included in the study and randomized to proprioceptive training (PT) and conventional rehabilitation (CR) groups.

INTERVENTION

One week after surgery, both groups received CR for 6 weeks. All participants were asked to perform home-based exercises daily in 3 sets with 10 repetitions. For the PT group, a 6-step PT program was conducted starting from Week 6. Both groups received face-to-face interventions twice a week for 12 weeks.

MAIN OUTCOME MEASURES

The outcome measures included the Purdue Pegboard Test (PPT), the joint position sense test (JPST), the Boston Carpal Tunnel Questionnaire, and the Patient-Specific Functional Scale. In total, 3 assessments were performed (at 1, 6 and 12 weeks postoperatively).

RESULTS

In the PT group, the results for PPT were statistically significant (P<.05). Although there was a greater decrease in the absolute angular error value (JPST) of the PT group compared to the CR group, the difference was nonsignificant (P>.05). Similar reductions in activity limitation were seen in both groups (PT: 176%, CR: 175%). Symptom severity decreased by 40% in the PT group vs 32% in the CR group. The effect sizes were larger for the changes between the second and third assessments in the PT group compared to the CR group in all parameters tested.

CONCLUSION

When applied after carpal tunnel release surgery, PT may potentially to improve hand functions, reduce activity limitation, increase participation in activities of daily living, and thus improve quality of life.

Effects of Type II Diabetes on Proprioception during a Reach to Pinch Task

Older adults with type II diabetes (T2D) are at risk of developing nerve disorders that result in functional impairment. Most work in proprioceptive dysfunction in older adults with T2D has focused on functional deficits of the lower limb. The purpose of this study was to examine proprioceptive effects of T2D on the upper limb in older adults. Kinematic performance of a reach-to-pinch action toward a virtual target was assessed in a T2D group (60+ years old with T2D) and a healthy age- and sex-matched control group. Tactile and vibratory thresholds did not differ between T2D and controls. Task accuracy via mean pinch location was significantly worse for persons with T2D (pwT2D) with differences in wrist extension/flexion (ex/fl), wrist abduction/adduction (ab/ad), 1st carpometacarpal (CMC) ab/ad, 2nd metacarpophalangeal (MCP2) ex/fl, MCP2 ab/ad, and digit 1 and hand transport trajectories. Group differences persisted with consideration of body mass index; sex differences in task accuracy emerged. Findings indicate that proprioception of the upper extremity is altered in pwT2D such that they exhibit a unique aperture position and aiming strategy during a reach-to-pinch action. These findings characterize functional sensorimotor impairment of the upper limb in pwT2D with respect to workspaces without visual or tactile feedback.

Feasibility and usability of a virtual-reality-based sensorimotor activation apparatus for carpal tunnel syndrome patients

PURPOSE

This study aimed to assess the usability of a virtual reality-assisted sensorimotor activation (VRSMA) apparatus for individual digit rehabilitation. The study had two main objectives: Firstly, to collect preliminary data on the expectations and preferences of patients with carpal tunnel syndrome (CTS) regarding virtual reality (VR) and an apparatus-assisted therapy for their affected digits. Secondly, to evaluate the usability of the VRSMA apparatus that was developed.

METHODS

The VRSMA system consists of an apparatus that provides sensory and motor stimulation via a vibratory motor and pressure sensor attached to a button, and a virtual reality-based visual cue provided by texts overlaid on top of a 3D model of a hand. The study involved 10 CTS patients who completed five blocks of VRSMA with their affected hand, with each block corresponding to the five digits. The patients were asked to complete a user expectations questionnaire before experiencing the VRSMA, and a user evaluation questionnaire after completing the VRSMA. Expectations for VRSMA were obtained from the questionnaire results using a House of Quality (HoQ) analysis.

RESULTS

In the survey for expectations, participants rated certain attributes as important for a rehabilitation device for CTS, with mean ratings above 4 for attributes such as ease of use, ease of understanding, motivation, and improvement of hand function based on clinical evidence. The level of immersion and an interesting rehabilitation regime received lower ratings, with mean ratings above 3.5. The survey evaluating VRSMA showed that the current prototype was overall satisfactory with a mean rating of 3.9 out of 5. Based on the HoQ matrix, the highest priority for development of the VRSMA was to enhance device comfort and usage time. This was followed by the need to perform more clinical studies to provide evidence of the efficacy of the VRSMA. Other technical characteristics, such as VRSMA content and device reliability, had lower priority scores.

CONCLUSION

The current study presents a potential for an individual digit sensorimotor rehabilitation device that is well-liked by CTS patients.

Does idiopathic carpal tunnel syndrome deteriorate proprioception of the hand? A case-control study

OBJECTIVES

This study aims to investigate the deterioration in kinesthetic kinesthesia (KKS) and visual kinesthesia (VKS) of the hand as a component of proprioception in patients with idiopathic carpal tunnel syndrome (CTS).

PATIENTS AND METHODS

This study included a total of 90 hands of 60 patients (9 males, 51 females; mean age: 47.6±9.4 years; range, 28 to 60 years) who were diagnosed with CTS and 25 hands of 25 healthy individuals (8 males, 17 females; mean age: 42.6±14.4 years; range, 20 to 60 years) as the controls between January 2019 and January 2021. The KKS and VKS scores were compared between the groups. Clinical parameters such as pain levels, hand grip strength (HGS) values, and two-point discrimination (2PD) test scores were compared between the patients with and without KKS or VKS deficits. The association between the severity of electromyographic findings and KKS or VKS deficits was examined.

RESULTS

The mean VKS score of the CTS group was 22.9±1.6 and the KKS score was 20.8±3.4, which was significantly lower than that of the control group (p=0.002 and p<0.001, respectively). The CTS patients performed less accurate repetitions in visually cued (60%) and kinesthetically cued (40%) positions than the control group (100% both). There were significantly more patients with VKS and KKS deficits in the moderate or severe CTS groups than in the mild CTS group (p<0.001 and p=0.007, respectively), and KKS or VKS deficits were significantly associated with the impaired HGS (p=0.042 and p=0.048, respectively) and functional status (p=0.020 and p=0.016, respectively) accompanied by the increased symptom severity (p=0.010 and p=0.002, respectively).

CONCLUSION

Our study results suggest that idiopathic CTS is associated with impaired proprioception and kinesthetic sense of the hand. In addition, idiopathic CTS is related to impaired hand function and severe symptoms. Screening kinesthetic sense in patients with idiopathic CTS prior to decompression surgery or postoperative hand therapy is helpful to set realistic goals and achieve superior clinical outcomes.

Innovative Quantitative Assessment of Hand Function in Carpal Tunnel Syndrome

BACKGROUND

Carpal tunnel syndrome (CTS) compromises fine sensorimotor function during activities of daily living and affects a large number of individuals with high burden costs for society. The purpose of this study was to quantitatively characterize fine movement skills in CTS patients preoperatively and at 1 month postoperatively by means of a sensor-engineered glove, in order to provide new insights for evaluative and finally therapeutic purposes.

METHODS

Forty-one CTS patients and 41 age- and gender-matched healthy controls (HC) were analyzed by adopting the engineered glove Hand Test System (HTS), which previously demonstrated its reliability and sensitivity to detect hands dysfunction in several neurological diseases. A sub-group of 11 CTS subjects was re-tested 1 month after surgery. Three parameters-touch duration (TD), inter-tapping interval (ITI), and movement rate (MR)-were considered to characterize hand function.

RESULTS

The affected hand of CTS patients generally showed worst finger opposition performances than HC. Comparing the dominant hand, all parameters were able to significantly discriminate CTS patients from HC. Considering the nondominant hand, the best performing parameter in discriminating CTS from HC was TD. The follow-up assessment at 1 month after surgery showed that considered parameters were able to monitor patients' recovery. In particular, the TD parameter recorded at the 3 different assigned task modalities resulted significantly enhanced.

CONCLUSIONS

Results of this pilot study proved the validity of the parameters obtained through the sensor-engineered glove to assess objectively hand functional status and surgical outcomes in CTS.

Using deep learning for ultrasound images to diagnose carpal tunnel syndrome with high accuracy

Recently, deep learning (DL) algorithms have been adapted for the diagnosis of medical images. The purpose of this study was to detect image features using DL without measuring median nerve cross-sectional area (CSA) in ultrasonography (US) images of carpal tunnel syndrome (CTS) and calculate the diagnostic accuracy from the confusion matrix obtained. US images of 50 hands without CTS and 50 hands diagnosed with CTS were used in this study. The short-axis image of the median nerve was visualized, and 5000 images of both groups were prepared. Forty hands in each group were used as training data for the DL algorithm, while the remainder were used as test data. Transfer learning was performed using three pre-trained models. The confusion matrix and receiver operating characteristic curves were used to evaluate diagnostic accuracy. Furthermore, regions where DL was determined to be important were visualized. The highest score had an accuracy of 0.96, precision of 0.99 and recall of 0.94. Visualization of the important features revealed that the DL models focused on the epineurium of the median nerve and the surrounding soft tissue. The proposed technique enables the accurate prediction of CTS without measurement of the CSA.

Hand dominance in the performance and perceptions of virtual reach control

PURPOSE

Efforts to optimize human-computer interactions are becoming increasingly prevalent, especially with virtual reality (VR) rehabilitation paradigms that utilize engaging interfaces. We hypothesized that motor and perceptional behaviors within a virtual environment are modulated uniquely through different modes of control of a hand avatar depending on limb dominance. This study investigated the effects of limb dominance on performance and concurrent changes in perceptions, such as time-based measures for intentional binding, during virtual reach-to-grasp.

METHODS

Participants (n = 16, healthy) controlled a virtual hand through their own hand motions with control adaptations in speed, noise, and automation.

RESULTS

A significant (p < 0.01) positive relationship between performance (reaching pathlength) and binding (time-interval estimation of beep-sound after grasp contact) was observed for the dominant hand. Unique changes in performance (p < 0.0001) and binding (p < 0.0001) were observed depending on handedness and which control mode was applied.

CONCLUSIONS

Developers of VR paradigms should consider limb dominance to optimize settings that facilitate better performance and perceptional engagement. Adapting VR rehabilitation for handedness may particularly benefit unilateral impairments, like hemiparesis or single-limb amputation.

A Detailed Comparison of Preoperative Complaints in Severe Carpal Tunnel Syndrome versus Recurrent Carpal Tunnel Syndrome Using the Boston Carpal Tunnel Questionnaire

Background: The Boston Carpal Tunnel Questionnaire (BCTQ) has a symptom severity scale (SSS) with 11 questions and a functional status scale (FSS) with 8 questions. The final score for each scale is the sum divided by the number of questions and ranges between 1 and 5. A score of 1 indicates they have no complaints and 5 indicates high severity and functional loss. Unfortunately, this single digit score does not permit a detailed analysis of the symptoms and functional status. The aim of this study is to conduct an in-depth comparison of preoperative complaints using the BCTQ between patients with severe carpal tunnel syndrome (SCTS) and recurrent carpal tunnel syndrome (RCTS). Methods: This is a retrospective cohort study on the preoperative status of 37 patients with SCTS and 18 patients with RCTS using the BCTQ. The questions in the SSS and FSS were classified into four groups based on the responses of patients, namely a low complaint (LC) (1-1.99), moderate complaint (MC) (2-2.99), high complaint (HC) (3-3.99), and severe complaint (SC) (4-5) groups. The patients in the SCTS and RCTS groups were compared to find differences in age, gender, hand dominance, and responses to questions in the SSS and FSS. Results: The age of patients in the SCTS group (76.06 years) was significantly higher compared to the RCTS group (51.11 years). There was no significant difference between the two groups with regard to gender or hand dominance. The top question with SC or HC response in the SCTS group was problems in grasping small objects (SSS) and fastening buttons (FSS) and in the RCTS group was tingling in the hand (SSS) and difficulty with opening a jar (FSS). Conclusions: An in-depth analysis of the BCTQ allowed us to compare and understand differences in symptoms and function between patients with SCTS and RCTS. Level of Evidence: Level III (Therapeutic).

Three-dimensional analysis of thumb motion recovery after carpal tunnel release

This study quantified recovery of thumb motion in patients with carpal tunnel syndrome after carpal tunnel release using three-dimensional motion analysis with a retroreflective surface-based marker method. Eighteen hands from 14 patients who underwent carpal tunnel release for idiopathic carpal tunnel syndrome were included. The angular movements of the three joints of the thumb, the path length of the thumb tip and the area enclosed by the perimeter path of the thumb tip were measured during circumduction. The range of joint movement, including abduction/adduction of the trapeziometacarpal joint, and flexion/extension of the interphalangeal and metacarpophalangeal joints and the path length of the thumb tips, improved significantly 1 year after surgery. The quantification of thumb kinematics helps to better understand motor dysfunction in carpal tunnel syndrome, assess the severity of the condition and decide on treatment.Level of evidence: IV.

Relationship between nerve conduction studies and the Functional Dexterity Test in workers with carpal tunnel syndrome

Background

Dexterity impairments caused by carpal tunnel syndrome (CTS) make working and daily activities challenging. We aimed to investigate: i) the relationship between dexterity and nerve conduction studies (NCS) in workers with classic symptoms presentation; ii) the ability of the Functional Dexterity Test (FDT) to discriminate different levels of CTS severity as classified by NCS; iii) the diagnostic accuracy of a clinical battery composed of the FDT, Phalen’s test and Tinel’s sign.

Methods

In a convenience sample of individuals diagnosed with CTS, we correlated FDT net scores with the NCS-based classification by means of Spearman’s (rho) test. Discriminative ability of the FDT was assessed by ANOVA, and a ROC curve determined cutoff thresholds. Sensitivity, specificity, and likelihood ratios (LRs) were used to investigate the diagnostic accuracy of the clinical battery.

Results

Data from 180 hands were collected. The FDT was significantly correlated (rho = 0.25, p <  0.001) with NCS. The FDT was able to discriminate subjects with severe/extreme NCS findings, and two thresholds (0.29–0.36) were identified. Adding the FDT to the provocative tests improved the overall diagnostic accuracy (specificity: 0.97, CI_95% 0.83–0.99; LR+: 14.49, CI_95% 2.09–100.53).

Conclusions

Sensorimotor impairments related to CTS can affect hand dexterity. The FDT discriminated patients with severe NCS involvement. Positive results on the clinical battery (Phalen, Tinel, and FDT) could help to confirm the CTS diagnosis, showing a very high specificity and LR+. On the contrary, the low sensitivity is not able to rule out CTS in individuals with negative results.

Agency and Performance of Reach-to-Grasp With Modified Control of a Virtual Hand: Implications for Rehabilitation

This study investigated how modified control of a virtual hand executing reach-to-grasp affects functional performance and agency (perception of control). The objective of this work was to demonstrate positive relationships between reaching performance and grasping agency and motivate greater consideration of agency in movement rehabilitation. We hypothesized that agency and performance have positive correlation across varying control modes of the virtual hand. In this study, each participant controlled motion of a virtual hand through motion of his or her own hand. Control of the virtual hand was modified according to a specific control mode. Each mode involved the virtual hand moving at a modified speed, having noise, or including a level of automation. These specific modes represent potential control features to adapt for a rehabilitation device such as a prosthetic arm and hand. In this study, significant changes in agency and performance were observed across the control modes. Overall, a significant positive relationship (p < 0.001) was observed between the primary performance metric of reach (tracking a minimum path length trajectory) and an implicit measurement of agency (intentional binding). Intentional binding was assessed through participant perceptions of time-intervals between grasp contact and a sound event. Other notable findings include improved movement efficiency (increased smoothness, reduced acceleration) during expression of higher agency and shift toward greater implicit versus explicit agency with higher control speed. Positively relating performance and agency incentivizes control adaptation of powered movement devices, such as prostheses or exoskeletons, to maximize both user engagement and functional performance. Agency-based approaches may foster user-device integration at a cognitive level and facilitate greater clinical retention of the device. Future work should identify robust and automated methods to adapt device control for increased agency. Objectives include how virtual reality (VR) may identify optimal control of real-world devices and assessing real-time agency from neurophysiological signals.

Exercises using a touchscreen tablet application improved functional ability more than an exercise program prescribed on paper in people after surgical carpal tunnel release: a randomised trial

QUESTION

In people who have undergone surgical carpal tunnel release, do sensorimotor-based exercises performed on the touchscreen of a tablet device improve outcomes more than a conventional home exercise program prescribed on paper?

DESIGN

Randomised, parallel-group trial with concealed allocation, assessor blinding, and intention-to-treat analysis.

PARTICIPANTS

Fifty participants within 10 days of surgical carpal tunnel release.

INTERVENTION

Each participant was prescribed a 4-week home exercise program. Participants in the experimental group received the ReHand tablet application, which administered and monitored exercises via the touchscreen. The control group was prescribed a home exercise program on paper, as is usual practice in the public hospital system.

OUTCOME MEASURES

The primary outcome was functional ability of the hand, reported using the shortened form of the Disabilities of the Arm, Shoulder and Hand (QuickDASH) questionnaire. Secondary outcomes were grip strength, pain intensity measured on a 10-cm visual analogue scale, and dexterity measured with the Nine-Hole Peg Test. Outcomes were measured by a blinded assessor at baseline and at the end of the 4-week intervention period.

RESULTS

At Week 4, functional ability improved significantly more in the experimental group than the control group (MD -21, 95% CI -33 to -9) on the QuickDASH score (0 to 100). Although the mean estimates of effect on the secondary outcome also all favoured the experimental group, none reached statistical significance: grip strength (MD 5.6 kg, 95% CI -0.5 to 11.7), pain (MD -1.4 cm, 95% CI -2.9 to 0.1), and dexterity (MD -1.3 seconds, 95% CI -3.7 to 1.1).

CONCLUSION

Use of the ReHand tablet application for early rehabilitation after carpal tunnel release is more effective in the recovery of functional ability than a conventional home exercise program. It remains unclear whether there are any benefits in grip strength, pain or dexterity.

TRIAL REGISTRATION

ACTRN12618001887268.

Comparison of grip and pinch strength in young women with and without hyperkyphosis: A cross-sectional study

BACKGROUND

Hyperkyphosis is a common postural defect with high prevalence in the 20 to 50 year old population. It appears to compromise proximal scapular stability. Grip and pinch strength are used to evaluate general upper extremity function.

OBJECTIVE

The aim of this study was to compare pinch and grip strength between young women with and without hyperkyphosis.

METHODS

Thirty young women (18-40 years old) with hyperkyphosis and 30 healthy women matched for age and body mass index participated in the study. Hyperkyphosis was confirmed by measuring the kyphosis angle with a flexible ruler. Grip strength was measured with the Waisa method and a dynamometer. Pinch strength was assessed with a pinch meter.

RESULTS

Grip (P= 0.03) and pinch strength (P= 0.04) were significantly lower in women with hyperkyphosis compared to the control group. Kyphosis angle correlated weakly with grip (r= 0.26) and pinch strength (r= 0.23).

CONCLUSIONS

Hyperkyphotic posture has led to decreased grip and pinch strength compared to people without hyperkyphosis.

Assessment of dexterity and diagnostic accuracy of the Functional Dexterity Test in patients with carpal tunnel syndrome

BACKGROUND

The diagnosis of carpal tunnel syndrome (STC) is centered on the symptoms. However, patients also show an impairment of sensorimotor functions, but the relationship between STC and manual dexterity has never been investigated.

OBJECTIVES

To analyze the correlation between manual dexterity and severity of the STC. Another objective was the diagnostic accuracy of the clinical battery including provocative tests (Phalen, Tinel) and Functional Dexterity Test (FDT).

METHODS

A sample of 80 subjects with suspected STC was subdivided into 4 groups based on EMG (severe/extreme-GrA, moderate-GrB, mild/minimal-GrC, negative-GrD) and evaluated in blind by Phalen, Tinel and FDT. The relationship between the FDT and the allocation of subjects was investigated by Spearman's rho, while the groups were compared with univariate ANOVA and Tukey's post hoc analysis. Diagnostic accuracy of the clinical battery was expressed by sensitivity, specificity, and likelihood ratios (LR).

RESULTS

A moderate (r=0.48, p minor of 0.001) correlation was found between FDT and the 4 groups. ANOVA has returned a significant difference between GrA vs. all others and between GrB vs. GrD. The battery showed a sensitivity, specificity, positive likelihood ratio (LR+) and negative likelihood ratio (LR-) of 70%, 94%, 11.98 and 0.31 respectively.

CONCLUSIONS

The results of this study supported the hypothesis that STC patients also have a dexterity impairment. The FDT was able to discriminate between three levels of severity (negative, mild to moderate, severe to extreme), maintaining a good level of diagnostic accuracy in addition to provocative tests.

Carpal tunnel syndrome impairs index finger responses to unpredictable perturbations

The fine-tuning of digit forces to object properties can be disrupted by carpal tunnel syndrome (CTS). CTS' effects on hand function have mainly been investigated using predictable manipulation tasks; however, unpredictable perturbations are commonly encountered during manual tasks, presenting situations which may be more challenging to CTS patients given their hand impairments. The purpose of this study was to investigate muscle and force responses of the index finger to unpredictable perturbations in patients with CTS. Nine CTS patients and nine asymptomatic controls were instructed to stop the movement of a sliding plate by increasing index finger force following an unexpected perturbation. The electrical activity of the first dorsal interosseous muscle and forces exerted by the index finger were recorded. CTS patients demonstrated 20.9% greater muscle response latency and 12.0% greater force response latency compared to controls (p<0.05). The duration of plate sliding was significantly different between groups (p<0.05); the CTS group's duration was 142.2±5.8ms compared to the control group's duration of 133.1±8.4ms. Although CTS patients had increased muscle and force response durations comparatively, these differences were not statistically significant. Findings from this study suggest CTS-induced sensorimotor deficits interfere with accurate detection, processing and response to unpredictable perturbations. These deficits could be accounted for at multiple levels of the peripheral and central nervous systems. Delayed and decreased responses may indicate inefficient object manipulation by CTS patients and may help to explain why CTS patients tend to drop objects.

Unanticipated Insights into Biomedicine from the Study of Acupuncture

Research into acupuncture has had ripple effects beyond the field of acupuncture. This paper identifies five exemplars to illustrate that there is tangible evidence of the way insights gleaned from acupuncture research have informed biomedical research, practice, or policy. The first exemplar documents how early research into acupuncture analgesia has expanded into neuroimaging research, broadening physiologic understanding and treatment of chronic pain. The second describes how the acupuncture needle has become a tool to enhance biomedical knowledge of connective tissue. The third exemplar, which illustrates use of a modified acupuncture needle as a sham device, focuses on emergent understanding of placebo effects and, in turn, on insights into therapeutic encounters in treatments unrelated to acupuncture. The fourth exemplar documents that two medical devices now in widespread use were inspired by acupuncture: transcutaneous electrical nerve stimulators for pain control and antinausea wrist bands. The final exemplar describes how pragmatic clinical trial designs applied in acupuncture research have informed current general interest in comparative effectiveness research. In conclusion, these exemplars of unanticipated outcomes of acupuncture research comprise an additional rationale for continued support of basic and clinical research evaluating acupuncture and other under-researched therapies.

Digit mechanics in relation to endpoint compliance during precision pinch

This study investigates the mechanics of the thumb and index finger in relation to compliant endpoint forces during precision pinch. The objective was to gain insight into how individuals modulate motor output at the digit endpoints and joints according to compliance-related sensory feedback across the digits. Thirteen able-bodied subjects performed precision pinch upon elastic resistance bands of a customized apparatus instrumented with six degree-of-freedom load-cells. Compliance levels were discretely adjusted according to the number of bands connected. Subjects were provided visual feedback to control the rate of force application. Fifteen repetitions of low-to-moderate force (<20N) pinches were analyzed at each of five compliance levels, during which force and motion data were collected. Joint angles and moments normalized by pinch force magnitude were computed. Second-order polynomials were used to characterize joint mechanics as a function of compliance. The joint degrees-of-freedom (DOFs) at the finger showed greater dependence on compliance for angular position while the thumb joint DOFs demonstrated greater dependence for normalized joint moment. The digits also adjusted coordination of their endpoint forces according to compliance. Overall, the finger may be altering its position to increase load to the joints of the thumb with changing compliance. These findings describe naturally emergent changes in digit mechanics for compliant precision pinch, which involves motor execution in response to endpoint sensory feedback. Identifying and understanding these motor patterns may provide theoretical basis for restoring and rehabilitating sensorimotor pathologies of the hand.

Are movement disorders and sensorimotor injuries pathologic synergies? When normal multi-joint movement synergies become pathologic

The intact nervous system has an exquisite ability to modulate the activity of multiple muscles acting at one or more joints to produce an enormous range of actions. Seemingly simple tasks, such as reaching for an object or walking, in fact rely on very complex spatial and temporal patterns of muscle activations. Neurological disorders such as stroke and focal dystonia affect the ability to coordinate multi-joint movements. This article reviews the state of the art of research of muscle synergies in the intact and damaged nervous system, their implications for recovery and rehabilitation, and proposes avenues for research aimed at restoring the nervous system’s ability to control movement.