Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis

Spatial mapping of posture-dependent resistance to passive displacement of the hypertonic arm post-stroke

BACKGROUND

Muscles in the post-stroke arm commonly demonstrate abnormal reflexes that result in increased position- and velocity-dependent resistance to movement. We sought to develop a reliable way to quantify mechanical consequences of abnormal neuromuscular mechanisms throughout the reachable workspace in the hemiparetic arm post-stroke.

METHODS

Survivors of hemiparetic stroke (HS) and neurologically intact (NI) control subjects were instructed to relax as a robotic device repositioned the hand of their hemiparetic arm between several testing locations that sampled the arm's passive range of motion. During transitions, the robot induced motions at either the shoulder or elbow joint at three speeds: very slow (6°/s), medium (30°/s), and fast (90°/s). The robot held the hand at the testing location for at least 20 s after each transition. We recorded and analyzed hand force and electromyographic activations from selected muscles spanning the shoulder and elbow joints during and after transitions.

RESULTS

Hand forces and electromyographic activations were invariantly small at all speeds and all sample times in NI control subjects but varied systematically by transport speed during and shortly after movement in the HS subjects. Velocity-dependent resistance to stretch diminished within 2 s after movement ceased in the hemiparetic arms. Hand forces and EMGs changed very little from 2 s after the movement ended onward, exhibiting dependence on limb posture but no systematic dependence on movement speed or direction. Although each HS subject displayed a unique field of hand forces and EMG responses across the workspace after movement ceased, the magnitude of steady-state hand forces was generally greater near the outer boundaries of the workspace than in the center of the workspace for the HS group but not the NI group.

CONCLUSIONS

In the HS group, electromyographic activations exhibited abnormalities consistent with stroke-related decreases in the stretch reflex thresholds. These observations were consistent across repeated testing days. We expect that the approach described here will enable future studies to elucidate stroke's impact on the interaction between the neural mechanisms mediating control of upper extremity posture and movement during goal-directed actions such as reaching and pointing with the arm and hand.

Technology-assisted assessment of spasticity: a systematic review

BACKGROUND

Spasticity is defined as "a motor disorder characterised by a velocity dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks". It is a highly prevalent condition following stroke and other neurological conditions. Clinical assessment of spasticity relies predominantly on manual, non-instrumented, clinical scales. Technology based solutions have been developed in the last decades to offer more specific, sensitive and accurate alternatives but no consensus exists on these different approaches.

METHOD

A systematic review of literature of technology-based methods aiming at the assessment of spasticity was performed. The approaches taken in the studies were classified based on the method used as well as their outcome measures. The psychometric properties and usability of the methods and outcome measures reported were evaluated.

RESULTS

124 studies were included in the analysis. 78 different outcome measures were identified, among which seven were used in more than 10 different studies each. The different methods rely on a wide range of different equipment (from robotic systems to simple goniometers) affecting their cost and usability. Studies equivalently applied to the lower and upper limbs (48% and 52%, respectively). A majority of studies applied to a stroke population (N = 79). More than half the papers did not report thoroughly the psychometric properties of the measures. Analysis identified that only 54 studies used measures specific to spasticity. Repeatability and discriminant validity were found to be of good quality in respectively 25 and 42 studies but were most often not evaluated (N = 95 and N = 78). Clinical validity was commonly assessed only against clinical scales (N = 33). Sensitivity of the measure was assessed in only three studies.

CONCLUSION

The development of a large diversity of assessment approaches appears to be done at the expense of their careful evaluation. Still, among the well validated approaches, the ones based on manual stretching and measuring a muscle activity reaction and the ones leveraging controlled stretches while isolating the stretch-reflex torque component appear as the two promising practical alternatives to clinical scales. These methods should be further evaluated, including on their sensitivity, to fully inform on their potential.

Predicting post-stroke motor recovery of upper extremity using clinical variables and performance assays: A prospective cohort study protocol

BACKGROUND AND PURPOSE

Measurement of movement quality is essential to distinguish motor recovery patterns and optimize rehabilitation strategies post-stroke. Recently, the Stroke Recovery and Rehabilitation Roundtable Taskforce (SRRR) recommended four kinetic and kinematic performance assays to measure upper extremity (UE) movements and distinguish behavioral restitution and compensation mechanisms early post-stroke. The purpose of this study is to develop and validate a prediction model to analyze the added prognostic value of performance assays over clinical variables assessed up to 1-month post stroke for predicting recovery of UE motor impairment, capacity and quality of movement (QoM) measured at 3 months post-stroke onset.

METHODS

In this prospective cohort study, 120 stroke survivors will be recruited within seven days post-stroke. Candidate predictors such as baseline characteristics, demographics and performance assays as per SRRR recommendations along with tonic stretch reflex threshold will be measured up to 1-month post-stroke. Upper extremity motor recovery will be evaluated in terms of motor impairment (Fugl-Meyer assessment for UE), UE capacity measured with Action Research Arm Test (ARAT) and QoM (movement smoothness in the form of peak metrics [PM]) assessed with a reach-to-grasp-to-mouth task (mimicking a drinking task) at 3 months post-stroke. Three multivariable linear regression models will be developed to predict factors responsible for the outcomes of Fugl-Meyer assessment for upper extremity (FM-UE), ARAT and movement quality. The developed models will be internally validated using a split-sample method.

DISCUSSION

This study will provide a validated prediction model inclusive of clinical and performance assays that may assist in prediction of UE motor recovery. Predicting the amount of recovery and differentiating between behavioral restitution and compensation (as reflected by the FM-UE, QoM and ARAT) would enable us in realistic goal formation and planning rehabilitation. It would also help in encouraging patients to partake in early post-stroke rehabilitation thus improving the recovery potential.

A Novel and Clinically Feasible Instrument for Quantifying Upper Limb Muscle Tone and Motor Function via Indirect Measure Methods

Objective: Quantifying muscle tone is often based on a tester’s subjective judgment in clinical settings. There is, however, a lack of suitable tools that can be used to objectively assess muscle tone. This study thus introduces a reliable, clinically-feasible device, called the Arm Circumference Motor Evaluation System (ACMES), for quantifying the muscle tone of upper limbs without using mechanical torque transducers. Methods: While the ACMES conducts continuously passive arm circumduction motions, the voltage and current of the driving motor is transduced into torque values via a least square approximation. A torque sensor and springs with different spring constants were used for the validity and reliability test in the first part of this study. Fifteen healthy adults and two patients who had experienced a stroke participated in the second part, which was a clinical experiment used to examine the in-vivo test-retest reliability and to explore the inspection differences between healthy and patient participants. Results: The results showed that the ACMES has high validity (R²: ~0.99) and reliability (R²: 0.96~0.99). The reliability of the ACMES used on human subjects was acceptable (R²: 0.83~0.85). The various muscle tone patterns could be found among healthy and stroke subjects via the ACMES. Conclusion: Clinically, abnormal muscle tone, which seriously affects motion performance, will be found in many diagnoses, such as stroke or cerebral palsy. However, objectively and feasibly measuring abnormal tone in modern clinical settings is still a challenging task. Thus, the ACMES was developed and tested to verify its feasibility as a measurement system for detecting the mechanical torque associated with muscle tone.

Non-uniform upregulation of the autogenic stretch reflex among hindlimb extensors following lateral spinal lesion in the cat

Successful propagation throughout the step cycle is contingent on adequate regulation of whole-limb stiffness by proprioceptive feedback. Following spinal cord injury (SCI), there are changes in the strength and organization of proprioceptive feedback that can result in altered joint stiffness. In this study, we measured changes in autogenic feedback of five hindlimb extensor muscles following chronic low thoracic lateral hemisection (LSH) in decerebrate cats. We present three features of the autogenic stretch reflex obtained using a mechanographic method. Stiffness was a measure of the resistance to stretch during the length change. The dynamic index documented the extent of adaptation or increase of the force response during the hold phase, and the impulse measured the integral of the response from initiation of a stretch to the return to the initial length. The changes took the form of variable and transient increases in the stiffness of vastus (VASTI) group, soleus (SOL), and flexor hallucis longus (FHL), and either increased (VASTI) or decreased adaptation (GAS and PLANT). The stiffness of the gastrocnemius group (GAS) was also variable over time but remained elevated at the final time point. An unexpected finding was that these effects were observed bilaterally. Potential reasons for this finding and possible sources of increased excitability to this muscle group are discussed.

SpES: A new portable device for objective assessment of hypertonia in clinical practice

Spasticity is a motor disorder that affects millions around the world. It is a particular type of hypertonia characterized by the speed-dependent increase of the muscle stretch reflex, where its correct evaluation is essential for rehabilitation. The preferred method for this assessment is the Modified Ashworth Scale (MAS), a rank derived from clinical observations. Currently, few methods can quantify this disorder objectively. Tonic Stretch Reflex Threshold (TSRT) is a parameter speed-dependent obtained from electromyographic (EMG) measurements and angular signals. Therefore, the objective was to develop portable equipment for quantitative assessments of hypertonia based on TSRT. To this end, we designed an instrument composed of single-channel EMG, flexible optical goniometer, and software for the online computing of TSRT from acquired signals. The new equipment named SpES (Spasticity Evaluation System) was applied to measuring hypertonia of the biceps brachii in twenty-two participants. The experiment was performed during manual passive stretching of the affected limb at predefined speeds. The results provided by SpES presented a satisfactory coefficient of determination (0.70) and a strong correlation with MAS (0.79). In summary, while MAS depends on precise clinical observations, SpES has the TSRT quantitative method embedded for reaching an objective assessment of hypertonia in clinical practice.

Wearable vibrotactile stimulation for upper extremity rehabilitation in chronic stroke: clinical feasibility trial using the VTS Glove

OBJECTIVE

Evaluate the feasibility and potential impacts on hand function using a wearable stimulation device (the VTS Glove) which provides mechanical, vibratory input to the affected limb of chronic stroke survivors.

METHODS

A double-blind, randomized, controlled feasibility study including sixteen chronic stroke survivors (mean age: 54; 1-13 years post-stroke) with diminished movement and tactile perception in their affected hand. Participants were given a wearable device to take home and asked to wear it for three hours daily over eight weeks. The device intervention was either (1) the VTS Glove, which provided vibrotactile stimulation to the hand, or (2) an identical glove with vibration disabled. Participants were randomly assigned to each condition. Hand and arm function were measured weekly at home and in local physical therapy clinics.

RESULTS

Participants using the VTS Glove showed significantly improved Semmes-Weinstein monofilament exam results, reduction in Modified Ashworth measures in the fingers, and some increased voluntary finger flexion, elbow and shoulder range of motion.

CONCLUSIONS

Vibrotactile stimulation applied to the disabled limb may impact tactile perception, tone and spasticity, and voluntary range of motion. Wearable devices allow extended application and study of stimulation methods outside of a clinical setting.

Upper limb robotic assessment: Pilot study comparing velocity dependent resistance in individuals with acquired brain injury to healthy controls

Introduction

Assessment of velocity dependent resistance (VDR) can provide insights into spasticity in individuals with upper motor neuron syndrome. This study investigates the relationship between Modified Ashworth scores and a biomechanical based representation of VDR using a rehabilitation robot. Comparisons in VDR are made for the upper limb (UL) between individuals with acquired brain injury and healthy controls for the para-sagittal plane.

Methods

The system manipulates the individual’s limb through five flexion and extension motions at increasing speeds to obtain force profiles at different velocities. An approximation of VDR is calculated and analyzed statistically against clinical scales and tested for interactions.

Results

All individuals (aged 18–65), including healthy controls exhibited VDR greater than 0 (P < 0.05). MAS scores were found to be related to VDR (P < 0.05) with an interaction found between MAS Bicep and Tricep scores (P < 0.01). Considering this interaction, evidence of differences in VDR were found between several neighboring assessment score combinations.

Conclusion

The robot can detect and quantify VDR that captures information relevant to UL spasticity. Results suggests a better categorization of VDR is possible and supports further development of rehabilitation robotics for assisting spasticity assessment.

Artificial Neural Network Learns Clinical Assessment of Spasticity in Modified Ashworth Scale

OBJECTIVE

To propose an artificial intelligence (AI)-based decision-making rule in modified Ashworth scale (MAS) that draws maximum agreement from multiple human raters and to analyze how various biomechanical parameters affect scores in MAS.

DESIGN

Prospective observational study.

SETTING

Two university hospitals.

PARTICIPANTS

Hemiplegic adults with elbow flexor spasticity due to acquired brain injury (N=34).

INTERVENTION

Not applicable.

MAIN OUTCOME MEASURES

Twenty-eight rehabilitation doctors and occupational therapists examined MAS of elbow flexors in 34 subjects with hemiplegia due to acquired brain injury while the MAS score and biomechanical data (ie, joint motion and resistance) were collected. Nine biomechanical parameters that quantify spastic response described by the joint motion and resistance were calculated. An AI algorithm (or artificial neural network) was trained to predict the MAS score from the parameters. Afterwards, the contribution of each parameter for determining MAS scores was analyzed.

RESULTS

The trained AI agreed with the human raters for the majority (82.2%, Cohen's kappa=0.743) of data. The MAS scores chosen by the AI and human raters showed a strong correlation (correlation coefficient=0.825). Each biomechanical parameter contributed differently to the different MAS scores. Overall, angle of catch, maximum stretching speed, and maximum resistance were the most relevant parameters that affected the AI decision.

CONCLUSIONS

AI can successfully learn clinical assessment of spasticity with good agreement with multiple human raters. In addition, we could analyze which factors of spastic response are considered important by the human raters in assessing spasticity by observing how AI learns the expert decision. It should be noted that few data were collected for MAS3; the results and analysis related to MAS3 therefore have limited supporting evidence.

Biomechanical parameters of the elbow stretch reflex in chronic hemiparetic stroke

We sought to determine the relative velocity sensitivity of stretch reflex threshold angle and reflex stiffness during stretches of the paretic elbow joint in individuals with chronic hemiparetic stroke, and to provide guidelines to streamline spasticity assessments. We applied ramp-and-hold elbow extension perturbations ranging from 15 to 150°/s over the full range of motion in 13 individuals with hemiparesis. After accounting for the effects of passive mechanical resistance, we modeled velocity-dependent reflex threshold angle and torque-angle slope to determine their correlation with overall resistance to movement. Reflex stiffness exhibited substantially greater velocity sensitivity than threshold angle, accounting for ~ 74% (vs. ~ 15%) of the overall velocity-dependent increases in movement resistance. Reflex stiffness is a sensitive descriptor of the overall velocity-dependence of movement resistance in spasticity. Clinical spasticity assessments can be streamlined using torque-angle slope, a measure of reflex stiffness, as their primary outcome measure, particularly at stretch velocities greater than 100°/s.

Motor Overflow and Spasticity in Chronic Stroke Share a Common Pathophysiological Process: Analysis of Within-Limb and Between-Limb EMG-EMG Coherence

The phenomenon of exaggerated motor overflow is well documented in stroke survivors with spasticity. However, the mechanism underlying the abnormal motor overflow remains unclear. In this study, we aimed to investigate the possible mechanisms behind abnormal motor overflow and its possible relations with post-stroke spasticity. 11 stroke patients (63.6 ± 6.4 yrs; 4 women) and 11 healthy subjects (31.18 ± 6.18 yrs; 2 women) were recruited. All of them were asked to perform unilateral isometric elbow flexion at submaximal levels (10, 30, and 60% of maximum voluntary contraction). Electromyogram (EMG) was measured from the contracting biceps (iBiceps) muscle and resting contralateral biceps (cBiceps), ipsilateral flexor digitorum superficialis (iFDS), and contralateral FDS (cFDS) muscles. Motor overflow was quantified as the normalized EMG of the resting muscles. The severity of motor impairment was quantified through reflex torque (spasticity) and weakness. EMG-EMG coherence was calculated between the contracting muscle and each of the resting muscles. During elbow flexion on the impaired side, stroke subjects exhibited significant higher motor overflow to the iFDS muscle compared with healthy subjects (ipsilateral or intralimb motor overflow). Stroke subjects exhibited significantly higher motor overflow to the contralateral spastic muscles (cBiceps and cFDS) during elbow flexion on the non-impaired side (contralateral or interlimb motor overflow), compared with healthy subjects. Moreover, there was significantly high EMG-EMG coherence in the alpha band (6–12 Hz) between the contracting muscle and all other resting muscles during elbow flexion on the non-impaired side. Our results of diffuse ipsilateral and contralateral motor overflow with EMG-EMG coherence in the alpha band suggest subcortical origins of motor overflow. Furthermore, correlation between contralateral motor overflow to contralateral spastic elbow and finger flexors and their spasticity was consistently at moderate to high levels. A high correlation suggests that diffuse motor overflow to the impaired side and spasticity likely share a common pathophysiological process. Possible mechanisms are discussed.

Changes in the Neural and Non-neural Related Properties of the Spastic Wrist Flexors After Treatment With Botulinum Toxin A in Post-stroke Subjects: An Optimization Study

Quantifying neural and non-neural contributions to the joint resistance in spasticity is essential for a better evaluation of different intervention strategies such as botulinum toxin A (BoTN-A). However, direct measurement of muscle mechanical properties and spasticity-related parameters in humans is extremely challenging. The aim of this study was to use a previously developed musculoskeletal model and optimization scheme to evaluate the changes of neural and non-neural related properties of the spastic wrist flexors during passive wrist extension after BoTN-A injection. Data of joint angle and resistant torque were collected from 21 chronic stroke patients before, and 4 and 12 weeks post BoTN-A injection using NeuroFlexor, which is a motorized force measurement device to passively stretch wrist flexors. The model was optimized by tuning the passive and stretch-related parameters to fit the measured torque in each participant. It was found that stroke survivors exhibited decreased neural components at 4 weeks post BoNT-A injection, which returned to baseline levels after 12 weeks. The decreased neural component was mainly due to the increased motoneuron pool threshold, which is interpreted as a net excitatory and inhibitory inputs to the motoneuron pool. Though the linear stiffness and viscosity properties of wrist flexors were similar before and after treatment, increased exponential stiffness was observed over time which may indicate a decreased range of motion of the wrist joint. Using a combination of modeling and experimental measurement, valuable insights into the treatment responses, i.e., transmission of motoneurons, are provided by investigating potential parameter changes along the stretch reflex pathway in persons with chronic stroke.

Sound-Evoked Biceps Myogenic Potentials Reflect Asymmetric Vestibular Drive to Spastic Muscles in Chronic Hemiparetic Stroke Survivors

Aberrant vestibular nuclear function is proposed to be a principle driver of limb muscle spasticity after stroke. We sought to determine whether altered cortical modulation of descending vestibulospinal pathways post-stroke could impact the excitability of biceps brachii motoneurons. Twelve chronic hemispheric stroke survivors aged 46–68 years were enrolled. Sound evoked biceps myogenic potentials (SEBMPs) were recorded from the spastic and contralateral biceps muscles using surface EMG electrodes. We assessed the impact of descending vestibulospinal pathways on biceps muscle activity and evaluated the relationship between vestibular function and the severity of spasticity. Spastic SEBMP responses were recorded in 11/12 subjects. Almost 60% of stroke subjects showed evoked responses solely on the spastic side. These data strongly support the idea that vestibular drive is asymmetrically distributed to biceps motoneuron pools in hemiparetic spastic stroke survivors. This abnormal vestibular drive is very likely to be a factor mediating the striking differences in motoneuron excitability between the clinically affected and clinically spared sides. This study extends our previous observations on vestibular nuclear changes following hemispheric stroke and potentially sheds light on the underlying mechanisms of post-stroke spasticity.

FUNCTION AND BIOMECHANICS OF UPPER LIMB IN POST-STROKE PATIENTS — A SYSTEMATIC REVIEW

Current clinical services are struggling to provide the most favorable rehabilitation treatment for patients with stroke, which inspired researchers to investigate and explore the use of rehabilitation devices suitable for the patients and rehabilitation therapy. This review paper addresses the importance of biomechanical features in patients who experienced stroke to the upper limb. First and foremost, a review was done on general biomechanical description associated with motor control, shoulder, elbow, wrist and fingers joint. This included the ability of the patients to move their affected arm and the affect on peak joint torque, range of motion, joint forces, grip strength and muscle activities during the activities of daily living. In addition, we also reviewed the material properties and geometrical condition of tissue in stroke patient. The repercussions of post-stroke patient regarding the bone density, stiffness of muscle as well as the thickness of cartilage are described in this review. Based on the findings, the movement of affected stroke hand is associated with the motor control and material properties of tissue. To strengthen the motor control and maintaining tissue properties, early physical training on patients should be conducted in two to four weeks after stroke. In conclusion, this report suggests a new approach for future biomechanical studies in order to enhance the quality of physiotherapy rehabilitation peculiarly for post-stroke patients.

Modification of Spastic Stretch Reflexes at the Elbow by Flexion Synergy Expression in Individuals With Chronic Hemiparetic Stroke

OBJECTIVE

To systematically characterize the effect of flexion synergy expression on the manifestation of elbow flexor stretch reflexes poststroke, and to relate these findings to elbow flexor stretch reflexes in individuals without neurologic injury.

DESIGN

Controlled cohort study.

SETTING

Academic medical center.

PARTICIPANTS

Participants (N=20) included individuals with chronic hemiparetic stroke (n=10) and a convenience sample of individuals without neurologic or musculoskeletal injury (n=10).

INTERVENTIONS

Participants with stroke were interfaced with a robotic device that precisely manipulated flexion synergy expression (by regulating shoulder abduction loading) while delivering controlled elbow extension perturbations over a wide range of velocities. This device was also used to elicit elbow flexor stretch reflexes during volitional elbow flexor activation, both in the cohort of individuals with stroke and in a control cohort. In both cases, the amplitude of volitional elbow flexor preactivation was matched to that generated involuntarily during flexion synergy expression.

MAIN OUTCOME MEASURES

The amplitude of short- and long-latency stretch reflexes in the biceps brachii, assessed by electromyography, and expressed as a function of background muscle activation and stretch velocity.

RESULTS

Increased shoulder abduction loading potentiated elbow flexor stretch reflexes via flexion synergy expression in the paretic arm. Compared with stretch reflexes in individuals without neurologic injury, paretic reflexes were larger at rest but were approximately equal to control muscles at matched levels of preactivation.

CONCLUSIONS

Because flexion synergy expression modifies stretch reflexes in involved muscles, interventions that reduce flexion synergy expression may confer the added benefit of reducing spasticity during functional use of the arm.

Neural and non-neural related properties in the spastic wrist flexors: An optimization study

Quantifying neural and non-neural contributions to increased joint resistance in spasticity is essential for a better understanding of its pathophysiological mechanisms and evaluating different intervention strategies. However, direct measurement of spasticity-related manifestations, e.g., motoneuron and biophysical properties in humans, is extremely challenging. In this vein, we developed a forward neuromusculoskeletal model that accounts for dynamics of muscle spindles, motoneuron pools, muscle activation and musculotendon of wrist flexors and relies on the joint angle and resistant torque as the only input measurement variables. By modeling the stretch reflex pathway, neural and non-neural related properties of the spastic wrist flexors were estimated during the wrist extension test. Joint angle and resistant torque were collected from 17 persons with chronic stroke and healthy controls using NeuroFlexor, a motorized force measurement device during the passive wrist extension test. The model was optimized by tuning the passive and stretch reflex-related parameters to fit the measured torque in each participant. We found that persons with moderate and severe spasticity had significantly higher stiffness than controls. Among subgroups of stroke survivors, the increased neural component was mainly due to a lower muscle spindle rate at 50% of the motoneuron recruitment. The motoneuron pool threshold was highly correlated to the motoneuron pool gain in all subgroups. The model can describe the overall resistant behavior of the wrist joint during the test. Compared to controls, increased resistance was predominantly due to higher elasticity and neural components. We concluded that in combination with the NeuroFlexor measurement, the proposed neuromusculoskeletal model and optimization scheme served as suitable tools for investigating potential parameter changes along the stretch-reflex pathway in persons with spasticity.

Spinal Cord Stimulation for Spasticity: Historical Approaches, Current Status, and Future Directions

INTRODUCTION

Millions of people worldwide suffer with spasticity related to irreversible damage to the brain or spinal cord. Typical antecedent events include stroke, traumatic brain injury, and spinal cord injury, although insidious onset is also common. Regardless of the cause, the resulting spasticity leads to years of disability and reduced quality of life. Many treatments are available to manage spasticity; yet each is fraught with drawbacks including incomplete response, high cost, limited duration, dose-limiting side effects, and periodic maintenance. Spinal cord stimulation (SCS), a once promising therapy for spasticity, has largely been relegated to permanent experimental status.

METHODS

In this review, our goal is to document and critique the history and assess the development of SCS as a treatment of lower limb spasticity. By incorporating recent discoveries with the insights gained from the early pioneers in this field, we intend to lay the groundwork needed to propose testable hypotheses for future studies.

RESULTS

SCS has been tested in over 25 different conditions since a potentially beneficial effect was first reported in 1973. However, the lack of a fully formed understanding of the pathophysiology of spasticity, archaic study methodology, and the early technological limitations of implantable hardware limit the validity of many studies. SCS offers a measure of control for spasticity that cannot be duplicated with other interventions.

CONCLUSIONS

With improved energy-source miniaturization, tailored control algorithms, novel implant design, and a clearer picture of the pathophysiology of spasticity, we are poised to reintroduce and test SCS in this population.

Assessing muscle spasticity with Myotonometric and passive stretch measurements: validity of the Myotonometer

Spasticity of the biceps brachii muscle was assessed using the modified Ashworth Scale (MAS), Myotonometry and repeated passive stretch techniques, respectively. Fourteen subjects with chronic hemiplegia participated in the study. Spasticity was quantified by muscle displacements and compliance from the Myotonometer measurements and resistive torques from the repeated passive stretch at velocities of 5 °/s and 100 °/s, respectively. Paired t-tests indicated a significant decrease of muscle displacement and compliance in the spastic muscles as compared to the contralateral side (muscle displacement: spastic: 4.84 ± 0.33 mm, contralateral: 6.02 ± 0.49 mm, p = 0.038; compliance: spastic: 1.79 ± 0.12 mm/N, contralateral: 2.21 ± 0.18 mm/kg, p = 0.048). In addition, passive stretch tests indicated a significant increase of total torque at the velocity of 100 °/s compared with that of 5 °/s (T_t5 = 2.82 ± 0.41 Nm, T_t100 = 6.28 ± 1.01 Nm, p < 0.001). Correlation analysis revealed significant negative relationships between the stretch test and the Myotonometer measurements (r < −0.5, p < 0.05). Findings of this study provided validation of the Myotonometry technique and its high sensitivity in examination of spasticity in stroke.

Robot-aided assessment of lower extremity functions: a review

The assessment of sensorimotor functions is extremely important to understand the health status of a patient and its change over time. Assessments are necessary to plan and adjust the therapy in order to maximize the chances of individual recovery. Nowadays, however, assessments are seldom used in clinical practice due to administrative constraints or to inadequate validity, reliability and responsiveness. In clinical trials, more sensitive and reliable measurement scales could unmask changes in physiological variables that would not be visible with existing clinical scores.In the last decades robotic devices have become available for neurorehabilitation training in clinical centers. Besides training, robotic devices can overcome some of the limitations in traditional clinical assessments by providing more objective, sensitive, reliable and time-efficient measurements. However, it is necessary to understand the clinical needs to be able to develop novel robot-aided assessment methods that can be integrated in clinical practice.This paper aims at providing researchers and developers in the field of robotic neurorehabilitation with a comprehensive review of assessment methods for the lower extremities. Among the ICF domains, we included those related to lower extremities sensorimotor functions and walking; for each chapter we present and discuss existing assessments used in routine clinical practice and contrast those to state-of-the-art instrumented and robot-aided technologies. Based on the shortcomings of current assessments, on the identified clinical needs and on the opportunities offered by robotic devices, we propose future directions for research in rehabilitation robotics. The review and recommendations provided in this paper aim to guide the design of the next generation of robot-aided functional assessments, their validation and their translation to clinical practice.

Tonic Stretch Reflex Threshold as a Measure of Ankle Plantar-Flexor Spasticity After Stroke

BACKGROUND

Commonly used spasticity scales assess the resistance felt by the evaluator during passive stretching. These scales, however, have questionable validity and reliability. The tonic stretch reflex threshold (TSRT), or the angle at which motoneuronal recruitment begins in the resting state, is a promising alternative for spasticity measurement. Previous studies showed that spasticity and voluntary motor deficits after stroke may be characterized by a limitation in the ability of the central nervous system to regulate the range of the TSRT.

OBJECTIVE

The study objective was to assess interevaluator reliability for TSRT plantar-flexor spasticity measurement.

DESIGN

This was an interevaluator reliability study.

METHODS

In 28 people after stroke, plantar-flexor spasticity was evaluated twice on the same day. Plantar-flexor muscles were stretched 20 times at different velocities assigned by a portable device. Plantar-flexor electromyographic signals and ankle angles were used to determine dynamic velocity-dependent thresholds. The TSRT was computed by extrapolating a regression line through dynamic velocity-dependent thresholds to the angular axis.

RESULTS

Mean TSRTs in evaluations 1 and 2 were 66.0 degrees (SD=13.1°) and 65.8 degrees (SD=14.1°), respectively, with no significant difference between them. The intraclass correlation coefficient (2,1) was .851 (95% confidence interval=.703, .928).

LIMITATIONS

The notion of dynamic stretch reflex threshold does not exclude the possibility that spasticity is dependent on acceleration, as well as on velocity; future work will study both possibilities.

CONCLUSIONS

Tonic stretch reflex threshold interevaluator reliability for evaluating stroke-related plantar-flexor spasticity was very good. The TSRT is a reliable measure of spasticity. More information may be gained by combining the TSRT measurement with a measure of velocity-dependent resistance.

Normative NeuroFlexor data for detection of spasticity after stroke: a cross-sectional study

Background and Objective

The NeuroFlexor is a novel instrument for quantification of neural, viscous and elastic components of passive movement resistance. The aim of this study was to provide normative data and cut-off values from healthy subjects and to use these to explore signs of spasticity at the wrist and fingers in patients recovering from stroke.

Methods

107 healthy subjects (age range 28–68 years; 51 % females) and 39 stroke patients (age range 33–69 years; 33 % females), 2–4 weeks after stroke, were assessed with the NeuroFlexor. Cut-off values based on mean + 3SD of the reference data were calculated. In patients, the modified Ashworth scale (MAS) was also applied.

Results

In healthy subjects, neural component was 0.8 ± 0.9 N (mean ± SD), elastic component was 2.7 ± 1.1 N, viscous component was 0.3 ± 0.3 N and resting tension was 5.9 ± 1 N. Age only correlated with elastic component (r = −0.3, p = 0.01). Elasticity and resting tension were higher in males compared to females (p = 0.001) and both correlated positively with height (p = 0.01). Values above healthy population cut-off were observed in 16 patients (41 %) for neural component, in 2 (5 %) for elastic component and in 23 (59 %) for viscous component. Neural component above cut-off did not correspond well to MAS ratings. Ten patients with MAS = 0 had neural component values above cut-off and five patients with MAS ≥ 1 had neural component within normal range.

Conclusion

This study provides NeuroFlexor cut-off values that are useful for detection of spasticity in the early phase after stroke.

Ascending vestibular drive is asymmetrically distributed to the inferior oblique motoneuron pools in a subset of hemispheric stroke survivors

OBJECTIVE

Aberrant vestibular nuclear function is proposed to be a principle driver of limb muscle spasticity after stroke. Although spasticity does not manifest in ocular muscles, we sought to determine whether altered cortical modulation of ascending vestibuloocular pathways post-stroke could impact the excitability of ocular motoneurons.

METHODS

Nineteen chronic stroke survivors, aged 49-68 yrs. were enrolled. Vestibular evoked myogenic potentials (VEMPs) were recorded from the inferior oblique muscles of the eye using surface EMG electrodes. We assessed the impact of ascending otolith pathways on eye muscle activity and evaluated the relationship between otolith-ocular function and the severity of spasticity.

RESULTS

VEMP responses were recorded bilaterally in 14/19 subjects. Response magnitude on the affected side was significantly larger than on the spared side. In a subset of subjects, there was a strong relationship between affected response amplitude and the severity of limb spasticity, as estimated using a standard clinical scale.

CONCLUSIONS

This study suggests that alterations in ascending vestibular drive to ocular motoneurons contribute to post-stroke spasticity in a subset of spastic stroke subjects. We speculate this imbalance is a consequence of the unilateral disruption of inhibitory corticobulbar projections to the vestibular nuclei.

SIGNIFICANCE

This study potentially sheds light on the underlying mechanisms of post-stroke spasticity.

Robotic pilot study for analysing spasticity: clinical data versus healthy controls

BACKGROUND

Spasticity is a motor disorder that causes significant disability and impairs function. There are no definitive parameters that assess spasticity and there is no universally accepted definition. Spasticity evaluation is important in determining stages of recovery. It can determine treatment effectiveness as well as how treatment should proceed. This paper presents a novel cross sectional robotic pilot study for the primary purpose of assessment. The system collects force and position data to quantify spasticity through similar motions of the Modified Ashworth Scale (MAS) assessment in the Sagittal plane. Validity of the system is determined based on its ability to measure velocity dependent resistance.

METHODS

Forty individuals with Acquired Brain Injury (ABI) and 45 healthy individuals participated in a robotic pilot study. A linear regression model was applied to determine the effect an ABI has on force data obtained through the robotic system in an effort to validate it. Parameters from the model were compared for both groups. Two techniques were performed in an attempt to classify between healthy and patients. Dynamic Time Warping (DTW) with k-nearest neighbour (KNN) classification is compared to a time-series algorithm using position and force data in a linear discriminant analysis (LDA).

RESULTS

The system is capable of detecting a velocity dependent resistance (p<0.05). Differences were found between healthy individuals and those with MAS 0 who are considered to be healthy. DTW with KNN is shown to improve classification between healthy and patients by approximately 20 % compared to that of an LDA.

CONCLUSIONS

Quantitative methods of spasticity evaluation demonstrate that differences can be observed between healthy individuals and those with MAS of 0 who are often clinically considered to be healthy. Exploiting the time-series nature of the collected data demonstrates that position and force together are an accurate predictor of patient health.

Estimation of musculotendon kinematics under controlled tendon indentation

The effects of tendon indentation on musculotendon unit mechanics have been left largely unexplored. Tendon indentation is however routinely used in the tendon reflex exam to diagnose the state of reflex pathways. Because muscle mechanoreceptors are sensitive to mechanical changes of the musculotendon unit, this gap in knowledge could potentially impact our understanding of these neurological exams. Accordingly, we have used ultrasound (US) imaging to compare the effects of tendon indentation with the effects angular rotation of the elbow in six neurologically intact individuals. We used sagittal ultrasound movies of the biceps brachii to compare length changes induced by each of these perturbations. Length changes were quantified using a pixel-tracking protocol. Our results show that a 20mm indentation of the distal tendon is broadly equivalent to a 15° elbow rotation. We also show that within the imaging window the strain differences between the two stretching protocols are statistically insignificant. Finally, we show that there exists a significant linear relationship between the two stretching techniques and that this relationship spans a large rotational angle to indentation depth. We have used a novel tendon probe to administer controlled tendon indentations as a way to characterize musculotendon kinematics. Using this probe, we confirm that tendon indentation can be physiologically equated with joint rotation, and can thus be used as an input for muscle stretching protocols. Furthermore, this is potentially a simpler and more practical alternative to externally imposed angular joint motion.

In vivo relationship between pelvis motion and deep fascia displacement of the medial gastrocnemius: anatomical and functional implications

Different authors have modelled myofascial tissue connectivity over a distance using cadaveric models, but in vivo models are scarce. The aim of this study was to evaluate the relationship between pelvic motion and deep fascia displacement in the medial gastrocnemius (MG). Deep fascia displacement of the MG was evaluated through automatic tracking with an ultrasound. Angular variation of the pelvis was determined by 2D kinematic analysis. The average maximum fascia displacement and pelvic motion were 1.501 ± 0.78 mm and 6.55 ± 2.47 °, respectively. The result of a simple linear regression between fascia displacement and pelvic motion for three task executions by 17 individuals was r = 0.791 (P < 0.001). Moreover, hamstring flexibility was related to a lower anterior tilt of the pelvis (r = 0.544, P < 0.024) and a lower deep fascia displacement of the MG (r = 0.449, P < 0.042). These results support the concept of myofascial tissue connectivity over a distance in an in vivo model, reinforce the functional concept of force transmission through synergistic muscle groups, and grant new perspectives for the role of fasciae in restricting movement in remote zones.

Assessment of robotic patient simulators for training in manual physical therapy examination techniques

Robots that simulate patients suffering from joint resistance caused by biomechanical and neural impairments are used to aid the training of physical therapists in manual examination techniques. However, there are few methods for assessing such robots. This article proposes two types of assessment measures based on typical judgments of clinicians. One of the measures involves the evaluation of how well the simulator presents different severities of a specified disease. Experienced clinicians were requested to rate the simulated symptoms in terms of severity, and the consistency of their ratings was used as a performance measure. The other measure involves the evaluation of how well the simulator presents different types of symptoms. In this case, the clinicians were requested to classify the simulated resistances in terms of symptom type, and the average ratios of their answers were used as performance measures. For both types of assessment measures, a higher index implied higher agreement among the experienced clinicians that subjectively assessed the symptoms based on typical symptom features. We applied these two assessment methods to a patient knee robot and achieved positive appraisals. The assessment measures have potential for use in comparing several patient simulators for training physical therapists, rather than as absolute indices for developing a standard.

Mechanical Measures of Spasticity in Stroke

Mechanical measurements of stretch reflexes show promise for the quantification of spasticity after stroke. Mechanical measurements can increase the objectivity, repeatability, and precision of spasticity quantification and provide additional insight into the neuropathology that is not available with current clinical measurements. Several techniques are reviewed and the advantages and disadvantages of quantification of spasticity using mechanical measurements are considered. Although mechanical measures of spasticity offer many advantages, much research needs to be done to establish a standard measurement of spasticity that can be easily implemented in the clinic.

Contributions of motoneuron hyperexcitability to clinical spasticity in hemispheric stroke survivors

OBJECTIVE

Muscle spasticity is one of the major impairments that limits recovery in hemispheric stroke survivors. One potential contributing mechanism is hyperexcitability of motoneurons. Previously, the response latency of the surface electromyogram (EMG) record evoked by joint rotation has been used to characterize motoneuron excitability. Given the limitations of this method, the objective of the current study was to reexamine the excitability of motoneurons in chronic stroke survivors by estimating reflex latency using single motor unit discharge.

METHODS

We quantified the excitability of spastic motoneurons using the response latency of a single motor unit discharge elicited by a position controlled tap on the biceps brachii tendon. We applied tendon taps of different amplitudes on the biceps tendons of both arms of the stroke survivors. Unitary reflex responses were recorded using intramuscular EMG recordings.

RESULTS

Our results showed that the latency of unitary discharge was systematically shorter in the spastic muscle compared with the contralateral muscle, and this effect was consistent across multiple tap amplitudes.

CONCLUSIONS

This method allowed us to quantify latencies more accurately, potentially enabling a more rigorous analysis of contributing mechanisms.

SIGNIFICANCE

The findings provide evidence supporting a contribution of hyperexcitable motoneurons to muscle spasticity.

Quantifying the deep tendon reflex using varying tendon indentation depths: applications to spasticity

The deep tendon reflex (DTR) is often utilized to characterize the neuromuscular health of individuals because it is cheap, quick to implement, and requires limited equipment. However, DTR assessment is unreliable and assessor-dependent improve the reliability of the DTR assessment, we devised a novel standardization procedure. Our approach is based on the hypothesis that the neuromuscular state of a muscle changes systematically with respect to the indentation depth of its tendon. We tested the hypothesis by progressively indenting the biceps tendons on each side of nine hemiplegic stroke survivors to different depths, and then superimposing a series of brief controlled taps at each indentation depth to elicit a reflex response. Our results show that there exists a unique indentation depth at which reflex responses are consistently recorded (termed the Reflex Threshold) with increasing amplitude along increasing indentation depth. We further show that the reflex threshold depth is systematically smaller on the affected side of stroke survivors and that it is negatively correlated with the Modified Ashworth Score (VAF 70%). Our procedure also enables measurement of passive mechanical properties at the indentation location. In conclusion, our study shows that controlling for the indentation depth of the tendon of a muscle alters its reflex response predictably. Our novel device and method could be used to estimate neuromuscular changes in muscle (e.g., spasticity). Although some refinement is needed, this method opens the door to more reliable quantification of the DTR.

Disturbances of motor unit rate modulation are prevalent in muscles of spastic-paretic stroke survivors

Stroke survivors often exhibit abnormally low motor unit firing rates during voluntary muscle activation. Our purpose was to assess the prevalence of saturation in motor unit firing rates in the spastic-paretic biceps brachii muscle of stroke survivors. To achieve this objective, we recorded the incidence and duration of impaired lower- and higher-threshold motor unit firing rate modulation in spastic-paretic, contralateral, and healthy control muscle during increases in isometric force generated by the elbow flexor muscles. Impaired firing was considered to have occurred when firing rate became constant (i.e., saturated), despite increasing force. The duration of impaired firing rate modulation in the lower-threshold unit was longer for spastic-paretic (3.9 ± 2.2 s) than for contralateral (1.4 ± 0.9 s; P < 0.001) and control (1.1 ± 1.0 s; P = 0.005) muscles. The duration of impaired firing rate modulation in the higher-threshold unit was also longer for the spastic-paretic (1.7 ± 1.6 s) than contralateral (0.3 ± 0.3 s; P = 0.007) and control (0.1 ± 0.2 s; P = 0.009) muscles. This impaired firing rate of the lower-threshold unit arose, despite an increase in the overall descending command, as shown by the recruitment of the higher-threshold unit during the time that the lower-threshold unit was saturating, and by the continuous increase in averages of the rectified EMG of the biceps brachii muscle throughout the rising phase of the contraction. These results suggest that impairments in firing rate modulation are prevalent in motor units of spastic-paretic muscle, even when the overall descending command to the muscle is increasing.

Spasticity

Antispastic medications that are directed to reduce clinical signs of spasticity, such as exaggerated reflexes and muscle tone, do not improve the movement disorder. Medication can even increase weakness which might interfere with functional movements, such as walking. In this chapter we address how spasticity affects mobility and how this should be taken into account in the treatment of spasticity. In clinical practice, signs of exaggerated tendon tap reflexes associated with muscle hypertonia are the consequence of spinal cord injury (SCI). They are generally thought to be responsible for spastic movement disorders. Most antispastic treatments are, therefore, directed at the reduction of reflex activity. In recent years, a discrepancy between spasticity as measured in the clinic and functional spastic movement disorder was noticed, which is primarily due to the different roles of reflexes in passive and active states, respectively. We now know that central motor lesions are associated with loss of supraspinal drive and defective use of afferent input with impaired behavior of short-latency and long-latency reflexes. These changes lead to paresis and maladaptation of the movement pattern. Secondary changes in mechanical muscle fiber, collagen tissue, and tendon properties (e.g., loss of sarcomeres, subclinical contractures) result in spastic muscle tone, which in part compensates for paresis and allows functional movements on a simpler level of organization. Antispastic drugs should primarily be applied in complete SCI. In mobile patients they can accentuate paresis and therefore should be applied with caution.

Simultaneous characterizations of reflex and nonreflex dynamic and static changes in spastic hemiparesis

This study characterizes tonic and phasic stretch reflex and stiffness and viscosity changes associated with spastic hemiparesis. Perturbations were applied to the ankle of 27 hemiparetic and 36 healthy subjects under relaxed or active contracting conditions. A nonlinear delay differential equation model characterized phasic and tonic stretch reflex gains, elastic stiffness, and viscous damping. Tendon reflex was characterized with reflex gain and threshold. Reflexively, tonic reflex gain was increased in spastic ankles at rest (P < 0.038) and was not regulated with muscle contraction, indicating impaired tonic stretch reflex. Phasic-reflex gain in spastic plantar flexors was higher and increased faster with plantar flexor contraction (P < 0.012) than controls (P < 0.023) and higher in dorsi-flexors at lower torques (P < 0.038), primarily because of its increase at rest (P = 0.045), indicating exaggerated phasic stretch reflex especially in more spastic plantar flexors, which showed higher phasic stretch reflex gain than dorsi-flexors (P < 0.032). Spasticity was associated with increased tendon reflex gain (P = 0.002) and decreased threshold (P < 0.001). Mechanically, stiffness in spastic ankles was higher than that in controls across plantar flexion/dorsi-flexion torque levels (P < 0.032), and the more spastic plantar flexors were stiffer than dorsi-flexors at comparable torques (P < 0.031). Increased stiffness in spastic ankles was mainly due to passive stiffness increase (P < 0.001), indicating increased connective tissues/shortened fascicles. Viscous damping in spastic ankles was increased across the plantar flexion torque levels and at lower dorsi-flexion torques, reflecting increased passive viscous damping (P = 0.033). The more spastic plantar flexors showed higher viscous damping than dorsi-flexors at comparable torque levels (P < 0.047). Simultaneous characterizations of reflex and nonreflex changes in spastic hemiparesis may help to evaluate and treat them more effectively.

Gait disorders

This chapter deals with the neuronal mechanisms underlying impaired gait. The aim is, first, a better understanding of the underlying pathophysiology and, second, the selection of an adequate treatment. One of the first symptoms of a lesion within the central motor system perceived by patients is a movement disorder, which is most characteristic during locomotion, e.g. in patients suffering spasticity after stroke or a spinal cord injury or Parkinson disease. By the recording and analysis of electrophysiological and biomechanical signals during a movement, the significance of impaired reflex behavior or muscle tone and its contribution to the movement disorder can reliably be assessed. Adequate treatment should not be restricted to the correction of an isolated clinical sign but should be based on the mechanisms underlying the movement disorder that impairs the patient. Therapy should be directed toward functional training, which takes advantage of the plasticity of the nervous system. In the future a combination of repair and functional training will further improve the mobility of disabled patients.

The relationship between the flexion synergy and stretch reflexes in individuals with chronic hemiparetic stroke

This study utilized a novel robotic device, the ACT-4D, to investigate the relationship between the flexion synergy and stretch reflexes in individuals with chronic hemiparetic stroke. Because the flexion synergy influences the amount of elbow flexor muscle activation present in the paretic limb during tasks requiring shoulder abduction loading, it was hypothesized that stretch reflexes may be modulated by expression of this abnormal muscle coactivation pattern. To test this hypothesis, the ACT-4D was used to enable 10 individuals with chronic hemiparetic stroke to generate varying amounts of shoulder abduction torque while concurrently receiving elbow extension position perturbations. It was found that increased expression of the flexion synergy led to greater reflex amplitudes as well as lower reflex velocity thresholds. The physiological basis of the flexion synergy is briefly discussed, as are the implications of the flexion synergy and stretch reflexes for purposeful movement.

Upper-extremity H-reflex measurement post-stroke: reliability and inter-limb differences

OBJECTIVE

To establish test-retest reliability of flexor carpi radialis (FCR) H-reflexes in non-disabled and stroke participants. We also investigated inter-limb differences and effects of chronicity post-stroke compared to non-disabled group and age-related effects in the non-disabled group.

METHODS

Sixteen chronic stroke and twenty-two non-disabled participants were recruited. Bilateral FCR H-reflexes were tested on two separate days by stimulating the median nerve and recording surface electromyography responses. FCR recruitment curves were plotted for H-reflex (H) and motor (M) waves and normalized as a percentage of maximal M-wave (ordinate) and motor threshold (abscissa).

STATISTICS

Intraclass correlation coefficients [two-way mixed model-ICC (1, 2)], one-way ANOVA, Bland-Altman plots, standard error of measurement (SEM), and smallest real difference (SRD).

RESULTS

ICCs ranged from 0.55 to 0.95 (stroke) and 0.69-0.88 (non-disabled). SEM% (% of the mean) ranged from 9% to 24% (stroke) and 18-38% (non-disabled); SRD% ranged from 18% to 66% (stroke) and 6% to 50% (non-disabled). H-reflex amplitude and slope were greater in the paretic vs. non-paretic arm post-stroke (p=0.07 and 0.01, respectively) and the paretic arm vs. non-disabled participants (p=0.007 and 0.002, respectively). Stroke participants with longer chronicity (mean 9.4 years) revealed a significantly greater Hslp/Mslp on the paretic side compared to shorter chronicity (2.5 years; p=0.05). Mean Hslp/Mslp was significantly greater in the young (mean 29 years) compared to the older group (62 years; p=0.045).

CONCLUSIONS

These results establish reliability of FCR H-reflexes in stroke and non-disabled participants. SEM and SRD measurements can be used to interpret recovery patterns and longitudinal effects of therapeutic interventions.

SIGNIFICANCE

FCR H-reflex amplitude and slope can be reliably measured and used to investigate neurophysiological mechanisms of motor recovery post-stroke.

Transient impact of prolonged versus repetitive stretch on hand motor control in chronic stroke

BACKGROUND AND PURPOSE

The purpose of this study was to investigate the influence of prolonged and repetitive passive range of motion (PROM) stretching of the fingers on hand function in stroke survivors.

PARTICIPANTS

Fifteen chronic stroke survivors with moderate to severe hand impairment took part in the study.

METHOD

Participants underwent 3 experimental sessions consisting of 30 minutes of rest, prolonged, or repetitive stretching of the finger flexor muscles by a powered glove orthosis (X-Glove). Outcome measures, comprised of 3 selected tasks from the Graded Wolf Motor Function Test (GWMFT), grip strength, lateral pinch strength, and grip relaxation time, were recorded at the start and end of each session. Change in outcome score for each session was used for analysis.

RESULTS

Data suggested a trend for improvement following stretching, especially for the repetitive PROM case. For one GWMFT task (lift washcloth), the effect of stretching condition on performance time approached a statistical significance (P = .015), with repetitive PROM stretching producing the greatest mean reduction. Similarly, repetitive stretching led to a 12% ± 16% increase in grip strength, although this change was not statistically different across groups (P = .356); and grip termination time was reduced, albeit non-significantly, by 66% ± 133%.

CONCLUSION

Repetitive PROM stretching exhibited trends to be more effective than prolonged stretching for improving hand motor control. Although the results were highly variable and the effects are undoubtedly transient, an extended period of repetitive PROM stretching may prove advantageous prior to hand therapy sessions to maximize treatment.

Effect of sensory feedback from the proximal upper limb on voluntary isometric finger flexion and extension in hemiparetic stroke subjects

This study investigated the potential influence of proximal sensory feedback on voluntary distal motor activity in the paretic upper limb of hemiparetic stroke survivors and the potential effect of voluntary distal motor activity on proximal muscle activity. Ten stroke subjects and 10 neurologically intact control subjects performed maximum voluntary isometric flexion and extension, respectively, at the metacarpophalangeal (MCP) joints of the fingers in two static arm postures and under three conditions of electrical stimulation of the arm. The tasks were quantified in terms of maximum MCP torque [MCP flexion (MCP(flex)) or MCP extension (MCP(ext))] and activity of targeted (flexor digitorum superficialis or extensor digitorum communis) and nontargeted upper limb muscles. From a previous study on the MCP stretch reflex poststroke, we expected stroke subjects to exhibit a modulation of voluntary MCP torque production by arm posture and electrical stimulation and increased nontargeted muscle activity. Posture 1 (flexed elbow, neutral shoulder) led to greater MCP(flex) in stroke subjects than posture 2 (extended elbow, flexed shoulder). Electrical stimulation did not influence MCP(flex) or MCP(ext) in either subject group. In stroke subjects, posture 1 led to greater nontargeted upper limb flexor activity during MCP(flex) and to greater elbow flexor and extensor activity during MCP(ext). Stroke subjects exhibited greater elbow flexor activity during MCP(flex) and greater elbow flexor and extensor activity during MCP(ext) than control subjects. The results suggest that static arm posture can modulate voluntary distal motor activity and accompanying muscle activity in the paretic upper limb poststroke.

Reorganization of multi-muscle and joint withdrawal reflex during arm movements in post-stroke hemiparetic patients

OBJECTIVES

To investigate the behavior of the nociceptive withdrawal reflex (NWR) in the upper limb during reaching and grasping movements in post-stroke hemiparetic patients.

METHODS

Eight patients with chronic stroke and moderate motor deficits were included. An optoelectronic motion analysis system integrated with a surface EMG machine was used to record the kinematic and EMG data. The NWR was evoked through a painful electrical stimulation of the index finger during a movement which consisted of reaching out, picking up a cylinder, and returning it to the starting position.

RESULTS

We found that: (i) the NWR is extensively rearranged in hemiparetic patients, who were found to present different kinematic and EMG reflex patterns with respect to controls; (ii) patients partially lose the ability to modulate the reflex in the different movement phases; (iii) the impairment of the reflex modulation occurs at single-muscle, single-joint and multi-joint level.

CONCLUSIONS

Patients with chronic and mild-moderate post-stroke motor deficits lose the ability to modulate the NWR dynamically according to the movement variables at individual as well as at multi-muscle and joint levels.

SIGNIFICANCE

The central nervous system is unable to use the NWR substrate dynamically and flexibly in order to select the muscle synergies needed to govern the spatio-temporal interaction among joints.

Validation of a New Biomechanical Model to Measure Muscle Tone in Spastic Muscles

Background. There is no easy and reliable method to measure spasticity, although it is a common and important symptom after a brain injury. Objective. The aim of this study was to develop and validate a new method to measure spasticity that can be easily used in clinical practice. Methods. A biomechanical model was created to estimate the components of the force resisting passive hand extension, namely ( a) inertia (IC), ( b) elasticity (EC), ( c) viscosity (VC), and ( d) neural components (NC). The model was validated in chronic stroke patients with varying degree of hand spasticity. Electromyography (EMG) was recorded to measure the muscle activity induced by the passive stretch. Results. The model was validated in 3 ways: ( a) NC was reduced after an ischemic nerve block, ( b) NC correlated with the integrated EMG across subjects and in the same subject during the ischemic nerve block, and ( c) NC was velocity dependent. In addition, the total resisting force and NC correlated with the modified Ashworth score. According to the model, the neural and nonneural components varied between patients. In most of the patients, but not in all, the NC dominated. Conclusions. The results suggest that the model allows valid measurement of spasticity in the upper extremity of chronic stroke patients and that it can be used to separate the neural component induced by the stretch reflex from resistance caused by altered muscle properties.