Reliability of elbow stretch reflex assessment in chronic post-stroke hemiparesis

System identification: a feasible, reliable and valid way to quantify upper limb motor impairments

BACKGROUND

Upper limb impairments in a hemiparetic arm are clinically quantified by well-established clinical scales, known to suffer poor validity, reliability, and sensitivity. Alternatively, robotics can assess motor impairments by characterizing joint dynamics through system identification. In this study, we establish the merits of quantifying abnormal synergy, spasticity, and changes in joint viscoelasticity using system identification, evaluating (1) feasibility and quality of parametric estimates, (2) test-retest reliability, (3) differences between healthy controls and patients with upper limb impairments, and (4) construct validity.

METHODS

Forty-five healthy controls, twenty-nine stroke patients, and twenty cerebral palsy patients participated. Participants were seated with the affected arm immobilized in the Shoulder-Elbow-Perturbator (SEP). The SEP is a one-degree-of-freedom perturbator that enables applying torque perturbations to the elbow while providing varying amounts of weight support to the human arm. Participants performed either a 'do not intervene' or a resist task. Elbow joint admittance was quantified and used to extract elbow viscosity and stiffness. Fifty-four of the participants performed two sessions to establish the test-retest reliability of the parameters. Construct validity was assessed by correlating system identification parameters to parameters extracted using a SEP protocol that objectifies current clinical scales (Re-Arm protocol).

RESULTS

Feasibility was confirmed by all participants successfully completing the study protocol within ~ 25 min without reporting pain or burden. The parametric estimates were good with a variance-accounted-for of ~ 80%. A fair to excellent test-retest reliability was found ([Formula: see text]) for patients, except for elbow stiffness with full weight support ([Formula: see text]). Compared to healthy controls, patients had a higher elbow viscosity and stiffness during the 'do not intervene' task and lower viscosity and stiffness during the resist task. Construct validity was confirmed by a significant (all [Formula: see text]) but weak to moderate ([Formula: see text]) correlation with parameters from the Re-Arm protocol.

CONCLUSIONS

This work demonstrates that system identification is feasible and reliable for quantifying upper limb motor impairments. Validity was confirmed by differences between patients and controls and correlations with other measurements, but further work is required to optimize the experimental protocol and establish clinical value.

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.

Measuring Mechanical Properties of Spastic Muscles After Stroke. Does Muscle Position During Assessment Really Matter?

OBJECTIVE

To investigate the influence of muscle position (relaxed vs stretched) on muscle mechanical properties and the ability of myotonometry to detect differences between sides, groups, and sites of testing in patients with stroke. We also analyzed the association between myotonometry and clinical measures of spasticity.

DESIGN

Cross-sectional study.

SETTING

Outpatient rehabilitation units including private and public centers.

PARTICIPANTS

Seventy-one participants (20 subacute stroke, 20 chronic stroke, 31 controls) were recruited (N=71).

INTERVENTION

Muscle mechanical properties were measured bilaterally with a MyotonPRO at muscle belly and musculotendinous sites during 2 protocols (muscle relaxed or in maximal bearable stretched position).

MAIN OUTCOME MEASURES

Muscle tone and stiffness of the biceps brachii and gastrocnemius. Poststroke spasticity was evaluated with the Modified Tardieu Scale (MTS). A mixed-model analysis of variance was used to detect differences in the outcome measures.

RESULTS

The analysis of variance showed a significant effect of muscle position on muscle mechanical properties (higher tone and stiffness with the muscle assessed in stretched position). Measurements with the stretched muscle could help discriminate between spastic and nonspastic sides, but only at the biceps brachii. Overall, there was a significant increase in tone and stiffness in the chronic stroke group and in myotendinous sites compared with muscle belly sites (all, P<.05). No correlations were found between myotonometry and the MTS.

CONCLUSIONS

Myotonometry assessment of mechanical properties with the muscle stretched improves the ability of myotonometry to discriminate between sides in patients after stroke and between people with and without stroke.

The left-right side-specific endocrine signaling in the effects of brain lesions: questioning of the neurological dogma

Each cerebral hemisphere is functionally connected to the contralateral side of the body through the decussating neural tracts. The crossed neural pathways set a basis for contralateral effects of brain injury such hemiparesis and hemiplegia as it has been already noted by Hippocrates. Recent studies demonstrated that, in addition to neural mechanisms, the contralateral effects of brain lesions are mediated through the humoral pathway by neurohormones that produce either the left or right side-specific effects. The side-specific humoral signaling defines whether the left or right limbs are affected after a unilateral brain injury. The hormonal signals are released by the pituitary gland and may operate through their receptors that are lateralized in the spinal cord and involved in the side-specific control of symmetric neurocircuits innervating the left and right limbs. Identification of features and a proportion of neurological deficits transmitted by neurohormonal signals vs. those mediated by neural pathways is essential for better understanding of mechanisms of brain trauma and stroke and development of new therapies. In a biological context, the left–right side-specific neuroendocrine signaling may be fundamental for the control of the left- and right-sided processes in bilaterally symmetric animals.

Impact of Voluntary Muscle Activation on Stretch Reflex Excitability in Individuals With Hemiparetic Stroke

Objective

To characterize how, following a stretch-induced attenuation, volitional muscle activation impacts stretch reflex activity in individuals with stroke.

Methods

A robotic device rotated the paretic elbow of individuals with hemiparetic stroke from 70° to 150°, and then back to 70° elbow flexion at an angular speed of 120°/s. This stretching sequence was repeated 20 times. Subsequently, participants volitionally activated their elbow musculature or rested. Finally, the stretching sequence was repeated another 20 times. The flexors' stretch reflex activity was quantified as the net torque measured at 135°.

Results

Data from 15 participants indicated that the stretching sequence attenuated the flexion torque (p < 0.001) and resting sustained the attenuation (p = 1.000). Contrastingly, based on data from 14 participants, voluntary muscle activation increased the flexion torque (p < 0.001) to an initial pre-stretch torque magnitude (p = 1.000).

Conclusions

Stretch reflex attenuation induced by repeated fast stretches may be nullified when individuals post-stroke volitionally activate their muscles. In contrast, resting may enable a sustained reflex attenuation if the individual remains relaxed.

Significance

Stretching is commonly implemented to reduce hyperactive stretch reflexes following a stroke. These findings suggest that stretch reflex accommodation arising from repeated fast stretching may be reversed once an individual volitionally moves their paretic arm.

An Exoneuromusculoskeleton for Self-Help Upper Limb Rehabilitation After Stroke

This article presents a novel electromyography (EMG)-driven exoneuromusculoskeleton that integrates the neuromuscular electrical stimulation (NMES), soft pneumatic muscle, and exoskeleton techniques, for self-help upper limb training after stroke. The developed system can assist the elbow, wrist, and fingers to perform sequential arm reaching and withdrawing tasks under voluntary effort control through EMG, with a lightweight, compact, and low-power requirement design. The pressure/torque transmission properties of the designed musculoskeletons were quantified, and the assistive capability of the developed system was evaluated on patients with chronic stroke (n = 10). The designed musculoskeletons exerted sufficient mechanical torque to support joint extension for stroke survivors. Compared with the limb performance when no assistance was provided, the limb performance (measured as the range of motion in joint extension) significantly improved when mechanical torque and NMES were provided (p < 0.05). A pilot trial was conducted on patients with chronic stroke (n = 15) to investigate the feasibility of using the developed system in self-help training and the rehabilitation effects of the system. All the participants completed the self-help device-assisted training with minimal professional assistance. After a 20-session training, significant improvements were noted in the voluntary motor function and release of muscle spasticity at the elbow, wrist, and fingers, as indicated by the clinical scores (p < 0.05). The EMG parameters (p < 0.05) indicated that the muscular coordination of the entire upper limb improved significantly after training. The results suggested that the developed system can effectively support self-help upper limb rehabilitation after stroke. ClinicalTrials.gov Register Number NCT03752775.

Test-retest reliability and responsiveness of isokinetic dynamometry to assess wrist flexor muscle spasticity in subacute post-stroke hemiparesis

INTRODUCTION

To overcome the limitations of clinical scales, objective measurement methods are becoming prominent in spasticity assessment. The aim of this study was to assess the test-retest reliability and responsiveness of isokinetic dynamometry to evaluate wrist flexor spasticity in patients with subacute stroke.

METHODS

Twenty six patients with hemiparetic stroke (13 men, 13 women, mean age 51.38 ± 12.64 years) volunteered to take part in this study. Resistive torque in the wrist flexor muscles was measured twice, 1 day apart, with an isokinetic dynamometer. Wrist extension was tested at four speeds (5, 60, 120 and 180°/s). Torque response at the lowest speed (5°/s) was attributed to the non-neural component of the wrist flexor muscles, and was subtracted from the torque response at the higher speeds to calculate reflex torque (spasticity). The reliability of reflex torque measurements at 60, 120 and 180°/s was evaluated with the intraclass correlation coefficient (ICC_2,1) and standard error of measurement (SEM and SEM%), which reflect reproducibility and measurement error, respectively. Responsiveness was calculated as the smallest real difference (SRD and SRD%).

RESULTS

Reproducibility was excellent at different movement speeds (ICC_{2, 1} 0.76-0.85). SEM% ranged from 11% to 21%, and SRD% ranged from 30% to 58%. ICC values increased, and SEM% and SRD% decreased, as test speed increased.

CONCLUSION

Our results support the reliability and responsiveness of isokinetic dynamometry to quantify spasticity in wrist flexor muscles in patients with subacute stroke. Reliability and responsiveness increased as the speed of wrist movement increased.

Hindlimb motor responses to unilateral brain injury: spinal cord encoding and left-right asymmetry

Mechanisms of motor deficits (e.g. hemiparesis and hemiplegia) secondary to stroke and traumatic brain injury remain poorly understood. In early animal studies, a unilateral lesion to the cerebellum produced postural asymmetry with ipsilateral hindlimb flexion that was retained after complete spinal cord transection. Here we demonstrate that hindlimb postural asymmetry in rats is induced by a unilateral injury of the hindlimb sensorimotor cortex, and characterize this phenomenon as a model of spinal neuroplasticity underlying asymmetric motor deficits. After cortical lesion, the asymmetry was developed due to the contralesional hindlimb flexion and persisted after decerebration and complete spinal cord transection. The asymmetry induced by the left-side brain injury was eliminated by bilateral lumbar dorsal rhizotomy, but surprisingly, the asymmetry after the right-side brain lesion was resistant to deafferentation. Pancuronium, a curare-mimetic muscle relaxant, abolished the asymmetry after the right-side lesion suggesting its dependence on the efferent drive. The contra- and ipsilesional hindlimbs displayed different musculo-articular resistance to stretch after the left but not right-side injury. The nociceptive withdrawal reflexes evoked by electrical stimulation and recorded with EMG technique were different between the left and right hindlimbs in the spinalized decerebrate rats. On this asymmetric background, a brain injury resulted in greater reflex activation on the contra- versus ipsilesional side; the difference between the limbs was higher after the right-side brain lesion. The unilateral brain injury modified expression of neuroplasticity genes analysed as readout of plastic changes, as well as robustly impaired coordination of their expression within and between the ipsi- and contralesional halves of lumbar spinal cord; the effects were more pronounced after the left side compared to the right-side injury. Our data suggest that changes in the hindlimb posture, resistance to stretch and nociceptive withdrawal reflexes are encoded by neuroplastic processes in lumbar spinal circuits induced by a unilateral brain injury. Two mechanisms, one dependent on and one independent of afferent input may mediate asymmetric hindlimb motor responses. The latter, deafferentation resistant mechanism may be based on sustained muscle contractions which often occur in patients with central lesions and which are not evoked by afferent stimulation. The unusual feature of these mechanisms is their lateralization in the spinal cord.

Reliability, validity and discriminant ability of a robotic device for finger training in patients with subacute stroke

Background

The majority of stroke survivors experiences significant hand impairments, as weakness and spasticity, with a severe impact on the activity of daily living. To objectively evaluate hand deficits, quantitative measures are needed. The aim of this study is to assess the reliability, the validity and the discriminant ability of the instrumental measures provided by a robotic device for hand rehabilitation, in a sample of patients with subacute stroke.

Material and methods

In this study, 120 patients with stroke and 40 controls were enrolled. Clinical evaluation included finger flexion and extension strength (using the Medical Research Council, MRC), finger spasticity (using the Modified Ashworth Scale, MAS) and motor control and dexterity during ADL performance (by means of the Frenchay Arm Test, FAT). Robotic evaluations included finger flexion and extension strength, muscle tone at rest, and instrumented MAS and Modified Tardieu Scale. Subjects were evaluated twice, one day apart, to assess the test-retest reliability of the robotic measures, using the Intraclass Correlation Coefficient (ICC). To estimate the response stability, the standard errors of measurement and the minimum detectable change (MDC) were also calculated. Validity was assessed by analyzing the correlations between the robotic metrics and the clinical scales, using the Spearman’s Correlation Coefficient (r). Finally, we investigated the ability of the robotic measures to distinguish between patients with stroke and healthy subjects, by means of Mann-Whitney U tests.

Results

All the investigated measures were able to discriminate patients with stroke from healthy subjects (p < 0.001). Test-retest reliability was found to be excellent for finger strength (in both flexion and extension) and muscle tone, with ICCs higher than 0.9. MDCs were equal to 10.6 N for finger flexion, 3.4 N for finger extension, and 14.3 N for muscle tone. Conversely, test-retest reliability of the spasticity measures was poor. Finally, finger strength (in both flexion and extension) was correlated with the clinical scales (r of about 0.7 with MRC, and about 0.5 with FAT).

Discussion

Finger strength (in both flexion and extension) and muscle tone, as provided by a robotic device for hand rehabilitation, are reliable and sensitive measures. Moreover, finger strength is strongly correlated with clinical scales. Changes higher than the obtained MDC in these robotic measures could be considered as clinically relevant and used to assess the effect of a rehabilitation treatment in patients with subacute stroke.

Measuring muscle tone with isokinetic dynamometer technique in stroke patients

Study aim: Increased muscle tone, a common consequence of stroke, has neural and non-neural components. Spasticity is related to the neural component. Non-neural resistance arises from passive stiffness. This study was designed to assess the feasibility of using isokinetic dynamometry to evaluate wrist flexor muscle spasticity in stroke patients.

Materials and methods: Twenty-six patients with hemiplegia in the subacute phase of stroke participated in this study. An isokinetic dynamometer was used to stretch wrist flexor muscles at four velocities of 5, 60, 120 and 180°/s on both the paretic and non-paretic sides. Peak torque at the lowest speed (5°/s) and reflex torque at the three higher speeds were quantified. Peak torque at the lowest speed was attributed to the non-neural component of muscle tone, and was subtracted from the torque response at higher velocities to estimate reflex torque (spasticity). Data from the two sides were compared.

Results: There was no significant difference in peak torque between the paretic (2.47 ± 0.22 N·m) and non-paretic side (2.41 ± 0.28 N·m) at the lowest velocity of 5°/s (p=0.408). However, compared to the non-paretic side, the paretic side showed higher reflex torque (p<0001), and reflex torque increased rapidly with increasing velocity (p < 0.05).

Conclusion: The isokinetic dynamometer distinguished spasticity from the non-neural component and showed higher reflex torque on the paretic side compared to the non-paretic side. This instrument is potentially useful to assess the efficacy of therapeutic interventions aimed at modifying spasticity.

Comparison of interobserver agreement between the evaluation of bicipital and the patellar tendon reflex in healthy dogs

The reliability of reflex-assessment is currently debatable, with current literature regarding the patellar tendon reflex (PTR) as highly reliable, while the biceps tendon reflex (BTR) is regarded to be of low reliability in the dog. Such statements are, however, based on subjective observations rather than on an empirical study. The goals of this study were three-fold: (1) the quantification of the interobserver agreement (IA) on the evaluation of the canine bicipital (BTR) and patellar tendon (PTR) reflex in healthy dogs, (2) to compare the IA of the BTR and PTR evaluation and (3) the identification of intrinsic (sex, age, fur length, weight) and extrinsic (observer´s expertise, body side) risk factors on the IA of both reflexes. The observers were subdivided into three groups based on their expected level of expertise (neurologists = highest -, practitioners = middle–and veterinary students = lowest level of expertise). For the BTR, 54 thoracic limbs were analyzed and compared to the evaluation of the PTR on 64 pelvic limbs. Each observer had to evaluate the reflex presence (RP) (present or absent) and the reflex activity (RA) using a 5-point ordinal scale. Multiple reliability coefficients were calculated. The influence of the risk factors has been calculated using a mixed regression-model. The Odds Ratio for each factor was presented. The higher the level of expertise the higher was the IA of the BTR. For RP(BTR), IA was highest for neurologists and for RA(BTR) the IA was lowest for students. The level of expertise had a significant impact on the degree of the IA in the evaluation of the bicipital tendon reflex: for the RA(BTR), practitioners had a 3.4-times (p = 0.003) and students a 7.0-times (p < 0.001) higher chance of discordance. In longhaired dogs the chance of disagreement was 2.6-times higher compared to shorthaired dogs in the evaluation of RA(BTR) (p = 0.003). Likewise, the IA of the RP(PTR) was the higher the higher the observers´ expertise was with neurologists having significantly highest values (p < 0.001). The RA(PTR) has been evaluated more consistent by practitioners and students than the RA(BTR). For practitioners this difference was significant (< 0.01). Our data suggests that neurologists assess the bicipital and patellar tendon reflex in dogs most reliably. None of the examined risk factors had a significant impact on the degree of IA in the evaluation of RP(PTR), while students had a 4.4-times higher chance of discordance when evaluating the RA(PTR) compared to the other groups. This effect was significant (p < 0.001). Neurologists can reliably assess the bicipital and patellar tendon reflex in healthy dogs. Observer´s level of expertise and the fur length of the dog affect the degree of IA of RA(BTR). The influence of the observer´s expertise is higher on the evaluation of the BTR than on the PTR.

A Regression-Based Framework for Quantitative Assessment of Muscle Spasticity Using Combined EMG and Inertial Data From Wearable Sensors

There have always been practical demands for objective and accurate assessment of muscle spasticity beyond its clinical routine. A novel regression-based framework for quantitative assessment of muscle spasticity is proposed in this paper using wearable surface electromyogram (EMG) and inertial sensors combined with a simple examination procedure. Sixteen subjects with elbow flexor or extensor (i.e., biceps brachii muscle or triceps brachii muscle) spasticity and eight healthy subjects were recruited for the study. The EMG and inertial data were recorded from each subject when a series of passive elbow stretches with different stretch velocities were conducted. In the proposed framework, both lambda model and kinematic model were constructed from the recorded data, and biomarkers were extracted respectively from the two models to describe the neurogenic component and biomechanical component of the muscle spasticity, respectively. Subsequently, three evaluation methods using supervised machine learning algorithms including single-/multi-variable linear regression and support vector regression (SVR) were applied to calibrate biomarkers from each single model or combination of two models into evaluation scores. Each of these evaluation scores can be regarded as a prediction of the modified Ashworth scale (MAS) grade for spasticity assessment with the same meaning and clinical interpretation. In order to validate performance of three proposed methods within the framework, a 24-fold leave-one-out cross validation was conducted for all subjects. Both methods with each individual model achieved satisfactory performance, with low mean square error (MSE, 0.14 and 0.47) between the resultant evaluation score and the MAS. By contrast, the method using SVR to fuse biomarkers from both models outperformed other two methods with the lowest MSE at 0.059. The experimental results demonstrated the usability and feasibility of the proposed framework, and it provides an objective, quantitative and convenient solution to spasticity assessment, suitable for clinical, community, and home-based rehabilitation.

Position as Well as Velocity Dependence of Spasticity-Four-Dimensional Characterizations of Catch Angle

We investigated the muscle alterations related to spasticity in stroke quantitatively using a portable manual spasticity evaluator.

Methods: Quantitative neuro-mechanical evaluations under controlled passive elbow stretches in stroke survivors and healthy controls were performed in a research laboratory of a rehabilitation hospital. Twelve stroke survivors and nine healthy controls participated in the study. Spasticity and catch angle were evaluated at 90°/s and 270°/s with the velocities controlled through real-time audiovisual feedback. The elbow range of motion (ROM), stiffness, and energy loss were determined at a slow velocity of 30°/s. Four-dimensional measures including joint position, torque, velocity and torque change rate were analyzed jointly to determine the catch angle.

Results: The catch angle was dependent on the stretch velocity and occurred significantly later with increasing velocity (p < 0.001), indicating position dependence of spasticity. The higher resistance felt by the examiner at the higher velocity was also due to more extreme joint position (joint angle) since the spastic joint was moved significantly further to a stiffer elbow position with the higher velocity. Stroke survivors showed smaller ROM (p < 0.001), higher stiffness (p < 0.001), and larger energy loss (p = 0.005). Compared to the controls, stroke survivors showed increased reflex excitability with higher reflex-mediated torque (p < 0.001) and at higher velocities (p = 0.02).

Conclusion: Velocity dependence of spasticity is partially due to joint angle position dependence with the joint moved further (to a stiffer position where higher resistance was felt) at a higher velocity. The “4-dimensional characterization” including the joint angle, velocity, torque, and torque change rate provides a systematic tool to characterize catch angle and spasticity quantitatively.

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.

Quantitative Ultrasound Imaging to Assess the Biceps Brachii Muscle in Chronic Post-Stroke Spasticity: Preliminary Observation

We prospectively investigated the feasibility of using quantitative ultrasound imaging (QUI) to assess the biceps brachii muscle (BBM) in individuals with chronic post-stroke spasticity. To quantify muscle echogenicity and stiffness, we measured QUI parameters (gray-scale pixel value and shear wave velocity [SWV, m/s]) of the BBM in three groups: 16 healthy BBMs; 12 post-stroke, non-spastic BBMs; and 12 post-stroke, spastic BBMs. The QUI results were compared with the Modified Ashworth Scale and Tardieu Scale. A total of 20 SWVs were measured in each BBM, once at elbow in 90° flexion and again at maximally achievable extension using acoustic radiation force impulse imaging. BBM pixel value was measured in gray-scale images captured at 90° elbow flexion using ImageJ software. Statistical analyses included analysis of variance for examining the difference in SWV and pixel values among the three groups; Bonferroni correction for testing the difference in SWV and pixel values in a paired group; t-test for examining the difference in SWV values measured at two elbow angles; and Pearson correlation coefficient for analyzing the correlation of QUI to Modified Ashworth Scale and Tardieu Scale. SWV significantly differed between spastic BBMs and non-spastic or healthy BBMs. For pixel values, each of the three groups significantly differed from the others at elbow 90° flexion. The difference in SWV measured between the two elbow angles was also significant (p <0.01). A strong negative correlation was found between SWV and passive range of motion (R² = -0.88, p <0.0001) in spastic upper limbs. These results suggest that the use of QUI is feasible in quantitative assessment of spastic BBM.

Improving the test-retest and inter-rater reliability for stretch reflex measurements using an isokinetic device in stroke patients with mild to moderate elbow spasticity

The conventional tools to measure spasticity exhibited insufficient test-retest or inter-rater reliability. Therefore, the spasticity measurement using an isokinetic device has been proposed to improve these reliabilities of the angle of catch (AoC) measurements; however, this proposal has not been investigated in a standardized manner. In this study, the comparison of the AoC measurement was performed using two modes (isokinetic and manual motion) to investigate whether the standardized isokinetic motion could increase the reliabilities. Motion consistency was calculated using a newly developed index. To analyze the effect of the motion standardization, AoC were estimated using EMG data for both modes, and to compare the measurement reliability, AoC for isokinetic mode was estimated using both EMG and torque data. Although the test-retest reliability for manual motion was excellent, the use of isokinetic motion improved it to the level of extremely excellent. Intraclass correlation coefficient (ICC) for the inter-rater reliability of manual motion was 0.788, which was near the lower limit of the excellent. Isokinetic motion improved it to the ICC of 0.890 and 0.931 based on the EMG and torque, respectively. These improvements in reliabilities reduced the measurement errors, sample size, and need for the same rater in clinical trials.

Day-to-day features of soleus stretch reflexes in sub-acute stroke patients

The aim of the study was to assess the reliability and variability of stretch reflex magnitude (SRmag) in sub-acute stroke patients. For testing, rapid dorsiflexion stretches were induced 24 h apart in 22 patients and 34 controls. SRmag between sessions in patients and controls was not different and the SRmag on the more-affected side was significantly larger than the less-affected, dominant, and non-dominant sides. The SRmag was consistent between sessions. Therefore, patients were not as variable between sessions as we had hypothesized.

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.

Manually controlled instrumented spasticity assessments: a systematic review of psychometric properties

AIM

The first aim of this study was to systematically review and critically assess manually controlled instrumented spasticity assessment methods that combine multidimensional signals. The second aim was to extract a set of quantified parameters that are psychometrically sound to assess spasticity in a clinical setting.

METHOD

Electronic databases were searched to identify studies that assessed spasticity by simultaneously collecting electrophysiological and biomechanical signals during manually controlled passive muscle stretches. Two independent reviewers critically assessed the methodological quality of the psychometric properties of the included studies using the COSMIN guidelines.

RESULTS

Fifteen studies with instrumented spasticity assessments met all inclusion criteria. Parameters that integrated electrophysiological signals with joint movement characteristics were best able to quantify spasticity. There were conflicting results regarding biomechanical-based parameters that quantify the resistance to passive stretch. Few methods have been assessed for all psychometric properties. In particular, further information on absolute reliability and responsiveness for more muscles is needed.

INTERPRETATION

Further research is required to determine the correct parameters for quantifying spasticity based on integration of signals, which especially focuses on distinguishing the neural from non-neural contributions to increased joint torque. These parameters should undergo more rigorous exploration to establish their psychometric properties for use in a clinical environment.

Kinetic measurements of hand motor impairments after mild to moderate stroke using grip control tasks

BACKGROUND

The aim of this study is to investigate quantitative outcome measurements of hand motor performance for subjects after mild to moderate stroke using grip control tasks and characterize abnormal flexion synergy of upper extremities after stroke.

METHODS

A customized dynamometer with force sensors was used to measure grip force and calculate rotation torque during the sub-maximal grip control tasks. The paretic and nonpartic sides of eleven subjects after stroke and the dominant sides of ten healthy persons were tested. Their maximal voluntary grip force was measured and used to set sub-maximal grip control tasks at three different target force levels. Force control ability was characterized by the maximal grip force, mean force percentage, coefficient of variation (CV), target deviation ratio (TDR), and rotation torque ratio (RTR). The motor impairments of subjects after stroke were also evaluated using the Fugl-Meyer assessment for upper extremity (FMA-UE) and Wolf Motor Function Test (WMFT).

RESULTS

Maximal grip force of the paretic side was significantly reduced as compared to the nonparetic side and the healthy group, while the difference of maximal grip force between the nonparetic side and the healthy group was not significant. TDR and RTR increased for all three groups with increasing target force level. There were significant differences of CV, TDR and RTR between the paretic side and the healthy group at all the force levels. CV, TDR and RTR showed significant negative correlations with FMA-UE and WMFT at 50% of maximum grip force.

CONCLUSIONS

This study designed a customized dynamometer together with an innovative measurement, RTR, to investigate the hand motor performance of subjects after mild to moderate stroke during force control tasks. And stroke-induced abnormal flexion synergy of wrist and finger muscles could be characterized by RTR. This study also identified a set of kinetic parameters which can be applied to quantitatively assess the hand motor function of subjects after mild to moderate stroke.

Instrumented assessment of the effect of Botulinum Toxin-A in the medial hamstrings in children with cerebral palsy

This study examined the sensitivity of an instrumented spasticity assessment of the medial hamstrings (MEH) in children with cerebral palsy (CP). Nineteen children received Botulinum Toxin type A (BTX-A) injections in the MEH. Biomechanical (position and torque) and electrophysiological (surface electromyography, EMG) signals were integrated during manually-performed passive stretches of the MEH at low, medium and high velocity. Signals were examined at each velocity and between stretch velocities, and compared pre and post BTX-A (43 ± 16 days). Average change between pre and post BTX-A was interpreted in view of the minimal detectable change (MDC) calculated from previously published reliability results. Improvements greater than the MDC were found for nearly all EMG-parameters and for torque parameters at high velocity and at high versus low velocity (p<0.03), however large inter-subject variability was noted. Moderate correlations were found between the improvement in EMG and in torque (r=0.52, p<0.05). Biomechanical and electrophysiological parameters proved to be adequately sensitive to assess the response to treatment with BTX-A. Furthermore, studying both parameters at different velocities improves our understanding of spasticity and of the physiological effect of selective tone-reduction. This not only provides a clinical validation of the instrumented assessment, but also opens new avenues for further spasticity research.

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.

A clinical measurement to quantify spasticity in children with cerebral palsy by integration of multidimensional signals

Most clinical tools for measuring spasticity, such as the Modified Ashworth Scale (MAS) and the Modified Tardieu Scale (MTS), are not sufficiently accurate or reliable. This study investigated the clinimetric properties of an instrumented spasticity assessment. Twenty-eight children with spastic cerebral palsy (CP) and 10 typically developing (TD) children were included. Six of the children with CP were retested to evaluate reliability. To quantify spasticity in the gastrocnemius (GAS) and medial hamstrings (MEH), three synchronized signals were collected and integrated: surface electromyography (sEMG); joint-angle characteristics; and torque. Muscles were manually stretched at low velocity (LV) and high velocity (HV). Spasticity parameters were extracted from the change in sEMG and in torque between LV and HV. Reliability was determined with intraclass-correlation coefficients and the standard error of measurement; validity by assessing group differences and correlating spasticity parameters with the MAS and MTS. Reliability was moderately high for both muscles. Spasticity parameters in both muscles were higher in children with CP than in TD children, showed moderate correlation with the MAS for both muscles and good correlation to the MTS for the MEH. Spasticity assessment based on multidimensional signals therefore provides reliable and clinically relevant measures of spasticity. Moreover, the moderate correlations of the MAS and MTS with the objective parameters further stress the added value of the instrumented measurements to detect and investigate spasticity, especially for the GAS.

Concurrent neuromechanical and functional gains following upper-extremity power training post-stroke

BACKGROUND

Repetitive task practice is argued to drive neural plasticity following stroke. However, current evidence reveals that hemiparetic weakness impairs the capacity to perform, and practice, movements appropriately. Here we investigated how power training (i.e., high-intensity, dynamic resistance training) affects recovery of upper-extremity motor function post-stroke. We hypothesized that power training, as a component of upper-extremity rehabilitation, would promote greater functional gains than functional task practice without deleterious consequences.

METHOD

Nineteen chronic hemiparetic individuals were studied using a crossover design. All participants received both functional task practice (FTP) and HYBRID (combined FTP and power training) in random order. Blinded evaluations performed at baseline, following each intervention block and 6-months post-intervention included: Wolf Motor Function Test (WMFT-FAS, Primary Outcome), upper-extremity Fugl-Meyer Motor Assessment, Ashworth Scale, and Functional Independence Measure. Neuromechanical function was evaluated using isometric and dynamic joint torques and concurrent agonist EMG. Biceps stretch reflex responses were evaluated using passive elbow stretches ranging from 60 to 180º/s and determining: EMG onset position threshold, burst duration, burst intensity and passive torque at each speed.

RESULTS

PRIMARY OUTCOME

Improvements in WMFT-FAS were significantly greater following HYBRID vs. FTP (p = .049), regardless of treatment order. These functional improvements were retained 6-months post-intervention (p = .03).

SECONDARY OUTCOMES

A greater proportion of participants achieved minimally important differences (MID) following HYBRID vs. FTP (p = .03). MIDs were retained 6-months post-intervention. Ashworth scores were unchanged (p > .05). Increased maximal isometric joint torque, agonist EMG and peak power were significantly greater following HYBRID vs. FTP (p < .05) and effects were retained 6-months post-intervention (p's < .05). EMG position threshold and burst duration were significantly reduced at fast speeds (≥120º/s) (p's < 0.05) and passive torque was reduced post-washout (p < .05) following HYBRID.

CONCLUSIONS

Functional and neuromechanical gains were greater following HYBRID vs. FPT. Improved stretch reflex modulation and increased neuromuscular activation indicate potent neural adaptations. Importantly, no deleterious consequences, including exacerbation of spasticity or musculoskeletal complaints, were associated with HYBRID. These results contribute to an evolving body of contemporary evidence regarding the efficacy of high-intensity training in neurorehabilitation and the physiological mechanisms that mediate neural recovery.

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.

Characterization of spasticity in cerebral palsy: dependence of catch angle on velocity

AIM

To evaluate spasticity under controlled velocities and torques in children with cerebral palsy (CP) using a manual spasticity evaluator.

METHOD

The study involved 10 children with spastic CP (six males, four females; mean age 10 y 1 mo, SD 2 y 9 mo, range 7-16 y; one with quadriplegia, six with right hemiplegia, three with left hemiplegia; Gross Motor Function Classification System levels I [n=2], II [n=3], III [n=2], IV [n=2], and V [n=1]; Manual Ability Classification System levels II [n=5], III [n=4], and V [n=1]) and 10 typically developing participants (four males, six females; mean age 10 y 3 mo, SD 2 y 7 mo, range 7-15 y). Spasticity and catch angle were evaluated using joint position, resistance torque, and torque rate at velocities of 90 degrees, 180 degrees, and 270 degrees per second, controlled using real-time audio-visual feedback. Biomechanically, elbow range of motion (ROM), stiffness, and energy loss were determined during slow movement (30 degrees/s) and under controlled terminal torque.

RESULTS

Compared with typically developing children, children with CP showed higher reflex-mediated torque (p<0.001) and the torque increased more rapidly with increasing velocity (p<0.001). Catch angle was dependent on velocity and occurred later with increasing velocity (p=0.005). Children with CP showed smaller ROM (p<0.05), greater stiffness (p<0.001), and more energy loss (p=0.003).

INTERPRETATION

Spasticity with velocity dependence may also be position-dependent. The delayed catch angle at higher velocities indicates that the greater resistance felt by the examiner at higher velocities was also due to position change, because the joint was moved further to a stiffer position at higher velocities.

Reliability and Sensitivity of a Wrist Rig to Measure Motor Control and Spasticity in Poststroke Hemiplegia

Background. Objective assessment of impairments after stroke is vital for evidence-based therapy and progress monitoring. Objective. This study determines the utility of outcome measures obtained from an instrumented wrist rig for future rehabilitation trials. The tests undertaken were evaluated in terms of sensitivity to detect differences between normal and impaired participants, test-retest repeatability (repeatability coefficient and intraclass correlation coefficient [ICC]), and interrater agreement (Bland and Altman limits of agreement). Methods . Twelve participants with chronic poststroke hemiparesis (mean 5.6 years); and 12 unimpaired volunteers performed a series of tasks in the rig. The hemiparetic arm (impaired group) and dominant arm (unimpaired group) were tested in 3 sessions on the same day by 2 assessors. Signals were analyzed to derive a tracking index (motor control), stretch index (spasticity), flexor modulation index (FMI) (muscle activation), force angle index (FAI) (stiffness), range of movement, and isometric force. Results and Conclusions. The means of all tests differed between impaired and unimpaired participants except for range of movement into flexion, the FAI, and the FMI. Repeatability coefficients for each test are presented as benchmark values for use in future trials in which the wrist rig tests may be used to detect change. Test-retest reliability was excellent in the impaired group (ICC = 0.88-0.98) and poor to excellent in the unimpaired group (ICC = 0.06-0.89). The Bland-Altman ranges showed no bias between assessors, and that the interassessor variability was similar to that between repeats by the same assessor for most tests.

Spasticity measurement based on tonic stretch reflex threshold in stroke using a portable device

OBJECTIVES

We investigated intra- and inter-evaluator reliability to quantify spasticity based on the tonic stretch reflex threshold (TSRT) and the correlation between TSRT and resistance to stretch.

METHODS

Spasticity was evaluated in 20 subjects with chronic stroke-related spasticity using a portable device and the Modified Ashworth Scale (MAS). Evaluations were done on 2 days, by three evaluators. Biceps brachii EMG signals and elbow displacement were recorded during 20 elbow stretches applied at different velocities for each evaluation. Velocity-dependent dynamic stretch reflex thresholds (angle where EMG signal increased in the biceps for a given velocity of stretch) were recorded. These values were used to compute TSRT (excitability of motoneurons at 0 degrees /s). Spasticity was also measured with MAS.

RESULTS

Reliability was moderately good for subjects with moderate to high spasticity (intra-evaluator: 0.46-0.68, and inter-evaluator: 0.53-0.68). The TSRT measure of spasticity did not correlate with resistance to stretch (MAS).

CONCLUSIONS

TSRT may be a more representative measure for subjects with moderate to high spasticity. Further improvements are suggested for the portable device in order to quantify all the levels of spasticity.

SIGNIFICANCE

TSRT may be an alternative clinical measure to current clinical scales.

Altered multijoint reflex coordination is indicative of motor impairment level following stroke

Following stroke, individuals often are unable to activate their elbow and shoulder muscles independently. There is growing evidence that altered reflex pathways may contribute to these abnormal patterns of activation or muscle synergies. Most studies investigating reflex function following stroke have examined only individual joints at rest. Thus, the purpose of this study was to quantify multijoint reflex contributions to the stereotyped muscle synergies commonly observed following stroke. We hypothesized that the patterns of reflex coordination mirror the abnormal muscle coactivity patterns previously reported for voluntary activation. 10 chronic stroke and 8 age-matched control subjects participated. Reflexes were elicited by perturbing the arm with a 3 degree of freedom robot while subjects exerted voluntary forces at the elbow and shoulder. The force conditions tested were selected to assess the influence of gravity and the influence of joint torque generation without gravity on reflex coordination. Reflex magnitude was quantified by the average rectified electromyogram, recorded from 8 muscles that span the elbow and shoulder. Patterns of reflex coordination were quantified using independent components analysis. Results show significant reflex coupling between elbow flexor and shoulder abductor-extensor muscles in stroke patients during isolated elbow and shoulder torque generation and during active arm support against gravity. Identified patterns of stretch reflex coordination were consistent with the stereotyped voluntary flexion synergy, suggesting reflex pathways contribute to abnormal muscle coordination following stroke.

Spastic movement disorder: impaired reflex function and altered muscle mechanics

In clinical practice, signs of exaggerated tendon tap reflexes associated with muscle hypertonia 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, however, researchers have noticed a discrepancy between spasticity as measured in the clinic and functional spastic movement disorders, 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 behaviour of short-latency and long-latency reflexes. These changes lead to paresis and maladaptation of the movement pattern. Secondary changes in mechanical muscle fibre, collagen tissue, and tendon properties (eg, 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 organisation. Antispastic drugs can accentuate paresis and therefore should be applied with caution in mobile patients.

Evaluation of Spastic Muscle in Stroke Survivors Using Magnetic Resonance Imaging and Resistance to Passive Motion

OBJECTIVE

To assess the feasibility of using magnetic resonance imaging (MRI) and resistance to passive movement to evaluate spastic muscle.

DESIGN

T2-weighted MRI scans of the upper arm were obtained at rest and after the performance of upper-arm exercise. In addition, resistance to passive movement was measured subjectively (Modified Ashworth Scale [MAS]) and objectively by an isokinetic device while the arm was moved at varying speeds (stretch reflex torque).

SETTING

Research laboratory.

PARTICIPANTS

Six hemiplegic stroke survivors (single group) with spasticity in the elbow flexors and extensors.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Strength, stretch reflex torque, MAS, MRI-derived muscle cross-sectional area (CSA), and transverse relaxation time (T2).

RESULTS

The affected sides exhibited spasticity (as assessed through MAS), with the extensors displaying a range of 0 to 3, and the flexors between 1 and 1+. The affected muscle groups were significantly weaker than the unaffected muscle groups (extensors: 61% less, flexors: 65% less; P< or =.05). The affected CSA of the triceps was 25% smaller than that of the unaffected side (P=.01), but the biceps muscle group was similar (5% less on the affected side, P> or =.05). There was a tendency (P=.07; effect size, .48) for the resting T2 to be higher in affected versus unaffected biceps, but triceps values were similar (P> or =.05). Both muscle groups showed an increase in T2 after exercise ( approximately 30%, P< or =.05); however, the affected sides did not show an increase (P> or =.05). For both muscle groups, the affected side had a greater stretch reflex torque, with the range of torque values being greater than the range of MAS scores.

CONCLUSIONS

MRI and quantitative resistance to passive movement may be useful in the evaluation of spasticity. This is clinically relevant for the development and evaluation of antispasticity treatments.