Rectus femoris hyperreflexia contributes to Stiff-Knee gait after stroke

Differences in uneven-surface walking characteristics: high-functioning vs low-functioning people with stroke

BACKGROUND

Differences in gait parameters between even- and uneven-surface walking in people with stroke (PwS) with different functional abilities remain unclear.

OBJECTIVES

We aimed to assess whether there are differences in the adjustments of gait parameters on uneven surfaces between PwS based on their even-surface gait speed (≥0.8 and < 0.8 m/s).

METHODS

We calculated the root mean square (RMS) of trunk acceleration and maximum joint angles and co-contraction indexes of the lower limbs during even- and uneven-surface walking between the high-functioning group (HG) (n = 38; ≥0.8 m/s) and low-functioning group (LG) (n = 24; <0.8 m/s).

RESULTS

Compared to the HG, the LG showed a greater reduction in gait speed (p = .015). Meanwhile, the RMS of trunk acceleration increased in the HG but remained unchanged in the LG on uneven surfaces. The increase in knee flexion angle during the swing phase was smaller in the LG than in the HG on uneven surfaces (p < .001). A reduction in the thigh co-contraction index during the stance phase was observed only in the HG on uneven surfaces (p = .005).

CONCLUSIONS

The LG responded with a conservative strategy, reducing gait speed more than the HG to maintain stability, whereas the HG exhibited decreased stability but a more flexible adaptation. The smaller increase in knee flexion during the swing phase in the LG suggests impaired motor control, while the reduction in thigh co-contraction during stance observed only in the HG indicates an adaptive response. These findings highlight that adaptation to uneven surfaces differs depending on gait ability on even surface.

Management Approaches to Spastic Gait Disorders

Spastic gait presents clinically as the net mechanical consequence of neurological impairments of spasticity, weakness, and abnormal synergies and their interactions with the ground reaction force in patients with upper motor neuron syndromes and with some neuromuscular diseases. It is critical to differentiate whether the primary problem is weakness or spasticity, thus better understanding different phenotypes of spastic gait disorders. Pelvic girdle abnormality plays a pivotal role in determining the clinical presentation of gait disorders, since it determines the body vector and compensatory kinetic chain reactions in the knee and ankle joints. Knee joint abnormality can be a mechanical compensation for hip and/or ankle and foot abnormality. Diagnostic nerve blocks and instrumented gait analysis may be needed for diagnosing the underlying problems and developing an individualized plan of care. A wide spectrum of treatment options has been used to manage spastic gait disorders. Some are in early and investigational stages, such as neuromodulation modalities, while others are well-developed, such as therapeutic exercise, ankle-foot orthoses, botulinum toxin treatment, and surgical interventions. Physicians and other healthcare providers who manage spastic gait disorders should be familiar with these treatment options and should employ appropriate interventions concurrently rather than serially. The most effective treatments can be selected based on careful evaluation, inputs from patients, family, and therapists, along with appropriate goal setting. Treatment plans need to be re-evaluated for effectiveness, relevance, and in concordance with disease progress. This is particularly important for patients with progressive neuromuscular diseases such as amyotrophic lateral sclerosis.

Post-stroke Stiff-Knee gait: are there different types or different severity levels?

Stiff-Knee gait (SKG) commonly occurs in individuals after stroke, loosely defined as reduced peak knee flexion angle during swing. The causes of SKG are multifaceted and debated. Further, clinical interventions have not been consistently effective, possibly resulting from multiple undiagnosed subtypes of SKG. Thus, our primary goal of this study is to explore the existence of potential subtypes associated with different levels of motor control complexity. We used retrospective kinematics, kinetics and muscle activity from 50 stroke survivors and 15 healthy, age-matched controls during treadmill walking. We used a time-series kernel k-means cluster analysis based on compensatory frontal plane kinematics associated with SKG to separate participants into three groups, Cluster A (hip hiking, lowest knee flexion, highest propulsion asymmetry, lowest gait speed), Cluster B (hip hiking and hip abduction, moderate knee flexion, middle gait speed) and Cluster C (highest knee flexion, highest gait speed). The highest proportion of individuals with SKG as diagnosed by a clinician were in Cluster A, but with a substantial proportion in Cluster B, indicating that these two clusters can be considered subtypes of SKG. Despite differences in kinematics and kinetics, we did not observe fundamental differences in underlying motor control between clusters as determined by non-negative matrix factorization of measured muscle activations. We conclude that the differences between clusters were most likely attributed to the severity of gait impairment, as reflected by slower gait speed and propulsion asymmetry, rather than being a different type of SKG.

Between-limb difference in peak knee flexion angle can identify persons post-stroke with Stiff-Knee gait

BACKGROUND

Stiff-Knee gait affects 25-75 % of individuals with post-stroke gait impairment and is typically defined as reduced swing phase knee flexion. Different studies use various measures to identify Stiff-Knee gait, such as peak swing knee flexion angle, timing of peak knee flexion, knee range of motion, and ankle push-off acceleration, leading to inconsistent results.

METHODS

This study used univariate cluster analysis to examine the independence, consistency, validity, and accuracy of different definitions in 50 post-stroke individuals (24 with and 26 without Stiff-Knee gait), as determined by a physiatrist. Spearman's rank correlation was used for correlation analysis, and five clustering techniques along with clinician evaluations were used for validity analysis.

FINDINGS

Correlation analysis showed that peak knee flexion timing and knee hyperextension are poorly correlated with reduced swing-phase knee flexion angle (ρ = -0.09 and ρ = -0.26 respectively). Validity analysis indicated that the between-limb difference in peak swing knee flexion angle and peak swing knee flexion angle at self-selected gait speeds were the most valid differentiators. At the fastest comfortable gait speed, the between-limb difference of peak knee flexion angle had the highest sensitivity, lowest specificity, and highest F1 scores.

INTERPRETATION

We determined thresholds of less than 44.3° for peak swing knee flexion angle and greater than 17.0° for the between-limb difference of peak knee flexion angle identify Stiff-Knee gait during self-selected walking. We recommend using the difference in peak swing knee flexion angle between limbs to diagnose post-stroke Stiff-Knee gait due to its robustness to changes in gait speed.

Comparative electromyography analysis of subphase gait disorder in chronic stroke survivors

Abnormal lower limb muscle activity is the most common cause of the alterative pattern of gait in stroke survivors, resulting from spastic and paralytic muscles around the hip, knee, and ankle joints. However, the activity of the major lower limb muscles that control the legs to facilitate walking in stroke patients have not been clearly understood in each subphase of the gait. This study differentiated the characteristics of surface electromyography (sEMG) signals of lower limb muscles during four subphases of gait cycle between stroke patients and healthy subjects. Sixteen chronic stroke patients and sixteen healthy subjects were recruited. All participants completed three walking trials with a self-selected walking speed. The sEMG signals were recorded on the gluteus medius, rectus femoris, long head of biceps femoris, medial gastrocnemius, tibialis anterior, and peroneus longus muscles. The characteristics of sEMG signals were processed and analyzed in the time and frequency features, considering the first double support, single support, second double support, and swing phases of the gait cycle.The stroke patients had altered sEMG characteristics on both paretic and non-paretic sides compared to healthy subjects across the sub-phases of gait cycle for all six muscles. All time domain features of sEMG signal showed that the medial gastrocnemius muscle has the most significant impaired activity (p < 0.05) and affected gait disturbance during all four subphases of the gait cycle. The findings demonstrated that the medial gastrocnemius muscle had impaired activity and was most affected during all four sub-phases of the gait cycle. This indicates that sEMG of medial gastrocnemius muscle can be used to measure the improvement of gait rehabilitation.

Can We Target Close Therapeutic Goals in the Gait Re-Education Algorithm for Stroke Patients at the Beginning of the Rehabilitation Process?

(1) Background: The study aimed to determine the most important activities of the knee joints related to gait re-education in patients in the subacute period after a stroke. We focused on the tests that a physiotherapist could perform in daily clinical practice. (2) Methods: Twenty-nine stroke patients (SG) and 29 healthy volunteers (CG) were included in the study. The patients underwent the 5-meter walk test (5mWT) and the Timed Up and Go test (TUG). Tests such as step up, step down, squat, step forward, and joint position sense test (JPS) were also performed, and the subjects were assessed using wireless motion sensors. (3) Results: We observed significant differences in the time needed to complete the 5mWT and TUG tests between groups. The results obtained in the JPS show a significant difference between the paretic and the non-paretic limbs compared to the CG group. A significantly smaller range of knee joint flexion (ROM) was observed in the paretic limb compared to the non-paretic and control limbs in the step down test and between the paretic and non-paretic limbs in the step forward test. (4) Conclusions: The described functional tests are useful in assessing a stroke patient's motor skills and can be performed in daily clinical practice.

Patterns and assessment of spastic hemiplegic gait

Hemiparetic gait disorders are common in stroke survivors. A circumductory gait is often considered the typical hemiparetic gait. In clinical practice, a wide spectrum of abnormal gait patterns is observed, depending on the severity of weakness and spasticity, and the anatomical distribution of spasticity. Muscle strength is the key determinant of gait disorders in hemiparetic stroke survivors. Spasticity and its associated involuntary activation of synergistic spastic muscles often alter posture of involved joint(s) and subsequently the alignment of hip, knee, and ankle joints, resulting in abnormal gait patterns. Due to combinations of various levels of muscle weakness and spasticity and their interactions with ground reaction force, presentations of gait disorders are variable. From a neuromechanical perspective, a stepwise visual gait analysis approach is proposed to identify primary underlying causes. In this approach, the pelvic and hip joint movement is examined first. The pelvic girdle constitutes three kinematic determinants. Its abnormality determines the body vector and compensatory kinetic chain reactions in the knee and ankle joints. The second step is to assess the ankle and foot complex abnormality. The last step is to examine abnormality of the knee joint. Assessment of muscle strength and spasticity of hip, knee, and ankle/foot joints needs to be performed before these steps. Lidocaine nerve blocks can be a useful diagnostic tool. Recognizing different patterns and identifying the primary causes are critical to developing clinical interventions to improve gait functions.

Case report: Intrathecal baclofen therapy improved gait pattern in a stroke patient with spastic dystonia

Background

Intrathecal baclofen (ITB) therapy, a viable alternative for unsuitable candidates of conventional spasticity medications, is a preferred method of administration over the oral route. Owing to its enhanced bioavailability, ITB ensures a more effective delivery at the target site.

Objective

There is a lack of conclusive evidence regarding the use of ITB treatment in managing ambulatory patients with spastic dystonia. Before ITB pump implantation, patients commonly undergo an ITB bolus injection trial to rule out potential adverse reactions and verify the therapeutic effects on hypertonic issues. In this report, we highlight a case of spastic dystonia, particularly focusing on an ambulatory patient who demonstrated significant improvement in both the modified Ashworth scale (MAS) score and gait pattern following the ITB injection trial.

Case report

This case report outlines the medical history of a 67-year-old male diagnosed with left-side hemiplegia and spastic dystonia, resulting from his second episode of intracranial hemorrhage in the right thalamus. An ITB injection trial was initiated because the patient was not suitable for continued botulinum toxin injections and oral medications. This was due to the persistent occurrence of spastic dystonia in both the upper and lower extremities. The patient underwent a four-day ITB injection trial with progressively increasing doses, resulting in improved MAS scores and gait parameters, including cadence, step length, step time, stride length, and stride time were increased. Particularly, kinematic gait analysis demonstrates a substantial improvement of increased knee flexion in the swing phase in stiff knee gait pattern. These findings indicated a gradual reduction in spasticity-related symptoms, signifying the positive effect of the ITB injection trial. The patient eventually received an ITB pump implantation.

Conclusion

In this post-stroke patient with spastic dystonia, ITB therapy has demonstrated effective and substantial management of spasticity, along with improvement in gait patterns.

Anatomical landmarks for ultrasound-guided rectus femoris diagnostic nerve block in post-stroke spasticity

Introduction/Purpose

To determine the location of the rectus femoris (RF) motor branch nerve, as well as its coordinates with reference to anatomical and ultrasound landmarks.

Methods

Thirty chronic stroke patients with stiff knee gait (SKG) and RF hyperactivity were included. The motor nerve branch to the RF muscle was identified medially to the vertical line from anterior superior iliac spine and the midpoint of the superior margin of the patella (line AP) and vertically to the horizontal line from the femoral pulse and its intersection point with the line AP (line F). The point of the motor branch (M) was located with ultrasound, and nerve depth and subcutaneous tissue thickness (ST) were calculated.

Results

The coordinates of the motor branch to the RF were 2.82 (0.47) cm medially to the line AP and 4.61 (0.83) cm vertically to the line F. Nerve depth and subcutaneous tissue thickness were 2.71 (0.62) cm and 1.12 (0.75) cm, respectively.

Conclusion

The use of specific coordinates may increase clinicians' confidence when performing RF motor nerve block. This could lead to better decision-making when assessing SKG in chronic stroke patients.

Hip and Knee Joint Kinematics Predict Quadriceps Hyperreflexia in People with Post-stroke Stiff-Knee Gait

Wearable assistive technology for the lower extremities has shown great promise towards improving gait function in people with neuromuscular injuries. But common secondary impairments, such as hypersensitive stretch reflexes or hyperreflexia, have been often neglected. Incorporation of biomechanics into the control loop could improve individualization and avoid hyperreflexia. However, adding hyperreflexia prediction to the control loop would require expensive or complex measurement of muscle fiber characteristics. In this study, we explore a clinically accessible biomechanical predictor set that can accurately predict rectus femoris (RF) reaction after knee flexion assistance in pre-swing by a powered orthosis. We examined a total of 14 gait parameters based on gait kinematic, kinetic, and simulated muscle-tendon states from 8 post-stroke individuals with Stiff-Knee gait (SKG) wearing a knee exoskeleton robot. We independently performed both parametric and non-parametric variable selection approaches using machine learning regression techniques. Both models revealed the same four kinematic variables relevant to knee and hip joint motions were sufficient to effectively predict RF hyperreflexia. These results suggest that control of knee and hip kinematics may be a more practical method of incorporating quadriceps hyperreflexia into the exoskeleton control loop than the more complex acquisition of muscle fiber properties.

Self-modulation of rectus femoris reflex excitability in humans

Hyperreflexia is common after neurological injury such as stroke, yet clinical interventions have had mixed success. Our previous research has shown that hyperreflexia of the rectus femoris (RF) during pre-swing is closely associated with reduced swing phase knee flexion in those with post-stroke Stiff-Knee gait (SKG). Thus, reduction of RF hyperreflexia may improve walking function in those with post-stroke SKG. A non-pharmacological procedure for reducing hyperreflexia has emerged based on operant conditioning of H-reflex, an electrical analog of the spinal stretch reflex. It is currently unknown whether operant conditioning can be applied to the RF. This feasibility study trained 7 participants (5 neurologically intact, 2 post-stroke) to down-condition the RF H-reflex using visual feedback. We found an overall decrease in average RF H-reflex amplitude among all 7 participants (44% drop, p < 0.001, paired t-test), of which the post-stroke individuals contributed (49% drop). We observed a generalized training effect across quadriceps muscles. Post-stroke individuals exhibited improvements in peak knee-flexion velocity, reflex excitability during walking, and clinical measures of spasticity. These outcomes provide promising initial results that operant RF H-reflex conditioning is feasible, encouraging expansion to post-stroke individuals. This procedure could provide a targeted alternative in spasticity management.

Stiff Knee Gait Disorders as Neuromechanical Consequences of Spastic Hemiplegia in Chronic Stroke

Stiff knee gait (SKG) is defined as decreased knee flexion during the swing phase. It is one of the most common gait disorders following stroke. Knee extensor spasticity is commonly accepted as the primary cause. Clinical management has focused on the reduction in knee extensor spasticity. Recent advances in understanding of post-stroke hemiplegic gait suggest that SKG can present as mechanical consequences between muscle spasticity, weakness, and their interactions with ground reactions during walking. Various underlying mechanisms are presented through sample cases in this article. They include ankle plantar flexor spasticity, knee extensor spasticity, knee flexor and extensor coactivation, and hip flexor spasticity. Careful and thorough clinical assessment is advised to determine the primary cause for each patient. Understanding of these various presentations of SKG is helpful to guide clinical assessment and select appropriate target muscles for interventions.

Altered biomechanical strategies of the paretic hip and knee joints during a step-up task

BACKGROUND

Stroke often leads to chronic motor impairments in the paretic lower limb that can constrain lower extremity movement and negatively impact the ability to navigate stairs or curbs. This cross-sectional study investigated the differences in hip and knee biomechanical strategies during a step-up task between five adults with hemiparetic stroke and five age-matched adults without stroke.

METHODS

Participants were instructed to step up onto a 10.2 cm platform, where joint biomechanics were quantified for the hip in the frontal plane and the hip and knee in the sagittal plane. Peak joint kinematics were identified during the leading limb swing phase, and peak joint moments and power were identified during the leading limb pull-up phase of stance. Mixed effects regression models estimated fixed effects of limb (three levels: control dominant, stroke non-paretic, and stroke paretic) on biomechanical outcomes, while a random effect of participant controlled for within-participant correlations.

RESULTS

Repeated assessments within participants (approximately 60 trials per lower limb) increased the effective sample size to between 12.0 and 19.6. Altered biomechanical strategies of the paretic lower limb included reduced flexion angles and increased pelvic obliquity angles during swing, decreased power generation in the hip frontal plane during stance, and decreased moment and power generation in the knee sagittal plane during stance. A strategy of substantial interest was the elevated hip sagittal plane moment and power generation in both stroke limbs.

CONCLUSIONS

Our findings suggest that chronic motor impairments following stroke can lead to inefficient biomechanical strategies when stepping up.

Treatment of spasticity

Spasticity is characterized by an enhanced size and reduced threshold for activation of stretch reflexes and is associated with "positive signs" such as clonus and spasms, as well as "negative features" such as paresis and a loss of automatic postural responses. Spasticity develops over time after a lesion and can be associated with reduced speed of movement, cocontraction, abnormal synergies, and pain. Spasticity is caused by a combination of damage to descending tracts, reductions in inhibitory activity within spinal cord circuits, and adaptive changes within motoneurons. Increased tone, hypertonia, can also be caused by changes in passive stiffness due to, for example, increase in connective tissue and reduction in muscle fascicle length. Understanding the cause of hypertonia is important for determining the management strategy as nonneural, passive causes of stiffness will be more amenable to physical rather than pharmacological interventions. The management of spasticity is determined by the views and goals of the patient, family, and carers, which should be integral to the multidisciplinary assessment. An assessment, and treatment, of trigger factors such as infection and skin breakdown should be made especially in people with a recent change in tone. The choice of management strategies for an individual will vary depending on the severity of spasticity, the distribution of spasticity (i.e., whether it affects multiple muscle groups or is more prominent in one or two groups), the type of lesion, and the potential for recovery. Management options include physical therapy, oral agents; focal therapies such as botulinum injections; and peripheral nerve blocks. Intrathecal baclofen can lead to a reduction in required oral antispasticity medications. When spasticity is severe intrathecal phenol may be an option. Surgical interventions, largely used in the pediatric population, include muscle transfers and lengthening and selective dorsal root rhizotomy.

Effects of dry needling intervention on lower limb dysfunction after stroke: study protocol for a randomised controlled trial

INTRODUCTION

Lower limb dysfunction is among the common sequelae of patients who had a poststroke and often results in the reduction of the quality of life. This study aims to assess the short and interim-term efficacy of dry needling (DN) intervention on lower extremity function, balance and gait in lower limb dysfunction after stroke.

METHODS AND ANALYSIS

This protocol entails an assessor and statistician-blinded, single-centre study with a randomised controlled trial. Forty-four patients who had a poststroke will be randomly allocated (1:1) to either the conventional treatment group (n=22) or the DN group (n=22). The conventional treatment group will receive conventional rehabilitation treatment once a day for 40 min each time. The treatment will be performed five times a week for 2 weeks. In the DN group, participants will be treated with DN on the basis of the conventional treatment. The intervention will be performed thrice a week for 2 weeks. The primary outcome that determines the efficacy of lower limb dysfunction will be the change in the Fugl-Meyer Assessment of Lower Extremity scale. The secondary indicators include the range of motion of knee and ankle joints, limits of stability, modified Clinical Test of Sensory Interaction on Balance, Timed Up and Go test, Modified Ashworth Scale and Barthel Index. Results will be evaluated at baseline, at 24 hours after intervention, at 2 weeks after intervention and at 3-month follow-up. Data will be released after the completion of the study. Adverse events will be reported.

ETHICS AND DISSEMINATION

The experiment was approved by the Ethical Committee of Shanghai Tong Ren Hospital in October 2021 (approval number: 202105702). The results of this study will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

ChiCTR2000040754.

Differences in causes of stiff knee gait in knee extensor activity or ankle kinematics: A cross-sectional study

BACKGROUND

Stiff knee gait (SKG), a common occurrence after the onset of stroke, is caused by hyperactivity of the rectus femoris during the swing phase. Another cause of SKG is the weakness of push-off in hemiparetic gait. Prior research did not consider the effect of the magnitude of knee extensors in their subjects.

RESEARCH QUESTION

Does the cause of SKG differ between patients with high and low knee extensor activities during the swing phase?

METHODS

We examined 38 patients with chronic stroke hemiplegia who presented with SKG. After placing an inertia sensor and an electromyogram, patients walked 10 m at a comfortable speed. All patients were categorized per the sign of the principal component 2 (PC2) as a component with large factor loadings of knee extensors attained from the electromyographic amplitude during the early swing phase of the paretic limb. Then, the kinematic parameters of knee flexion and other gait parameters in each group were compared, and a correlation analysis was performed.

RESULTS

In the high PC2 group, the timing of peak knee flexion during the swing phase was early, and vastus lateralis activity during the preswing phase negatively correlated with the knee-flexion angle during the swing phase. In the low PC2 group, the angular velocity of ankle plantar flexion at the toe-off was slow, which positively correlated with the knee-flexion angle during the swing phase.

SIGNIFICANCE

The cause of SKG could be an inappropriate activity of the vastus lateralis rather than the rectus femoris in patients with high knee extensor activity and slow plantar-flexion velocity at toe-off in patients with low knee extensor activity. Not all causes of SKG in patients with hemiplegia are common, and different treatment strategies are needed per the individuality of spastic knee extensor activity.

Biomechanical mechanism of peak braking force modulation during increased walking speed in healthy young adults

Walking speed is an important indicator of health and function across a variety of populations. Faster walking requires both larger propulsive and braking forces, thoughof the two, propulsive force generation has been far more extensively investigated. This study seeks to develop and validatea quasi-static biomechanical model of braking forcein healthy individualsacrossself-selected and fast walking speeds. Additionally, the model was used to quantify the relative contribution of knee extension torque versus leading limb angle (LLA) to changes in braking force across walking speeds. Kinetic and kinematic data from 44 young healthy participants walking overground at 2 different speeds were analyzed. The model prediction correlated strongly with actual braking force production at the self-selected speed (r = 0.9; p < 0.01), the fast speed (r = 0.97; p < 0.01) andthe change between speeds (r = 0.95, p < 0.01). On average, increases in knee extension torque and the LLA contributed 132 % and 12 %, respectively, to increases in peak braking force (PBF). Increases in the external lever arm length operated to reduce predicted braking force by 56 %. The results highlight the importance of rapid eccentric contraction of the knee extensors during braking force modulation in healthy gait.

Thigh and Shank, Kinetic and Potential Energies during Gait Swing Phase in Healthy Adults and Stroke Survivors

Background/Problem. Given the treatment-resistant gait deficits after stroke and known elevated energy cost of gait after stroke, it is important to study the patterns of mechanical energies of the lower limb segments. There is a dearth of information regarding mechanical energies specifically for the thigh and shank across the gait cycle. Therefore, the purpose of the current work was to characterize the following: (1) relative patterns of oscillation kinetic energy (KE) and potential energy (PE) within lower limb segments and across lower limb segments in healthy adults during the swing phase at chosen and slow gait speeds; (2) KE and PE swing phase patterns and values for stroke survivors versus healthy adults walking at slow speed; and (3) KE and PE patterns during the swing phase for two different compensatory gait strategies after stroke,. Methods. This was a gait characterization study, a two-group, parallel-cohort study of fourteen stroke survivors with gait deficits, walking at <0.4 m/s and eight adults with no gait deficits. For testing, the eight healthy adults walked at their chosen speed, and then at the imposed slow speed of <0.04 m/s. We used a standard motion capture system and calculation methods to acquire, calculate, and characterize oscillation patterns of KE and PE of the limb segments (thigh and shank) across the gait cycle. Results. In healthy adults, we identified key energy conservation mechanisms inherent in the interactions of KE and PE, both within the thigh and shank segments and across those limb segments, partially explaining the low cost of energy of the normal adult chosen speed gait pattern, and the underlying mechanism affording the known minimal set of activated muscles during walking, especially during the early swing phase. In contrast, KE was effectively absent for both healthy adults at imposed slow walking speed and stroke survivors at their very slow chosen speed, eliminating the normal conservation of energy between KE and PE within the thigh and across the thigh and shank. Moreover, and in comparison to healthy adult slow speed, stroke survivors exhibited greater abnormalities in mechanical energies patterns, reflected in either a compensatory stepping strategy (over-flexing the hip) or circumducting strategy (stiff-legged gait, with knee extended throughout the swing phase). Conclusions and contribution to the field. Taken together, these findings support targeted training to restore normal balance control and normal activation and de-activation coordination of hip, knee, and ankle muscles, respectively (agonist/antagonist at each joint), so as to eliminate the known post-stroke abnormal co-contractions; this motor training is critical in order to release the limb to swing normally in response to mechanical energies and afford the use of conservation of KE and PE energies within the thigh and across thigh and shank.

Muscle contributions to pre-swing biomechanical tasks influence swing leg mechanics in individuals post-stroke during walking

Background

Successful walking requires the execution of the pre-swing biomechanical tasks of body propulsion and leg swing initiation, which are often impaired post-stroke. While excess rectus femoris activity during swing is often associated with low knee flexion, previous work has suggested that deficits in propulsion and leg swing initiation may also contribute. The purpose of this study was to determine underlying causes of propulsion, leg swing initiation and knee flexion deficits in pre-swing and their link to stiff knee gait in individuals post-stroke.

Methods

Musculoskeletal models and forward dynamic simulations were developed for individuals post-stroke (n = 15) and healthy participants (n = 5). Linear regressions were used to evaluate the relationships between peak knee flexion, braking and propulsion symmetry, and individual muscle contributions to braking, propulsion, knee flexion in pre-swing, and leg swing initiation.

Results

Four out of fifteen of individuals post-stroke had higher plantarflexor contributions to propulsion and seven out of fifteen had higher vasti contributions to braking on their paretic leg relative to their nonparetic leg. Higher gastrocnemius contributions to propulsion predicted paretic propulsion symmetry (p = 0.005) while soleus contributions did not. Higher vasti contributions to braking in pre-swing predicted lower knee flexion (p = 0.022). The rectus femoris had minimal contributions to lower knee flexion acceleration in pre-swing compared to contributions from the vasti. However, for some individuals with low knee flexion, during pre-swing the rectus femoris absorbed more power and the iliopsoas contributed less power to the paretic leg. Total musculotendon work done on the paretic leg in pre-swing did not predict knee flexion during swing.

Conclusions

These results emphasize the multiple causes of propulsion asymmetry in individuals post-stroke, including low plantarflexor contributions to propulsion, increased vasti contributions to braking and reliance on compensatory mechanisms. The results also show that the rectus femoris is not a major contributor to knee flexion in pre-swing, but absorbs more power from the paretic leg in pre-swing in some individuals with stiff knee gait. These results highlight the need to identify individual causes of propulsion and knee flexion deficits to design more effective rehabilitation strategies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12984-022-01029-z.

Merged swing-muscle synergies and their relation to walking characteristics in subacute post-stroke patients: An observational study

In post-stroke patients, muscle synergy (the coordination of motor modules during walking) is impaired. In some patients, the muscle synergy termed module 1 (hip/knee extensors) is merged with module 2 (ankle plantar flexors), and in other cases, module 1 is merged with module 4 (knee flexors). However, post-stroke individuals with a merging pattern of module 3 (hip flexor and ankle dorsiflexor) and module 4, which is the swing-muscle synergy, have not been reported. This study aimed to determine the muscle-synergy merging subtypes of post-stroke during comfortable walking speed (cws). We also examined the effect of experimental lower-limb angle modulation on the muscle synergy patterns of walking in each subtype. Forty-one participants were assessed under three conditions: cws, long stepping on the paretic side (p-long), and long stepping on the non-paretic side (np-long). Lower-limb flexion and extension angles and the electromyogram were measured during walking. Subtype classification was based on the merging pattern of the muscle synergies, and we examined the effect of different lower-limb angles on the muscle synergies. We identified three merging subtypes: module 1 with module 2 (subtype 1), module 1 with module 4 (subtype 2), and module 3 with module 4 (subtype 3). In the cws condition, the lower-limb flexion angle was reduced in subtype 3, and the lower-limb extension angle was decreased in subtype 1. A more complex muscle synergy was observed only in subtype 3 in the p-long condition versus cws (p = 0.036). This subtype classification of walking impairments based on the merging pattern of the muscle synergies could be useful for the selection of a rehabilitation strategy according to the individual's particular neurological condition. Rehabilitation with increased lower-limb flexion may be effective for the training of patients with merging of modules 3 and 4 in comfortable walking.

Necessity and Content of Swing Phase Gait Coordination Training Post Stroke; A Case Report

Background/Problem: Standard neurorehabilitation and gait training has not proved effective in restoring normal gait coordination for many stroke survivors. Rather, persistent gait dyscoordination occurs, with associated poor function, and progressively deteriorating quality of life. One difficulty is the array of symptoms exhibited by stroke survivors with gait deficits. Some researchers have addressed lower limb weakness following stroke with exercises designed to strengthen muscles, with the expectation of improving gait. However, gait dyscoordination in many stroke survivors appears to result from more than straightforward muscle weakness.

PURPOSE

Thus, the purpose of this case study is to report results of long-duration gait coordination training in an individual with initial good strength, but poor gait swing phase hip/knee and ankle coordination.

METHODS

Mr. X was enrolled at >6 months after a left hemisphere ischemic stroke. Gait deficits included a 'stiff-legged gait' characterized by the absence of hip and knee flexion during right mid-swing, despite the fact that he showed good initial strength in right lower limb quadriceps, hamstrings, and ankle dorsiflexors. Treatment was provided 4 times/week for 1.5 h, for 12 weeks. The combined treatment included the following: motor learning exercises designed for coordination training of the lower limb; functional electrical stimulation (FES) assisted practice; weight-supported coordination practice; and over-ground and treadmill walking. The FES was used as an adjunct to enhance muscle response during motor learning and prior to volitional recovery of motor control. Weight-supported treadmill training was administered to titrate weight and pressure applied at the joints and to the plantar foot surface during stance phase and pre-swing phase of the involved limb. Later in the protocol, treadmill training was administered to improve speed of movement during the gait cycle. Response to treatment was assessed through an array of impairment, functional mobility, and life role participation measures.

RESULTS

At post-treatment, Mr. X exhibited some recovery of hip, knee, and ankle coordination during swing phase according to kinematic measures, and the stiff-legged gait was resolved. Muscle strength measures remained essentially constant throughout the study. The modified Ashworth scale showed improved knee extensor tone from baseline of 1 to normal (0) at post-treatment. Gait coordination overall improved by 12 points according to the Gait Assessment and Intervention Tool, Six Minute Walk Test improved by 532', and the Stroke Impact Scale improved by 12 points, including changes in daily activities; mobility; and meaningful activities.

DISCUSSION

Through the combined use of motor learning exercises, FES, weight-support, and treadmill training, coordination of the right lower limb improved sufficiently to exhibit a more normal swing phase, reducing the probability of falls, and subsequent downwardly spiraling dysfunction. The recovery of lower limb coordination during swing phase illustrates what is possible when strength is sufficient and when coordination training is targeted in a carefully titrated, highly incrementalized manner. Conclusions/Contribution to the Field: This case study contributes to the literature in several ways: (1) illustrates combined interventions for gait training and response to treatment; (2) provides supporting case evidence of relationships among knee flexion coordination, swing phase coordination, functional mobility, and quality of life; (3) illustrates that strength is necessary, but not sufficient to restore coordinated gait swing phase after stroke in some stroke survivors; and (4) provides details regarding coordination training and progression of gait training treatment for stroke survivors.

Effect of Leg Extension Angle on Knee Flexion Angle during Swing Phase in Post-Stroke Gait

Background and Objectives: Leg extension angle is important for increasing the propulsion force during gait and is a meaningful indicator for evaluating gait quality in stroke patients. Although leg extension angle during late stance might potentially also affect lower limb kinematics during the swing phase, the relationship between these two remains unclear. This study aimed to investigate the relationship between leg extension angle and knee flexion angle during pre-swing and swing phase in post-stroke gait. Materials and Methods: Twenty-nine stroke patients walked along a 16 m walkway at a self-selected speed. Tilt angles and acceleration of pelvis and paretic lower limb segments were measured using inertial measurement units. Leg extension angle, consisting of a line connecting the hip joint with the ankle joint, hip and knee angles, and increments of velocity during pre-swing and swing phase were calculated. Correlation analysis was conducted to examine the relationships between these parameters. Partial correlation analysis adjusted by the Fugl-Meyer assessment-lower limb (FMA-LL) was also performed. Results: On the paretic side, leg extension angle was positively correlated with knee flexion angle during the swing phase (r = 0.721, p < 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.740–0.846, p < 0.001). Partial correlation analysis adjusted by the FMA-LL showed significant correlation between leg extension angle and knee flexion angle during the swing phase (r = 0.602, p = 0.001) and knee flexion angle and increments of velocity during the pre-swing phase (r = 0.655–0.886, p < 0.001). Conclusions: Leg extension angle affected kinematics during the swing phase in post-stroke gait regardless of the severity of paralysis, and was similar during the pre-swing phase. These results would guide the development of effective gait training programs that enable a safe and efficient gait for stroke patients.

Predictive simulation of post-stroke gait with functional electrical stimulation

Post-stroke patients present various gait abnormalities such as drop foot, stiff-knee gait (SKG), and knee hyperextension. Functional electrical stimulation (FES) improves drop foot gait although the mechanistic basis for this effect is not well understood. To answer this question, we evaluated the gait of a post-stroke patient walking with and without FES by inverse dynamics analysis and compared the results to an optimal control framework. The effect of FES and cause-effect relationship of changes in knee and ankle muscle strength were investigated; personalized muscle–tendon parameters allowed the prediction of pathologic gait. We also predicted healthy gait patterns at different speeds to simulate the subject walking without impairment. The passive moment of the knee played an important role in the estimation of muscle force with knee hyperextension, which was decreased during FES and knee extensor strengthening. Weakening the knee extensors and strengthening the flexors improved SKG. During FES, weak ankle plantarflexors and strong ankle dorsiflexors resulted in increased ankle dorsiflexion, which reduced drop foot. FES also improved gait speed and reduced circumduction. These findings provide insight into compensatory strategies adopted by post-stroke patients that can guide the design of individualized rehabilitation and treatment programs.

Immediate Effect of Whole Body Vibration on Knee Extensor Tendon Stiffness in Hemiparetic Stroke Patients

Background and Objectives: Whole body vibration is widely used to enhance muscle performance, but evidence of its effects on the tendon stiffness of the knee extensor tendon in stroke remains inconclusive. Our study was aimed to determine the difference in patellar and quadriceps tendon stiffness between hemiparetic and unaffected limbs in stroke patients and to investigate the immediate effect of whole body vibration on tendon stiffness. Materials and Methods: The patellar and quadriceps tendon stiffness of first-ever hemiplegic stroke patients was evaluated with elastography to compare the differences between hemiparetic and unaffected limbs. After one 20 min session of whole body vibration exercise in the standing position, tendon stiffness was again measured to evaluate the immediate effects of whole body vibration on tendon stiffness. Results: The results showed no significant differences in the tendon stiffness of the patellar and quadriceps tendons between hemiparetic and unaffected limbs. However, significant associations were found between the tendon stiffness of the patellar and quadriceps tendons and knee extensor spasticity on the hemiparetic side (ρ = 0.62; p = 0.044). There were no significant changes in tendon stiffness after a single session of whole body vibration. Conclusions: In conclusion, knee extensor tendon stiffness in hemiparetic limbs is positively correlated to the degree of knee extensor spasticity in stroke patients. However, a single session of whole body vibration does not alter tendon stiffness.