Dynamics of lower limb & standing balance recovery early post-stroke : measurement, mechanisms and treatment

Abstract: Stroke is one of the main causes of serious adult disability in Europe. Approximately 80% of people after a stroke suffer from motor impairments, typically affecting unilateral motor control of the face, arm, and leg; this condition is referred to as hemiplegia. These impairments cause poor execution of balance control with a resultant elevated risk of falls. Therefore, improving balance control is a cornerstone of stroke rehabilitation when aiming to improve activities of daily life and enable home discharge. Most patients show spontaneous motor recovery of the hemiplegic leg in the initial weeks post-stroke, measured with, for example, the Fugl-Meyer (FM-LE) and the Motricity Index lower extremity subscale (MI-LE). Unfortunately, how these unilateral motor improvements contribute to recovery in balance control during complex tasks as standing has not been thoroughly investigated. To this end, it is crucial to acknowledge that task improvements may be compensatory by relying on the less-affected limb, as typically observed in this population. Improving our knowledge of behavioural recovery mechanisms after stroke requires well-designed longitudinal studies with instrumented measurements. For example, center of pressure (COP) movements may serve as a biomechanical measure of individual limb contributions to standing balance, called the dynamic control asymmetry (DCA). These measures may overcome limitations of traditional clinical outcomes, such as the Berg Balance Scale, which cannot distinguish re-emergence of more \u201cnormal\u201d movement patterns \u2013 a process called behavioural restitution \u2013 from compensatory strategies. Hence, kinematics and kinetics applied serially in time are the only way to capture quality of movement (QoM) during tasks, and changes therein due to motor recovery or an intervention. This thesis describes the design of an observational study, the TARGEt-1 trial, which unravels the finer-grained changes in balance performance early post-stroke. We chose a quiet standing task with relatively low functional demands to start measurements as early as 3 weeks post-stroke and relate subsequent performance changes to ongoing motor recovery (FM-LE and MI-LE) at 5-, 8-, and 12-weeks post-stroke follow-up. In total, 60 first-ever stroke survivors participated in TARGEt-1, of which 48 were tested on sufficient occasions to be included in the analyses. Consistent with the literature, we found significant FM-LE and MI-LE improvements post-stroke, which were most pronounced in the first 5-8 weeks. During the same period, patients exhibited improvements in their postural stability while standing. However, when observed within subjects, reductions in intralimb motor impairments were not significantly associated with improved postural stability, or with changes in DCA and weight-bearing asymmetry (WBA). In fact, DCA and WBA were quite invariant for change and remained significantly different from normative symmetry scores. Hence, QoM did not normalize, and behavioural restitution of motor functions in the hemiplegic limb appears to hardly contribute to balance improvements. Rather, early balance improvements post-stroke seem to reflect optimizing compensations with the less-affected limb. The innate ability of the brain to undergo plastic changes raises the question of how to capitalize on an enhanced state of brain plasticity early post-stroke. Clinical evidence emphasizes the amount of task practice to improve daily activities. Likewise, a literature review with meta-analyses (15 studies, 915 subjects) described in this thesis found that starting higher training intensities within the first month post-stroke \u2013 the critical period for motor recovery \u2013 is safe and likely important for promoting walking independence. This may involve the use of therapeutic robots that enable training in patients when otherwise not feasible. A subsequent pilot rehabilitation study, the TARGEt-2 trial, involved 19 stroke patients. Here, we hypothesized that restorative effects of additional training with a wearable exoskeleton \u2013 a bilateral robotic orthosis that steers the lower limb in symmetric patterns \u2013 are enhanced if delivered within the first 5 weeks post-stroke, when compared with a delayed delivery 8 weeks post-stroke. However, our findings suggest that robotic exercises were generally ineffective in enhancing FM-LE scores beyond spontaneous recovery. Therefore, we were unable to reduce compensations with the less-affected leg, even if robotic training was applied during the critical recovery period. In this thesis, we suggest that current robotic designs that focus on \u201ccorrecting\u201d kinematics to mimic trajectories as seen in healthy controls are inadequate. After all, the enforced symmetric gait patterns hardly allow adaptions in which patients develop compensatory movements to optimally cope with existing deficits. Although our results suggest that even \u201cwell-recovered\u201d patients may rely on behavioural compensation with the less-affected limb to recover balance, this needs further investigation, including more difficult balance tasks. Only then can we judge whether a patient\u2019s preferred asymmetry is actually beneficial in improving activities and preventing falls, and whether these adaptions should be encouraged early during rehabilitation to enable home discharge

Time course and mechanisms underlying standing balance recovery early after stroke : design of a prospective cohort study with repeated measurements

INTRODUCTION: Although most stroke survivors show some spontaneous neurological recovery from motor impairments of the most-affected leg, the contribution of this leg to standing balance control remains often poor. Consequently, it is unclear how spontaneous processes of neurological recovery contributes to early improvements in standing balance. OBJECTIVE: We aim to investigate (1) the time course of recovery of quiet stance balance control in the first 12 weeks poststroke and (2) how clinically observed improvements of lower limb motor impairments longitudinally relate to this limb's relative contribution to balance control. METHODS AND ANALYSIS: In this prospective longitudinal study, a cohort of 60 adults will be recruited within the first 3 weeks after a first-ever hemispheric stroke and mild-to-severe motor impairments. Individual recovery trajectories will be investigated by means of repeated measurements scheduled at 3, 5, 8, and 12 weeks poststroke. The Fugl-Meyer Motor Assessment and Motricity Index of the lower limb serve as clinical measures of motor impairments at the hemiplegic side. As soon as subjects are able to stand independently, bilateral posturography during quietly standing will be measured. First, the obtained center-of-pressure (COP) trajectories at each foot will be used for synchronization and contribution measures that establish (a-)symmetries between lower limbs. Second, the COP underneath both feet combined will be used to estimate overall stability. Random coefficient analyses will be used to model time-dependent changes in these measures and, subsequently, a hybrid model will be used to investigate longitudinal associations with improved motor impairments. DISCUSSION: The current study aims to investigate how stroke survivors “re-learn” to maintain standing balance as an integral part of daily life activities. The knowledge gained through this study may contribute to recommending treatment strategies for early stroke rehabilitation targeting behavioral restitution of the most-affected leg or learning to compensate with the less-affected leg

The association between visuospatial neglect and balance and mobility post-stroke onset : a systematic review

BACKGROUND: Although previous narrative reviews have highlighted a potential association between visuospatial neglect (VSN) and balance disorders, to what extent different areas of balance and mobility could be affected is still unclear. OBJECTIVES: This systematic review updates previous literature findings and systematically reviews sitting balance, standing balance and mobility outcomes. METHODS: PubMed, Web of Science, ScienceDirect, Naric-Rehabdata, PEDro and the Cochrane Trials Library were systematically searched. Methodological quality was assessed by the National Heart, Lung, and Blood Institute Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. The association between VSN and sitting balance, standing balance and mobility (walking, stair climbing/descending and transfers) was investigated. RESULTS: In total, 48 studies were included (4595 stroke survivors): at least 1319 (29%) showed symptoms of VSN. VSN was associated with less independence during sitting, with an asymmetric posture toward the affected body side. For standing balance, we revealed a significant negative association between VSN and mediolateral stability and weight shifting, whereas only activities of daily living-related VSN was associated with weight-bearing asymmetry during static stance. While walking, patients with VSN laterally deviated from their path. Results were inconclusive regarding other aspects of mobility. The association between VSN and balance/mobility seemed to decrease over time. CONCLUSIONS: Despite great heterogeneity in results, this study suggests that stroke survivors with VSN show specific deviations in posture and movement in the mediolateral direction. Although the association between VSN and balance/mobility has been extensively investigated, explanatory studies evaluating underlying mechanisms of the frequently present association are lacking. Future studies should address this by combining clinical and instrumented assessment of balance and gait performance, preferably longitudinally to investigate the associations over time

Lower limb muscle synergies during walking after stroke : a systematic review

Purpose: The aim of this systematic review was to determine the number of muscle synergies and the distribution of muscle weightings in stroke patients during gait. Material and Methods: This review is registered on PROSPERO (number: CRD42018088701) and is written following the PRISMA guidelines. A systematic search was conducted using following databases: PubMed, Web of Science, Naric, Cochrane and PEDro. Methodological quality was assessed by the Newcastle-Ottawa Scale and data extraction (subject characteristics, outcome measures and walking protocols) was performed by two independent researchers. The amount and structure of the muscle synergies were the two main outcome measures. Results: In total, ten studies were included in this review. While four synergies are common in healthy controls, stroke patients often showed less synergies during gait. Synergies were determined by the number of muscles measured which varied greatly between studies. Only Tibialis Anterior, Soleus, Gastrocnemius and Rectus Femoris were assessed in all studies. Conclusions: A consensus regarding the amount and composition of muscle synergies in stroke patients is difficult. The majority observed three to four muscle synergies. The decrease in amount of synergies can be explained by merging of synergies, often seen in hip/knee extensors with plantar flexors and hip/knee extensors with knee flexors.IMPLICATIONS FOR REHABILITATIONMuscle synergy analyses are a powerful tool for assessing and classifying neurological deficits.A decreased amount of muscle synergies is related to impaired motor function.Differences in coordinated muscle activity was seen in the paretic and non-paretic side.Merging was often seen in hip/knee extensors with plantar flexors and hip/knee extensors with knee flexors. Muscle synergy analyses are a powerful tool for assessing and classifying neurological deficits. A decreased amount of muscle synergies is related to impaired motor function. Differences in coordinated muscle activity was seen in the paretic and non-paretic side. Merging was often seen in hip/knee extensors with plantar flexors and hip/knee extensors with knee flexors.</p