Pathophysiological mechanisms in cerebral palsy

Combined translational and rotational perturbations of standing balance reveal contributions of reduced reciprocal inhibition to balance impairments in children with cerebral palsy

Balance impairments are common in cerebral palsy. When balance is perturbed by backward support surface translations, children with cerebral palsy have increased co-activation of the plantar flexors and tibialis anterior muscle as compared to typically developing children. However, it is unclear whether increased muscle co-activation is a compensation strategy to improve balance control or is a consequence of reduced reciprocal inhibition. During translational perturbations, increased joint stiffness due to co-activation might aid balance control by resisting movement of the body with respect to the feet. In contrast, during rotational perturbations, increased joint stiffness will hinder balance control as it couples body to platform rotation. Therefore, we expect increased muscle co-activation in response to rotational perturbations if co-activation is caused by reduced reciprocal inhibition but not if it is merely a compensation strategy. We perturbed standing balance by combined backward translational and toe-up rotational perturbations in 20 children with cerebral palsy and 20 typically developing children. Perturbations induced forward followed by backward movement of the center of mass. We evaluated reactive muscle activity and the relation between center of mass movement and reactive muscle activity using a linear feedback model based on center of mass kinematics. In typically developing children, perturbations induced plantar flexor balance correcting muscle activity followed by tibialis anterior balance correcting muscle activity, which was driven by center of mass movement. In children with cerebral palsy, the switch from plantar flexor to tibialis anterior activity was less pronounced than in typically developing children due to increased muscle co-activation of the plantar flexors and tibialis anterior throughout the response. Our results thus suggest that a reduction in reciprocal inhibition causes muscle co-activation in reactive standing balance in children with cerebral palsy.

Increased muscle responses to balance perturbations in children with cerebral palsy can be explained by increased sensitivity to center of mass movement

BACKGROUND

Balance impairments are common in children with cerebral palsy (CP). Muscle activity during perturbed standing is higher in children with CP than in typically developing (TD) children, but we know surprisingly little about how sensorimotor processes for balance control are altered in CP. Sensorimotor processing refers to how the nervous system translates incoming sensory information about body motion into motor commands to activate muscles. In healthy adults, muscle activity in response to backward support-surface translations during standing can be reconstructed by center of mass (CoM) feedback, i.e., by a linear combination of delayed (due to neural transmission times) CoM displacement, velocity, and acceleration. The level of muscle activity in relation to changes in CoM kinematics, i.e., the feedback gains, provides a metric of the sensitivity of the muscle response to CoM perturbations.

RESEARCH QUESTION

Can CoM feedback explain reactive muscle activity in children with CP, yet with higher feedback gains than in TD children?

METHODS

We perturbed standing balance by backward support-surface translations of different magnitudes in 20 children with CP and 20 age-matched TD children and investigated CoM feedback pathways underlying reactive muscle activity in the triceps surae and tibialis anterior.

RESULTS

Reactive muscle activity could be reconstructed by delayed feedback of CoM kinematics and hence similar sensorimotor pathways might underlie balance control in children with CP and TD children. However, sensitivities of both agonistic and antagonistic muscle activity to CoM displacement and velocity were higher in children with CP than in TD children. The increased sensitivity of balance correcting responses to CoM movement might explain the stiffer kinematic response, i.e., smaller CoM movement, observed in children with CP.

SIGNIFICANCE

The sensorimotor model used here provided unique insights into how CP affects neural processing underlying balance control. Sensorimotor sensitivities might be a useful metric to diagnose balance impairments.

Reduced reciprocal inhibition during clinical tests of spasticity is associated with impaired reactive standing balance control in children with cerebral palsy

Background

Joint hyper-resistance is a common symptom in cerebral palsy (CP). It is assessed by rotating the joint of a relaxed patient. Joint rotations also occur when perturbing functional movements. Therefore, joint hyper-resistance might contribute to reactive balance impairments in CP.

Aim

To investigate relationships between altered muscle responses to isolated joint rotations and perturbations of standing balance in children with CP.

Methods & procedures

20 children with CP participated in the study. During an instrumented spasticity assessment, the ankle was rotated as fast as possible from maximal plantarflexion towards maximal dorsiflexion. Standing balance was perturbed by backward support-surface translations and toe-up support-surface rotations. Gastrocnemius, soleus, and tibialis anterior electromyography was measured. We quantified reduced reciprocal inhibition by plantarflexor-dorsiflexor co-activation and the neural response to stretch by average muscle activity. We evaluated the relation between muscle responses to ankle rotation and balance perturbations using linear mixed models.

Outcomes & results

Co-activation during isolated joint rotations and perturbations of standing balance was correlated across all levels. The neural response to stretch during isolated joint rotations and balance perturbations was not correlated.

Conclusions & implications

Reduced reciprocal inhibition during isolated joint rotations might be a predictor of altered reactive balance control strategies.

Neurophysiological Assessments of Brain and Spinal Cord Associated with Lower Limb Functions in Children with Cerebral Palsy: A Protocol for Systematic Review and Meta-Analysis

Background: Task-dependent neurophysiological adaptations in people with cerebral palsy have been examined using various techniques such as functional magnetic resonance imaging, peripheral nerve stimulation in order to assess H-reflexes, and transcranial magnetic stimulation. This activity-dependent plasticity is hypothesized to improve specific gross motor function in individuals with cerebral palsy. Although these adaptations have been examined extensively, most studies examined tasks utilizing the upper limbs. The aim of this review is to assess the neurophysiological adaptations of the central nervous system in individuals with cerebral palsy during lower limb functional tasks. Methods: A systematic review and meta-analysis will be conducted to evaluate the neurophysiological changes in the brain and spinal cord associated with lower extremity tasks in individuals with cerebral palsy. We will search within PubMed, MEDLINE, Embase, PsychINFO, and CINAHL using a predetermined search string to identify and evaluate relevant studies. Two independent reviewers will screen these studies against our inclusion criteria and risks of bias, and will extract the data from each study. A third reviewer will be used to resolve any disagreement regarding the inclusion of a study between reviewers. Randomized controlled trials as well as cross-sectional studies published in English 10 years before May 2021 that investigate the neurophysiological adaptations in the brain and spinal cord in people with cerebral palsy will be included if they meet the eligibility criteria. Primary outcomes will include scalar values of fractional anisotropy (FA), H-reflex gains or measures of amplitude, as well as motor cortex (M1) cortical excitability as measured by transcranial magnetic stimulation. Discussion: Since no identifiable data will be involved in this study, no ethical approval is required. Our results will provide insight into the neurophysiological adaptations in children with cerebral palsy, which will be useful in guiding directions for clinical decision making and future development of targeted interventions in pediatrics rehabilitation for children with cerebral palsy. Systematic review registration: The protocol for this systematic review is registered with the International Prospective Register of Systematic Reviews (PROSPERO; registration number: CRD42020215902).

Effect of whole-body vibration on abdominal thickness and sitting ability in children with spastic diplegia

Objective

Reduced muscle and bone mass, improper muscle function, and varying degrees of mobility dysfunctions are the main complications of cerebral palsy (CP). Many children with CP also present with poor abdominal muscle activation. Whole-body vibration (WBV) is a unique approach for enhancing strength and motor abilities in several clinical conditions. This study aimed to determine the influence of a 12-week WBV intervention on the thickness of the abdominal muscles and the sitting ability of children with diplegia.

Methods

A total of 30 children with spastic diplegic CP (aged 4–6 years) were randomly divided into two groups (control and experimental). The control group received a selected physical therapy program for 1 h, and the study group received WBV training for 10 min in addition to the same selected program for the control group for 3 times/week over a period of 12 weeks. Thereafter, abdominal muscle thickness and sitting ability were measured using ultrasonography and the Gross Motor Function Measure-88 (GMFM-88, sitting domain).

Results

Post treatment values revealed significant improvement in the measured variables in favour of the experimental group (p < 0.05), as there was improvement in the thickness of the four abdominal muscles compared to the control group (external oblique: F = 38.783; internal oblique: F = 99.547; transverse abdominis: F = 111.557, and rectus abdominis: F = 129.940, p < 0.05). Additionally, the study group showed a significantly greater improvement in GMFM-88 values compared to the control group (F = 129.940, p < 0.05).

Conclusion

WBV can be a viable strategy for improving sitting ability and abdominal muscle thickness among children with spastic diplegia.

Clinical Relevance of State-of-the-Art Analysis of Surface Electromyography in Cerebral Palsy

Surface electromyography (sEMG) can be used to assess the integrity of the neuromuscular system and its impairment in neurological disorders. Here we will consider several issues related to the current clinical applications, difficulties and limited usage of sEMG for the assessment and rehabilitation of children with cerebral palsy. The uniqueness of this methodology is that it can determine hyperactivity or inactivity of selected muscles, which cannot be assessed by other methods. In addition, it can assist for intervention or muscle/tendon surgery acts, and it can evaluate integrated functioning of the nervous system based on multi-muscle sEMG recordings and assess motor pool activation. The latter aspect is especially important for understanding impairments of the mechanisms of neural controllers rather than malfunction of individual muscles. Although sEMG study is an important tool in both clinical research and neurorehabilitation, the results of a survey on the clinical relevance of sEMG in a typical department of pediatric rehabilitation highlighted its limited clinical usage. We believe that this is due to limited knowledge of the sEMG and its neuromuscular underpinnings by many physiotherapists, as a result of lack of emphasis on this important methodology in the courses taught in physical therapy schools. The lack of reference databases or benchmarking software for sEMG analysis may also contribute to the limited clinical usage. Despite the existence of educational and technical barriers to a widespread use of, sEMG does provide important tools for planning and assessment of rehabilitation treatments for children with cerebral palsy.

Gait synergetic neuromuscular control in children with cerebral palsy at different gross motor function classification system levels

Cerebral palsy (CP) is a neural developmental disease featured with gait abnormalities. CP gait assessment is usually performed with the Gross Motor Function Classification System (GMFCS) in clinics, which does not involve a thorough assessment of neuromuscular control. To understand how the neuromuscular control disorders lead to gait abnormalities, we explored the relationship between GMFCS levels and the gait synergetic control characteristics in this study. In total, 18 children with CP at different GMFCS levels (mean age: 4.41±1.30 yr) and 8 age-matched typically developing (TD) children (mean age: 4.43±1.36 yr) were recruited to perform a straight walking task, and the surface electromyographic (sEMG) signals from eight lower limb muscles on each side and accelerometer data were collected. A nonnegative matrix factorization method was applied to obtain the muscle synergies from the sEMG signals. Next, synergy structures were projected onto the basic gait synergies to test the completeness of those structures. Subsequently, synergy activation parameters, including total activation duration and coactivation index, were compared across the participants. This study showed that children with CP at GMFCS levels I and II and the TD children had similar synergy structures, but the synergy activations of these children with CP were different from those of TD children. In addition, similar to previous research, we also found that children with CP at GMFCS level III could not access all four basic synergies on both sides. Based on the synergy analysis results, a gait assessment paradigm was proposed to facilitate the clinical CP gait evaluation.

NEW & NOTEWORTHY Understanding the mechanism of gait abnormality has important clinical significance for the diagnosis, prognosis, and possible treatment of motor dysfunction in children with cerebral palsy (CP). In this study, the comparisons of the lower limb muscle synergies among different groups of children with CP at different Gross Motor Function Classification System levels might provide some new insight into the mechanism underlying the gait disorder. In particular, the discrepancies of gait synergy structure and activation patterns across the study groups may indicate different neurophysiological and pathological attributes in different groups of patients.

Bimanual coordination during a physically coupled task in unilateral spastic cerebral palsy children

Background

Single object bimanual manipulation, or physically-coupled bimanual tasks, are ubiquitous in daily lives. However, the predominant focus of previous studies has been on uncoupled bimanual actions, where the two hands act independently to manipulate two disconnected objects. In this paper, we explore interlimb coordination among children with unilateral spastic cerebral palsy (USCP), by investigating upper limb motor control during a single object bimanual lifting task.

Methods

15 children with USCP and 17 typically developing (TD) children performed a simple single-object bimanual lifting task. The object was an instrumented cube that can record the contact force on each of its faces alongside estimating its trajectory during a prescribed two-handed lifting motion. The subject’s performance was measured in terms of the duration of individual phases, linearity and monotonicity of the grasp-to-load force synergy, interlimb force asymmetry, and movement smoothness.

Results

Similar to their TD counterparts, USCP subjects were able to produce a linear grasp-to-load force synergy. However, they demonstrated difficulties in producing monotonic forces and generating smooth movements. No impairment of anticipatory control was observed within the USCP subjects. However, our analysis showed that the USCP subjects shifted the weight of the cube onto their more-abled side, potentially to minimise the load on the impaired side, which suggests a developed strategy of compensating for inter-limb asymmetries, such as muscle strength.

Conclusion

Bimanual interaction with a single mutual object has the potential to facilitate anticipation and sequencing of force control in USCP children unlike previous studies which showed deficits during uncoupled bimanual actions. We suggest that this difference could be partly due to the provision of adequate cutaneous and kinaesthetic information gathered from the dynamic exchange of forces between the two hands, mediated through the physical coupling.

Full Activation Profiles and Integrity of Corticospinal Pathways in Adults With Bilateral Spastic Cerebral Palsy

Background. Dysfunction of corticospinal pathways has been implicated in motor impairments in people with bilateral spastic cerebral palsy (CP). While structural damage to corticospinal pathways in people with CP is known, its impact on the activation of these pathways is not. Objective. To provide the first, complete activation profile of corticospinal pathways in adults with CP using a full range of transcranial magnetic stimulation (TMS) intensities and voluntary contractions. Methods. TMS targeted the soleus muscle of 16 adults with bilateral spastic CP and 15 neurologically intact (NI) control participants. Activation profiles were generated using motor-evoked potentials (MEPs) produced by varying both stimulation intensity and degree of voluntary muscle activity. Anatomical integrity of corticospinal pathways was also measured with diffusion tractography. Results. Participants with CP had smaller MEPs produced by TMS at 1.2× active motor threshold during submaximal (20%) muscle activity and smaller maximal MEPs produced under any combination of stimulation intensity and voluntary muscle activity. At a fixed stimulation intensity, increasing voluntary muscle activity facilitated MEP amplitudes to a lesser degree in the participants with CP. Consistent differences in diffusion tractography suggested structural abnormalities in the corticospinal pathways of participants with CP that correlated with maximal MEPs. Conclusion. People with bilateral spastic CP have impaired activation of low and high-threshold corticospinal pathways to soleus motoneurons by TMS and reduced facilitation by voluntary activity that may be associated with structural damage to these pathways. These impairments likely contribute to impaired voluntary movement.

Vibration therapy in patients with cerebral palsy: a systematic review

The neurological disorder cerebral palsy (CP) is caused by unprogressive lesions of the immature brain and affects movement, posture, and the musculoskeletal system. Vibration therapy (VT) is increasingly used to reduce the signs and symptoms associated with this developmental disability. The purpose of this narrative review was systematically to appraise published research regarding acute and long-term effects of VT on functional, neuromuscular, and structural parameters. Systematic searches of three electronic databases identified 28 studies that fulfilled the inclusion criteria. Studies were analyzed to determine participant characteristics, VT-treatment protocols, effect on gross motor function (GMF), strength, gait, posture, mobility, spasticity, reflex excitability, muscle tone, mass, and bone strength within this population, and outcome measures used to evaluate effects. The results revealed that one acute session of VT reduces reflex excitability, spasticity, and coordination deficits. Subsequently, VT has a positive effect on the ability to move, manifested for GMF, strength, gait, and mobility in patients with CP. Effects persist up to 30 minutes after VT. Long-term effects of VT manifest as reduced muscle tone and spasticity occurring concomitantly with improved movement ability in regard to GMF, strength, gait, and mobility, as well as increased muscle mass and bone-mineral density. Posture control remained unaffected by VT. In conclusion, the acute and chronic application of VT as a nonpharmacological approach has the potential to ameliorate CP symptoms, achieving functional and structural adaptations associated with significant improvements in daily living. Even though further studies including adult populations validating the neuromuscular mechanisms underlying the aforementioned adaptations should be fostered, growing scientific evidence supports the effectiveness of VT in regard to supplementing conventional treatments (physiotherapy and drugs). Therefore, VT could reduce CP-associated physical disability and sensorimotor handicaps. Goals for patients and their caregivers referring to greater independence and improved safety may be achieved more easily and time efficiently.

Spinal inhibition and motor function in adults with spastic cerebral palsy

KEY POINTS

Abnormal activation of motoneurons in the spinal cord by sensory pathways is thought to contribute to impaired movement control and spasticity in individuals with cerebral palsy. Here we use single motor unit recordings to show how individual motoneurons in the spinal cord respond to sensory inputs in a group of participants with cerebral palsy having different degrees of motor dysfunction. In participants who had problems walking independently and required assistive devices such as wheelchairs, sensory pathways only excited motoneurons in the spinal cord. In contrast, in participants with cerebral palsy who walked independently for long distances, sensory inputs both inhibited and excited motoneurons in the spinal cord, similar to what we found in uninjured control participants. These findings demonstrate that in individuals with severe cerebral palsy, inhibitory control of motoneurons from sensory pathways is reduced and may contribute to motor dysfunction and spasticity.

ABSTRACT

Reduced inhibition of spinal motoneurons by sensory pathways may contribute to heightened reflex activity, spasticity and impaired motor function in individuals with cerebral palsy (CP). To measure if the activation of inhibitory post-synaptic potentials (IPSPs) by sensory inputs is reduced in CP, the tonic discharge rate of single motor units from the soleus muscle was plotted time-locked to the occurrence of a sensory stimulation to produce peri-stimulus frequencygrams (PSFs). Stimulation to the medial arch of the foot was used to activate cutaneomuscular afferents in 17 adults with bilateral spastic CP and 15 neurologically intact (NI) peers. Evidence of IPSP activation from the PSF profiles, namely a marked pause or reduction in motor unit firing rates at the onset of the cutaneomuscular reflex, was found in all NI participants but in only half of participants with CP. In the other half of the participants with CP, stimulation of cutaneomuscular afferents produced a PSF profile indicative of a pure excitatory post-synaptic potential, with firing rates increasing above the mean pre-stimulus rate for 300 ms or more. The amplitude of motoneuron inhibition during the period of IPSP activation, as measured from the surface EMG, was less in participants with poor motor function as evaluated with the Gross Motor Functional Classification System (r = 0.72, P < 0.001) and the Functional Mobility Scale (r = -0.82, P < 0.001). These findings demonstrate that in individuals with CP, reduced activation of motoneuron IPSPs by sensory inputs is associated with reduced motor function and may contribute to enhanced reflexes and spasticity in CP.

Abnormal coactivation of knee and ankle extensors is related to changes in heteronymous spinal pathways after stroke

BACKGROUND

Abnormal coactivation of leg extensors is often observed on the paretic side of stroke patients while they attempt to move. The mechanisms underlying this coactivation are not well understood. This study (1) compares the coactivation of leg extensors during static contractions in stroke and healthy individuals, and (2) assesses whether this coactivation is related to changes in intersegmental pathways between quadriceps and soleus (Sol) muscles after stroke.

METHODS

Thirteen stroke patients and ten healthy individuals participated in the study. Levels of coactivation of knee extensors and ankle extensors were measured in sitting position, during two tasks: maximal isometric voluntary contractions in knee extension and in plantarflexion. The early facilitation and later inhibition of soleus voluntary EMG evoked by femoral nerve stimulation were assessed in the paretic leg of stroke participants and in one leg of healthy participants.

RESULTS

Coactivation levels of ankle extensors (mean ± SEM: 56 ± 7% of Sol EMG max) and of knee extensors (52 ± 10% of vastus lateralis (VL) EMG max) during the knee extension and the ankle extension tasks respectively were significantly higher in the paretic leg of stroke participants than in healthy participants (26 ± 5% of Sol EMG max and 10 ± 3% of VL EMG max, respectively). Early heteronymous facilitation of Sol voluntary EMG in stroke participants (340 ± 62% of Sol unconditioned EMG) was significantly higher than in healthy participants (98 ± 34%). The later inhibition observed in all control participants was decreased in the paretic leg. Levels of coactivation of ankle extensors during the knee extension task were significantly correlated with both the increased facilitation (Pearson r = 0.59) and the reduced inhibition (r = 0.56) in the paretic leg. Measures of motor impairment were more consistently correlated with the levels of coactivation of biarticular muscles than those of monoarticular muscles.

CONCLUSION

These results suggest that the heteronymous pathways linking quadriceps to soleus may participate in the abnormal coactivation of knee and ankle extensors on the paretic side of stroke patients. The motor impairment of the paretic leg is strongly associated with the abnormal coactivation of biarticular muscles.

Trunk use and co-contraction in cerebral palsy as regulatory mechanisms for accuracy control

In the present study, we examined whether individuals with cerebral palsy (CP) systematically vary motion of the trunk and co-contraction in the upper limb as a function of accuracy demands. Four participants with spastic tetraparesis, four with spastic hemiparesis, and four healthy controls were asked to repeatedly move a spoon back-and-forth between two target locations. The task was externally paced. In half the trials the accuracy demands were increased by filling the spoon with water. In addition, a condition in which the trunk was fixated was examined. When the movements were controlled for speed, trunk motion hardly varied as a function of accuracy. Co-contraction in the shoulder, however, was systematically higher under high-accuracy demands. Trunk fixation yielded differential group effects on the co-contraction of the shoulder muscles. It increased in control participants, tended to decrease in hemiparetic participants, and was unaffected in tetraparetic participants. Collectively, the present findings show that the increased trunk involvement and high co-contraction levels in CP should not exclusively be regarded as disorder-related phenomena. Regulation of co-contraction in the shoulder is a general strategy to cope with variations in movement-accuracy constraints, while increased trunk involvement proves a secondary reaction to these constraints.

Correlation of polyelectromyographic patterns and clinical motor manifestations in children with cerebral palsy

OBJECTIVE

We investigated the correlation between movement patterns, measured by polyelectromyography (PEMG), and clinical motor manifestations in children with cerebral palsy.

DESIGN

Subjects included 53 children with spastic cerebral palsy (diplegic [n = 43] and quadriplegic [n = 10] groups) and 18 normal children. All children underwent PEMG assessments, recorded from pairs of flexor/extensor muscles during voluntary movement. We correlated PEMG patterns with clinical motor assessments, including muscle tone, range of motion, and ambulatory and functional capacities in the children with cerebral palsy.

RESULTS

Children with cerebral palsy exhibited four distinct PEMG patterns, ranging from partial reciprocal to complete synchrony. Lower PEMG pattern scores were significantly associated with better ambulatory (rho = 0.88, P < 0.01) and functional (rho = 0.78, P < 0.01) capacities. PEMG patterns also had weakly positive relationships with muscle tone (rho > 0.33, P < 0.01) and range of motion of both lower limbs (rho > 0.31, P < 0.01). Most children of spastic diplegia with PEMG patterns II and III had independent ambulatory capacities and mild limitation of functional capacity, whereas most children with pattern of IV and V had no ambulatory abilities and no independent functional capacities (P < 0.01).

CONCLUSIONS

These findings suggest that PEMG patterns correlate with clinical motor deficits and may allow us to plan treatment strategies based on underlying motor control in cerebral palsy.

Objective measurement of muscle strength in children with spastic diplegia after selective dorsal rhizotomy

OBJECTIVES

To examine changes in isometric muscle strength at the elbow, knee, and ankle at 6 months and 1 year after selective dorsal rhizotomy (SDR) and to determine if SDR altered the frequency of muscle cocontraction.

DESIGN

Prospective outcome study of a consecutive sample.

SETTING

Children's hospital.

PATIENTS

Ten children with spastic diplegia (7 independent and 3 dependent ambulators who used assistive devices) and 8 age-matched controls.

INTERVENTIONS

SDR; physical and occupational therapy; elbow, knee, and ankle measured for flexion and extension strength during three 10-second isometric contractions for each muscle group; and monitored cocontraction measured via muscle electrodes.

MAIN OUTCOME MEASURES

Absolute and normalized values of isometric strength; and alterations in the frequency of cocontraction at 6 months and 1 year postoperatively.

RESULTS

Children with spastic diplegia showed significantly weaker knee extensors, ankle dorsiflexors, and ankle plantarflexors than age-matched controls. There were no significant differences in strength between the 2 groups in the elbow flexors, elbow extensors, and knee flexors. Isometric strength did not increase or decrease significantly after SDR. Cocontraction during knee extension was normalized after SDR, whereas cocontraction during ankle plantarflexion was unchanged by SDR in the majority of children.

CONCLUSION

SDR did not result in a significant decrease in muscle strength in ambulatory children with spastic diplegia. The normalization of the electromyographic patterns at the knee and not the ankle after SDR lends support to the premise that in children with cerebral palsy cocontraction is multifaceted, representing a volitional strategy to enhance control, as well as a disorder of the mechanisms that govern patterns of muscle activity.

A dynamical model of locomotion in spastic hemiplegic cerebral palsy: influence of walking speed

OBJECTIVE

The objective of this study was to assess the capability of an escapement-driven inverted pendulum with springs and damping model to estimate the effects of impairments (e.g. spasticity, muscle weakness) on the dynamics and patterns of locomotion of children with spastic cerebral palsy.

METHODS

Kinematic data of six children with spastic hemiplegic cerebral palsy and six matched, typically developing children were collected at five different self-selected overground walking speeds ('very slow' to 'very fast'). Changes in forcing, stiffness and gravitational potentials were estimated during the stance phase of each leg according to the model's equation of motion.

RESULTS

Significantly greater stiffness and decreased forcing was observed in the more affected limbs of children with spastic hemiplegic cerebral palsy and compared to typically developing peers. The forcing term of the non-affected limb was greater than that of the matched typically developing children.

CONCLUSIONS

Results support the claim that disabled individuals with losses in dynamic resources (stiffness, muscle forcing capability) exploit and develop the remaining resources in their adapted gait patterns. It was suggested that clinical interventions aimed at normalizing a gait pattern may be contraindicated, and that rehabilitation might be more effective if focused at the level of dynamics.

RELEVANCE

Pattern formation is seen as an optimal solution based on the individuals' action capabilities and dynamic properties under environmental and task demands. This perspective could lead to the development of interventions that address these dynamic variables with the objective of improving the functional capabilities of children with cerebral palsy.

Correlation of polyelectromyographic patterns and clinical upper motor neuron syndrome in hemiplegic stroke patients

OBJECTIVE

To investigate the correlation between movement patterns, measured by polyelectromyography (PEMG), and clinical upper motor neuron (UMN) syndrome in stroke patients.

DESIGN

PEMG patterns, recorded from pairs of flexor-extensor muscles during voluntary maneuvers, and motor outcomes were assessed approximately 1 month after stroke (early stage). Motor outcomes were reassessed 6 months later (late stage).

PARTICIPANTS

Thirty-nine hemiplegic stroke patients and 18 healthy control subjects.

MAIN OUTCOME MEASURES

Passive stretch reflexes (PSRs), Brunnstrom's stages, and walking ability.

RESULTS

Six PEMG patterns, varying from complete reciprocal to complete synchrony, were identified. Higher PEMG pattern scores were associated with better Brunnstrom's stages (r > .80), walking ability (r > .39), and some PSRs (r < -.37). PEMG patterns could separate patterns 1 and 2 from patterns 3 and 4 for patients with early Brunnstrom's stages 1 and 2. Patterns 1 and 2 (reduced agonist electromyographic activities) indicated weakness and resulted in the worst motor outcomes. Patterns 3 and 4 (cocontraction and coactivation) indicated spasticity and associated synergistic movements. Patients with patterns of 5 and 6 (reciprocal electromyographic activities) had more selective motor control.

CONCLUSIONS

PEMG patterns correlate with clinical UMN syndromes and may allow treatment strategy planning on the basis of underlying motor control, as well as the prediction of final motor outcomes soon after stroke, even in patients who cannot move their legs initially.

Retraction of muscle afferents from the rat ventral horn during development

The postnatal reorganization of rat proprioreceptive muscle afferent spinal terminal fields was explored by labelling transganglionically afferents from extensor digitorum communis with cholera toxin B sub-unit at different ages. Immunocytochemistry revealed labelled afferents in all segments examined (C4-T2) as well as retrogradely labelled motoneurones (C5-T1). Dorsal horn innervation appeared similar at all ages, but there were striking changes in the ventral horn. Many afferent boutons were seen closely apposed to labelled motoneurone proximal dendrites at postnatal day 7 (P7) and P14, but in the adult such contacts were almost entirely confined to distal dendrites. Between P7 and adult, a significant decrease in bouton density was found in the area dorsomedial to the labelled motoneurones that contained labelled dendrites and antagonist motoneurones. This anatomical reorganization may explain both the increasing stretch reflex threshold and its concomitant decrease in magnitude with age, and the reduction in excitatory connections to antagonist motoneurones, previously described in developmental neurophysiological studies.

Neuropathophysiology of movement disorders in cerebral palsy

Recent developments in understanding the pathophysiology of disordered motor control in cerebral palsy are reviewed. In spastic cerebral palsy, evidence for abnormal segmental as well as supraspinal control of motor neuron output exists. Impaired Ia inhibition of antagonist muscles has been suggested but recently contested. Evidence also supports the role of decreased presynaptic inhibition of Ia afferents and decreased nonreciprocal Ib inhibition. Furthermore, early cerebral injury results in reorganization of supraspinal (corticospinal) inputs to motor neuron pools. In extrapyramidal cerebral palsy, injury of basal ganglia or thalamus has been demonstrated. A scheme for understanding the neurochemical circuitry of the extrapyramidal system is discussed. Animal models and certain specific human diseases provide examples of how this circuitry may be disturbed, thereby resulting in an imbalance between the direct and indirect striatal output systems and in impaired motor control. Future studies employing postmortem neurochemical analysis, functional magnetic resonance imaging, and positron emission tomographic scanning may foster progress in this area.

Self-Optimization of Walking in Nondisabled Children and Children With Spastic Hemiplegic Cerebral Palsy

Children voluntarily adopt a frequency and movement pattern for walking. The force-driven harmonic oscillator (FDHO) model was used in this study for accurate prediction of the preferred walking frequency of nondisabled children and children with spastic hemiplegic cerebral palsy. Four potential optimality criteria with which the preferred walking pattern was forced to comply were examined: minimization of physiological costs, maximization of mechanical energy conservation, minimization of asymmetry in lower limb movements and minimization of variability of interlimb and intralimb coordination. Age and gender-matched nondisabled children (n = 6) and children with spastic hemiplegic cerebral palsy (n = 6) were tested under six frequency conditions of walking at a constant speed on a treadmill. For the nondisabled children, the results indicated that their preferred walking frequency could be accurately predicted by the FDHO model. They freely adopted a walking pattern that minimized physiological costs, asymmetry, and variability of inter- and intralimb coordination. For the children with spastic hemiplegic cerebral palsy, the prediction of preferred overground walking frequency required that the FDHO model be modified to account for muscle mass and leg length discrepancies between limbs and increased stiffness. Most of the children achieved the same optimality goals as the nondisabled when walking at the preferred frequency. However, the children were found to use different mechanisms to attain these goals: for example, a steeper increase observed in physiological cost at higher frequencies; a lowered center of gravity of the body, which allowed for angular symmetry; and greater variability of between-joint coordination in the nonaffected limb and less variability in the affected limb.

Effect of isokinetic strength-training on functional ability and walking efficiency in adolescents with cerebral palsy

This study investigated changes in knee extensor and flexor strength of 17 mildly involved adolescents with cerebral palsy in response to an eight-week isokinetic strength-training program. Peak torque and work were used as strength outcome measures. Subsequent changes in gross motor function and walking efficiency were evaluated. The significant strength gains of 21 to 25 per cent observed were similar in magnitude to those previously reported for able-bodied individuals. A significant number of subjects showed an increase in gross motor ability. However, walking velocity and walking efficiency were unchanged. Strength gains of 15 to 17 per cent were maintained for three months after the cessation of isokinetic training.

Control of isometric muscle activity in cerebral palsy

Voluntary control of muscle contraction was examined in five adults with cerebral palsy, who were required to track a moving target by continuously varying the level of isometric contraction of elbow flexor muscles (measured by EMG). First performance varied from minimal control to almost normal control, depending on the severity of disability. Practice over 12 weeks reduced inappropriate muscle activity in the most disabled patients, but there was no increase in appropriate muscle activity for any patient beyond that observed after the first few minutes of tracking. Thus their ability to translate a visual response into the appropriate motor activity was impaired, and there was no evidence of potential to overcome this. This supports the authors' earlier proposal that impairment of sensory-motor learning is the primary cause of functional disability in cerebral palsy. The EMG tracking task may provide a technique for assessing the ability of individuals with cerebral palsy to control muscle contraction.

Gross motor patterns in children with cerebral palsy and spastic diplegia

Rolling, sitting, and crawling patterns were motoscopically analyzed in 72 children with cerebral palsy and spastic diplegia; the relation between these patterns and the severity of the locomotive disability was studied. In rolling, trunk rotation and elbow support were difficult for the most severely diplegic children. When sitting, most patients had a between-heel sitting pattern in which the thighs were adducted and the knees were flexed. When crawling, the reciprocal thigh movements were insufficient and accompanied by lateral bending of the trunk in many patients. In the more impaired patients, the thighs supported the weight in flexion and did not move reciprocally. Creeping on the elbows without reciprocal leg movements was demonstrated in the most severely affected children after 2 years of age.

Do injuries to the developing human brain alter corticospinal projections?

Experimental lesions of the mammalian brain involving the developing corticospinal pathways may cause these pathways to become redirected. In humans, injury to the developing brain results in disorders of movement known collectively as 'cerebral palsy'. These motor disorders differ from those produced by similar lesions in adults. We present evidence that abnormal corticospinal projections exist in subjects who have had an injury to the brain in the perinatal period. These aberrant connections, which may represent misdirected corticospinal fibers, help to explain the impairment of voluntary movements experienced by these subjects.

Reducing spasticity to control muscle contracture of children with cerebral palsy

A biofeedback training technique to control spasticity, previously successful with adults with cerebral palsy, was adapted for three children with spastic diplegia at risk for contractures. Visual feedback of muscle stretch reflex sensitivity is provided by video games, which are played by reducing reflex sensitivity. After a 10-week training period two of the three children had significantly reduced spasticity in the gastrocnemius muscle. The technique can be used with children as young as four years, is inexpensive, and can be carried out by parents with supervision by a physiotherapist.

Spastic cerebral palsy: possible spinal interneuronal contributions

The author explores the possibility that abnormal and immature spinal interneuronal circuits play a rôle in spastic cerebral palsy. Interneuronal abnormalities could account for a number of characteristic signs: sensitivity to normally innocuous stimuli, hyperreflexia, abnormal and inappropriate co-ordination patterns, and limitations in acquiring, planning, executing and correcting skillful actions. The precise pattern of interneuronal anomalies present will depend on the original site of the lesion, age at onset, and on how central and segmental development were affected. Although the number of relevant studies is very small, there are indications that long-term training can produce changes in segmental response, both by altering descending inhibition and by producing lasting changes in spinal neuronal organisation and responsiveness. Modern recording techniques have introduced the prospect of tracing immature and abnormal segmental components and of establishing their impacts on movement control.

Stance posture control in select groups of children with cerebral palsy: deficits in sensory organization and muscular coordination

This study has focused upon the automatic components of posture and movement in a group of ten cerebral palsy children carefully selected to represent a spectrum of abnormalities relatively pure by clinical standards and ten age-matched normals. Each subject stood unsupported upon a movable platform and within a movable visual surround and was then exposed to external perturbations or was asked to pull with one arm upon a movable handle. In comparing the performance of cerebral palsy children in each clinical category with the age-matched normals and with normal adults assessed in previous studies, the process of maintaining stance was subdivided into two component functions: substrates which determined the onset timing, direction and amplitude of postural actions from somatosensory, vestibular, and visual stimuli were termed "sensory organization", and those establishing temporal and spatial patterns of muscular contractions appropriate to produce effective movements were termed "muscle coordination". We found among seven of the ten cerebral palsy children a clear localization of dysfunction within either sensory organization or muscle coordination mechanisms. These results are providing some new insights into the organization of each of these processes as well as suggesting methods for developing a more systematic understanding of the abnormalities of movement control.

Self-regulation of spasm and spasticity in cerebral palsy

Four young adult cerebral palsied subjects with a mixture of spasticity and athetosis attended an experimental reflex training program for three one-hour sessions each week over an 18 month period. During each session on-line measures of contraction level and tonic stretch reflex sensitivity from the biceps brachii muscle were shown to the subject on meter displays. Subjects were asked to attempt to control the displays. They were given goals such as: (1) reduce both contraction level and reflex sensitivity displays to zero and (2) increase the contraction level display to 10% of maximum while keeping the reflex sensitivity display at a minimum. Achievement of goals was automatically sensed and used to activate a cassette tape of the subject's favourite music. Contraction level and reflex sensitivity scores were averaged over one-minute intervals to provide a record of long term progress. Elbow-angle and IEMG data were recorded on FM tape for off-line analysis. All four subjects learned to suppress involuntary muscle activity and resting tonic stretch reflex responses. They also learned to produce a two or three-fold variation in action tonic stretch reflex sensitivity while sustaining 10% maximum voluntary contraction. In other words, subjects learned to self-regulate spasm and spasticity at the elbow and to regulate tonic stretch reflex sensitivity independently of contraction level. A visual tracking task requiring voluntary movement about the elbow was employed to assess improvement in functional control of elbow movement. One athetotic subject improved tracking accuracy as a consequence of reducing the amount of involuntary arm movement while the other three subjects showed negligible improvement in functional control.

Chronic cerebellar stimulation for cerebral palsy. Prospective and double-blind studies

The effects of chronic electrical stimulation of the cerebellum in patients with cerebral palsy have been studied using objective tests of joint compliance, and standardized assessments of developmental reflexes and motor skills. Of 14 patients studied prospectively for 1 to 44 months, 11 showed improvement in motor function. A double-blind test of 10 patients off and on stimulation for an average 8-week period showed no significant changes. Thus, we have no proof that the functional improvements seen with long-term stimulation are the result of cerebellar stimulation.