Plantarflexor muscle and spatiotemporal gait characteristics of children with hemiplegic cerebral palsy: an observational study

How Ankle Exoskeleton Assistance Affects the Mechanics of Incline Walking and Stair Ascent in Cerebral Palsy

Graded terrains, like slopes and stairs, are particularly challenging for people with neurological disorders like cerebral palsy (CP) due to increased selective muscle control and muscle strength requirements. Lower-limb exoskeletons may be able to assist individuals with CP when navigating graded terrains. This study sought to determine the effects of untethered ankle exoskeleton assistance on lower-limb joint angles, moments, and muscle activity during up-incline walking and up-stair stepping in CP (n=7). We hypothesized that powered assistance would result in improved ankle mechanics (i.e., increased total ankle moments) across both terrains. During incline walking, we found that peak ankle dorsiflexion angle increased by $7^{\mathrm{o}}$(p=0.006) during walking with ankle assistance compared to walking without the device (Shod). Compared to without the device, the peak total ankle plantarflexor moment increased by 8% (p=0.022) while peak biological ankle plantarflexor moment decreased by 17% (p< 0.001). Incline walking with ankle assistance reduced stance phase muscle activity of the soleus (20%, p=0.010) and vastus lateralis (18%, p=0.004), and swing phase tibialis activity (19%, p=0.028) compared to Shod. During stair ascent with the device, the peak total ankle plantarflexor moment increased by 17% (p=0.011) and the peak knee extensor moment increased by 40% (p=0.018) compared to Shod. These findings provide insight into the biomechanical benefits of ankle exoskeleton assistance during incline and stair walking. This work aims to advance the use of robotic assistive technology to improve mobility for people with CP.

Do Muscle Changes Contribute to the Neurological Disorder in Spastic Paresis?

Background

At the onset of stroke-induced hemiparesis, muscle tissue is normal and motoneurones are not overactive. Muscle contracture and motoneuronal overactivity then develop. Motor command impairments are classically attributed to the neurological lesion, but the role played by muscle changes has not been investigated.

Methods

Interaction between muscle and command disorders was explored using quantified clinical methodology-the Five Step Assessment. Six key muscles of each of the lower and upper limbs in adults with chronic poststroke hemiparesis were examined by a single investigator, measuring the angle of arrest with slow muscle stretch (XV1) and the maximal active range of motion against the resistance of the tested muscle (XA). The coefficient of shortening CSH = (XN-XV1)/XN (XN, normally expected amplitude) and of weakness CW = (XV1-XA)/XV1) were calculated to estimate the muscle and command disorders, respectively. Composite CSH (CCSH) and CW (CCW) were then derived for each limb by averaging the six corresponding coefficients. For the shortened muscles of each limb (mean CSH > 0.10), linear regressions explored the relationships between coefficients of shortening and weakness below and above their median coefficient of shortening.

Results

A total of 80 persons with chronic hemiparesis with complete lower limb assessments [27 women, mean age 47 (SD 17), time since lesion 8.8 (7.2) years], and 32 with upper limb assessments [18 women, age 32 (15), time since lesion 6.4 (9.3) years] were identified. The composite coefficient of shortening was greater in the lower than in the upper limb (0.12 ± 0.04 vs. 0.08 ± 0.04; p = 0.0002, while the composite coefficient of weakness was greater in the upper limb (0.28 ± 0.12 vs. 0.15 ± 0.06, lower limb; p < 0.0001). In the lower limb shortened muscles, the coefficient of weakness correlated with the composite coefficient of shortening above the 0.15 median CSH (R = 0.43, p = 0.004) but not below (R = 0.14, p = 0.40).

Conclusion

In chronic hemiparesis, muscle shortening affects the lower limb particularly, and, beyond a threshold of severity, may alter descending commands. The latter might occur through chronically increased intramuscular tension, and thereby increased muscle afferent firing and activity-dependent synaptic sensitization at the spinal level.

Kinematic and Temporospatial Changes in Children with Cerebral Palsy during the Initial Stages of Gait Development

PURPOSE

To identify changes in the gait kinematics and temporospatial parameters of children with bilateral Cerebral Palsy (CP) at 8 months after the onset of independent walking and identify differences to Typical Development (TD) children at the onset of independent walking and at 8 months follow up.

METHOD

Sixteen children with bilateral CP, GMFCS levels I and II, and 15 TD children were recruited. Gait kinematics and temporospatial parameters were recorded using a 3-D gait analysis system; the sagittal plane of the lower limb joints was analyzed. Baseline measurements were recorded at the individual's onset of independent walking and follow up was after 8 months.

RESULTS

Compared to baseline, children with bilateral CP demonstrated increased (mean difference ± SE) plantar flexion (11.79 ± 2.96), single support (0.04 ± 0.01), step length (0.2 ± 0.05) and stride length (0.4 ± 0.09), at follow up; all p < .05. Compared to TD children, they also had lower gait speed (0.16 ± 0.05), higher single support (0.02 ± 0.01) and lower maximum knee extension (9.14 ± 4.49) during the swing phase, at baseline and follow up (0.1 ± 0.04, 0.05 ± 0.01, 23.04 ± 4.17, respectively); all p < .05.

CONCLUSION

There are changes in the sagittal plane kinematics and temporospatial parameters of the gait during the first 8 months of independent walking. These indicate gait maturation changes and highlight the impact of walking experience on the gait characteristics of children with bilateral CP.

Relationship between ankle function and walking ability for children and young adults with cerebral palsy: A systematic review of deficits and targeted interventions

BACKGROUND

A primary goal of treatment for children with cerebral palsy is improved walking ability to allow for a more active and independent lifestyle. With the importance of ankle function to walking ability, and the deficits in ankle function associated with cerebral palsy, there is good rationale for targeting this joint in an effort to improve walking ability for this population.

RESEARCH QUESTION

How do deficits and targeted interventions of the ankle joint influence walking ability in children with cerebral palsy?

METHODS

A specific search criteria was used to identify articles that either (1) provided information on the relationship between ankle function and walking ability or (2) investigated the effect of a targeted ankle intervention on walking ability in cerebral palsy. PubMed, Embase, CINAHL, and Web of Science databases were searched from 1980-April, 2020. Resulting citations were compared against a prospective set of inclusion and exclusion criteria. Data relevant to the original research question was extracted, and the level of evidence for each intervention study was scored. Interpretation was focused on specific, pre-determined mobility measures.

RESULTS

Sixty-one citations met all criteria for data extraction, six of which were observational, and fifty-five of which were interventional. Level of evidence ranged from 2 to 4. Self-selected walking speed was the most common measure of walking ability, while physical activity level was the least common.

SIGNIFICANCE

Ankle function is an important contributor to the walking ability of children with cerebral palsy, and most interventions targeting the ankle seem to demonstrate a benefit on walking ability, but future higher-powered and/or controlled studies are necessary to confirm these findings.

Improving the Energy Cost of Incline Walking and Stair Ascent with Ankle Exoskeleton Assistance in Cerebral Palsy

OBJECTIVE

Many individuals with cerebral palsy (CP) experience gait deficits resulting in metabolically-inefficient ambulation that is exacerbated by graded walking terrains. The primary goal of this study was to clinically-validate the accuracy and efficacy of adaptive ankle exoskeleton assistance during steady-state incline walking and stair ascent in individuals with CP. Exploratory goals were to assess safety and feasibility of using adaptive ankle exoskeleton assistance in real-world mixed-terrain settings.

METHODS

We used a novel battery-powered ankle exoskeleton to provide adaptive ankle plantar-flexor assistance during stance phase. Seven ambulatory individuals with CP completed the study.

RESULTS

Adaptive controller accuracy was 85% for incline walking and 81% for stair-stepping relative to the biological ankle moment. Assistance improved energy cost of steady-state incline walking by 14% (p = 0.004) and stair ascent by 21% (p = 0.001) compared to walking without the device. Assistance reduced the muscular demand for the soleus and vastus lateralis during both activities. All participants were able to safely complete the real-world mixed-terrain route, with adaptive ankle assistance resulting in improved outcomes compared to walking with the device providing zero-torque; no group-level differences were found compared to walking without the device, yet individuals with more impairment exhibited a marked improvement.

CONCLUSION

Adaptive ankle exoskeleton assistance can improve the energy cost of steady-state incline walking and stair ascent in individuals with CP.

SIGNIFICANCE

As the first study to demonstrate safety and performance benefits of ankle assistance on graded terrains in CP, these findings encourage further investigation in free-living settings.

An Analytical Insight Into How Walking Speed and Spatial and Temporal Symmetry Are Related to Ankle Dysfunctions in Children With Hemiplegic Cerebral Palsy

OBJECTIVE

The aim of the study was to identify the major determining factors among ankle dysfunctions for walking speed and symmetry in children with hemiplegic cerebral palsy.

DESIGN

This was a prospective analysis that included 52 children with hemiplegic cerebral palsy, aged between 5 and 8 yrs, had mild spasticity, and were functioning at Gross Motor Function Classification System level I or II. The dorsiflexor and plantar flexor strength, dynamic spasticity (represented by gastrocnemius muscle lengthening velocity during stance phase), plantar flexors stiffness, ankle joint position sense, and walking performance (spatiotemporal parameter) were assessed.

RESULTS

The least absolute shrinkage and selection operator regression analyses showed that the dorsiflexor strength of the paretic limb was the major determining factor of walking speed (R2 = 0.38, P < 0.001). Dynamic spasticity of the plantar flexors explained a portion of the variance in walking speed (R2 = 0.15, P < 0.001) and the highest portion of the variance in spatial walking symmetry (R2 = 0.18, P = 0.002). In addition, the ankle joint position sense was the primary determinant of temporal walking symmetry (R2 = 0.10, P = 0.021).

CONCLUSIONS

In children with hemiplegic cerebral palsy, walking speed is mostly influenced by dorsiflexor muscle strength, temporal walking symmetry is associated with the joint position sense, whereas spatial walking symmetry is explicated by the dynamic spasticity of the plantar flexor muscles.

Are spasticity, weakness, selectivity, and passive range of motion related to gait deviations in children with spastic cerebral palsy? A statistical parametric mapping study

This study aimed to identify the relationships between clinical impairments and gait deviations in children with cerebral palsy (CP). A retrospective convenience sample of 367 children with CP was selected (3-18 years old) and divided in two groups based on clinical symptomatology [unilateral (uCP) / bilateral CP (bCP), (n = 167/200)]. All children underwent a three-dimensional gait analysis and a standardized clinical examination. Gait was inspected on a vector level (all sagittal motions combined), and an individual joint level (pelvis, hip, knee and ankle joint motions). Statistical non-parametric mapping was applied to identify specific parts of the gait cycle displaying relationships between the gait deviations of both groups and the impairment scores of spasticity, weakness, selectivity, and passive range of motion. Impairment scores were summarized in two ways: a) composite impairment scores (e.g. combined spasticity of all assessed muscles acting around the hip, knee and ankle joints) and b) joint specific impairment scores (e.g. spasticity of the muscles acting around the knee joint). Results showed that the vector and most of the individual motions were related to the composite scores. Direct and carry-over relationships were found between certain individual motions and joint impairment scores (around the same or neighboring joints, respectively). All correlations were more prominent for children with bCP compared to uCP, especially regarding the relationships of gait deviations with weakness and reduced selectivity. In conclusion, this study enabled the mapping of relationships between clinical impairments and gait deviations in children with CP, by identifying specific parts of the gait cycle that are related to each of these impairments. These results provide a comprehensive description of these relationships, while simultaneously highlighting the differences between the two CP groups. Integration of these findings could lead to a better understanding of the pathophysiology of gait deviations and, eventually, support individualized treatment planning.

Mechanisms contributing to gait speed and metabolic cost in children with unilateral cerebral palsy

BACKGROUND

Gait speed and metabolic cost are indicators of functional capacity in children with cerebral palsy. Uncovering their mechanisms helps guide therapeutic actions.

OBJECTIVES

To investigate the contributions of energy-generating and energy-conserving mechanisms to gait speed and metabolic cost of children with unilateral cerebral palsy.

METHODS

Data on eccentric and concentric muscle work, co-contraction, elastic torque and vertical stiffness of the affected-limb, forcing torque of the non-affected limb, gait speed and metabolic cost were collected from 14 children with unilateral cerebral palsy, aged 6-12 years. Analyses included two groups of multiple regression models. The first group of models tested the association between each dependent variable (i.e., speed and metabolic cost) and the independent variables that met the input criteria. The second group verified the contribution of the non-selected biomechanical variables on the predictors of the first model.

RESULTS

Gait speed (R²=0.80) was predicted by elastic torque (β=0.62; 95%CI: 0.60, 0.63), vertical stiffness (β=-0.477; 95%CI: -0.479, -0.474) and knee co-contraction (β=0.27; 95%CI: -1.96, 2.49). The production of eccentric work by the affected limb proved relevant in adjusting the vertical stiffness (R²=0.42; β=-0.64; 95%CI: 0.86, -0.42); elastic torque of the affected-leg was associated with impulsive torque of the non-affected leg (R²=0.31; β=0.55; 95%CI: 0.46, 0.64). Metabolic cost of gait (R²=0.48) was partially predicted by knee co-contraction (β=0.69; 95%CI: 0.685, 0.694).

CONCLUSIONS

The chain of associations revealed by the two steps models helped uncover the mechanisms involved in the locomotion of children with unilateral cerebral palsy. Intervention that changes specific energy conserving and generating mechanisms may improve gait of these children.

External Mechanical Work and Pendular Energy Transduction of Overground and Treadmill Walking in Adolescents with Unilateral Cerebral Palsy

PURPOSE

Motor impairments affect functional abilities and gait in children and adolescents with cerebral palsy (CP). Improving their walking is an essential objective of treatment, and the use of a treadmill for gait analysis and training could offer several advantages in adolescents with CP. However, there is a controversy regarding the similarity between treadmill and overground walking both for gait analysis and training in children and adolescents. The aim of this study was to compare the external mechanical work and pendular energy transduction of these two types of gait modalities at standard and preferred walking speeds in adolescents with unilateral cerebral palsy (UCP) and typically developing (TD) adolescents matched on age, height and body mass.

METHODS

Spatiotemporal parameters, external mechanical work and pendular energy transduction of walking were computed using two inertial sensors equipped with a triaxial accelerometer and gyroscope and compared in 10 UCP (14.2 ± 1.7 year) and 10 TD (14.1 ± 1.9 year) adolescents during treadmill and overground walking at standard and preferred speeds.

RESULTS

The treadmill induced almost identical mechanical changes to overground walking in TD adolescents and those with UCP, with the exception of potential and kinetic vertical and lateral mechanical works, which are both significantly increased in the overground-treadmill transition only in UCP (P < 0.05).

CONCLUSIONS

Adolescents with UCP have a reduced adaptive capacity in absorbing and decelerating the speed created by a treadmill (i.e., dynamic stability) compared to TD adolescents. This may have an important implication in rehabilitation programs that assess and train gait by using a treadmill in adolescents with UCP.