Sensory feedback to ankle plantar flexors is not exaggerated during gait in spastic children with cerebral palsy.
ABSTRACT It is commonly assumed that exaggerated stretch reflex activity and the resulting increased muscle tone in ankle plantar flexors contribute to reduced ankle joint movement during gait in children with cerebral palsy (CP). We investigated the contribution of sensory feedback mechanisms to ankle plantar flexor muscle activity during treadmill walking in 20 children with CP and 41 control children. Stretch responses in plantar flexor muscles evoked in stance by dorsiflexion perturbations showed an age-related decline in control children but not in children with CP. In swing responses were abolished in control children, but not in children with CP. Removal of sensory feedback to the soleus muscle in stance by shortening the plantar flexors produced a drop in soleus EMG activity of a similar size and latency in control children and children with CP. Soleus EMG activity was observed in swing in a similar proportion in both groups. Shortening of the plantar flexors in swing caused a larger drop in Soleus EMG in control children than in children with CP. The lack of age related decline in stretch reflexes in the stance phase and the inability to suppress the reflex in the swing phase is likely related to lack of maturation of corticospinal control in children with CP. However, since they did not show soleus EMG activity to a larger extent than control children in swing and since sensory afferent feedback did not contribute more to their muscle activity, spasticity is unlikely to contribute to foot drop and toe walking.
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ABSTRACT: Clinical assessment of spasticity is compromised by the difficulty to distinguish neural from non-neural components of increased joint torque. Quantifying the contributions of each of these components is crucial to optimize the selection of anti-spasticity treatments such as Botulinum Toxin (BTX). The aim of this study was to compare different biomechanical parameters that quantify the neural contribution to ankle joint torque measured during manually-applied passive stretches to thegastrocsoleus in children with spastic cerebral palsy (CP). The gastrocsoleus of 53 children with CP (10.9 ± 3.7yrs; females n=14; bilateral/unilateral involvement n=28/25; Gross Motor Functional Classification Score I-IV) and 10 age-matched typically developing (TD) children were assessed using a manually-applied, instrumented spasticity assessment. Joint angle characteristics, root mean square electromyography and joint torque were simultaneously recorded during passive stretches atincreasing velocities. From the CP cohort, 10 muscles were re-assessed for intra-rater reliability and 19 muscles were re-assessed 6 weeks post-BTX. A parameter related to mechanical work, containing both neural and non-neural components, was compared to newly developed parameters that were based on the modeling of passive stiffness and viscosity. The difference between modeled and measured response provided a quantification of the neural component. Both types of parameters were reliable (ICC>0.95) and distinguished TD from spastic muscles (p<0.001). However, only the newly developed parameters significantly decreased post-BTX (p=0.012). Identifying the neural and non-neural contributions to increased joint torque allows for the development of individually tailored tone management.Gait & posture 07/2014; · 2.58 Impact Factor
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ABSTRACT: There is much debate about how spasticity contributes to the movement abnormalities seen in children with spastic cerebral palsy (CP). This study explored the relation between stretch reflex characteristics in passive muscles and markers of spasticity during gait. Twenty-four children with CP underwent 3D gait analysis at three walking velocity conditions (self-selected, faster and fastest). The gastrocnemius (GAS) and medial hamstrings (MEHs) were assessed at rest using an instrumented spasticity assessment that determined the stretch-reflex threshold, expressed in terms of muscle lengthening velocity. Muscle activation was quantified with root mean square electromyography (RMS-EMG) during passive muscle stretch and during the muscle lengthening periods in the swing phase of gait. Parameters from passive stretch were compared to those from gait analysis. In about half the children, GAS peak muscle lengthening velocity during the swing phase of gait did not exceed its stretch reflex threshold. In contrast, in the MEHs the threshold was always exceeded. In the GAS, stretch reflex thresholds were positively correlated to peak muscle lengthening velocity during the swing phase of gait at the faster (r=0.46) and fastest (r=0.54) walking conditions. In the MEHs, a similar relation was found, but only at the faster walking condition (r=0.43). RMS-EMG during passive stretch showed moderate correlations to RMS-EMG during the swing phase of gait in the GAS (r=0.46-0.56) and good correlations in the MEHs (r=0.69-0.77) at all walking conditions. RMS-EMG during passive stretch showed no correlations to peak muscle lengthening velocity during gait. We conclude that a reduced stretch reflex threshold in the GAS and MEHs constrains peak muscle lengthening velocity during gait in children with CP. With increasing walking velocity, this constraint is more marked in the GAS, but not in the MEHs. Hyper-activation of stretch reflexes during passive stretch is related to muscle activation during the swing phase of gait, but has a limited contribution to reduced muscle lengthening velocity during swing. Larger studies are required to confirm these results, and to investigate the contribution of other impairments such as passive stiffness and weakness to reduced muscle lengthening velocity during the swing phase of gait.Research in Developmental Disabilities 09/2014; 35(12):3354-3364. · 3.40 Impact Factor