Functional assessment of stretch hyperreflexia in children with cerebral palsy using treadmill perturbations

Abstract

Background As hyperactive muscle stretch reflexes hinder movement in patients with central nervous system disorders, they are a common target of treatment. To improve treatment evaluation, hyperactive reflexes should be assessed during activities as walking rather than passively. This study systematically explores the feasibility, reliability and validity of sudden treadmill perturbations to evoke and quantify calf muscle stretch reflexes during walking in children with neurological disorders. Methods We performed an observational cross-sectional study including 24 children with cerebral palsy (CP; 6–16 years) and 14 typically developing children (TD; 6–15 years). Short belt accelerations were applied at three different intensities while children walked at comfortable speed. Lower leg kinematics, musculo-tendon lengthening and velocity, muscle activity and spatiotemporal parameters were measured to analyze perturbation responses. Results We first demonstrated protocol feasibility: the protocol was completed by all but three children who ceased participation due to fatigue. All remaining children were able to maintain their gait pattern during perturbation trials without anticipatory adaptations in ankle kinematics, spatiotemporal parameters and muscle activity. Second, we showed the protocol’s reliability: there was no systematic change in muscle response over time (P = 0.21–0.54) and a bootstrapping procedure indicated sufficient number of perturbations, as the last perturbation repetition only reduced variability by ~ 2%. Third, we evaluated construct validity by showing that responses comply with neurophysiological criteria for stretch reflexes: perturbations superimposed calf muscle lengthening (P < 0.001 for both CP and TD) in all but one participant. This elicited increased calf muscle activity (359 ± 190% for CP and 231 ± 68% for TD, both P < 0.001) in the gastrocnemius medialis muscle, which increased with perturbation intensity (P < 0.001), according to the velocity-dependent nature of stretch reflexes. Finally, construct validity was shown from a clinical perspective: stretch reflexes were 1.7 times higher for CP than TD for the gastrocnemius medialis muscle (P = 0.017). Conclusions The feasibility and reliability of the protocol, as well as the construct validity—shown by the exaggerated velocity-dependent nature of the measured responses—strongly support the use of treadmill perturbations to quantify stretch hyperreflexia during gait. We therefore provided a framework which can be used to inform clinical decision making and treatment evaluation.

A comprehensive dataset on biomechanics and motor control during human walking with discrete mechanical perturbations

“…The vertical and horizontal force data, EMG envelope, and motion capture data for each participant were divided into gait cycles using the ground reaction forces recorded from the right force plate. For each gait cycle, the angle of the trunk, right/left hip, right/left knee, and right/left ankle are calculated from the sagittal plane marker coordinates ( Flux et al, 2021 ). Then, using the perturbation information recorded from D-Flow, each gait cycle was labeled based on the kind of perturbation that occurred during that gait cycle: no perturbation, 10%, 20%, … 80%.…”

“…Absence or insufficiency of reflexes would increase the risk of falling and injury. On the other hand, hyperactive reflexes can cause abnormal movements with certain neurological disorders, such as cerebral palsy and stroke ( Flux et al, 2021 ; Li & Francisco, 2015 ). Clinically, reflexes can be evaluated with the familiar tendon tap tests.…”

Stretch hyperreflexia in children with cerebral palsy

“…Additionally, several studies attempted to quantify the relationship between muscle stretch and increased muscle activity during unperturbed gait. [82][83][84][85][86][87] Results from these studies are conflicting, with some studies finding evidence for stretch reflexes during the swing 88 or stance phase 89,90 or no evidence for a relation between muscle-tendon stretch and increased muscle activation. 87 While these studies used different assessment methods, they all relied on the modeled lengthening velocity of the entire musculotendon unit to represent muscle spindle stretch during gait.…”

“…Stretch hyperreflexia can cause deviating muscle activation patterns in children with spastic CP with a toewalking pattern: they often experience stretch on the calf muscles and show a rapid increase in calf muscle activity during early stance, 25,26,81,116 which has been attributed to stretch hyperreflexia. 25,83 Colborne et al 116 performed a functional training in which they provided visual feedback on these deviating calf muscle activation patterns. By down-conditioning the rapid increase in soleus activity after initial contact, it was hypothesized that stretch hyperreflexia would also be down-conditioned.…”