Sensory feedback to ankle plantar flexors is not exaggerated during gait in spastic hemiplegic children with cerebral palsy

Abstract

Willerslev-Olsen M, Andersen JB, Sinkjaer T, Nielsen JB. Sensory feedback to ankle plantar flexors is not exaggerated during gait in spastic hemiplegic children with cerebral palsy. J Neurophysiol 111: 746 -754, 2014. First published November 13, 2013 doi:10.1152/jn.00372.2013.-It is still widely believed that exaggerated stretch reflexes and increased muscle tone in ankle plantar flexors contribute to reduced ankle joint movement during gait in children with cerebral palsy (CP). However, no study has directly measured stretch reflex activity during gait in these children. We investigated sensory feedback mechanisms during walking in 20 CP children and 41 control children. Stretch responses in plantar flexor muscles evoked in stance showed an age-related decline in control but not CP children. In swing the responses were abolished in control children, but significant responses were observed in 14 CP children. This was related to reduced activation of dorsiflexors in swing. Removal of sensory feedback in stance produced a drop in soleus activity of a similar size in control and CP children. Soleus activity was observed in swing to the same extent in control and CP children. Removal of sensory feedback in swing caused a larger drop in soleus activity in control children than in CP children. The lack of age-related decline in stretch reflexes and the inability to suppress reflexes in swing is likely related to lack of maturation of corticospinal control in CP children. Since soleus activity was not seen more frequently than in control children in swing and since sensory feedback did not contribute more to their soleus activity, spasticity is unlikely to contribute to foot drop and toe walking. We propose that altered central drive to the ankle muscles and increased passive muscle stiffness are the main causes of foot drop and toe walking. age-dependent changes; stretch reflex; biomechanical evaluation; cerebral palsy; electrophysiology; spasticity THE MAJORITY OF CHILDREN with cerebral palsy (CP) have gait problems, which impact their quality of life (af Klint et al.

Impaired gait function in adults with cerebral palsy is associated with reduced rapid force generation and increased passive stiffness

“…This suggests that reflex-mediated stiffness at rest plays no or only a very small role for the functional ability of these patients at least based on the measures that we have included here. This is consistent with other studies, which have failed to find any relation between the extent of spasticity measured biomechanically and the functional ability of patients with spasticity (Sinkjaer et al, 1994, Marsden et al, 2012, Willerslev-Olsen et al, 2014. The finding underscores that spasticity is not the cause of functional impediments by necessity, but may in some cases help to ensure sufficient muscle activity for the patients to maintain upright posture and walk (Dietz, 2003).…”

“…These concerns also challenge previous assumptions regarding the significance of spasticity in the population of people with CP (Willerslev-Olsen et al, 2014). The fundamental problem that these new studies have identified is that muscle resistance caused by pathological changes in passive muscle properties is extremely difficult to distinguish from the muscle resistance caused by hyperactive stretch reflexes, especially since these often co-exist to some extent in many of the patients (Mirbagheri et al, 2004, Lorentzen et al, 2010, Willerslev-Olsen et al, 2013.…”

“…Although hyperactive reflexes may be elicited by external perturbations in specific phases of the gait cycle, sensory feedback mechanisms seem if anything to contribute less to the muscle activity recorded during gait in spastic subjects with stroke or CP (Mazzaro et al, 2007, Willerslev-Olsen et al, 2014. Other studies on subjects with hereditary spastic paraparesis have also failed to find any correlation between measures of exaggerated reflex activity and impairments of gait (Marsden et al, 2012).…”

“…Several studies have documented that reflex modulation is abnormal during gait in spastic subjects with multiple sclerosis (Sinkjaer et al, 1996), stroke (Mazzaro et al, 2007), spinal cord injury (Faist et al, 1999) and cerebral palsy (CP) (Hodapp et al, 2007, Willerslev-Olsen et al, 2014, but it is unclear to what extent this contributes to the impairment of gait observed in these subjects. Although hyperactive reflexes may be elicited by external perturbations in specific phases of the gait cycle, sensory feedback mechanisms seem if anything to contribute less to the muscle activity recorded during gait in spastic subjects with stroke or CP (Mazzaro et al, 2007, Willerslev-Olsen et al, 2014.…”

Treadmill training with an incline reduces ankle joint stiffness and improves active range of movement during gait in adults with cerebral palsy

“…[26] Since increased reflex stiffness also appears to play only a small role for the gait disability in the population of adults with CP, this finding is probably of little significance in any case. [9,27,28] The lack of correlation between the reduced passive stiffness and improved gait ability in the training group suggests that other mechanisms contributed to the improvement in gait and may have obscured the contribution from the changes in passive stiffness. Chief among these are changes in the neural drive to the muscles and improved coordination of the muscle activity during gait.…”