Impaired Transmission in the Corticospinal Tract and Gait Disability in Spinal Cord Injured Persons

Abstract

Rehabilitation following spinal cord injury is likely to depend on recovery of corticospinal systems. Here we investigate whether transmission in the corticospinal tract may explain foot drop (inability to dorsiflex ankle) in persons with spinal cord lesion. The study was performed in 24 persons with incomplete spinal cord lesion (C1 to L1) and 15 healthy controls. Coherence in the 10- to 20-Hz frequency band between paired tibialis anterior muscle (TA) electromyographic recordings obtained in the swing phase of walking, which was taken as a measure of motor unit synchronization. It was significantly correlated with the degree of foot drop, as measured by toe elevation and ankle angle excursion in the first part of swing. Transcranial magnetic stimulation was used to elicit motor-evoked potentials (MEPs) in the TA. The amplitude of the MEPs at rest and their latency during contraction were correlated to the degree of foot drop. Spinal cord injured participants who exhibited a large foot drop had little or no MEP at rest in the TA muscle and had little or no coherence in the same muscle during walking. Gait speed was correlated to foot drop, and was the lowest in participants with no MEP at rest. The data confirm that transmission in the corticospinal tract is of importance for lifting the foot during the swing phase of human gait.

Functional implications of corticospinal tract impairment on gait after spinal cord injury

“…A third subgroup (n ¼ 6) exhibited a clear foot drag at the onset of swing. 8 For all subjects, the maximum toe elevation during swing was calculated and used in the following correlations.…”

“…All laboratory procedures used in this paper were described in details in Barthélemy et al 8 Briefly, gait ability of participants was assessed on a treadmill (TechnoGym, Køge, Denmark) for 5 min at their maximum comfortable speed. SCI participants did not wear any orthosis during the assessments.…”

“…[5][6][7] We have recently shown that measurement of maximum toe elevation during swing can be used as a simple and objective measurement of foot drop and reflects CST impairment in persons with spinal cord injury (SCI). 8 Notably, MEP latency was correlated to maximum toe elevation but not to overground speed. In parallel, maximum toe elevation was correlated to overground speed, suggesting that a direct link between MEP characteristics and gait function might be difficult to establish.…”

Supraspinal Control Predicts Locomotor Function and Forecasts Responsiveness to Training after Spinal Cord Injury

“…56 Imaging and electrophysiological measures associated with walking capacity In recent years, there has been growing interest in identifying electrophysiological and radiographical biomarkers that can predict locomotor outcomes. 60,144,145 Recent evidence from studies of TMS 146 and EMG coherence 60,144 have provided additional support for the importance of corticospinal pathways in human walking. More generally, there is some evidence that magnetic resonance imaging (MRI)-based measures are correlated with impairment.…”

“…attention, with studies showing direct contributions to the ankle dorsiflexors, 59,60 including activation on a step-to-step basis. 59 The role of the motor cortex in human walking has been elucidated by studies in humans showing that: (1) subthreshold transcranial magnetic stimulation (TMS) to activate inhibitory interneurons in the motor cortex suppresses the locomotor EMG in the ankle dorsi -and plantar flexor muscles, 61 (2) suprathreshold TMS activates dorsiflexors to the same extent as during volitional contractions in sitting, 62 and (3) electroencephalographic (EEG)-EMG coherence shows synchrony in the frequency domain between the primary motor cortex and the dorsiflexors during walking.…”