Abstract
BackgroundCoherence estimation has been used as an indirect measure of voluntary neurocontrol of residual motor activity following spinal cord injury (SCI). Here intramuscular Tibialis Anterior (TA) coherence estimation was performed within specific frequency bands for the 10-60 Hz bandwidth during controlled ankle dorsiflexion in subjects with incomplete SCI with and without spasticity.MethodsIn the first cohort study 15 non-injured and 14 motor incomplete SCI subjects were recruited to evaluate TA coherence during controlled movement. Specifically 15-30 Hz EMG was recorded during dorsiflexion with: i) isometric activation at 50, 75 and 100% of maximal voluntary torque (MVT), ii) isokinetic activation at 60 and 120°/s and iii) isotonic dorsiflexion at 50% MVT. Following identification of the motor tasks necessary for measurement of optimal TA coherence a second cohort was analyzed within the 10-16 Hz, 15-30 Hz, 24-40 Hz and 40-60 Hz bandwidths from 22 incomplete SCI subjects, with and without spasticity.ResultsIntramuscular 40-60 Hz, but not 15-30 Hz TA, coherence calculated in SCI subjects during isometric activation at 100% of MVT was lower than the control group. In contrast only isometric activation at 100% of MVT 15-30 Hz TA coherence was higher in subjects with less severe SCI (AIS D vs. AIS C), and correlated functionally with dorsiflexion MVT. Higher TA coherence was observed for the SCI group during 120°/s isokinetic movement. In addition 15-30 Hz TA coherence calculated during isometric activation at 100% MVT or 120°/s isokinetic movement correlated moderately with walking function and time from SCI, respectively. Spasticity symptoms correlated negatively with coherence during isometric activation at 100% of MVT in all tested frequency bands, except for 15-30 Hz. Specifically, 10-16 Hz coherence correlated inversely with passive resistive torque to ankle dorsiflexion, while clinical measures of muscle hypertonia and spasm severity correlated inversely with 40-60 Hz.ConclusionAnalysis of intramuscular 15-30 Hz TA coherence during isometric activation at 100% of MVT is related to muscle strength and gait function following incomplete SCI. In contrast several spasticity symptoms correlated negatively with 10-16 Hz and 40-60 Hz TA coherence during isometric activation at 100% MVT. Validation of the diagnostic potential of TA coherence estimation as a reliable and comprehensive measure of muscle strength, gait and spasticity should facilitate SCI neurorehabilation.
Highlights
Spinal cord injury (SCI) has a devastating impact on sensorimotor function, often leading to reduced quality of life, presenting a serious socioeconomic problem for national healthcare systems [1]
Spinal damage is incomplete in approximately half of all spinal cord injury (SCI) cases [2], only limited recovery of residual voluntary motor function is observed during the subacute phase of neurorehabilitation [3]
Systematic analysis of Tibialis Anterior (TA) coherence in this study revealed consistently higher values for all the frequency bands when calculated during fast isokinetic dorsiflexion in subjects with SCI, compared to healthy subjects
Summary
Spinal cord injury (SCI) has a devastating impact on sensorimotor function, often leading to reduced quality of life, presenting a serious socioeconomic problem for national healthcare systems [1]. The development of specific motor disorder symptoms associated with the spasticity syndrome [7,8] may further limit the recovery of voluntary motor strength, gait and activities of daily living [6,7,8,9,10]. As such the development of an objective and comprehensive measure of residual motor function recorded during subacute SCI neurorehabilitation which in turn reflects recovery or deterioration of descending or spinal neuromotor control mechanisms would help facilitate clinical diagnosis and improve treatment strategies. Intramuscular Tibialis Anterior (TA) coherence estimation was performed within specific frequency bands for the 10-60 Hz bandwidth during controlled ankle dorsiflexion in subjects with incomplete SCI with and without spasticity
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