Neurophysiological assessment of lower-limb voluntary control in incomplete spinal cord injury

Abstract

Study design: Cross-sectional retrospective study of a neurophysiological method of voluntary motor control characterization. Objectives: This study was undertaken to validate the surface electromyography (sEMG)-based voluntary response index (VRI) as an objective, quantitative, laboratory measure of spinal cord injury severity in terms of voluntary motor control disruption. Setting: VA Medical Centers in Houston and Dallas Texas, USA. Methods: A total of 67 subjects with incomplete spinal cord injury (iSCI), American Spinal Injury Association Impairment Scale (AIS)-C (n ¼ 32) and -D (n ¼ 35) were studied. sEMG recorded during a standardized protocol including eight lower-limb voluntary motor tasks was analyzed using the VRI method that relates multi-muscle activation patterns of SCI persons to those of healthy-subject prototypes (n ¼ 15). The VRI is composed of a measure of the amount of the sEMG activity (magnitude) and the distribution of activity across muscle groups compared to that of healthy subjects for each motor task (similarity index, SI). These resulting VRI components, normalized magnitude and SI, were compared to AIS clinical findings in this study. Receiver operating characteristic analysis was performed to determine the SI values best separating AIS-C and AIS-D subjects. Results: Magnitude and SI for AIS-C subjects had mean values of 0.2770.32 and 0.6570.21, respectively. Both parameters were significantly larger in the AIS-D subjects (0.7870.43 and 0.9370.06), respectively (Po0.01). An SI value of 0.85 was found to separate AIS-C and AIS-D groups with a sensitivity of 0.89 and a specificity of 0.81. Further, the VRI of each leg strongly correlated with the respective AIS motor score (0.80, ro0.01). Conclusions: In the domains of voluntary motor control, the sEMG-based VRI demonstrated adequate face validity and sensitivity to injury severity as currently measured by the AIS.

Reliability of surface EMG as an assessment tool for trunk activity and potential to determine neurorecovery in SCI

“…published for SIs in individuals with SCI (0.48). 13 Moreover, the consistency in the computed SIs (approaching 1) among our neurologically-intact subjects for different maneuvers demonstrate Table 4 Complete list of muscle groups chosen for each maneuver Pre-ES is pre-electrical stimulation interventions. Post-ES alone is after 60 sessions of bilateral ES of the lower limbs while supine and post-ST+ES is after 51 sessions of intense-active-stand training using body-weight support with bilateral ES of the lower limbs.…”

“…5 The multi-muscle RMS sEMG during each maneuver were further evaluated by adapting a 'vector-based analyses method', termed the voluntary response index (VRI), and previously developed for the lower-limb BMCA protocol. 6 The VRI calculation has been shown to have strong-face validity, sensitivity and specificity 13 and good test-retest reliability for set-motor tasks of the lower limbs. 7 The computation of the VRI incorporates two values associated with sEMG: the magnitude of the signal and the similarity index (SI).…”

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“…The voluntary response index was developed using the analysis of the results of EMG recorded during elementary voluntary motor tasks performed in the supine position (Lim et al, 2005). In brief, the voluntary re-…”

“…sponse index is a mathematical function that incorporates data on the similarity index and the magnitude of the response vector (Lim et al, 2005). The similarity index was estimated from a comparison of the distribution of activity (or response vector) in 10 lower-extremity muscles of a spinal cord injured individual to the responses among healthy individuals (Lim et al, 2005).…”

Lower Limb Voluntary Movement Improvement Following a Robot-Assisted Locomotor Training in Spinal Cord Injury

“…Literature reveals muscle weakness [10,11], abnormal increase in muscle tone (i.e., spasticity) [5,10] and abnormal co-activation in muscular patterns between agonists and antagonists [7,11]. In incomplete SCI ambulatory patients, these symptoms drive a reduction of voluntary movement at the ankle joint.…”