Abstract Information


Characterization of Volitional Electromyographic Signals in the Lower Extremity after Motor Complete Spinal Cord Injury

1Heald E, 2Hart R, 1Kilgore K, 1Peckham P
1Case Western Reserve Univsity, Cleveland, OH, United states; 2Louis Stokes Veterans Affairs Medical Center, Cleveland, OH, United states

Objective: The International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) is a standard clinical exam used to classify the neurological injury in SCI, but it does not include electrophysiological testing. Thus it may lack sensitivity to differentiate small levels of residual motor activity, as it is quite possible for this activity to occur without producing observable joint movements. Previous studies have demonstrated the presence of intact neuronal axons across the spinal cord lesion, even in those clinically diagnosed with complete SCI. Though in the past such low-level below-injury activity may have had limited utility, today rehabilitative and restorative technologies might be able to use this activity to assist or restore function to a person with SCI. The objective of this study was to quantify residual volitional motor activity in chronic, clinically complete SCI.

Design/Methods: Twenty-four subjects with chronic (>9 months post-injury) cervical SCI (levels C4-C7) who had been classified as motor complete, AIS A (n=16) or B (n=8), were tested for the presence of volitional below-injury EMG activity. Bipolar surface electrodes recorded EMG from 8-12 locations of each lower limb. In each trial, participants were asked to attempt a specific movement of the lower extremity in response to visual and audio cues. Trials were repeated 2-3 times for each movement type, for a total of approximately 30 trials per limb. EMG trials were ranked through visual inspection, and were scored using an amplitude threshold algorithm to identify channels of interest with motor unit activity correlated to movement cues.

Results: Significant below-injury muscle activity was identified through visual inspection in 16 of 24 participants, and visual inspection rankings were well correlated to the algorithm scoring. In 5 of the 24 participants, robust, command-quality EMG signals were found in at least one lower extremity muscle, despite no visible joint movement.

Conclusion: The majority of subjects tested were able to produce a volitional EMG signal in the lower extremity, despite being classified as motor complete. The presence of this volitional, recordable, myoelectric activity in the lower extremity could provide an innovative new command signal source for implanted neuroprostheses or other assistive technology, and the algorithm we developed allows fast and automatic identification of signals of interest. The surface EMG protocol utilized here is relatively simple and non-invasive, ideal for a clinical screening tool. Our future work will explore the effects of biofeedback training on these signals with the goal of further improving the signal quality.

Support: National Institutes of Health (NINDS R01-NS-078789, T32-EB04314); National Science Foundation (DGE-0951783), Neilsen Foundation #477004.


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