LOCALIZATION OF INNERVATION ZONE (IZ) BASED ON HIGH-DENSITY EMG ARRAY RECORDINGS IN HEALTHY AND STROKE SUBJECTS.

Objectives: Botulinum toxin injection remains the first line management for focal spasticity in stroke patients. Botulinum toxin blocks presynaptic release of acetylcholine at the neuromuscular junction. Current knowledge of the innervation zone (IZ) of motor points is based on histological cadaver studies. The specific aim was to localize IZ non-invasively using high-density EMG recordings in healthy (Exp 1) and stroke (Exp 2) subjects. Design: We enrolled 11 young and healthy subjects in Exp 1 and 10 hemiparetic stroke subjects in Exp 2. The subjects had similar procedures in Exp 1 and 2. A high-density linear electrode array was placed from the proximal to distal tendon junction of biceps brachii muscle. EMG recordings were made on each side in a randomized order during the following two conditions: 1) maximum voluntary contraction (MVC) of elbow flexion and 2) electrical stimulation of the musculocutenous nerve at the intensity that generated maximum responses (M-wave) using an electrical stimulator. Stimulus artifacts were removed from EMG recordings offline. The IZ was localized where the polarity of motor unit action potentials changes, i.e., cross-correlation between adjacent two bipolar signals is the lowest. Results: Innervation zones were easily detected visually and were confirmed by cross-correlation analysis in both MVC and M-wave conditions for both healthy and stroke subjects. There were no differences in IZ locations between two sides in healthy and stroke subjects, and between MVC and M-wave methods. Conclusions: This study demonstrated successful and reliable localization of IZ of biceps muscles in both healthy and stroke subjects. The findings suggest that the M-wave technique could be applied to patients with severe spasticity to detect IZ. These patients usually can not produce voluntary contractions. High-density EMG recordings with M-wave technique could be used for accurate IZ location, which could guide botulinum toxin injection for maximum outcomes. [ABSTRACT FROM AUTHOR]