Anatomical Localization of Motor Endplate Bands in the Human Biceps Brachii

Objectives: Botulinum neurotoxin (BoNT) reduces disabling muscle contraction in numerous disorders with muscle overactivity. While motor endplates are the primary site of action for BoNT, their location is unknown in most human muscles. This study localized the motor endplate bands (MEB) within human biceps brachii (BB) muscles in relation to external landmarks. Methods: Five human BB muscles were obtained from autopsy. Three muscles were processed for Sihler's stain, a nerve staining technique, and 2 were processed by whole-mount acetylcholinesterase stain. Results: The major MEB in BB is an inverted V-shaped band, 1 cm in width, located 7 cm superior to the olecranon laterally, 11 cm superior to the olecranon in the middle, and 8 cm above the olecranon medially. The ratio of MEB location to total olecranon-acromion length is 0.25 at the lateral edge, 0.39 in the midline, and 0.28 at the medial edge. Conclusions: This study localized MEB in human BB in reference to external landmarks. This data should improve the feasibility of endplate targeting when injecting BoNT in BB, which might enhance the clinical efficacy of these injections.

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