The Neuromuscular Junction Distribution in the Upper Face: An Anatomy-to-Practice Review to Inform Botulinum Toxin Type A Treatment Planning.

BACKGROUND

Upper-face botulinum toxin treatment planning often relies on surface landmarks and standardized injection patterns, yet neuromuscular junctions are distributed in muscle-specific motor zones that vary in topography, depth, and overlap. Injecting near an optimal motor zone has been associated with greater clinical effect, suggesting that mapping these patterns may refine anatomy-guided targeting and reduce variability.

AIMS: To synthesize anatomical evidence on micro-innervation and neuromuscular junction clustering in the frontalis, corrugator supercilii, orbicularis oculi, procerus, and depressor supercilii.

METHODS

A clinician-oriented "anatomy-to-practice" narrative review was conducted. Studies with extractable human, muscle-level micro-innervation mapping were synthesized qualitatively, emphasizing cluster location, depth, and distribution.

RESULTS

Neuromuscular junctions were nonuniformly distributed, forming muscle-specific distribution patterns, ranging from more discrete, clustered territories to diffuse fields. They tended to concentrate in the mid- to upper-frontalis belly along the deep fascial surface; in the corrugator supercilii, predominantly within the medial portion and at greater depth, centrally and inferiorly along the orbital rim in the depressor supercilii; and inferiorly near the nasion in the procerus. In the orbicularis oculi, neuromuscular junctions were diffusely distributed across the muscle. Given heterogeneous and often proxy-based mapping, these territories are best interpreted as probabilistic fields.

CONCLUSIONS

Micro-innervation and neuromuscular junction distribution represent a complementary anatomical layer that may inform upper-face botulinum toxin treatment planning alongside dynamic assessment, clinical judgment, and established safety considerations.