Thyrohyoideus muscle innervation in the horse.
Authors: Genton Martin, Robert Celine, Jerbi Hassen, Huet Hélène, Cordonnier Nathalie, Vitte-Rossignol Amelie, Perkins Justin D, Rossignol Fabrice
Journal: Veterinary surgery : VS
Summary
# Thyrohyoideus Muscle Innervation in the Horse: Clinical Implications for Laryngeal Surgery The thyrohyoideus muscle plays a crucial role in laryngeal function, yet its neural supply has remained poorly characterised in equine anatomy—a gap that becomes significant when surgeons operate in the cervical region to address conditions such as laryngeal hemiplegia and dorsal displacement of the soft palate. Martin and colleagues undertook a two-phase investigation combining detailed dissection of 14 equine specimens (20 sides total) with histological confirmation, then validated their anatomical findings through intraoperative nerve stimulation in 17 clinical cases undergoing cervical nerve grafting. Their work demonstrated that the thyrohyoideus receives innervation predominantly directly from the first cervical (C1) nerve in 85% of dissections, with the remainder showing variable anastomotic connections between C1 and the hypoglossal nerve (CN XII); importantly, no direct CN XII supply was identified, and histological analysis confirmed that any anastomotic fibres originated from C1. Clinical validation proved robust, with C1 stimulation eliciting thyrohyoideus contraction in 16 of 17 horses, establishing clear neuromuscular connectivity. These findings carry direct surgical relevance: preservation of C1 nerve integrity should be prioritised during prosthetic laryngoplasty procedures, and current C1 nerve grafting protocols warrant reconsideration given the muscle's documented dependence on this nerve, whilst emerging therapeutic approaches for soft palate displacement may benefit from this improved anatomical understanding.
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Practical Takeaways
- •Preserve the C1 nerve during prosthetic laryngoplasty procedures to maintain thyrohyoideus function and avoid iatrogenic denervation
- •Consider C1 nerve anatomy and variable branching patterns when planning cervical nerve grafts for laryngeal hemiplegia treatment
- •Recognition of C1 innervation of TH muscle may inform development of new surgical approaches for dorsal displacement of the soft palate management
Key Findings
- •Thyrohyoideus muscle innervation originates from the C1 nerve in 17 of 20 dissections (85%), with variable branching patterns including anastomotic connections with CN XII
- •Histological analysis confirmed C1 nerve fibers form the anastomosis with CN XII, with no direct CN XII connection to the TH muscle
- •C1 nerve stimulation induced TH muscle contraction in 16 of 17 clinical horses (94%), confirming in vitro anatomical findings