Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications.

This research examines the dorsal cricoarytenoid muscle of the horse to gain a better understanding of its neuroanatomy in an effort to develop a neuroprosthesis for a condition known as recurrent laryngeal neuropathy. Key characteristics such as the muscle’s structure, nerve supply, fibre types, and function were analyzed.

Research methodology

• The researchers started by collecting 31 horse larynges at necropsy, specifically from horses with no history of upper airway disease.
• 25 of these were then subjected to gross dissection to identify key anatomical features.
• Several larynges were prepared for histochemical staining (5), Sihler’s and acetylcholinesterase staining for motor endplates (2). These staining techniques were used to visualize specific components of the muscle and its nerve supply.
• An additional six larynges were used for a muscle stimulation study to observe the reaction of the muscle when electrical stimuli were applied.

Research findings

• Two neuromuscular compartments (NMCs), each supplied by a primary nerve branch from the recurrent laryngeal nerve, were found in all the larynges.
• Through the muscle stimulation study, the lateral NMC was found to produce a greater lateral displacement of the arytenoid cartilage, while the medial NMC tended to rotate the cartilage dorsally.
• The main motor nerves, called endplates, were discovered at the junction of the middle and caudal thirds of each NMC.
• Should the grouping of fiber types exist, it would always be present in both NMCs.

Study implications

• The research found two distinct compartments within the equine dorsal cricoarytenoid muscle, each supplied by a different nerve branch and having different functions.
• The lateral NMC seems to play a more significant role in increasing the cross-sectional area of the rima glottidis, the opening between the vocal cords.
• This improved understanding of the muscle’s neuroanatomy can assist in surgical planning for reinnervation procedures, and provide the necessary knowledge for developing a neuroprosthesis for recurrent laryngeal neuropathy in horses.