Attempts to restore abduction of the paralyzed equine arytenoid cartilage. I. Nerve-muscle pedicle transplants.

The purpose of this project was to adapt a surgical technique from humans and dogs to horses in which a portion of an accessory muscle of respiration and its nerve supply is transplanted to a denervated dorsal cricoarytenoid muscle. Anatomical dissections in seven horses revealed two possible donor nerve-pedicle grafts: the omohyoid and the sternothyrohyoid, both innervated by a branch of the first and second cervical nerves. Histochemical evaluations in two ponies of the dorsal cricoarytenoid, omohyoid and sternothyrohyoid muscles revealed similar proportions of fiber types 1 and 2 in all three muscles. Electromyographic studies in these two ponies revealed that the omohyoid and sternothyrohyoid muscles contract synchronously with respirations during forced inspiration under general anesthesia. Based on surgical ease of access, a 1 cm2 portion of the omohyoid muscle at the point of penetration of the second cervical nerve was used as a nerve-muscle pedicle graft in an attempt to reinnervate the left dorsal cricoarytenoid muscle in four ponies. These four ponies (as well as three others which served as controls) had previously undergone left recurrent laryngeal nerve transection. All seven ponies endoscopically showed signs of complete left laryngeal hemiplegia immediately postoperatively. Animals were monitored endoscopically for 30 weeks after surgery. The three control ponies showed no abduction of the arytenoid cartilage. In addition, in these three ponies, histological and histochemical expected changes of muscle fiber atrophy and fibrosis were present in the dorsal cricoarytenoid muscle.(ABSTRACT TRUNCATED AT 250 WORDS)