Sternothyroideus Myotomy for the Treatment of Dorsal Displacement of the Soft Palate

The medical records of 41 racing Standardbreds, diagnosed as having dorsal displacement of the soft palate (DDSP), that underwent sternothyroideus myotomy and soft palate resection were reviewed. All horses had endoscopy of their upper respiratory tract, but not necessarily by Dr. Llewellyn.a The history had to confirm the diagnosis of DDSP. Surgery in each patient was performed by Dr. Llewellyn, using the same surgical protocol in each instance.b Postsurgical racing results were obtained for each of the patients to analyze improvement in on-track performance from the USTA. The race times for each horse were analyzed and adjusted for the track upon which the fastest presurgical and postsurgical results were obtained, using the experimental track ratings, also provided by the USTA. All horses, which were randomly selected for this review, raced at least once after the surgery had been performed. Overall, 29 (70%) of the horses in this study showed some degree of performance improvement after the surgery, whereas six (15%) and six (15%) horses either returned or failed to return to their previous level of performance, respectively, following the surgery. Dorsal displacement of the soft palate is a normal phenomenon that occurs during normal deglutition. Dorsal displacement of the soft palate during exercise is usually an intermittent problem in horses. This displacement of the soft palate occurs when the palatolaryngeal seal is suddenly broken and the free edge of the soft palate lies within the rima glottis of the larynx.1 Elevation of the soft palate above the epiglottis and into the airway as a result of DDSP redirects expiratory gases dorsal and ventral to the soft palate, resulting in airflow through the oral cavity and nasal passages of the exercising horse. The caudal border of the soft palate vibrates violently in the laryngeal opening when expiratory airflow velocity increases during exercise, resulting in the loud expiratory noise associated with DDSP.3 This obstruction to free airflow contributes significantly to the total resistance to airflow in the upper airway, which normally comprises 40% of the total resistance to airflow in the resting horse. Because the horse is an obligate nasal respirator, as a result of the tight seal formed between the soft palate and larynx, the soft-tissue obstruction to free airflow through the nasopharynx and the larynx results in dyspnea. A condition of relative tissue SOFT-TISSUE SURGERY