Sternothyrohyoideus myectomy or staphylectomy for treatment of intermittent dorsal displacement of the soft palate in racehorses: 209 cases (1986-1991)

Abstract

Summary The efficacy of sternothyrohyoideus myectomy (SM) and staphylectomy as treatments for intermittent dorsal displacement of the soft palate was evaluated in 209 racehorses (126 Thoroughbreds, 83 Standardbreds). The 2 most common complaints were respiratory tract noise (75% of horses) and exercise intolerance (51% of horses). Stopping, defined as the inability to finish the race at racing speed, was reported in 40% of the horses. Endoscopy at rest revealed evidence of abnormal epiglottic anatomy (hypoplasia or flaccidity) in 51 % of the horses and abnormal soft palate function in 36% of the horses. Race records were available for 149 (77 Thoroughbreds, 72 Standardbreds) horses. The sex distribution consisted of 38% sexually intact males, 20% geldings, and 42% females, with a mean age of 3.4 years. Sixty-nine horses underwent staphylectomy, with a mean of 16 weeks to first start after surgery. Eighty horses underwent SM, with a mean of 10 weeks to first start. Sternothyrohyoideus myectomy was performed on significantly more ( P < 0.05) Thoroughbreds than Standardbreds, and staphylectomy was performed on significantly ( P < 0.0001; χ 2 = 39.56) more Standardbreds than Thoroughbreds. After surgery, most horses (74%) had no change in class; however, more moved up in class (17%) than down (9%). On the basis of comparison of earnings for 3 starts before surgery with that for 3 starts after surgery, successful outcome was obtained in 60% of the horses (35 Thoroughbreds, 13 Standardbreds) that received SM and in 59% of the horses (11 Thoroughbreds, 30 Standardbreds) that received a staphylectomy. The likelihood of achieving a successful outcome was greatest in horses with total earnings between $5,000 and $25,000. This difference was only significant, however, when this group was compared with those horses with total earnings of less than $5,000 ( P = 0.048; χ 2 = 3.89). Presurgical endoscopic findings were not significantly associated with the outcome after surgical treatment.