Dynamic Upper Airway Evaluation of 37 Horses with Residual Poor Performance after Laryngoplasty

Upper airway high-speed videoendoscopic evaluation after laryngoplasty revealed dynamic collapse in 81.6% of horses; 100% of horses with excellent laryngoplasty abduction, 60.9% of horses with moderate to mild laryngoplasty abduction, and 20% of horses without laryngoplasty abduction maintained arytenoid position. Eighty percent of horses with excellent laryngoplasty abduction, 73.9% of horses with moderate to mild laryngoplasty abduction, and 100% of horses without laryngeal abduction had collapse of other laryngeal structures.

1. Introduction

The success rate for prosthetic laryngoplasty ranges from 48% to 95% depending on the success criteria [1-5]. Laryngoplasty failure has been attributed to an inability to maintain arytenoid abduction, and the degree of laryngeal arytenoid abduction has been subjectively related to post-operative success [1,6]. However, some loss of arytenoid abduction will occur in most horses within 6 wk of surgery [6], and the degree of abduction does not necessarily correlate to a successful surgical outcome [7].

The use of videoendoscopic evaluation of the upper respiratory tract during exercise is well documented, and it is indicated for horses with questionable laryngeal function [8-10]. The purpose of this study was to report the findings of dynamic upper airway evaluation of horses presented for poor performance after laryngoplasty and to compare the results with resting endoscopic findings.

2. Materials and Methods

Medical records of horses who had dynamic endoscopic evaluations of the upper airway after laryngoplasty were reviewed. Signalment, performance type, presenting complaints, days after laryngoplasty, and physical examination findings were recorded. Resting videoendoscopic evaluation, including the degree of laryngeal arytenoid abduction, and post-surgical exercising videoendoscopic findings were evaluated and recorded.

3. Results

Thirty-seven horses completing 38 examinations were included. There were 29 geldings, 7 intact males, and 2 females, and the average age was 5.5 yrs (range = 2 - 14 yrs). There were 26 Thoroughbreds, 7 Standardbreds, 3 Warmbloods, and 1 pony. Twenty-three of 26 Thoroughbreds and all Standardbreds were used for racing. Of the remaining horses, two were used for dressage, two were used for eventing, one was a show hunter, and one was a show jumper; the pony was used for driving.

Thirty-four (91.9%) horses presented with a history of poor performance, 30 (81.1%) horses had an abnormal respiratory noise, and 6 (15.8%) horses presented with a cough. Thirty-seven horses presented post left laryngoplasty, and five examinations were performed after repeat laryngoplasty.

The mean number of days after surgery was 378 (range = 67 - 842 days). In six horses, the exact surgical date was not known because of ownership change; however, it was estimated to be at least 1 yr before the examination. The date of surgery was unknown in two horses. External palpation revealed laryngeal thickening in 25 of 28 (89.3%) horses.

Standing endoscopic evaluation revealed an immobile left arytenoid in all 38 examinations. The degree of laryngoplasty arytenoid abduction was judged to be excellent in 5 horses, moderate to mild in 23 horses, and none (resting position) in 10 horses. In addition to prosthetic laryngoplasty, left ventriculectomy had been performed in 6 (15.8%) horses and ventriculocordectomy in 23 (60.5%) horses. Other abnormal upper airway findings included intermittent dorsal displacement of the soft palate in six horses, arytenoid chondropathy in four horses, granulation tissue in the cranial trachea in one horse, ulceration along the caudal free edge of the soft palate in one horse, and right ventriculocordectomy in one horse. Endoscopic evaluation of the trachea revealed mucus in 20 (52.6%) horses and food particles in 7 (18.4%) horses.

The average total exercising videoendoscopic time was 4.63 min (range = 1.5 - 10.87 min). The average maximum speed was 11.3 m/s (range = 4 - 14.3 m/s). Average total distance traveled was 2463 m (range = 772 - 5300 m). The average incline of the high-speed treadmill was 1° (range = 0 - 3°). Complications occurred during nine high-speed examinations; eight horses lost one or more horse shoes, and one horse broke the halter.

High-speed videoendoscopic evaluation revealed dynamic collapse in 31 (81.6%) examinations (Table 1). Dynamic collapse of the right vocal fold (Fig. 1) was noted in 18 (58.1%) horses, left arytenoid (Fig. 1) in 17 (54.8%) horses, axial deviation of the left aryepiglottic tissue in 15 (48.4%) horses, left vocal fold (Fig. 2) in 14 (45.2%) horses, axial deviation of the right aryepiglottic tissue (Fig. 2) in 9 (29. 0%) horses, intermittent dorsal displacement of the soft palate in 5 (16.1%) horses, left corniculate process (Fig. 3) in 5 (16.1%) horses, and permanent dorsal displacement of the soft palate in 1 horse.

Figure 1. Exercising videoendoscopic examination of a 4-yr-old Thoroughbred gelding with moderate resting arytenoid abduction. Dynamic collapse of the left arytenoid (white arrow) and right vocal fold (yellow arrow) was identified.

Figure 2. Exercising videoendoscopic examination of a 7-yr-old Thoroughbred gelding with moderate resting arytenoid abduction. Dynamic collapse of the right aryepiglottic fold (white arrow) and the left vocal fold (yellow arrow) were identified.

Figure 3. Exercising videoendoscopic examination of a 5-yr-old Thoroughbred gelding with moderate resting arytenoid abduction .Dynamic collapse of the corniculate process (arrow) of the left arytenoid was identified.

All horses with collapse of the left arytenoid also had collapse of another soft-tissue structure. Thirteen of 14 horses with collapse of the left vocal fold did not have a previous ventriculectomy or ventriculocordectomy. One-hundred percent of horses with excellent abduction, 60. 9% of horses with moderate to mild abduction (Fig. 4), and 20% of horses with no abduction maintained laryngoplasty arytenoid position. Four of 5 (80%) horses with excellent abduction, 17 of 23 (73.9%) horses with moderate to mild abduction, and 10 of 10 (100%) horses with no abduction had dynamic collapse of other laryngeal or pharyngeal structures (Fig. 2).

Figure 4. Exercising videoendoscopic examination of a 5-yr-old Standardbred colt with moderate resting arytenoid abduction. The left arytenoid maintained its fixed position during exercise.

4. Discussion

The degree of laryngeal arytenoid abduction has been used to assess surgical efficacy. In one study, horses with greater laryngoplasty arytenoid abduction were more likely to return to full work than horses with lesser abduction [4]. In another study, horses with >70% of maximal arytenoid abduction received a higher performance score [1]. However, in an experimental study, the stability of the prosthesis and not the degree of abduction was the major factor in determining inspiratory resistance [8]. The majority of horses in this study had moderate to no laryngoplasty abduction. This was not unexpected, because these horses presented for poor performance, presumably from a failed laryngoplasty. The degree of laryngeal arytenoid abduction was related to dynamic arytenoid collapse; 100% with excellent abduction, 60.9% with moderate to mild abduction, and only 20% with no laryngoplasty abduction maintained arytenoid position.

Owners and trainers often associate the presence of an abnormal upper respiratory noise with failed surgery. However, it has been suggested that noise should not be used as a sole criteria for defining failure [2]. Experimental studies using respiratory sound recordings found residual noise during exercise in all horses with laryngoplasty. The noise was actually louder in horses with the greatest surgical arytenoid abduction [11], and bilateral ventriculocordectomy was the only surgical procedure resulting in noise reduction [12]. Noise production may also be associated with activity level; 60% of racehorses and 76% of sport and pleasure horses had resolution of noise after laryngoplasty [4]. In this study, 81.1% of horses presented with a complaint of an abnormal noise, and 93.5% (29 of 31 examinations) had dynamic laryngeal collapse. All horses with dynamic collapse of the left arytenoid and/or left vocal fold and 17 of 18 (94.4%) horses with right vocal fold collapse made a noise.

High-speed treadmill videoendoscopy post-laryngoplasty identified dynamic collapse in 81.1% of the horses. However, only 17 (54.8%) examinations had arytenoid collapse because of a failed laryngoplasty. In addition, concurrent collapse of additional upper respiratory tract structures was noted in all 17 examinations. Fourteen (45.2%) examinations without arytenoid compromise had collapse of other laryngeal or pharyngeal structures. Exercising videoendoscopic evaluation of the upper airway should be considered for accurate diagnosis of laryngeal and pharyngeal function, appropriate treatment management, and surgical intervention in horses with residual poor performance and/or upper respiratory tract noise after laryngoplasty.