CHAPTER 55 Surgical Advancement of the Larynx for Treatment of Dorsal Displacement of the Soft Palate
The primary cause for dorsal displacement of the soft palate (DDSP) is likely neuromuscular dysfunction of the palatinus and palatopharyngeus muscles. Surgical repositioning of the larynx appears to decrease the likelihood of DDSP. The postulated principle of this procedure is provision of extrinsic stability to the nasopharynx by reducing the likelihood that DDSP occurs. This is achieved by replacing thyrohyoideus muscle function so the larynx is fixed in a more dorsal and rostral position. The hypothesis was developed in experimental treadmill studies in which bilateral thyrohyoideus resection resulted in exercise-induced DDSP that was corrected by forward transposition of the larynx. This experimental study was followed by a clinical phase in which 116 racehorses were treated and had an 80% to 82% success rate that resulted in increased earnings after surgery. A 6% recurrence of DDSP was seen 4 to 12 months after surgery in these horses. At the time of writing this chapter, 341 horses (including the 116 horses mentioned) comprising 57% Standardbred and 42% Thoroughbred racehorses and 1% sport horses have undergone the surgical procedure. Thirty-one percent were 2-year-olds, 38% were 3-year-olds, and the remainder were older than 4 years of age.
SURGICAL TECHNIQUE
Original Technique Performed in 214 Horses
A 3.2-mm drill bit is used to create a hole in the midportion of the basihyoid bone. Two size 5 polybend sutures (Fiberwire Arthrex Inc., Naples, FL) are passed through the hole in the basihyoid bone from ventral to dorsal while protecting the underlying vessels with a curved gauge (Figure 55-1). Vessels are best avoided if the sutures and dissection are limited to the dorsal midline area of the basihyoid bone. The sternothyroideus muscle’s tendon of insertion on each of the thyroid cartilage laminae is undermined and isolated in preparation for transection, if this was not already performed in a prior surgery. The suture is then inserted at the ventral aspect of the right sternothyroideus tendon of insertion and exits rostrally and slightly dorsally approximately 1 cm from the entry point (Figure 55-2). A second suture is placed through the right lamina of the thyroid cartilage slightly more dorsal and exits 0.5 cm more dorsally than the previous bite (thus forming a loop) in the thyroid lamina. The procedure is repeated on the left side. The sternothyroideus tendons of insertion are transected after the sutures are placed in the thyroid lamina.
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