Page 657 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

632 CHAPTER 3

VetBooks.ir 3.66 occurs during racing. Comparison between resting
and treadmill endoscopy does show that findings of
DDSP or palatal/pharyngeal flaccidity at rest are not
predictive for DDSP at exercise (Fig. 3.66).

Management
The most common surgical procedure used for
DDSP is the laryngeal advancement or ‘tie forward’
procedure. A permanent suture is placed between
the thyroid cartilage on either side and the basihyoid
bone (Fig. 3.67). The head is flexed as the sutures
are tightened, resulting in rostral displacement of
the larynx relative to the basihyoid of 4–5 cm. The
basis of this procedure is the experimental data
showing DDSP at exercise following transection
of the thyrohyoid muscle, which is subsequently
reversed by a tie forward. Objective studies compar-
ing racing performance suggest the success rate is in
excess of 80%.
Many other procedures have been used to treat
DDSP over the years. If any primary or pre- disposing
Fig. 3.66 Dorsal displacement of the soft palate and conditions are diagnosed these need to be treated.
collapse of the ventral wall of the nasopharynx, or Conservative measures include a period of rest fol-
billowing of the soft palate at exercise, observed by lowed by increasing the fitness of the horse. Studies
overground endoscopy during fast gallop exercise. have shown that this approach may be as effective
as surgical treatment. A tongue tie has tradition-
ally been advocated to stop the horse retracting its
3.67 tongue and consists of a leather or other material
(such as a pair of tights) tied around the tongue, and
then around the lower jaw. Recent research has failed
to show any benefit. Australian or ‘figure-of-eight’
nosebands have been used to stop the horse open-
ing its mouth during exercise, although with modern
concepts of the pathophysiology of this condition
they seem unlikely to work. Many of these devices
are subject to regulations under the rules of racing
or competition of the relevant organisations – in the
UK the Cornell collar is banned for racing and a
tongue tie must be declared and inspected prior to
the start.
Surgical myotomy of the ‘strap’ muscles (sterno-
thyrohyoid muscles) was advocated to prevent caudal
retraction of the larynx and hence DDSP. Research
Fig. 3.67 Postoperative radiograph following a tie has shown that myotomy results in increased respi-
forward procedure. The suture eyes in the thyroid ratory impedance and that these muscles are impor-
cartilage are visible and the ossification of the thyroid tant secondary muscles of respiration. The technique
cartilage (arrows) is rostral to the ceratohyoid bone. has been adapted to tenotomy of the insertion of the