Proceedings of a Workshop on - The Havemeyer Foundation

Equine Recurrent Laryngeal Neuropathy
IMPROVEMENTS IN LARYNGOPLASTY
E. J. Parente
University <strong>of</strong> Pennsylvania, New Bolton Centre, 382 West Street Road, Kennet Square, PA 19348, USA
Despite recognition <strong>of</strong> laryngeal hemiplegia for
over 100 years and development <strong>of</strong> the
laryngoplasty procedure over 30 years ago, there
have been no major changes to treatment <strong>of</strong>
laryngeal hemiplegia since its description by
Marks et al. (1970). There is still reluctance by
trainers to have the procedure performed as it does
not return the horse to ‘normal’, and has potential
complications. Furthermore, failure to maintain
abduction <strong>of</strong> the arytenoid, both short-term and
long-term, is a documented problem. This has led
to interest in modifications <strong>of</strong> the standard
laryngoplasty and alternative procedures.
Unfortunately, alternative procedures such as reinnervation
have had limited success and require a
longer return to return to training.
A minor but significant improvement in
laryngoplasty is removal <strong>of</strong> the vocal cord. While
early research did not detect a significant
improvement in airway mechanics with a
ventriculectomy, most surgeons now believe that
removal <strong>of</strong> the vocal cord is beneficial based on
both clinical and experimental evidence. Treadmill
endoscopy clearly demonstrates the deviation <strong>of</strong>
the vocal cord during inspiration if it is not
removed as an adjunctive procedure with
laryngoplasty. While the sacculectomy may not
truly stabilise the cord, there is some question
whether a sacculectomy is beneficial by creating
fibrous support for the abducted arytenoid.
The majority <strong>of</strong> efforts to improve
laryngoplasty deal with maintenance <strong>of</strong> arytenoid
abduction and thus suture retention (Dixon et al.
2003). Causes <strong>of</strong> failure are thought to be
associated with suture pull out, assumed through
the muscular process based on experimental
models (Dean et al. 2001). Yet, more <strong>of</strong>ten it
appears to be ‘loosening’ in clinical cases that
results in decreased abduction. One technique
developed to minimise loosening was concurrent
recurrent laryngeal neurectomy while performing
laryngoplasty for horses with remaining laryngeal
motion (Davenport et al. 2001). The hypothesis
was that cycling from remaining muscular pull
resulted in suture loosening. Performing the
neurectomy was ineffective in improving the
prognosis relative to standard laryngoplasty.
Other methods to maintain arytenoid
abduction include techniques to place sutures and
different suture materials. Mechanical testing <strong>of</strong> in
vitro models has been promising but these
methods do not yet have long-term clinical followup
and may present greater difficulty in placement
in vivo than present standard procedures.
We have pursued 2 other methods. We now
<strong>of</strong>ten approach the muscular process from behind
the cricopharyngeus muscle. This can be
performed with appropriate positioning <strong>of</strong> the
horse under general anaesthesia. Dissection is
performed easily just above a branch <strong>of</strong> the cranial
thyroid vein and just caudal to the
cricopharyngeus muscle through dense fascia to
access the muscular process <strong>of</strong> the arytenoid. This
approach should minimise any slack <strong>of</strong> the suture
material by fascial interference and prevent
crossing <strong>of</strong> suture that could occur when passing
multiple strands under the cricopharyngeus
muscle belly.
An approach to improve stability <strong>of</strong> the larynx
with laryngoplasty has also been developed by
creating an arthrosis <strong>of</strong> the cricoarytenoid (CA)
joint. The hypotheses for the experimental model
were: 1) that surgical destruction <strong>of</strong> the CA joint
could be performed using a motorised burr via a
routine laryngoplasty surgical approach; 2) that
surgical destruction <strong>of</strong> the CA joint with a
motorised burr in conjunction with laryngoplasty
would result in joint fusion and improved stability
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