FRANK J. MILNE STATE-OF-THE-ART LECTURE


as determined by measurement of upper airway me- chanics? This question may not be relevant in some cases, aside from cases affected with arytenoid chondritis when the location and extent of the dis- ease process affecting the arytenoid cartilage influ- ence the selection of procedure. In experimental animals, left laryngeal hemiplegia was created in unaffected horses and a sub-total arytenoidectomy was performed.252 No significant improvement in airway mechanics was reported indicating that this procedure is not recommended in the treatment of RLN or in performance horses with arytenoid chon- dritis. It may, however, be indicated in the treat- ment of arytenoid chondritis in broodmare/ nonathletic horses. This is because this surgery effectively removes the infected cartilage and it is believed (although not tested) that this procedure is less likely to expose the horse to postoperative tra- cheal aspirations. On the contrary, the partial ar- ytenoidectomy procedure has been shown, also in an experimental model of laryngeal hemiplegia, to im- prove airway mechanics in horses during exer- cise.67,69 This improvement was not as good as seen after laryngoplasty either using historical con- trols230,246 or within the same horse submitted to the two subsequent procedures.69 In a clinical population, partial arytenoidectomy


was once thought of as a salvage procedure66,253 but is now recognized as an effective alternative to laryngoplasty.68,69,236,254 Recent clinical studies indicate that in horses that have raced before, re- turn to racing is approximately 80%, perhaps higher than after laryngoplasty, which is reported to be approximately 70%. Both partial arytenoidectomy and laryngoplasty procedures properly result in shorter racing careers when compared with peers,216,217 although that result has been chal- lenged recently.255 The level of performance (using earning as a surrogate for airway patency) after partial arytenoidectomy seems to be inferior to that of racehorses with laryngoplasty,236 indicating the superiority of the latter procedure when successful (i.e., successful tieback is better than a successful partial arytenoidectomy). In summary, the data suggest that laryngoplasty


yields superior results in terms of improving airway patency, although results after a partial arytenoid- ectomy seem to be more uniform. The degree of restoration of airway patency is of course dependent on the demand of the desired athletic endeavor of a particular horse.


Laryngeal Reinnervation


Laryngeal reinnervation procedures (nerve-pedicle or nerve implantation) were first introduced in hu- mans.256,257 At the time, the value of the reinner- vation was to prevent atrophy and provide bulk to the reinnervated muscle. This is still considered of value in reinnervation of the vocal cord.258 The nerve-pedicle, nerve implantation procedures, as well as nerve anastomosis of the first or second


106 2016  Vol. 62  AAEP PROCEEDINGS


cervical nerve to the recurrent laryngeal nerve were then adapted to experimental horses in 1989.259–261 In experimental horses, the value of the nerve-muscle pedicle transplant procedure was evaluated by Ful- ton et al, 1991.262,263 This group was able to show an improvement of the airway patency as assessed by determination in airway mechanics after trans- plantation of nerve-muscle pedicle(s) in the left CAD muscle of a recently denervated muscle. However, the time for this maximal effect (52 weeks) re- mains the main negative of this procedure: the long delay associated with reinnervation. The target clinical patient for a reinnervation is a clinically affected horse (often 1–2 years old) with laryngeal Grade II or III where the muscle volume of the CAD is still significant. Is there a need for transection of the native recurrent laryngeal nerve to avoid the blocking effect of dual innervation? These horses still have significant arytenoid move- ment and transecting the native recurrent laryngeal nerve would worsen the laryngeal collapse until re- innervation occurs. Other questions not answered by the study in experimental animal were: What are the results in horses with naturally-occurring disease? Is there a way to speed up the reinnerva- tion process? Here we are missing a double blind study, yet much progress has been made in answer- ing this question in great part by the work of Ian Fulton and colleagues in Australia.264,265 In his population, his group has not transected the native recurrent laryngeal nerve and still reported success in terms of return to racing as similar to what is seen after laryngoplasty. The hypothesis is that the transplanted nerve-pedicle reinnervated the dener- vated muscle and muscle still innervated by native recurrent laryngeal nerve are excluded from this process. The reported successes confirm that the procedure is applicable in horses with naturally oc- curring RLN. The main advantage of the laryngeal reinnerva-


tion technique is its lower morbidity once the horse has recovered from general anesthesia. This is be- cause it provides a more physiological restoration of function without compromising airway protective mechanisms. The complication rate after laryn- geal reinnervation is consequently very low. How can reinnervation be improved? The au-


thor currently has abandoned the nerve-pedicle procedure in favor of a newer technique intro- duced in human laryngeal reinnervation described by the group led by J. P. Marie in Rouen, France.266 There is a question as to the quantity and extent of the reinnervation obtained from the first/second cer- vical nerve. As a result, the abduction of the ary- tenoid cartilage might not be sufficient after reinnervation to prevent vocal cord collapse during exercise. Therefore, unilateral ventriculocordec- tomy with reinnervation procedures was performed. How can the speed of reinnervation be improved?


Tessa Gordon and colleagues have shown that 1-hour electrical stimulation at the time of injury


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