Attempts to restore abduction of the paralyzed equine arytenoid cartilage. III. Nerve anastomosis.

This research investigates a surgical technique for restoring the function of a specific muscle involved in horse larynx, which can be paralyzed in certain cases. The technique involves connecting a healthy nerve to the damaged one to stimulate function recovery. The tests were conducted on ten horses, some of which had the procedure, and others as control subjects. The results show some recovery in the surgically-treated horses, but no improvement was observed in the respiratory function of all horses after the operation.

Objective of the Research

• The aim of the study was to attempt to restore the muscle function that controls the opening of the windpipe in horses which got paralyzed due to nerve damage (denervation).
• This was done by transecting and ligating the damaged nerve (left recurrent laryngeal nerve) and then connecting it with a different healthy nerve (the first cervical nerve) which still conducts impulses – a process known as nerve anastomosis.

Methodology

• The researchers used ten horses in total, out of which six horses underwent surgery for nerve anastomosis.
• The remaining four horses were the control group. These horses also had the damaged nerve cut and tied off, but they were not given the nerve anastomosis treatment.
• Various tests such as endoscopy and upper airway resistance were done before and at certain intervals (one week, three months, and six months) after surgery to assess the effects of the surgical procedure.

Findings

• Post surgery, all ten horses exhibited signs of complete laryngeal hemiplegia, a condition where one side of the larynx is paralyzed.
• From the third month after surgery, involuntary spasms of the left arytenoid cartilage (part of the larynx) were observed in four of the horses that underwent nerve anastomosis, but no such movement was noticed in the control group horses.
• By the sixth month of post-surgery, five of the treated horses showed involuntary spasms in the larynx.
• When the researchers measured the resistance in the upper airway (an indication of difficulty in breathing), they found no significant difference between the readings before and after surgery for both control and experimental groups.
• After euthanizing the horses at the end of the six months, a comparison of the weights of the treated and untreated larynx muscles showed no significant difference in the treated group, but the untreated muscle in the control group horses weighed less.

Conclusion

• While the nerve anastomosis procedure was able to cause some movement in the laryngeal muscle, it didn’t contribute towards an improvement in the horses’ respiration. Also, the recovery was not standard across all surgically treated horses.
• The findings call for further research to understand why the technique resulted in minimal to no improvements, and how it could be refined for better recovery of laryngeal function in horses.