Acute effects of perineural administration of sodium hyaluronate on palmar digital neurectomy sites in horses.

The research examines the short-term effects of injecting sodium hyaluronate directly into the nerves of horses’ lower limbs after undergoing neurectomy, a surgical nerve removal procedure. The study finds that neither lameness nor the development of painful nerve growth (neuroma) were observed, however, swelling at surgery sites was common.

Experimental Design and Procedure

The trial involved six mixed-breed adult male horses, on which a two-axis surgical nerve removal operation – “palmar digital neurectomy” – was performed on all legs. Following the operation, the horses were divided into three groups:

• The first group received an injection of 20mg (or 2ml) of sodium hyaluronate, a substance commonly present in connective, epithelial and neural tissue.
• The second group got a 2ml injection of a saline solution buffered with phosphate.
• The third group had a catheter put in place but did not receive any injection.

The procedure was carried out after the surgical wounds were closed and the catheter was subsequently removed.

Observations and Measures

Over a nine-week period post-surgery, the horses were evaluated for signs of lameness, swelling, and observable changes via ultrasound. These evaluations took place daily for the first week before switching to weekly tests. The researchers monitored heel sensation, which the neurectomy halted in all limbs for the duration of the study. All surgical sites manifested swelling.

Results and Conclusion

Based on the measures of pastern circumference, which is the part of a horse’s lower limb located between the fetlock and hoof, and ultrasound evaluations of incisional swelling, the researchers found no significant differences between the three treatment groups. The horse’s ultrasonographic hyperechogenicity – an ultrasound effect where tissues appear brighter than normal – increased over time, but displayed no significant variance between the treatments.

After the nine weeks, the horses were euthanised, and the operated sites were extracted for a histological study focusing on axonal regrowth, inflammation, and fibrosis. The histopathological analysis revealed the presence of neuromas – noncancerous growth of nerve tissue – at all operative sites. However, there were no significant differences observed among the treatment groups in terms of cross-sectional areas of neuromas and assessments of neuroma density and fibrous tissue content.