Histological examination of the interspinous ligament in horses with overriding spinous processes.

The research article is a histological study comparing the structural anatomy and innervation of the interspinous ligament in horses with clinically significant overriding spinous processes (ORSPs) to normal horses. The study discovered significant alterations in ORSP horses, including altered collagen structure, increased fibrocartilaginous tissue, and a higher number of nerves, which may explain thoracolumbar pain in these animals.

Objective of the Study

• The research aimed to understand the structural anatomy and innervation of the interspinous ligament (ISL) in horses with clinically significant overriding spinous processes (ORSPs). This was done by conducting a comparative study with horses that do not have any spinal pathology

Methodology

• The researchers sampled the ISL from 10 horses with ORSPs undergoing subtotal ostectomy. They obtained control samples from horses without spinal issues.
• For an accurate evaluation of the ISL structures, they performed histological staining of the sections with haematoxylin and eosin. This aided in assessing the ligament morphology.
• The proteoglycan and glycosaminoglycan content within the ISL was determined using Alcian blue-periodic acid-Schiff.
• The research encompassed a quantitative assessment of nerves within the ISL by employing immunohistochemistry for S100.

Findings

• The ISL of horses with ORSPs revealed a significant deviation in the alignment of collagen fibres and the arrangement of ligamentous layers than the control group.
• There was a substantial surge in fibrocartilaginous tissue with evidence of the transformation into fibrocartilaginous tissue (P=0.001).
• The quantity of nerves found in the ISL samples of horses with ORSPs was significantly more than in the control group (P=0.017).

Conclusion

• The study concluded that structural changes in the ISL, such as altered fibre alignment and increased fibrocartilaginous tissue, are associated with ORSPs in horses.
• The increase in innervation of the ISL in horses with ORSPs could potentially account for the thoracolumbar pain experienced by some of these horses compared to normal horses.