Microanatomic characteristics of the insertion of the distal sesamoidean impar ligament and deep digital flexor tendon on the distal phalanx in healthy feet obtained from horses.

This study examined the microanatomic structure attaching the deep sesamoidean impar ligament and deep digital flexor tendon to the distal phalanx in a horse’s foot. The scientists found different amounts of a material called proteoglycan in various age groups of horses. They propose that changes in the amount of this substance may be the foot’s adaptive response to stress rather than aging-related changes.

Objective and Methodology

• The research aimed to describe the microanatomic structure of the horse foot’s distal sesamoidean impar ligament (DSIL) and deep digital flexor tendon (DDFT) attachment to the distal phalanx.
• Feet from 62 different horses were used in the study.
• 23 horse feet were histologically examined for the DSIL and DDFT’s insertion, its vasculature, and neural elements.
• The other 39 horse feet were used to study the proteoglycan (a complex protein) content in the insertion zone.

Findings

• They found that the DSIL and DDFT’s insertion, along with the dorsal half of the DDFT, were composed of collagen fibers with loose connective tissue having arteriovenous complexes (AVC) and nerve fibers.
• Through microscopic examination, they noticed changes in the proteoglycan content at the insertion site with age.
• Younger horses showed no or only slight staining for proteoglycans. In middle-aged horses, moderate proteoglycan staining was observed, while the older horses showed little proteoglycan staining at the insertion.

Conclusions

• The study reinforced the existence of a dense neurovascular complex amidst the collagen bundles.
• New evidence was observed with regards to the adaptive change in the production of proteoglycans based on the level of physical stress imposed on these connectors, rather than due to the advancing age of the horses.
• The researchers suggest that this region could be more susceptible to stress during the horse’s stance and impact loading phases. This is because this region appears to play a crucial role in controlling the critical neurovascular functions of the horse’s foot.