Digital cushions in horses comprise coarse connective tissue, myxoid tissue, and cartilage but only little unilocular fat tissue.

This study focuses on uncovering the structural details of digital cushions in horses, specifically analysing their vascularization, tissue constituents, and matrix components. It found that these cushions mostly consist of coarse connective tissue, myxoid tissue, and cartilage, with very little presence of unilocular fat tissue, and are designed to absorb mechanical shocks.

Tissue Composition and Vascularization

• The digital cushions of horses, the researchers found, are mainly composed of a network of coarse collagen bundles. The spaces within this network are filled with loosely interwoven connective tissue, myxoid tissue, and fibrocartilage.
• Contrary to what might be expected, the cushions did not contain significant amounts of fat tissues. Instead, the researchers found only occasional solitary adipocytes (fat cells) or smaller groups of them.
• Another finding of the study was that these cushions have a remarkably poor vascular supply, meaning that there are few blood vessels running through them.

Myxoid Tissue and Matrix Components

• The researchers found that the myxoid matrix, a gelatinous substance within the cushions, is largely made up of a substance called hyaluronan and smaller amounts of sulphated glycosaminoglycans. This matrix had cells of varying shapes and a propensity to store glycogen and lipid droplets.
• The myxoid cells in this matrix were identified to be reactive to neuron specific enolase and glial fibrillary acidic protein, markers that are usually found in neural tissues.

Transformations and Interactions

• In the areas where the myxoid tissue was transforming into loosely organized interstitial connective tissue, the resultant fibroblasts remained unreactive for neuroectodermal markers, going against behavior seen elsewhere.
• A lack of clear demarcation was observed between the myxoid tissue and irregularly interspersed islets of fibrocartilage or hyaline cartilage.
• A small amount of unilocular fat cells were located in the myxoid areas. These cells reacted with certain neural markers but not neuron-specific enolase.

Implications

• The study concludes that the transformation of myxoid tissue into cartilage, along with the reactivity for certain neural markers, suggests a close relationship between myxoid cells and chondrocytes (cartilage cells). The same can be said for the relationship between myxoid cells and adipocytes.
• The digital cushions in horses, consisting of coarse connective tissue, myxoid tissue, fibrocartilage, and fat cells, are functionally designed to absorb and withstand mechanical shock, maintaining the integrity of the hooves.