The Pathogenesis of Soft Tissue Injuries in Horses

Understanding the injury cascade and how to help horses on the road to recovery

s an equine veterinarian who practices a fair bit of performance horse medicine, I often hear from clients, “Well, thank goodness it’s just a bowed tendon,” as opposed to arthritic changes. I am uneasy with that mindset and try to express to clients that soft tissue injuries are not ideal scenarios by any means.

There is no such thing as just a strained sesamoidean ligament, just a torn intercarpal ligament, just a ruptured collateral ligament. Rather, these injuries can be very serious, and the prognosis for return to function is far from guaranteed.

The Injury Cascade

Soft tissue injuries and healing occur in three phases, as described below. 

The inflammatory phase

Whether the horse has a tendon strain, ligament rupture, or muscle belly hematoma, the inflammatory phase of injury occurs immediately and is characterized by redness, heat, pain, and swelling.

“At the cellular level this corresponds to constriction of blood vessels for immediate hemostasis (arrest of bleeding) and formation of a blood clot, which serves as a preliminary scaffold for invading white blood cells that act to minimize infection and digest necrotic (dying) tissue by phagocytosis,” says Kelly Giunta, VMD, Dipl. ACVSMR, an associate at Blue Ridge Equine, in Earlysville, Virginia. “Release of histamine and serotonin by mast cells leads to increased blood flow to the site of injury.”

This increased blood flow allows cells, growth factors, and oxygen to the site of injury so the second phase of healing can begin.

The proliferative phase

The second stage, known as the proliferative or reparative phase, typically begins a few days after the injury occurs and continues for a couple of months.

“Cytokines produced by the white blood cells signal fibroblasts (cells that play important roles in tissue repair) to migrate to the site of injury and proliferate,” Giunta explains. “Fibroblasts synthesize matrix proteins, including collagen, elastin, and proteoglycans. The initial matrix is composed of type III collagen, which has different structural properties than the normal type I collagen found in tendons and ligaments.”

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