Which structure is primarily involved in the stay apparatus and is affected by desmitis?

• A. Dorsal patellar ligament
• B. Nuchal ligament
• C. Suspensory ligament
• D. Interosseous ligament

Answer: (C)

The stay apparatus relies on a set of ligaments that lock joints in place so the horse can stand with little muscular effort. The suspensory ligament is the key component of this system, especially in the fetlock region. When the limb bears weight, the suspensory ligament becomes taut and acts to prevent the fetlock from dropping into hyperextension, helping to transfer load along the leg and maintain an upright stance.

Desmitis, or inflammation of a ligament, most commonly affects this suspensory structure, leading to instability, pain, and lameness that disrupts the stay mechanism. While other ligaments around the knee or stifle contribute to limb stability in various ways, the suspensory ligament is the primary structure tied to the stay apparatus and its failure is the classic source of stay-apparatus–related lameness.