Which structures are most frequently involved in stay apparatus-related lameness?

Which structures are most frequently involved in stay apparatus-related lameness?

• A. Proximal suspensory region, distal sesamoidean ligaments behind the fetlock, and the suspensory apparatus around the metacarpus.
• B. Carpal bones and the distal phalanx.
• C. The dorsal laminae only.
• D. Deep digital flexor tendon alone.

Answer: (A)

The stay apparatus relies on ligaments and connections that keep the fetlock and pastern in extension while the horse bears weight. The most important parts involved are the proximal suspensory region (the proximal suspensory ligament and surrounding supporting tissues near the cannon), the distal sesamoidean ligaments behind the fetlock (connecting the sesamoid bones to the distal phalanx and stabilizing the fetlock-pastern alignment), and the suspensory apparatus around the metacarpus (the interosseous ligament along the cannon with its associated check ligaments that help resist flexion). When these structures are injured or compromised, the stay mechanism fails and lameness related to the stay apparatus arises. The other options involve parts of the limb that aren’t central to the stay mechanism: the carpal bones and distal phalanx are not the primary stay players; the dorsal laminae are hoof structures; and the deep digital flexor tendon alone is not part of the stay apparatus.