What are the two primary tendons implicated in the stay mechanism?

What are the two primary tendons implicated in the stay mechanism?

• A. The biceps brachii tendon and the triceps tendon
• B. The superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT)
• C. The extensor carpi radialis tendon and common digital extensor tendon
• D. The flexor carpi ulnaris tendon and flexor digitorum profundus tendon

Answer: (B)

The stay mechanism relies on the tension of the digital flexor tendons to lock the limb in a standing position. The superficial digital flexor tendon and the deep digital flexor tendon run along the back of the limb and, when weight-bearing, they stay under constant tension. This tension works together with the suspensory apparatus and the ligaments around the fetlock to prevent the joint from collapsing, keeping the fetlock and adjacent joints in a stable, extended position with minimal muscular effort. In essence, these two tendons provide the key passive support that lets a horse stand for long periods. Other tendons, like those controlling shoulder or elbow extension or those primarily involved in flexion or extension of the carpus and digits, don’t form the same integrated passive support across the stay apparatus, so they aren’t the primary contributors to this mechanism.

The stay mechanism relies on the tension of the digital flexor tendons to lock the limb in a standing position. The superficial digital flexor tendon and the deep digital flexor tendon run along the back of the limb and, when weight-bearing, they stay under constant tension. This tension works together with the suspensory apparatus and the ligaments around the fetlock to prevent the joint from collapsing, keeping the fetlock and adjacent joints in a stable, extended position with minimal muscular effort. In essence, these two tendons provide the key passive support that lets a horse stand for long periods.

Other tendons, like those controlling shoulder or elbow extension or those primarily involved in flexion or extension of the carpus and digits, don’t form the same integrated passive support across the stay apparatus, so they aren’t the primary contributors to this mechanism.