Injury to distal sesamoidean ligaments can lead to fetlock instability and lameness.

• A. Fetlock arthritis.
• B. Laminitis.
• C. Navicular disease.
• D. Distal sesamoidean ligament injury (desmitis), which can lead to fetlock instability and lameness.

Answer: (D)

Injury to the distal sesamoidean ligaments disrupts the fetlock’s suspensory support. These ligaments help constrain the fetlock joint during weight-bearing, preventing excessive bending or hyperextension. When they are damaged (desmitis), that restraint is lost, allowing abnormal, unstable movement of the fetlock. The result is pain and lameness that are directly tied to the joint’s instability rather than to primary bone or hoof diseases.

Fetlock arthritis is a joint degeneration problem and can cause lameness, but it isn’t primarily about ligament failure or joint instability. Laminitis affects the hoof laminae and coffin bone alignment, not the fetlock’s ligamentous support. Navicular disease targets structures behind the coffin joint and again doesn’t center on fetlock instability. The option describing distal sesamoidean ligament injury best explains the mechanism of instability and the associated lameness.