Which structure prevents flexion of the fetlock joint?

• A. SDF
• B. Common digital extensor
• C. DDF
• D. Suspensory ligament

Answer: (B)

The fetlock joint is kept from bending mainly by the extensor mechanism. When the common digital extensor muscle contracts, its tendon crosses the cranial (top) surface of the fetlock and pulls the joint into extension. This action directly opposes any tendency for the fetlock to flex, so it’s the structure most responsible for preventing flexion at that joint.

In contrast, the superficial and deep digital flexors are flexors of the digits and tend to pull the joint toward flexion, not away from it. The suspensory ligament helps support the limb and resists hyperextension (over-extension) during weight bearing, but it doesn’t actively prevent flexion in the way the extensor mechanism does.