Which joint is primarily involved in the patellar locking mechanism?

Which joint is primarily involved in the patellar locking mechanism?

• A. Stifle
• B. Hock
• C. Elbow
• D. Shoulder

Answer: (A)

The patellar locking mechanism is centered in the hind limb’s stifle joint, the animal’s knee. When the limb bears weight and the knee is in a slight flexion, the patella slides over the medial part of the femoral trochlea and the medial patellar ligament tightens against the medial ridge. This engagement effectively “locks” the stifle in an extended position, so the animal can stand with little muscular effort. This mechanism is a key part of the stay apparatus that helps large quadrupeds tolerate long periods of standing. The other joints listed don’t house this locking system—the hock is involved in the stay apparatus in a broader sense, but the patellar locking is specific to the stifle, while the elbow and shoulder are different limb joints that don’t participate in this mechanism.

The patellar locking mechanism is centered in the hind limb’s stifle joint, the animal’s knee. When the limb bears weight and the knee is in a slight flexion, the patella slides over the medial part of the femoral trochlea and the medial patellar ligament tightens against the medial ridge. This engagement effectively “locks” the stifle in an extended position, so the animal can stand with little muscular effort. This mechanism is a key part of the stay apparatus that helps large quadrupeds tolerate long periods of standing.

The other joints listed don’t house this locking system—the hock is involved in the stay apparatus in a broader sense, but the patellar locking is specific to the stifle, while the elbow and shoulder are different limb joints that don’t participate in this mechanism.