Which structure encircles the head of the radius and enables rotation of the forearm?

Which structure encircles the head of the radius and enables rotation of the forearm?

• A. Ulnar Collateral Ligament
• B. Interosseous Membrane
• C. Annular Ligament
• D. Radial Collateral Ligament

Answer: (C)

Rotation of the forearm happens at the proximal radioulnar joint, where the head of the radius needs to rotate while staying aligned with the ulna. The structure that does this by forming a ring around the radial head is the annular ligament. It wraps around the head of the radius and attaches to the ulna on both sides, creating a secure sleeve that allows the radius to rotate within it as you pronate and supinate. The interosseous membrane runs between the shafts of the two bones and helps stabilize them and transmit forces, but it does not encircle the radial head. The ulnar collateral ligament and radial collateral ligament stabilize the elbow from the inside and outside, respectively, and do not encircle the head of the radius.

Rotation of the forearm happens at the proximal radioulnar joint, where the head of the radius needs to rotate while staying aligned with the ulna. The structure that does this by forming a ring around the radial head is the annular ligament. It wraps around the head of the radius and attaches to the ulna on both sides, creating a secure sleeve that allows the radius to rotate within it as you pronate and supinate. The interosseous membrane runs between the shafts of the two bones and helps stabilize them and transmit forces, but it does not encircle the radial head. The ulnar collateral ligament and radial collateral ligament stabilize the elbow from the inside and outside, respectively, and do not encircle the head of the radius.