A boy falls on his outstretched hand and tears the annular ligament. Which joint is this ligament associated with?

The annular ligament is a key structure that encircles the head of the radius at the proximal radioulnar joint, allowing for the rotation of the radius during pronation and supination of the forearm. This ligament stabilizes the joint and prevents the radius from dislocating during movements. When a boy falls on his outstretched hand, it's possible for this ligament to be torn, leading to instability and pain in the elbow and forearm.

While the distal interphalangeal joint, glenohumeral joint, and radiocarpal joint are essential in their respective functions, they are not associated with the annular ligament. Therefore, recognizing that the annular ligament is specifically linked to the proximal radioulnar joint clarifies why this answer is the most accurate choice.