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

The annular ligament is a crucial structure that encircles the head of the radius at the proximal radioulnar joint. Its primary function is to stabilize the radius, allowing for smooth rotation during pronation and supination of the forearm. When a boy falls on his outstretched hand, the force can exert significant stress on the wrist and forearm, potentially resulting in injury to the ligaments associated with those areas.

While the radiocarpal joint, which is part of the wrist, is involved in movements of the hand, the annular ligament is specifically related to the function and stability of the proximal radioulnar joint. This joint permits the rotation of the forearm, which is vital for twisting movements and everyday activities. The impact from a fall can lead to a tear in the annular ligament without necessarily affecting the other joints mentioned.

Hence, recognizing that the annular ligament is specifically associated with the proximal radioulnar joint provides clarity on the relevant anatomy and explains why that response is the most accurate choice in this context.