What shape is the head of the radius?

The head of the radius is correctly described as disk-shaped. This shape allows the radius to effectively articulate with the humerus (upper arm bone) at the elbow joint, as well as with the ulna at the proximal radioulnar joint. The disk shape provides a broad surface for these articulations, contributing to the stability and flexibility of the joint movement.

The unique cylindrical body of the radius itself helps with its rotation during pronation and supination of the forearm, but the head specifically, being disk-shaped, is crucial for its function in joint movement and load distribution.