Head of radius

The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament.

Articular surfaces

The head of the radius is shaped to articulate with a complex of articular surfaces during both flexion-extension at the elbow and supination-pronation in the forearm:

Humeroradial joint

The head's proximal surface is concave and cup-shaped to correspond to the spherical surface of the capitulum of the humerus. The radius can thus glide on the capitulum during elbow flexion-extension while simultaneously rotate about its own main axis during supination-pronation.

Between the capitulum and the trochlea of the humerus is the capitulotrochlear groove. A semi-lunar surface around the circumference of head is shaped to articulate continuously with this groove.