Articular facet of head of radius

The radial head has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum (or capitellum) of the humerus.

The deepest point in the fovea is not axi-symmetric with the long axis of the radius, creating a cam effect during pronation and supination.

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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.

The capitulum does not extend to the posterior side of the humerus and, consequently, during full elbow extension only the anterior half of the head articulates with the capitulum.

In full flexion the head similarly reaches beyond the capitulum to enter the shallow radial fossa on the anterior side of the humerus.