Radius vs ulna: how they differ, in 3D

Frequently asked questions

Which forearm bone is on the thumb side?

The radius is on the thumb side and the ulna is on the little-finger side. The bony point you can feel at the wrist below the thumb is the styloid process of the radius.

Which bone matters more at the elbow, and which at the wrist?

At the elbow it is the ulna: its trochlear notch forms the hinge joint with the humerus, and the point of the elbow, the olecranon, is part of it. At the wrist it is the radius: its lower end meets the wrist bones directly, while the lower end of the ulna is kept apart from them by an articular disc.

How do the two bones move when the palm turns over?

At the radioulnar joints near the elbow and the wrist, the radius turns around the ulna. Turning the palm down (pronation) crosses the radius over the ulna, and turning it up (supination) brings the two bones parallel again.