Joint · Elbow

Proximal radioulnar joint

Articulatio radioulnaris proximalis

The pivot at the elbow end of the forearm, where the disc-shaped head of the radius spins inside a ring formed by the ulna and the annular ligament. This is one half of the mechanism that turns your palm up and down — the radius rotates while the ulna stays put. It shares a capsule with the elbow, and its motion is inseparable from the matching joint at the wrist end: neither can turn without the other.