Anatomy of the radioulnar joints

The radioulnar joints are two joints between the two bones of the forearm: the ulna, on the medial side, and the radius, on the lateral side.

There’s one superior, or proximal radioulnar joint, and one inferior, or distal radioulnar joint, and together they allow for the movements of pronation and supination.

This is gonna be short and sweet, so let’s dive right in!

The proximal radioulnar joint is a pivot type of synovial joint, which consists of the head of the radius articulating with the radial notch of the ulna.

The radial head is tightly bound into the radial notch of the ulna by the anular ligament that secures it in place.

The two articulating surfaces are covered by a synovial membrane, over which lies the joint capsule.

The joint capsule of the proximal radioulnar joint is an extension of the elbow’s joint capsule.

Next up, in the distal forearm, the radius and the ulna form another pivot type of synovial joint called the distal radioulnar joint, which is also covered by a fibrous joint capsule lined internally with a synovial membrane.

For this joint, the rounded head of the ulna articulates with the ulnar notch of the distal radius.

The articulating surfaces are mainly bound together by a fibrocartilaginous structure called the articular disc, which is triangular in shape, so it’s also known as the triangular ligament.

The articular disc attaches to the edge of the ulnar notch of the radius, and the base of the styloid process of the ulna.