Proximal radioulnar joint
The joint capsule encloses the joint; both it and the synovial membrane are continuous with that of the elbow joint.
Rotatory movements of the head of the radius within the collar formed by the annular ligament and the radial notch, allowing supination (primarily by the action of the biceps brachii and supinator muscles) and pronation (by the action of pronator teres and pronator quadratus muscles).
The annular ligament is a strong ligament attached to the anterior and posterior aspects of the radial notch of the ulna. It (along with the radial notch of the ulna) encircles the head of the radius.
From the radial portion of the peri-articular arterial anastomosis of the elbow joint.