Relationship between Elbow and Proximal Radioulnar Joints

Articular capsule

Both share an articular capsule, attaches to articular margins of humerus and ulna with no direct attachment to radius, thickest and strongest on sides where reinforced by capsular ligaments

Synovial membrane

Both share a synovial membrane and have extra-synovial fat pads which occupy fossae when bon projections do not

Annular ligament (proximal radioulnar joint)

Ring shaped, attaches to anterior and posterior margins of radial notch of ulnar, encircles head of radius to hold in place, allows for pronation and supination of forearm, wider superiorly than inferiorly to prevent inferior dislocation of radial head

Ulnar (medial) collateral ligament (elbow joint)

From medial epicondyle of humerus to coronoid process and olecranon of ulna, made of three bands, prevents forearm abduction

Radial (lateral) collateral ligament (elbow joint)

From lateral epicondyle of humerus to annular ligament - blends distally, fan shaped, prevents forearm adduction