The joint capsule of the elbow has sides that are thickened by ulnar and radial collateral ligaments. The front surface of the capsule is reinforced by fibers from a muscle (brachialis) in the upper arm.
The three parts of the elbow joint include the humeroulnar, humeroradial, and proximal radioulnar joints. A common synovial membrane surrounds all of these.
The ligaments in the joint include the annular, ulnar collateral, and radial collateral ligaments.