Articular capsule of the elbow
The articular capsule of the elbow is a fibrous capsule that completely lines the elbow joint. Extending from the elbow joint are three main bones that make up the elbow: the humerus, radius, and ulna. The ligaments on the front and back of the capsule are thinner and weaker. This means they are easier to tear through trauma. The triangular-shaped collateral ligaments are thicker and stronger. This makes them harder to tear. The lining of the capsule is called the synovial membrane, which extends from the articular surfaces to the proximal radioulnar joint. The anterior ligament is located on the front side of the humerus bone, while the posterior ligament is located on the back side of the humerus bone. The two triangular, thicker ligaments located on the sides of the humerus are the ulnar collateral ligament and the radial collateral ligament. The ulnar collateral ligament is made up of three bands: anterior, posterior, and oblique. The articular capsule of the elbow is a hinge joint. When the joint is flexed, the anterior band of the ulnar collateral ligament is taut. When the joint is extended, the posterior band becomes taut.