The elbow is a hinge joint. It is made up of three bones: the humerus, ulna, and radius. The humerus is the upper arm bone, while the ulna and radius are the bones of the forearm. The ulnohumeral joint is where movement between the ulna and humerus occurs, while the radiohumeral joint is where movement between the radius and humerus occurs. The proximal radioulnar joint is where movement between the radius and ulna occurs. The elbow joint is surrounded by a joint capsule that contains synovial fluid, which lubricates the joint. The joint is stabilized by ligaments, including the medial collateral ligament on the inside of the elbow and the lateral collateral ligament on the outside of the elbow. The elbow joint is also supported by tendons, including the biceps tendon and the triceps tendon.