The elbow is both a hinge and a pivot joint that allows a person to bend, extend, and rotate the arm. It connects the end of the upper arm bone (distal humerus) to the bones of the forearm (radius and ulna) with ligaments, tendons, and muscles.
The two bones of the forearm (radius and ulna) fit into the ends of the upper arm bone like a hinge, forming the elbow joint. The upper arm bone (distal humerus) flares out to form the medial and lateral epicondyles. Some of the forearm muscles attach to the upper arm bone.
The olecranon is the large bump of the ulna behind the elbow joint. It forms the bony prominence of the elbow and connects with the triceps muscle of the upper arm.