The elbow (or olecranon joint) is the part of the upper limb between the arm and forearm. This articulation includes the region of the "elbow fold" (or ulnar fossa). It is a synovial joint complex of the upper human limb connecting the arm to the forearm. He thus unites three bones between them: the radius, the ulna and the humerus.
The ulna is a long bone of the forearm, located at its inner side while the radius, the second bone of the forearm, is located at the level of the outer part (the same side of the thumb)