Stock Photo: ELBOW, X-RAY. ELBOW, X-RAY The elbow is the articular region forming the joint between the upper arm and the forearm. The elbow joint is composed of three bony articulations: the humeroradial, humeroulnar and radioulnar joints. In the anterior region of the elbow joint, the biceps is situated in the antecubital fossa. The olecranon, the upper extremity of the ulna, forms the posterior aspect of the elbow joint over which passes the medial nerve. Colorized x-ray.