The upper limb consists of the arm, forearm, wrist, and hand bones. The humerus is the single bone of the upper arm region. Proximally, it has a large, spherical, smooth head that articulates with the glenoid cavity of the scapula to form the glenohumeral or shoulder joint. The margin of the head is the anatomical neck, a residual epiphyseal plate. Laterally it extends to form bony projections called the greater tubercle and the lesser tubercle. Next to the tubercles is the surgical neck, a clinically significant part and a common site for fractures. It joins the narrow shaft of the humerus. A small V-shaped roughened projection called the deltoid tuberosity in the middle of the humeral shaft attaches to the deltoid muscle. Distally, the shaft of the humerus stretches to prominent protrusions on the sides, called epicondyles, which also serve as attachment sites for the muscles.
Additionally, the distal end has two articulation areas — the trochlea that articulates with the ulna, and the capitulum that articulates with the radius. These articulations form the elbow joint. The humerus also has three major depressions, called ‘fossae,' that help position the forearm bones during movement at the elbow joint. Superior to the trochlea is the coronoid fossa, which articulates with the coronoid process of the ulna. Above the capitulum is the radial fossa, which receives the head of the radius when the elbow is flexed. Posteriorly, the humerus has the olecranon fossa, which articulates with the olecranon process of the ulna when the forearm is fully extended. Several muscles run through the humerus's grooves and tubercles, connecting the shoulder joint through proximal tendons and the distal elbow joint through distal tendons. Overusing the shoulder is common among athletes, often leading to an inflamed proximal bicep tendon.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 8.2: Bones of the Upper Limb
