humerus

The humerus is the long bone of the upper arm, extending from the shoulder to the elbow. It supports muscles and acts as a lever for arm movement, forming the proximal component of the shoulder joint and the distal component of the elbow joint.

Proximal end: The spherical head articulates with the glenoid cavity of the scapula, enabling the wide range of shoulder motion. The head is surrounded by the anatomical neck, and just below lies the surgical neck, a common fracture site. The greater and lesser tubercles project laterally and anteriorly, serving as attachment points for rotator cuff muscles. The intertubercular (bicipital) groove between the tubercles houses the tendon of the long head of the biceps brachii.

Shaft: The body has a deltoid tuberosity on its lateral surface for deltoid muscle attachment. A posterior radial groove runs along the midshaft, where the radial nerve and profunda brachii artery lie closely to the bone.

Distal end: The distal articular surface comprises the capitulum, which articulates with the head of the radius, and the trochlea, which articulates with the trochlear notch of the ulna. Projections above the joint surface include the medial and lateral epicondyles. On the anterior and posterior surfaces are fossae for muscle and forearm contact, including the coronoid fossa, radial fossa, and olecranon fossa, respectively.

Articulations, nerves, and vessels: Proximally, the humerus forms the glenohumeral joint with the scapula; distally, it participates in the elbow joint with the radius and ulna. The axillary nerve winds around the surgical neck, and the radial nerve traverses the radial groove in the posterior arm, with the profunda brachii artery accompanying it.

Ossification and clinical notes: The humerus develops from a primary ossification center in the shaft and multiple secondary centers at the ends, which fuse in adolescence. Clinically, fractures occur at the surgical neck, distal end, or along the shaft, with potential injury to nearby nerves or vessels.