Humerus Anatomy: The Upper Arm Bone's Structure, Articulations, and Function

The humerus is the long bone of the upper arm, extending from the shoulder to the elbow. It is the longest bone in the arm and the second longest in the human body, after the femur.

Articulations

• Proximal end: Articulates with the scapula (glenoid cavity) to form the shoulder joint (glenohumeral joint).
• Distal end: Articulates with the ulna (trochlea) and radius (capitulum) to form the elbow joint.

Key Anatomical Features

• Head: Smooth, spherical; fits into glenoid cavity.
• Anatomical & surgical necks: Common fracture sites.
• Greater & lesser tubercles: Rotator cuff attachment sites.
• Deltoid tuberosity: Deltoid muscle attachment.
• Radial groove: Houses radial nerve and profunda brachii artery.
• Medial & lateral epicondyles: Forearm muscle origins.
• Trochlea & capitulum: Articular surfaces for ulna and radius.
• Olecranon, coronoid, radial fossae: Accommodate forearm bones during flexion/extension.

Function

The humerus serves as an attachment site for muscles that move the shoulder, elbow, and forearm, enabling a wide range of arm movements—flexion, extension, abduction, adduction, rotation, and forearm pronation/supination.

Clinical Relevance

• Common fracture sites: surgical neck (elderly), shaft (trauma), supracondylar (children).
• Radial nerve injury risk with mid-shaft fractures.
• Shoulder dislocation typically involves humeral head displacement from glenoid.