Humerus is a long bone, a bone with an elongated shaft and expanded ends, located in the upper arm between the shoulder and elbow. Its upper end joins the scapula, or shoulder blade, and its lower end joins the radius and ulna, the bones of the forearm.
Where is the humerus located?
Within the skeletal system, the humerus forms the bony framework of the upper arm. It lies beneath the surrounding muscles and does not extend into the forearm. In the anatomical position, the radius lies on the thumb side of the forearm, while the ulna lies on the little-finger side.
The proximal end, meaning the end nearer the trunk, lies at the shoulder. The distal end, meaning the end farther from the trunk, lies at the elbow. In anatomical descriptions, medial means towards the body's midline, lateral means away from it, anterior means towards the front, and posterior means towards the back.
What are the landmarks at the upper end?
The head of the humerus is its rounded joint surface. It faces medially, upwards and slightly backwards towards the scapula. The anatomical neck is the narrow boundary immediately around the head.
The greater and lesser tubercles are raised areas for muscle attachment. The greater tubercle lies laterally, and the lesser tubercle lies anteriorly. Between them is the intertubercular groove, a channel containing the tendon of the long head of biceps brachii; a tendon is the connective tissue that joins a muscle to its attachment.
The surgical neck is the region below the tubercles where the expanded upper end narrows into the shaft. The axillary nerve, which carries signals to shoulder muscles and skin, passes behind this region with the posterior circumflex humeral artery, a blood vessel supplying nearby tissues.
What are the surfaces and landmarks of the shaft?
The shaft is the elongated central part of the bone. It has anteromedial, anterolateral and posterior surfaces: respectively, the front-inner, front-outer and back surfaces. Its outline becomes more angular towards the lower end.
The deltoid tuberosity is a roughened area on the lateral shaft where the deltoid muscle attaches. On the posterior shaft, the radial groove provides a route for the radial nerve and profunda brachii artery. The radial nerve supplies several muscles that straighten the elbow, wrist and fingers, while the artery supplies tissues of the upper arm.
A nutrient foramen is an opening through which a blood vessel enters the bone. The nutrient arteries of humerus supply its internal tissues. The shaft has a thick outer layer of compact bone surrounding a marrow cavity, an internal space containing bone marrow.
What are the landmarks at the lower end?
The lower end broadens to form joint surfaces and attachment areas. The capitulum is the rounded lateral joint surface, while the trochlea is the pulley-shaped medial joint surface. The medial and lateral epicondyles are projections beside these surfaces that provide attachment for muscles and ligaments, the connective tissue bands that stabilise joints.
Depressions called fossae provide space for forearm bones during elbow movement. The ulnar nerve passes behind the medial epicondyle before entering the forearm; it supplies muscles in the forearm and hand and carries sensory signals from skin in the hand.
| Landmark | Position | Main anatomical role |
|---|---|---|
| Capitulum | Lateral lower end | Meets the head of the radius |
| Trochlea | Medial lower end | Meets the trochlear notch of the ulna |
| Medial epicondyle | Inner side of the lower end | Provides attachment for the common forearm flexor tendon |
| Lateral epicondyle | Outer side of the lower end | Provides attachment for the common forearm extensor tendon |
| Radial and coronoid fossae | Anterior lower end | Accommodate the radial head and the ulna's coronoid process during bending |
| Olecranon fossa | Posterior lower end | Accommodates the ulna's olecranon during straightening |
Flexor muscles bend joints, whereas extensor muscles straighten them. The coronoid process and olecranon are projections at the upper end of the ulna.
Which joints does the humerus form?
At the shoulder, the humeral head meets the glenoid cavity, the shallow socket on the scapula. This forms the glenohumeral joint, a ball-and-socket joint allowing the arm to move forwards, backwards, sideways and around its long axis. The humerus does not directly join the clavicle, or collarbone.
At the elbow, the trochlea meets the ulna and the capitulum meets the radius. These contacts contribute to bending and straightening the elbow. The radial head also turns against the capitulum as the forearm rotates.
The joint surfaces are covered by articular cartilage, a smooth tissue that reduces friction between the contacting bones.
What does the humerus do?
The humerus supports the upper arm and acts as a lever moved by muscles of the muscular system. Its rounded shoulder surface permits movement in several directions, while its lower joint surfaces guide movement at the elbow.
Important muscle attachments include:
- The rotator cuff muscles, a group that helps steady and rotate the shoulder, attach around the greater and lesser tubercles.
- The deltoid attaches to the deltoid tuberosity and helps raise the arm away from the trunk.
- Brachialis begins on the anterior lower shaft and bends the elbow.
- Parts of triceps brachii begin on the posterior shaft and help straighten the elbow.
How can you find the humerus in the 3D model?
In the 3D model beside this article, select the left humerus or right humerus, then isolate it and rotate it. Zoom in for a closer view, then rotate the isolated bone to view it from different directions. Zoom out again, switch layers, or hide or fade selected structures to adjust the view; you can also cut a section along a sagittal, coronal or transverse plane.