Humerus anatomy: the upper arm bone labelled from shoulder to elbow

What it is

The long bone of the upper arm.

Location

Extends from the shoulder (glenoid cavity of the scapula) to the elbow, articulating with the radius and ulna.

Function

Provides a lever for arm movement and attachment for muscles of the shoulder and arm.

Body system

Skeletal · paired (left and right)

FMA ID

FMA23131 (Foundational Model of Anatomy)

Key facts

• Its surgical neck lies below the tubercles; the radial groove lies on the posterior shaft.
• Distally the capitulum articulates with the radius and the trochlea with the ulna.
• The greater tubercle receives supraspinatus, infraspinatus and teres minor; the lesser tubercle receives subscapularis.
• The ulnar nerve passes behind the medial epicondyle (the 'funny bone').

Clinical relevance

A fracture of the surgical neck endangers the axillary nerve, a midshaft fracture the radial nerve, and a supracondylar fracture the brachial artery and median nerve.

The head of the humerus is the smooth, rounded upper end. It is covered by hyaline cartilage and faces medially, upward and backward to meet the glenoid fossa of the scapula. (Kenhub: Humerus.)

The anatomical neck is the slight groove just around the margin of the head, and the shoulder joint capsule attaches along it. The surgical neck is the narrower region just below the tubercles, where the head end meets the shaft. The difference matters clinically, because the surgical neck is a common fracture site. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

The axillary nerve and the posterior circumflex humeral artery wrap around the surgical neck, so they are the structures at risk when it breaks. (TeachMeAnatomy: The Humerus.)

The greater tubercle (greater tuberosity) is the lateral bump on the upper end. It has three facets for three rotator cuff tendons: supraspinatus on the superior facet, infraspinatus on the middle facet and teres minor on the inferior facet. The smaller lesser tubercle faces forward and receives subscapularis. (TeachMeAnatomy: The Humerus.)

Between them runs the intertubercular sulcus (bicipital groove), which carries the tendon of the long head of biceps brachii. Pectoralis major inserts on the lateral lip of the groove, teres major on the medial lip and latissimus dorsi on the floor between them, often remembered as "a lady between two majors". (TeachMeAnatomy: The Humerus.)

The shaft is round in cross-section near the top and becomes triangular and flatter toward the elbow. Halfway down its lateral side is the deltoid tuberosity, a rough V-shaped area where deltoid inserts. (Kenhub: Humerus.)

On the back of the shaft, a shallow diagonal groove, the radial (spiral) groove, runs parallel to the deltoid tuberosity. The radial nerve and the profunda brachii (deep brachial) artery lie in it. The groove separates the origins of the lateral and medial heads of triceps. (TeachMeAnatomy: The Humerus.)

Coracobrachialis attaches to the middle of the medial (anteromedial) side of the shaft, and brachialis arises from the lower half of the front of the bone. (Kenhub: Humerus.)

At the lower end, the medial and lateral borders of the shaft become the supracondylar ridges, which end in two bony projections that you can feel at the elbow: the medial and lateral epicondyles. The medial epicondyle is larger and sticks out further. (TeachMeAnatomy: The Humerus.)

The medial epicondyle is the common origin of the superficial forearm flexors, including flexor carpi ulnaris, palmaris longus, flexor carpi radialis and pronator teres. The lateral epicondyle is the common origin of superficial extensors such as extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris and anconeus. (Kenhub: Humerus.)

The ulnar nerve runs in a groove on the back of the medial epicondyle, where you can roll it under your finger. (TeachMeAnatomy: The Humerus.)

The articular part of the lower end has two surfaces. The pulley-shaped trochlea on the medial side articulates with the trochlear notch of the ulna. The rounded capitulum on the lateral side articulates with the head of the radius. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

Three hollows receive parts of the forearm bones. On the back, the deep olecranon fossa takes the olecranon of the ulna when the elbow is straightened. On the front, the coronoid fossa takes the coronoid process of the ulna, and the radial fossa takes the rim of the radial head, when the elbow is fully bent. (Kenhub: Humerus.)

Three clues give the side. The head faces medially, toward the body's midline. The lesser tubercle faces forward and the greater tubercle is lateral, so the bicipital groove lies on the front of the bone. At the lower end, the deep olecranon fossa is on the back and the larger epicondyle is the medial one. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

To use these clues, hold the bone upright beside your own arm with the bicipital groove facing forward, away from you. If the head points to your left, toward your own midline, it is a right humerus; if it points to your right, it is a left humerus. The deltoid tuberosity, on the lateral side of the shaft, is a second check. (Kenhub: Humerus.)

Three nerves lie directly on the humerus: the axillary nerve at the surgical neck, the radial nerve in the radial groove, and the ulnar nerve behind the medial epicondyle. The median nerve lies close to the lower end in front. (Kenhub: Humerus.)

A surgical neck fracture, usually from a fall on an outstretched hand or a direct blow, can injure the axillary nerve. Deltoid and teres minor are then weak, so lifting the arm sideways is impaired, and skin over the lower deltoid (the "regimental badge" area) may be numb. (TeachMeAnatomy: The Humerus.)

A midshaft fracture can damage the radial nerve in its groove. The wrist extensors are paralysed, causing wrist drop, and sensation may be lost over the back of the hand. (TeachMeAnatomy: The Humerus.)

A supracondylar fracture, just above the elbow, is most common in children after a fall on an outstretched hand. It can injure the brachial artery, the anterior interosseous branch of the median nerve, the ulnar nerve or the radial nerve. Severe loss of blood supply can lead to Volkmann's ischaemic contracture, a permanent flexion deformity of the wrist and fingers. (TeachMeAnatomy: The Humerus.)

Proximally the humerus forms the glenohumeral (shoulder) joint, a ball-and-socket joint. The head is much larger than the shallow glenoid fossa, which allows a wide range of movement at the cost of stability. (TeachMeAnatomy: The Shoulder (Glenohumeral) Joint.)

Distally it forms the elbow: the trochlea with the ulna (humeroulnar joint) and the capitulum with the radial head (humeroradial joint). (TeachMeAnatomy: The Humerus.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Long head of biceps brachii · muscular
• Short head of biceps brachii · muscular
• Deep brachial artery · cardiovascular
• Brachial artery · cardiovascular
• Lateral head of triceps brachii · muscular
• Long head of triceps brachii · muscular
• Medial head of triceps brachii · muscular
• Coracobrachialis · muscular
• Brachialis · muscular
• Thoracodorsal artery · cardiovascular