Humerus

The long bone of the upper arm, running from the shoulder joint above to the elbow joint below.

At a glance

English: Humerus
Latin (TA2): Humerus
System: Bone
Region: Upper limb
Side: Paired, left and right

About the humerus

The humerus is the single bone of the upper arm, spanning the distance between shoulder and elbow. Above, its head fits against the shallow glenoid cavity of the scapula at the shoulder joint; below, it meets both forearm bones, the ulna and the radius, at the elbow. Like other long bones it is described as a proximal end, a shaft and a distal end.

The proximal end carries a smooth, almost half-spherical head that faces upwards, inwards and slightly back. A shallow ring around the cartilage, the anatomical neck, marks where the joint capsule attaches. Lateral to the head sits the greater tubercle and in front lies the smaller lesser tubercle; the intertubercular (bicipital) groove between them guides the tendon of the long head of biceps. Just below both tubercles the bone narrows again at the surgical neck. The shaft is round in section near the top and becomes three-sided lower down. Halfway along its lateral face is the deltoid tuberosity, and behind it the radial (spiral) groove winds obliquely across the back of the bone.

Distally the bone widens into a flattened end with a medial and a lateral epicondyle. Between them lie two articular parts: the pulley-shaped trochlea, which takes the ulna, and the rounded capitulum, which takes the head of the radius. Three hollows receive forearm processes when the elbow moves: the coronoid and radial fossae in front during bending, and the deep olecranon fossa behind during straightening. The medial epicondyle is the larger and gives origin to the common flexor tendon of the forearm; the lateral one anchors the common extensor tendon.

Three nerves lie on the bone and explain its main clinical risks. The axillary nerve wraps around the surgical neck with the posterior circumflex humeral artery, so a fracture there or a shoulder dislocation can damage it. The radial nerve lies in the spiral groove behind the shaft, where a midshaft break may leave the wrist unable to extend. The ulnar nerve passes behind the medial epicondyle, the spot people call the funny bone. Fractures of the anatomical neck are uncommon compared with those of the surgical neck.

Function and supply

Function: Gives the arm its lever at the shoulder and elbow, carrying the attachments for the rotator cuff, deltoid, biceps, triceps and the forearm flexors and extensors.
Nerve supply: Not innervated as a muscle is; the axillary, radial and ulnar nerves lie directly on the bone at the surgical neck, spiral groove and medial epicondyle.
Blood supply: A nutrient artery, usually from the brachial artery, enters through a foramen on the anteromedial shaft; the anterior and posterior circumflex humeral arteries supply the proximal end.

Parts of the humerus

Each number is marked on the model. Press one, here or on the model, to see it named in place.

Anatomical neck of humerusCollum anatomicum humeriA slight groove ringing the edge of the articular head, set at an obtuse angle to the shaft. The capsule of the shoulder joint attaches along most of it, and breaks here are rare.
Anterior border of humerusMargo anterior humeriA ridge down the front of the shaft from the greater tubercle towards the coronoid fossa. It divides the anteromedial from the anterolateral surface, and its upper part is the ridge on which pectoralis major inserts.
Anterolateral surface of humerusFacies anterolateralis humeriThe front and outer face of the shaft, between the anterior and lateral borders. The deltoid tuberosity lies on it near the middle, and brachialis arises from its lower half.
Anteromedial surface of humerusFacies anteromedialis humeriThe front and inner face of the shaft, between the anterior and medial borders, narrower than the anterolateral face. Coracobrachialis inserts near its middle and brachialis covers its lower part; the nutrient foramen usually opens here.
Body of humerusCorpus humeriThe shaft of the bone between the surgical neck and the widened lower end. It is rounded above and three-sided below, carrying the deltoid tuberosity and the radial groove.
Capitulum of humerusCapitulum humeriA smooth, rounded knob on the lateral part of the lower articular surface. It meets the concave top of the radial head at the elbow.
Condyle of humerusCondylus humeriThe whole lower end of the humerus, made up of the articular trochlea and capitulum together with the fossae above them. It forms the upper half of the elbow joint.
Coronoid fossaFossa coronoideaA small hollow on the front of the bone just above the trochlea. When the elbow is fully bent, the ulna's coronoid process fits into it; it sits beside the radial fossa.
Crest of greater tubercleCrista tuberculi majorisA ridge running down from the greater tubercle along the lateral lip of the intertubercular groove. The tendon of pectoralis major inserts on it.
Crest of lesser tubercleCrista tuberculi minorisA ridge running down from the lesser tubercle along the medial lip of the intertubercular groove. Teres major inserts on it.
Deltoid tuberosityTuberositas deltoideaA roughened, V-shaped area on the lateral side of the shaft about halfway down. The deltoid muscle inserts here.
Greater tubercleTuberculum majusThe large prominence on the lateral side of the upper end, beyond the head. Its three facets receive, from top to back, supraspinatus, infraspinatus and teres minor, and it is a common site of avulsion fracture.
Groove for ulnar nerveSulcus nervi ulnarisA shallow channel on the back of the medial epicondyle. The ulnar nerve runs in it close to the skin, which is why a knock here causes tingling down to the little finger.
Head of humerusCaput humeriThe smooth, near half-sphere at the top of the bone, facing upwards, inwards and a little back. It sits against the shallow glenoid socket of the shoulder blade, which is much smaller than the head.
Intertubercular sulcusSulcus intertubercularisA deep groove on the front of the upper end, between the greater and lesser tubercles. It carries the tendon of the long head of biceps and its synovial sheath, held in place by the transverse humeral ligament.
Lateral border of humerusMargo lateralis humeriA ridge from the back of the greater tubercle down to the lateral epicondyle, dividing the front-and-outer face from the back of the shaft. The radial groove crosses it, and lower down it sharpens into the lateral supracondylar ridge.
Lateral epicondyle of humerusEpicondylus lateralis humeriA small, rough projection on the outer side of the lower end. The lateral (radial) collateral ligament and the common extensor tendon anchor to it, and overuse there causes tennis elbow.
Lateral supracondylar ridgeCrista supracondylaris lateralis cristaThe sharp, rough lower stretch of the lateral border, rising from the lateral epicondyle. Brachioradialis and extensor carpi radialis longus arise from it.
Lesser tubercleTuberculum minusA smaller but sharper prominence on the front of the upper end, facing forwards and inwards. Subscapularis inserts on it.
Medial border of humerusMargo medialis humeriA ridge running from the lesser tubercle down towards the medial epicondyle. Above it forms the crest for teres major, and below it becomes the medial supracondylar ridge.
Medial epicondyle of humerusEpicondylus medialis humeriThe large, prominent projection on the inner side of the lower end, easily felt at the elbow. It gives origin to the common flexor tendon and the ulnar collateral ligament, and repeated strain here causes golfer's elbow.
Medial supracondylar ridgeCrista supracondylaris medialis cristaThe lower part of the medial border, becoming more prominent just above the medial epicondyle. Pronator teres arises from its lower end, and the brachialis and triceps attach to its front and back lips.
Olecranon fossaFossa olecraniA deep, triangular hollow on the back of the lower end, above the trochlea. It takes the olecranon of the ulna when the elbow is straightened.
Posterior surface of humerusFacies posterior humeriThe back of the shaft, bounded by the medial and lateral borders and slightly twisted along its length. The radial groove crosses its upper part, and two of the three heads of triceps arise from it, one on each side of that groove.
Radial fossaFossa radialisA shallow hollow on the front of the bone above the capitulum. It receives the rim of the radial head when the elbow is fully bent.
Radial grooveSulcus nervi radialisA broad, shallow, slanting channel across the back of the shaft. The radial nerve and the deep brachial artery run in it, so a midshaft fracture can injure the nerve and cause wrist drop.
Surgical neck of humerusCollum chirurgicum humeriThe narrowed part of the bone just below the tubercles, where the upper end joins the shaft. It is a common fracture site, and the axillary nerve and posterior circumflex humeral artery wind around it.
Trochlea of humerusTrochlea humeriThe pulley-shaped medial part of the lower articular surface. It fits into the deep notch on the front of the ulna's upper end and guides the hinge movement of the elbow.

Anthromica

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At a glance

About the humerus

Function and supply

Related structures

See the humerus where it really sits, with every layer of the body around it.