Humerus

The humerus is a long bone in the arm or fore-legs (animals) that runs from the shoulder to the elbow. On a skeleton, it fits between the scapula and the radius and ulna. It consists of the following three sections:

Articulations

The head of the humerus (caput humeri) articulates with the glenoid cavity of the scapula at the glenohumeral joint. Also known as the "shoulder joint," it is a ball-and-socket joint, which allows a wide range of movement. This joint has two bursae: the subacromial bursa and the subscapular bursa. The subacromial bursa separates the tendon of the supraspinatus muscle from the deltoid muscle. The subscapular bursa separates the scapular fossa from the tendon of the subscapularis muscle. The glenohumeral joint is stabilized by the rotator cuff muscles and the tendon of the long head of the biceps brachii muscle.

The distal end of the humerus (at the elbow) creates a hinge joint with the ulna, allowing only flexion and extension. This happens on the trochlea of the humerus. Two pits at this end of the humerus (the coronoid fossa and the olecranon fossa) allow the ulna room to move, but prevent it from over-flexing/extending.

There is also a pivot joint between the capitulum (sometimes called the capitellum) of the humerus, and the head of the radius. This allows the hand to pronate and supinate (turn to face downwards or upwards).

Muscle attachments

A variety of muscles attach to the humerus. These enable movement at the elbow and at the shoulder.

The rotator cuff muscles attach at the proximal humerus, and can rotate and abduct the arm at the shoulder.

Some of the forearm muscles, (such as pronator teres, and the flexors and extensors of the wrist) also attach to the distal humerus.

lateral epicondyle

Extensor carpi radialis brevis muscle - attaches to the lateral epicondyle
Extensor carpi ulnaris muscle - attaches to the lateral epicondyle (and also to the posterior border of the ulna
Extensor digiti minimi muscle - attaches to the lateral epicondyle
Extensor digitorum muscle - attaches to the lateral epicondyle
Supinator muscle - attaches to the lateral epicondyle (and also to the radial collateral ligament, anular ligament, the supinator fossa, and the crest of the ulna

medial epicondyle

Flexor carpi radialis muscle - attaches to the medial epicondyle
Flexor carpi ulnaris muscle - its humeral head attaches to the medial epicondyle
Flexor digitorum superficialis muscle - its humeroulnar head attaches to the medial epicondyle of the humerus (and also to the ulnar collateral ligament and the coronoid process of the ulna
Palmaris longus muscle - attaches to the medial epicondyle
Pronator teres muscle - attaches to the medial epicondyle (and also to the coronoid process of the ulna)

intertubercular groove

Latissimus dorsi muscle - attaches to the floor of the intertubercular groove
Pectoralis major muscle - attaches to the lateral lip of the intertubercular groove
Teres major muscle - attaches to the medial lip of the intertubercular groove

greater tubercle and lesser tubercle (rotator cuff muscles)

Infraspinatus muscle - attaches to the middle facet on the greater tubercle
Supraspinatus muscle - attaches to the superior facet on the greater tubercle
Teres minor muscle - attaches to the inferior facet on the greater tubercle
Subscapularis muscle - attaches to the lesser tubercle

other

Anconeus muscle - attaches to the lateral surface of the olecranon (and also to the superior part of the posterior surface of the ulna)
Brachioradialis muscle - attaches to the proximal two-thirds of the lateral supracondylar ridge
Coracobrachialis muscle - attaches to the middle third of the medial humerus
Extensor carpi radialis longus muscle - attaches to the lateral supracondylar ridge
Deltoid muscle - attaches to the deltoid tuberosity

Actions

Deltoid has a variety of actions on the top of the arm.

Pectoralis major, teres major and latissimus dorsi, which all insert at the intertubercular groove of the humerus, adduct and medially rotate the humerus.

Biceps brachii, brachialis, coracobrachialis, and brachioradialis (which attaches very distally), act to flex the elbow. Biceps however does not attach to the humerus.

Triceps brachii and anconeus extend the elbow, and attach to the posterior side of the humerus.

Clinical Considerations

The most common type of shoulder (glenohumeral joint) dislocation is an anterior or inferior dislocation of the humerus. This dislocation has the potential to injure the axillary nerve or axillary artery. Signs and symptoms of this dislocation are: a loss of the normal contour of the shoulder, a depression under the acromion that you can feel, and being able to feel the head of humerus in the axilla (armpit).

References

Chung, Kyung Won. Board Review Series: Gross Anatomy, 4th ed. (2000).
Dudek, Ronald W. High Yield Gross Anatomy, 2nd ed. (2002).
Moore, Keith L. and Arthur F. Dalley. Clinically Oriented Anatomy, 4th ed. (1999).

Skeletal system | Upper limb anatomy

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