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Bone: Ulna
	Upper extremity
	Ulna is #2
Gray's	subject #52 214
MeSH	Ulna

The ulna is a long bone, prismatic in form. In anatomical position the ulna is placed at the medial side of the forearm closest to the body, parallel with the radius on both arms.

[edit] Articulations

The ulna articulates with:

trochlea of the humerus, at the right side elbow as a hinge joint with semilunar trochlear notch of the ulna.
the radius, near the elbow as a pivot joint, this allows the radius to cross over the ulna in pronation.
the distal radius, where it fits into the ulna notch.
the radius along its length via the interosseous membrane that forms a syndesmoses joint.

[edit] Proximal and distal aspects

The ulna is broader proximally, and narrower distally.

Proximally, the ulna has a bony process, the olecranon process, a hook-like structure that fits into the olecranon fossa of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus. There is also a radial notch for the head of the radius, and the ulnar tuberosity to which muscles can attach.

At the distal end of the ulna is a styloid process.

[edit] Structure

The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface.

At the extremities the compact layer thins.

The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellæ parallel.

From the inner surface of this plate and the compact layer below it trabeculæ arch forward toward the olecranon and coronoid and cross other trabeculæ, passing backward over the medullary cavity from the upper part of the shaft below the coronoid.

Below the coronoid process there is a small area of compact bone from which trabeculæ curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone.

The trabeculæ at the lower end have a more longitudinal direction.

[edit] Muscle attachments

Muscle	Direction	Attachment
Triceps brachii muscle	Insertion	Olecranon process (via common tendon)
Anconeus muscle	Insertion	Olecranon process (lateral aspect)
Brachialis muscle	Insertion	Coronoid process of the ulna
Pronator teres muscle	Origin	Coronoid process (also shares origin with medial epicondyle of the humerus)
Flexor carpi ulnaris muscle	Origin	Olecranon process and posterior surface of ulna (also shares origin with medial epicondyle of the humerus)
Flexor digitorum superficialis muscle	Origin	Coronoid process (also shares origin with medial epicondyle of the humerus and shaft of the radius)
Flexor digitorum profundus muscle	Origin	Coronoid process, anteromedial surface of ulna (also shares origin with the interosseous membrane)
Pronator quadratus muscle	Origin	Distal portion of anterior ulnar shaft
Extensor carpi ulnaris muscle	Origin	Posterior border of ulna (also shares origin with lateral epicondyle of the humerus)
Supinator muscle	Origin	Proximal ulna (also shares origin with lateral epicondyle of the humerus)
Abductor pollicis longus muscle	Origin	Posterior surface of ulna (also shares origin with the posterior surface of the radius bone)
Extensor pollicis longus muscle	Origin	Dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)
Extensor pollicis brevis muscle	Origin	Dorsal shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane)
Extensor indicis muscle	Origin	Posterior surface of distal ulna (also shares origin with the interosseous membrane)

[edit] In other animals

In four-legged animals, the radius is the main load-bearing bone of the lower forelimb, and the ulna is important primarily for muscular attachment. In many mammals, the ulna is partially or wholly fused with the radius, and may therefore not exist as a separate bone. However, even in extreme cases of fusion, such as in horses, the olecranon process is still present, albeit as a projection from the upper radius.^[1]

[edit] Additional images

Ulna l. dx. - ant. view	Ulna l. dx. - lat. view	Right posterior human radius and ulna	Human arm bones diagram
Bones of left forearm. Anterior aspect.	The radius and ulna of the left forearm, posterior surface.	Left elbow-joint, showing anterior and ulnar collateral ligaments.	Cross-section through the middle of the forearm.
The Supinator.	Transverse section across distal ends of radius and ulna.

[edit] See also

[edit] External links

Ulnar fractures

[edit] References

^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 200. ISBN 0-03-910284-X.

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

[VB-0] Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 200. ISBN 0-03-910284-X.

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