Ulna

Ulna
Ulna
	An example of a human ulna, shown in red (in standard anatomical position).
Details
Pronunciation	/ˈʌlnə/
Identifiers
Latin	ulna
MeSH	D014457
TA98	A02.4.06.001
TA2	1230
FMA	23466
	Anatomical terms of bone [ edit on Wikidata]

Last updated March 13, 2024

The ulna or ulnal bone (pl.: ulnae or ulnas)^[3] is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm. The corresponding bone in the lower leg is the fibula.

Structure

The ulna is a long bone found in the forearm that stretches from the elbow to the wrist, and when in standard anatomical position, is found on the medial side of the forearm. It is broader close to the elbow, and narrows as it approaches the wrist.

Close to the elbow, 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 attach.

Close to the wrist, the ulna has a styloid process.

Near the elbow

Proximal extremity of left ulna. Lateral aspect. Gray212.png — Proximal extremity of left ulna. Lateral aspect.

Near the elbow, the ulna has two curved processes, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches.

The olecranon is a large, thick, curved eminence, situated at the upper and back part of the ulna. It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus in extension of the forearm. Its base is contracted where it joins the body and the narrowest part of the upper end of the ulna. Its posterior surface, directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. Its superior surface is of quadrilateral form, marked behind by a rough impression for the insertion of the triceps brachii; and in front, near the margin, by a slight transverse groove for the attachment of part of the posterior ligament of the elbow joint. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. Its borders present continuations of the groove on the margin of the superior surface; they serve for the attachment of ligaments: the back part of the ulnar collateral ligament medially, and the posterior ligament laterally. From the medial border a part of the flexor carpi ulnaris arises; while to the lateral border the anconeus is attached.

The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna. Its base is continuous with the body of the bone, and of considerable strength. Its apex is pointed, slightly curved upward, and in flexion of the forearm is received into the coronoid fossa of the humerus. Its upper surface is smooth, concave, and forms the lower part of the semilunar notch. Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the brachialis. At the junction of this surface with the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the brachialis; to the lateral border of this tuberosity the oblique cord is attached. Its lateral surface presents a narrow, oblong, articular depression, the radial notch. Its medial surface, by its prominent, free margin, serves for the attachment of part of the ulnar collateral ligament. At the front part of this surface is a small rounded eminence for the origin of one head of the flexor digitorum superficialis; behind the eminence is a depression for part of the origin of the flexor digitorum profundus; descending from the eminence is a ridge which gives origin to one head of the pronator teres. Frequently, the flexor pollicis longus arises from the lower part of the coronoid process by a rounded bundle of muscular fibers.

The semilunar notch is a large depression, formed by the olecranon and the coronoid process, and serving as articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process. The notch is concave from above downward, and divided into a medial and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transversely; the lateral is convex above, slightly concave below.

The radial notch is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before backward, and its prominent extremities serve for the attachment of the annular ligament.

Body

The body of the ulna at its upper part is prismatic in form, and curved so as to be convex behind and lateralward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward, and has three borders and three surfaces.

Borders

The volar border (margo volaris; anterior border) begins above at the prominent medial angle of the coronoid process, and ends below in front of the styloid process. Its upper part, well-defined, and its middle portion, smooth and rounded, give origin to the flexor digitorum profundus; its lower fourth serves for the origin of the pronator quadratus. This border separates the volar from the medial surface.
The dorsal border (margo dorsalis; posterior border) begins above at the apex of the triangular subcutaneous surface at the back part of the olecranon, and ends below at the back of the styloid process; it is well-marked in the upper three-fourths, and gives attachment to an aponeurosis which affords a common origin to the flexor carpi ulnaris, the extensor carpi ulnaris, and the flexor digitorum profundus; its lower fourth is smooth and rounded. This border separates the medial from the dorsal surface.
The interosseous crest (crista interossea; external or interosseous border) begins above by the union of two lines, which converge from the extremities of the radial notch and enclose between them a triangular space for the origin of part of the supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the interosseous membrane, and separates the volar from the dorsal surface.

Surfaces

The volar surface (facies volaris; anterior surface), much broader above than below, is concave in its upper three-fourths, and gives origin to the flexor digitorum profundus; its lower fourth, also concave, is covered by the pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely downward and medialward, which marks the extent of origin of the pronator quadratus. At the junction of the upper with the middle third of the bone is the nutrient canal, directed obliquely upward.
The dorsal surface (facies dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the middle; narrow, smooth, and rounded below. On its upper part is an oblique ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the anconeus, while the upper part of the ridge affords attachment to the supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the supinator, the abductor pollicis longus, the extensor pollicis longus, and the extensor indicis proprius.
The medial surface (facies medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the flexor digitorum profundus; its lower fourth is subcutaneous.

Near the wrist

The head of ulna presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disc which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius.

Near the wrist, the ulnar, with two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process.

The head presents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius.
The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint.

The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the extensor carpi ulnaris.

Vertical section through the articulations at the wrist, showing the synovial cavities.
Bones of left forearm. Anterior aspect.
Bones of left forearm. Posterior aspect.
Ligaments of wrist. Anterior view
Ligaments of wrist. Posterior view.

Microanatomy

The ulna is a long bone. The long, narrow medullary cavity of the ulna is enclosed in a strong wall of cortical 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 lamellae parallel. From the inner surface of this plate and the compact layer below it trabeculae arch forward toward the olecranon and coronoid and cross other trabeculae, 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 trabeculae curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabeculae at the lower end have a more longitudinal direction.^[4]

Development

The ulna is formed into bone from three centres, shown here.

The ulna is ossified from three centers: one each for the body, the wrist end, and the elbow end, near the top of the olecranon. Ossification begins near the middle of the body of the ulna, about the eighth week of fetal life, and soon extends through the greater part of the bone.

At birth, the ends are cartilaginous. About the fourth year or so, a center appears in the middle of the head, and soon extends into the ulnar styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year.

Function

Joints

The ulna forms part of the wrist joint and elbow joints. Specifically, the ulna joins (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 ulnar notch.
the radius along its length via the interosseous membrane that forms a syndesmosis joint

Muscle attachments

Bones of left forearm. Anterior aspect.

The radius and ulna of the left forearm, posterior surface.

Muscle	Direction	Attachment
Triceps brachii muscle	Insertion	posterior part of superior surface of Olecranon process (via common tendon)
Anconeus muscle	Insertion	olecranon process (lateral aspect)
Brachialis muscle	Insertion	anterior surface of the coronoid process of the ulna
Pronator teres muscle	Origin	medial surface on middle portion of 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	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 indicis muscle	Origin	posterior surface of distal ulna (also shares origin with the interosseous membrane)

Clinical significance

Fractures

Specific types of ulna fracture include:

Monteggia fracture - a fracture of the proximal third of the ulna with the dislocation of the head of the radius
Hume fracture - a fracture of the olecranon with an associated anterior dislocation of the radial head

Conservative management is possible for ulnar fractures when they are located in the distal two-thirds, only involve the shaft, with no shortening, less than 10° angulation and less than 50% displacement.^[5] In such cases, a cast should be applied that goes above the elbow.^[5]

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.^[6]

In birds and other dinosaurs, the ulna forms a surface of attachment for the secondary feathers. These often leave osteological evidence in the form of quill knobs, allowing for identification of feathers in fossils that otherwise lack integumentary information.^[7]

Gallery

Position of ulna (red). Animation
3D image
Bones of the right arm, showing the ulna, radius, wrist and humerus
Cross-section through the middle of the forearm, showing the two bones and the muscles, nerves and blood vessels surrounding them.
Ulna anatomy

Related Research Articles

The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The term "carpus" and "carpal" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the main role of the carpal bones is to articulate with the radial and ulnar heads to form a highly mobile condyloid joint, to provide attachments for thenar and hypothenar muscles, and to form part of the rigid carpal tunnel which allows the median nerve and tendons of the anterior forearm muscles to be transmitted to the hand and fingers.

The humerus is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes. The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes, and 3 fossae. As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.

In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; (2) the wrist joint or radiocarpal joint, the joint between the radius and the carpus and; (3) the anatomical region surrounding the carpus including the distal parts of the bones of the forearm and the proximal parts of the metacarpus or five metacarpal bones and the series of joints between these bones, thus referred to as wrist joints. This region also includes the carpal tunnel, the anatomical snuff box, bracelet lines, the flexor retinaculum, and the extensor retinaculum.

The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, technically, means only the region of the upper arm, whereas the lower "arm" is called the forearm. It is homologous to the region of the leg that lies between the knee and the ankle joints, the crus.

In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is common. This nerve is directly connected to the little finger, and the adjacent half of the ring finger, innervating the palmar aspect of these fingers, including both front and back of the tips, perhaps as far back as the fingernail beds.

The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is longer than the radius, but the radius is thicker. The radius is a long bone, prism-shaped and slightly curved longitudinally.

The triquetral bone is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the hand, but does not directly articulate with the ulna. Instead, it is connected to and articulates with the ulna through the Triangular fibrocartilage disc and ligament, which forms part of the ulnocarpal joint capsule. It connects with the pisiform, hamate, and lunate bones. It is the 2nd most commonly fractured carpal bone.

<span class="mw-page-title-main">Ulnar collateral ligament of elbow joint</span> Ligament on the elbow

The ulnar collateral ligament (UCL) or internal lateral ligament is a thick triangular ligament at the medial aspect of the elbow uniting the distal aspect of the humerus to the proximal aspect of the ulna.

<span class="mw-page-title-main">Ulnar artery</span> Artery of the forearm

The ulnar artery is the main blood vessel, with oxygenated blood, of the medial aspects of the forearm. It arises from the brachial artery and terminates in the superficial palmar arch, which joins with the superficial branch of the radial artery. It is palpable on the anterior and medial aspect of the wrist.

The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint.

The olecranon, is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon serves as a lever for the extensor muscles that straighten the elbow joint.

The pronator teres is a muscle that, along with the pronator quadratus, serves to pronate the forearm. It has two origins, at the medial humeral supracondylar ridge and the ulnar tuberosity, and inserts near the middle of the radius.

<span class="mw-page-title-main">Trochlea of humerus</span> Articular surface of the elbow joint which articulates with the trochlear notch of the ulna

In the human arm, the humeral trochlea is the medial portion of the articular surface of the elbow joint which articulates with the trochlear notch on the ulna in the forearm.

The trochlear notch, also known as semilunar notch and greater sigmoid cavity, is a large depression in the upper extremity of the ulna that fits the trochlea of the humerus as part of the elbow joint. It is formed by the olecranon and the coronoid process.

The styloid process of the ulna is a bony prominence found at distal end of the ulna in the forearm.

The triangular fibrocartilage complex (TFCC) is formed by the triangular fibrocartilage discus (TFC), the radioulnar ligaments (RULs) and the ulnocarpal ligaments (UCLs).

The coronoid process of the ulna is a triangular process projecting forward from the anterior proximal portion of the ulna.

The following outline is provided as an overview of and topical guide to human anatomy:

The elbow is the region between the upper arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa, and the lateral and the medial epicondyles of the humerus. The elbow joint is a hinge joint between the arm and the forearm; more specifically between the humerus in the upper arm and the radius and ulna in the forearm which allows the forearm and hand to be moved towards and away from the body. The term elbow is specifically used for humans and other primates, and in other vertebrates forelimb plus joint is used.

<span class="mw-page-title-main">Extrinsic extensor muscles of the hand</span>

The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. Extrinsic denotes their location outside the hand. Extensor denotes their action which is to extend, or open flat, joints in the hand. They include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI).

References

This article incorporates text in the public domain from page 214 of the 20th edition of Gray's Anatomy (1918)

↑ OED 2nd edition, 1989.
↑ Entry "ulna" in Merriam-Webster Online Dictionary .
↑ "ULNA | Meaning & Definition for UK English". Lexico.com. Archived from the original on January 20, 2021. Retrieved 2022-08-24.
↑ "Ulna". InnerBody.
1 2 Sebastian Dawson-Bowling; Pramod Achan; Timothy Briggs; Manoj Ramachandran (2014). Orthopaedic Trauma: The Stanmore and Royal London Guide. CRC Press. ISBN 9781444148831. Page 158
↑ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 200. ISBN 0-03-910284-X.
↑ Turner, Alan H.; Makovicky, Peter J.; Norell, Mark A. (2007-09-21). "Feather Quill Knobs in the Dinosaur Velociraptor" (PDF). Science. 317 (5845): 1721. Bibcode:2007Sci...317.1721T. doi:10.1126/science.1145076. ISSN 0036-8075. PMID 17885130. S2CID 11610649.

External links

Bone and Spine : Musculoskeletal-Anatomy

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[1] OED 2nd edition, 1989.

[2] Entry "ulna" in Merriam-Webster Online Dictionary .

[3] "ULNA | Meaning & Definition for UK English". Lexico.com. Archived from the original on January 20, 2021. Retrieved 2022-08-24.

[4] "Ulna". InnerBody.

[Bowling-5] 1 2 Sebastian Dawson-Bowling; Pramod Achan; Timothy Briggs; Manoj Ramachandran (2014). Orthopaedic Trauma: The Stanmore and Royal London Guide. CRC Press. ISBN 9781444148831. Page 158

[VB-6] Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 200. ISBN 0-03-910284-X.

[7] Turner, Alan H.; Makovicky, Peter J.; Norell, Mark A. (2007-09-21). "Feather Quill Knobs in the Dinosaur Velociraptor" (PDF). Science. 317 (5845): 1721. Bibcode:2007Sci...317.1721T. doi:10.1126/science.1145076. ISSN 0036-8075. PMID 17885130. S2CID 11610649.

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