The radius or radial bone (
pl.: radii or radiuses) 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 radius is part of two
joints: the
elbow and the
wrist. At the elbow, it joins with the
capitulum of the humerus, and in a separate region, with the ulna at the
radial notch. At the wrist, the radius forms a joint with the ulna bone.
The long narrow
medullary cavity is enclosed in a strong wall of
compact bone. It is thickest along the interosseous border and thinnest at the extremities, same over the cup-shaped articular surface (fovea) of the head.
The
trabeculae of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli (the
humerus's cup-shaped articulatory notch); they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. It is missing in
radial aplasia.
Anterior and posterior view of radius bone - labelled.
Near the wrist
The distal end of the radius is large and of quadrilateral form.
Joint surfaces
It is provided with two articular surfaces – one below, for the
carpus, and another at the medial side, for the
ulna.
The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the
scaphoid bone; the medial, quadrilateral, with the
lunate bone.
The articular surface for the ulna is called the
ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna.
These two articular surfaces are separated by a prominent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation.
Other surfaces
This end of the bone has three non-articular surfaces – volar, dorsal, and lateral.
The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the
extensor pollicis longus muscle.
The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the brachioradialis, and by its apex to the
radial collateral ligament of wrist joint. The lateral surface of this process is marked by a flat groove, for the tendons of the
abductor pollicis longus muscle and
extensor pollicis brevis muscle.
Body
The body of the radius (or shaft of radius) is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces.
Borders
The volar border (margo volaris; anterior border; palmar;) extends from the lower part of the
tuberosity above to the anterior part of the base of the
styloid process below, and separates the
volar from the lateral surface. Its upper third is prominent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the
flexor digitorum superficialis muscle (also flexor digitorum sublimis) and
flexor pollicis longus muscle; the surface above the line gives insertion to part of the
supinator muscle. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the
pronator quadratus muscle, and attachment to the
dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the
brachioradialis muscle is inserted.
The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the
styloid process; it separates the posterior from the lateral surface. is indistinct above and below, but well-marked in the middle third of the bone.
The interosseous border (internal border; crista interossea; interosseous crest;) begins above, at the back part of the
tuberosity, and its upper part is rounded and indistinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the
ulnar notch. To the posterior of the two ridges the lower part of the
interosseous membrane is attached, while the triangular surface between the ridges gives insertion to part of the
pronator quadratus muscle. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. The connection between the two bones is actually a joint referred to as a
syndesmosis joint.
Surfaces
The volar surface (facies volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the
flexor pollicis longus muscle; it is broad and flat in its lower fourth, and affords insertion to the
Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the
volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward.
The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the
Supinator. Its middle third is broad, slightly concave, and gives origin to the
Abductor pollicis longus above, and the
extensor pollicis brevis muscle below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone.
The lateral surface (facies lateralis; external surface) is convex throughout its entire extent and is known as the convexity of the radius, curving outwards to be convex at the side. Its upper third gives insertion to the
supinator muscle. About its center is a rough ridge, for the insertion of the
pronator teres muscle.[2] Its lower part is narrow, and covered by the tendons of the
abductor pollicis longus muscle and
extensor pollicis brevis muscle.
Near the elbow
The upper extremity of the radius (or proximal extremity) presents a head, neck, and tuberosity.
The radial head has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the
capitulum (or capitellum) of the
humerus. The circumference of the head is smooth; it is broad medially where it articulates with the
radial notch of the ulna, narrow in the rest of its extent, which is embraced by the
annular ligament. The deepest point in the fovea is not axi-symmetric with the long axis of the radius, creating a cam effect during pronation and supination.
The head is supported on a round, smooth, and constricted portion called the neck, on the back of which is a slight ridge for the insertion of part of the
supinator muscle.
Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the
biceps brachii muscle, and an anterior, smooth portion, on which a
bursa is interposed between the
tendon and the bone.
Development
The radius is
ossified from three centers: one for the body, and one for each extremity. That for the body makes its appearance near the center of the bone, during the eighth week of
fetal life.
Ossification commences in the lower end between 9 and 26 months of age.[citation needed] The ossification center for the upper end appears by the fifth year.
The upper
epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty.
An additional center sometimes found in the
radial tuberosity, appears about the fourteenth or fifteenth year.
Proximal radius fracture. A fracture within the capsule of the
elbow joint results in the
fat pad sign or "sail sign" which is a displacement of the
fat pad at the elbow.
The word radius is
Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally[clarification needed] from center of
capitulum to the center of distal
ulna. While the
ulna is the major contributor to the elbow joint, the radius primarily contributes to the
wrist joint.[4]
The radius is named so because the radius (bone) acts like the radius (of a circle). It rotates around the ulna and the far end (where it joins to the bones of the hand), known as the styloid process of the radius, is[clarification needed] the distance from the ulna (center of the circle) to the edge of the radius (the circle). The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move.
Other animals
In four-legged animals, the radius is the main load-bearing bone of the lower forelimb. Its structure is similar in most terrestrial
tetrapods, but it may be fused with the ulna in some
mammals (such as
horses) and reduced or modified in animals with flippers or vestigial forelimbs.[5]
The radius or radial bone (
pl.: radii or radiuses) 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 radius is part of two
joints: the
elbow and the
wrist. At the elbow, it joins with the
capitulum of the humerus, and in a separate region, with the ulna at the
radial notch. At the wrist, the radius forms a joint with the ulna bone.
The long narrow
medullary cavity is enclosed in a strong wall of
compact bone. It is thickest along the interosseous border and thinnest at the extremities, same over the cup-shaped articular surface (fovea) of the head.
The
trabeculae of the spongy tissue are somewhat arched at the upper end and pass upward from the compact layer of the shaft to the fovea capituli (the
humerus's cup-shaped articulatory notch); they are crossed by others parallel to the surface of the fovea. The arrangement at the lower end is somewhat similar. It is missing in
radial aplasia.
Anterior and posterior view of radius bone - labelled.
Near the wrist
The distal end of the radius is large and of quadrilateral form.
Joint surfaces
It is provided with two articular surfaces – one below, for the
carpus, and another at the medial side, for the
ulna.
The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the
scaphoid bone; the medial, quadrilateral, with the
lunate bone.
The articular surface for the ulna is called the
ulnar notch (sigmoid cavity) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna.
These two articular surfaces are separated by a prominent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation.
Other surfaces
This end of the bone has three non-articular surfaces – volar, dorsal, and lateral.
The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the
extensor pollicis longus muscle.
The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the brachioradialis, and by its apex to the
radial collateral ligament of wrist joint. The lateral surface of this process is marked by a flat groove, for the tendons of the
abductor pollicis longus muscle and
extensor pollicis brevis muscle.
Body
The body of the radius (or shaft of radius) is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateralward. It presents three borders and three surfaces.
Borders
The volar border (margo volaris; anterior border; palmar;) extends from the lower part of the
tuberosity above to the anterior part of the base of the
styloid process below, and separates the
volar from the lateral surface. Its upper third is prominent, and from its oblique direction has received the name of the oblique line of the radius; it gives origin to the
flexor digitorum superficialis muscle (also flexor digitorum sublimis) and
flexor pollicis longus muscle; the surface above the line gives insertion to part of the
supinator muscle. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the
pronator quadratus muscle, and attachment to the
dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the
brachioradialis muscle is inserted.
The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the
styloid process; it separates the posterior from the lateral surface. is indistinct above and below, but well-marked in the middle third of the bone.
The interosseous border (internal border; crista interossea; interosseous crest;) begins above, at the back part of the
tuberosity, and its upper part is rounded and indistinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the
ulnar notch. To the posterior of the two ridges the lower part of the
interosseous membrane is attached, while the triangular surface between the ridges gives insertion to part of the
pronator quadratus muscle. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. The connection between the two bones is actually a joint referred to as a
syndesmosis joint.
Surfaces
The volar surface (facies volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the
flexor pollicis longus muscle; it is broad and flat in its lower fourth, and affords insertion to the
Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the
volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward.
The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the
Supinator. Its middle third is broad, slightly concave, and gives origin to the
Abductor pollicis longus above, and the
extensor pollicis brevis muscle below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone.
The lateral surface (facies lateralis; external surface) is convex throughout its entire extent and is known as the convexity of the radius, curving outwards to be convex at the side. Its upper third gives insertion to the
supinator muscle. About its center is a rough ridge, for the insertion of the
pronator teres muscle.[2] Its lower part is narrow, and covered by the tendons of the
abductor pollicis longus muscle and
extensor pollicis brevis muscle.
Near the elbow
The upper extremity of the radius (or proximal extremity) presents a head, neck, and tuberosity.
The radial head has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the
capitulum (or capitellum) of the
humerus. The circumference of the head is smooth; it is broad medially where it articulates with the
radial notch of the ulna, narrow in the rest of its extent, which is embraced by the
annular ligament. The deepest point in the fovea is not axi-symmetric with the long axis of the radius, creating a cam effect during pronation and supination.
The head is supported on a round, smooth, and constricted portion called the neck, on the back of which is a slight ridge for the insertion of part of the
supinator muscle.
Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the
biceps brachii muscle, and an anterior, smooth portion, on which a
bursa is interposed between the
tendon and the bone.
Development
The radius is
ossified from three centers: one for the body, and one for each extremity. That for the body makes its appearance near the center of the bone, during the eighth week of
fetal life.
Ossification commences in the lower end between 9 and 26 months of age.[citation needed] The ossification center for the upper end appears by the fifth year.
The upper
epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty.
An additional center sometimes found in the
radial tuberosity, appears about the fourteenth or fifteenth year.
Proximal radius fracture. A fracture within the capsule of the
elbow joint results in the
fat pad sign or "sail sign" which is a displacement of the
fat pad at the elbow.
The word radius is
Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally[clarification needed] from center of
capitulum to the center of distal
ulna. While the
ulna is the major contributor to the elbow joint, the radius primarily contributes to the
wrist joint.[4]
The radius is named so because the radius (bone) acts like the radius (of a circle). It rotates around the ulna and the far end (where it joins to the bones of the hand), known as the styloid process of the radius, is[clarification needed] the distance from the ulna (center of the circle) to the edge of the radius (the circle). The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move.
Other animals
In four-legged animals, the radius is the main load-bearing bone of the lower forelimb. Its structure is similar in most terrestrial
tetrapods, but it may be fused with the ulna in some
mammals (such as
horses) and reduced or modified in animals with flippers or vestigial forelimbs.[5]