Radius (bone)

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Radius (bone)_table_infobox_0

RadiusRadius (bone)_header_cell_0_0_0
DetailsRadius (bone)_header_cell_0_1_0
IdentifiersRadius (bone)_header_cell_0_2_0
LatinRadius (bone)_header_cell_0_3_0 RadiusRadius (bone)_cell_0_3_1
MeSHRadius (bone)_header_cell_0_4_0 Radius (bone)_cell_0_4_1
TA98Radius (bone)_header_cell_0_5_0 Radius (bone)_cell_0_5_1
TA2Radius (bone)_header_cell_0_6_0 Radius (bone)_cell_0_6_1
FMARadius (bone)_header_cell_0_7_0 Radius (bone)_cell_0_7_1

The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. Radius (bone)_sentence_0

It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. Radius (bone)_sentence_1

The ulna is usually slightly longer than the radius, but the radius is thicker. Radius (bone)_sentence_2

Therefore the radius is considered to be the larger of the two. Radius (bone)_sentence_3

It is a long bone, prism-shaped and slightly curved longitudinally. Radius (bone)_sentence_4

The radius is part of two joints: the elbow and the wrist. Radius (bone)_sentence_5

At the elbow, it joins with the capitulum of the humerus, and in a separate region, with the ulna at the radial notch. Radius (bone)_sentence_6

At the wrist, the radius forms a joint with the ulna bone. Radius (bone)_sentence_7

The corresponding bone in the lower leg is the fibula. Radius (bone)_sentence_8

Structure Radius (bone)_section_0

The long narrow medullary cavity is enclosed in a strong wall of compact bone. Radius (bone)_sentence_9

It is thickest along the interosseous border and thinnest at the extremities, same over the cup-shaped articular surface (fovea) of the head. Radius (bone)_sentence_10

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. Radius (bone)_sentence_11

The arrangement at the lower end is somewhat similar. Radius (bone)_sentence_12

It is missing in radial aplasia. Radius (bone)_sentence_13

The radius has a body and two extremities. Radius (bone)_sentence_14

The upper extremity of the radius consists of a somewhat cylindrical head articulating with the ulna and the humerus, a neck, and a radial tuberosity. Radius (bone)_sentence_15

The body of the radius is self-explanatory, and the lower extremity of the radius is roughly quadrilateral in shape, with articular surfaces for the ulna, scaphoid and lunate bones. Radius (bone)_sentence_16

The distal end of the radius forms two palpable points, radially the styloid process and Lister's tubercle on the ulnar side. Radius (bone)_sentence_17

Along with the proximal and distal radioulnar articulations, an interosseous membrane originates medially along the length of the body of the radius to attach the radius to the ulna. Radius (bone)_sentence_18

Near the wrist Radius (bone)_section_1

The distal end of the radius is large and of quadrilateral form. Radius (bone)_sentence_19

Radius (bone)_description_list_0

It is provided with two articular surfaces – one below, for the carpus, and another at the medial side, for the ulna. Radius (bone)_sentence_20

Radius (bone)_unordered_list_1

  • 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.Radius (bone)_item_1_0
  • 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.Radius (bone)_item_1_1

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. Radius (bone)_sentence_21

Radius (bone)_description_list_2

This end of the bone has three non-articular surfaces – volar, dorsal, and lateral. Radius (bone)_sentence_22

Radius (bone)_unordered_list_3

Body Radius (bone)_section_2

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. Radius (bone)_sentence_23

It presents three borders and three surfaces. Radius (bone)_sentence_24

Radius (bone)_description_list_4

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. Radius (bone)_sentence_25

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. Radius (bone)_sentence_26

The middle third of the volar border is indistinct and rounded. Radius (bone)_sentence_27

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. Radius (bone)_sentence_28

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. Radius (bone)_sentence_29

is indistinct above and below, but well-marked in the middle third of the bone. Radius (bone)_sentence_30

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. Radius (bone)_sentence_31

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. Radius (bone)_sentence_32

This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. Radius (bone)_sentence_33

The connection between the two bones is actually a joint referred to as a syndesmosis joint. Radius (bone)_sentence_34

Radius (bone)_description_list_5

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. Radius (bone)_sentence_35

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. Radius (bone)_sentence_36

At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward. Radius (bone)_sentence_37

The dorsal surface (facies dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Radius (bone)_sentence_38

Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the extensor pollicis brevis muscle below. Radius (bone)_sentence_39

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. Radius (bone)_sentence_40

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. Radius (bone)_sentence_41

Its upper third gives insertion to the supinator muscle. Radius (bone)_sentence_42

About its center is a rough ridge, for the insertion of the pronator teres muscle. Radius (bone)_sentence_43

Its lower part is narrow, and covered by the tendons of the abductor pollicis longus muscle and extensor pollicis brevis muscle. Radius (bone)_sentence_44

Near the elbow Radius (bone)_section_3

The upper extremity of the radius (or proximal extremity) presents a head, neck, and tuberosity. Radius (bone)_sentence_45

Radius (bone)_unordered_list_6

  • 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.Radius (bone)_item_6_8
  • 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.Radius (bone)_item_6_9
  • 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.Radius (bone)_item_6_10

Development Radius (bone)_section_4

The radius is ossified from three centers: one for the body, and one for each extremity. Radius (bone)_sentence_46

That for the body makes its appearance near the center of the bone, during the eighth week of fetal life. Radius (bone)_sentence_47

Ossification commences in the lower end between 9 and 26 months of age. Radius (bone)_sentence_48

The ossification center for the upper end appears by the fifth year. Radius (bone)_sentence_49

The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. Radius (bone)_sentence_50

An additional center sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. Radius (bone)_sentence_51

Function Radius (bone)_section_5

Muscle attachments Radius (bone)_section_6

The biceps muscle inserts on the radial tuberosity of the upper extremity of the bone. Radius (bone)_sentence_52

The upper third of the body of the bone attaches to the supinator, the flexor digitorum superficialis, and the flexor pollicis longus muscles. Radius (bone)_sentence_53

The middle third of the body attaches to the extensor ossis metacarpi pollicis, extensor primi internodii pollicis, and the pronator teres muscles. Radius (bone)_sentence_54

The lower quarter of the body attaches to the pronator quadratus muscle and the tendon of the supinator longus. Radius (bone)_sentence_55

Clinical significance Radius (bone)_section_7

Radial aplasia refers to the congenital absence or shortness of the radius. Radius (bone)_sentence_56

Fracture Radius (bone)_section_8

Specific fracture types of the radius include: Radius (bone)_sentence_57

Radius (bone)_unordered_list_7

  • 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.Radius (bone)_item_7_11

Radius (bone)_unordered_list_8

History Radius (bone)_section_9

The word radius is Latin for "ray". Radius (bone)_sentence_58

In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally from center of capitulum to the center of distal ulna. Radius (bone)_sentence_59

While the ulna is the major contributor to the elbow joint, the radius primarily contributes to the wrist joint. Radius (bone)_sentence_60

The radius is named so because the radius (bone) acts like the radius (of a circle). Radius (bone)_sentence_61

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 the distance from the ulna (center of the circle) to the edge of the radius (the circle). Radius (bone)_sentence_62

The ulna acts as the center point to the circle because when the arm is rotated the ulna does not move. Radius (bone)_sentence_63

Other animals Radius (bone)_section_10

In four-legged animals, the radius is the main load-bearing bone of the lower forelimb. Radius (bone)_sentence_64

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. Radius (bone)_sentence_65


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Radius (bone).