Editing Radius (bone)

{{Short description|One of the two long bones of the forearm}}
{{Infobox bone
| Name          = Radius
| Latin         = radius
| Image         = Radius - anterior view2.png
| Caption       = The radius (shown in red) is a bone in the [[forearm]].
| Articulations =
}}
The '''radius''' or '''radial bone''' ({{plural form}}: '''radii''' or '''radiuses''') is one of the two large [[bone]]s of the [[forearm]], the other being the [[ulna]]. It extends from the [[Anatomical terms of location|lateral]] side of the [[Elbow-joint|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 (geometry)|prism]]-shaped and slightly curved longitudinally. 

The radius is part of two [[joint (anatomy)|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 corresponding bone in the [[human leg|lower leg]] is the [[tibia]].

==Structure==
[[File:Human radius.stl|thumb|3D model.]]
[[File:Full Anterior View of Right Radius.png|thumb|Full anterior view of right radius]]
[[File:Full Posterior View of Right Radius.png|thumb|Full posterior view of right radius]]
[[File:Full Medial View of Right Radius.png|thumb|Full medial view of right radius]]
[[File:Full Lateral View of Right Radius.png|thumb|Full lateral view of right radius]]

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]].

The radius has a body and two extremities. The [[upper extremity of radius|upper extremity of the radius]] consists of a somewhat cylindrical head articulating with the ulna and the humerus, a neck, and a [[radial tuberosity]].<ref>{{Cite journal |date=1905-11-25 |title=Gray's Anatomy. Descriptive and Surgical. New American from the 15th English edition. Revised, enlarged and rewritten |url=http://dx.doi.org/10.1001/jama.1905.02510220061023 |journal=JAMA: The Journal of the American Medical Association |volume=XLV |issue=22 |pages=1675 |doi=10.1001/jama.1905.02510220061023 |issn=0098-7484|url-access=subscription }}</ref> The [[body of radius|body of the radius]] is self-explanatory, and the [[lower extremity of radius|lower extremity of the radius]] is roughly quadrilateral in shape, with articular surfaces for the [[ulna]], [[scaphoid]] and [[lunate bone]]s. The distal end of the radius forms two palpable points, radially the [[Radial styloid process|styloid process]] and [[Lister's tubercle]] on the ulnar side. Along with the [[Proximal radioulnar articulation|proximal]] and [[distal radioulnar articulation]]s, an [[Interosseous membrane of forearm|interosseous membrane]] originates medially along the length of the body of the radius to attach the radius to the ulna.<ref>{{ Citation | last=Clemente | first=Carmine D. | title=Anatomy: A Regional Atlas of the Human Body | publisher=Lippincott Williams & Wilkins | place=Philadelphia, PA | edition=5th | year=2007}}</ref>
{{multiple image|perrow = 2|total_width=800
| align = none
| image1 = Radius Anteiror Proximal.png
| image2 = Posterior Radius Proximal.png
| image3 = Radius Anteiror Distal 01.png
| image4 = Radius Posterior Distal.png
| footer = 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 [[Carpal bones|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 ''volar surface'', rough and irregular, affords attachment to the [[volar radiocarpal ligament]].
* The ''dorsal surface'' is convex, affords attachment to the [[dorsal radiocarpal ligament]], and is marked by three grooves. Enumerated from the lateral side:
** The ''first'' groove is broad, but shallow, and subdivided into two by a slight ridge: the lateral of these two, transmits the tendon of the [[extensor carpi radialis longus muscle]]; the medial, the tendon of the [[extensor carpi radialis brevis muscle]]. 
** 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 ''third'' is broad, for the passage of the tendons of the [[extensor indicis proprius]] and [[extensor digitorum communis]].
* 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 [[radial tuberosity|tuberosity]] above to the anterior part of the base of the [[Radial styloid process|styloid process]] below, and separates the [[anatomical terms of location#Hands and feet|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 [[Extensor retinaculum of the hand|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 [[Radial styloid process|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 [[radial tuberosity|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 of the radius|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 muscle|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 [[Palmar radiocarpal ligament|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 muscle|Supinator]]. Its middle third is broad, slightly concave, and gives origin to the [[Abductor pollicis longus muscle|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]].<ref>{{cite book | last = Moore | first = Keith |author2=Anne Agur | title = Essential Clinical Anatomy Third Edition | publisher = Lippincott Williams & Wilkins | year = 2007 | location = USA | pages = 446 | isbn = 978-0-7817-6274-8 }}</ref> 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 of the humerus|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 of radius|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|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|date=November 2019}} 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.

==Function==

===Muscle attachments===
The [[biceps]] muscle inserts on the [[radial tuberosity]] of the upper extremity of the bone. The upper third of the body of the bone attaches to the [[supinator muscle|supinator]], the [[flexor digitorum superficialis]], and the [[flexor pollicis longus]] muscles.
The middle third of the body attaches to the [[abductor pollicis longus|extensor ossis metacarpi pollicis]], [[extensor pollicis brevis|extensor primi internodii pollicis]], and the [[pronator teres]] muscles.
The lower quarter of the body attaches to the [[pronator quadratus]] muscle and the [[tendon]] of the [[brachioradialis|supinator longus]].

==Clinical significance==
[[Radial aplasia]] refers to the congenital absence or shortness of the radius.

===Fracture===
[[File:Pradialheadfrac.png|thumb| A subtle radial head fracture with associated positive [[Fat pad sign|sail sign]]]]
Specific [[bone fracture|fracture]] types of the radius include:
*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.
[[File:Forearm fracture - Radius fracture 2 -- Smart-Servier.png|thumb|250px|Illustration showing radius shaft fracture]]
**[[Essex-Lopresti fracture]] – a fracture of the [[Head of radius|radial head]] with concomitant dislocation of the [[Distal radioulnar articulation|distal radio-ulnar joint]] with disruption of the [[Interosseous membrane of the forearm|interosseous membrane]].<ref name="wheeless">[http://www.wheelessonline.com/ortho/essex_lopresti_fracture Essex Lopresti fracture] at Wheeless' Textbook of Orthopaedics online</ref>
*Radial shaft fracture
*[[Distal radius fracture]]
**[[Galeazzi fracture]] – a fracture of the radius with dislocation of the [[distal radioulnar joint]]
**[[Colles' fracture]] – a distal fracture of the radius with dorsal (posterior) displacement of the wrist and hand
**[[Smith's fracture]] – a distal fracture of the radius with volar (ventral) displacement of the wrist and hand
**[[Barton's fracture]] – an [[intra-articular fracture]] of the distal radius with dislocation of the [[radiocarpal joint]].

==History==
The word ''radius'' is [[Latin (language)|Latin]] for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally{{clarify|reason=how is a line centre-to-centre diagonal?|date=January 2015}} from center of [[capitulum of the humerus|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.<ref>{{ Citation | last1=Marieb | first1=E., R.N., Ph.D | last2=Mallatt | first2=J., Ph.D. | last3=Wilhelm | first3=P., Ph.D. | name-list-style=amp | title=Human Anatomy | publisher=Pearson Benjamin Cummings | place=San Francisco, CA | edition=5th | year=2008 | page=188}}</ref>

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{{clarify|reason=the far end is the distance?|date=January 2015}} 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 [[mammal]]s (such as [[horse]]s) and reduced or modified in animals with flippers or vestigial forelimbs.<ref name=VB>{{cite book |author=Romer, Alfred Sherwood|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|page= 199|isbn= 0-03-910284-X}}</ref>

==Gallery==
{{Gallery
|File:Radius Bone and Radius of a circle comparison.gif|Radius bone and radius of a circle comparison.
|File:Radius - animation2.gif|Position of radius (shown in red).
|Image:Radius4.jpg|Radius, styloid process - anterior view
|Image:Radius3.jpg|Radius, ulnar notch - posterior view
|Image:Radius2.jpg|Radius, radial head – posterior view
|Image:Radius.jpg|Radius, radial head – anterior view
|Image:Radius ant.jpg|Radius l. dx. – ant. view
|Image:Radius post.jpg|Radius l. dx. – post. view
|Image:Gray213.png|Anterior surface of radius (at right)
|Image:Gray214.png|Posterior surface of radius (at left)
|Image:Posterior_View_of_Right_Proximal_Radius.png|Posterior view of right proximal radius
|Image:Posterior_View_of_Right_Distal_Radius.png|Posterior view of right distal radius
|Image:Medial_View_of_Right_Proximal_Radius.png|Medial view of right proximal radius
|Image:Medial_View_of_Right_Distal_Radius.png|Medial view of right distal radius
|Image:Lateral_View_of_Right_Distal_Radius.png|Lateral view of right distal radius
|Image:Anterior_View_of_Right_Distal_Radius.png|Anterior view of right distal radius
|Image:Anterior_View_of_Right_Proximal_Radius.png|Anterior view of right proximal radius
|File:Radius Bone Anatomy by Jason Christian.webm|Radius bone anatomy
}}

==References==
{{Gray's}}
{{Reflist|2}}

{{Bones of upper extremity}}
{{Portal bar|Anatomy}}
{{Authority control}}

[[Category:Radius (bone)| ]]
[[Category:Long bones]]
[[Category:Bones of the upper limb]]