Radius (bone)

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 radius is shorter and smaller than the ulna. It 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 corresponding bone in the lower leg is the fibula.

Radius - anterior view2
The radius (shown in red) is a bone in the forearm.
Anatomical terms of bone


Human radius.stl
3D model.

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 the radius consists of a somewhat cylindrical head articulating with the ulna and the humerus, a neck, and a radial tuberosity. 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. The distal end of the radius forms two palpable points, radially the styloid process and Lister's tubercle on the ulnar side. 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.[1]

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 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.


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.


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.


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.[3] 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.


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, the flexor digitorum superficialis, and the flexor pollicis longus muscles. The middle third of the body attaches to the extensor ossis metacarpi pollicis, 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 supinator longus.

Clinical significance

Radial aplasia refers to the congenital absence or shortness of the radius.


A subtle radial head fracture with associated positive sail sign

Specific fracture types of the radius include:


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 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.[5]

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 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.[6]


Radius - animation2

Position of radius (shown in red).


Radius, styloid process - anterior view


Radius, ulnar notch - posterior view


Radius, radial head – posterior view


Radius, radial head – anterior view

Radius l. dx. – ant. view

Radius l. dx. – post. view


Anterior surface of radius (at right)


Posterior surface of radius (at left)


This article incorporates text in the public domain from page 219 of the 20th edition of Gray's Anatomy (1918)

  1. ^ Clemente, Carmine D. (2007), Anatomy: A Regional Atlas of the Human Body (5th ed.), Philadelphia, PA: Lippincott Williams & Wilkins
  2. ^ Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy Third Edition. USA: Lippincott Williams & Wilkins. p. 446. ISBN 0-7817-6274-X.
  3. ^ Balachandran, Ajay; Anooj Krishna; Moumitha Kartha; Thomas Jerry; Prem T.N.; Libu G.K. (December 2013). "Ossification of Distal end of Radius & Base of Fist Metacarpal in Forensic Age Estimation in the Kerala Population" (PDF). Scholars Journal of Applied Medical Sciences. 1 (6): 796–800. Retrieved 4 January 2014.
  4. ^ Essex Lopresti fracture at Wheeless' Textbook of Orthopaedics online
  5. ^ Marieb, E., R.N., Ph.D; Mallatt, J., Ph.D. & Wilhelm, P., Ph.D. (2008), Human Anatomy (5th ed.), San Francisco, CA: Pearson Benjamin Cummings, p. 188
  6. ^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 199. ISBN 0-03-910284-X.

Cardiocorax is an extinct genus of elasmosaurid known from the Late Cretaceous (early Maastrichtian stage) Mocuio Formation of Namibe Province, southern Angola. It contains a single species, Cardiocorax mukulu.


Colles may refer to:

Abraham Colles, Irish professor of anatomy

Christopher Colles, engineer and inventor

Colles' fracture, a fracture of the distal radius bone

Fascia of Colles, serves to bind down the muscles of the root of the penis

Plural of collis, a term used in planetary nomenclature to refer to small hills or knobs


Corythoraptor (meaning "crested raptor") is a genus of crested oviraptorid theropod dinosaur from the Nanxiong Formation of China. It is known from one species, C. jacobsi, named after palaeontologist Louis L. Jacobs. Including it, there are seven oviraptorids known from the Nanxiong Formation, showing a high level of diversity in the area, and that the different taxa may have occupied different ecological niches.

Distal radius fracture

A distal radius fracture, also known as wrist fracture, is a break of the part of the radius bone which is close to the wrist. Symptoms include pain, bruising, and rapid-onset swelling. The wrist may be deformed. The ulna bone may also be broken.In younger people, these fractures typically occur during sports or a motor vehicle collision. In older people, the most common cause is falling on an outstretched hand. Specific types include Colles, Smith, Barton, and Chauffeur's fractures. The diagnosis is generally suspected based on symptoms and confirmed with X-rays.Treatment is with casting for six weeks or surgery. Surgery is generally indicated if the joint surface is broken and does not line up, the radius is overly short, or the joint surface of the radius is tilted more than 10% backwards. Among those who are cast, repeated X-rays are recommended within three weeks to verify that a good position is maintained.Distal radius fractures are common. They represent between 25% and 50% of all broken bones. They occur most commonly in young males and older females. A year or two may be required for healing to occur.

External fixation

External fixation is a surgical treatment used to stabilize bone and soft tissues at a distance from the operative or injury focus. They provide unobstructed access to the relevant skeletal and soft tissue structures for their initial assessment and also for secondary interventions needed to restore bony continuity and a functional soft tissue cover. It is an alternative to internal fixation, where the components used to provide stability are positioned entirely within the patient's body.

Head of radius

The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum 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.

Lister's tubercle

Lister's tubercle or dorsal tubercle of radius is a bony prominence located at the distal end of the radius, palpable on the dorsum of the wrist.


RCL may refer to:

Radial collateral ligament, one of three ligaments in the upper limb on the side of the radius bone:

Radial collateral ligament of elbow joint

Radial collateral ligament of thumb

Radial collateral ligament of wrist joint

Ramped Cargo Lighter, Canadian built landing craft of WW2

Ramped Craft Logistic, Landing craft operated by the Royal Logistic Corps of the British Army

Ramsey County Library

RC Lens (Racing Club de Lens), a French Ligue 2 football team

Recoilless rifle

Reliance Capital Limited

Remotely Controlled Laboratory

Revised Common Lectionary

Revolutionary Communist League (France)

RLC circuit, an electrical circuit consisting of a resistor (R), inductor (L) and capacitor (C) connected in series or in parallel, sometimes referred to as RCL circuit

Robot Combat League, a television program hosted by Chris Jericho

Royal Canadian Legion

Royal Caribbean Cruises Ltd., NYSE ticker code RCL

RCL may also refer to its subsidiary cruise line Royal Caribbean International

Rugby Club Luxembourg, a rugby union club in Luxembourg City

Radial aplasia

Radial aplasia is a congenital defect which affects the formation of the radius bone in the arm. The radius is the lateral bone (thumb side) which connects the humerus of the upper arm to the wrist via articulation with the carpal bones. A child born with this condition has either a short or absent radius bone in one or both of his or her arms. Radial aplasia also results in the thumb being either partly formed or completely absent from the hand, which can result in difficulties performing activities of daily living. Radial aplasia is connected with the condition VACTERL association, under the 'L' for limb malformations.

Radial aplasia is not inherited. The cause for radial aplasia is unknown, but it widely believed to occur within the first ten weeks of gestation.

Radial styloid process

The radial styloid process is a projection of bone on the lateral surface of the distal radius bone. It extends obliquely downward into a strong, conical projection. The tendon of the brachioradialis attaches at its base, and the radial collateral ligament of the wrist attaches at its apex. The lateral surface is marked by a flat groove for the tendons of the abductor pollicis longus and extensor pollicis brevis.

Breakage of the radius at the radial styloid is known as a Chauffeur's fracture; it is typically caused by compression of the scaphoid bone of the hand against the styloid.

Radial tuberosity

Beneath the neck of the radius, 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.

an anterior, smooth portion, on which a bursa is interposed between the tendon and the bone.

Rear naked choke

The rear naked choke (RNC) is a chokehold in martial arts applied from an opponent's back. The word "naked" in this context suggests that, unlike other strangulation techniques found in Jujutsu/Judo, this hold does not require the use of a keikogi ("gi") or training uniform.

The choke has two variations: in one version, the attacker's arm encircles the opponent's neck and then grabs his own biceps on the other arm (see below for details); in the second version, the attacker clasps his hands together instead after encircling the opponent's neck.


Somphospondylans are an extinct clade of titanosauriform sauropods that lived throughout the world from the Late Jurassic through the Cretaceous. The group can be defined as "the most inclusive clade that includes Saltasaurus loricatus but excludes Brachiosaurus altithorax". Features found as diagnostic of this clade by Mannion et al. (2013) include the possession of at least 15 cervical vertebrae; a bevelled radius bone end; sacral vertebrae with camellate internal texture; convex posterior articular surfaces of middle to posterior caudal vertebrae; biconvex distal caudal vertebrae; humerus anterolateral corner "squared"; among multiple others.


A squitten is a cat with a genetic deformity which causes a partial formation or complete absence of the radius bone making it resemble a squirrel. These cats should be kept indoors and seen to by specialist veterinarians as long term management of the condition is essential for quality of life in these cats It is an example of a cat body type genetic mutation. The word is a portmanteau of squirrel and kitten.

The term kangaroo cat is also, rarely, used; this derives from a 1953 specimen known as the Stalingrad Kangaroo Cat.

Styloid process

In anatomy, a styloid process (from Greek stylos (στῦλος), "pillar"), usually serving as points of attachment for muscles, refers to the slender, pointed process (protrusion) of:

temporal bone of the skull - Temporal styloid process

radius bone of the lower arm - Radial styloid process

ulna bone of the lower arm - Ulnar styloid process

Third metacarpal - Third metacarpal styloid process

Tibia and Fibula - Tibial process, fibular process.

5th metatarsal of the foot - also known as the tuberosity of the fifth metatarsalIn botany, a styloid is a needle-shaped crystal of calcium oxalate found in some plants. It is a form of raphide.

TAR syndrome

TAR syndrome (thrombocytopenia with absent radius) is a rare genetic disorder that is characterized by the absence of the radius bone in the forearm and a dramatically reduced platelet count.


Trochlea (Latin for pulley) is a term in anatomy. It refers to a grooved structure reminiscent of a pulley's wheel.

Ulnar notch of the radius

The articular surface for the ulna is called the ulnar notch (sigmoid cavity) of the radius; it is in the distal radius, and is narrow, concave, smooth, and articulates with the head of the ulna forming the distal radioulnar joint.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.