Upper limb · Forearm
Radius
The radius is the lateral bone of the forearm, on the thumb side. Its small head turns against the ulna and the capitulum at the elbow, while its broad lower end forms the main bony part of the wrist joint.
- Latin (TA)
- Radius
- Type
- Long bone: a shaft with two ends
- Side
- Paired — right and left
- Model size
- 23.7 cm longest
Showing a right bone. Rotate it to inspect every surface; switch sides to practise siding.
3D model: Z-Anatomy (CC BY-SA 4.0), derived from BodyParts3D © DBCLS (CC BY-SA 2.1 JP). Adapted by PharmaWallah. Credits & licence
Landmarks
19 of 19 marked on the modelTap a landmark to find it on the bone and read what it is.
A short, disc-shaped cylinder at the upper end.
Where: Proximal end of the bone.
Why it matters: Articulates with the capitulum above and with the radial notch of the ulna at the side; held in place by the annular ligament.
Related: Elbow and proximal radioulnar joints
Viva: Which ligament holds the head of the radius against the ulna?
Marked on the model at the point Z-Anatomy places this label.
The shallow cup on the upper surface of the head.
Where: Top of the head.
Why it matters: Articulates with the capitulum of the humerus.
Related: Elbow joint (humeroradial part)
Marked on the model at the point Z-Anatomy places this label.
The smooth rim around the side of the head.
Where: Circumference of the head, broadest medially.
Why it matters: Rotates within the annular ligament and against the radial notch of the ulna in pronation and supination.
Related: Proximal radioulnar joint
Marked on the model at the point Z-Anatomy places this label.
The narrowed part below the head.
Where: Between the head and the radial tuberosity.
Why it matters: Lies within the lower edge of the annular ligament; a fracture site in children.
Marked on the model at the point Z-Anatomy places this label.
An oval roughened projection below the neck.
Where: Anteromedial side of the shaft, just below the neck.
Why it matters: Insertion of biceps brachii, which makes biceps a strong supinator.
Related: Biceps brachii (insertion)
Viva: What inserts into the radial tuberosity?
Marked on the model at the point Z-Anatomy places this label.
The shaft, gently convex laterally and widening downwards.
Where: Between the neck and the lower end.
Why it matters: Its lateral bow lets the radius swing round the ulna in pronation.
Marked on the model at the point Z-Anatomy places this label.
The sharp crest on the medial side of the shaft.
Where: Medial side of the shaft, facing the ulna.
Why it matters: Attachment of the interosseous membrane; its medial position helps side the bone.
Related: Interosseous membrane
Marked on the model at the point Z-Anatomy places this label.
A roughened area on the lateral surface of the shaft.
Where: Middle of the lateral surface, at the point of greatest lateral convexity.
Why it matters: Insertion of pronator teres.
Related: Pronator teres (insertion)
Marked on the model at the point Z-Anatomy places this label.
A blunt projection on the lateral side of the lower end.
Where: Lateral side of the distal end; it reaches further distally than the ulnar styloid.
Why it matters: Brachioradialis inserts at its base; the radial collateral ligament of the wrist attaches to it. A reliable feature for siding.
Viva: Which styloid process reaches further down, the radial or the ulnar?
Marked on the model at the point Z-Anatomy places this label.
A palpable ridge on the back of the lower end.
Where: Posterior surface of the distal end, about its middle.
Why it matters: The tendon of extensor pollicis longus turns around its medial side; marks the posterior surface when siding.
Viva: Which tendon hooks around the dorsal tubercle of the radius?
Marked on the model at the point Z-Anatomy places this label.
Shallow grooves on the back and lateral side of the lower end.
Where: Posterior and lateral surfaces of the distal end, on either side of the dorsal tubercle.
Why it matters: Carry the extensor tendons under the extensor retinaculum; identify the posterior surface.
Related: Extensor retinaculum
Marked on the model at the point Z-Anatomy places this label.
A shallow concave facet on the medial side of the lower end.
Where: Medial side of the distal end.
Why it matters: Articulates with the head of the ulna; the articular disc of the wrist attaches to its lower margin.
Related: Distal radioulnar joint
Marked on the model at the point Z-Anatomy places this label.
The concave inferior articular surface, divided by a faint ridge into two areas.
Where: Inferior surface of the distal end.
Why it matters: Lateral area articulates with the scaphoid, medial area with the lunate.
Related: Wrist (radiocarpal) joint
Viva: Which carpal bones articulate with the radius?
Marked on the model at the point Z-Anatomy places this label.
Classification & region
Long bone: a shaft with two ends; narrow above and broad below, the opposite of the ulna.
- Upper (proximal) end
- Disc-shaped head, neck and radial tuberosity.
- Shaft (body)
- Convex laterally, with a sharp medial interosseous border; widens towards the lower end.
- Lower (distal) end
- The broadest part of the bone: carpal articular surface, radial styloid process, ulnar notch and dorsal tubercle.
Hold it in the anatomical position
- Hold the bone vertically with the small disc-shaped head at the top and the broad end at the bottom.
- Turn the lower end so the styloid process points laterally and the ridged, grooved surface (with the dorsal tubercle) faces backwards.
- The sharp interosseous border of the shaft then faces medially, towards the ulna.
Right or left? Side determination
- Upper end: the small disc-shaped head is proximal; the broad end is distal.
- Lateral: the radial styloid process at the lower end is lateral.
- Posterior: the lower end's back carries the dorsal tubercle and grooves for the extensor tendons; the front is smooth and concave.
- Medial: the sharp interosseous border, the ulnar notch (lower end) and the radial tuberosity (below the neck, anteromedially) face medially.
- With the styloid lateral and the grooves behind, the bone belongs to the side on which the styloid points away from your midline.
Check yourself: switch the 3D model to “Left bone” and apply the same steps.
Articulations
- With the capitulum of humerus at the Elbow joint (humeroradial part) — Articular facet (concavity) on top of the head..
- With the radial notch of ulna at the Proximal radioulnar joint — Articular circumference of the head..
- With the head of ulna at the Distal radioulnar joint — Ulnar notch..
- With the scaphoid and lunate at the Wrist (radiocarpal) joint — Carpal articular surface..
Muscle and ligament attachments
| Structure | Type | Where on the bone |
|---|---|---|
| Biceps brachii | insertion | Radial tuberosity (posterior rough part). |
| Supinator | insertion | Upper part of the lateral surface of the shaft. |
| Pronator teres | insertion | Middle of the lateral surface (point of greatest convexity). |
| Pronator quadratus | insertion | Lower part of the anterior surface. |
| Brachioradialis | insertion | Lateral side of the lower end, at the base of the styloid process. |
| Flexor digitorum superficialis (radial head) | origin | Anterior oblique line. |
| Flexor pollicis longus | origin | Anterior surface of the shaft. |
| Abductor pollicis longus and extensor pollicis brevis | origin | Posterior surface of the shaft. |
| Interosseous membrane | ligament | Interosseous border. |
| Annular ligament (surrounds the head; attached to the ulna, not the radius) | ligament | Encircles the head and neck. |
| Articular disc of the distal radioulnar joint | ligament | Lower margin of the ulnar notch. |
| Palmar and dorsal radiocarpal ligaments; radial collateral ligament of wrist | ligament | Margins of the lower end; styloid process. |
| Extensor retinaculum | ligament | Anterior border of the lower end (lateral side). |
Functions
- Carries the hand: the wrist joint is formed mainly by the radius, so force from the hand passes chiefly to the radius.
- Rotates around the ulna in pronation and supination, turning the palm down and up.
- Gives attachment to the supinator and pronator muscles, the biceps, and the thumb muscles of the forearm.
Clinical & practical relevance
- Colles' fracture: a fracture of the distal radius with the distal fragment displaced backwards, producing a "dinner-fork" deformity; typically from a fall on the outstretched hand, often in older adults with osteoporosis.
- Smith's fracture: a distal radius fracture with the distal fragment displaced forwards (sometimes called a reversed Colles').
- Pulled elbow: in young children a sudden pull on the arm can slip the radial head partly out of the annular ligament.
- Fractures of the radial head occur from a fall on the outstretched hand and can limit pronation and supination.
- The radial pulse is felt at the wrist against the lower end of the radius, lateral to the tendon of flexor carpi radialis.
Identification tips
- Radius and ulna are opposites: the radius is small at the elbow and big at the wrist; the ulna is big at the elbow and small at the wrist.
- The radius is on the thumb side; its styloid is lateral and reaches further down than the ulnar styloid.
- The grooved surface of the lower end is posterior; the smooth concave surface is anterior.
Common student mistakes
- Calling the large end the head. The head of the radius is the small disc at the upper end.
- Saying the ulna takes part in the wrist joint directly: it is separated from the carpus by the articular disc; the radius forms the joint.
- Saying the annular ligament is attached to the radius: it encircles the head but is attached to the ulna.
- Placing the interosseous border laterally: it faces the ulna, medially.
Common exam questions
How do you side a radius?Show answer
Head upwards; styloid process lateral; dorsal tubercle and extensor grooves posterior; interosseous border medial.
What inserts into the radial tuberosity?Show answer
Biceps brachii.
Which carpal bones articulate with the radius?Show answer
The scaphoid and the lunate.
What is a Colles' fracture?Show answer
A fracture of the distal radius with backward displacement of the distal fragment, giving a dinner-fork deformity.
Which ligament encircles the head of the radius?Show answer
The annular ligament, attached to the margins of the radial notch of the ulna.
Where does pronator teres insert?Show answer
Middle of the lateral surface of the radius, at its point of greatest convexity.
What is the significance of the dorsal tubercle?Show answer
The extensor pollicis longus tendon turns around it, and it marks the back of the lower end.
Revision summary
- Lateral forearm bone; small head above, broad end below.
- Head: articular facet (capitulum) and circumference (radial notch of ulna).
- Radial tuberosity: biceps.
- Mid-lateral shaft: pronator teres. Lower anterior: pronator quadratus.
- Lower end: styloid lateral, ulnar notch medial, dorsal tubercle posterior.
- Carpal surface: scaphoid and lunate.
- Colles' (dorsal displacement) and Smith's (palmar displacement) fractures.
Test yourself on the radius
Spotting questions on bones, sides and landmarks — untimed, with explanations.
Joints of the radius
References
- Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 5th ed. Philadelphia: Elsevier; 2023.
- Moore KL, Dalley AF, Agur AMR. Moore's Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
- Federative International Programme for Anatomical Terminology (FIPAT). Terminologia Anatomica. 2nd ed. FIPAT.library.dal.ca; 2019. fipat.library.dal.ca/TA2
- Kervyn G, Zielinski M, Vinent L, et al. Z-Anatomy: the libre 3D atlas of anatomy. Models derived from BodyParts3D, The Database Center for Life Science (CC BY-SA 2.1 JP). CC BY-SA 4.0. www.z-anatomy.com/
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy