Radius
Radius
location_on Lateral (thumb-side) forearm, between the elbow and wrist
The radius is the lateral bone of the forearm that widens distally to form the major articulation with the wrist (carpus). It rotates around the ulna during pronation and supination, allowing the hand to turn palm-up or palm-down. Despite being shorter and smaller than the ulna proximally, the radius is the dominant forearm bone at the wrist, bearing about 80% of the load transmitted from the hand.
Key Anatomical Features
- Radial head is disc-shaped and rotates within the annular ligament during supination and pronation
- Radial tuberosity on the medial shaft is the insertion point of the biceps tendon
- Interosseous border is a sharp ridge for attachment of the interosseous membrane
- Styloid process is the most distal palpable bony point on the lateral wrist
- Distal articular surface is concave and articulates with the scaphoid and lunate
- Lister's tubercle (dorsal tubercle) is a bony ridge on the distal dorsal surface
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Biceps brachii | Radial tuberosity | Supinates the forearm and flexes the elbow |
| Supinator | Proximal lateral shaft | Supinates the forearm |
| Pronator teres | Middle lateral shaft | Pronates the forearm |
| Pronator quadratus | Distal anterior shaft | Pronates the forearm |
| Brachioradialis | Lateral supracondylar ridge to styloid process | Flexes the forearm from the midprone position |
| Flexor digitorum superficialis (radial head) | Anterior oblique line | Flexes the proximal interphalangeal joints |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Proximal radioulnar joint | Synovial pivot | Ulna |
| Radiocarpal (wrist) joint | Synovial ellipsoid (condyloid) | Scaphoid and lunate |
| Distal radioulnar joint | Synovial pivot | Ulna |
Common Pathologies
Distal radius fracture (Colles fracture)
The most common fracture in adults, caused by a fall on an outstretched hand. The distal fragment displaces dorsally creating the classic dinner fork deformity.
Smith fracture (reverse Colles)
Distal radius fracture with volar (palmar) displacement of the distal fragment, caused by a fall on the back of the hand or a direct blow.
Radial head fracture
The most common elbow fracture in adults, typically from a fall on an outstretched hand. Pain with forearm rotation is the hallmark finding.
Galeazzi fracture
Fracture of the radial shaft with dislocation of the distal radioulnar joint. Called a fracture of necessity because it requires surgical fixation.
Clinical Relevance
Distal radius fractures are the most common fracture seen in emergency departments. The radial styloid extends about 1 cm more distally than the ulnar styloid; loss of this relationship on radiographs indicates a displaced distal radius fracture. The radial artery pulse is palpated at the distal radius between the flexor carpi radialis tendon and the radial styloid process.
Development and Ossification
The radius ossifies from three centers: one for the shaft (8th fetal week), one for the distal end (around age 1), and one for the proximal end (around age 5). The distal epiphysis fuses around age 18-20 and the proximal around age 14-17. The distal radial epiphysis is the most frequently injured growth plate in the pediatric population.
Did You Know?
- Radius means ray or spoke of a wheel in Latin, referring to how the bone rotates around the ulna
- The radius bears about 80% of the forces transmitted from the hand to the forearm at the wrist
- Colles fracture was described by Abraham Colles in 1814, before the invention of X-rays, based purely on clinical deformity
Scan this bone yourself
Download Osteo+ and identify the radius instantly with your camera. Get all the details above and more from a single photo.