Radius anatomy: the thumb-side forearm bone labelled from elbow to wrist

What it is

The lateral bone of the forearm.

Location

Lies on the thumb side of the forearm. At the elbow it articulates with the humerus and ulna; at the wrist it articulates with the scaphoid, lunate and ulna.

Function

Allows forearm pronation and supination by rotating around the ulna, and transmits hand forces to the arm.

Body system

Skeletal · paired (left and right)

FMA ID

FMA23465 (Foundational Model of Anatomy)

Key facts

• Its head is disc-shaped and the radial tuberosity gives attachment to biceps brachii.
• Its distal end has a styloid process.

Clinical relevance

Distal radius fractures are among the most common fractures, usually after a fall on an outstretched hand. A Colles fracture is one with dorsal displacement of the distal fragment ("dinner fork" deformity).

The radius is the lateral bone of the forearm, on the thumb side when the palm faces forward. It lies parallel to the ulna, joined to it by the interosseous membrane. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

It takes part in four joints: the elbow (head with the capitulum of the humerus), the proximal radioulnar joint (head with the radial notch of the ulna), the distal radioulnar joint (ulnar notch with the head of the ulna) and the wrist joint (lower end with the carpal bones). (TeachMeAnatomy: The Radius.)

The head of the radius is disc-shaped. Its upper surface is concave where it meets the capitulum, and its rim is thicker on the medial side, where it turns within the radial notch of the ulna. (TeachMeAnatomy: The Radius.)

The annular ligament encircles the radial head and holds it against the radial notch. This proximal radioulnar joint is a pivot joint that lets the forearm pronate and supinate. (OpenStax Anatomy and Physiology 2e, 9.6: Anatomy of Selected Synovial Joints.)

Below the head is the neck, a short narrow part of the bone that leads down to the radial tuberosity. (TeachMeAnatomy: The Radius.)

The radial tuberosity is a rough bony projection just below the neck. The tendon of biceps brachii inserts on it. (TeachMeAnatomy: The Radius.)

The shaft widens as it runs toward the wrist. Like the ulna it is triangular in cross-section, with a slightly convex lateral surface and a sharp interosseous border facing the ulna. (Kenhub: The radius and the ulna.)

A small roughened area on the middle of the lateral surface of the shaft marks the insertion of pronator teres. (TeachMeAnatomy: The Radius.)

The lower end of the radius is broad and roughly rectangular. Its lateral side extends downward as the styloid process of the radius, and its medial side has a concave ulnar notch that receives the head of the ulna at the distal radioulnar joint. (TeachMeAnatomy: The Radius.)

The ulnar notch is called incisura ulnaris in Latin (in full, incisura ulnaris radii) and is also known as the sigmoid notch. Together with the ulnar head it forms the distal radioulnar joint, which works with the proximal joint during pronation and supination. (IMAIOS e-Anatomy: Ulnar notch (incisura ulnaris radii).)

The radial styloid process projects further down than the styloid process of the ulna. The lower surface of the radius has two facets that articulate with the scaphoid and the lunate to form the wrist (radiocarpal) joint. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

On the back of the lower end is the dorsal tubercle of the radius, often called Lister's tubercle, a small bony ridge on the dorsal surface of the lower end. (Kenhub: The radius and the ulna.)

Supination turns the palm to face forward (the anatomical position). Pronation turns the palm to face backward. Pronation is produced by the radius rotating at the proximal radioulnar joint; because its shaft is slightly curved, its lower end crosses over the ulna so that the two bones form an X. Supination rotates the radius back until the bones are parallel again. (OpenStax Anatomy and Physiology 2e, 9.5: Types of Body Movements.)

The ulna is the stable bone in this movement, and the radius pivots around it at the proximal and distal radioulnar joints. (TeachMeAnatomy: The Radius.)

At the elbow, the radial head shares one joint capsule with the humeroulnar and humeroradial joints. The radial (lateral) collateral ligament runs down from the lateral epicondyle of the humerus and blends into the annular ligament. (OpenStax Anatomy and Physiology 2e, 9.6: Anatomy of Selected Synovial Joints.)

Along the shafts, the interosseous membrane firmly joins the radius to the ulna. At the wrist, the radius articulates with the scaphoid, lunate and triquetrum at the radiocarpal joint, while the ulnar notch meets the ulnar head at the distal radioulnar joint. (Kenhub: The radius and the ulna.)

The radius and ulna receive blood from the radial, ulnar, anterior interosseous and posterior interosseous arteries, which enter through several nutrient foramina near the ends of the bones. (Kenhub: The radius and the ulna.)

A Colles fracture is the most common fracture of the radius. It is a break of the distal radius after a fall on an outstretched hand, with the lower fragment pushed backward (dorsally). The resulting bend is called a dinner fork deformity. (TeachMeAnatomy: The Radius.)

OpenStax describes the Colles fracture as the most common forearm fracture and notes that it is especially common in people over 50 with osteoporosis. (OpenStax Anatomy and Physiology 2e, 8.2: Bones of the Upper Limb.)

A Smith fracture is the reverse pattern. It follows a fall onto the back of the hand, and the lower fragment is displaced forward (anteriorly). A radial head fracture usually follows a fall on an outstretched hand that drives the radial head into the capitulum. (TeachMeAnatomy: The Radius.)

A Galeazzi fracture is a fracture of the lower part of the radial shaft with dislocation of the distal radioulnar joint. It is the counterpart of the Monteggia fracture of the ulna. (Kenhub: The radius and the ulna.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Extensor carpi radialis brevis · muscular
• Radial vein · cardiovascular
• Radial artery · cardiovascular
• Anterior interosseous artery · cardiovascular
• Extensor carpi radialis longus · muscular
• Extensor carpi ulnaris · muscular
• Interosseous membrane of forearm · skeletal
• Flexor carpi radialis · muscular
• Ulnar vein · cardiovascular
• Ulnar artery · cardiovascular