Radius

An anatomical and biomechanical study guide focusing on the lateral bone of the forearm — the mobile bone that pivots around the ulna to facilitate pronation and supination.

1. Osteology of the Radius

Divided into proximal end, shaft (diaphysis), and distal end

Region	Landmark	Description
Proximal	Head	A disc-shaped structure with a concave superior surface that articulates with the capitulum of the humerus.
	Neck	The constricted part just distal to the head.
	Radial (Bicipital) Tuberosity	A prominent oval projection on the medial side, distal to the neck, for the insertion of the biceps brachii tendon.
Shaft	Anterior Border	Extends from the radial tuberosity to the styloid process.
	Posterior Border	Most prominent in its middle third.
	Interosseous Border	The sharp medial edge for the attachment of the interosseous membrane connecting it to the ulna.
Distal	Ulnar Notch	A concave facet on the medial surface that articulates with the head of the ulna.
	Styloid Process	A large, pointed projection on the lateral side.
	Dorsal (Lister's) Tubercle	A bony prominence on the posterior surface that acts as a pulley for the extensor pollicis longus tendon.
	Articular Facets	Two facets on the distal surface for articulation with the scaphoid (laterally) and lunate (medially) carpal bones.

2 & 3. Muscular Attachments

Muscles originating from and inserting onto the radius

These muscles have their proximal attachment on the radius and typically act on the thumb and fingers.

Muscle	Origin Site	Action
Flexor Pollicis Longus	Anterior surface of the radial shaft and interosseous membrane	Flexion of the thumb IP joint
Flexor Digitorum Superficialis (radial head)	Proximal anterior surface (oblique line)	Flexion of PIP joints of digits 2-5
Abductor Pollicis Longus	Posterior surface of the radius (and ulna and interosseous membrane)	Abduction and extension of the thumb at the CMC joint
Extensor Pollicis Brevis	Posterior surface of the distal third of the radius	Extension of the thumb at the MCP joint

These muscles originate from the humerus, ulna, or scapula and insert onto the radius, primarily acting on elbow flexion, pronation, and supination.

Muscle	Insertion Site	Action
Biceps Brachii	Radial (bicipital) tuberosity	Elbow flexion and powerful forearm supination
Supinator	Lateral surface of the proximal third of the radius	Forearm supination
Pronator Teres	Lateral surface of the mid-shaft	Forearm pronation and assists elbow flexion
Brachioradialis	Lateral surface of the distal end, proximal to the styloid process	Elbow flexion (especially in mid-pronation)
Pronator Quadratus	Anterior surface of the distal quarter of the radius	Primary pronator of the forearm

4. Memory Tricks & Key Concept

Radius memory tricks: B.S.P.B.P. insertions mnemonic, F.F.A.E. origins mnemonic, and key concept showing radius as the mobile bone

Insertions Mnemonic: B.S.P.B.P.

"Big Strong Players Bench Press"

Remember all 5 muscles inserting onto the radius:

BBiceps Brachii

SSupinator

PPronator Teres

BBrachioradialis

PPronator Quadratus

Origins Mnemonic: F.F.A.E.

Only 4 muscles originate from the radius:

Flexor Pollicis Longus

Flexor Digitorum Superficialis

Abductor Pollicis Longus

Extensor Pollicis Brevis

Key Concept: Radius = Rotation

The radius is the mobile bone of the forearm. It rotates around the stable ulna during pronation and supination. This is in contrast to the ulna, which remains relatively fixed. Remember: Radius = Rotation.

5. Clinical Notes

Common fracture patterns — FOOSH = Fall On OutStretched Hand

$Radius clinical notes: radial head fracture, Colles' fracture, Smith fracture, and Galeazzi fracture$

Proximal (Head)

Radial Head Fracture

Fall on outstretched hand (FOOSH) forces the radial head into the capitulum of the humerus.

Often results in pain during forearm rotation. Can be associated with loss of full elbow extension. Common in adults after a FOOSH injury.

Distal (Colles' Fracture)

Colles' Fracture

The most common forearm fracture. A fracture of the distal radius with posterior displacement of the distal fragment.

Produces the classic 'dinner fork' deformity when viewed from the side. Caused by a FOOSH injury. Most common in elderly individuals with osteoporosis.

Distal (Smith Fracture)

Smith Fracture

A 'reverse Colles' fracture. A fracture of the distal radius with anterior (volar) displacement.

Caused by a fall on the back of the hand (a flexed wrist). Less common than Colles' but important to differentiate.

Shaft (Galeazzi Fracture)

Galeazzi Fracture

A fracture of the radial shaft combined with dislocation of the distal radioulnar joint (DRUJ).

A serious injury that typically requires surgical fixation. The counterpart to the Monteggia fracture of the ulna.