Overview

Proximal end: the disc-shaped head, concave above, articulates with the capitulum of the humerus and, by its rim, with the radial notch of the ulna, held in place by the annular ligament (proximal radioulnar joint). Below the neck, the radial tuberosity on the medial side receives the biceps brachii tendon — making biceps a powerful supinator.

Shaft: slightly bowed laterally (the "pronator bow"), with a sharp interosseous border medially for the interosseous membrane; a rough area at its lateral convexity receives pronator teres.

Distal end: the widest part of the bone. Laterally it projects as the radial styloid process (≈1 cm more distal than the ulnar styloid — hence greater ulnar than radial deviation). Medially, the ulnar notch receives the head of the ulna (distal radioulnar joint). The inferior carpal articular surface has facets for the scaphoid and lunate. On the dorsal surface, the dorsal (Lister) tubercle acts as a pulley for the tendon of extensor pollicis longus, with grooves for the other extensor tendons. In pronation the distal radius rotates across the ulna, carrying the hand with it.

Location: Lateral forearm, from the elbow to the thumb side of the wrist.

Parts & subdivisions

Head
Articulates with the capitulum and the radial notch of the ulna; encircled by the annular ligament.
Neck
Narrow region below the head.
Radial tuberosity
Insertion of biceps brachii.
Interosseous border
Attachment of the interosseous membrane.
Styloid process
Lateral distal projection; brachioradialis inserts at its base.
Ulnar notch
Articulates with the ulnar head (distal radioulnar joint).
Dorsal (Lister) tubercle
Pulley for extensor pollicis longus.
Carpal articular surface
Facets for scaphoid and lunate.

Anatomy

Articulations: Humerus (humeroradial), ulna (proximal and distal radioulnar joints), scaphoid and lunate (radiocarpal joint).
Ossification: Primary centre in the shaft ≈week 8. Distal epiphysis appears ≈1 year and fuses ≈17–19 years (the "growing end"); head appears ≈5 years and fuses ≈14–17 years.

Function

Transmits most forces from the hand to the forearm (≈80% of axial load at the wrist)
Rotates around the ulna for pronation and supination
Forms the lateral part of the elbow and the main forearm part of the wrist joint

Clinical significance

Colles fracture

Transverse fracture of the distal radius within ≈2.5 cm of the wrist with dorsal displacement and angulation of the distal fragment, radial shortening and often an ulnar styloid avulsion — the "dinner-fork" deformity. Typically a fall on the outstretched hand (FOOSH) in an older woman with osteoporosis. Complications: median nerve compression, malunion, complex regional pain syndrome, extensor pollicis longus rupture.

Smith fracture

"Reverse Colles": distal fragment displaced volarly (palmar), from a fall on the back of the flexed wrist ("garden-spade" deformity).

Radial head fracture and pulled elbow

Radial head fractures follow FOOSH in adults (elbow effusion, "sail sign"). In toddlers, a sudden pull on the arm subluxes the radial head out of the annular ligament (nursemaid’s elbow), reduced by supination and flexion.

Galeazzi fracture–dislocation

Fracture of the distal third of the radial shaft with dislocation of the distal radioulnar joint.

Mnemonics

Galeazzi vs Monteggia

"GRUM": Galeazzi = Radius fracture (+ distal radioulnar dislocation); Ulna fracture = Monteggia (+ radial head dislocation).

Test yourself

An elderly woman falls on her outstretched hand and has a "dinner-fork" deformity of the wrist. What is the fracture?

Colles fracture — dorsal displacement and angulation of the distal radius
Smith fracture — volar displacement of the distal radius
Barton fracture — intra-articular rim fracture with carpal dislocation
Galeazzi fracture — radial shaft fracture with DRUJ dislocation

Answer: Colles fracture — dorsal displacement and angulation of the distal radius

Colles fracture is a distal radial fracture with dorsal displacement and angulation, radial shortening and often ulnar styloid avulsion, typically in osteoporotic women after a FOOSH. Smith fracture is the reverse (volar displacement).