Upper limb

Radius

Before you say anything

The radius and ulna are handed out together to see whether you can tell them apart, and the answer is at the ends: the radius is small above and large below, the ulna the other way round. Once you have decided which bone it is, the styloid process gives you the side without any further thought.

Which side? Three checks

Hold it like this first: Hold it vertically with the disc-like head uppermost, the styloid process at the lower end pointing downwards and laterally, and the sharp interosseous border facing medially.

Check 1 — Compare the ends
One end carries a small disc-like head, the other is broad and expanded
The small head is the upper end, so the bone can only stand one way
Check 2 — Find the styloid process
A pointed projection descending from the broad lower end
It is lateral, so it points to the side the bone belongs to
Check 3 — Feel the borders
One border of the shaft is sharp and crest-like
That is the interosseous border and it faces medially, towards the ulna

Drill this against the clock →

Work it out, one rung at a time

Answer each question in your head first. Then open it.

1
Identify
Which forearm bone is this?
2
Orient
Which end is up?
3
Side
Which side?
4
Landmarks
What can you point out?
5
Attachments
What is attached?
6
Applied
Why does it matter?

Landmarks to point out

Head
Upper end, disc-shaped with a shallow upper hollow
Articulates with the capitulum above and the radial notch of the ulna medially.
Neck
Constriction below the head
Encircled by the annular ligament; in a child the head can be pulled through it — a pulled elbow.
Radial tuberosity
Medial aspect just below the neck
Insertion of biceps brachii, the chief supinator of the flexed forearm.
Interosseous border
Sharp medial border of the shaft
Gives attachment to the interosseous membrane and faces the ulna.
Dorsal tubercle
Posterior aspect of the lower end
The tendon of extensor pollicis longus hooks around it, which is why that tendon can rupture after a distal radial fracture.
Styloid process
Lateral aspect of the lower end
Descends further than the ulnar styloid; the relationship is lost in a Colles' fracture.
Ulnar notch
Medial aspect of the lower end
Articulates with the head of the ulna at the distal radio-ulnar joint.

Attachments

Biceps brachii — Radial tuberosity
Supinator — Upper lateral shaft
Pronator teres — Middle of the lateral surface
Flexor digitorum superficialis (radial head) — Anterior oblique line
Flexor pollicis longus — Anterior surface of the shaft
Pronator quadratus — Lower anterior surface
Brachioradialis — Base of the styloid process

Articulations

Elbow joint — with Capitulum of the humerus
Proximal radio-ulnar joint — with Radial notch of the ulna
Distal radio-ulnar joint — with Head of the ulna
Wrist joint — with Scaphoid and lunate

Ossification

One primary centre appears in the shaft in about the eighth week of intrauterine life.

Lower end: about the second year, fusing at about 20 years
Head: about the fifth year, fusing at about 16 to 18 years

The lower end is the growing end, which is why it is the last to fuse.

Viva voce

1 of 5 · 0 answered

Say your answer out loud before you open it. That is the exam skill.

How do you tell the radius from the ulna at a glance?

Say these first

A small disc-like head at the upper end
A broad lower end with a styloid process
A tuberosity just below the neck

Do not confuse it with

The ulna
The radius is small above and broad below; the ulna is large and hook-shaped above and narrow below. The ulnar head is at the lower end, the radial head at the upper end.

Examiner trap

Calling the broad lower end the upper end because it is bigger. In the radius the large end is distal — the opposite of the ulna, which is exactly why the pair are handed out together.

Memory hook

Radius: small head up, styloid down and lateral.

Why it matters

A Colles' fracture is a fracture of the lower end with dorsal displacement of the distal fragment, giving the dinner-fork deformity and loss of the normal downward projection of the radial styloid.
A Smith's fracture is the reverse, with volar displacement.
In a Galeazzi fracture the lower shaft of the radius is fractured and the distal radio-ulnar joint dislocated.
A pulled elbow occurs in a small child when a sharp tug slips the radial head through the annular ligament.

Senior’s 30-second takeaway

Radius — the whole bench in four lines. Read this on the way in.

If you see this: A small disc-like head at one end · A broad opposite end with a pointed styloid · A tuberosity just below the neck
If asked to identify it: This is a radius; the head is at the upper end and the styloid process at the lower end points laterally, giving the side.
If asked one more: Biceps inserts into the radial tuberosity, and the lower end is the growing end.
If asked why it matters: The lower end is the site of a Colles' fracture, with the dinner-fork deformity.

Then stop. Let the examiner ask the next question.

🩺 Before you say anything