Forearm Bones: Radius and Ulna

Amanda Thomas Apr 22, 2024
Skeleton with Nursing Student

Have you ever wondered what makes your wrist twist and turn with such ease?

Or what enables you to perform a good handshake?

Look no further than the dynamic duo within your forearm, the radius and ulna. Together, these bones form a symphony of movement and support. 

Both are crucial for everything that a person can do with their hands. But if you’re among the nursing students who mix them up, don’t fret. 

Jump to Section

  1. Structure and Function
  2. How Do You Remember the Radius and Ulna?
  3. Which is Bigger: Ulna or Radius?
  4. Ulna Anatomy
  5. Radius Anatomy

Follow this blog for an easy way to remember the radius and ulna anatomy.

Structure and Function

The forearm consists of two primary bones — the radius and the ulna.

The radius is on the forearm’s lateral side, commonly known as the thumb side. It’s the shorter of the two bones and plays a significant role in forming the wrist joint.

The ulna lies on the medial side of the forearm, commonly referred to as the pinky side. It’s longer than the radius and extends from the elbow to the smallest finger.

Here are the radius and ulna labeled in a diagram: 

Radius and Ulna Labeled

The radius and ulna work together to facilitate various forearm and hand movements. While the radius primarily allows forearm rotation, the ulna provides stability and support during these movements.

Understanding the distinct functions of these bones is essential for understanding the biomechanics of the upper limb.

How Do You Remember the Radius and Ulna?

A handy way to differentiate between the two is “ulna is under.”

When the arm is in the anatomical position (palm facing upwards), the ulna is directly under the radius. Additionally, the radius allows the wrist to rotate, so remember: radius for rotation.

Which is Bigger: Ulna or Radius?

In terms of size, the ulna is typically longer than the radius.

This length difference contributes to the distinctive appearance of the forearm, where the ulna protrudes more prominently along the back of the arm compared to the radius. Understanding the relative sizes of these bones can aid in visualizing their positions and roles within the forearm’s skeletal structure.

Ulna Anatomy

The ulna anatomy features key landmarks crucial for its function within the forearm.


Positioned at the top end of the bone closest to the elbow, the head of the ulna is a small rounded structure that forms part of the elbow joint. 

It’s one of two articulating surfaces in this hinge-like joint, along with the humerus (upper arm bone).

Olecranon process

The olecranon process is a bony projection found at the proximal end of the ulna, forming the prominent point of the elbow.

It’s an attachment site for muscles and ligaments that assist in extending and stabilizing the elbow joint.

Coronoid process

The coronoid process, a sharp projection on the anterior surface of the ulna, serves as an attachment site for the brachialis muscle.

This muscle helps flex the elbow joint.

Trochlear Notch

The trochlear notch is a deep groove on the proximal end of the ulna that articulates with the trochlea of the humerus.

This joint allows for extension and flexion movements of the forearm.

Radial Notch

The radial notch is a shallow depression on the medial side of the ulna that articulates with the head of the radius.

This joint allows for rotation movements of the forearm.

Styloid process

At the distal end of the ulna, there is a small bony protrusion called the styloid process.

It anchors various ligaments and helps stabilize the wrist joint.

Radius Anatomy

Like the ulna anatomy, the radius also plays a vital role in the forearm’s overall structure and function.

It features distinct anatomical landmarks that aid in its movement and support of the wrist.


At the proximal end of the radius is a smooth, rounded surface known as the radial head.

This articulates with the capitulum of the humerus to form the elbow joint and allows for rotational movements of the forearm.

Proximal Radioulnar Joint

The radial head and notch on the ulna form the proximal radioulnar joint.

This allows for rotation of the radius over the ulna, which is necessary for various tasks like turning a doorknob or twisting a screwdriver.


The neck of the radius is a narrowed area just below the radial head.

It’s an attachment site for ligaments that help stabilize the elbow joint.

Radial Tuberosity

Located just below the radial head is a rough, bumpy area called the radial tuberosity.

This is an attachment site for tendons that aid in flexing the elbow joint.

Styloid Process

Like the ulnar styloid process, there is also a styloid process at the distal end of the radius.

This helps stabilize and support the wrist joint by providing attachment points for ligaments.

Ulnar Notch

The distal end of the radius also features an ulnar notch. The notch articulates with the ulna head to form the distal radioulnar joint.

Distal Radioulnar Joint

The distal radioulnar joint enables the radius and ulna to move in opposite directions, allowing the forearm to supine and pronate.

Enhance Your Knowledge with SimpleNursing

To learn more about the anatomy of the forearm and other body systems, check out SimpleNursing!

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