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Elbow and forearm

Overview of the bones that define the forearm, the radius and ulna.

Extending from the wrist to the elbow joint is the region of the upper extremity called the forearm (antebrachium). The forearm helps the shoulder and the arm in force application and the precise placement of the hand in space, with the help of the elbow and radioulnar joints.

This article is a guide to help you master the anatomy of the forearm and the elbow joint, using the beautiful content of Kenhub.

Key facts about the elbow and forearm
Forearm Bones: radius, ulna
Joints: humeroradial, radioulnar joints (proximal, distal)
Muscles:
- Extensors: superficial (brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and the anconeus) and deep (supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis)
- Flexors: superficial (flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres), intermediate (flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus) and deep (pronator quadratus).
Mnemonic: 'Rule of 3s' (3 wrist flexors, 3 finger flexors, 3 wrist extensors, 3 finger extensors, 3 thumb extensors)
Elbow joint Bones: humerus, radius, ulna
Type: synovial, hinged joint
Ligaments: annular ligament and collateral (radial, ulnar) ligaments
Movements: 
- Flexion - biceps brachii, brachialis, brachioradialis muscles
- Extension - triceps brachii muscle
Contents
  1. Forearm anatomy
    1. Bones
    2. Muscles
  2. Elbow anatomy
  3. Frequent questions
  4. Sources
  5. Related articles
  6. Related videos
+ Show all

Forearm anatomy

Bones

The forearm consists of two long bones; the radius and the ulna. The ulna is located medially and is both longer and larger than the radius, which runs parallel to it laterally. These two bones are held together by the intervening interosseous membrane.

These forearm bones articulate with each other in two locations. The head of the radius forms a joint with the radial notch of the ulna proximally (proximal radioulnar joint), while the head of the ulna forms a joint with the ulnar notch of the radius distally (distal radioulnar joint). Alongside the humeroradial joint, the two radio-ulnar joints allow the pronation and supination movements of the forearm.

Practice and consolidate your knowledge with this interactive quiz about the radius and ulna.

Muscles

Just like the arm, the forearm is divided into two compartments by deep fascia; the interosseous membrane, and the fibrous intermuscular septa. This creates an anterior compartment that contains the flexor muscles, and a posterior one that contains the extensor muscles.

Extensors of the forearm

Residing in the posterior compartment of the forearm, the extensor muscles can be further divided into superficial and deep extensors.

Superficial extensors consist of seven muscles; brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and the anconeus.

Deep extensors include five muscles; supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis.
This sound like a lot, right? Don’t worry, we have you covered with our comprehensive learning materials that help you expand and test your knowledge.

Flexors of the forearm

As seen in this forearm muscles diagram, the flexor muscles reside in the anterior compartment of the forearm, and are separated into the three following layers:

Nothing makes the anatomy of the forearm flexors fun and easy-to-learn like our video tutorials, quizzes, and articles. Don’t miss checking them out in our study unit!

Mnemonics

The forearm muscles are responsible for flexion and extension of the wrist and digits. Remembering the action of each one can be quite difficult. Use the following mnemonic to make your life a little easier!

'Rule of 3s'

  • 3 wrist flexors (flexor carpi radialis, flexor carpi ulnaris, palmaris longus)
  • 3 finger flexors (flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus)
  • 3 wrist extensors (extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris)
  • 3 finger extensors (extensor digitorum, extensor indicis, extensor digiti minimi)
  • 3 thumb extensors (abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus)

Elbow anatomy

The elbow joint is a synovial joint that connects the arm and the forearm, providing 150 ْ of extension-flexion movement. It consists of three joints; the humeroulnar joint, the humeroradial joint, and the proximal radioulnar joint, all within one articular capsule!

The elbow joint is supported by three ligaments: 

  • The annular ligament
  • The radial collateral ligament
  • The ulnar collateral ligament
Key Facts about elbow joint
Type Hinge joint
Bones Humerus, radius, ulna
Ligaments Ulnar collateral, radial collateral, annular, quadrate ligaments
Blood supply Proximal to elbow joint - ulnar collateral, radial collateral, middle collateral arteries
Distal to elbow joint - radial recurrent, ulnar recurrent arteries
Movements Flexion - biceps brachii, brachialis, brachioradialis muscles
Extension - triceps brachii muscle
Clinical Fractures, epicondylitis, arthritis, venipunctures

Watching our videos and taking our quizzes on the elbow joint will guarantee you an all-inclusive understanding of this topic with these learning materials.

Finish this lecture about the bones, joints, muscles, nerves and vessels of the forearm with a specially designed quiz that covers it all!

Frequent questions

What are the muscles in the forearm?

The forearm contains numerous muscles, which are best organized using the classical anatomical classification, dividing them into anterior and posterior compartments.

The anterior compartment includes the pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, and pronator quadratus muscles.

The posterior compartment consists of the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, anconeus, supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis muscles.

How to remember the muscles of the forearm?

Remembering all the muscles of the forearm and their actions can be challenging. One trick to make it easier is to remember the "rule of 3s":

  • 3 wrist flexors (flexor carpi radialis, flexor carpi ulnaris, palmaris longus)
  • 3 finger flexors (flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus)
  • 3 wrist extensors (extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris)
  • 3 finger extensors (extensor digitorum, extensor indicis, extensor digiti minimi)
  • 3 thumb extensors (abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus)

Which part of the arm is the forearm?

The term "arm" is commonly used by most people to refer to the entire upper limb between the shoulder and wrist joints. However, in anatomy, the term "arm" refers specifically to the region between the shoulder and elbow joints, while the area between the elbow and wrist joints is called the forearm.

How many muscles are in the forearm?

The forearm comprises numerous muscles. An effective way to categorize them is by organizing them into the traditional anterior and posterior groups along with their respective layers:

  • Anterior Compartment:

    • Superficial Layer: 4 muscles (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris)
    • Intermediate Layer: 1 muscle (flexor digitorum superficialis)
    • Deep Layer: 2 muscles (flexor digitorum profundus and flexor pollicis longus), 1 muscle only for pronation (pronator quadratus)
  • Posterior Compartment:

    • Superficial Layer: 7 muscles (brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus)
    • Deep Extensors: 5 muscles (supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis)

This results in a total of 20 muscles.

Which muscle extends the forearm?

The primary extensor of the forearm at the elbow joint is the triceps brachii muscle, located in the posterior compartment of the arm. The anconeus muscle, a small triangular muscle located at the back of the elbow, assists the triceps brachii in extension of the forearm and stabilizes the elbow joint.

What muscle supinates the forearm?

Supination is the movement of rotating the forearm so that the palm of the hand faces upward. The primary supinators of the forearm are the biceps brachii muscle, a muscle located in the anterior compartment of the arm, and the supinator muscle, located in the posterior compartment of the forearm. The biceps brachii is the main supinator when the elbow is flexed and also during active movement, while the supinator works better when the elbow is extended. An accessory supinator of the forearm is the brachioradialis muscle, which can return the forearm to a neutral position when the forearm is fully pronated.

A needle would pierce the epidermal layers of the forearm in which order?

The epidermis of the skin has five layers. From superficial to deep, these layers are:

  • Stratum corneum: Formed by dead, keratinized cells, that act as a protective layer
  • Stratum granulosum: Consisting mainly of keratinocytes
  • Stratum spinosum: Consisting of keratinocytes joined by desmosomes
  • Stratum basale (germinativum): A single layer of basal cells that are mitotically active and maintain the epidermis

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