Extensor Pollicis Brevis – Anatomy, Nerve Supply, Function

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 3 min read
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Extensor Pollicis Brevis (EPB) found in current anatomical textbooks describes its origin as the posterior surface of the radius and the adjacent part of the interosseous membrane, distal to the attachment of the abductor pollicis longus (APL). Its tendon is described as inserting into the...

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Article Summary

Extensor Pollicis Brevis (EPB) found in current anatomical textbooks describes its origin as the posterior surface of the radius and the adjacent part of the interosseous membrane, distal to the attachment of the abductor pollicis longus (APL). Its tendon is described as inserting into the posterior surface of the base of the proximal phalanx of the thumb after passing under the extensor retinaculum.[rx] Its primary...

Key Takeaways

  • This article explains Structure in simple medical language.
  • This article explains Origin and Insertion in simple medical language.
  • This article explains Nerve Supply of in simple medical language.
  • This article explains Blood Supply of in simple medical language.
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Definition

Extensor Pollicis Brevis (EPB) found in current anatomical textbooks describes its origin as the posterior surface of the radius and the adjacent part of the interosseous membrane, distal to the attachment of the abductor pollicis longus (APL). Its tendon is described as inserting into the posterior surface of the base of the proximal phalanx of the thumb after passing under the extensor retinaculum. Its primary function is described as extending the metacarpophalangeal joint (MCPJ) of the thumb, with contributions to the abduction of the thumb and carpus, as well as stabilizing the MCPJ of the thumb by integrating into the extensor hood.,

In human anatomy, the extensor pollicis brevis is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus.

Extensor pollicis brevis is a short and slender muscle located in the posterior compartment of the forearm, extending from the posterior surface of the radius to the proximal phalanx of the thumb. It is one of the deep extensors of the forearm, together with the supinator, abductor pollicis longus, extensor pollicis longus and extensor indices muscles.

Structure

The extensor pollicis brevis arises from the ulna distal to the abductor pollicis longus, from the interosseous membrane, and from the dorsal surface of the radius. [rx]

Its direction is similar to that of the abductor pollicis longus, its tendon passing the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb.

Extensor Pollicus Brevis
  • Function: Extension of the thumb by acting on the carpometacarpal joint and the metacarpophalangeal joint
  • Origin: Dorsal aspects of middle radius and interosseous membrane
  • Insertion: Distal phalanx of 1st finger
  • innervation: Posterior interosseous nerve (C7, C8)

Origin and Insertion

Extensor pollicis brevis muscle (Musculus extensor pollicis brevis)
Extensor pollicis brevis originates from the posterior surface of the distal third of radius, inferior to the origin of extensor pollicis longus. The origin area extends to the adjacent interosseous membrane. From here, the muscle runs downwards towards the wrist, ending in a cord-like tendon proximally to the wrist.

The tendon passes deep to the extensor retinaculum, between the tendons of abductor pollicis longus and extensor carpi radialis longus. Along with abductor pollicis longus, it is located in the first extensor (dorsal) compartment of the wrist. After passing under the retinaculum, the tendon runs laterally to insert onto the dorsal surface of the base of the proximal phalanx of the thumb.

Nerve Supply of

Extensor pollicis brevis is innervated by the posterior interosseous nerve which is a continuation of a deep branch of the radial nerve (root value C7 and C8).

Blood Supply of

Extensor pollicis brevis receives its blood supply by the posterior interosseous artery and perforating branches from the anterior interosseous artery, which are the branches of the common interosseous artery. The common interosseous artery arises immediately below the tuberosity of the radius from the ulnar artery.

Function of 

In a close relationship to the abductor pollicis longus, the extensor pollicis brevis both extends and abducts the thumb[rx] at the carpometacarpal and metacarpophalangeal joints.[rx]

Together with extensor pollicis longus, extensor pollicis brevis is in charge of extension of the thumb in the first metacarpophalangeal joint. It also extends the thumb in the carpometacarpal joint of the thumb. This movement is important in the anatomy of the grip, as it enables letting go of an object. As it crosses the wrist, extensor pollicis brevis also participates in the extension and abduction of this joint.

References

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Questions to ask
  • What is the most likely cause of my symptoms?
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Care roadmap for: Extensor Pollicis Brevis – Anatomy, Nerve Supply, Function

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Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
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Frequently Asked Questions

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No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

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