Through which compartment does the tendon of the extensor pollicis brevis pass?

The tendon passes through the first osteofibrous compartment beneath the extensor retinaculum (retinaculum musculorum extensorum). It shares this compartment with the tendon of the abductor pollicis longus (m. abductor pollicis longus).

Which structures form the boundaries of the anatomical snuffbox?

The lateral (radial) boundary is formed by the tendons of the extensor pollicis brevis and abductor pollicis longus. The medial (ulnar) boundary is formed by the tendon of the extensor pollicis longus.

What is De Quervain syndrome and how does it relate to this muscle?

De Quervain syndrome is tenosynovitis of the first extensor compartment containing the tendons of the extensor pollicis brevis and abductor pollicis longus. It causes pain near the radial styloid process, which is assessed using Finkelstein's test.

What is the innervation of the extensor pollicis brevis?

The muscle is innervated by the radial nerve (n. radialis), specifically via the posterior interosseous nerve, with motor fibers originating from spinal segments C7–C8.

Extensor Pollicis Brevis: Anatomy, Origin, and Function

Extensor Pollicis Brevis Muscle

m. extensor pollicis brevis

For medical students2 min readUpdated 2026-10-10

The extensor pollicis brevis (m. extensor pollicis brevis) is a muscle located in the deep layer of the posterior compartment of the forearm. It is responsible for extending the proximal phalanx and abducting the thumb. Together with the abductor pollicis longus, its tendon passes through the first extensor compartment and forms the lateral border of an important topographical landmark: the anatomical snuffbox.

CompartmentDeep layer of the posterior forearm

InsertionBase of the proximal phalanx of the thumb

Clinical RelevanceDe Quervain syndrome (tenosynovitis of the 1st dorsal compartment)

Origin and Insertion

The muscle is situated on the posterior surface of the forearm and has the following attachment points:

Origin: Posterior surface of the radius and the interosseous membrane (membrana interossea). The muscle belly lies lateral and distal to the m. abductor pollicis longus.
Tendon course: Travels toward the hand, passing through the first osteofibrous canal beneath the extensor retinaculum (retinaculum musculorum extensorum) alongside the tendon of the m. abductor pollicis longus. Along their path, these two tendons run superficially, crossing over the tendons of the extensor carpi radialis longus and brevis. They are located proximal to the tendon of the m. extensor pollicis longus.
Insertion: Dorsal surface of the base of the proximal phalanx of the thumb.

Functions

Contraction of the extensor pollicis brevis produces the following movements:

Extends the proximal phalanx of the thumb.
Abducts the thumb.
Assists in radial deviation (abduction) of the wrist.

Blood Supply and Innervation

Innervation: Radial nerve (n. radialis), specifically via its branch, the posterior interosseous nerve (n. interosseus posterior). Motor fibers originate from spinal segments C7–C8.
Blood supply: Posterior interosseous artery (a. interossea posterior) and radial artery (a. radialis).

Topography and Clinical Significance

Anatomical snuffbox: The tendon of the m. extensor pollicis brevis (along with the m. abductor pollicis longus) forms the lateral (radial) border of this triangular depression on the wrist. The medial border is formed by the tendon of the extensor pollicis longus. The floor of the snuffbox is formed by the scaphoid (os scaphoideum) and trapezium bones. Subcutaneous structures passing through this area include the cephalic vein (v. cephalica) and the superficial branch of the radial nerve, while the radial artery lies deep to the deep fascia, where its pulse can be palpated.
De Quervain syndrome: Stenosing tenosynovitis of the first dorsal compartment, through which the tendons of the m. extensor pollicis brevis and m. abductor pollicis longus travel. This pathology presents as pain over the radial styloid process, which is evaluated clinically using Finkelstein's test.

Do Not Confuse: Extensor Hallucis Brevis

In anatomical nomenclature, there is a similarly named muscle in the lower extremity: the extensor hallucis brevis (m. extensor hallucis brevis). It originates from the dorsal surface of the anterior calcaneus and inserts into the base of the proximal phalanx (or sesamoid bone) of the great toe. Its function is to extend the great toe, and it is innervated by the deep peroneal nerve (n. peroneus profundus, spinal segments L4–S1).

Frequently asked questions

Through which compartment does the tendon of the extensor pollicis brevis pass?: The tendon passes through the first osteofibrous compartment beneath the extensor retinaculum (retinaculum musculorum extensorum). It shares this compartment with the tendon of the abductor pollicis longus (m. abductor pollicis longus).
Which structures form the boundaries of the anatomical snuffbox?: The lateral (radial) boundary is formed by the tendons of the extensor pollicis brevis and abductor pollicis longus. The medial (ulnar) boundary is formed by the tendon of the extensor pollicis longus.
What is De Quervain syndrome and how does it relate to this muscle?: De Quervain syndrome is tenosynovitis of the first extensor compartment containing the tendons of the extensor pollicis brevis and abductor pollicis longus. It causes pain near the radial styloid process, which is assessed using Finkelstein's test.
What is the innervation of the extensor pollicis brevis?: The muscle is innervated by the radial nerve (n. radialis), specifically via the posterior interosseous nerve, with motor fibers originating from spinal segments C7–C8.

Go deeper

Abductor pollicis longus muscle
Extensor pollicis longus muscle
Anatomical snuffbox and its contents
De Quervain tenosynovitis