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Extensor pollicis brevis tendon

The extensor pollicis brevis (EPB) tendon is the distal tendinous continuation of the extensor pollicis brevis muscle, one of the deep muscles of the posterior forearm. It passes through the first dorsal compartment of the wrist alongside the tendon of the abductor pollicis longus (APL) and extends to the thumb. The tendon functions primarily to extend the proximal phalanx of the thumb at the metacarpophalangeal (MCP) joint and assists in extension and abduction of the thumb at the carpometacarpal (CMC) joint.

Because of its superficial position and close proximity to the APL tendon, the EPB tendon is a key structure involved in De Quervain’s tenosynovitis, a common overuse condition causing radial wrist pain.

Synonyms

  • Short extensor tendon of the thumb

  • Brevis extensor of the thumb

Origin, Course, and Insertion

Origin: From the posterior surface of the radius and the adjacent interosseous membrane, distal to the origin of the abductor pollicis longus.
Course: The tendon passes obliquely downward and laterally, traveling beneath the extensor retinaculum in the first dorsal compartment, together with the abductor pollicis longus tendon.
Insertion: The tendon inserts onto the base of the proximal phalanx of the thumb on its dorsal aspect. In some individuals, it may extend further to attach partly to the extensor hood or proximal joint capsule.

Relations

Proximally: Abductor pollicis longus muscle and tendon
Distally: Dorsal aspect of the thumb’s metacarpophalangeal joint capsule
Medially: Extensor pollicis longus tendon (separated by the Lister’s tubercle of radius)
Laterally: Radial styloid process and the first metacarpal base
Anteriorly: Radial artery and tendons of the first compartment
Posteriorly: Extensor retinaculum and radius

Tendon Attachments

  • Enclosed within the first extensor compartment beneath the extensor retinaculum

  • Shares a common synovial sheath with the abductor pollicis longus tendon

  • Inserts on the dorsal base of the proximal phalanx of the thumb

  • In some cases, a fibrous septum separates it from the APL tendon sheath

Nerve Supply

Posterior interosseous nerve, a branch of the radial nerve (C7–C8)

Function

  • Extension of thumb MCP joint: Primary extensor of the proximal phalanx of the thumb

  • Assists thumb abduction: Helps abduct the thumb at the CMC joint in coordination with the abductor pollicis longus

  • Stabilization: Contributes to thumb stability during grip and opposition

  • Fine control: Supports precision movements in writing, typing, and pinch grip

Clinical Significance

  • De Quervain’s tenosynovitis: Inflammation of the common synovial sheath of EPB and APL tendons, causing pain at the radial styloid

  • Tendon rupture: Rare but may occur following trauma or rheumatoid arthritis

  • Accessory slips: Variations can alter compartmental anatomy, contributing to chronic friction or entrapment

  • Postoperative evaluation: Important in wrist decompression surgeries for tenosynovitis

  • Imaging relevance: MRI is the modality of choice for diagnosing tendon tears, tenosynovitis, and compartmental variations

MRI Appearance

T1-weighted images:

  • Normal tendon: low signal (dark linear band) within bright peritendinous fat

  • Surrounding fat: bright, enhancing contrast

  • Muscle belly (proximal): intermediate signal intensity

  • Pathology: thickened or irregular tendon with intermediate signal in tendinopathy; discontinuity in rupture

T2-weighted images:

  • Normal tendon: low signal intensity, sharply marginated

  • Muscle: intermediate-to-low, slightly darker than on T1

  • Pathologic tendon (tenosynovitis or tear): bright hyperintense fluid signal in or around tendon sheath

  • Peritendinous edema: hyperintense, often tracking along the first dorsal compartment

STIR:

  • Normal tendon: intermediate-to-dark

  • Pathologic changes: bright hyperintense signal within tendon sheath and surrounding soft tissue in tenosynovitis or partial tear

  • Excellent for detecting inflammatory edema, even when subtle

Proton Density Fat-Saturated (PD FS):

  • Normal tendon: uniformly dark, well-defined fibers

  • Tenosynovitis: bright peritendinous signal and tendon thickening

  • Partial tear: focal bright area within tendon substance

  • Fluid within the first compartment appears hyperintense, outlining tendon contours

T1 Fat-Sat Post-Contrast:

  • Normal tendon: minimal enhancement

  • Inflamed tendon sheath: intense peripheral enhancement

  • Tendinopathy: patchy or diffuse enhancement along tendon margins

  • Postoperative changes: enhancing granulation tissue or fibrosis around decompressed sheath

CT Appearance

Non-Contrast CT:

  • Tendon: soft-tissue density, difficult to separate from adjacent structures

  • Retinaculum and bone landmarks: clearly visible for compartment localization

  • Chronic tendinopathy: may show peritendinous soft-tissue thickening or calcific foci near radial styloid

Post-Contrast CT (standard):

  • Normal tendon: mild homogeneous soft-tissue enhancement

  • Inflamed sheath or surrounding tissue: focal or circumferential enhancement

  • Helpful for assessing postoperative inflammation, scarring, or synovial proliferation

MRI images

Extensor pollicis brevis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Extensor pollicis brevis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI images

Extensor pollicis brevis tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

MRI images

Extensor pollicis brevis tendon sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT images

Extensor pollicis brevis tendon ct axial 1

CT images

Extensor pollicis brevis tendon ct axial 2