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Extensor carpi radialis brevis tendon

The extensor carpi radialis brevis (ECRB) tendon is a strong, flat tendon in the posterior compartment of the forearm. It forms the distal continuation of the ECRB muscle, one of the primary wrist extensors. The tendon contributes significantly to wrist extension and stabilization, particularly during gripping or lifting activities.

The ECRB tendon lies deep to the extensor carpi radialis longus (ECRL) tendon near the lateral aspect of the wrist and is intimately associated with the common extensor origin at the lateral epicondyle of the humerus. It plays a central role in lateral epicondylitis (tennis elbow), where repetitive microtrauma leads to tendinosis or partial tearing near its origin.

Synonyms

  • ECRB tendon

  • Short radial wrist extensor tendon

  • Common extensor tendon component

Origin, Course, and Insertion

Origin: From the lateral epicondyle of the humerus, common extensor tendon, and adjacent lateral collateral ligament of the elbow joint
Course:

  • Passes distally beneath the extensor retinaculum in the second dorsal wrist compartment

  • Runs alongside the tendon of the extensor carpi radialis longus (ECRL)
    Insertion: Onto the dorsal surface of the base of the third metacarpal bone, just distal to the ECRL insertion at the second metacarpal base

Relations

Superiorly: Common extensor tendon, extensor carpi radialis longus tendon
Inferiorly: Capsule of the wrist joint and carpometacarpal articulations
Medially: Extensor digitorum and extensor digiti minimi tendons
Laterally: Extensor carpi radialis longus tendon
Posteriorly: Dorsal skin and subcutaneous fascia

Nerve Supply

Posterior interosseous nerve (deep branch of the radial nerve, roots C6–C7)

Function

Wrist extension: Extends the wrist, especially when the fingers are flexed
Radial deviation: Assists extensor carpi radialis longus in abducting the wrist
Dynamic stability: Stabilizes the wrist joint during gripping and resisted extension
Elbow support: Acts as a secondary stabilizer to the lateral epicondyle during forceful extension

Clinical Significance

Lateral epicondylitis (tennis elbow): Chronic tendinosis or partial tear of the ECRB tendon near its origin due to repetitive overuse
Tendinopathy: Thickening, signal alteration, or partial tearing near the lateral epicondyle
Rupture: Rare, may follow chronic degeneration or corticosteroid injections
Post-surgical relevance: Key landmark in lateral epicondyle debridement or repair procedures
Imaging role: MRI is gold standard for diagnosing tendinopathy, partial tears, and peritendinous inflammation

MRI Appearance

T1-weighted images:

  • Normal tendon: low signal (dark), homogeneous linear band extending from the lateral epicondyle to third metacarpal base

  • Muscle belly: intermediate signal

  • Fat planes around tendon: bright contrast

  • Partial tear or tendinosis: intermediate-to-bright intratendinous signal and tendon thickening near origin

T2-weighted images:

  • Normal tendon: low signal, sharply marginated

  • Pathology: focal or diffuse bright hyperintense signal in partial tears or tendinopathy

  • Peritendinous edema and lateral epicondyle marrow edema: hyperintense

  • Chronic degeneration: irregular, thickened tendon with intermediate T2 signal

STIR:

  • Normal tendon: dark signal (flow void)

  • Pathology: bright hyperintense peritendinous and intratendinous areas due to edema or inflammation

  • Excellent for identifying acute tendinopathy and reactive changes at common extensor origin

Proton Density Fat-Saturated (PD FS):

  • Normal tendon: uniformly dark, continuous fibers

  • Tendinosis: bright signal, loss of fibrillar pattern, tendon thickening

  • Partial tear: focal bright gap extending from cortical attachment

  • Surrounding soft tissue edema or bursitis also bright on PD FS

T1 Fat-Sat Post-Contrast:

  • Normal tendon: minimal enhancement

  • Active tendinitis or peritendinitis: patchy or diffuse enhancement near lateral epicondyle

  • Post-surgical or chronic fibrotic areas: mild peripheral enhancement

  • Partial tears: enhancement along disrupted fibers or peritendinous tissues

CT Appearance

Non-Contrast CT:

  • Tendon: soft-tissue density extending from lateral epicondyle to dorsum of hand

  • Bone attachment: sharply defined at third metacarpal base

  • Chronic pathology: calcifications or cortical irregularity at lateral epicondyle

  • Indirect signs: focal thickening, loss of fat plane, or adjacent sclerosis

Post-Contrast CT (standard):

  • Normal tendon: uniform mild enhancement

  • Tendinopathy or tear: focal enhancement and adjacent soft-tissue changes

  • Useful for identifying calcific tendinitis, post-surgical scarring, or subtle osseous involvement

MRI image

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

MRI image

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

MRI image

Extensor carpi radialis brevis tendon SAG cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Extensor carpi radialis brevis tendon ct axial 1

CT image

Extensor carpi radialis brevis tendon ct axial