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Extensor carpi radialis longus muscle

The extensor carpi radialis longus (ECRL) is a long, slender muscle located in the superficial layer of the posterior compartment of the forearm. It lies on the lateral side of the forearm and acts as one of the principal wrist extensors and abductors. The ECRL works synergistically with the extensor carpi radialis brevis (ECRB) and flexor carpi radialis to maintain wrist stability during gripping and lifting.

This muscle is particularly important in repetitive wrist extension activities and is often implicated in lateral epicondylitis (tennis elbow) and radial nerve entrapment syndromes. Its long tendon crosses the wrist to insert on the second metacarpal base, contributing to the contour of the radial side of the forearm.

Synonyms

  • Long radial wrist extensor

  • Radial extensor of the carpus (longus)

Origin, Course, and Insertion

  • Origin: Lower third of the lateral supracondylar ridge of the humerus and adjacent lateral intermuscular septum

  • Course:

    • Descends along the lateral side of the forearm, superficial to the extensor carpi radialis brevis

    • Passes deep to the brachioradialis in the upper forearm and the extensor retinaculum near the wrist

    • The tendon runs through the second dorsal compartment of the wrist along with the ECRB tendon

  • Insertion: Dorsal surface of the base of the second metacarpal bone (index finger)

Relations

  • Anteriorly: Brachioradialis, radial artery in the distal forearm

  • Posteriorly: Extensor digitorum and extensor carpi radialis brevis

  • Medially: Extensor carpi radialis brevis

  • Laterally: Brachioradialis muscle

  • Distally: Extensor retinaculum, second dorsal wrist compartment, and metacarpal base

Nerve Supply

  • Radial nerve (C6–C7) before its bifurcation into superficial and deep branches

Arterial Supply

  • Radial artery (main supply)

  • Additional branches from the radial recurrent artery and posterior interosseous artery

Venous Drainage

  • Venae comitantes of the radial artery

  • Drains into the radial veins, then into the brachial veins

Function

  • Extension of wrist: Acts as a primary wrist extensor

  • Radial deviation (abduction): Works with flexor carpi radialis to abduct the wrist

  • Assists in elbow flexion: Due to its proximal humeral origin

  • Dynamic stabilizer: Maintains wrist alignment during gripping and lifting movements

  • Synergist: With ECRB and extensor carpi ulnaris for balanced wrist motion

Clinical Significance

  • Lateral epicondylitis: Chronic overuse can cause tendinopathy at its origin near the lateral epicondyle

  • Radial tunnel syndrome: Compression of radial nerve fibers supplying ECRL causes weakness or pain in lateral forearm

  • Tendon rupture or avulsion: Rare, but may occur from trauma or degenerative disease

  • Surgical relevance: ECRL tendon used in tendon transfer procedures for wrist and finger extension restoration

  • Imaging importance: MRI key for detecting tendinopathy, muscle tears, and nerve entrapment

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity, distinct fascicular pattern

    • Tendon: low signal (dark) linear structure crossing the wrist

    • Fat planes: bright, separating muscle from adjacent structures

    • Pathology: muscle atrophy shows increased fatty bright signal

  • T2-weighted images:

    • Normal muscle: intermediate-to-low signal, slightly darker than T1

    • Tendon: low signal

    • Pathology: bright hyperintense foci in tendon or myotendinous junction (tendinitis, tear)

    • Surrounding soft-tissue edema: hyperintense on T2

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathologic regions (inflammation, strain, edema): bright hyperintensity

    • Useful for early detection of overuse injury or myotendinous inflammation

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark muscle, uniform low-signal tendon

    • Pathology: bright focal signal indicating tendon degeneration or microtear

    • Demonstrates peritendinous fluid and inflammatory reaction clearly

  • T1 Fat-Sat Post-Contrast:

    • Normal: mild homogeneous enhancement of muscle

    • Tendinitis or synovitis: focal or peritendinous enhancement

    • Chronic tendinopathy: peripheral enhancement surrounding non-enhancing fibrotic tendon core

CT Appearance

Non-Contrast CT:

  • Muscle: soft-tissue density with well-defined margins on the lateral forearm

  • Tendon: visible as a fine linear density extending to the second metacarpal base

  • Bone attachments: cortical smoothness at lateral supracondylar ridge and metacarpal base

  • Chronic tendinopathy: may show cortical irregularity or calcification near insertion

Post-Contrast CT (standard):

  • Normal muscle: homogeneous enhancement

  • Pathology:

    • Inflammation or tendon injury: focal enhancement at tendon origin or insertion

    • Chronic cases: thickened tendon with peritendinous enhancement

    • Postsurgical or posttraumatic changes: identifiable enhancement patterns around repair sites

MRI images

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

MRI images

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

MRI images

Extensor carpi radialis longus muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00002

MRI images

Extensor carpi radialis longus muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00003

MRI images

Extensor carpi radialis longus muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00004

MRI images

Extensor carpi radialis longus muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00005

CT images

Extensor carpi radialis longus muscle ct axial