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Abductor pollicis longus muscle

The abductor pollicis longus (APL) is a deep muscle of the posterior compartment of the forearm. It lies in the deep extensor group and primarily functions to abduct and extend the thumb at the carpometacarpal (CMC) joint. Its long tendon passes through the first dorsal compartment of the wrist, along with the extensor pollicis brevis (EPB) tendon.

The APL plays an essential role in thumb movement, grip stabilization, and radial wrist abduction. Due to its location and tendon path, it is frequently implicated in De Quervain’s tenosynovitis, a painful stenosing condition of the first dorsal compartment. Anatomical variations, such as multiple tendon slips, are common and clinically significant during surgery and imaging.

Synonyms

  • Long abductor of the thumb

  • Abductor longus pollicis

Origin, Course, and Insertion

  • Origin: Posterior surfaces of the ulna and radius, and the interosseous membrane, in the middle third of the forearm

  • Course:

    • Fibers converge into a thick tendon that passes obliquely distally and laterally

    • Crosses under the extensor retinaculum within the first dorsal compartment of the wrist, accompanied by the extensor pollicis brevis tendon

    • Often divides into two or more tendon slips before insertion

  • Insertion:

    • Primarily into the base of the first metacarpal bone (radial side)

    • Occasionally gives accessory slips to the trapezium, thenar fascia, or abductor pollicis brevis muscle

Tendon Attachments

  • The tendon runs lateral to the EPB tendon in the first dorsal compartment beneath the retinaculum

  • Enclosed in a common synovial sheath with EPB, which is a common site for tenosynovitis

  • Inserts on the radial base of the first metacarpal, contributing to thumb abduction and extension

Relations

  • Anteriorly: Extensor retinaculum and skin of dorsal wrist

  • Posteriorly: Extensor carpi radialis longus and brevis muscles

  • Laterally: Radial artery (distally) and anatomical snuffbox

  • Medially: Extensor pollicis brevis tendon

  • Inferiorly: Base of first metacarpal and trapezium

Nerve Supply

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

Arterial Supply

  • Posterior interosseous artery and branches of the radial artery

Venous Drainage

  • Radial vein and posterior interosseous veins, draining into the brachial venous system

Function

  • Abduction of thumb: Moves thumb away from the palm at the carpometacarpal joint

  • Extension of thumb: Assists in thumb extension with EPB

  • Radial deviation: Aids in abduction of wrist (radial flexion)

  • Grip stability: Helps position thumb for opposition and grasp

  • Synergistic action: Works with abductor pollicis brevis and extensor pollicis brevis

Clinical Significance

  • De Quervain’s Tenosynovitis:

    • Inflammation of APL and EPB tendons in the first dorsal compartment

    • Presents with pain and swelling over radial styloid and pain during thumb movement

  • Accessory tendons: Multiple APL slips may complicate surgical decompression or cause recurrent symptoms

  • Tendon rupture: Rare, may result from trauma or rheumatoid arthritis

  • Entrapment or irritation: APL tendon sheath thickening may cause radial wrist pain

  • Imaging relevance: MRI best identifies tendon pathology, sheath fluid, or accessory slips

MRI Appearance

  • T1-weighted images:

    • Muscle belly: intermediate signal intensity with distinct fascicular pattern

    • Tendon: low signal (dark) extending obliquely along radial aspect of wrist

    • Fat planes and surrounding fascia: bright, aiding contrast

    • Hypertrophy or thickening in tendinopathy shows intermediate-to-bright signal intensity

  • T2-weighted images:

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

    • Normal tendon: low signal (dark linear structure)

    • Pathology: bright hyperintense signal within tendon sheath or substance (tenosynovitis, tendinitis, or partial tear)

    • Fluid within tendon sheath: bright, outlining tendon contours

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathology: bright hyperintense peritendinous signal indicating edema or inflammation

    • Useful for detecting subtle fluid accumulation or early tenosynovitis

  • Proton Density Fat-Saturated (PD FS):

    • Normal: muscle and tendon appear intermediate-to-dark, sharply marginated

    • Pathologic: focal bright hyperintensity within or around tendon

    • Excellent for evaluating partial tears, peritendinous edema, or synovial thickening

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: minimal enhancement

    • Tendinitis or tenosynovitis: diffuse or sheath-like enhancement pattern

    • Chronic fibrosis or scar tissue: peripheral rim enhancement with central low signal

CT Appearance

Non-Contrast CT:

  • Muscle: homogeneous soft-tissue density in posterior-lateral forearm

  • Tendon: fine linear structure crossing radial styloid to first metacarpal base

  • Bone insertion site: visible at radial base of first metacarpal

  • Chronic enthesopathy: may show tiny calcifications or cortical irregularity at insertion

Post-Contrast CT (standard):

  • Muscle: uniform enhancement pattern

  • Inflamed tendon sheath or peritendinous tissues: focal or diffuse enhancement

  • Useful for assessing calcific tendinitis, peritendinous abscess, or post-surgical changes

MRI image

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MRI image

Abductor pollicis longus axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

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MRI image

Abductor pollicis longus axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00003

MRI image

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