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Palmaris longus tendon

The palmaris longus tendon is the distal tendinous continuation of the palmaris longus muscle, located in the superficial anterior compartment of the forearm. It is a slender, fusiform tendon that passes anterior to the flexor retinaculum and inserts into the palmar aponeurosis. The tendon is superficial and easily visible in individuals who possess it, though it is absent in approximately 10–20% of the population, unilaterally or bilaterally.

Functionally, it acts as a weak flexor of the wrist and tenses the palmar fascia. Owing to its superficial course, consistent length, and minimal functional significance, it is widely used as a tendon graft donor in reconstructive and cosmetic procedures.

Synonyms

  • Long palmar tendon

  • Tendon of palmaris longus

  • Palmar aponeurotic tendon

Origin, Course, and Insertion

  • Origin: Continuation of the palmaris longus muscle, which arises from the medial epicondyle of the humerus via the common flexor tendon.

  • Course:

    • The tendon descends superficially in the midline of the forearm.

    • Lies superficial to the flexor retinaculum and between the tendons of flexor carpi radialis (laterally) and flexor carpi ulnaris (medially).

    • It becomes most prominent when the wrist is flexed and thumb opposed.

  • Insertion: Expands into the palmar aponeurosis, blending with superficial fascia and fibers of the thenar and hypothenar regions.

Relations

  • Anteriorly: Skin and superficial fascia of the wrist

  • Posteriorly: Flexor retinaculum and median nerve

  • Laterally: Flexor carpi radialis tendon

  • Medially: Flexor carpi ulnaris tendon

  • Superiorly: Palmaris longus muscle belly

  • Inferiorly: Palmar aponeurosis of the hand

Variations

  • May be absent in one or both limbs (10–20% of individuals)

  • Occasionally duplicated, bifid, or reversed (tendinous proximally, muscular distally)

  • Rarely inserts into flexor retinaculum or thenar fascia instead of palmar aponeurosis

Nerve Supply

  • Median nerve (C7–C8) — same as the muscle belly

Function

  • Flexion of wrist: Acts as a weak wrist flexor

  • Tension of palmar fascia: Tightens the palmar aponeurosis to improve grip strength

  • Protective role: Shields the median nerve and underlying vessels in the distal forearm

  • Surgical importance: Common donor for tendon grafts, ligament reconstructions, and facial reanimation procedures

Clinical Significance

  • Tendon graft use: Ideal for reconstructive surgery due to expendability and uniform length

  • Absence: Important to recognize preoperatively before harvesting or median nerve exposure

  • Tendinopathy: Rare, but repetitive strain or trauma can lead to inflammation

  • Median nerve proximity: Anomalous courses may compress or mimic nerve symptoms

  • Imaging relevance: Crucial in identifying anatomical variants and differentiating from neighboring tendons

MRI Appearance

  • T1-weighted images:

    • Normal tendon: Uniformly low signal (dark) linear structure extending from mid-forearm to palmar aponeurosis

    • Peritendinous fat: Bright, delineating tendon margins

    • Tendon tear or degeneration: Focal intermediate signal replacing normal dark appearance

    • Median nerve: Seen deep to tendon, as oval structure with intermediate signal

  • T2-weighted images:

    • Normal tendon: Low signal (dark) due to tightly packed collagen fibers

    • Muscle belly (if present proximally): Intermediate signal, slightly darker than subcutaneous fat

    • Pathology: Partial tears or tenosynovitis appear as bright hyperintense areas along the tendon sheath

  • STIR:

    • Normal tendon: Intermediate-to-dark flow void appearance

    • Inflamed or edematous tissue: Bright hyperintense signal indicating peritendinous inflammation or strain

  • Proton Density Fat-Saturated (PD FS):

    • Normal tendon: Uniform dark low-signal band

    • Partial tear or tendinopathy: Focal bright signal within tendon or sheath

    • Excellent for subtle peritendinitis and postoperative changes

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: Minimal enhancement

    • Inflamed sheath or granulation tissue: Focal or diffuse enhancement around tendon

    • Tendinopathy: Peripheral enhancement with central low signal

CT Appearance

Non-Contrast CT:

  • Tendon: Linear soft-tissue density superficial to flexor retinaculum

  • Fat planes: Well-defined, aiding identification of tendon boundaries

  • Calcifications: May be seen in chronic tendinopathy

  • Absence or duplication: Easily visualized on thin-slice multiplanar reconstructions

Post-Contrast CT (standard):

  • Normal tendon: Does not enhance

  • Inflamed or thickened sheath: Mild peripheral enhancement

  • Useful for identifying post-traumatic changes, adhesions, or scarring in graft donor evaluation

MRI image

Palmaris longus tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

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

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Palmaris longus tendon sagl cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Palmaris longus tendon sagl cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Palmaris longus tendon ct axial image

CT image

Palmaris longus tendon ct axial