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Extensor hallucis longus muscle

The extensor hallucis longus (EHL) is a thin, elongated muscle in the anterior compartment of the leg. It lies between the tibialis anterior and extensor digitorum longus, and functions as the primary extensor of the great toe. It also assists in dorsiflexion of the ankle and contributes to foot stabilization during gait.

The EHL has a long tendon, which becomes prominent on the dorsum of the foot, inserting onto the distal phalanx of the hallux. Due to its long course and narrow tendon, it is vulnerable to tendinopathy, laceration, and entrapment. It is clinically important in conditions such as foot drop, tendon ruptures, and deep fibular nerve lesions.

Synonyms

  • Extensor of the great toe

  • Hallucis extensor longus

Origin, Course, and Insertion

  • Origin: Middle third of the anterior surface of the fibula and the adjacent interosseous membrane

  • Course: Fibers run vertically downwards in the anterior compartment, forming a tendon that passes deep to the superior and inferior extensor retinacula of the ankle

  • Insertion: Dorsal surface of the base of the distal phalanx of the great toe

Tendon Attachments

  • Crosses anterior to the ankle joint, within its own synovial sheath beneath the extensor retinacula

  • Inserts into the distal phalanx of the hallux

  • May give accessory slips to the proximal phalanx or first metatarsophalangeal joint capsule in some anatomical variants

Relations

  • Superiorly: Tibialis anterior and extensor digitorum longus

  • Inferiorly: Dorsum of the foot and hallux tendon sheath

  • Medially: Tibialis anterior tendon

  • Laterally: Extensor digitorum longus and anterior tibial vessels

  • Posteriorly: Fibula and interosseous membrane

Nerve Supply

  • Deep fibular (peroneal) nerve (L4–L5), branch of the common fibular nerve

Arterial Supply

  • Anterior tibial artery and its muscular branches

Venous Drainage

  • Anterior tibial vein and its tributaries, draining into the popliteal vein

Function

  • Extension of hallux: Main extensor of the distal and proximal phalanges of the great toe

  • Dorsiflexion of ankle: Assists tibialis anterior in raising the foot

  • Foot stabilization: Contributes to medial balance during walking and running

  • Clinical marker: Weakness or paralysis is an early sign of deep fibular nerve palsy

Clinical Significance

  • Tendon injuries: Lacerations, ruptures, or tendinopathy from overuse (running, climbing)

  • Nerve lesions: Weakness indicates deep fibular nerve compression or L5 radiculopathy

  • Surgical relevance: Tendon transfers may involve the EHL for foot drop correction

  • Imaging importance: EHL tendon tears, tendinitis, or entrapment best visualized on MRI

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity

    • Tendon: low signal (dark band) extending to distal phalanx

    • Tears: discontinuity or focal hyperintensity within tendon

    • Fat planes around tendon appear bright

  • T2-weighted images:

    • Normal muscle: darker than on T1, still intermediate signal

    • Normal tendon: very low signal (black)

    • Pathology: tendinopathy or partial tear shows bright hyperintense signal within tendon

    • Peritendinous edema highlighted as hyperintense

  • STIR:

    • Muscle belly: normally intermediate-to-dark

    • Pathology: hyperintense signal in tendon or muscle (edema, inflammation, tear)

  • Proton Density Fat-Saturated (PD FS):

    • Normal tendon: uniformly dark

    • Tears: focal bright signal indicating fluid or fiber disruption

    • Subtle peritendinitis well visualized

  • T1 Fat-Sat Post-Contrast:

    • Normal tendon: minimal or no enhancement

    • Tendinitis/synovitis: enhances due to inflammatory changes

    • Partial tears: peripheral enhancement; complete rupture shows gap with enhancement around hematoma

CT Appearance

Non-Contrast CT:

  • Muscle belly: soft-tissue density, not well distinguished

  • Tendon: seen as a fine dense structure across the ankle joint

  • Indirect findings: tendon thickening or calcification in chronic tendinopathy

Post-Contrast CT (standard):

  • Muscle enhances homogeneously

  • Inflamed tendon sheath may show enhancement

MRI image

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

MRI image

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

MRI image

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

MRI image

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

MRI image

Extensor hallucis longus muscle MRI sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Extensor hallucis longus axial ct image