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Abductor hallucis muscle

The abductor hallucis is a superficial muscle of the medial plantar compartment of the foot. It lies along the medial border of the foot and forms part of the muscular prominence of the medial arch. It primarily functions to abduct and flex the great toe at the metatarsophalangeal joint, and also helps maintain the integrity of the longitudinal arch of the foot.

It is clinically relevant as it may become hypertrophied or fibrotic, contributing to tarsal tunnel syndrome by compressing the tibial nerve or its branches.

Synonyms

  • Medial abductor of hallux

  • Abductor of the great toe

Origin, Course, and Insertion

  • Origin: Medial process of the calcaneal tuberosity, plantar aponeurosis, and flexor retinaculum

  • Course: Fibers run distally and medially along the medial plantar surface of the foot

  • Insertion: Medial side of the base of the proximal phalanx of the hallux via a tendon blending with the medial sesamoid bone and medial capsule of the first metatarsophalangeal joint

Tendon Attachments

  • Inserts into the proximal phalanx of the great toe

  • Associated with the medial sesamoid bone of the hallux

  • Merges with the medial capsule of the first MTP joint

Relations

  • Superficial: Skin, plantar fascia

  • Deep: Flexor hallucis brevis, flexor digitorum brevis, plantar vessels and nerves

  • Medially: Skin overlying the medial border of foot

  • Laterally: Flexor digitorum brevis

Nerve Supply

  • Medial plantar nerve (branch of the tibial nerve, roots S1–S2)

Arterial Supply

  • Medial plantar artery (branch of posterior tibial artery)

  • Anastomoses with branches of the plantar arch

Venous Drainage

  • Medial plantar vein, draining into the posterior tibial vein

Function

  • Abduction of hallux: Moves great toe medially away from midline of the foot

  • Flexion of hallux: Assists flexion at the first MTP joint

  • Arch support: Contributes to maintaining the medial longitudinal arch

  • Stabilization: Provides medial foot stability during stance and gait

Clinical Significance

  • Hypertrophy or fibrosis: May compress the tibial nerve or medial plantar nerve, contributing to tarsal tunnel syndrome

  • Tendinopathy and strain: Overuse can cause medial foot pain in athletes and runners

  • Surgical relevance: Landmark in medial foot surgeries and decompression procedures

  • Imaging importance: Hypertrophy, fatty atrophy, or mass-like enlargement best visualized on MRI

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity

    • Fat planes surrounding muscle: bright

    • Atrophy: muscle replaced by bright fat signal

  • T2-weighted images:

    • Normal muscle: darker than T1 but intermediate overall

    • Pathology: hyperintense signal in strains, tears, or edema

    • Tendon insertions: normally dark; bright when inflamed

  • STIR:

    • Normal muscle: intermediate-to-dark signal

    • Pathology (edema, myositis, trauma): bright hyperintense signal

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: intermediate-to-dark signal

    • Pathology: focal or diffuse hyperintensity indicating edema, tendinopathy, or fascial irritation

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: minimal or no enhancement

    • Inflammatory changes: focal or diffuse enhancement

    • Nerve entrapment syndromes: perineural enhancement adjacent to hypertrophied muscle

CT Appearance

Non-Contrast CT:

  • Muscle seen as a soft tissue density along medial plantar surface

  • Hypertrophy appears as increased bulk compared to contralateral side

  • Chronic degeneration: fatty infiltration may decrease density

Post-Contrast CT (standard):

  • Muscle enhances homogeneously

  • Pathology: localized or diffuse enhancement in cases of inflammation or neoplasm

  • Helpful for surgical planning in cases of space-occupying lesions (hypertrophy, masses)

MRI image

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

MRI image

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

MRI image

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

MRI image

Abductor hallucis muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Abductor hallucis muscle ct sagittal image