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Abductor digiti minimi muscle

The abductor digiti minimi (ADM) is a superficial intrinsic muscle of the sole of the foot, located along the lateral border. It forms the most medial muscle of the lateral plantar compartment. The ADM abducts and flexes the fifth toe (little toe) at the metatarsophalangeal joint and provides lateral stability to the foot during gait.

It is clinically relevant in plantar fasciitis, heel pain syndromes, and nerve entrapments such as Baxter’s neuropathy, which affects the first branch of the lateral plantar nerve.

Synonyms

  • Abductor of the little toe

  • Abductor of the fifth digit

Origin, Course, and Insertion

  • Origin: Medial and lateral processes of the calcaneal tuberosity, plantar aponeurosis, and intermuscular septum

  • Course: Fibers run forward along the lateral margin of the foot

  • Insertion: Lateral aspect of the base of the proximal phalanx of the 5th toe; sometimes attaches to the tendon of the flexor digiti minimi brevis

Tendon Attachments

  • Attaches distally into the lateral base of the proximal phalanx of the fifth toe

  • Occasionally merges with the tendon of flexor digiti minimi brevis for reinforcement

Relations

  • Superficial: Plantar fascia

  • Deep: Flexor digitorum brevis, quadratus plantae, lateral plantar vessels and nerve

  • Medial: Flexor digitorum brevis

  • Lateral: Lateral margin of foot and skin

Nerve Supply

  • Lateral plantar nerve (first branch), from tibial nerve (S1–S3)

Arterial Supply

  • Lateral plantar artery, branch of posterior tibial artery

Venous Drainage

  • Tributaries of the lateral plantar vein, draining into the posterior tibial vein

Function

  • Abduction of the 5th toe: Moves toe laterally at the metatarsophalangeal joint

  • Flexion: Assists in flexion of the 5th toe at the MTP joint

  • Support: Helps maintain the lateral longitudinal arch of the foot

  • Stabilization: Provides lateral balance during stance and gait

Clinical Significance

  • Baxter’s neuropathy: Entrapment of the inferior calcaneal branch of the lateral plantar nerve may cause selective ADM atrophy, seen on MRI

  • Heel pain syndromes: Often involved in chronic plantar fasciitis

  • Tears or strain: Can occur with trauma or overuse, presenting with lateral plantar foot pain

  • Atrophy: Early marker of peripheral neuropathy and chronic compression

MRI Appearance

  • T1-weighted images:

    • Normal ADM: intermediate signal intensity muscle belly

    • Fat planes and subcutaneous tissue: bright signal

    • Chronic denervation: fatty replacement with bright signal

  • T2-weighted images:

    • Normal muscle: intermediate-to-dark signal (darker than on T1)

    • Acute injury or denervation: hyperintense changes in muscle belly

    • Chronic tendinopathy or strain: irregular bright signal at origin or insertion

  • STIR (Short Tau Inversion Recovery):

    • Normal muscle: intermediate to dark signal

    • Pathology: bright hyperintensity in edema, tears, or nerve-related denervation

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark muscle signal

    • Tears or inflammation: bright hyperintense signal within muscle fibers

    • Excellent for detecting subtle denervation or tendon injury

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: minimal enhancement

    • Pathology: focal or diffuse enhancement in myositis, tendon origin inflammation, or post-surgical change

CT Appearance

Non-Contrast CT:

  • Muscle appears as a soft tissue density on the lateral sole

  • Calcifications may indicate chronic tendinopathy or trauma

  • Atrophy manifests as reduced bulk compared to contralateral side

Post-Contrast CT:

  • Normal ADM enhances homogeneously

  • Pathology such as inflammation or soft tissue tumor shows focal or diffuse increased enhancement

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