Abductor Digiti Minimi Muscle: Anatomy, Function, Imaging

Topic

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