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Adductor pollicis muscle (Oblique head)

The oblique head of the adductor pollicis is the larger and deeper component of the adductor pollicis muscle, located in the palmar compartment of the hand. It plays a crucial role in adduction of the thumb, drawing the thumb toward the palm and index finger during pinching and gripping movements.

It forms the distal part of the thenar eminence, lying deep to the flexor tendons and superficial palmar arch. The oblique head works in coordination with the transverse head of the adductor pollicis, the first dorsal interosseous, and flexor pollicis brevis to provide thumb stability and precision control during fine motor activities.

Synonyms

  • Oblique portion of the adductor pollicis

  • Oblique head of adductor pollicis brevis (archaic term)

Origin, Course, and Insertion

  • Origin:

    • Bases of the second and third metacarpal bones

    • Capitate and adjacent carpal bones (trapezoid and trapezium)

    • Occasionally from the sheath of the flexor carpi radialis tendon

  • Course:

    • Fibers converge obliquely distally and laterally across the palm

    • Forms a thick muscular mass deep to the flexor tendons and superficial palmar arch

    • Joins with fibers of the transverse head near the first metacarpal

  • Insertion:

    • Medial side of the base of the proximal phalanx of the thumb and the ulnar sesamoid bone

    • Some fibers blend with the extensor expansion of the thumb

Tendon Attachments

  • Inserts via a short, thick tendon on the ulnar (medial) side of the proximal phalanx of the thumb

  • A sesamoid bone (ulnar sesamoid) is embedded within the tendon at its insertion site

  • Some fibers merge with the fibrous capsule of the first metacarpophalangeal (MCP) joint and the adductor aponeurosis

Relations

  • Superficial: Flexor tendons of the fingers, superficial palmar arch, and palmar fascia

  • Deep: Metacarpal bones and interossei muscles

  • Medial: Transverse head of adductor pollicis

  • Lateral: First dorsal interosseous and flexor pollicis brevis

  • Superior (proximal): Flexor retinaculum and capitate bone

  • Inferior (distal): Base of the thumb proximal phalanx and MCP joint capsule

Nerve Supply

  • Deep branch of the ulnar nerve (C8–T1)

Arterial Supply

  • Deep palmar arch, chiefly from the radial artery

  • Additional contribution from the palmar metacarpal arteries

Function

  • Adduction of the thumb: Moves the thumb toward the palm and second digit in the plane of the palm

  • Power grip: Provides strength and stability during grasping and pinching

  • Fine motor control: Stabilizes the thumb in precision tasks such as writing or buttoning

  • Joint support: Reinforces the ulnar side of the MCP joint capsule and sesamoid complex

Clinical Significance

  • Ulnar nerve lesions: Weakness or paralysis causes loss of thumb adduction and a positive Froment’s sign (thumb flexes at IP joint when pinching)

  • Atrophy: Common in long-standing ulnar neuropathy, producing hollowing in the first web space

  • Tendinopathy or strain: May occur in athletes, musicians, or repetitive hand use

  • Surgical relevance: Important structure during ulnar artery or nerve decompression, and palmar flap dissection

  • Imaging importance: MRI helps assess muscle atrophy, denervation, or mass lesions in the deep thenar compartment

MRI Appearance

  • T1-weighted images:

    • Muscle belly: Intermediate signal intensity, clearly demarcated from surrounding fat (bright).

    • Tendon: Low signal (dark linear band) inserting onto proximal phalanx.

    • Fatty atrophy (neuropathy): Increased intramuscular brightness with volume loss.

    • Fibrous septa: Low-signal lines separating muscle lobules.

  • T2-weighted images:

    • Normal muscle: Intermediate-to-low signal, slightly darker than on T1.

    • Tendon: Low signal, continuous with insertion.

    • Edema or inflammation: Bright hyperintense areas in acute strain or myositis.

    • Denervation changes: Early hyperintense edema followed by fatty infiltration on chronic studies.

  • STIR:

    • Normal muscle: Intermediate-to-dark signal.

    • Pathology: Bright hyperintense signal in acute muscle injury, inflammation, or compartment edema.

    • Excellent for differentiating acute denervation from chronic fatty change.

  • Proton Density Fat-Saturated (PD FS):

    • Normal muscle: Intermediate-to-dark signal with clear fascicular texture.

    • Pathologic muscle: Bright hyperintensity indicating edema or fiber disruption.

    • Useful for detecting small intramuscular tears or peritendinous inflammation.

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: Homogeneous mild enhancement.

    • Inflamed or denervated muscle: Diffuse or patchy enhancement.

    • Chronic fibrosis: Minimal enhancement with low-signal scarring.

    • Enhancing nodules may represent neuromas, vascular lesions, or post-surgical changes.

CT Appearance

Non-Contrast CT:

  • Muscle: Homogeneous soft-tissue density within deep thenar region.

  • Tendon: Linear soft-tissue band inserting onto medial base of thumb proximal phalanx.

  • Adjacent bones: First and second metacarpals, proximal phalanx, and sesamoid easily visualized.

  • Pathology: Detects calcifications, fibrotic thickening, or chronic muscular atrophy with fat replacement.

Post-Contrast CT (standard):

  • Normal muscle: Uniform moderate enhancement.

  • Inflamed muscle: Focal or diffuse increased enhancement.

  • Mass lesions or abscess: Heterogeneous enhancement with low-density central core.

  • Chronic atrophy: Poor enhancement with fat attenuation replacement in deep thenar space.

MRI images

Adductor Pollicis Muscle (Oblique Head) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Adductor Pollicis Muscle (Oblique Head) CORONAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Adductor Pollicis Muscle (Oblique Head) CORONAL cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001