Topics

Topic

design image
Adductor pollicis muscle (Transverse head)

The transverse head of the adductor pollicis muscle is one of two heads forming the adductor pollicis, the other being the oblique head. It lies in the deep compartment of the palm, contributing to the bulk of the first web space and forming the deep boundary of the thenar eminence. This head is primarily responsible for adduction of the thumb, drawing it toward the palm and providing stability during pinch and grip activities.

The transverse head is short, flat, and triangular, arising from the anterior surface of the third metacarpal shaft and inserting medially onto the base of the proximal phalanx of the thumb and ulnar sesamoid bone of the metacarpophalangeal (MCP) joint.

Synonyms

  • Transverse head of adductor pollicis

  • Horizontal head of adductor pollicis

  • Deep thenar adductor

Origin, Course, and Insertion

  • Origin: Anterior surface and distal two-thirds of the shaft of the third metacarpal bone.

  • Course: Fibers run transversely laterally across the palm toward the thumb, forming a flat, muscular band deep to the flexor tendons.

  • Insertion: Medial side of the base of the proximal phalanx of the thumb and the ulnar sesamoid bone of the MCP joint capsule, blending with the oblique head fibers.

Relations

  • Superficially: Flexor tendons and superficial palmar arch

  • Deeply: First dorsal interosseous muscle

  • Laterally: Oblique head of adductor pollicis and first metacarpal

  • Medially: Palmar interossei and deep palmar arch

  • Anteriorly: Palmar fascia and skin of the thenar region

Tendon Attachments

  • The terminal tendon blends with the oblique head of adductor pollicis and inserts into the ulnar sesamoid bone and the MCP joint capsule.

  • The tendon acts as a dynamic stabilizer of the first MCP joint, balancing the forces of the flexor pollicis longus and extensors.

Nerve Supply

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

Arterial Supply

  • Deep palmar arch (mainly from the radial artery)

  • Additional twigs from palmar metacarpal arteries

Function

  • Adduction of the thumb: Brings the thumb toward the palm in opposition to abduction.

  • Pinch and grip stabilization: Maintains firm contact between thumb and fingers during grasping.

  • MCP joint stability: Reinforces ulnar side of the thumb’s MCP joint.

  • Synergy: Works with flexor pollicis longus, opponens pollicis, and interossei for precision grip.

Clinical Significance

  • Ulnar nerve lesion (Froment’s sign): Paralysis causes weakness in thumb adduction; patient compensates by flexing the thumb IP joint using flexor pollicis longus.

  • Atrophy: Flattening of the first web space due to chronic ulnar neuropathy.

  • Overuse strain: Seen in activities involving repetitive thumb pinching or grasping.

  • Surgical relevance: Important in reconstructive tendon transfers and carpal tunnel decompression procedures.

  • Imaging relevance: Assessed in cases of ulnar neuropathy, intrinsic muscle atrophy, and deep palmar space infections.

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with clear fascicular architecture.

    • Surrounding fat: bright, enhancing muscle margins.

    • Atrophy or fatty infiltration: increased T1 signal with volume loss.

  • T2-weighted images:

    • Normal muscle: intermediate-to-dark signal, darker than on T1.

    • Acute injury, edema, or denervation: bright hyperintense signal within the muscle belly.

    • Chronic atrophy: loss of muscle bulk with persistent high signal due to fatty change.

  • STIR:

    • Normal: intermediate-to-dark signal.

    • Pathologic: bright hyperintense signal representing edema, inflammation, or early denervation.

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, homogeneous texture.

    • Abnormal: bright hyperintensity in muscle or tendon attachment (strain, tenosynovitis, or inflammatory myopathy).

  • T1 Fat-Sat Post-Contrast:

    • Normal: mild homogeneous enhancement.

    • Inflammation or denervation: patchy or diffuse enhancement.

    • Infection or tumor: irregular, nodular, or rim enhancement patterns.

CT Appearance

Non-Contrast CT:

  • Muscle belly: soft-tissue density between first and third metacarpals.

  • Clear distinction from adjacent interosseous muscles on thin-slice images.

  • Chronic atrophy: reduced bulk with increased surrounding fat density.

  • Calcification or myositis ossificans: focal hyperdense areas within the muscle.

Post-Contrast CT (standard):

  • Normal: homogeneous enhancement along muscular belly.

  • Pathologic: increased or irregular enhancement in inflammation, abscess, or neoplasm.

  • Useful for assessing deep palmar space infection, trauma, and postoperative changes.

MRI image

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

MRI image

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