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Opponens pollicis muscle

The opponens pollicis is one of the three thenar muscles of the hand, situated deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis. It plays a critical role in thumb opposition, allowing the pad of the thumb to touch the pads of the other fingers—a movement essential for grasp, precision, and manipulation.

It forms the deep muscular foundation of the thenar eminence and acts synergistically with the abductor and flexor pollicis brevis muscles to position the thumb across the palm. Its integrity is vital for fine motor control and hand dexterity.

Synonyms

  • Opponent of the thumb

  • Opponens muscle of the thumb

Origin, Course, and Insertion

  • Origin: Flexor retinaculum and tubercle of the trapezium bone

  • Course: Fibers pass obliquely downward and laterally, deep to the abductor pollicis brevis and flexor pollicis brevis

  • Insertion: Entire length of the lateral border and radial surface of the first metacarpal bone

Relations

  • Superficially: Abductor pollicis brevis and flexor pollicis brevis

  • Deeply: First metacarpal bone and adductor pollicis (transverse head)

  • Medially: Flexor pollicis brevis

  • Laterally: Thenar skin and subcutaneous tissue

  • Posteriorly: Radial artery branches and first metacarpal shaft

Nerve Supply

  • Recurrent branch of the median nerve (C8, T1)

  • Occasionally receives a communicating branch from the ulnar nerve (in Martin-Gruber or Riche-Cannieu anastomosis)

Arterial Supply

  • Superficial palmar branch of the radial artery

  • Princeps pollicis artery and radialis indicis artery contribute minor branches

Function

  • Opposition of the thumb: Rotates and flexes the first metacarpal medially toward the palm and other fingers

  • Grip and manipulation: Enables precision movements such as pinching, writing, and tool handling

  • Stabilization: Maintains thumb position during grasp and prevents collapse of the thumb column

  • Synergy: Works with abductor pollicis brevis and flexor pollicis brevis to complete opposition and flexion movements

Clinical Significance

  • Median nerve injury: Paralysis causes loss of opposition, flattening of the thenar eminence (“ape hand deformity”)

  • Thenar atrophy: Seen in carpal tunnel syndrome or chronic denervation

  • Muscle strain: Can occur in repetitive gripping or fine manipulation tasks

  • Surgical relevance: Important landmark during carpal tunnel release and thumb reconstructive procedures

  • Imaging role: MRI essential for assessing thenar atrophy, denervation edema, or traumatic injury

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity, well-defined with distinct fascicular pattern

    • Fat between thenar muscles: bright signal

    • Atrophy: increased intramuscular fat (bright signal) with volume loss

    • Denervation (subacute): slightly increased signal due to fatty infiltration

  • T2-weighted images:

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

    • Acute denervation or myositis: bright hyperintense signal within muscle belly

    • Chronic atrophy: remains dark with fatty replacement (loss of normal texture)

    • Surrounding tendons and retinaculum: low signal intensity

  • STIR:

    • Normal: intermediate-to-dark signal

    • Pathology: bright hyperintense regions indicating edema, inflammation, or acute denervation

    • Useful in detecting early muscle pathology before atrophy becomes visible

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, homogeneous muscle appearance

    • Pathologic: bright hyperintense areas corresponding to edema, partial tear, or neuritis

    • Highlights subtle inflammation within thenar compartment

  • T1 Fat-Sat Post-Contrast:

    • Normal: mild homogeneous enhancement

    • Denervated or inflamed muscle: focal or diffuse enhancement

    • Chronic fibrosis: minimal or absent enhancement

CT Appearance

Non-Contrast CT:

  • Muscle: uniform soft-tissue density forming bulk of the thenar eminence

  • Fat planes between thenar muscles clearly visualized

  • Chronic atrophy: visible as volume loss and fatty replacement (low attenuation)

  • Useful for preoperative anatomical assessment in reconstructive surgery

Post-Contrast CT (standard):

  • Normal muscle: mild homogeneous enhancement

  • Inflamed or hyperemic muscle: increased focal enhancement

MRI image

Opponens Pollicis Muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Opponens Pollicis Muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Opponens Pollicis Muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Opponens Pollicis Muscle axial ct image