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Opponens digiti minimi muscle (hand)

The opponens digiti minimi (ODM) is one of the three hypothenar muscles of the hand, located deep to the abductor digiti minimi and flexor digiti minimi brevis. It lies along the ulnar border of the palm and acts to cup the hand by drawing the fifth metacarpal bone anteriorly and medially toward the thumb, enabling opposition and grip.

This muscle plays an essential role in hand dexterity and precision grasping, particularly during tasks requiring opposition between the thumb and little finger. Its function is closely coordinated with the hypothenar group and ulnar nerve–innervated intrinsic hand muscles.

Synonyms

  • Opponens muscle of the little finger

  • Opponens minimi digiti

  • Hypothenar opponens

Origin, Course, and Insertion

  • Origin: Hook of the hamate and flexor retinaculum of the wrist

  • Course: Fibers run obliquely downward and laterally along the ulnar side of the palm, deep to the flexor digiti minimi brevis

  • Insertion: Entire length of the ulnar (medial) border of the fifth metacarpal bone

Relations

  • Superficial: Flexor digiti minimi brevis and palmar fascia

  • Deep: Fifth metacarpal bone and interosseous muscles

  • Medial: Abductor digiti minimi

  • Lateral: Flexor tendons of the fingers and palmar arch vessels

Tendon Attachments

  • No distinct tendon; muscle fibers insert directly onto the shaft of the fifth metacarpal

  • Fibers blend with adjacent hypothenar muscles, forming a unified functional unit for little finger opposition

Nerve Supply

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

Arterial Supply

  • Deep palmar branch of the ulnar artery

  • Contributions from the deep palmar arch

Function

  • Opposition of little finger: Brings the fifth metacarpal forward and medially toward the thumb

  • Cupping of palm: Assists in creating the hollow of the hand for gripping objects

  • Stabilization: Helps maintain ulnar border tension during power grasp

  • Synergistic role: Works with abductor digiti minimi and flexor digiti minimi to control fine hypothenar movements

Clinical Significance

  • Ulnar nerve palsy: Causes weakness or paralysis of ODM, leading to impaired opposition and poor grip strength

  • Atrophy: Chronic nerve injury results in flattening of hypothenar eminence

  • Tendon or muscle strain: May occur from repetitive gripping or trauma to hypothenar area

  • Surgical relevance: Important landmark in carpal tunnel and Guyon’s canal decompression surgeries

  • Imaging importance: Evaluated in ulnar neuropathies, muscle atrophy, trauma, or post-surgical changes

MRI Appearance

  • T1-weighted images:

    • Normal muscle: intermediate signal intensity with clear fascicular pattern

    • Surrounding fat: bright, providing contrast to muscle belly

    • Atrophy or fatty infiltration: muscle replaced by bright signal fat

    • Adjacent tendons and retinaculum: low-signal (dark linear structures)

  • T2-weighted images:

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

    • Pathology (strain, inflammation, denervation): hyperintense bright signal within muscle belly

    • Fascial planes: well-defined dark boundaries

  • STIR:

    • Normal ODM: intermediate-to-dark signal

    • Pathologic: bright hyperintensity indicating edema, inflammation, or acute denervation

    • Sensitive for early muscle edema or myositis

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark uniform signal

    • Muscle strain or edema: bright hyperintense regions within muscle

    • Helpful for differentiating edema from fatty infiltration

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: uniform mild enhancement

    • Inflammatory or neoplastic lesions: show focal or diffuse enhancement

    • Post-traumatic or post-surgical changes: peripheral enhancement around scar tissue

CT Appearance

Non-Contrast CT:

  • Muscle: homogeneous soft-tissue density along the ulnar side of the palm

  • Clear separation from the flexor tendons and hypothenar fascia

  • Chronic denervation or fatty infiltration: reduced bulk and lower soft-tissue density

Post-Contrast CT (standard):

  • ODM enhances uniformly along with other intrinsic hand muscles

  • Inflamed or hypertrophic muscle: focal enhancement

  • Useful for assessing space-occupying lesions, trauma, or post-surgical changes in hypothenar region

MRI image

Opponens Digiti Minimi Muscle (Hand) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Opponens Digiti Minimi Muscle (Hand) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

Opponens Digiti Minimi Muscle (Hand) coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Opponens Digiti Minimi Muscle (Hand) ct axial image