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Palmaris brevis muscle

The palmaris brevis is a small, thin, quadrilateral superficial muscle located on the ulnar side of the palm within the hypothenar region. It lies within the subcutaneous tissue over the hypothenar eminence and functions primarily to tense the skin of the palm, improving grip and protecting the ulnar neurovascular bundle.

Though often overlooked due to its small size, it plays an important biomechanical and protective role, particularly in tasks involving sustained or forceful grasp. Its activity is associated with the stabilization of the palmar skin and deep structures during hand movements.

Synonyms

  • Subcutaneous palmar muscle

  • Palmaris cutaneus muscle

Origin, Course, and Insertion

Origin: Flexor retinaculum and medial margin of the palmar aponeurosis
Course: Fibers run transversely across the hypothenar eminence, superficial to the hypothenar muscles and ulnar nerve and vessels
Insertion: Dermis of the skin along the ulnar border of the palm

Tendon Attachments

The palmaris brevis has no discrete tendon; instead, its muscle fibers blend directly into the palmar dermis, creating a firm attachment that allows tensioning of the skin during grip or hypothenar compression.

Relations

Superficial: Skin and superficial palmar fascia
Deep: Hypothenar muscles (abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi) and ulnar nerve and artery
Medially: Ulnar border of the hand
Laterally: Continuation of the palmar aponeurosis

Nerve Supply

Superficial branch of the ulnar nerve (C8–T1)

Arterial Supply

Superficial palmar branch of the ulnar artery and small twigs from the superficial palmar arch

Function

  • Tenses palmar skin: Improves grip and prevents skin folding during grasping

  • Protects ulnar neurovascular bundle: Shields ulnar artery and nerve from compression and trauma

  • Assists in hypothenar contour: Enhances palmar surface conformity around the ulnar side of the hand

  • Reflex activity: Contracts involuntarily during tight fist clenching or pressure grip

Clinical Significance

  • Atrophy or absence: May be seen in ulnar nerve palsy but has minimal functional deficit

  • Spasm or hypertrophy: Can mimic subcutaneous mass or cause ulnar-sided palm pain

  • Electromyography: Used in clinical testing of ulnar nerve motor function

  • Surgical importance: Acts as a surface landmark during ulnar nerve decompression and palmar fascial surgeries

  • Imaging relevance: Helps differentiate superficial soft-tissue masses or edema from hypothenar muscle lesions

MRI Appearance

T1-weighted images:

  • Muscle belly: intermediate signal intensity, well-defined, superficial to hypothenar group

  • Surrounding subcutaneous fat: bright signal, creating clear contrast

  • Fascia and aponeurosis: low signal (dark linear bands)

  • Hypertrophy or spasm: mild thickening or bulging of muscle contour

T2-weighted images:

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

  • Pathology (strain, edema): focal bright signal areas within the muscle

  • Subcutaneous fat: bright; separates muscle from underlying hypothenar group

STIR:

  • Normal muscle: intermediate-to-dark signal

  • Pathology: bright hyperintense signal in edema, inflammation, or contusion

  • Highlights perimuscular fluid and fascial inflammation

Proton Density Fat-Saturated (PD FS):

  • Normal muscle: intermediate-to-dark signal intensity

  • Partial strain or fascial irritation: bright focal signal within muscle fibers

  • Useful for detecting subtle edema or soft-tissue injury from repetitive compression

T1 Fat-Sat Post-Contrast:

  • Normal: mild homogeneous enhancement

  • Inflamed or hypertrophic muscle: diffuse enhancement

  • Fascial inflammation: shows rim-like or patchy enhancement along palmar aponeurosis

CT Appearance

Non-Contrast CT:

  • Muscle seen as thin, soft-tissue density layer overlying hypothenar eminence

  • Separated from subcutaneous fat by fascial plane

  • Useful for evaluating trauma, atrophy, or subcutaneous lesions in the hypothenar region

Post-Contrast CT (standard):

  • Normal muscle enhances uniformly

  • Inflammation, fibrosis, or hypertrophy show localized increased enhancement

  • Differentiates between superficial edema, hematoma, and soft-tissue tumors overlying hypothenar muscles

MRI image

palmaris brevis muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

palmaris brevis muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI image

palmaris brevis muscle coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

palmaris brevis muscle sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

palmaris brevis muscle ct axial image