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Flexor digiti minimi brevis muscle (hand)

The flexor digiti minimi brevis (FDMB) is one of the three hypothenar muscles located on the ulnar side of the palm. It lies lateral to the abductor digiti minimi and medial to the opponens digiti minimi, forming part of the muscular eminence controlling the movement of the little finger.

It functions primarily to flex the proximal phalanx of the fifth digit at the metacarpophalangeal (MCP) joint, aiding in gripping and cupping of the palm. It plays an essential role in precision grip and fine hand control, especially in opposition and flexion of the little finger.

Synonyms

  • Short flexor of the little finger

  • Flexor brevis digiti minimi

Origin, Course, and Insertion

  • Origin: Hook of the hamate bone and flexor retinaculum

  • Course: Fibers run distally and slightly medially across the hypothenar eminence

  • Insertion: Medial side of the base of the proximal phalanx of the fifth digit, often blending with the tendon of the abductor digiti minimi

Tendon Attachments

  • The muscle forms a short, thick tendon inserting onto the proximal phalanx.

  • In some individuals, the FDMB may share partial insertional fibers with the abductor digiti minimi.

  • The palmar digital fascia and fibrous digital sheath reinforce the tendon along its course.

Relations

  • Superficial: Palmaris brevis and palmar fascia

  • Deep: Opponens digiti minimi and fifth metacarpal

  • Medial: Abductor digiti minimi

  • Lateral: Tendon of flexor digitorum superficialis to the fifth digit

  • Anterior: Skin and superficial palmar arch (ulnar artery lies just deep to it)

Nerve Supply

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

Arterial Supply

  • Deep palmar branch of the ulnar artery

  • Additional contributions from the superficial palmar arch

Function

  • Flexion: Flexes the proximal phalanx of the little finger at the MCP joint

  • Synergistic role: Assists opponens digiti minimi in drawing the little finger toward the thumb

  • Grip stability: Enhances the concavity of the palm during grasping

  • Precision control: Helps in fine hand positioning during writing or small object manipulation

Clinical Significance

  • Ulnar nerve lesions: Weakness or paralysis of FDMB results in impaired flexion of the fifth digit

  • Muscle hypertrophy or inflammation: Can compress branches of the ulnar nerve in the Guyon’s canal region

  • Tendinopathy: Overuse from repetitive gripping or occupational strain

  • Surgical relevance: Important landmark in ulnar nerve decompression and hypothenar flap procedures

  • Imaging role: Evaluated in cases of ulnar neuropathy, hypothenar trauma, or mass lesions

MRI Appearance

  • T1-weighted images:

    • Muscle: intermediate signal intensity with visible fascicular texture

    • Tendon: low signal (dark) band extending to proximal phalanx

    • Surrounding fat: bright, defining muscle margins

    • Pathology: fatty atrophy or denervation increases overall brightness

  • T2-weighted images:

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

    • Tendon: low signal intensity

    • Pathologic changes (tendinopathy, edema): bright hyperintense signal within muscle or tendon

    • Peritendinous inflammation and fluid accumulation: bright signal around tendon sheath

  • STIR:

    • Normal muscle: intermediate-to-dark signal intensity

    • Pathology: bright hyperintense signal in edema, strain, or denervation

    • Excellent for identifying early inflammatory or ischemic changes

  • Proton Density Fat-Saturated (PD FS):

    • Normal: intermediate-to-dark, uniform muscle signal

    • Abnormal: focal bright hyperintensity indicating tendinitis or myofascial edema

    • Ideal for visualizing subtle muscle tears or peritendinous fluid

  • T1 Fat-Sat Post-Contrast:

    • Normal muscle: uniform mild enhancement

    • Tendinitis or fasciitis: diffuse or focal enhancement

    • Denervation atrophy: shows mild homogeneous enhancement with fatty replacement

CT Appearance

Non-Contrast CT:

  • Muscle: homogenous soft-tissue density lateral to the hypothenar eminence

  • Tendon: linear soft-tissue structure inserting onto proximal phalanx

  • Adjacent bones (hamate, fifth metacarpal): clearly visualized cortical landmarks

  • Pathology: chronic tendinopathy or calcific changes may show soft-tissue swelling or focal calcification

Post-Contrast CT (standard):

  • Muscle: homogenous enhancement pattern

  • Inflammatory or traumatic lesions: show focal or diffuse hyperenhancement

  • Useful in evaluating hypothenar masses, traumatic tears, or postoperative scarring

MRI image

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

MRI image

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

MRI image

Flexor Digiti Minimi Brevis Muscle (Hand) axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

MRI image

Flexor Digiti Minimi Brevis Muscle (Hand) coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00002

CT image

Flexor Digiti Minimi Brevis Muscle (Hand) ct axial image