Third Dorsal Interosseous Muscle of Hand: Anatomy, Function, Imaging

Topic

Third dorsal interosseous muscle of hand

The third dorsal interosseous muscle is one of the four dorsal interossei muscles located in the intermetacarpal spaces of the hand. These muscles form part of the deep layer of intrinsic hand musculature and are primarily responsible for finger abduction and assisting flexion at the metacarpophalangeal joints with extension at the interphalangeal joints.

The third dorsal interosseous muscle lies between the third and fourth metacarpal bones and abducts the middle finger laterally (toward the ring finger). It is a bipennate muscle, arising from adjacent metacarpal shafts, and contributes significantly to fine motor control and grip precision.

Synonyms

Third dorsal interosseus
Dorsal interosseous III
Third interosseous muscle of hand

Origin, Course, and Insertion

Origin: Adjacent sides of the third and fourth metacarpal bones.
Course: Fibers converge dorsally to form a slender tendon that passes toward the base of the proximal phalanx.
Insertion:
- Base of the proximal phalanx of the middle finger (digit III) on the ulnar side.
- Dorsal digital expansion (extensor hood) of the same finger.

Relations

Superficially: Dorsal metacarpal arteries and veins, dorsal fascia of the hand.
Deeply: Interosseous fascia and palmar interossei.
Medially: Fourth dorsal interosseous muscle.
Laterally: Second dorsal interosseous muscle.
Anteriorly (palmar side): Deep palmar arch and interosseous branches of the ulnar artery.
Posteriorly: Dorsal aponeurosis and extensor tendons of the fingers.

Tendon Attachments

Inserts partly into the base of the proximal phalanx and partly into the extensor expansion, allowing simultaneous metacarpophalangeal flexion and interphalangeal extension.
Blends with the lumbrical fibers contributing to complex coordinated hand movements.

Nerve Supply

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

Arterial Supply

Dorsal metacarpal arteries (from the dorsal carpal arch).
Small branches from the deep palmar arch (ulnar artery contribution).

Function

Abduction: Moves the middle finger laterally toward the ring finger.
Flexion: Assists in flexing the metacarpophalangeal joint of the middle finger.
Extension: Helps extend both interphalangeal joints through the dorsal digital expansion.
Stabilization: Maintains dynamic balance of the fingers during gripping, pinching, and precision tasks.

Clinical Significance

Ulnar nerve palsy: Weakness or paralysis of the third dorsal interosseous causes loss of finger abduction and impaired grip precision.
Atrophy: Wasting of interosseous muscles visible on the dorsum of the hand in chronic neuropathies.
Compartment syndromes: Deep palmar space infections or trauma can compress interossei, leading to pain and dysfunction.
Injury: Lacerations or deep contusions may affect tendon continuity or cause fibrosis limiting motion.
Imaging relevance: MRI helps evaluate denervation, fibrosis, or muscle atrophy in ulnar neuropathies.

MRI Appearance

T1-weighted images:
- Muscle belly: Intermediate signal intensity with clear fascicular pattern.
- Fat planes: Bright, separating adjacent interossei.
- Atrophy: Fatty replacement shows as bright intramuscular signal.
- Tendons: Low-signal linear bands inserting into the dorsal expansion.
T2-weighted images:
- Normal muscle: Intermediate-to-low signal, slightly darker than on T1.
- Tendons: Low signal (black linear structures).
- Pathology: Edema or denervation shows bright hyperintensity within muscle belly.
STIR:
- Normal muscle: Intermediate-to-dark signal intensity.
- Pathology: Bright signal indicates edema, inflammation, or early denervation changes.
Proton Density Fat-Saturated (PD FS):
- Normal: Homogeneous intermediate-to-dark signal.
- Denervation or strain: Patchy or diffuse bright signal in muscle fibers.
- Tendon injury: Focal hyperintensity or discontinuity.
T1 Fat-Sat Post-Contrast:
- Normal muscle: Mild, uniform enhancement.
- Inflamed or ischemic muscle: Focal or diffuse enhancement.
- Chronic atrophy: Minimal or no enhancement, with fatty signal predominance.

CT Appearance

Non-Contrast CT:

Muscle: Soft-tissue density between third and fourth metacarpals.
Tendons: Thin linear densities inserting dorsally into the base of the proximal phalanx.
Bony landmarks: Third and fourth metacarpals clearly outlined; intermetacarpal space visible.
Pathology: Detects calcification, fibrosis, or atrophy as decreased bulk.

Post-Contrast CT (standard):

Normal muscle: Homogeneous mild enhancement.
Inflammation or infection: Increased enhancement and soft-tissue stranding.
Chronic denervation: Decreased density, fatty infiltration, and reduced enhancement.

MRI image

CT image

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