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

Topic

Second dorsal interosseous of hand

The second dorsal interosseous muscle is one of four dorsal interossei located in the intermetacarpal spaces of the hand. It lies between the second and third metacarpal bones, functioning primarily to abduct the middle finger (digit III) laterally toward the radial side. Each dorsal interosseous muscle is bipennate, arising from adjacent metacarpal shafts, and inserts into the base of the proximal phalanx and the extensor expansion of its respective finger.

The second dorsal interosseous plays a crucial role in finger abduction, metacarpophalangeal (MCP) joint flexion, and interphalangeal joint extension, contributing to precision grip, balance, and fine motor control of the hand.

Synonyms

Dorsal interosseous II
Second intermetacarpal muscle
Second dorsal metacarpal muscle

Origin, Course, and Insertion

Origin: Adjacent sides of the second (index) and third (middle) metacarpal bones.
Course: The muscle fibers converge toward the dorsum of the hand, forming a tendon that passes along the radial side of the middle finger.
Insertion: Into the radial side of the base of the proximal phalanx of the middle finger, and into the extensor expansion of the same digit.

Relations

Dorsally: Dorsal fascia and extensor tendons of the middle finger.
Palmarly: Third palmar interosseous and deep palmar arch.
Laterally: First dorsal interosseous muscle.
Medially: Third dorsal interosseous muscle.
Superiorly: Overlaid by dorsal aponeurosis and skin.
Inferiorly: Lies over the dorsal interosseous fascia and intermetacarpal ligament.

Tendon Attachments

The tendon blends with the extensor expansion on the dorsum of the proximal phalanx.
The radial insertion contributes to lateral stability of the MCP joint.
Functions synergistically with the lumbricals to extend interphalangeal joints while flexing MCP joints.

Nerve Supply

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

Arterial Supply

Dorsal metacarpal arteries, arising from the dorsal carpal arch.
Additional supply from the deep palmar arch via perforating branches.

Function

Abduction: Abducts the middle finger toward the radial side.
Flexion: Assists in flexing the MCP joint of the middle finger.
Extension: Contributes to extension of both interphalangeal joints via the extensor expansion.
Stabilization: Maintains MCP joint alignment and finger coordination during fine movements.
Gripping: Assists in delicate hand actions and balance of finger motion.

Clinical Significance

Muscle weakness: Seen in ulnar nerve palsy, leading to impaired finger abduction and loss of fine control.
Atrophy: Visible flattening of the dorsal interosseous spaces in chronic neuropathies.
Injury: May occur in crush or penetrating trauma of the dorsum of the hand.
Overuse strain: Pain and swelling between second and third metacarpals in repetitive hand activities.
Imaging role: MRI is essential for evaluating muscular integrity, denervation, or traumatic injury.

MRI Appearance

T1-weighted images:
- Muscle belly: Intermediate signal intensity with well-defined fascicular architecture.
- Tendons: Low-signal (dark) linear bands inserting into proximal phalanx and extensor expansion.
- Fat planes: Bright, separating the muscle from adjacent structures.
- Atrophy or denervation: Increased intramuscular fat, appearing bright on T1.
T2-weighted images:
- Normal muscle: Intermediate-to-low signal intensity, slightly darker than on T1.
- Tendons: Low signal intensity, maintaining continuity.
- Pathology: Muscle edema or strain appears as bright hyperintense foci within or around the muscle.
- Chronic denervation: Fatty infiltration causes mild hyperintensity.
STIR:
- Normal muscle: Intermediate-to-dark signal intensity.
- Abnormal: Bright hyperintensity due to edema, inflammation, or acute denervation.
- Sensitive for detecting early myositis or trauma-related changes.
Proton Density Fat-Saturated (PD FS):
- Normal muscle: Intermediate-to-dark signal with uniform texture.
- Injury or inflammation: Bright hyperintense areas indicating edema or strain.
- Denervation: Patchy signal increase along the intermetacarpal space.
T1 Fat-Sat Post-Contrast:
- Normal muscle: Mild homogeneous enhancement.
- Inflamed or injured muscle: Focal or diffuse enhancement, depending on severity.
- Chronic fibrosis: Minimal enhancement with low-signal scar tissue.

CT Appearance

Non-Contrast CT:

Muscle appears as soft-tissue density between second and third metacarpals.
Well-defined fascial planes separate it from adjacent interossei.
Useful for detecting calcifications, hemorrhage, or foreign bodies in trauma.

Post-Contrast CT (standard):

Homogeneous muscle enhancement.
Inflamed or contused muscle: shows localized increased enhancement.
Excellent for evaluating post-traumatic or postsurgical soft-tissue changes and muscle mass lesions.

MRI image

CT image

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