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Interosseous lateral band

The interosseous lateral band is one of the key components of the extensor mechanism of the finger. It is formed by fibers from the palmar and dorsal interosseous muscles and merges with contributions from the lumbrical tendons and the extensor hood.

The lateral bands run obliquely along the radial and ulnar sides of each finger, extending dorsally to unite with the central slip and ultimately inserting into the dorsal base of the distal phalanx as part of the terminal extensor tendon. They act as critical stabilizers during finger extension, transmitting force from intrinsic and extrinsic muscles to extend the PIP and DIP joints.

Synonyms

  • Lateral slips of the extensor mechanism

  • Interosseous lateral slips

  • Lateral extensions of extensor hood

Location and Structure

  • Located on both sides of the finger, running from the proximal phalanx to the dorsal distal phalanx.

  • Formed from fibers of:

    • Palmar interosseous muscles

    • Dorsal interosseous muscles

    • Lumbrical tendons

    • Transverse fibers of extensor hood

  • Unite dorsally near the middle phalanx and continue distally as part of the terminal extensor tendon.

  • Positioned superficial to collateral ligaments and deep to the skin and dorsal fascia.

Relations

  • Dorsally: Central slip of extensor digitorum tendon

  • Volar: PIP joint capsule, collateral ligaments, and flexor tendon sheath

  • Laterally: Skin and dorsal digital fascia

  • Proximally: Extensor hood at MCP joint

  • Distally: Terminal extensor tendon and base of distal phalanx

Attachments

  • Origin fibers: From interosseous muscles and lumbricals at level of proximal phalanx

  • Course: Runs along the sides of the proximal and middle phalanges

  • Insertion: Contributes to the terminal tendon inserting on the dorsal base of distal phalanx

Function

  • Transmits intrinsic muscle force to extend PIP and DIP joints

  • Stabilizes the extensor mechanism during flexion and extension

  • Balances radial and ulnar forces to prevent lateral deviation

  • Helps coordinate simultaneous extension of MCP, PIP, and DIP joints

Clinical Significance

  • Boutonnière deformity: Lateral bands slip volar to the PIP joint

  • Swan-neck deformity: Hyperextension of PIP with increased lateral band tension

  • Lateral band rupture or subluxation: Leads to extensor lag

  • Trauma or rheumatoid disease: May disrupt the extensor mechanism

  • Imaging relevance: Essential in evaluating extensor hood injuries, tendon imbalance, and deformities

MRI Appearance

T1-weighted images:

  • Lateral band appears as a thin, low-signal (dark) linear structure along the radial and ulnar finger margins

  • Surrounding fat: bright, aiding visualization

  • Central slip and terminal tendon: same low-signal intensity

T2-weighted images:

  • Normal lateral bands remain low signal, though slightly more distinct against brighter joint fluid or soft tissue

  • Collateral ligaments and extensor hood structures show similar low-signal linear patterns

STIR:

  • Lateral band maintains dark to intermediate signal, consistent with fibrous tendon

  • Fat suppression creates clearer contrast with adjacent tissues

  • Normal band remains sharply defined

T1 Fat-Saturated Post-Contrast:

  • Normal lateral band shows minimal to no enhancement

  • Peritendinous soft tissues demonstrate smooth mild enhancement

  • Extensor hood fibers identifiable as non-enhancing linear structures

CT Appearance

Non-Contrast CT:

  • Lateral band is not directly visualized due to small size and soft-tissue density

MRI image

Interosseous lateral band hand MRI axial image-img-00000-00000