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Interosseous scapholunate ligament

The interosseous scapholunate ligament (SLL) is a key intrinsic ligament of the wrist that connects the scaphoid and lunate bones. It is the primary stabilizer of the scapholunate joint, maintaining synchronous motion between the two bones during wrist movements. Injury to this ligament is the most common cause of carpal instability, leading to the well-known scapholunate dissociation pattern seen in wrist trauma.

The SLL has a C-shaped orientation and consists of three distinct parts—dorsal, proximal (membranous), and volar components—each with unique structural and biomechanical properties. The dorsal portion is the thickest and strongest, providing most of the ligament’s stability, while the proximal membranous portion is thin and avascular, and the volar part contributes to rotational stability.

Synonyms

  • Scapholunate interosseous ligament

  • SLL

  • Scapholunar ligament

Location and Structure

  • Connects the proximal articular surfaces of the scaphoid and lunate within the central carpal row.

  • Triangular or C-shaped in cross-section.

  • Thickness varies from 2 to 4 mm, with a fibrous-to-fibrocartilaginous composition.

  • The dorsal portion is collagen-rich and provides tensile strength; the membranous portion is fibrocartilaginous; and the volar portion is thinner but contributes to palmar stability.

Attachments

  • Proximal attachment: Dorsal ridge and adjacent articular surface of the scaphoid.

  • Distal attachment: Corresponding ridge on the proximal lunate.

  • Dorsal component: Blends with dorsal intercarpal and radiocarpal ligaments.

  • Volar component: Connects with volar intercarpal and radioscaphocapitate ligaments.

Relations

  • Dorsally: Dorsal intercarpal ligament and extensor tendons.

  • Ventrally: Radioscaphocapitate and long radiolunate ligaments.

  • Proximally: Radiocarpal joint capsule.

  • Distally: Midcarpal joint cavity.

  • Laterally: Scaphoid; medially: Lunate.

Function

  • Stabilization: Maintains proper alignment and motion between the scaphoid and lunate bones.

  • Load distribution: Transfers mechanical stress evenly across the proximal carpal row.

  • Kinematic coupling: Ensures synchronized flexion-extension and rotational movement of the scaphoid and lunate.

  • Prevents instability: Key structure preventing scapholunate dissociation and dorsal intercalated segment instability (DISI).

Clinical Significance

  • Injury: Common in fall-on-outstretched-hand (FOOSH) injuries, leading to scapholunate ligament tear.

  • Instability: Partial or complete tear causes scapholunate diastasis and altered carpal alignment.

  • Degeneration: Chronic attrition due to repetitive stress can lead to scapholunate advanced collapse (SLAC wrist).

  • Arthroscopy: Gold standard for grading tears (Geissler classification).

  • Surgical relevance: Repair or reconstruction of the SLL is critical in restoring wrist stability and preventing degenerative changes.

MRI Appearance

  • T1-weighted images:

    • Ligament appears as a thin, low-signal (dark) band connecting scaphoid and lunate.

    • Adjacent marrow in scaphoid and lunate shows bright signal (fatty).

    • Discontinuity or non-visualization indicates a tear.

    • Fluid between scaphoid and lunate may appear intermediate-to-bright.

  • T2-weighted images:

    • Normal ligament: dark, well-defined band.

    • Partial tear: focal hyperintensity or irregular thickening.

    • Complete tear: disruption with bright fluid-signal cleft separating scaphoid and lunate.

    • Associated bone marrow edema may show hyperintense signal in scaphoid or lunate poles.

  • STIR:

    • Normal ligament: low-to-intermediate signal.

    • Injury or inflammation: bright hyperintensity indicating edema or hemorrhage.

    • Detects subtle intercarpal fluid and ligamentous strain.

  • Proton Density Fat-Saturated (PD FS):

    • Ligament: normally low signal.

    • Partial tear: bright focal signal within the ligament substance.

    • Complete tear: high-signal defect across the scapholunate interval with fluid extending through.

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal or no enhancement.

    • Inflamed or healing ligament: focal enhancement.

    • Chronic tear: no enhancement within defect; enhancement of surrounding granulation tissue possible.

CT Appearance

Non-Contrast CT:

  • Ligament itself is not directly visualized due to soft-tissue density.

  • Indirect signs:

    • Widened scapholunate gap (>3 mm).

    • Malalignment of scaphoid and lunate (ring sign on PA view).

    • Subchondral sclerosis or cystic change in chronic cases.

  • 3D reconstructions: Show spatial relationship and carpal instability patterns.

Post-Contrast CT (Standard):

  • Rarely used; soft-tissue definition remains limited.

  • May demonstrate periligamentous enhancement or edema.

CT Arthrography Appearance

  • Normal: Contrast confined within radiocarpal and midcarpal compartments, not traversing the scapholunate interval.

  • Partial tear: Small amount of contrast seen tracking through a narrow defect in the ligament.

  • Complete tear: Free passage of contrast between radiocarpal and midcarpal joints, confirming intercompartmental communication.

  • Chronic injury: Irregular widened gap, with contrast pooling between scaphoid and lunate.

  • Advantages: Excellent for evaluating small perforations or subtle partial tears when MRI is equivocal.

MRI images

Interosseous scapholunate ligament axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Interosseous scapholunate ligament coronal mri image

MRI images

Interosseous scapholunate ligament sagittal mri image