Volar Scapholunate Ligament: Anatomy, Function, Imaging

Topic

Volar scapholunate ligament

The volar scapholunate ligament (SLL), also known as the palmar scapholunate ligament, is a strong fibrous band connecting the volar (palmar) aspect of the scaphoid and lunate bones. It forms part of the scapholunate interosseous ligament complex, which stabilizes the scapholunate joint and maintains proper carpal alignment during wrist motion.

The SLL has three distinct parts — dorsal, proximal (membranous), and volar — with the volar portion being thick and well-defined. Though not as strong as the dorsal component, the volar band contributes significantly to rotational stability and acts as a restraint during wrist extension and radial deviation.

Tears or attenuation of the volar SLL can lead to carpal instability, altered scaphoid motion, and eventual scapholunate advanced collapse (SLAC wrist) if left untreated.

Synonyms

Palmar scapholunate ligament
Volar band of the scapholunate interosseous ligament
Anterior scapholunate ligament

Origin and Insertion

Origin: Palmar surface of the scaphoid, near its articular margin with the lunate.
Insertion: Volar surface of the lunate, blending with the joint capsule and volar intercarpal ligaments.
The ligament lies obliquely, running proximal and medial from the scaphoid to the lunate.

Relations

Anteriorly (superficial): Wrist joint capsule and flexor carpi radialis tendon sheath
Posteriorly (deep): Radiocarpal joint cavity and cartilage surfaces of scaphoid and lunate
Laterally: Radioscaphocapitate ligament
Medially: Long radiolunate and short radiolunate ligaments
Superiorly: Palmar radiocarpal ligaments of the wrist
Inferiorly: Scapholunate joint space and proximal carpal row

Structure and Composition

Composed of dense regular collagen fibers with interspersed fibrocartilaginous tissue.
Average thickness: 2–3 mm; width approximately 5–8 mm.
Contains mechanoreceptors that provide proprioceptive feedback for wrist stability.
Works synergistically with the dorsal SLL to maintain scapholunate alignment throughout motion.

Function

Stabilization: Maintains the anatomical relationship between scaphoid and lunate.
Load transmission: Transfers compressive and shear forces across the proximal carpal row.
Motion control: Restrains excessive scaphoid flexion and lunate extension during wrist movement.
Proprioception: Provides sensory feedback to wrist joint for coordinated movement.

Clinical Significance

Tears or partial ruptures: Result in abnormal motion between scaphoid and lunate leading to scapholunate dissociation.
Instability: Chronic ligament insufficiency may lead to rotary subluxation of the scaphoid and SLAC wrist.
Injury mechanism: Commonly caused by a fall on an outstretched hand (FOOSH) with wrist extension and ulnar deviation.
Symptoms: Dorsal wrist pain, clicking, weakness, and reduced grip strength.
Imaging importance: MRI and CT are crucial for evaluating integrity, thickness, and signal alterations.

MRI Appearance

T1-weighted images:
- Normal ligament: low signal (dark) linear band between the scaphoid and lunate.
- Fat in adjacent spaces appears bright, outlining the ligament clearly.
- Partial tears: localized intermediate signal or irregular contour.
- Complete rupture: discontinuity or gap between scaphoid and lunate with adjacent fluid signal.
T2-weighted images:
- Normal ligament: low signal (dark, continuous band).
- Partial tears: focal hyperintensity within ligament fibers with maintained contour.
- Complete tear: bright fluid signal replacing ligament with gapping between bones.
- Associated findings: joint effusion, bone marrow edema, and early widening of scapholunate space.
STIR:
- Normal ligament: intermediate-to-dark signal.
- Pathology: bright hyperintense regions indicating ligament edema, hemorrhage, or synovial fluid infiltration.
- Useful for identifying acute ligament injuries and associated bone bruises.
Proton Density Fat-Saturated (PD FS):
- Normal: low to intermediate signal, sharply defined.
- Partial tear: bright focal signal within ligament substance.
- Complete tear: disruption with high-signal fluid gap between scaphoid and lunate.
- Excellent for evaluating subtle sprains and fiber irregularities.
T1 Fat-Sat Post-Contrast:
- Normal ligament: minimal to no enhancement.
- Inflammation or synovitis: peripheral or diffuse enhancement.
- Post-traumatic scar or fibrosis: variable enhancement along ligament margins.

CT Appearance

Non-Contrast CT:

Ligament itself is not directly visualized, but bone alignment provides indirect clues.
Normal: scapholunate interval < 3 mm.
Tear or chronic instability: widening of scapholunate space (“Terry Thomas sign”), scaphoid flexion, and lunate dorsiflexion.
May show secondary subchondral sclerosis or small cortical avulsions.

Post-Contrast CT (standard):

Contrast enhancement of joint capsule and periligamentous tissues may be seen in inflammation.
CT arthrography (if performed) shows contrast leakage through scapholunate space confirming ligament disruption.
Useful for preoperative assessment of carpal instability and chronic ligament insufficiency.

MRI images

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