Long Radiolunate Ligament: Anatomy, Function, Imaging

Topic

Long radiolunate ligament

The long radiolunate ligament, also known as the radiolunotriquetral ligament, is a major component of the volar (palmar) radiocarpal ligament complex of the wrist. It provides stability between the distal radius and proximal carpal row, particularly supporting the lunate and triquetrum.

It plays a crucial role in maintaining normal wrist biomechanics by limiting excessive dorsiflexion and ulnar translation of the carpus. Damage to this ligament can lead to carpal instability, lunate subluxation, or volar intercalated segment instability (VISI).

Synonyms

Radiolunotriquetral ligament
Long volar radiocarpal ligament
Long radiocarpal ligament (volar portion)

Origin, Course, and Insertion

Origin: Arises from the anterior (palmar) margin of the distal radius, just medial to the long radiocapitate ligament.
Course: Passes obliquely distomedially across the volar aspect of the radiocarpal joint.
Insertion:
- Primary attachment: Palmar surface of the lunate.
- Secondary attachment: Extends medially to insert on the palmar surface of the triquetrum, hence the name radiolunotriquetral.

Relations

Anteriorly: Overlapped by the flexor tendons and the flexor retinaculum.
Posteriorly: In contact with the joint capsule of the radiocarpal joint.
Laterally: Adjacent to the long radiocapitate ligament.
Medially: Continuous with the short radiolunate and ulnolunate ligaments.
Superiorly: Related to the distal radius palmar rim.
Inferiorly: Overlying the palmar surface of the lunate and triquetrum.

Structure

Flat, fibrous band of dense collagen fibers forming part of the volar radiocarpal complex.
Lies deep to the flexor tendons and contributes to the palmar capsule of the wrist.
Blends distally with the palmar intercarpal ligament and ulnocarpal ligaments, forming a continuous volar support sheet.

Function

Stabilization: Maintains congruence between the radius, lunate, and triquetrum during wrist motion.
Motion limitation: Restrains excessive wrist dorsiflexion and ulnar deviation.
Load transmission: Transfers axial loads from the hand to the radius through the proximal carpal row.
Carpal alignment: Prevents volar subluxation of the lunate and triquetrum.
Proprioception: Contains mechanoreceptors that contribute to wrist position sense and reflex control.

Clinical Significance

Ligament injury: May occur in hyperextension or rotational wrist trauma, leading to partial or complete tear.
Volar carpal instability: Injury may result in VISI deformity (volar flexion of lunate, extension of scaphoid).
Degeneration: Chronic strain or degenerative changes contribute to carpal instability in rheumatoid arthritis or repetitive stress.
Associated injuries: Often coexists with tears of the short radiolunate or lunotriquetral interosseous ligament.
Surgical importance: Serves as a landmark during volar wrist arthroscopy and ligament reconstruction procedures.

MRI Appearance

T1-weighted images:
- Normal ligament: low signal intensity (dark band) connecting the distal radius to lunate and triquetrum.
- Surrounded by bright periligamentous fat, enhancing visualization.
- Partial tear: focal thinning or discontinuity with intermediate intraligamentous signal.
T2-weighted images:
- Normal ligament: low to intermediate signal, continuous smooth contour.
- Acute tear: focal bright hyperintense signal indicating fiber disruption or edema.
- Chronic injury: irregular contour with mixed intermediate signal from fibrosis.
STIR:
- Normal ligament: dark to intermediate signal.
- Pathology: bright hyperintense signal due to edema or hemorrhage in acute injury.
- Sensitive for detecting subtle partial tears and periligamentous fluid.
Proton Density Fat-Saturated (PD FS):
- Normal: dark, well-defined band from radius to lunate and triquetrum.
- Partial tears: focal bright signal within ligament fibers.
- Complete rupture: discontinuity with adjacent joint fluid extending into defect.
T1 Fat-Sat Post-Contrast:
- Normal: minimal enhancement of ligament.
- Inflamed or torn ligament: linear or patchy enhancement along fiber course.
- Chronic scarring or fibrosis: minimal peripheral enhancement with central low signal.

CT Appearance

Non-Contrast CT:

Ligament not directly visualized due to soft-tissue density.
May show indirect findings such as widening of radiolunate or lunotriquetral spaces in ligamentous injury.
Chronic degeneration: subchondral sclerosis or cystic changes in lunate or triquetrum surfaces.

Post-Contrast CT (standard):

Enhancing soft tissue may outline periligamentous regions in inflammatory or traumatic conditions.
CT arthrography: clearly demonstrates leakage of contrast through torn ligament fibers, outlining communication between radiocarpal and midcarpal joints.
Useful in evaluating partial-thickness tears, carpal instability, and degenerative defects when MRI is contraindicated.

MRI images

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