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Triangular fibrocartilage disc

The triangular fibrocartilage articular disc is the central and deepest component of the triangular fibrocartilage complex (TFCC) of the wrist. It is a strong, fibrocartilaginous structure that separates the distal radioulnar joint (DRUJ) from the radiocarpal joint, providing cushioning, stability, and smooth articulation between the distal ulna and the carpal bones.

It is triangular in shape on coronal section, with its base attached to the ulnar notch of the radius and apex attached to the ulnar styloid process. Its superior surface articulates with the distal radius and ulna, while its inferior surface supports the lunate and triquetrum via the ulnocarpal meniscus homologue.

Synonyms

  • Articular disc of the distal radioulnar joint

  • TFCC central disc

  • Ulnocarpal meniscal disc

Location and Structure

  • Situated in the ulnar side of the wrist, between the distal end of the ulna and the carpal bones (lunate and triquetrum).

  • Shape: Triangular in coronal plane; concave proximally and slightly convex distally.

  • Composition: Dense fibrocartilage with limited vascularity (central portion avascular).

  • Thickness: Thicker peripherally, tapering centrally where degenerative perforations commonly occur.

  • Orientation: Lies horizontally between the ulnar head and carpus, blending with the joint capsule and other TFCC components.

Attachments

  • Base (radial side): Attaches to the u notch of the distal radius (sigmoid notch).

  • Apex (ulnar side): Anchors to the fovea and base of the ulnar styloid process via deep radioulnar ligaments.

  • Superior surface: Contacts the distal ulna, forming part of the DRUJ articulation.

  • Inferior surface: Contacts the triquetrum and lunate through the ulnocarpal meniscus homologue and ulnolunate ligament.

  • Peripheral margin: Fuses with the dorsal and volar radioulnar ligaments and the joint capsule.

Relations

  • Superiorly: Distal ulna head and DRUJ capsule

  • Inferiorly: Lunate, triquetrum, and ulnocarpal ligaments

  • Medially: Ulnar styloid process and ulnar collateral ligament of wrist

  • Laterally: Ulnar notch of distal radius (sigmoid notch)

  • Anteriorly: Palmar (volar) radioulnar ligament

  • Posteriorly: Dorsal radioulnar ligament

Function

  • Load transmission: Distributes axial load from the carpus to the ulna during wrist motion (transmits up to 20% of ulnar load).

  • Shock absorption: Acts as a cushion between ulna and carpal bones.

  • Joint stabilization: Maintains congruity and stability of the distal radioulnar joint.

  • Articular separation: Physically separates the DRUJ and radiocarpal joint cavities.

  • Smooth articulation: Provides a low-friction surface for pronation-supination.

Clinical Significance

  • Tears: Commonly injured during falls on an outstretched hand, repetitive pronation-supination, or ulnar deviation loading.

  • Degeneration: Central perforations occur with aging and ulnar impaction syndrome.

  • Ulnar variance correlation: Positive ulnar variance increases stress on the TFCC and predisposes to tears.

  • Symptoms: Ulnar-sided wrist pain, clicking, weakness in pronation-supination.

  • Imaging importance: MRI and MRI arthrography are gold standards for TFCC tear detection; arthroscopy remains reference standard.

  • Surgical role: Arthroscopic debridement or repair restores DRUJ stability and pain-free motion.

MRI Appearance

  • T1-weighted images:

    • Normal disc: Homogeneous low signal (dark) due to dense fibrocartilage composition.

    • Surrounding fat: Bright, enhancing contrast with the disc.

    • Tear or degeneration: Appears as intermediate or bright signal focus interrupting low-signal continuity.

  • T2-weighted images:

    • Normal disc: Low-to-intermediate signal (darker than muscle).

    • Tear or perforation: Linear or focal bright hyperintense region within the normally dark disc.

    • Fluid in perforation: Bright hyperintensity communicating with DRUJ or radiocarpal joint.

  • STIR:

    • Normal: Intermediate-to-dark signal fibrocartilage with smooth margins.

    • Pathology: Bright hyperintense regions representing edema, tear, or adjacent soft-tissue inflammation.

  • Proton Density Fat-Saturated (PD FS):

    • Normal: Homogeneous intermediate-to-dark signal triangular band.

    • Tear: Bright linear or focal hyperintense signal breaching the disc surface or extending between DRUJ and ulnocarpal joint.

    • Ideal for subtle peripheral or central perforations.

  • T1 Fat-Sat Post-Contrast:

    • Normal disc: Minimal or no enhancement.

    • Tear margins: May show mild peripheral enhancement from reactive synovitis.

    • Post-surgical repair: Enhancing soft tissue at reattachment site without central enhancement.

MRI Arthrogram Appearance

  • Technique: Intra-articular contrast injected into radiocarpal and/or DRUJ compartments.

  • Normal: Contrast remains confined to respective joint compartments; TFCC disc remains intact and non-communicating.

  • Tear or perforation: Contrast passes through the articular disc, filling both the DRUJ and radiocarpal spaces—diagnostic of a TFCC perforation.

  • Central perforation: Contrast seen in mid-disc region connecting both joint spaces.

  • Peripheral tear: Contrast extravasation along ulnar attachment or capsular margins.

  • MRI arthrography increases sensitivity for small or partial-thickness TFCC tears, especially in the avascular central zone.

CT Appearance

Non-Contrast CT:

  • Disc: Thin, low-density fibrocartilaginous structure between distal ulna and lunate/triquetrum.

  • Difficult to delineate on routine CT due to similar soft-tissue density.

  • Indirect signs: Widening of DRUJ, subchondral sclerosis, or ulnar styloid irregularity in chronic tears.

Post-Contrast CT (standard):

  • Contrast outlines joint spaces; tear indicated by communication between distal radioulnar and radiocarpal compartments.

  • Chronic degeneration: May show thinning, discontinuity, or calcification of the disc.

  • Useful in: TFCC evaluation when MRI is contraindicated or equivocal.

MRI images

Triangular Fibrocartilage Articular Disc axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Triangular Fibrocartilage Articular Disc coronal mri image

MRI images

Triangular Fibrocartilage Articular Disc sag mri image