Triangular Fibrocartilage Complex (TFCC)

Components

Central Structures

Triangular fibrocartilage (TFC)

• A biconcave fibrocartilaginous disc
• Lies between the distal ulna and proximal carpal row
• Poorly vascularised centrally — predisposes to degenerative tears

Dorsal and volar radioulnar ligaments

• Attach the radius to the ulna
• Primary stabilisers of the DRUJ
• Taut in pronation (dorsal) and supination (volar)

Peripheral Structures

Meniscus homologue

• Connects the TFC to the triquetrum and ulnar styloid
• Fibrocartilaginous tissue with meniscus-like morphology
• Variable thickness and size
• Important in load transmission to the ulnar carpus

Ulnolunate and ulnotriquetral ligaments

• Extend from the ulnar fovea to the respective carpal bones
• Secondary stabilisers
• More prominent in ulnar deviation

Extensor carpi ulnaris (ECU) subsheath

• Fibrous sheath deep to the ECU tendon
• Stabilises the tendon within the ulnar groove
• Considered part of the TFCC by some authors
• Rupture may contribute to DRUJ instability

Ulnar collateral ligament

• Spans the ulnar styloid to the pisiform and triquetrum
• Prevents radial deviation
• Often confluent with the capsule

Attachments

• Radial attachment: sigmoid notch of the distal radius
• Ulnar attachment: ulnar styloid and ulnar fovea via the ligamentum subcruentum
• Distal attachments: blend with joint capsule and ulnocarpal ligaments

Function

• Stabilises the DRUJ during pronation and supination
• Distributes axial load between the ulnar head and carpus
• Provides a smooth articulating surface for rotation
• Enhances congruity of the ulnar wrist

Vascular Supply

• Peripheral 15–20% is vascularised via branches of the ulnar artery and anterior interosseous artery
• Central portion is avascular — poor healing potential
• Vascular penetration is best appreciated on histological analysis and gadolinium-enhanced MRI

Imaging

MRI

• Best seen on coronal T2 or PD FS sequences
• Normal TFC: low signal, bowtie appearance
• Peripheral ligaments best seen in oblique coronal or axial planes
• Intrinsic tears: high signal cleft, irregularity, or discontinuity
• Degenerative tears may present with thinning and fraying
• Must assess for associated DRUJ effusion or synovitis

MR Arthrography

• Superior to conventional MRI for detecting perforations
• Contrast entering the DRUJ from the radiocarpal compartment suggests full-thickness tear
• Allows assessment of peripheral attachments and communicating defects

Variants

Thinning or absence of the central TFC

• Can be normal in elderly patients
• Must be distinguished from a degenerative tear

Ulnar variance effects

• Positive ulnar variance: increased axial load on the TFCC → predisposes to tears
• Negative ulnar variance: decreased load transmission, but altered ligament tension

Meniscus homologue variations

• May mimic a mass or ganglion
• Shape and signal can vary widely

Clinical Correlates

TFCC Tear (Palmer Classification)

• Type 1 (traumatic)
  • IA: central perforation
  • IB: ulnar-sided detachment
  • IC: disruption of ulnocarpal ligaments
  • ID: radial attachment tear
• Type 2 (degenerative)
  • IIA: central wear
  • IIB: central wear + lunate chondromalacia
  • IIC: + TFCC perforation
  • IID: + ulnocarpal ligament perforation
  • IIE: + DRUJ instability

DRUJ Instability

• May result from complete tears of the dorsal and volar radioulnar ligaments
• Often coexists with ECU subsheath disruption
• Clinically presents with ulnar-sided wrist pain, clicking, and loss of grip strength

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Overview

The triangular fibrocartilage complex is a load-bearing structure between the lunate, triquetrum and ulnar head, which functions to stabilise the ulnar aspect of the wrist. It has an elongated shape with apex pointed towards the radius.

Structures

The triangular fibrocartilage complex consists of:

• Triangular fibrocartilage disc – an articular disc that lies on the distal pole of the ulnar. It has a triangular shape and biconcave body which thickens at the periphery.
• Extensor carpi ulnaris tendon subsheath
• Ulnocarpal ligaments
  • Ulnotriquetral, ulnocapitate and ulnolunate ligaments – originate from the ulnar styloid and insert on to respective bones, preventing dorsal migration of the distal ulnar
• Radiounlar ligaments
  • Dorsal and volar distal radioulnar ligaments – principal stabilisers of the distal radioulnar joint. Originates from the distal radius medial border and insert on the ulnar at the styloid and at the fovea.
• Meniscal homolog
• Ulnocarpal collateral ligament