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Triquetrum

The triquetrum (also called triquetral bone or os triquetrum) is one of the eight carpal bones in the wrist, located in the proximal row on the ulnar side. It articulates with the lunate laterally, pisiform anteriorly, and the hamate distally. Triangular in shape, it plays a key role in stabilizing the ulnar side of the carpus, transmitting load between the hand and forearm, and contributing to wrist flexion and extension mechanics.

It is often involved in carpal trauma, especially dorsal chip fractures and pisotriquetral joint injuries, due to its position and articulation with the ulnar aspect of the wrist.

Synonyms

  • Triquetral bone

  • Cuneiform bone (old term)

  • Os triquetrum

Location and Structure

The triquetrum lies on the ulnar side of the proximal carpal row, between the lunate and pisiform bones. It is the third bone from the radial side in the proximal carpal row and forms part of the wrist joint complex.

  • Shape: Pyramidal or wedge-shaped with three main articular surfaces

  • Surfaces:

    • Superior (proximal): Articulates with the ulnar articular disc (triangular fibrocartilage complex, TFCC)

    • Inferior (distal): Articulates with the hamate

    • Lateral: Articulates with the lunate

    • Anterior (palmar): Small oval facet for articulation with the pisiform

    • Posterior (dorsal): Rough for ligamentous attachment

Articulations

  • Laterally: Lunate bone

  • Medially (distally): Hamate bone

  • Anteriorly: Pisiform bone via the pisotriquetral joint

  • Superiorly: Triangular fibrocartilage complex (TFCC)

Relations

  • Dorsally: Extensor carpi ulnaris tendon passes over its posterior surface

  • Ventrally (palmar): Pisiform and ulnar nerve/artery within Guyon’s canal

  • Laterally: Lunate and intercarpal ligaments

  • Medially: Hamate bone

  • Proximally: TFCC and ulnar head

  • Distally: Interosseous ligaments connecting to hamate

Ligamentous Attachments

  • Dorsal radiocarpal ligament

  • Ulnocarpal ligaments (ulnolunate and ulnotriquetral)

  • Pisotriquetral ligament

  • Intercarpal ligaments connecting it to lunate and hamate

Function

  • Load transmission: Distributes compressive forces from the hand to the ulna via the TFCC

  • Stability: Contributes to ulnar carpal stability during wrist motion

  • Wrist motion: Participates in flexion, extension, and ulnar deviation

  • Pisotriquetral articulation: Provides gliding movement and enhances grip efficiency

  • Shock absorption: Protects ulnar carpal structures during loading

Clinical Significance

  • Triquetral fractures: Second most common carpal fracture after scaphoid; typically dorsal chip type

  • Mechanism: Fall on outstretched hand with wrist extension and ulnar deviation

  • Symptoms: Ulnar-sided wrist pain, tenderness distal to ulnar styloid

  • Associated injuries: TFCC tears, lunotriquetral ligament injury, pisotriquetral arthritis

  • Imaging role: MRI and CT crucial for detecting occult fractures and ligamentous instability

  • Surgical relevance: May require fixation in displaced fractures or debridement in chronic instability

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Marrow: Bright, due to fatty bone marrow content

    • Articular cartilage: Smooth, thin intermediate-to-low signal over articular surfaces

    • Fracture: Linear low-signal line across cortex or subchondral region with surrounding bright marrow

    • Ligaments: Low-signal linear structures adjoining carpal surfaces

  • T2-weighted images:

    • Normal bone: Intermediate-to-low signal; marrow appears bright but less than fat on T1

    • Cartilage: Intermediate-to-bright smooth line at articular margins

    • Fracture or contusion: Bright hyperintense marrow edema with cortical irregularity

    • TFCC: Low-signal triangular structure proximal to triquetrum; injury appears as hyperintense gap or irregularity

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Pathologic marrow: Bright hyperintensity in edema, contusion, or bone bruise

    • Soft-tissue swelling or ligament injury: Bright hyperintense pericarpal signal

  • Proton Density Fat-Saturated (PD FS):

    • Normal bone: Intermediate-to-dark signal with sharply defined cortex

    • Fractures or marrow edema: Bright hyperintense signal replacing normal dark pattern

    • Excellent for detecting subtle dorsal chip fractures and ligament tears

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Mild homogeneous enhancement

    • Fracture or inflammation: Peripheral or patchy enhancement around lesion

    • Osteonecrosis: Non-enhancing central region with peripheral enhancement ring

    • Synovitis or post-traumatic inflammation: Enhancing pericapsular soft tissue

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, smooth and intact in normal bone

  • Trabecular pattern: Fine honeycomb appearance

  • Fracture: Seen as a lucent cortical break or displaced fragment, especially dorsally (chip fracture)

  • Articular surfaces: Well defined; small cortical disruptions or step-offs visible in high resolution

  • Pisotriquetral joint: Clearly outlined for assessment of arthritis or incongruity

CT VRT 3D image

Triquetrum bone CT 3D VRT image -img-00000-00000

MRI image

Triquetrum axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Triquetrum coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Triquetrum sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Triquetrum ct coronal image

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Triquetrum ct sag image