Topics

Topic

design image
Distal radioulnar joint

The distal radioulnar joint (DRUJ) is a pivot-type synovial joint between the head of the ulna and the ulnar notch of the radius. It allows the radius to rotate around the ulna during pronation and supination of the forearm, maintaining wrist and hand positioning. This joint, along with the proximal radioulnar joint, enables the unique rotational movement of the forearm.

The DRUJ is stabilized by the triangular fibrocartilage complex (TFCC), which provides structural support, transmits load from the hand to the forearm, and maintains congruity between the distal radius and ulna.

Synonyms

  • Inferior radioulnar joint

  • DRUJ (Distal radio-ulnar joint)

  • Radioulnar articulation (distal)

Location and Structure

  • Articulating surfaces:

    • Head of ulna: convex surface.

    • Ulnar notch of radius: concave surface on the medial distal end of the radius.

  • Type of joint: Synovial pivot joint (uniaxial).

  • Articular disc (TFCC): Triangular fibrocartilage attaches from the ulnar notch of the radius to the base of the ulnar styloid, separating the joint cavity from the wrist joint.

  • Joint capsule: Thin and loose, permitting rotation; reinforced anteriorly and posteriorly by small radioulnar ligaments.

  • Synovial membrane: Lines the capsule and encloses a small amount of synovial fluid.

Relations

  • Anteriorly: Pronator quadratus muscle.

  • Posteriorly: Extensor digiti minimi and extensor carpi ulnaris tendons.

  • Laterally: Distal radius.

  • Medially: Ulnar styloid process and TFCC.

  • Superiorly: Shaft of ulna and radius.

  • Inferiorly: Ulnocarpal joint and wrist capsule.

Ligamentous Attachments

  • Palmar radioulnar ligament: Strengthens the anterior capsule; tight in supination.

  • Dorsal radioulnar ligament: Reinforces the posterior capsule; tight in pronation.

  • Articular disc (TFCC): Principal stabilizer of DRUJ, preventing separation of radius and ulna.

  • Interosseous membrane (distal fibers): Provides additional stability during rotation.

Function

  • Pronation and supination: Allows the radius to pivot around the ulna, enabling rotational forearm movement.

  • Load transmission: TFCC distributes axial load from the wrist to the forearm bones.

  • Joint stability: Maintains alignment of the radius and ulna during wrist motion.

  • Shock absorption: The TFCC cushions and stabilizes during compressive and rotational forces.

Clinical Significance

  • Instability: Results from TFCC tears or ligamentous disruption, leading to abnormal ulnar translation.

  • Arthritis: Common in chronic instability or post-fracture conditions.

  • Fractures: Distal radius or ulnar styloid fractures often affect DRUJ congruency.

  • Dislocation: May occur independently or with Galeazzi fracture-dislocations.

  • Pain syndromes: Ulnar-sided wrist pain often indicates TFCC pathology or degenerative DRUJ changes.

  • Imaging relevance: MRI and CT provide superior evaluation of alignment, TFCC integrity, and degenerative changes.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark).

    • Bone marrow: Bright signal (fatty content in distal radius and ulna).

    • TFCC: Homogeneous low signal, thin triangular structure between ulna and carpus.

    • Ligaments: Low signal bands anteriorly and posteriorly.

    • Pathology: TFCC tears show focal intermediate-to-bright signal within low-signal structure.

  • T2-weighted images:

    • Bone cortex: Low signal.

    • Marrow: Bright, slightly less intense than on T1.

    • TFCC: Normally dark; high-signal linear defects suggest tear or degeneration.

    • Joint fluid: Bright hyperintense outlining the ulnar head and notch.

    • Inflammation or synovitis: Hyperintense pericapsular signal and joint effusion.

  • STIR:

    • Normal marrow and TFCC: Intermediate-to-dark signal.

    • Edema, inflammation, or TFCC injury: Bright hyperintense areas within or adjacent to the TFCC or capsule.

    • Useful for detecting early soft-tissue edema or bone contusion.

  • Proton Density Fat-Saturated (PD FS):

    • Normal TFCC and ligaments: Uniformly dark low signal.

    • Tears or degeneration: Bright linear or focal signal in TFCC or surrounding capsule.

    • Highlights small joint effusions and soft-tissue injury.

  • T1 Fat-Sat Post-Contrast:

    • Normal capsule and TFCC: Minimal enhancement.

    • Inflamed synovium or capsule: Diffuse enhancement.

    • Chronic degeneration: Peripheral rim enhancement; active synovitis or tear: focal bright enhancement.

CT Appearance

Non-Contrast CT:

  • Cortical margins: Sharp, high attenuation outlining distal radius and ulna.

  • Joint space: Clearly defined; narrow in degenerative or arthritic changes.

  • TFCC: Not directly visualized, but indirect signs include joint space asymmetry or subchondral sclerosis.

  • Pathology: Detects fractures, subluxation, osteophytes, and articular incongruity with high spatial resolution.

CT VRT 3D image

Distal radioulnar joint CT 3D VRT image -img-00000-00000

MRI image

Distal radioulnar joint axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Distal radioulnar joint coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Distal radioulnar joint ct image