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Ulnar styloid process

The ulnar styloid process is a conical bony projection from the posteromedial aspect of the distal ulna, located at the medial side of the wrist. It serves as an important attachment site for ligaments and the articular disc of the distal radioulnar joint (DRUJ), contributing to wrist stability and distal forearm biomechanics.

The styloid process is clinically significant because of its involvement in ulnar styloid fractures, TFCC (triangular fibrocartilage complex) injuries, and distal radioulnar joint instability.

Synonyms

  • Styloid process of ulna

  • Ulnar styloid projection

  • Distal ulna process

Location and Structure

  • Projects downward from the posteromedial aspect of the distal ulna.

  • Lies medial to the ulnar head and posterior to the ulnar notch of the radius.

  • Tip often palpable at the wrist’s ulnar border.

  • The base is continuous with the ulnar head, while the apex serves as a ligamentous anchor point.

Relations

  • Anteriorly: Ulnar head and articular disc (TFCC) of the distal radioulnar joint

  • Posteriorly: Extensor carpi ulnaris tendon and its sheath

  • Laterally: Ulnar notch of the radius and distal radioulnar joint

  • Medially: Ulnar collateral ligament and pisoulnar ligament

  • Inferiorly: Ulnocarpal joint capsule and TFCC attachments

Attachments

  • Apex: Gives attachment to the ulnar collateral ligament of the wrist, extending to the triquetrum and pisiform bones.

  • Base: Provides insertion for the triangular fibrocartilage complex (TFCC) and capsule of the distal radioulnar joint.

  • The TFCC fibers attach between the ulnar styloid and the sigmoid notch of the radius, stabilizing the DRUJ during pronation-supination.

Function

  • Joint stabilization: Key stabilizer of the distal radioulnar and ulnocarpal joints.

  • Ligament anchorage: Serves as attachment for the ulnar collateral ligament and TFCC, maintaining wrist alignment.

  • Load distribution: Assists in transmitting compressive and rotational forces through the TFCC during wrist motion.

  • Movement support: Enables smooth forearm pronation and supination by maintaining DRUJ integrity.

Clinical Significance

  • Fracture: Ulnar styloid fractures are common with distal radius fractures; involvement of TFCC determines instability.

  • TFCC injury: Tears at the base or apex attachment cause pain, clicking, and limited rotation.

  • DRUJ instability: Results from disruption of ligamentous or TFCC attachments.

  • Nonunion: Chronic pain may persist if ulnar styloid fractures fail to unite, especially at the base.

  • Post-traumatic arthritis: May develop in the DRUJ following fracture or instability.

  • Imaging role: MRI and CT help assess fractures, TFCC attachment integrity, and DRUJ alignment.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Bone marrow: Bright, reflecting fatty marrow content.

    • TFCC attachment: Thin low-signal band extending from styloid base.

    • Fractures: Appear as linear low-signal defects with adjacent marrow changes.

  • T2-weighted images:

    • Cortex: Low signal.

    • Marrow: Bright, slightly less than on T1.

    • TFCC: Low-signal triangular structure attaching at styloid base.

    • Edema or fracture: Focal hyperintense signal in marrow or surrounding soft tissues.

  • STIR:

    • Normal bone: Intermediate-to-dark.

    • Pathology: Bright hyperintense areas in cases of bone contusion, fracture, or TFCC tear.

    • Useful for detecting subtle marrow edema and inflammatory changes.

  • Proton Density Fat-Saturated (PD FS):

    • Normal bone and cortex: Intermediate-to-dark.

    • Fracture or inflammation: Bright hyperintense signal at styloid tip or base.

    • Excellent for visualizing TFCC attachment and peristyloid soft-tissue pathology.

  • T1 Fat-Sat Post-Contrast:

    • Normal marrow: Mild homogeneous enhancement.

    • Fracture or inflammation: Focal enhancement at fracture margins or ligament insertions.

    • Chronic fibrotic regions: Minimal or no enhancement.

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined conical projection from distal ulna.

  • Trabecular bone: Fine internal pattern; marrow cavity continuous with ulnar head.

  • Fractures: Appear as cortical breaks or displaced fragments; base fractures may indicate TFCC disruption.

  • Chronic nonunion: Marginal sclerosis or smooth corticated fragment separation.

  • Usefulness: Excellent for defining fracture configuration and pre-surgical assessment.

CT VRT 3D image

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MRI image

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MRI image

Ulnar styloid process sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Ulnar styloid process ct coronal image