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Head of ulna

The head of the ulna is the distal, rounded end of the ulnar bone, located at the wrist region on the medial side of the forearm. It articulates with the ulnar notch of the radius to form the distal radioulnar joint (DRUJ), and with the triangular fibrocartilage complex (TFCC) superiorly and laterally, contributing to wrist stability and smooth forearm rotation.

The ulnar head is slightly smaller than the distal radius and projects distally and posteriorly. The ulnar styloid process extends from its posteromedial aspect, serving as an important attachment site for ligaments of the TFCC and ulnar collateral complex.

It plays a crucial role in forearm pronation and supination, acting as a pivot point for the radius and maintaining stability of the distal radioulnar articulation.

Synonyms

  • Distal head of ulna

  • Ulnar head

  • Inferior end of ulna

Location and Structure

  • The head of the ulna forms the distal articular segment of the bone.

  • Articular surfaces:

    • Lateral surface: Smooth convex facet articulating with the ulnar notch of the radius (forming the DRUJ).

    • Inferior surface: Covered by fibrocartilage of the TFCC, which separates it from the wrist joint proper.

  • Styloid process: Projects distally and posteriorly from the medial aspect, providing attachment for ligaments.

  • Shape: Rounded, smaller than the radial head, and slightly offset posteriorly.

Relations

  • Anteriorly: Pronator quadratus muscle and anterior capsule of the distal radioulnar joint

  • Posteriorly: Extensor carpi ulnaris tendon within its groove

  • Laterally: Ulnar notch of the radius

  • Medially: Ulnar styloid process and ulnar collateral ligament

  • Inferiorly: Triangular fibrocartilage complex (TFCC) separating it from the triquetral region of the wrist

Attachments

  • Ligamentous attachments:

    • Articular disc (TFCC): Attaches to the base of the ulnar styloid process and to the ulnar head’s inferior margin

    • Ulnar collateral ligament: Inserts on the medial aspect of the styloid process

    • Capsule of the DRUJ: Surrounds the joint and attaches near the articular margins of the head

  • Muscular relations:

    • Pronator quadratus: Covers the anterior aspect

    • Extensor carpi ulnaris tendon: Passes posteriorly along the groove behind the ulnar head

Function

  • Forearm rotation: Serves as the pivot for pronation and supination of the radius around the ulna

  • Joint stability: Provides structural support to the distal radioulnar joint and TFCC

  • Load transmission: Assists in transferring forces between the forearm and wrist

  • Ligament attachment: Anchors the TFCC and distal ulnar ligaments for wrist stabilization

Clinical Significance

  • Fractures: Common in wrist trauma, often associated with distal radius fractures (Galeazzi or DRUJ injuries)

  • Ulnar impaction syndrome: Repetitive loading causes TFCC degeneration and ulnar head erosion

  • Arthritis: Degenerative or inflammatory involvement of the DRUJ causing pain and restricted rotation

  • TFCC tears: Lead to instability and pain on ulnar deviation

  • Ulnar variance abnormalities: Positive variance can cause impaction; negative variance associated with Kienböck’s disease

  • Imaging importance: MRI and CT are essential for evaluating subtle fractures, degenerative changes, or TFCC lesions

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Marrow: Bright (fatty marrow signal)

    • Articular cartilage and TFCC: Intermediate-to-low signal

    • Joint capsule: Low signal rim surrounding the DRUJ

    • Fractures: Linear low-signal lines crossing cortex or subchondral bone

  • T2-weighted images:

    • Cortex: Dark, sharply defined

    • Marrow: Bright, slightly less intense than T1

    • Cartilage: Intermediate to bright; irregularity suggests chondral degeneration

    • TFCC: Normally low signal; tears or inflammation appear bright

    • Effusion or synovitis: Hyperintense fluid outlining DRUJ cavity

  • STIR:

    • Normal bone marrow: Intermediate-to-dark signal

    • Pathologic marrow (edema, contusion, infection): Bright hyperintensity

    • Excellent for detecting early bone marrow edema or occult fractures

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark signal

    • Pathologic: Bright areas indicating edema, inflammation, or cystic degeneration

    • TFCC or capsular pathology: Bright hyperintensity in tears or fluid collections

  • T1 Fat-Sat Post-Contrast:

    • Normal head: Mild homogeneous enhancement

    • Synovitis or arthritis: Diffuse or marginal enhancement

    • Osteomyelitis: Patchy, irregular marrow enhancement

    • TFCC tears or inflammation: Enhancing margins and adjacent capsule

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined cortical outline

  • Trabecular bone: Fine internal pattern

  • Articular surface: Smooth convex contour, well-defined against ulnar notch

  • TFCC attachment: Seen as soft-tissue density between ulna and carpal bones

  • Pathology: Detects subtle fractures, erosions, osteophytes, cystic changes, and subchondral sclerosis

  • Ulnar variance: Easily measured on coronal or sagittal reconstructions

Post-Contrast CT (standard):

  • Enhancing capsule or soft tissue: Indicates synovitis or pericapsular inflammation

  • Erosions or irregularities: Better delineated with contrast outlining joint recesses

  • Fractures or arthritis: Enhancing pericortical changes aid differentiation of acute vs chronic lesions

CT VRT 3D image

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MRI image

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MRI image

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MRI image

Head of ulna coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Head of ulna ct coronal