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Radial notch of ulna

The radial notch of the ulna is a smooth, concave depression located on the lateral aspect of the coronoid process near the proximal end of the ulna. It serves as the articular surface for the head of the radius, forming the proximal radioulnar joint, which is essential for forearm pronation and supination.

The notch is covered by hyaline cartilage and bounded by the annular ligament, which encircles the radial head and secures it against the ulna during rotation. The structural congruence of the notch with the radial head provides both mobility and stability of the elbow complex, particularly during twisting and lifting actions.

Synonyms

  • Sigmoid cavity of the ulna

  • Radial articular facet of the ulna

  • Lateral ulnar notch

Location and Structure

  • Position: On the lateral side of the coronoid process at the proximal ulna, just inferior to the trochlear notch.

  • Shape: Small, oval and concave depression directed slightly anteriorly and laterally.

  • Surface: Covered by smooth hyaline cartilage, continuous with the articular surface of the ulna’s trochlear notch.

  • Borders:

    • Anterior and posterior margins: Provide attachment to the annular ligament.

    • Superior border: Continuous with the trochlear notch (humeroulnar articulation).

    • Inferior border: Merges with the shaft of the ulna below the coronoid process.

  • Articulation: With the circumference of the radial head, forming the proximal radioulnar joint.

Relations

  • Laterally: Head of the radius enclosed by the annular ligament

  • Medially: Coronoid process and ulna shaft

  • Anteriorly: Supinator muscle fibers and joint capsule of the elbow

  • Posteriorly: Anconeus muscle and posterior part of the annular ligament

  • Superiorly: Trochlear notch articulating with the trochlea of the humerus

Attachments

  • Annular ligament: Attaches to the anterior and posterior margins of the notch, holding the head of the radius in place.

  • Joint capsule: Surrounds the proximal radioulnar joint, blending with the annular ligament.

  • Interosseous membrane (proximal fibers): Arises just distal to the notch, linking radius and ulna for forearm stability.

  • Muscular relations: The supinator and anconeus muscles partially cover the area externally.

Function

  • Articulation: Forms the ulnar component of the proximal radioulnar joint, permitting rotation of the radius during pronation and supination.

  • Stabilization: Works with the annular ligament to stabilize the radial head during movement.

  • Load transmission: Helps transfer forces between radius and ulna during lifting or gripping.

  • Joint congruency: Maintains alignment between the radius and ulna, preventing dislocation.

Clinical Significance

  • Dislocation (nursemaid’s elbow): Subluxation of the radial head can involve stretching or detachment of the annular ligament from the radial notch.

  • Fracture involvement: Coronoid or proximal ulnar fractures may extend into the radial notch, disrupting the radioulnar joint.

  • Arthritis: Degenerative or post-traumatic arthritis can narrow the notch or erode its cartilage, limiting pronation-supination.

  • Congenital dysplasia: Shallow or malformed notch can cause chronic instability of the proximal radioulnar joint.

  • Imaging role: MRI and CT provide excellent evaluation of joint congruity, annular ligament integrity, and post-traumatic changes.

MRI Appearance

T1-weighted images:

  • Cortical bone: low signal (dark) outlining the notch margins.

  • Bone marrow: bright due to fatty content in adults.

  • Articular cartilage: smooth intermediate-to-low signal covering the concave surface.

  • Annular ligament: low signal band encircling the radial head.

  • Joint capsule and adjacent fat: bright contrast against darker bone.

T2-weighted images:

  • Cortical bone: dark (low signal).

  • Bone marrow: bright with slightly lower intensity than on T1.

  • Articular cartilage: intermediate-to-bright signal, best for assessing thickness and defects.

  • Joint fluid: hyperintense, outlining the proximal radioulnar joint.

  • Ligaments: low signal, continuous and smooth when intact.

STIR:

  • Normal marrow: intermediate-to-dark signal.

  • Pathologic changes (edema, fracture, inflammation): bright hyperintense signal in adjacent marrow or soft tissues.

  • Highlights subtle bone contusion or ligamentous strain.

Proton Density Fat-Saturated (PD FS):

  • Bone: intermediate-to-dark signal.

  • Cartilage and fluid: bright contrast allows delineation of joint surfaces.

  • Ligament or capsule injury: focal bright hyperintensity at attachment sites.

  • Excellent for subtle annular ligament tears or marrow edema.

T1 Fat-Sat Post-Contrast:

  • Normal notch: mild homogeneous enhancement of synovium.

  • Synovitis or inflammation: marked enhancement around the joint recesses.

  • Post-traumatic or post-surgical change: irregular enhancement in scar tissue or granulation.

CT Appearance

Non-Contrast CT:

  • Cortical bone: high attenuation, clearly outlining the notch’s smooth concave contour.

  • Articular surface: dense, uniform margin; cartilage appears as a low-density interface.

  • Useful for detecting fracture lines, subchondral sclerosis, or osteophytes.

  • Provides precise visualization of joint congruity with the radial head.

Post-Contrast CT (standard):

  • Articular cartilage and joint capsule better delineated with contrast in joint space.

  • Detects subtle inflammatory or erosive changes at the proximal radioulnar articulation.

  • Helpful for evaluating post-traumatic deformities or arthritic remodeling.

CT VRT 3D image

Radial notch of ulna 3d image

MRI image

Radial notch of ulna axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

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

CT image

Radial notch of ulna ct image