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Proximal radioulnar joint

The proximal radioulnar joint is a synovial pivot-type joint located in the elbow region, formed between the head of the radius and the radial notch of the ulna. It functions in coordination with the distal radioulnar joint to allow pronation and supination of the forearm, enabling the radius to rotate around the ulna.

This joint is enclosed within a fibrous capsule that is continuous with that of the elbow joint and stabilized by the annular ligament, which encircles the head of the radius and holds it securely against the radial notch of the ulna.

Synonyms

  • Superior radioulnar joint

  • Upper radioulnar articulation

Location and Structure

  • Articulating surfaces:

    • Head of the radius: Cylindrical surface articulates medially with the radial notch of the ulna.

    • Radial notch of ulna: Concave surface on the lateral side of the coronoid process.

  • Joint type: Synovial pivot joint (uniaxial).

  • Capsule: Fibrous capsule continuous with the elbow joint capsule, lined by synovial membrane.

  • Ligamentous support: Primarily stabilized by the annular ligament surrounding the radial head.

Relations

  • Anteriorly: Supinator and biceps brachii tendon.

  • Posteriorly: Anconeus muscle and supinator.

  • Medially: Ulna and annular ligament.

  • Laterally: Radial collateral ligament and forearm extensor muscles.

  • Superiorly: Capitulum of the humerus and humeroradial joint.

  • Inferiorly: Continuation into the interosseous membrane connecting the radius and ulna.

Ligamentous Attachments

  • Annular ligament:

    • Strong band encircling the head of the radius, attached to the anterior and posterior margins of the radial notch of the ulna.

    • Keeps the radial head in position while allowing smooth rotation.

  • Quadrate ligament:

    • Extends from the inferior border of the radial notch of the ulna to the neck of the radius.

    • Limits excessive rotation and reinforces the capsule.

  • Interosseous membrane (proximal part):

    • Begins inferiorly from the joint and assists in transmitting load between radius and ulna.

Function

  • Forearm rotation: Permits pronation and supination by allowing the radial head to rotate within the annular ligament.

  • Stability: Provides secure articulation between radius and ulna during elbow motion.

  • Force transmission: Distributes compressive forces from the hand through the radius to the ulna and humerus.

  • Load sharing: Acts in concert with the interosseous membrane to equalize forearm stress.

Clinical Significance

  • Dislocation (Nursemaid’s elbow): Common in children; radial head slips from the annular ligament.

  • Arthritis: Degenerative or post-traumatic changes can restrict pronation and supination.

  • Fracture involvement: Radial head or coronoid process fractures may disrupt the joint and stability.

  • Synovitis: Inflammation may accompany rheumatoid or septic arthritis, leading to pain and stiffness.

  • Post-surgical evaluation: MRI and CT are vital for assessing joint alignment and ligament integrity.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark).

    • Marrow: Bright due to fatty content in radius and ulna.

    • Articular cartilage: Thin intermediate-to-low signal over radial head and notch.

    • Annular ligament: Low-signal band encircling the radial head.

    • Synovium and capsule: Thin low-signal outline; thickened in inflammation.

  • T2-weighted images:

    • Cartilage: Intermediate-to-bright, smooth contour around radial head.

    • Joint fluid: Bright hyperintense within the articular space.

    • Annular ligament: Dark linear structure encircling radial head.

    • Pathology: Effusion, edema, or synovial hypertrophy appear bright.

    • Fractures: Hypointense cortical disruptions with surrounding hyperintense marrow edema.

  • STIR:

    • Normal bone marrow: Intermediate-to-dark signal.

    • Pathologic areas: Bright hyperintensity in edema, fracture, or inflammation.

    • Useful for early detection of bone stress or capsulitis.

  • Proton Density Fat-Saturated (PD FS):

    • Normal joint: Intermediate-to-dark signal in marrow and cartilage.

    • Abnormal findings: Bright hyperintense fluid or inflammatory tissue.

    • Highlights ligament tears, joint effusion, and marrow edema.

  • T1 Fat-Sat Post-Contrast:

    • Normal: Mild enhancement of synovium.

    • Inflammation or arthritis: Diffuse synovial enhancement.

    • Postoperative or infective conditions: Patchy or irregular enhancement around capsule and annular ligament.

CT Appearance

Non-Contrast CT:

  • Bones: High-attenuation cortices, smooth articular surfaces of radius and ulna.

  • Joint space: Uniform radiolucent line between radial head and ulnar notch.

  • Ligamentous structures: Not directly seen but inferred from soft-tissue contours.

  • Pathology: Excellent for detecting fractures of the radial head, coronoid process, or subluxation.

Post-Contrast CT (standard):

  • Capsule and synovium: Enhancing in inflammatory conditions.

  • Pericapsular soft tissue: Shows enhancement in infection or postoperative inflammation.

  • Used to evaluate joint integrity, bony alignment, and post-traumatic changes.

CT VRT 3D image

Proximal radioulnar joint 3D VRT

MRI image

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

MRI image

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

CT images

Proximal radioulnar joint ct joint