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Humeroradial joint

The humeroradial joint is the articulation between the capitulum of the humerus and the head of the radius. It forms one of the three components of the elbow joint complex (along with the humeroulnar and proximal radioulnar joints). This articulation allows both flexion–extension and rotation (pronation–supination) of the forearm, functioning as a combined hinge and pivot joint.

The joint’s stability depends primarily on the surrounding capsule, collateral ligaments, and annular ligament, which bind the radial head to the ulna and humerus. The smooth curvature of the capitulum and concavity of the radial head permit efficient motion while transmitting forces between the hand and arm during weight-bearing or lifting.

Synonyms

  • Capitulum–radial head articulation

  • Lateral component of the elbow joint

  • Radiohumeral joint

Location and Structure

  • Type: Synovial joint with both hinge (ginglymus) and pivot (trochoid) characteristics

  • Articulating surfaces:

    • Capitulum of humerus: Rounded convex surface on the distal lateral humerus

    • Superior articular surface of radial head: Concave fovea articulating with capitulum

  • Joint capsule: Encloses the joint completely, continuous with the humeroulnar and proximal radioulnar joint capsules

  • Articular cartilage: Hyaline cartilage covers both the capitulum and radial head, providing a smooth, low-friction interface

  • Joint cavity: Shared with the elbow joint complex, containing synovial fluid for lubrication

Relations

  • Anteriorly: Brachialis and biceps brachii tendon

  • Posteriorly: Anconeus muscle and the lateral aspect of the olecranon

  • Laterally: Lateral collateral ligament complex and extensor muscles of forearm

  • Medially: Proximal radioulnar joint and annular ligament

  • Superiorly: Capitulum of humerus

  • Inferiorly: Neck of radius and proximal forearm flexors

Ligamentous Attachments

  • Annular ligament: Encircles the radial head, holding it against the radial notch of the ulna and stabilizing the pivot movement

  • Radial collateral ligament (RCL): Extends from lateral epicondyle of humerus to annular ligament; resists varus stress

  • Joint capsule: Encloses humeroradial and humeroulnar joints, strengthened laterally by RCL and medially by ulnar collateral ligament

  • Lateral ulnar collateral ligament: Supports posterolateral stability of the joint

Function

  • Flexion and extension: Occurs primarily between the capitulum and radial head along with the humeroulnar joint

  • Pronation and supination: Radial head rotates within annular ligament against the capitulum

  • Force transmission: Transfers load from hand and wrist to humerus during gripping or pushing

  • Stability contribution: Acts as secondary stabilizer of the elbow against valgus and rotational stress

Clinical Significance

  • Dislocations and subluxations: Common in children (“nursemaid’s elbow”) due to annular ligament displacement

  • Fractures: Radial head and capitellar fractures frequently involve this articulation

  • Degenerative arthritis: May occur in chronic overuse or post-traumatic conditions

  • Loose bodies or synovial impingement: Cause mechanical block or locking

  • Imaging importance: MRI and CT essential for assessing articular cartilage, ligament integrity, and subtle fractures

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark)

    • Bone marrow: Bright due to fatty content

    • Articular cartilage: Smooth intermediate-to-low signal layer on capitulum and radial head

    • Joint capsule: Thin low-signal band outlining the articulation

    • Pathology: Fractures appear as linear low-signal lines; bone marrow edema as intermediate-to-bright areas

  • T2-weighted images:

    • Cortex: Low signal

    • Marrow: Bright, slightly less intense than on T1

    • Cartilage: Intermediate-to-bright; surface irregularities indicate chondral wear

    • Joint fluid: Hyperintense signal within joint recesses

    • Pathology: Effusion, osteochondral lesions, or synovitis appear bright; subchondral cysts show hyperintensity

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Pathologic marrow: Bright hyperintensity in edema, inflammation, or fracture

    • Sensitive for early osteochondral injury or bone contusion

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark

    • Cartilage: Intermediate with clear margins

    • Pathology: Bright hyperintense regions indicating cartilage defects, synovial thickening, or small joint effusion

    • Ideal for detecting ligament injuries and bone bruises

  • T1 Fat-Sat Post-Contrast:

    • Normal joint: Mild homogeneous synovial enhancement

    • Synovitis or arthritis: Diffuse or focal enhancement of synovium

    • Osteochondral defect: Peripheral enhancement around low-signal defect

    • Infection: Intense enhancement of synovium and pericapsular soft tissues

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with sharply defined margins

  • Articular surfaces: Smooth, convex capitulum and concave radial head clearly delineated

  • Joint space: Uniform; visible as a thin hypodense line

  • Pathology:

    • Excellent for detecting radial head and capitellar fractures, small intra-articular fragments, or osteophytes

    • Evaluates joint congruity and post-traumatic deformity

Post-Contrast CT (standard):

  • Cartilage and synovium: Enhancement around inflammatory or degenerative lesions

  • Periarticular tissues: Enhanced in synovitis or infection

  • Useful for identifying joint effusion, subtle erosions, and postoperative complications

CT VRT 3D image

Humeroradial joint 3d vrt image

MRI image

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

MRI image

Humeroradial joint sag cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

CT images

Humeroradial Joint ct image