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Coronoid process of ulna

The coronoid process of the ulna is a prominent, triangular bony projection extending anteriorly from the proximal end of the ulna. It forms the anterior portion of the trochlear notch, contributing significantly to the stability and articulation of the elbow joint. The process prevents posterior dislocation of the ulna during flexion and provides attachment for important muscles and ligaments of the forearm.

It articulates with the trochlea of the humerus and provides an anchor for the brachialis muscle and the anterior capsule of the elbow joint. The ulnar tuberosity lies just distal to its base, serving as an additional muscular attachment site.

Synonyms

  • Anterior process of the ulna

  • Ulnar coronoid projection

Location and Structure

  • The coronoid process projects anteriorly and slightly upward from the proximal ulna, forming the lower boundary of the trochlear notch.

  • The superior surface contributes to the trochlear notch articulation with the humeral trochlea.

  • The anterior surface is smooth and provides attachment for the brachialis muscle.

  • The base is continuous with the shaft of the ulna, and its apex lies near the radial notch.

  • The medial surface gives attachment to the ulnar collateral ligament (anterior band).

  • The lateral surface forms the radial notch, articulating with the head of the radius.

Attachments

  • Brachialis muscle: Inserts into the anterior surface of the coronoid process and adjacent ulnar tuberosity.

  • Joint capsule: The anterior capsule of the elbow attaches to its anterior margin.

  • Ulnar collateral ligament: The anterior band attaches to the medial margin of the process.

  • Flexor digitorum superficialis: Some fibers originate from the medial border of the coronoid process.

Relations

  • Superiorly: Trochlear notch and trochlea of the humerus

  • Inferiorly: Ulnar tuberosity

  • Medially: Ulnar collateral ligament and flexor-pronator muscle mass

  • Laterally: Radial notch and radial head

  • Anteriorly: Brachialis tendon and deep fascia of forearm

  • Posteriorly: Olecranon process forming the posterior wall of trochlear notch

Function

  • Joint stability: Prevents posterior displacement of the ulna during elbow flexion

  • Muscular anchorage: Provides insertion for the brachialis muscle, contributing to elbow flexion strength

  • Ligamentous support: Attachment site for anterior joint capsule and collateral ligaments maintaining ulnohumeral congruency

  • Articulation: Completes the trochlear notch, forming a hinge-type joint with the humeral trochlea

  • Load transmission: Transfers compressive forces from the humerus to the ulna during arm movements

Clinical Significance

  • Coronoid fractures: Commonly associated with posterior elbow dislocations or radial head fractures (terrible triad injury)

  • Avulsion injuries: May occur at brachialis or ligament attachment sites

  • Fracture classification: Regan and Morrey classification—based on size of fragment (Type I–III)

  • Post-traumatic instability: Loss of coronoid height leads to recurrent posterior subluxation or dislocation

  • Arthritis and impingement: Osteophyte formation may limit elbow flexion or cause anterior impingement

  • Surgical importance: Accurate reconstruction essential for restoring elbow stability and preventing chronic instability

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Marrow: Bright, reflecting fatty marrow in adults

    • Brachialis insertion: Appears as low-signal tendon attaching to the anterior cortex

    • Capsular attachment: Low-signal band on anterior surface

    • Fractures: Linear low-signal lines crossing cortex or subchondral bone; marrow edema appears intermediate to bright

  • T2-weighted images:

    • Cortex: Dark, sharply defined

    • Marrow: Bright, slightly less than T1

    • Cartilage (at articulation): Intermediate to bright, smooth in normal state

    • Fracture or edema: Bright hyperintense regions adjacent to low-signal cortex

    • Ligamentous attachments: Low-signal structures overlying medial and anterior margins

  • STIR:

    • Normal marrow: Intermediate to dark

    • Pathology: Bright hyperintense signal in marrow or surrounding soft tissue due to edema, inflammation, or hematoma

    • Useful for identifying early stress or occult fractures

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate to dark

    • Fracture, contusion, or inflammation: Bright hyperintense signal in cortical or subcortical bone

    • Highlights soft-tissue edema, joint effusion, or periosteal reaction

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Uniform mild enhancement of marrow and periosteum

    • Fracture or osteitis: Peripheral enhancement with central marrow hyperemia

    • Post-surgical changes: Linear enhancement at repair sites or callus formation

    • Synovial inflammation: Diffuse enhancement of anterior capsule or adjacent soft tissues

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with sharp definition of anterior projection

  • Trabecular bone: Fine, regular pattern within the coronoid process

  • Fractures: Visualized as cortical disruption or displaced fragments

  • Chronic changes: Osteophytes, sclerosis, or flattening in impingement or arthritis

  • Useful for: Evaluating coronoid fracture morphology, joint congruity, and small avulsion fragments

Post-Contrast CT (standard):

  • Bone: Uniform enhancement pattern of trabecular marrow

  • Soft tissue: Enhancement around capsule or fracture site indicates inflammation or post-traumatic healing

  • Helpful in differentiating postoperative scar, infection, or heterotopic ossification around the elbow

CT VRT 3D image

Coronoid process of ulna 3D VRT IMAGE

MRI image

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

MRI image

Coronoid process of ulna sag cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

CT image

Coronoid process of ulna ct sag image