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Coronoid fossa

The coronoid fossa is a shallow depression located on the anterior surface of the distal humerus, just above the trochlea. It receives the coronoid process of the ulna during elbow flexion, allowing smooth articulation between the humerus and ulna. The fossa forms an important part of the elbow joint complex, accommodating the ulna and enabling full flexion without impingement.

It is one of three fossae on the distal humerus — the others being the radial fossa (laterally) and the olecranon fossa (posteriorly). The coronoid fossa lies anterior and medially, directly above the trochlea, and is separated from the olecranon fossa by a thin bony septum that may be perforated in some individuals (known as a supratrochlear foramen).

Synonyms

  • Anterior humeral fossa

  • Fossa for coronoid process of ulna

Location and Structure

  • Situated on the anterior aspect of the distal humerus, immediately superior to the trochlea

  • Shape: Triangular to oval depression with a smooth cortical surface

  • Depth: Approximately 6–8 mm in adults

  • Function: Receives the coronoid process of the ulna during elbow flexion

  • Composition: Cortical bone forming part of the humeral trochlear surface complex

Relations

  • Superiorly: Shaft of the humerus

  • Inferiorly: Trochlea of the humerus

  • Laterally: Radial fossa and capitulum

  • Medially: Medial epicondyle of the humerus

  • Posteriorly: Thin bony septum separating it from the olecranon fossa

  • Anteriorly: Brachialis muscle and elbow joint capsule

Attachments

  • The joint capsule of the elbow attaches along the rim of the fossa

  • Brachialis muscle fibers lie anterior to it, cushioning the joint during flexion

  • Provides bony accommodation for the coronoid process of the ulna to prevent impingement in full flexion

Function

  • Accommodative role: Receives the coronoid process of the ulna during elbow flexion, allowing complete range of motion

  • Joint stability: Prevents anterior displacement of the ulna during movement

  • Anatomical alignment: Ensures congruence between humerus and ulna within the elbow hinge mechanism

  • Protective function: Minimizes bony contact during dynamic movement, reducing wear at the trochlear surface

Clinical Significance

  • Fractures: Commonly involved in distal humeral fractures or intra-articular injuries extending into the trochlea

  • Osteophyte formation: May occur with chronic degenerative changes or post-traumatic arthritis, limiting elbow flexion

  • Supratrochlear foramen: Thin or perforated septum may appear as a foramen on radiographs; a normal anatomical variant

  • Elbow dislocation: Anterior translation of the ulna can impinge or deform the fossa region

  • Surgical relevance: Landmark during open reduction and internal fixation (ORIF) of distal humerus fractures

  • Imaging relevance: Critical in assessing distal humeral fractures, cartilage wear, and joint alignment

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark) with a smooth contour forming the anterior distal humeral surface

    • Bone marrow: Bright fatty signal within the distal humerus

    • Fossa cavity: Appears as a shallow low-signal depression above the trochlea

    • Pathology: Fractures or cortical defects appear as linear low-signal interruptions

  • T2-weighted images:

    • Cortex: Low signal intensity

    • Marrow: Bright, slightly less than on T1

    • Fossa: Low signal void due to cortical boundary; effusion or synovial thickening appears bright within joint recesses

    • Pathology: Fracture lines or cortical irregularities visible as low-signal lines with adjacent bright marrow edema

  • STIR:

    • Normal bone: Intermediate-to-dark signal intensity

    • Marrow edema, inflammation, or fracture: Bright hyperintense signal

    • Useful for: Early detection of bone stress, contusion, or occult fracture at the distal humerus

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark signal

    • Abnormal areas: Bright hyperintensity in edema, inflammation, or subchondral injury

    • Cartilage and joint recess: Seen as thin bright lines or focal fluid pockets during effusion

  • T1 Fat-Sat Post-Contrast:

    • Normal marrow: Uniform mild enhancement

    • Fracture or inflammation: Focal or patchy enhancement at cortical disruption or bone interface

    • Synovitis: Diffuse enhancement in anterior joint recess extending near the coronoid fossa

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined outline of the anterior distal humerus

  • Fossa: Appears as a shallow concavity above the trochlea

  • Trabecular bone: Fine honeycomb structure within humeral metaphysis

  • Pathology: Excellent for detecting subtle fractures, cortical thinning, osteophytes, or deformities

  • Supratrochlear foramen: Appears as a small, well-corticated lucent channel in thin septum between fossae

Post-Contrast CT (standard):

  • Bone enhancement: Mild homogeneous increase in attenuation of marrow

  • Periosteal or soft-tissue enhancement: Indicates inflammation, trauma, or adjacent synovitis

  • Joint evaluation: Enhances detection of intra-articular extension of fractures or effusion within elbow capsule

CT VRT 3D image

Coronoid fossa 3D VRT IMAGE

MRI image

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

MRI image

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

CT image

Coronoid fossa saf ct image