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Medial collateral ligament of elbow (transverse bundle)

The medial collateral ligament (MCL) of the elbow, also called the ulnar collateral ligament (UCL), is a key stabilizer of the elbow joint. It comprises three parts: anterior, posterior, and transverse bundles.
The transverse bundle (also known as the Cooper’s ligament) is the smallest and least functionally significant of the three. It spans between the olecranon and the coronoid process of the ulna, lying deep to the anterior and posterior bundles.

While it does not contribute significantly to valgus stability, the transverse bundle forms a supportive floor for the ulnohumeral joint capsule, completing the medial ligamentous complex and reinforcing the medial elbow wall.

Synonyms

  • Cooper’s ligament

  • Transverse ulnar collateral ligament

  • Transverse component of MCL

Origin, Course, and Insertion

  • Origin: Medial border of the olecranon process of the ulna

  • Course: Runs obliquely anteroinferiorly across the floor of the trochlear notch, deep to the anterior and posterior bundles

  • Insertion: Medial margin of the coronoid process of the ulna

Relations

  • Superiorly: Anterior and posterior bundles of the MCL

  • Inferiorly: Joint capsule of the elbow

  • Medially: Ulnar nerve (in cubital tunnel) and flexor carpi ulnaris

  • Laterally: Trochlear notch of the ulna and joint cavity

  • Posteriorly: Olecranon process and posterior band of MCL

Function

  • Provides minor reinforcement to the medial elbow capsule

  • Helps maintain congruity between the olecranon and trochlea during flexion

  • Acts as a fibrous support structure for the anterior and posterior MCL bundles

  • May serve as an attachment plane for the joint capsule and small vessels

Clinical Significance

  • Tears or sprains: Rare in isolation; usually occur with injury to the anterior or posterior bundles

  • Medial elbow pain: May occur with valgus overload, repetitive throwing, or chronic instability

  • Surgical relevance: Recognized during ulnar collateral ligament reconstruction; often preserved or repaired to support capsule

  • Degeneration: May calcify or thicken with chronic strain, visualized on imaging

  • Imaging importance: Helps differentiate full-thickness MCL tears from partial or complex ligamentous injuries

MRI Appearance

  • T1-weighted images:

    • Ligament: low signal (dark) band connecting the olecranon and coronoid processes

    • Adjacent marrow: bright fatty signal of ulna

    • Joint capsule: thin, low-signal structure just inferior to the ligament

    • Disruption or scarring: irregular or discontinuous low-signal bands

  • T2-weighted images:

    • Normal ligament: low-to-intermediate signal, clearly defined

    • Fluid or edema: bright hyperintense signal adjacent to ligament in partial tears

    • Chronic thickening: intermediate signal with irregular contour

    • Complete tear: discontinuity with fluid-filled gap between olecranon and coronoid

  • STIR:

    • Normal ligament: dark to intermediate signal

    • Injury: bright hyperintensity in adjacent soft tissues or ligament substance (edema, sprain, partial tear)

  • Proton Density Fat-Saturated (PD FS):

    • Normal: low to intermediate continuous band

    • Partial tear: focal bright signal within ligament fibers

    • Complete tear: high-signal fluid gap replacing ligament

    • Excellent for visualizing subtle strain or capsular detachment

  • T1 Fat-Sat Post-Contrast:

    • Normal: minimal enhancement

    • Acute injury: focal or diffuse enhancement at tear margins

    • Chronic degeneration: mild, heterogeneous enhancement with periligamentous fibrosis

MRI Arthrogram Appearance

  • Contrast outlines the joint capsule and trochlear notch

  • Intact transverse bundle: smooth low-signal band across medial capsule with no contrast leakage

  • Partial tear: contrast insinuates beneath or between fibers without extravasation

  • Complete tear: contrast extravasation into periarticular soft tissues or ulnar groove

  • Helpful in differentiating partial-thickness MCL tears and capsular defects

CT Appearance

Non-Contrast CT:

  • Ligament not directly visible but seen as a fine soft-tissue band bridging olecranon and coronoid

  • Adjacent bony landmarks (ulnar ridge, trochlear notch) sharply defined

  • Chronic changes: cortical irregularity, calcification, or ossification along ligament course

Post-Contrast CT (standard):

  • Ligament and capsule enhancement minimal in normal state

  • Tears or inflammation: show periligamentous soft-tissue enhancement

  • Useful for detecting calcific tendinopathy, avulsion fractures, or postsurgical fibrosis

CT Arthrogram Appearance

  • Contrast fills the ulnohumeral joint cavity and outlines the transverse bundle

  • Intact ligament: smooth, low-density linear structure separating joint contrast from subcutaneous tissues

  • Partial tear: subtle irregularity with minimal contrast tracking under the ligament

  • Complete tear: contrast leakage beyond the medial capsule, delineating ligament rupture

  • Provides superior delineation of capsular continuity and ligament avulsion sites

MRI images

Medial collateral ligament of elbow transverse bundle axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI images

Medial collateral ligament of elbow transverse bundle coronal cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI images

Medial collateral ligament of elbow transverse bundle coronal cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

MRI images

Medial collateral ligament of elbow transverse bundle sag cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00002