Topics

Topic

design image
Medial collateral ligament of elbow (posterior bundle)

The posterior bundle of the medial collateral ligament (MCL), also known as the ulnar collateral ligament, is one of three components that stabilize the medial elbow joint. It plays a key role in resisting valgus stress, particularly when the elbow is flexed beyond 60°.

This bundle is thinner and less taut than the anterior bundle but becomes an important secondary stabilizer in flexion. It forms the posterior margin of the cubital tunnel, contributing to the osseofibrous canal through which the ulnar nerve passes. The posterior bundle is clinically relevant in throwing injuries, valgus instability, and ulnar nerve compression syndromes.

Synonyms

  • Posterior oblique band of the ulnar collateral ligament

  • Posterior bundle of medial collateral ligament

  • Posterior ulnar collateral ligament (functional term)

Origin, Course, and Insertion

  • Origin: Medial epicondyle of the humerus, posterior and inferior to the origin of the anterior bundle

  • Course: Runs obliquely posteroinferiorly along the medial elbow, deep to the flexor carpi ulnaris and ulnar nerve, forming the posterior wall of the cubital tunnel

  • Insertion: Medial margin of the semilunar (trochlear) notch of the ulna, near the olecranon process

Relations

  • Anteriorly: Anterior bundle of the MCL

  • Posteriorly: Ulnar nerve and posterior capsule of the elbow joint

  • Superiorly: Medial epicondyle of the humerus

  • Inferiorly: Olecranon process of the ulna

  • Superficially: Flexor carpi ulnaris and its aponeurosis

  • Deep: Elbow joint capsule and articular cartilage of the trochlear notch

Structure and Function

  • Composition: Dense collagenous connective tissue with longitudinally aligned fibers

  • Function:

    • Stabilizes the elbow against valgus stress when flexed beyond 60°

    • Reinforces the posterior capsule and contributes to the cubital tunnel wall

    • Acts as a secondary restraint during elbow flexion when the anterior bundle relaxes

    • Prevents posterior displacement of the ulna relative to the humerus

Clinical Significance

  • Valgus instability: Overuse in throwing athletes can cause microtears or laxity

  • Ulnar neuropathy: Thickening or fibrosis may compress the ulnar nerve within the cubital tunnel

  • Trauma: Partial or complete tears may accompany dislocations or fractures

  • Degeneration: Chronic strain may cause mucoid degeneration and posterior capsular thickening

  • Surgical relevance: Identified and preserved during ulnar nerve transposition and ligament reconstruction (Tommy John surgery)

MRI Appearance

T1-weighted images:

  • Ligament: Low signal (dark), thin linear band posterior to the anterior bundle

  • Adjacent muscles and fat: Intermediate to bright, providing contrast

  • Tears: Discontinuity or irregular thickening, with localized intermediate signal intensity

  • Chronic degeneration: Thickened low-signal structure with adjacent scarring

T2-weighted images:

  • Normal ligament: Low signal (dark), continuous linear band

  • Acute tears: Bright hyperintense gap or fluid signal between retracted fibers

  • Chronic injury: Irregular intermediate signal due to fibrosis or mucoid change

  • Fluid in the cubital tunnel or posterior recess accentuates contour

STIR:

  • Normal ligament: Intermediate-to-dark signal

  • Pathologic changes: Bright hyperintense areas indicating edema or acute strain

  • Useful for detecting partial-thickness tears and periligamentous edema

Proton Density Fat-Saturated (PD FS):

  • Normal: Dark linear band, sharply defined

  • Partial tear or strain: Bright linear or focal hyperintense signal along the ligament fibers

  • Chronic injury: Diffuse thickening with patchy signal heterogeneity

  • Excellent for differentiating acute tears from chronic degeneration

T1 Fat-Sat Post-Contrast:

  • Normal: Minimal or no enhancement

  • Acute tear: Peripheral enhancement due to vascular granulation tissue

  • Chronic fibrosis: Mild, irregular enhancement

  • Inflammatory changes in ulnar nerve sheath or capsule: Diffuse enhancement along posterior cubital tunnel

MRI Arthrogram Appearance

  • Normal: Ligament appears as a dark continuous band posterior to the medial joint recess; no intra-ligamentous contrast penetration

  • Partial tear: Linear contrast infiltration between fibers or mild periligamentous leakage

  • Complete tear: Contrast extravasation into the cubital tunnel or posterior recess of the elbow joint

  • Ideal for evaluating occult tears, capsular disruptions, and early valgus instability

CT Appearance

Non-Contrast CT:

  • Ligament not directly visible due to soft-tissue density

  • Indirect visualization through fat planes and bony landmarks (medial epicondyle to olecranon)

  • Chronic injury: Calcification or ossification near insertion sites may be seen

  • Useful for identifying avulsion fractures involving the medial epicondyle or sublime tubercle

Post-Contrast CT (standard):

  • Mild enhancement of ligamentous tissue and adjacent capsule

  • In post-traumatic settings, demonstrates thickening or pericapsular enhancement

  • Detects hematoma, capsular injury, or post-surgical fibrosis

CT Arthrogram Appearance

  • Normal: Contrast outlines the posterior joint capsule without entering the ligament substance

  • Partial tear: Linear contrast tracking along or beneath the ligament

  • Complete tear: Contrast extravasation beyond posterior capsule into cubital tunnel

  • Provides excellent evaluation of ligament integrity and elbow capsule continuity, especially when MRI is contraindicated

MRI images

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

MRI images

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

MRI images

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

MRI images

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

MRI images

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