Lateral Ulnar Collateral Ligament: Anatomy, Function, Imaging

Topic

Lateral ulnar collateral ligament

The lateral ulnar collateral ligament (LUCL) is a key component of the lateral collateral ligament complex of the elbow, providing posterolateral stability. It extends from the lateral epicondyle of the humerus to the supinator crest of the ulna, blending with fibers of the annular ligament.

The LUCL prevents posterolateral rotatory instability (PLRI) of the elbow by stabilizing the ulnohumeral articulation during forearm rotation and valgus-varus stresses. It is distinct from the radial collateral ligament, although both share a common humeral origin and act synergistically.

Synonyms

Posterior band of the radial collateral complex
Posterolateral ulnar collateral ligament

Origin, Course, and Insertion

Origin: Posterior aspect of the lateral epicondyle of the humerus, adjacent to the origin of the radial collateral ligament and common extensor tendon.
Course: Passes obliquely posteriorly and distally, deep to the extensor carpi ulnaris and anconeus, blending partially with the annular ligament surrounding the radial head.
Insertion: Terminates at the supinator crest of the ulna, forming a sling-like structure that stabilizes the radial head and lateral ulnohumeral articulation.

Relations

Anteriorly: Annular ligament and radial head
Posteriorly: Anconeus muscle and joint capsule
Superiorly: Lateral epicondyle of the humerus
Inferiorly: Supinator crest and proximal ulna
Medially: Lateral joint capsule and radial collateral ligament complex
Laterally: Common extensor tendon

Attachments

Blends with fibers of the annular ligament to form a supportive ring around the radial head.
Forms the posterior portion of the lateral collateral ligament complex (with the radial collateral ligament and annular ligament).
Works synergistically with the ulnohumeral joint capsule for rotational stability.

Function

Primary stabilizer of the elbow against posterolateral rotatory instability (PLRI).
Prevents posterior subluxation of the radial head relative to the capitellum.
Provides static stability during supination and flexion.
Works in concert with the radial collateral ligament and annular ligament for lateral elbow support.

Clinical Significance

Injury: LUCL tears are the most common cause of posterolateral rotatory instability of the elbow, often due to falls on an outstretched hand or dislocation.
Chronic instability: Repeated injuries can cause recurrent subluxation and degenerative changes.
Post-surgical risk: Injury may occur after lateral epicondylitis surgery or overaggressive extensor tendon release.
Symptoms: Lateral elbow pain, clicking, locking, or “giving way” during supination.
Imaging importance: MRI is gold standard for detecting partial or complete tears; arthrography provides high diagnostic accuracy for ligament discontinuity and joint capsule defects.

MRI Appearance

T1-weighted images:
- Normal LUCL: low signal (dark linear band) from lateral epicondyle to supinator crest.
- Surrounded by intermediate muscle and bright periligamentous fat.
- Partial tear: discontinuity or ill-defined margins with intermediate signal.
- Complete tear: ligament absent or replaced by intermediate-to-bright signal fluid gap.
T2-weighted images:
- Normal: low signal linear band; surrounding joint capsule slightly brighter.
- Partial tear: focal bright signal within ligament.
- Complete tear: hyperintense fluid signal in ligament bed, discontinuity, or retraction.
- Associated findings: effusion, edema around lateral epicondyle, radial head subluxation.
STIR:
- Normal ligament: dark signal (low intensity).
- Pathology: bright hyperintense regions around ligament and capsule, indicating edema or hemorrhage.
Proton Density Fat-Saturated (PD FS):
- Normal: dark continuous band from humeral origin to ulnar insertion.
- Partial tear: bright intraligamentous signal with intact fibers.
- Complete tear: loss of continuity and bright signal fluid replacing ligament.
- Ideal for assessing subtle sprains, chronic degeneration, and PLRI-associated capsular changes.
T1 Fat-Sat Post-Contrast:
- Normal: minimal enhancement.
- Acute injury: focal or diffuse enhancement along ligament margins due to inflammation.
- Chronic scarring: peripheral enhancement with low-signal fibrotic center.
- Postoperative cases: differentiates scar tissue (enhancing) from recurrent tear (non-enhancing gap).

MRI Arthrogram Appearance

Intra-articular contrast highlights joint recesses and capsule.
Normal: Contrast confined within joint capsule; LUCL appears as low-signal linear band.
Tear: Contrast leaks into posterolateral recess or through the lateral capsule at the LUCL attachment.
Partial tear: Irregular contour and mild contrast insinuation around ligament.
Complete tear: Extravasation of contrast into periligamentous soft tissues or subcutaneous fat.
Enhances visualization of associated capsular defects and subtle posterolateral instability.

CT Appearance

Non-Contrast CT:

Ligament not directly visualized (soft-tissue density).
Indirect signs: small avulsion fragment from lateral epicondyle or ulna (supinator crest).
Detects associated bony avulsion, subluxation, or degenerative changes at radial head.

Post-Contrast CT (standard):

May show soft-tissue thickening or contrast enhancement in acute inflammation.
Chronic injury: calcification or fibrosis along ligament course.

CT Arthrogram Appearance

Normal: Contrast confined within elbow joint, outlining radial head and capitellar surfaces; LUCL intact as soft-tissue band.
Partial tear: Mild contrast extension into the posterolateral capsule or subtle irregularity along ligament path.
Complete tear: Clear contrast extravasation posterior to the radial head and supinator crest.
Excellent for visualizing capsular integrity, bony avulsion, and joint instability when MRI is contraindicated.