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Ulnar collateral ligament of wrist

The ulnar collateral ligament (UCL) of the wrist is a key stabilizing structure located on the ulnar (medial) side of the wrist joint. It reinforces the capsule of the ulnocarpal and radiocarpal joints, preventing excessive radial deviation and contributing to ulnar-sided wrist stability.

Anatomically, the UCL is not a single cord-like band but a two-part ligamentous complex composed of superficial (capsular) and deep (intrinsic) fibers that blend with the triangular fibrocartilage complex (TFCC). Together, these fibers form a continuous ulnar capsuloligamentous structure that stabilizes both the ulnocarpal and distal radioulnar joints during motion and load bearing.

Synonyms

  • Medial collateral ligament of wrist

  • Ulnocarpal collateral ligament

  • Ulnar capsular ligament complex

Origin, Course, and Insertion

Origin:

  • Arises from the ulnar styloid process and adjacent ulnar fovea at the base of the distal ulna.

Course:

  • Fibers descend distally and fan out to form two distinct but continuous components:

    • Superficial (capsular) part: Runs obliquely downward and anteriorly to attach to the pisiform and triquetrum, forming part of the anterior (palmar) ulnar carpal capsule.

    • Deep part: Passes deep to the superficial band and blends with the ulnolunate and ulnotriquetral ligaments of the TFCC, inserting onto the lunate and triquetrum.

Insertion:

  • Superficial fibers: Pisiform and triquetrum.

  • Deep fibers: Lunate and triquetrum, forming the ulnocarpal ligament complex.

Relations

  • Superficially: Flexor carpi ulnaris tendon and pisiform bone.

  • Deeply: Triangular fibrocartilage complex (TFCC) and articular capsule of the ulnocarpal joint.

  • Anteriorly: Palmar ulnocarpal ligament complex and ulnar head.

  • Posteriorly: Extensor carpi ulnaris tendon sheath and dorsal ulnar capsule.

  • Laterally: Ulnar head and triquetrum.

Components and Structure

1. Superficial (Capsular) Part

  • Also called the ulnocarpal collateral ligament.

  • Extends from the ulnar styloid to the pisiform and triquetrum.

  • Reinforces the palmar capsule and contributes to stability during wrist extension and radial deviation.

  • Provides protection to the ulnar neurovascular bundle.

2. Deep Part

  • Continuous with the ulnolunate and ulnotriquetral ligaments.

  • Anchors the carpus to the distal ulna, forming the deep stabilizing layer of the ulnocarpal joint.

  • Integrally associated with the TFCC, providing resistance to axial loading, pronation, and supination stresses.

Function

  • Primary ulnar stabilizer: Prevents excessive radial deviation of the wrist.

  • Joint integrity: Strengthens the ulnocarpal and radiocarpal capsules.

  • Load distribution: Works with the TFCC to transfer load from the carpus to the ulna.

  • Support during movement: Maintains alignment during pronation, supination, and gripping.

  • Dynamic coordination: Dorsal fibers tighten during wrist flexion; palmar fibers tighten during extension.

Clinical Significance

  • Ulnar-sided wrist pain: Commonly caused by UCL or TFCC injuries.

  • Sprains and tears: May result from forced radial deviation or twisting trauma.

  • TFCC degeneration: Often involves deep fibers of the UCL complex.

  • Instability: Chronic attenuation may lead to ulnocarpal instability or distal radioulnar joint subluxation.

  • Surgical importance: Must be preserved during wrist arthroscopy and ulnar shortening procedures.

MRI Appearance

T1-weighted images:

  • Ligament: low-signal (dark) linear structure on ulnar side of wrist.

  • Surrounding fat: bright, providing excellent contrast.

  • Superficial and deep components appear as parallel or converging dark bands.

  • Partial tear: localized thickening or indistinct fiber separation.

  • Complete rupture: discontinuity of the low-signal band with adjacent high-signal fluid.

T2-weighted images:

  • Normal ligament: low signal.

  • Acute injury: bright hyperintense areas due to edema or hemorrhage.

  • Chronic degeneration: thickened, irregular intermediate-signal ligament with periligamentous fluid.

  • TFCC-associated tear: increased signal extending into deep fibers.

STIR:

  • Normal ligament: dark to intermediate signal.

  • Pathologic: bright hyperintense signal representing edema, tear, or synovial reaction.

  • Useful in identifying acute ulnar-sided wrist injuries.

Proton Density Fat-Saturated (PD FS):

  • Normal: dark linear band.

  • Partial tear: focal bright signal with preserved contour.

  • Complete tear: fluid-filled gap between disrupted fibers.

  • Demonstrates periligamentous edema and ulnocarpal effusion clearly.

T1 Fat-Sat Post-Contrast:

  • Normal: mild enhancement of surrounding synovium only.

  • Ligament inflammation or scarring: linear or nodular enhancement.

  • Chronic injury: enhancing fibrotic tissue replacing normal ligament fibers.

CT Appearance

Non-Contrast CT:

  • Ligament appears as a thin soft-tissue band extending from the ulnar styloid to the triquetrum and pisiform.

  • Bone landmarks (ulnar styloid, lunate, triquetrum) clearly delineated.

  • Avulsion fractures or cortical irregularity at the ulnar styloid suggest ligament injury.

  • Chronic degeneration: may show calcification or ossification at the insertion site.

Post-Contrast CT (standard):

  • Periligamentous enhancement indicates inflammation or synovial thickening.

  • Enhancing fibrotic tissue or capsular irregularity seen in chronic injuries.

CT Arthrography Appearance

  • Contrast outlines the radiocarpal and ulnocarpal joint spaces.

  • Normal ligament: seen as a smooth non-opacified low-density band separating the compartments.

  • Partial tear: contrast tracks along one surface without complete continuity loss.

  • Complete tear: contrast extravasates freely between the radiocarpal and ulnocarpal spaces, confirming full disruption.

  • Excellent for assessing superficial vs. deep fiber integrity and TFCC association.

MRI images

ulnar collateral ligament of wrist mri coronal image axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

ulnar collateral ligament of wrist mri sagittal image