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Proper collateral ligament

The proper collateral ligament (PCL) of the finger is one of the two major collateral ligaments stabilizing the metacarpophalangeal (MCP) and interphalangeal (IP) joints. It is a strong, cord-like structure extending from the dorsal aspect of the proximal bone to the volar aspect of the adjacent distal bone. The PCL tightens in flexion and stabilizes the joint against side-to-side (varus/valgus) forces.

At the MCP joints, the PCL works together with the accessory collateral ligament to maintain stability during gripping. At the PIP and DIP joints, the PCL forms the primary stabilizing structure of lateral joint motion.

Synonyms

  • Proper collateral ligament of the digit

  • Radial or ulnar collateral ligament (depending on side)

  • True collateral ligament

Location and Structure

  • Present on both sides (radial and ulnar) of each MCP, PIP, and DIP joint

  • Origin: Dorsal lateral tubercle of the proximal phalanx (or metacarpal head for MCP joints)

  • Course: Strong oblique cord passing distally and slightly volarly

  • Insertion: Volar third of the collateral tubercle on the base of the middle or distal phalanx (or proximal phalanx at MCP)

  • Composition: Dense, organized collagen fiber bundles forming a thick, low-signal band on imaging

Relations

  • Volar: Accessory collateral ligament and volar plate

  • Dorsal: Extensor tendon and dorsal capsule

  • Medial/Lateral: Adipose tissue and fibrous pulley system

  • Deep: Joint space and articular cartilage

  • Superficial: Skin and subcutaneous tissue

Attachments

  • Proximal: Dorsolateral tubercle of metacarpal head or phalangeal head

  • Distal: Volar aspect of collateral tubercle on adjacent phalangeal base

  • Works with the volar plate and accessory collateral ligament to stabilize the joint

Function

  • Provides side-to-side stability of MCP, PIP, and DIP joints

  • Prevents excessive varus and valgus movement

  • Tightens during joint flexion, stabilizing grip

  • Important for fine motor control, pinch strength, and coordinated finger motion

Clinical Significance

  • Sprains and partial tears: Common in sports or falls

  • Complete ruptures: Cause lateral instability of PIP or MCP joints

  • Stener-like lesions: Can occur in thumb MCP ulnar collateral ligament injuries

  • Chronic instability: Leads to deformity, weakness, and degenerative changes

  • Imaging relevance: MRI detects partial/complete tears; CT shows avulsion fragments

MRI Appearance

T1-weighted images:

  • Ligament appears as a low-signal (dark) linear or thick band

  • Adjacent bone marrow: bright due to fatty content

  • Good for identifying ligament contour and thickness

T2-weighted images:

  • Proper collateral ligament remains low signal (dark)

  • Joint fluid appears bright, improving contrast with ligament

  • Normal ligament maintains smooth, continuous low-signal appearance

STIR:

  • Normal ligament: dark to intermediate

  • Adjacent fat suppressed to dark signal, highlighting ligament fibers clearly

  • Joint capsule and adjacent soft tissues appear intermediate

T1 Fat-Saturated Post-Contrast:

  • Normal ligament demonstrates minimal enhancement

  • Enhancing soft tissues (capsule, synovium, periligamentous tissue) outline the low-signal ligament

  • Ligament contour should remain sharply defined

CT Appearance

Non-Contrast CT:

  • Ligament visualized as a thin soft-tissue-density band along joint margins

  • Best seen with high-resolution small field-of-view scans

  • Osseous attachment points clearly defined

  • Collateral tubercles and cortical margins well visualized

MRI images

Proper collateral ligament HAND MRI AXIAL image-img-00000-00000

MRI images

Proper collateral ligament HAND MRI CORONAL image-img-00000-00000