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Dorsal capsule of the metacarpophalangeal joint

The dorsal capsule of the metacarpophalangeal (MCP) joint is a thin but critical fibrous layer forming the posterior aspect of the MCP joint capsule in the fingers and thumb. It integrates with the extensor apparatus, providing stability during finger extension and preventing dorsal subluxation of the proximal phalanx.

It contributes to MCP joint congruity, guides extensor tendon motion, resists hyperflexion, and protects the joint from dorsal impact forces. The capsule blends with the sagittal bands, the extensor hood, and the dorsal phalangeal periosteum, forming a functional dorsal support system.

Synonyms

  • Dorsal MCP joint capsule

Location and Structure

  • Position: Covers the dorsum of the MCP joint between the metacarpal head and the base of the proximal phalanx.

  • Composition: Dense fibrous connective tissue reinforced by extensor hood fibers.

  • Thickness: Thinner and more flexible than the volar plate, allowing full extension.

  • Biomechanics: Glides beneath extensor tendons during motion.

Relations

  • Dorsally: Extensor digitorum tendon, extensor hood, sagittal bands

  • Palmarly: Metacarpal head, proximal phalanx base, volar plate

  • Laterally: Collateral ligaments and extensor expansions

  • Proximally: Metacarpal neck and periosteum

  • Distally: Base of proximal phalanx and dorsal articular margin

MRI Appearance

T1-weighted images:

  • Dorsal capsule appears as a thin low-signal (dark) fibrous band over the MCP joint

  • Extensor tendons: low signal but slightly thicker and more linear

  • Surrounding fat pads: bright, outlining the capsule

T2-weighted images:

  • Capsule remains low signal, allowing distinction from adjacent higher-signal soft tissues

  • Joint space appears bright due to synovial fluid

  • Articular cartilage: intermediate-to-bright signal

STIR:

  • Capsule: dark-to-intermediate signal

  • Surrounding fat fully suppressed for clear visualization

  • Highlights joint effusion and soft-tissue contrast as bright signal

MRI image

dorsal capsule of the metacarpophalangeal (MCP) joint MRI AXIAL image-img-00000-00000