Topics

Topic

design image
Central slip of common extensor tendon

The central slip is the middle portion of the extensor mechanism on the dorsal side of the finger. It represents the continuation of the extensor digitorum communis (EDC) tendon as it crosses the proximal interphalangeal (PIP) joint. The central slip inserts into the dorsal base of the middle phalanx, allowing active extension of the PIP joint.

It is flanked by two lateral bands that continue distally to form the terminal extensor tendon. Together, these structures form the dorsal digital apparatus that coordinates extension across the MCP, PIP, and DIP joints. Injury to the central slip—such as in boutonnière deformity—results in loss of active PIP extension.

Synonyms

  • Central band of extensor apparatus

  • Central extensor tendon

  • Dorsal slip of the extensor tendon

Origin, Course, and Insertion

Origin:

  • Continuation of the extensor digitorum communis (EDC) tendon over the proximal phalanx

Course:

  • Runs centrally along the dorsal aspect of the proximal phalanx

  • Broadens as it crosses the PIP joint

  • Supported by sagittal bands, transverse fibers, and triangular ligament

Insertion:

  • Dorsal base of the middle phalanx, forming the primary extensor insertion for the PIP joint

Relations

  • Dorsally: Dorsal skin and extensor expansions

  • Ventrally: PIP joint capsule and volar plate

  • Laterally: Lateral bands of the extensor mechanism

  • Proximally: Extensor digitorum tendon at the MCP and proximal phalanx level

  • Distally: Dorsal base of middle phalanx

Function

  • Responsible for active PIP joint extension

  • Coordinates with lateral bands to synchronize finger extension

  • Maintains dorsal stability of the PIP joint

  • Prevents volar migration of the extensor mechanism

MRI Appearance

T1-weighted images:

  • Central slip appears as a thin, low-signal (dark) linear structure over the dorsal PIP joint

  • Middle phalanx marrow is bright due to fatty content

  • PIP joint capsule shows low-to-intermediate signal

  • Good for identifying tendon continuity

T2-weighted images:

  • Tendon remains low signal, darker than surrounding soft tissues

  • Joint fluid is bright, outlining the tendon and improving visibility

  • Helps evaluate subtle tendon thickening or irregularity

STIR:

  • Normal tendon: low-to-intermediate signal

  • Fat suppression improves contrast between tendon and surrounding soft tissue

  • Highlights edema in adjacent tissues when present

MRI images

Central slip of common extensor tendon hand MRI axial image-img-00000-00000