Topics

Topic

design image
Base of the middle phalanx

The base of the middle phalanx refers to the proximal expanded portion of the middle phalanx in the fingers, forming the distal articular component of the proximal interphalangeal (PIP) joint. It plays a central role in finger motion by articulating with the head of the proximal phalanx and serving as an attachment site for important capsuloligamentous and tendinous structures.

It is a key anatomical landmark in hand anatomy, trauma evaluation, sports medicine, and finger joint imaging.

Synonyms

  • Proximal base of the middle phalanx

  • Proximal articular base of the middle phalanx

Location

  • Situated at the proximal end of the middle phalanx

  • Forms the distal component of the proximal interphalangeal (PIP) joint

  • Distal to the head of the proximal phalanx

  • Proximal to the shaft of the middle phalanx

  • Centered within the finger ray between MCP and DIP joints

Anatomical components

  • Articular surface:

    • Concave surface for articulation with the proximal phalanx head

  • Osseous base:

    • Cortical shell with underlying cancellous bone

  • Capsuloligamentous attachments:

    • Collateral ligaments of the PIP joint

    • Volar plate insertion

  • Tendinous relations:

    • Central slip of the extensor tendon inserts on the dorsal base

Relations

Anteriorly (Volar):

  • Volar plate

  • Flexor tendon sheath

Posteriorly (Dorsal):

  • Central slip of the extensor tendon

Medially and Laterally:

  • PIP joint collateral ligaments

Inferiorly (Distal):

  • Shaft of the middle phalanx

Superiorly (Proximal):

  • Head of the proximal phalanx

X-ray appearance

Plain radiographs (AP, oblique, and lateral finger views):

  • Base: Appears as the widened proximal portion of the middle phalanx

  • Articular surface: Smooth and concave

  • Joint alignment: Forms the distal articular surface of the PIP joint

  • Cortical margins: Sharp and continuous

CT appearance

Non-contrast CT:

  • Base: Well-defined osseous structure with smooth cortical margins

  • Articular surface: Clearly delineated concavity

  • Trabecular pattern: Normal cancellous bone

  • Spatial resolution: Excellent for evaluating contour and subtle cortical detail

  • Joint relationship: Clear visualization of the PIP joint articulation

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity

  • Marrow within base: High signal intensity

  • Articular cartilage: Thin low-signal layer lining the base

T2-weighted images:

  • Cortex: Low signal

  • Joint fluid: High signal outlining the articular surface

  • Cartilage: Intermediate-to-low signal

STIR:

  • Fat suppression: Uniform suppression of marrow fat

  • Base margins: Well visualized

  • Joint recesses: High signal

Proton density fat-saturated (PD FS):

  • Bone marrow: Suppressed fat signal

  • Joint fluid: High signal

  • Volar plate and ligaments: Low-to-intermediate signal bands adjacent to the base

MRI image

Base of middle phalanx mri image

X-Ray image

Base of middle phalanx x ray