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Topic

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Base of middle phalanx

The base of the middle phalanx is the proximal expanded portion of the middle phalanx of the finger (or toe), forming the distal articular component of the proximal interphalangeal (PIP) joint. It plays a central role in digital articulation and stability by participating in joint congruency and ligamentous attachments.

It is an important landmark in hand and foot anatomy, trauma evaluation, joint imaging, and surgical planning.

Synonyms

  • Proximal base of the middle phalanx

  • Proximal articular end of the middle phalanx

Location

  • Situated at the proximal end of the middle phalanx

  • Distal to the head of the proximal phalanx

  • Forms the distal articular surface of the PIP joint

  • Present in both fingers and toes

  • Subcutaneous and superficial on the dorsal and lateral aspects

Anatomical components

  • Articular surface:

    • Concave surface articulating with the proximal phalanx head

  • Cortical shell with cancellous core

  • Attachment zones:

    • Collateral ligaments of the PIP joint

    • Volar plate insertion

  • Dorsal surface:

    • Extensor tendon insertion nearby

Relations

Proximally:

  • Head of the proximal phalanx

Distally:

  • Shaft of the middle phalanx

Dorsally:

  • Extensor tendon mechanism

Ventrally (volarly):

  • Volar plate of the PIP joint

Medially and laterally:

  • Collateral ligaments

X-ray appearance

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

  • Base: Seen as a widened proximal portion of the middle phalanx

  • Articular surface: Smooth concave contour facing proximally

  • Cortical margins: Well-defined

  • Joint space: Clearly visible at the PIP joint

CT appearance

Non-contrast CT:

  • Base of middle phalanx: Well-defined bony expansion with smooth cortical margins

  • Trabecular pattern: Normal cancellous bone architecture

  • Articular surface: Clearly delineated concavity

  • Spatial assessment: Excellent for subtle contour irregularities and joint congruity

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity

  • Marrow: High signal within cancellous bone

  • Articular surface: Well outlined against joint space

T2-weighted images:

  • Cortex: Low signal

  • Joint fluid: High signal highlighting the PIP joint

  • Surrounding soft tissues: Intermediate-to-high signal

STIR:

  • Marrow fat suppression: Uniform

  • Joint recesses: Bright signal

  • Ligamentous attachments: Clearly visualized

Proton density fat-saturated (PD FS):

  • Bone marrow: Suppressed fat signal

  • Joint fluid: High signal

  • Collateral ligaments and volar plate: Well visualized as low-signal structures

MRI image

Base of middle phalanx mri image

X-Ray image

Base of middle phalanx x ray