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Topic

Base of distal phalanx

The base of the distal phalanx forms the proximal articular end of the distal phalanx in each finger. It provides the concave articular surface for the head of the middle phalanx, forming the distal interphalangeal (DIP) joint. The base is essential for finger flexion and extension mechanics and acts as the anchor point for key soft-tissue structures.

It supports the extensor mechanism dorsally, receives the flexor digitorum profundus (FDP) tendon at the palmar surface, and stabilizes the DIP joint through collateral ligaments and the joint capsule. As a compact region bearing both tendon insertions and joint articulation, it is frequently involved in DIP joint injuries, avulsion fractures, and fingertip trauma.

Synonyms

  • Proximal articular surface of distal phalanx

  • Distal phalanx base

  • DIP joint articular base

Location and Structure

  • Position: Proximal end of the distal phalanx, articulating with the head of the middle phalanx.

  • Shape: Concave articular surface covered with hyaline cartilage; dorsal surface blends with extensor expansion; palmar surface thickened for tendon insertion.

  • Composition: Thin cortical shell with fatty cancellous bone internally.

Relations

  • Dorsally: Terminal extensor tendon

  • Palmarly: Flexor digitorum profundus tendon insertion

  • Laterally: Collateral ligaments of the DIP joint

  • Proximally: Head of the middle phalanx

  • Anteriorly (distally): Shaft and tuft of distal phalanx

Attachments

  • Dorsal: Terminal extensor tendon fibers attaching broadly to the dorsal base

  • Palmar: Flexor digitorum profundus tendon inserting into the palmar base

  • Lateral: Collateral ligaments anchoring the DIP joint capsule

  • Capsular: DIP joint capsule attaches circumferentially around the base

MRI Appearance

T1-weighted images:

  • Cortex: Uniformly low signal

  • Marrow: Bright, due to fatty content typical of distal phalanges

  • Articular cartilage: Thin, intermediate-to-low signal at concave articular surface

  • Tendon insertions: Low-signal bands attaching dorsally and palmarly

T2-weighted images:

  • Cortex: Low signal

  • Marrow: Bright, but slightly less intense than T1 fatty marrow

  • Cartilage: Intermediate-to-bright signal

  • Joint space: Hyperintense fluid outlines DIP joint

STIR:

  • Normal bone marrow: Intermediate-to-dark

  • Cortex: Dark

  • Soft tissues: Clear suppression of fat improves depiction of collateral ligaments and tendon insertions

CT Appearance

Non-Contrast CT:

  • Cortex: High-density, sharply defined arc outlining the base

  • Marrow: Lower-density cancellous bone

MRI image

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X Ray image

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