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Head of proximal phalanx

The head of the proximal phalanx is the distal articular end of the proximal phalanx of each finger. It forms the proximal interphalangeal (PIP) joint by articulating with the base of the middle phalanx. The head is convex, covered with hyaline cartilage, and shaped to permit flexion and extension while maintaining joint stability.

It plays a key role in grip mechanics, articulation, and load transmission along the digit. Its structural integrity and smooth curvature are critical for precise finger movement and stability during both power grip and fine motor tasks.

Synonyms

  • Proximal phalangeal head

  • Distal condyle of the proximal phalanx

Location and Structure

  • Position: At the distal end of the proximal phalanx in digits 2–5.

  • Surface:

    • Dorsal—smooth convex cartilage for articulation.

    • Palmar—slightly flattened surface supporting the volar plate.

  • Shape: Rounded, pulley-like condyle allowing flexion and extension.

  • Neck: Slight constriction between the shaft and head.

  • Articular partner: Base of middle phalanx (concave).

Relations

  • Dorsally: Extensor tendons forming the dorsal extensor expansion

  • Palmarly: Volar plate and flexor tendons (FDS + FDP)

  • Laterally: Collateral ligaments of the PIP joint

  • Proximally: Shaft of proximal phalanx

  • Distally: Base of middle phalanx

Attachments

  • Collateral ligaments: Attach on lateral aspects of the head

  • Volar plate: Anchors to palmar surface of the head

  • Extensor mechanism: Dorsal capsule blends with extensor hood over the head

Function

  • Forms the proximal interphalangeal (PIP) joint with the middle phalanx

  • Provides stable hinge articulation for finger flexion and extension

  • Transmits axial load during pinch and grasp

  • Supports the volar plate and extensor mechanism

MRI Appearance

T1-weighted images:

  • Cortex: Very low signal (dark)

  • Bone marrow: Bright, due to fatty marrow content

  • Cartilage: Thin, smooth intermediate-to-low signal lining the head

  • Joint space: Dark line separating articulating surfaces

  • Soft tissue: Flexor/ extensor tendons appear as low-signal linear bands

T2-weighted images:

  • Bone cortex: Low signal

  • Marrow: Bright, slightly less intense than on T1 but higher than muscle

  • Cartilage: Intermediate-to-bright signal

  • Joint fluid: Very bright

  • PIP joint structures: Clear contrast between bone, cartilage, and soft tissues

STIR:

  • Normal marrow: Intermediate-to-dark signal

  • Soft tissues: Flexor and extensor tendons remain low signal

  • Fat planes: Suppressed, enhancing contrast with bone

  • Excellent for delineating bone contours and joint capsule

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with well-defined margins

  • Marrow cavity: Lower attenuation central area consistent with fatty marrow

  • Articular surface: Smooth, forming the proximal surface of the PIP joint

  • Allows detailed evaluation of:

    • Subtle cortical irregularities

    • Small fractures

    • Joint congruity

MRI image

Head of proximal phalanx MRI CORONAL image-img-00000-00000

X-Ray image

Head of proximal phalanx x ray anatomy labelled image-img-00000-00000 - Copy (2)

MRI image

Head of proximal phalanx mri