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Body of proximal phalanx

The body (shaft) of the proximal phalanx is the long central portion of the bone located between the base (proximal articular end) and the head (distal articular end). It forms the structural support for the finger, providing attachment sites for tendon sheaths and surrounding soft tissues.

The shaft is slightly concave on its palmar surface and convex dorsally, allowing accommodation of flexor tendons. It contains a thin cortical layer with a central canal of fatty marrow, contributing to its strength and flexibility during fine finger movements.

It is the most frequently fractured portion of the proximal phalanx due to its exposed position and functional demands.

Synonyms

  • Shaft of proximal phalanx

  • Proximal phalangeal body

  • Midshaft of proximal phalanx

Location and Structure

  • Position: Midportion of the proximal phalanx between its base (proximally) and head (distally).

  • Shape: Long, narrow, and slightly curved bone shaft.

  • Surfaces:

    • Dorsal: Convex and smooth for extensor tendon gliding

    • Palmar: Slightly concave, accommodating flexor tendons and digital sheath

  • Composition: Dense cortical bone surrounding a medullary cavity with fatty marrow.

  • Ends:

    • Proximal base articulates with metacarpal head

    • Distal head articulates with the middle phalanx

Relations

  • Dorsally: Extensor tendon and dorsal digital apparatus

  • Palmarly: Flexor tendon sheath, flexor digitorum superficialis and profundus tendons

  • Laterally: Fibrous digital sheath, digital nerves and arteries

  • Proximally: Metacarpophalangeal joint

  • Distally: Proximal interphalangeal joint

Attachments

  • Fibrous digital sheath: Anchors along lateral and palmar surfaces

  • Tendons:

    • Flexor tendons run along palmar concavity

    • Extensor tendons glide over dorsal surface

  • Ligamentous:

    • Collateral ligament expansions attach near metaphyseal regions

Function

  • Provides structural support for finger movement

  • Serves as a lever arm for flexor and extensor tendons

  • Plays a key role in grip strength and fine motor control

  • Protects digital neurovascular bundles along its lateral margins

MRI Appearance

T1-weighted images:

  • Cortex: Very low signal (dark)

  • Medullary cavity: Bright, due to fatty marrow

  • Soft tissues: Tendons appear as dark linear structures around the bone

  • Clear demarcation between cortex and marrow

T2-weighted images:

  • Cortex: Low signal

  • Marrow: Bright, though slightly less intense than on T1

  • Cartilage at ends: Intermediate-to-bright

  • High contrast between bone, tendons, and surrounding soft tissues

STIR:

  • Normal marrow: Intermediate-to-dark signal

  • Fat suppression makes surrounding fat dark

  • Bone appears uniformly dark unless edema is present

CT Appearance

Non-Contrast CT:

  • Cortex: High-density, sharply defined

  • Medullary cavity: Lower density fatty content

  • Bone contour: Straight or slightly curved

  • Excellent for assessing fractures, cortical irregularity, and alignment

MRI image

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

X Ray image

Body of proximal phalanx x ray anatomy labelled image-img-00000-00000