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Body of middle phalanx

The body of the middle phalanx refers to the shaft (diaphysis) of the middle phalanx of the fingers or toes. It forms the central elongated portion of the bone between the proximal and distal articular ends and contributes to digital length, alignment, and mechanical stability.

It is a key anatomical region in hand and foot anatomy, fracture assessment, and musculoskeletal imaging.

Synonyms

  • Shaft of the middle phalanx

  • Diaphysis of the middle phalanx

Location

  • Situated between the proximal and distal ends of the middle phalanx

  • Forms the central portion of the bone

  • Present in digits II–V of the hand and foot

  • Between the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints

  • Absent in the thumb and great toe (which lack a middle phalanx)

Anatomical components

  • Cylindrical cortical shell

  • Central cancellous marrow cavity

  • Dorsal surface:

    • Flat and broad

  • Volar surface:

    • Slightly concave, related to flexor tendons

  • Lateral borders:

    • Sites of attachment for interosseous and lumbrical tendons

Relations

Dorsally:

  • Extensor tendon apparatus

Ventrally (volarly):

  • Flexor digitorum superficialis and profundus tendons

  • Volar plate (at adjacent joints)

Laterally:

  • Collateral ligaments of PIP and DIP joints

  • Digital neurovascular bundles (adjacent)

Proximally:

  • Base of the middle phalanx and PIP joint

Distally:

  • Head of the middle phalanx and DIP joint

X-ray appearance

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

  • Body: Elongated radiopaque shaft with smooth cortical margins

  • Medullary canal: Central radiolucent line

  • Alignment: Symmetric relative to adjacent phalanges

  • Cortex: Uniform thickness

CT appearance

Non-contrast CT:

  • Cortex: Dense, sharply defined cortical shell

  • Medullary cavity: Lower density central marrow

  • Surface contour: Smooth and cylindrical

  • Spatial detail: Excellent depiction of cortical integrity and geometry

MRI appearance

T1-weighted images:

  • Cortex: Low signal intensity

  • Marrow: High signal intensity (fatty marrow)

  • Body contour: Clearly outlined against surrounding soft tissues

T2-weighted images:

  • Cortex: Low signal

  • Marrow: Intermediate signal

  • Surrounding soft tissues: Higher signal than bone

STIR:

  • Fat suppression: Uniform suppression of marrow fat

  • Cortical margins: Well delineated

  • Soft tissues: Bright signal

Proton density fat-saturated (PD FS):

  • Marrow: Suppressed fat signal

  • Cortex: Low signal rim

  • Tendons and ligaments: Low signal against high-signal soft tissue background

MRI image

Body of middle phalanx mri image

X-Ray image

Body of middle phalanx x ray