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Metacarpal bone of thumb

The metacarpal bone of the thumb, also known as the first metacarpal, is a short, robust long bone forming the skeletal framework of the thumb. It is unique among the metacarpals due to its mobility and saddle-shaped articulation at the carpometacarpal joint, enabling the wide range of thumb movements essential for grip and precision.

It is a key structure in hand anatomy, trauma evaluation, and imaging of thumb-related disorders.

Synonyms

  • First metacarpal

  • Thumb metacarpal bone

Location

  • Located on the radial side of the hand

  • Situated between the trapezium proximally and the proximal phalanx distally

  • Forms the skeletal core of the thumb

  • Lies anterolateral to the second metacarpal

  • Participates in the first carpometacarpal (CMC) joint

Anatomical components

  • Base (proximal end):

    • Saddle-shaped articular surface for the trapezium

  • Shaft (body):

    • Short, thick, and slightly curved

  • Head (distal end):

    • Rounded surface articulating with the proximal phalanx

  • Cortical shell and cancellous core

Relations

Proximally:

  • Trapezium bone (first CMC joint)

Distally:

  • Proximal phalanx of the thumb (metacarpophalangeal joint)

Medially:

  • Second metacarpal bone

Laterally:

  • Thenar soft tissues

Anteriorly (palmar):

  • Flexor tendons and thenar muscles

Posteriorly (dorsal):

  • Extensor pollicis tendons

X-ray appearance

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

  • Bone outline: Short, thick metacarpal with flared base

  • Base: Saddle-shaped articulation with the trapezium

  • Head: Rounded and smooth

  • Alignment: Clear articulation at CMC and MCP joints

  • Best seen on: AP and oblique views of the thumb

CT appearance

Non-contrast CT:

  • Cortical margins: Sharp and well-defined

  • Trabecular pattern: Normal cancellous bone texture

  • Base contour: Clearly demonstrates saddle-shaped joint surface

  • Joint relationships: Precise depiction of CMC and MCP joints

  • Utility: Excellent for evaluating subtle cortical irregularities and joint congruity

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity

  • Marrow: High signal intensity

  • Articular surfaces: Clearly defined against joint space

T2-weighted images:

  • Cortex: Low signal

  • Joint fluid: High signal outlining articular surfaces

  • Adjacent soft tissues: Intermediate-to-high signal

STIR:

  • Fat suppression: Uniform suppression of marrow fat

  • Bone contours: Well visualized

  • Joint spaces and tendon sheaths: Bright signal

Proton density fat-saturated (PD FS):

  • Bone marrow: Suppressed fat signal

  • Joint fluid: High signal

  • Ligaments and tendons: Low-signal linear structures

MRI image

Metacarpal bone of thumb axial

MRI image

Metacarpal bone of thumb mri coronal

X-Ray image

Metacarpal bone of thumb x ray anatomy labelled image-img-00000-00000 - Copy