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Carpometacarpal joint of thumb

The carpometacarpal (CMC) joint of the thumb, also known as the first CMC joint, is a saddle-shaped synovial joint between the trapezium and the base of the first metacarpal. It is a highly mobile and biomechanically specialized joint that allows the thumb its wide range of motion, including opposition, making it essential for precision grip and hand function.

It is a key anatomical structure in hand anatomy, orthopedic evaluation, and imaging of thumb disorders.

Synonyms

  • First carpometacarpal joint

  • Trapeziometacarpal joint

  • Basal thumb joint

Location

  • Situated at the radial side of the wrist

  • Between the trapezium (carpal bone) and the base of the first metacarpal

  • Distal to the scaphoid and trapezoid

  • Proximal to the first metacarpal shaft

  • Forms the base of the thumb column

Anatomical components

  • Articular surfaces:

    • Distal surface of the trapezium

    • Proximal base of the first metacarpal

  • Joint type:

    • Saddle-shaped synovial joint

  • Capsule:

    • Thin but reinforced by strong ligaments

  • Key ligaments:

    • Anterior oblique (beak) ligament

    • Dorsoradial ligament

    • Posterior oblique ligament

    • Intermetacarpal ligament

Relations

Anteriorly (volarly):

  • Thenar muscles

  • Flexor pollicis longus tendon (nearby)

Posteriorly (dorsally):

  • Extensor pollicis longus and brevis tendons

Laterally (radially):

  • Radial artery (in the anatomical snuffbox region)

Medially (ulnarly):

  • Second metacarpal base and trapezoid bone

Proximally:

  • Trapezium

Distally:

  • First metacarpal base

X-ray appearance

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

  • Joint space: Well-defined between trapezium and first metacarpal base

  • Articular contours: Smooth and congruent

  • Alignment: Proper apposition without subluxation

  • Best seen on: Robert’s view and oblique projections

CT appearance

Non-contrast CT:

  • Osseous surfaces: Clearly defined saddle-shaped articulation

  • Cortical margins: Smooth and intact

  • Spatial assessment: Excellent visualization of joint congruity and bony morphology

  • Relationship: Precise depiction of trapezium–metacarpal alignment

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal

  • Marrow of trapezium and metacarpal: High signal

  • Joint capsule: Thin, low-to-intermediate signal outline

T2-weighted images:

  • Articular cartilage: Intermediate signal

  • Joint fluid: High signal

  • Surrounding ligaments: Low signal linear structures

STIR:

  • Fat suppression: Uniform suppression of marrow fat

  • Joint space: High-signal fluid well visualized

  • Capsule and ligaments: Clearly outlined

Proton density fat-saturated (PD FS):

  • Excellent contrast between fluid, cartilage, and ligaments

  • Joint recesses: Well visualized

  • Soft-tissue attachments: Clearly delineated around the joint

MRI image

Carpometacarpal joint of thumb mri anatomy labelled image-img-00000-00000

MRI image

Carpometacarpal joint of thumb mri anatomy labelled image-img-00000-00000_00001

X-Ray image

Carpometacarpal joint of thumb x ray anatomy labelled image-img-00000-00000 - Copy (2)