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Carpometacarpal joints

The carpometacarpal (CMC) joints are the articulations between the distal row of carpal bones and the bases of the metacarpal bones. These joints collectively contribute to the stability and dexterity of the hand, providing a balance between rigidity for grip and flexibility for fine motion.

There are five carpometacarpal joints in total. The first CMC joint (thumb) is a saddle-type synovial joint that allows extensive motion—flexion, extension, abduction, adduction, and opposition—while the second to fifth CMC joints are plane synovial joints, permitting limited gliding movements essential for cupping and gripping.

Synonyms

  • CMC joint

  • Carpal-metacarpal articulation

  • Trapeziometacarpal joint (thumb)

Location and Structure

  • First CMC joint: Between the base of the first metacarpal and the trapezium; saddle joint permitting multiplanar movement.

  • Second CMC joint: Between the base of the second metacarpal and the trapezium, trapezoid, and capitate; highly stable with minimal motion.

  • Third CMC joint: Between the base of the third metacarpal and the capitate; acts as a central pillar of the hand.

  • Fourth and fifth CMC joints: Between the bases of the fourth and fifth metacarpals and the hamate; these joints are more mobile and facilitate hand cupping.

  • All CMC joints are synovial joints with fibrous capsules and hyaline cartilage covering articular surfaces.

Relations

  • Dorsally: Extensor tendons and dorsal intercarpal ligaments

  • Ventrally (palmar): Flexor tendons, deep palmar fascia, and intercarpal ligaments

  • Laterally: Radial artery and tendons of abductor pollicis longus and extensor pollicis brevis (near the thumb joint)

  • Medially: Tendons of flexor carpi ulnaris and extensor carpi ulnaris

Ligamentous Attachments

  • Dorsal carpometacarpal ligaments: Strong fibrous bands stabilizing the dorsal aspect

  • Palmar carpometacarpal ligaments: Reinforce the volar surfaces and resist hyperextension

  • Intermetacarpal ligaments: Bind adjacent metacarpal bases together, ensuring coordinated motion

  • Radial and ulnar collateral ligaments: Provide lateral stability

  • Capsule: Fibrous and tight in the second and third CMC joints, looser in the fourth and fifth for flexibility

Function

  • Thumb (1st CMC joint): Allows opposition, abduction, adduction, flexion, extension, and circumduction—critical for grasping and pinching.

  • 2nd and 3rd CMC joints: Provide rigidity and support during power grip.

  • 4th and 5th CMC joints: Allow slight flexion and rotation to facilitate cupping of the palm.

  • Overall function: Combines stability and mobility to adapt the hand for fine manipulation and power tasks.

Clinical Significance

  • Osteoarthritis: Particularly common at the first CMC joint (basal thumb arthritis); causes pain, deformity, and decreased grip strength.

  • Trauma: Fracture-dislocations may occur, especially at the fifth CMC joint after falls or crush injuries.

  • Ligament injury: Sprains or tears can destabilize the CMC joint complex.

  • Inflammatory arthritis: Rheumatoid and psoriatic arthritis frequently involve CMC joints.

  • Surgical relevance: Trapeziectomy and ligament reconstruction commonly performed for thumb CMC arthritis.

MRI Appearance

  • T1-weighted images:

    • Bone cortex: Low signal (dark).

    • Bone marrow: Bright (fatty signal).

    • Articular cartilage: Smooth, thin intermediate-to-low signal.

    • Ligaments and capsule: Low-signal linear structures around the joint.

    • Pathology: Degenerative changes show cortical irregularity and subchondral low-signal sclerosis.

  • T2-weighted images:

    • Bone marrow: Bright, though slightly less than on T1.

    • Cartilage: Intermediate-to-bright; thinning or irregularity indicates early degeneration.

    • Joint fluid: Hyperintense (bright).

    • Pathology: Synovitis, bone marrow edema, and subchondral cysts appear bright; osteophytes appear low signal.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Pathologic marrow: Bright hyperintensity indicating edema or inflammation.

    • Sensitive for detecting bone contusions, erosions, and early arthritis.

  • Proton Density Fat-Saturated (PD FS):

    • Normal joint: Intermediate-to-dark signal in cartilage and bone.

    • Pathology: Bright hyperintense signal indicating edema, capsulitis, or synovitis.

    • Useful for evaluating early degenerative changes and ligament injuries.

  • T1 Fat-Sat Post-Contrast:

    • Normal synovium: Thin, mild homogeneous enhancement.

    • Inflammatory or degenerative arthritis: Marked synovial thickening with intense enhancement.

    • Post-traumatic changes: Enhancement of joint capsule and surrounding soft tissues.

CT Appearance

Non-Contrast CT:

  • Cortical bone: High attenuation with sharp margins.

  • Joint space: Narrow, uniform radiolucent line between carpal and metacarpal bases.

  • Articular surfaces: Smooth in normal joints; irregular or narrowed in degeneration.

  • Pathology: Excellent for detecting fractures, dislocations, osteophytes, and subchondral sclerosis.

  • First CMC joint arthritis: Shows joint space narrowing, subchondral cysts, and osteophyte formation at trapeziometacarpal articulation.

CT VRT 3D image

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MRI image

Carpometacarpal joints coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Carpometacarpal joint ct coronal image