CMC joint

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The carpometacarpal (CMC) joints are synovial joints formed by articulations of the distal carpal row and the metacarpal bones.

Gross anatomy

Articulations

The carpometacarpal joints are made up of a number of bony articulations .

  • first carpometacarpal: distinct synovial curved saddle joint situated between the trapezium proximally and the first metacarpal (of the thumb) distally

The second to fifth carpometacarpal joints are synovial joints which commonly communicate with the intercarpal joints and the articulations at the metacarpal bases . Structurally, they are most akin to ellipsoidal joints, however, their curvatures are so small that they are often disregarded, leading to a functional classification as plane synovial joints.

  • second carpometacarpal: trapezium, trapezoid and capitate proximally with the second metacarpal distally
  • third carpometacarpal: between the capitate and the third metacarpal
  • fourth carpometacarpal: capitate and hamate proximally with the fourth metacarpal distally
  • fifth carpometacarpal: between the hamate and the fifth metacarpal
Movements

First carpometacarpal joint

  • flexion
  • extension
    • abductor pollicis longus
    • extensor pollicis longus
    • extensor pollicis brevis
  • abduction
  • adduction
  • opposition: movement of the pulp of the thumb across the palm to approach the pulps of the digits
    • simultaneous abduction, flexion and pronation of the thumb generates opposition
  • retroposition: elevation of the pulp of the thumb into extension and ulnar adduction
    • extensor pollicis longus
  • circumduction
    • sequential occurrence of extension, abduction, flexion and abduction (or the reverse) produces circumduction

Second to fifth carpometacarpal joints

Moving from the radial to the ulnar side, the second to fifth carpometacarpal joints exhibit an increasing range of movement .  Minor gliding movements at these joints are generated by contraction of the long flexor and extensor digitorum muscles . The fifth carpometacarpal joint is considerably mobile; contraction of opponens digiti minimi generates flexion and lateral rotation at this joint, facilitating ‘cupping’ of the palm .

Ligaments

First carpometacarpal joint

Second to fifth carpometacarpal joints

  • dorsal carpometacarpal ligaments
    • strongest; contribute most to joint stability
  • palmar carpometacarpal ligaments
  • interosseous ligament
Joint capsule

First carpometacarpal joint

  • a separate synovial membrane lines the fibrous joint capsule

Second to fifth carpometacarpal joints

  • the synovial membranes are often continuous with those of the intercarpal joints
  • the fourth and fifth carpometacarpal joints may possess a shared synovial cavity, separated from the other carpometacarpal joints of the digits by extensions of the medial interosseous ligament into the palmar and dorsal parts of the capsule

Arterial supply

Arterial supply of the carpal joints is by the posterior carpal branches of the radial and ulnar arteries, and by the anterior interosseous artery .

First carpometacarpal joint

  • first dorsal metacarpal branch of the radial artery

Second to fifth carpometacarpal joints

  • posterior carpal branch of the radial artery
  • posterior carpal branch of the ulnar artery
  • anterior interosseous artery

Innervation

First carpometacarpal joint

Second to fifth carpometacarpal joints