What is the first CMC joint?

The CMC or carpometacarpal joints are the set of five joints in our wrist whose primary function is articulating the distal row of our carpal bones, as well as the proximal bases of metacarpal bones.

This CMC joint of our thumb (i.e., the first CMC joint called trapeziometacarpal or TMC joint), differs greatly from the other CMC joints. This joint got its name, “trapeziometacarpal joint” since it links the trapezium to the 1st metacarpal bone, thereby playing a remarkable part in the normal functioning of our thumb. Osteoarthritis of this TMC joint is a seriously disabling condition and is also more common among elderly women.

Pronation-supination of this first metacarpal is very significant for the movement of opposition. The movements of the 1st CMC are restricted due to several factors like:

  • The shape of its joint
  • Capsuloligamentous complex that surrounds the joint
  • Balance among the muscles involved

If the first metacarpal is unsuccessful in sitting sit well 'on the saddle' due to conditions like hypoplasia, the TMC joint will tend to become subluxated or lightly displaced towards the radius.