Basics and Beyond ® Anatomy of the Upper Extremity

Carpometacarpal Joints (CMC)

• Are the most proximal joints in the hand
• All CMC joints are synovial meaning it is a type of joint that is surrounded by a thick flexible membrane forming a sac into which is secreted a viscous fluid that lubricates the joint.
• Thumb CMC (1^st CMC) is different than digits 2-5 CMC joints.It allows for significant motion while there is virtually no motion at digits 2-5 CMC.
• 1^st CMC joint (trapeziometacarpal joint) is between the base of the thumb MC and the trapezium.  Axial rotation (opposition) is allowed here due to soft tissue restraints being somewhat lax. This rotation is what makes the thumb useful and functional.
• Virtually no motion is permitted at the 2^nd and 3^rd CMC joints. There is a small amount of motion at the 4^th and 5^th CMC joints that is important for gripping and manipulation of objects.

CLINICAL GEM:  CMC joints of index through small fingers articulate with the distal row of the carpus. The mnemonic That They Can’t Handle helps to remember these carpals: Trapezium, Trapezoid, Capitate and Hamate.