Named for the bones that make up the base joint of the thumb - the trapezium, one of the small Carpal bones of the wrist, and the Metacarpal or long bone of the thumb - the carpometacarpal (CMC) joint is the most common site for arthritis in the hand. In the most common form of arthritis, Osteoarthritis (OA) or Degenerative Joint Disease (DJD), the cartilage that covers and protects the joints, wears out. Without the protective cartilage, the bones in the joint grind against one another wearing the joint down and causing pain and instability.
As the disease progresses, the CMC joint may sublux (slip out of place), causing the thumb to collapse into the palm, forming a “Z” or zigzag deformity. This collapse deformity makes it difficult to open the thumb away from the palm and makes grasping and pinching progressively more difficult.
Pain at the base of the thumb where it joins the wrist is the most common symptom of CMC joint arthritis. Pain is most commonly felt when trying to pinch or grip something tightly or when holding onto something small like a pen or a key. Pressure that pushes down on the thumb may also cause pain that is often described as “grinding” pain.