The scar from my carpal tunnel surgery has healed, but suddenly there is a nickel sized hard knob beside the scar?

Scat: There can be suture material in the wound that is not dissolved depending in the time frame after surgery. You should return to your carpal tunnel surgeon. If they cannot guid you best then find dermatologist or plastic surgeon to advise you.

Internal Scarring: After carpal tunnel surgery, some of the normal fat around the wrist can move into a new location. This could what you are feeling as a hard knob. There is also some internall swelling that can take several months to fully heal. I usually advise patients that it takes about 2 months after surgery before they go through a day and not notice their hand.

Therapy: Occupational therapy may help you. A check up with your doctor would be a good idea.