Old surgical scars can suddenly become inflamed and itchy if there is some sort of internal infection.
Although the wound may be healed, any virus or bacteria inside your body can attack weak areas in your body, and a surgical scar is usually in an area where there has been tissue damage or other damage that can make that part of the body struggle with immunity.
You should be able to clear this up by taking some antibiotics, so get in touch with your medical care provider in the first instance.
