If an old scar begins to feel hot or painful, or becomes puffy and red, chances are good that you have an infection. Because scars penetrate several levels of skin and tissue, it is important to get treatment from a doctor quickly. You may receive a course of antibiotic pills or antibiotic ointment to apply. Large scars, particularly deep surgical scars, typically involve several types of overlapping tissue, which may not stretch or expand at the same pace. A childhood abdominal scar, for example, will have to stretch as a child becomes an adult. That process may cause the scar to itch or burn. as it is your ankle and we know ankle is always under load and movements so it is likely to happen but don t worry as it is not as serious as u might be thinking Massaging the scar with hypo-allergenic lotion or oil may be enough to loosen up and stretch scar tissues. If this fails to relieve the itching, anti-itch creams like hydro-cortisone may resolve the problem. More severe cases of itching may benefit from the use of over the counter lidocaine lotions. For stronger topical analgesic cream, your doctor can prescribe a topical 5 percent lidocaine ointment which will numb the effected area. if skin around scar is inflamed and tender ( i mean pain on touch ) than u need antibiotic regime and some rest along with medicine but i will advise you to have a visit to your Orthopedic Surgeon so that he can evaluate the underling condition if any because you have undergone ankle joint replacement and that too has been 10 year old so seriously i will advise to visit your Doc Thanks