How large is the scar from knee replacement surgery? Dr. Mary O'Connor: The length of the scar after knee replacement surgery is going to vary depending on what kind of surgical technique your surgeon uses. How big your leg is, because usually people with fat, big legs need longer scars and so that is a variable that really is dependent on the patient. I do want to say that, I tell my patients that I don’t focus so much on the length of the incision, but it’s what I am doing underneath to the muscles and tendons that are more important in terms of trying to speed their rehab than the actual length of the skin incision.