Hi,
How are you? Like any surgery,
knee surgery also has scar tissue which can remain for the rest
of the life, but it's size might decrease after the surgery. As you mentioned, it is 18 months after surgery I don't think this scar would dissappear.
Normally, the scar will be approximately six to eight inches long. It will be straight down the center of your knee unless you have previous scars, in which case they may use the prior scar. There will be some numbness around the scar.