After knee replacement surgery, it is not advisable to immediately start climbing stairs. Once you are discharged from the hospital after a few days of your surgery, you may start climbing stairs safely with the help of crutches. It is recommended to start by going up with the good leg and step down with the operated one. You may be required to continue using crutches for a few more weeks, depending on your condition. As you get stronger, you will be able to climb stairs normally.