It is my understanding that your knee has been immobilized in a straight position for a while in order for the fracture to heel. You want to start with some range of motion to improve your knee mobility. It is really important to work on getting this motion going as soon as possible because the longer you wait to move it, the harder it is to get the motion back. if your knee is really stiff (which is what I am thinking) you really may want to consider going to see a physical therapist a few times early on just to get your knee moving because alot of the manual stuff they would do is very helpful. Some of the more basic movements I may not have videos of and they will be listed below in a description. For any of the mobility stuff I give you, it will most likely be painful and or tight. If there is pain with the motion, go in and out of that motion without holding that position. As it feels like less pain and more of a stretch, you will start to hold the stretch initially 10sec for 10 reps and progress towards 5x30sec. If you have any issues or specific questions let me know. Start with the movements below 2-3x/day and use ice after as needed to decrease soreness.
Seated with back resting against couch or in bed with your foot resting on the floor, use a sheet to slide the foot up towards you