How do you get a triple poison ivy rash on the back of your knee?

Our guess would be: you are dragging something along (a lawnmower?) and you back into a vine that is in your way. 

The vine scrapes your skin and your skin scrapes the vine and its leaves. 

You end up with poison ivy oil on the back of your knee. And then you bend down so the oil gets transferred from the spot below the joint to the spot above the joint, like a mirror.

Another way to get this rash would be to get lots of urushiol poison ivy oil on your hands or gloves and then wipe the back of your knee…

The other bad rashes higher and lower on the leg suggest messing around where there were a lot of the bad plants.