hello
Kayaking isnt' a problem with an injured knee. Your knee is in a fixed position and the range of motion isn't that big.
There are a few problems:
- Swimming (If you can't swim without pain or risk to make it worse)
sooner or later you have to swim - especially in white water
- Get to or off the river & scouting
sometimes it's harder to get to the river or scouting rapids with an injured knee than run the rapid
It is possbile to walk with crutches to the river - run some rapids - and wait in your boat until a friend brings your crutches.
I would'nt recommend canoeing
cheers
fierin