I would definitely wait until your Dr clears you before trying the cleated shoes. My mom's doc had her use regular toe cages for a while after her surgery, just so she didn't have to twist her knee to get out of the cleats. I would also have your local bike shop adjust the tension on the pedals so you can get in and out comfortably.
Having said that, I tried a few different kinds and liked the Pearl Izumi's (with SPD cleats) the best. The ones I bought are very similar to the "Pearl Izumi Elite RD III Bike Shoes." I have to wear an orthotic due to a neuroma (pinchy nerves in the ball of my foot) so I had to get something comfy and something that I could fit my orthotics into. The Pearl Izumi's work great. I also tried a pair of Shimano's (sorry, not sure of the model), but those felt awful. They don't have to feel lousy to work well. Comfy is okay. :)
I've never had knee problems but love my old Shimano's. You can even find them on Zappos.com, where they have free shipping and free returns, so you have absolutely nothing to lose and can try them in the luxury of your own home.
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