Been awhile since I posted, but felt like popping in... so,
I had knee surgery at the beginning of September 2007 to fix a torn lateral meniscus in my left knee (not an aikido related injury, i actually think it was caused by improper instruction in Tai Chi). I got back on the mat at the beginning of February this year, after completing physical therapy. Knee feels great, no further problems. Still some trouble sitting in seiza, but that feels equally bad on both sides, more practice i suppose...
. Shikkyo is a possibility now, although frustrating to learn, i'm happy it's even possible. To be honest, the knee that got sliced generally feels better than the other one. It doesn't even ache when it rains, seriously, better than brand new!
I hear so many knee surgery horror stories, along the lines of: "It's all downhill after knee surgery" and "It'll never feel quite right ever again" and the worst I ever heard, "You'll be in and out of operating rooms for the rest of your life!"
Just wanted to post this as a glimmer of hope for aikidoka who may be suffering from this or any injury.
I feel better on the mat than I ever have before and look forward to many, many years of practice.
The biggest lesson I got out of the whole experience is how absolutely critical it is to maintain proper (or even above average, if possible) muscle in the legs, for aikido and all other aspects of life.
Keep those legs strong and be kind to your knees!