Got to see the knee consultant in a couple of days about having an operation for torn cartilage: knee arthroscopy (not aikido related). Obviously every situation is different, but I'd be interested to hear from anybody who's had this op with regard to how it affected their aiki training (especially how long they had to stop training on the mat post op).
Thanks in anticipation
I had a torn meniscus cleaned up. My surgeon said 8 weeks so I stayed off for 8 weeks. I trusted him enough to cut holes in me, I figured I should follow his advice. Two of my friends got back on the mat the day after surgery, I thought they were nuts. I felt good enough to play after about 3 weeks.
PT before and after surgery seemed to help.