To answer some questions in the thread, I saw my doctor on the day after I fell and initially hurt my knee. He told me to stay off of it as much as possible and no exercise for 6 weeks or until it was feeling all better. He had it xrayed and everything and could see nothing wrong with it, so he chalked it up to simply 'soft tissue damage' which is virtually impossible to diagnose accurately.
I tried the crutches for 3 days or so, but they were too much of an issue for me, and carting around 275 pounds on crutches was way too painful for me. I kept my knee wrapped and regularly iced it. After 3-4 weeks, the knee felt back to normal, but I still waited it out for the full 6 weeks before exercising again.
I tried aerobics, but after two days of 45 minutes of aerobics each day, my knee was a bit sore so I rested it again for two more weeks.
Once I started up at the gym, I was doing just great for about two months, my knee didn't flare up at all! Well, until I tried doing a spin class, that is.
Ever since that spin class, I've had frequent issues with my knee. I called an advice nurse at Kaiser with the intention of trying to get an appointment to see my doctor, but she told me that it can take months for a soft tissue injury to fully heal and that I likely just aggravated it when I did the spin class and that I should let it rest until it feels better. Once it was feeling better, I could try light activity again.
So that leads me to now - I've been trying to hit the gym a minimum of 1-2 times per week, knee dependent, if only to keep up with my upper body weights. I haven't had any major issues with my knee recently, but once in awhile it will become tender again, usually after a large amount of activity (for example, I was in San Fran this past weekend and walked quite a bit, so my knee is sore today because of the activity.)
I hope that better explains things.