Beth:

I had pretty much the same thing happen to me a week or two before you had your misfortune. (Hit from behind, knocked about 12-15 feet, and some pulled muscles behind the right calf. I was able to land okay, though, so no real bruising or anything.) I wore a knee brace for about 4 days or so, and Motrin was my friend. On the Saturday following the crash, I had to go teach a bike class for a Cub Scout pack, so I slipped off to the LBS the evening before and bought a replacement helmet, then got out my mountain bike the next morning and gave it a try. OUCH!! I had your same problem... that particular motion of the knee stretched things where they weren't fully healed yet. I was able to raise my saddle a little over an inch and a half where I got a lot more leg extension, and was able to ride... enough to keep up with the Cub Scouts anyway ;-)

Walking (had a business trip to DC the following week), avoiding stairs when possible, and some easy pedaling helped me work it out, but I definitely don't recommend my self-prescribed method. Take your time, take it easy, and get some quality healing there... your bike will be waiting for you when you're ready ;-)

Tom