Knees, Ouch!!! One of the more painful things you can have wrong with you.
I've been doing chiropractic for 32 years now and I see an awful lot of people hurt themselves doing Yoga. Why??
They think they're still young. Unless you've been doing Yoga since youth do not attempt the advanced positions.
For the average person that just wants to stay in good shape I do NOT recommend Yoga. Nor do I recommend running or treadmill.
What I teach is don't stretch the spine at all. You can losen it up a bit as with warm-up exercises but don't stretch it. Unless you're an advanced student of Yoga or an athlete, don't stretch your spine. The risk of hurting yourself and ending up in my office outweigh the possible benefit derived.
That being said, there ARE things you can do to keep your spine mechanically correct and strong. The stretching exercise that goes a long, long way to stabilizing the lower back is the hamstring stretch before bed EVERYNIGHT. Once in bed roll over on your stomach and arch your back a couple of time, then go to sleep.
If you're in trouble with a slipped disc I teach the toe pull that puts a little intersegmental traction on the involved disc.
Any lower back twisting warm-up exercises should be done while leaning slightly back. With the neck have your chin elevated a bit.
DON'T TWIST THE LUMBAR SPINE WHILE LEANING FORWARD OR CERVICAL SPINE WITH THE CHIN DOWN.
Knee problems, if not caused by direct trauma to the knee proper come from two sources related to the spine.
1. When the hips are not mechanically correct that causes the normal geometry of the muscle and ligament attachments to pull incorrectly into the legs, knees and even the ankles and feet. You feel this usually in the medial knee first.
2. The nerves that supply the knee area come from L1&2. If those nerve roots are "pinched" the knee will hurt and swell. This befuddles people because there was never a trauma to the knee and it shouldn't be hurting.
I don't advise running or even treadmill because the pounding hurts the spine. You can walk all you want, even a quick forced walk, but don't run. The only running I recommend is on a Rebounder, one of those little trampolines. 6 minutes of an easy jog on that is equal to a one mile run. It's cellular exercise and will get you breathing and sweating pretty good. You'll be surprised.
Barefoots BF&C is an excellent product to rebuild tissues. "B" = Bone. "F" = Flesh and "C" = Cartilage. It works.