When muscles in the thigh become unbalanced, then pressure is exerted on the knee in places it is not designed for.

The major culprit is the quads... the large front muscles of the knee that extend it. The hams in back tend to be stronger than the quads.
quads:
http://www.shapefit.com/training-quads.html
This shows a picture of the "quads".

When they get weaker than the muscles behind the thigh, then the knee suffers. You can strengthen the quads by just sitting a a chair with your back straight and lifting the leg until it is even with the thigh.

Over time you can add 1 pound a week, you can slowly develop the quads to balance the leg.

I had a Continuing Ed lesson a while back that said up to 70% of all knee pain and resulting osteoarthritis can be traced to imbalanced muscle actions on the knee from wear and tear.

If you have no swelling/heat then I would think you are not acute with an inflammatory process.

There are also patches over the counter called Salonpas, which may help in mild OA or muscle/tendon strain situations.
I've used them for years with success.

You need x-rays to show how much cartilage you have left.
If you are bone on bone, you are in a bad place. If you have some cartilage left you can improve it with SAMe, supplement that heals joints. But if cartilage is gone, that is not likely to work. If you search SAMe on Vitamin forum, there is a long thread on it. I use it daily too. I avoided a knee replacement with it, and also do the leg exercises.