The most common ailment I hear of for the knee is a meniscus tear. This is because of how easy it is to do this. The knee gets very little blood flow which unfortunately makes the knee one of the hardest to heal. The body has a natural ability to heal by bringing any injured area blood flow, but the rate at which it does so, especially for the knee, is very slow. To help increase mobility and and reduce the pain and stiffness with the knee, focus on things that increase the blood flow (but with minimal strain on the knee). I recommend treatments that don't require a lot of exertion in being able to do so. Things such as massage therapy, ultrasound, BFST, acupuncture, etc. These types of treatment give you the nutrients and oxygen you need to heal but reduce the risk factors involved with a lot of physical activity. It's also very important to follow anything physical with a cold compress. If the area is inflamed it impedes the blood flow even more than it would typically. Get the inflammation down, then increase the circulation. My main recommend is the BFST. I have heard and seen the results first hand and think it is wonderful.