Arthritis can be caused by a variety of factors including wear and tear on your joints, genetics, and previous injuries. Symptoms of arthritis in your knee can include pain, stiffness, swelling, and weakness/loss of function. These symptoms can often impact overall joint function and range of motion. Frequently, joint function can be improved with exercises provided by a physical therapist. I see range of motion loss as the most common problem in these folks, making it a problem that you can work on. Gaining full range of motion and improving your strength can spread out the pressure you are putting on the joints and therefore working to relieve pain.
Think of it like this: Imagine you are sitting on the couch without shoes on and a family member steps on your foot in a stiletto. It is going to hurt a lot because the weight of your family member is being funneled into an area the size of the stiletto. If that same person stepped on your foot with a sneaker, it would hurt significantly less. This is because the pressure is spread out over a much wider area.
So what does this mean for your body? If your knee is stiff, you are putting a lot of pressure in a small space, causing pain in the knee. Once your range of motion has improved, you are spreading the pressure of walking/standing throughout a larger area, often leading to less pain in the knee. Simple knee extension stretching can improve your range of motion, and help you spread out the pressure felt in the knee while standing, walking, and performing stairs. I suggest low pressure and long duration stretches, as opposed to high-intensity stretches that can aggravate the ligaments and tendons around the knee. In addition to stretching, a variety of manual techniques can be performed by a therapist to improve range of motion. Once your range of motion has improved, you can work on your strength to improve the stability in the knee.
Active stretches: This type of stretch is created when you are using your body to actively produce the force of the stretch. In this picture, the patient is using his hands to push the knee straight. This stretch can be done anywhere, but is easiest to perform when seated. This particular stretch is more aggressive than a passive stretch, but you should just feel mild discomfort around the knee, not true pain. Because it is more aggressive, only hold this stretch for about 30 seconds.
Passive stretches: This type of stretch is created when you are allowing an outside force, in this example gravity, to passively impose force onto your body. The heel is propped up to allow space for the calf. Then the weight of the heating pad over the knee is used to provide extra pressure if needed. This type of stretch is best done lying down, or anywhere you are comfortable with your leg propped up for several minutes. This stretch is less aggressive than the active stretch, and will be held for several minutes, rather than 20-30 seconds.