Treating knee osteoarthritis can be broken into two components. There's reducing the inflammation within the knee, and then there's getting all of the muscles and biomechanics right to take the pressure off the knee so that the same forces are not going through it so the inflammation does not re-accumulate.
When the pain is not getting better with physical therapy or the pain is interfering with the person's ability to participate in physical therapy, there are oral medications to help with the pain that won't fix anything but can certainly help with symptoms. There are also different kinds of injections that one can do to take away the pain and inflammation from the arthritis.
There are two broad categories: one is steroids. You can inject steroids into the knee, which will not fix the arthritis in the knee but it will open up a window of opportunity during which a person can take advantage of not having pain in the knee in order to stretch, strengthen, be more active, lose the weight, and tweak the biomechanics so that the pain does not come back in 3-6 months because the mechanics have shifted so that the same forces are not going through the knee.
The other broad category of injections is hyaluronic acids. This is basically like putting an oil change into the knee. Hyaluronic acid is basically joint fluid. What happens in the knee is that you start to lose some of the joint fluid. What the pharmaceutical companies have done is create a synthetic joint fluid that you can put back into the knee through a series of injections. Depending on the brand that you use, it can be one, three, four, or five injections.
This is like paving the potholes over a road. If you think of arthritis as potholes in the road, this just puts a coat of lubricant over it. Again, you are not fixing the arthritis; the injections do wear off over a period of typically 6 months. But if you use that time when the pain and inflammation is down as a window opportunity to stretch, strengthen, and affect the biomechanics, then ideally as the injection wears off, the pain will not come back because the mechanics have been tweaked.