Healthy joints are lubricated and cushioned by fluid inside the joint. Osteoarthritis causes the joints to become sore and stiff because the joint fluid loses its ability to lubricate and cushion.

Doctors have observed good results with a material called hyaluronin, a substance that imitates the fluid in your knee joint. The fluid is injected directly into the sore joint up to three times over a period of several weeks. Some people find that the benefits begin to wear off. When this happens, additional injections can be given every six months. 

Many patients who have had these shots report less pain and find it easier to do their activities. However, people with more advanced knee osteoarthritis don't always benefit from the shots.