Your knee isn't just a hingeit's a living, dynamic system built to move. Inside every healthy knee is synovial fluid, the natural lubricant that reduces friction, delivers nutrients to the cartilage, Gel injections (also called viscosupplementation) are used to treat joint pain from arthritis, especially in the knee. The gel acts as a lubricant and shock absorber inside the joint, helping reduce friction, Knee Osteoarthritis: Early Signs, Causes, Diagnosis, Treatment Joint fluid fills the small space between the ends of bones and acts like a natural lubricant. The synovial membrane creates this thick, silky fluid using long molecules that hold water and give it a Knee Gel Injections (Viscosupplementation): Uses & Side Effects