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 Osteoarthritis: Early Signs, Causes, Diagnosis, Treatment Knee Gel Injections (Viscosupplementation): Uses & Side Effects Is Knee Gel Injection the Right Solution for You? Promoting Synovial Fluid Production for Better Joint Health