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 How Hyaluronic Acid Injections Alleviate Arthritic Knee Pain The Spine and Sports Center Knee Gel Injections Non Surgical Knee Pain Treatment Joint Relief Institute 5 Ways to Increase Synovial Fluid wikiHow