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 Say Goodbye to Knee Pain With Knee Gel Injections Synovial Fluid = Knees Natural Lubricant, It reduces friction, nourishes cartilage & absorbs shock, Low or poor quality synovial fluid more friction cartilage wear knee arthritis, Why FSA Eligible Joint Lube Fast Acting Glucosamine, 16 fl oz. (2 Pack) FSA Store