The present invention relates to a polyacrylamide hydrogel for use in prevention and/or treatment of synovitis or pain associated with synovitis in a mammal by formation of an extra layer to the synovial membrane i.e. a sub-synovial layer and a novel synovial lining layer. Synovitis may occur in association with arthritis, such as osteoarthritis or rheumatoid arthritis, lupus, or gout, and the mammal suffering from synovitis is a preferably a human, a racing animal or a companion animal.