Hylan G-F 20 is similar to the fluid that surrounds the joints in your body. This fluid acts as a lubricant and shock absorber for the joints. Hylan G-F 20 is used to treat knee pain caused by osteoarthritis. Hylan G-F 20 is usually given after other arthritis medications have been tried without successful treatment of symptoms. Hylan G-F 20 may also be used for purposes not listed in this medication guide.