I had a shot in each knee every four months for about 3 1/2 years. Tried the series of Synvisc shots (one shot each knee for five weeks in a row) and they did nothgin. Cortisone helped to postpone my TKR because they said I was too young. Osteoarthritis progressed from fall at age 32 until first TKE at age 56. When Dr. had trouble getting needle in for shot I knew it was time for surgery. First TKR (right) in 12/09, second TKR (left) in 4/2011. Shots gave me no trouble and caused no damage. Just keep them to 3 or 4 a year.