306 patients were randomized to receive either intra-articular hyaluronic acid (HA) injections or placebo injections for the treatment of knee osteoarthritis. The purpose of this study was to compare the efficacy and safety of each treatment by investigating whether there is a difference in the number of patients displaying a clinical response to treatment in each group. It was found that a significantly higher proportion of patients in the HA group showed a clinical response to treatment compared to the placebo group at 40 months and that the use of repeated HA injections were more successful in alleviating pain and improving function.