495 patients with primary osteoarthritis were randomized to one of 3 groups: a group receiving intra-articular injections of hyaluronic acid and placebo pills, a group receiving sham injections and naproxen pills, or a group receiving a placebo (saline) injection and placebo pills. The purpose of the study was to compare the efficacy of hyaluronic acid treatment in pain reduction, compared to a placebo and to oral naproxen up to 26 weeks after starting treatment. The primary outcome of interest was pain after a 50ft. walk, while secondary outcomes included further pain measurements (WOMAC and global assessment) and adverse events. Results showed hyaluronic acid treatment to result in significantly lower pain scores following the 50ft walk test at 4, 5, 12, 21, and 26-week time points compared to placebo, and no significant difference compared to naproxen at any time point.