ObjectiveTo evaluate the safety and efficacy of a single intra-articular injection of 2% hyaluronic acid (HA)+mannitol in symptomatic knee osteoarthritis (KOA). Material and methodsPilot, multicentre, open, non-comparative study performed in eighty patients with painful KOA, of whom 79 completed the study. They received one injection of 2ml of 2% HA+0.5% mannitol (Day 0) and were followed-up for 6 months. On Days 0, 15, 30, 60, 90, 120, 150 and 180, pain and joint function were assessed using a visual analogue scale (VAS) and WOMAC index. Efficacy and safety by investigator and patient, and rescue medication, as an indirect measure of pain, were also recorded. ResultsA significant reduction in joint pain, stiffness and functional disability compared with baseline was observed at every follow-up visit (P<.001). Joint function improved by 38.7% on Day 30, reaching 47.5% on Day 180. Rescue medication use decreased from 58.2% at baseline to 2.5% on Day 90, increasing in the last visits. Efficacy and safety were positively evaluated by investigators and patients. No serious adverse events were observed. Mild side effects were reported in 4 patients (local pain and swelling in the infiltration area). DiscussionThere is evidence that repeated intra-articular injections of HA improve symptoms in KOA. However, studies with a single injection of HA have shown mixed results. This study demonstrates that one single intra-articular injection of non-cross-linked HA reduces joint pain and increases function in patients with KOA over a period of at least 6 months.