Résumé : Background: This pilot open noncontrolled study was designed to assess the efficacy of intra-articular injections of a solution combining hyaluronic acid (HA) and chondroitin sulphate (CS) in the treatment of outpatients affected by knee osteoarthrosis. Findings: Thirty patients with knee OA have been included. The primary objective was to assess clinical efficacy as measured by pain and Lequesne's index. Secondary objectives were to assess potential effect of the treatment on ultrasound parameters, safety and biomarkers of cartilage metabolism and joint inflammation. After a selection visit (V1), the study treatment was administered 3 times on a weekly basis (V2, V3, V4). Follow-up was planned 6 (V5) and 12 weeks (V6) after the first intra-articular injection. Efficacy results showed a reduction in mean pain at V3 and V6 and in functional impairment, the most marked changes being measured at the two follow-up visits (V5 and V6). Although statistical significance was not achieved due to small sample size, a clear tendency towards improvement was detectable for ultrasound assessments as well as biomarkers. Except for a mild injection site hematoma for which the drug causal relationship could not be excluded, no adverse effect of clinical relevance was recorded during the study. Conclusion: Although this pilot study was performed according to an open design only, the ultrasound as well as biomarkers changes strongly suggest a non-placebo effect. These preliminary results call now for a randomized controlled study to confirm the clinical relevance of the observed results. © 2012 Henrotin et al.; licensee BioMed Central Ltd.