 The primary efficacy outcome measure is represented by the change in the Lequesne algo-functional index assessed at clinic visits after 6 months in the intention-to treat population, analysed by the General Linear Model GLM procedure for ANOVA, with Dunnets pairwise comparisons versus placebo. Efficacy in patients completing treatment according to the protocol per-protocol completers will be also assessed. Secondary efficacy outcome measures include the changes in the WOMAC index and the calculation of the proportion of patients that can be defined responders to treatment according to the Osteoarthritis Research Society International OARSI criteria 2000. The use of the rescue medication is also assessed. 