Study of Evaluating the Duration of Efficacy of One Intra Articular Injection of Sodium Hyaluronate 2.0% in Patients With Painful Osteoarthritis of the Knee

Inclusion Criteria: 1. Patients of both genders between 40 and 70 years of age; 2. Primary tibiofemoral osteoarthritis of the knee according to American College of Rheumatology criteria; 3. Pain ≥ 4 on a 10 point scale for at least two out of five subscores of the WOMAC Section A at baseline; 4. Radiologically ascertained grade II or III severity knee osteoarthritis on the Kellgren-Lawrence scale; 5. Having given signed informed consent. Exclusion Criteria: 1. Secondary knee osteoarthritis, including: * septic arthritis; * inflammatory joint disease; * gout; * recurrent episodes of pseudogout; * Paget's disease of bone; * articular fracture; * ochronosis; * acromegaly; * haemochromatosis; * Wilson's disease; * primary osteochondromatosis. 2. Clinical signs of acute flare (pain, warm, erythema, effusion of signal knee) at baseline; 3. Axial deviation \> 15 degrees in valgus or varus on a standing X-ray; 4. Clinically significant medio-lateral or antero-posterior instability; 5. Rapid destructive arthritis, evolving arthritis requiring surgery within the coming year; 6. Significant injury to the signal knee within 6 months prior to baseline; 7. Complete loss of range of motion; 8. Painful knee conditions other than osteoarthritis (e.g., Sudeck's atrophy, intra-articular neoplasm, villonodular synovitis); 9. Necrosis of one of the femur condyles; 10. History or evidence of gout, chondrocalcinosis; 11. Peripheral neuropathy; 12. Concomitant rheumatic disease: * fibromyalgia; * rheumatoid arthritis; * collagen diseases; * psoriatic arthritis and other seronegative spondylarthropathies (e.g., ankylosing spondylitis); * metabolic and crystal-induced arthropathies; * other osteopathies. 13. Contraindications to intra-articular injection according to investigator's judgement (e.g., local infection at injection site, generalised infection with possible bacteraemia); 14. Skin disease in the area of injection; 15. Severe coagulopathy, ongoing anticoagulation therapy; 16. Accompanying OA of the hip of sufficient severity to interfere with the assessment of the signal knee; 17. Disease of spine, hip or other lower extremity joints of sufficient degree to affect assessment of the signal knee; 18. Poor general health interfering with compliance or assessment; 19. Concomitant disease/ailment other than knee OA requiring the regular use of the patient's normal analgesic medicine; 20. Initiation of chronic treatment with antihistaminics, glucocorticoids, antidepressants or tranquilisers, within less than 3 months prior to baseline; 21. Use of assistive devices other than a cane (walking stick); 22. Surgery of the signal knee other than arthroscopy; 23. Arthroscopy of the signal knee within one year prior to baseline; 24. Treatment with symptomatic slow acting drug for OA (SYSADOA, i.e., chondroitin sulfate, diacerein, glucosamine, piascledine), unless the patient has been on a stable dose for at least 4 months prior to baseline; 25. Intra-articular depocorticosteroid injection into the signal knee within 3 months prior to baseline; 26. Intra-articular SH injection into the signal knee within 6 months prior to baseline; 27. Ascertained hypersensitivity to any product used in the study (SH, paracetamol, diclofenac, omeprazole) or to similar compounds; 28. Pregnant or lactating female; 29. Female of childbearing potential without adequate contraceptive methods; 30. Participation in a drug clinical trial within 3 months prior screening; 31. Patients who, in the judgement of the investigator, will not comply with the protocol.