I. Introduction
Osteoarthritis (OA) is the most common joint disease for adults worldwide [1]. By 2020, OA is predicted to become the fourth leading cause of disability globally [2]. Standard treatments usually begin with non-pharmacologic approaches for symptom relief and functional recovery, including weight loss, orthotic devices, diet, exercise and physical therapy. Since these treatments usually provide limited pain relief, analgesics are widely used during the treatment of OA.