 The purpose of this study is to compare the effectiveness of tramadol hydrochloride 37.5 milligram mg plus acetaminophen 325 mg maintenance with that of non-steroidal anti-inflammatory drugs NSAIDs maintenance in participants with knee osteoarthritis a progressive and degenerative joint disease, in which the joints become painful and stiff whose pain was relieved after the add-on treatment of tramadol hydrochloride to NSAIDs. 