• WOMAC total score: Day 85 - Day 29 (randomization)
  

• Pain intensity, pain relief, subject's and investigator's overall evaluation on the study medication, swelling and tenderness
  

Osteoarthritis(OA) is a typical musculoskeletal condition that causes pain. It affects women more than men, and its prevalence increases with age. The worldwide prevalence of symptomatic OA among those aged>60 years is estimated to be 9.6% in men and 18.0% in women. OA affects an estimated 139 million worldwide. The severity of OA symptoms is influenced by attitudes, anxiety, depression, and activities of daily living. In the absence of a cure other than joint replacement surgery, patients with severe OA require pharmacologic control of their pain. NSAIDs, acetaminophen, tramadol, tramadol combination, glucosamine and chondroitin sulfate have been used to treat osteoarthritis pain. Tramadol/acetaminophen add-on treatment to non-steroidal anti-inflammatory drugs(NSAIDs) for the osteoarthritis flare pain improved significantly in pain intensity and pain relief, compared with placebo. Also, tramadol/acetaminophen add-on treatment for three months in the osteoarthritis patients taking NSAIDs had significantly relieved pain. In routine clinical practice, if pain is relieved to some degree after tramadol/acetaminophen and NSAID combination therapy, one of them is discontinued. This clinical study will compare the effectiveness of tramadol 37.5mg/acetaminophen 325mg maintenance with that of NSAIDs maintenance after their combination therapy. The study hypothesis is that the treatment effect of tramadol 37.5mg/acetaminophen 325mg group is not inferior compared to that of NSAIDs group for treatment of knee osteoarthritis pain. This is a multicenter, randomized, open comparative study to compare the efficacy of tramadol 37.5mg/acetaminophen 325mg maintenance with that of NSAIDs maintenance in patients whose pain was relieved after the add-on treatment of tramadol 37.5mg/acetaminophen 325mg to NSAID. All patients will receive tramadol 37.5mg/acetaminophen 325mg 1 tablet at night for the first 3 days, then 1 tablet twice a day for 4 days, and 1 tablet three times a day for next 3 days with NSAIDs(meloxicam or aceclofenac). If there is no pain relief, tramadol 37.5mg/acetaminophen 325mg can be increased up to 8 tablets per day for day 11~28 with NSAIDs, and then the patients will be randomized into 2 treatment groups at Visit 3(day 29). Tramadol 37.5mg/acetaminophen 325mg group will receive the dosage that is fixed at Visit 3 and this dosage shoud be maintained for day 29~85. There are two groups in NSAIDs group. Meloxicam group will receive 7.5mg or 15mg per day for day 29~85. Aceclofenac group will receive 100mg twice a day for day 29~85.

All patients receive tramadol 37.5mg/acetaminophen 325mg (T/A) 1T hs for 3 days followed by 1T twice a day for 4 days, then, 1T three times a day for 3 days with NSAIDs. T/A can be increased up to 8Ts/day for day 11~28 with NSAIDs. After randomization at Visit 3, T/A group will take the dosage fixed at Visit 3 and it shoud be maintained for day 29~85. There are two NSAID groups. Meloxicam group take 7.5mg or 15mg daily for day 29~85. Aceclofenac group take 100mg twice a day for day 29~85.

Inclusion Criteria:

• Patients who have suffered from knee osteoarthritis at least for one year and meet the criteria of American College of Rheumatology
• Patients who are taking stable dose of meloxicam 7.5mg/15mg daily or aceclofenac 100mg twice a day at least for four weeks
• Patients whose mean pain intensity has been 5 or higher on the numeric rating scale (NRS) for the last 48 hours
• Patients whose general health conditions are favorable, according to the criteria below: Medical and medication history, Physical examination before the study medication administration, Vital signs: Blood pressure, pulse. Clinical laboratory tests: Lab test results < 2 x normal range (Hepatic function: SGOT/SGPT < 2 X normal range, Renal function: Creatinine < 2.0mg/dl)
• Female patients of childbearing potential to use the proper contraceptive methods during the study period (Urine pregnancy test prior to the study participation should be negative)
• Patients who can read and understand written instructions
• Patients who can understand the characteristics of the study after listening to the explanation about the clinical study and sign on patient informed consent form

Exclusion Criteria:

• Patients who are applicable to Kellgren and Lawrence grade 4
• Patients who had failed tramadol treatment before or stopped taking tramadol due to adverse event(s)
• Patients who took antidepressant, anticonvulsant or cyclobenzaprine within 14 days prior to the study medication administration (However, patients who are taking stable dose of selective serotonin reuptake inhibitor (SSRI) or selective norepinephrine reuptake inhibitor (SNRI) for the purpose of treating depression or anxiety two months prior to the study medication administration and are supposed to continue the same dose of the medication during the study period are eligible for enrollment.)
• Patients who are taking stable dose of other analgesics than meloxicam or aceclofenac (including local therapeutic agents or anesthetics), sedative-hypnotic (e.g., diazepam), muscle relaxant, or other agents (e.g., diacerein), within five times the half life of the medication prior to the study medication administration
• Patients who started to take the nutraceutical(s)(e.g., glucosamine) within four weeks prior to the study medication administration(If a nutraceutical is used four weeks prior to the study medication administration, the same dose should be maintained during the study period.)
• Patients who are applicable to one of the following conditions: Rheumatoid arthritis, Ankylosing spondylitis, Active gout or active pseudo-gout, Diagnosis of fibromyalgia (according to ACR Criteria), Anserine bursitis, Major trauma of the target joint within six months prior to the study medication administration, Infection of the target joint within six months prior to the study medication administration, Apparent avascular necrosis of the target joint within six months prior to the study medication administration, Anatomical deformities of the target joint, which may interfere with assessment of the target joint, Surgical procedures associated with the target joint within one year prior to the study medication administration, Arthroscopic procedures associated with the target joint within six months prior to the study medication administration
• Patients who are applicable to warnings, cautions, or contraindications in the study medication instruction booklet
• Patients who were treated with corticosteroid injection to the target joint within two months prior to the study medication administration, who were treated with hyaluronan injection to the target joint within six months prior to the study medication administration, or who were treated systemic steroids within three months prior to the study medication administration
• Patients who have one of the following diseases: Significantly unstable diseases such as sleep disorder (e.g., sleep apnea or narcolepsy) or dementia, Functional damage or disease which may cause malabsorption, excessive accumulation, or metabolism or excretion disorder
• Patients who suffer from significant psychiatric illness (e.g., major depression) or is taking antipsychotics
• Patients who have tried to commit a suicide or have a tendency to commit a suicide
• Subjects who have a history of drug abuse or chronic alcohol abuse
• Patients who are pregnant or breast-feeding
• Patients who have participated in other clinical study within 30 days prior to the clinical study start