Evaluation of Effectiveness and Tolerability of Tapentadol Hydrochloride in Subjects With Severe Pain Due to Osteoarthritis Taking Either WHO Step I or Step II Analgesics or no Regular Analgesic

Inclusion Criteria: 1. Participants have signed an Informed Consent Form indicating that they understand the purpose of and the procedures required for the trial and are willing to participate in it. 2. Participants are men or non-pregnant, non-lactating women. Sexually active women must be postmenopausal, surgically sterile, or practicing an effective method of birth control (e.g., prescription oral contraceptives, contraceptive injections, intrauterine device, double barrier method, contraceptive patch, male partner sterilization) before entry and throughout the trial. Women of childbearing potential must have a negative pregnancy test at screening. 3. Participants must be appropriately communicative to verbalize and to differentiate with regard to location and intensity of the pain. 4. Participants must be at least 40 years of age. 5. Participants must have a diagnosis of osteoarthritis of the knee based on the American College of Rheumatology (ACR) classification criteria: * Knee pain and * Radiographic osteophytes or * Knee pain and * Aged 40 years or above, and * Morning stiffness of less than 30 minutes of duration and * Crepitus on motion. 6. Participants must have pain at the reference joint which has been present for at least 3 months. 7. Participant's pain must require a strong analgesic (defined as WHO Step III) as judged by the Investigator. 8. Participants must report a rate of satisfaction with their previous analgesic regimen not exceeding "fair" on a participant satisfaction with treatment scale (5-point VRS). 9. If under regular, daily pretreatment: * Participants must be taking a WHO Step I or Step II analgesic medication for osteoarthritis of the knee on a daily basis for at least 2 weeks prior to the Screening Visit. * The Investigator considers dose increase of WHO Step I analgesics (as mono- or combination therapy) and/or continuation with or dose increase of WHO Step II analgesics inadequate for the individual participant, whatever applicable. * Participants must have an average pain intensity score (NRS 3) greater than 5 points during the last 3 days prior to the Screening Visit. OR if no regular analgesic pretreatment is reported: * Participants must have an average pain intensity score (NRS-3)greater than 6 points in the last 3 days prior to the Screening Visit and related to osteoarthritis. Exclusion Criteria: 1. Presence of a clinically significant disease or laboratory findings that in the Investigator's opinion may affect eff…