Evaluation of Effectiveness and Tolerability of Tapentadol Hydrochloride in Subjects With Severe Pain Due to Osteoarthritis Taking WHO Step III Analgesics But Showing a Lack of Tolerability.

Inclusion Criteria: * Participants must have signed an Informed Consent Form indicating that they understand the purpose of and procedures required for the trial and are willing to participate in it. * 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. * Participants must be appropriately communicative to verbalize and to differentiate with regard to location and intensity of the pain. * Participants must be at least 40 years of age. * 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. * Participants must have pain at the reference joint which has been present for at least 3 months. * Participant's pain must require a strong analgesic (defined as WHO Step III) as judged by the Investigator * Participant must be taking a WHO Step III analgesic on a daily basis for at least 2 weeks prior to the Screening Visit. * Participant must have responded to the WHO Step III analgesic, i.e., participant must have a confirmed average pain intensity score (NRS 3) of smaller or equal to 5 points during the last 3 days prior to the Screening Visit. * Participant must report opioid-related side effects as the reason to change their analgesic * Participant must report a rate of satisfaction with their previous analgesic regimen not exceeding "fair" on a subject satisfaction with treatment scale (5-point VRS). Exclusion Criteria: * Presence of a clinically significant disease or laboratory findings that in the Investigator's opinion may affect efficacy or safety assessments. * Presence of active systemic or local infection that may, in the opinion of the Investigator, affect the efficacy, quality of life/function or safety assessments. * History of alcohol or drug abuse, or suspicion thereof in Investigator's judgement. * Presence of concomitant autoimmune inflammatory conditions. * Known history of or laboratory values …