OXN PR Compared to OXY PR in Subjects With Postoperative Pain After Knee Arthroplasty

Inclusion Criteria: * Males and females 18 - 75 years of age. * Body mass index (BMI) 18 - 35 kg/m2. * If female and less than one year post-menopausal: * negative serum or urine pregnancy test (positive beta-human chorionic gonadotrophin test) at screening. * using an adequate and highly effective method of contraception throughout the study. A highly effective method of contraception is defined as one with a failure rate of less than 1% per year when used consistently and correctly. Examples include sterilisation, implants, injectables, combined oral contraceptives, hormonal intra uterine devices, sexual abstinence or vasectomised partner. * Confirmed diagnosis of osteoarthritis of the knee. * Planned surgical arthroplasty on one knee. * Planned postoperative epidural analgesia for approximately 48 hours. * Anticipated requirement for daily opioid treatment after epidural analgesia for 2.5 days. * Able to participate in the study and have given written informed consent. Exclusion Criteria: * Females who are pregnant or lactating. * Opioid use within 3 months before the start of the screening period. Stable treatment with analgesics in World Health Organisation (WHO) Step I (non-opioid analgesics) is allowed. * History of laxative use to treat constipation within 3 months before the start of the screening period. * History of chronic constipation. * Concurrent rheumatoid arthritis. * Planned bilateral arthroplasty or revision knee arthroplasty. * History of moderate to severe hepatic impairment. * History of moderate to severe respiratory depression with hypoxia or hypercapnia, chronic obstructive pulmonary disease, cor pulmonale, bronchial asthma, or any severe impairment of pulmonary function. * History of uncontrolled hypothyroidism, Addison's disease (adrenal cortical insufficiency), psychosis, cholelithiasis, prostatic hypertrophy(with documented residual of over 100 ml after voiding), delirium tremens, pancreatitis, hypotension, uncontrolled hypertension, uncontrolled cardiovascular diseases, head injury, epileptic disorder or predisposition to convulsions, or treatment with monoamine oxidase inhibitors (concurrent or within 2 weeks of discontinuation). * Contraindication to treatment with opioids. * History of hypersensitivity to oxycodone, naloxone, or to any of the excipients of OXN PR tablets. * History of non-opioid induced paralytic ileus. * Previous or current history of drug abuse, including alcohol abuse or opioid abuse. * Evidence of clinically unstable disease * Receipt of an investigational medicinal product within 30 days before the start of the screening period. * Galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption. * Delayed gastric emptying. * Severe renal impairment (i.e. creatinine clearance \<10 mL/minute). * Weight \<50 kg.Inclusion Criteria: