A single center, randomized parallel group pilot study to investigate the mechanism of action of tapentadol PR and oxycodone CR in subjects with osteoarthritis knee pain

To assess which pain mechanisms (with specific focus on the descending inhibition) are modulated by daily administration of 2 x 100-250 mg tapentadol PR compared to 2 x 20-50 mg oxycodone CR in subjects with osteoarthritic (OA) knee pain during a treatment period of 4-weeks (preceded to a titration period of up to 15 days).