A single-centre double-blind randomized controlled trial in patients undergoing primary total knee arthroplasty. All subjects receive PCA morphine, paracetamol 1g every six hours, etoricoxib 120mg once daily postoperatively. Subjects receive either pregabalin 75mg po preoperatively followed by 75mg OM and 25mg ON for two days postoperatively or matching placebo. The primary outcome is cumulative morphine consumption at 72 hr following surgery. Secondary outcome measures included pain scores, knee range of motion and patient satisfaction.