Group A oral tramacet 2 tablets preoperatively, 2 tablets every 6 hours for 5 days then 1-2 tablets of tramacet prn to a maximum of 8 tablets per day. Naloxone infusion starting preop at 0.25ug/kg/hr and continuing during hospital stay (an equivalent of 400ug over 24 hours in a 70 kg man). The infusion will be discontinued 1 hour before patient discharge.

Group B will receive oral tramacet 2 tablets preoperatively and then 2 tablets every 6 hours for five days. ( or until discharge. Patient VAS after discontinuation of morphine PCA may dictate addition of oral narcotic oxycodone after discharge). This group will also receive saline infusion at 4-6mls / hour for the duration of the hospital stay.

Group C will receive oral Acetaminophen tablets 1 gm preoperatively and subsequently 6 hourly plus an infusion of saline (placebo) at a rate of 4-6mls / hour for the duration of their stay.

Group A: oral tramacet 2 tablets preoperatively, then 2 tablets every 6 hours for 5 days then 1-2 tablets of tramacet prn to a maximum of 8 tablets per day. A naloxone infusion will started preop at 0.25ug/kg/hr and will continue during patient's stay in hospital (an equivalent of 400ug over 24 hours in a 70 kg man). Infusion discontinued 1 hour before patient discharge. All the patients in groups A and B will be provided Morphine PCA for the duration of their hospital stay. Use of morphine PCA will be noted.Oral celebrex 200mg will be given to all the patient twice a day for five days as per our standard practice. All patients will receive peri-articular infiltration with local anesthetic solution intraoperatively by the surgeon as per our standard practice.