The study compares three different analgesic techniques in order to determine which one serves as the optimal method for postoperative pain management after Total Knee Arthroplasty in patients suffering from Osteoarthritis

Prospective, randomized, controlled study. Approval of the study from the University Hospital of Patras Ethics Committee. The Total Knee Arthroplasty procedure is performed always from the same team of Orthopedic surgeons who follow the same technique in each patient for the arthroplasty and the placement of the intraarticular catheter as well. The same team of Anesthesiologists (two Anesthesiologists) performs always the same technique for each analgesic method and is responsible for the patients' perioperative condition concerning anesthesia and analgesia.

Preoperatively, one hour prior to the surgery, all patients receive preemptive multimodal analgesia in the following way; 40mg Parecoxib (iv), 1gr Paracetamol (iv), 150mg Pregabalin (po), 8mg Dexamethasone (iv) και 50mg Ranitidine (iv).

All patients receive subarachnoid anesthesia with Ropivacaine 0.75% (7,5mg/ml) in a dosage of 2-3ml titrated according to patient's age and height.

Three groups

1. Continuous epidural infusion (control group) with Ropivacaine 0.2% + clonidine 150μg.
2. Continuous femoral nerve blockade infusion with Ropivacaine 0.2% + clonidine 150μg.
3. Continuous intraarticular infusion with Ropivacaine 0.2% + clonidine 150μg.

All the catheters remain for 48 hours while the infusion rate is 2ml/h + PCA with 0,5ml/15min and lock-out maximum dose 4/h in total volume of 150ml.

Postoperatively all patients also receive; Parecoxib, Paracetamol, Pregabalin, and Ranitidine up to the third postoperative day (doses titrated).

Rescue analgesia: Tramadol Chloride 50-100mg x 2 /24h depending on patient's age and medical history.

Inclusion Criteria:

1. Patients scheduled for unilateral total knee arthroplasty (TKA) to treat knee osteoarthritis (OA)
2. Fully conversant in the Greek language
3. Written informed consent to participate in the trial

Exclusion Criteria:

1. Age less than 50 years and greater than 85 years.
2. ASA score >III
3. Pregnancy
4. Subarachnoid anesthesia failure
5. Hypersensitivity/ allergy to certain agent used
6. Participation in other research/ study
7. Severe mental disease (schizophrenia, major depression, severe bipolar disorder, substance abuse)