The investigators aimed to demonstrate that dexamethasone added as an adjuvant to local anaesthetic agent in suprainguinal fascia iliaca block for effective postoperative analgesia after knee arthroplasty would prolong the duration of sensory block and reduce postoperative pain intensity and analgesic consumption.

Total knee arthroplasty is one of the major orthopedic surgeries that cause severe postoperative pain. A successful post-operative outcome is possible with strong and effective pain control followed by early mobilization and a good functional recovery. Suprainguinal fascia iliaca plan block (SFIB) has been shown to be an effective postoperative method in multimodal analgesia regime in lower extremity surgery. It has been reported in the literature that dexamethasone added to local anaesthetics in peripheral nerve blocks prolongs the duration of sensory block, improves the quality of analgesia, reduces postoperative pain intensity and opioid consumption.

In this study, the investigators aimed to demonstrate that dexamethasone added as an adjuvant to local anaesthetic agent in SFIB for effective postoperative analgesia after knee arthroplasty would prolong the duration of sensory block and reduce postoperative pain intensity and analgesic consumption.

An identification number will be randomly assigned to each participants, whose written consent was obtained before the surgery, when they are admitted to the postoperative recovery room. In the postoperative period, participants will be followed up with these numbers. Which group the participants will be included in will be determined by the closed envelope method.

Participants undergoing unilateral knee arthroplasty will be included in the study. Following the end of surgery, the participants will be divided into two groups in the recovery room and SFIB will be applied to both groups. Participants in group SFIB will receive 0.25% bupivacaine as local anaesthetic. Participants in group SFIB+dexamethasone will receive 0.25% bupivacaine as local anaesthetic and 8 mg dexamethasone as adjuvant.

The participant with the block will be followed in the recovery room and if the block is successful, morphine patient controlled analgesia (PCA) treatment will be started and the participant will be taken to the ward. A standard analgesia regimen (1 g iv paracetamol every 8 hours, 50 mg iv dexketoprofen every 12 hours) was used in all participants.

Evaluation of postoperative pain will be done with numerical rating scale (NRS). Pain levels will be questioned in two different ways as rest and passive moving.

Inclusion Criteria:

• Having undergone unilateral knee replacement surgery under elective conditions,
• Age range of 18-75 years,
• American Society of Anesthesiologist's physiologic state I-III patients,
• written consent who agreed to participate in the study.

Exclusion Criteria:

• BMI>35
• who do not want to be included in the study by not signing the voluntary consent form,
• Local infection, hematoma, hernia, neoplasm etc. in the area to be blocked. found,
• Coagulopathy, hepatic or renal failure,
• Allergic to a local anesthetic agent or one of the drugs used in the study,
• Having a history of chronic opioid and corticosteroid use,
• who cannot use the patient-controlled analgesia system and have a psychiatric disease,
• with operative time less than 20 minutes and more than 120 minutes for better standardization of studies.

Researched data and statistical analyzes will be available from the journal in which the clinical study was published

The patient will not know which study group he is in. The anesthetist, who will perform the regional block, will give the block to be applied in a sealed envelope by an assistant staff outside the study, and at the same time, the patient will not know which block has been made. The anesthesiologist who made the block will not participate in the pain follow-up of the patients. Postoperative pain assessment and data collection will be performed by another investigator blinded to the study.