The objective of this clinical trial is to compare two regional analgesia techniques in patients undergoing total knee arthroplasty: IPACK (Infiltration of local anesthetic between the Popliteal Artery and Capsule of the Knee) vs selective tibial nerve block. The main question is whether one of these peripheral blocks is more effective in reducing postoperative pain than the other. All patients will have a spinal block with an adductor canal block. One group will receive an IPACK block and the other group, a selective tibial nerve block. Postoperative pain scores and morphine consumption, among others, will be compared between groups.