The goal of this observational study is to compare the equivalent analgesic efficacy of three regional anesthesia techniques in total knee replacement surgery. The main question it aims to answer is:

• Non inferiority of each technique in relation to the others Participants will receive selective spinal anesthesia and the antalgic nerve block depending on the group they happen to be in.

Researchers will compare the Femoral Nerve Group+IPACK block, the Saphenous Nerve block+IPACK and the Subsartorial Block groups to see if there is any difference in the pain control in the 24 hours after the surgery.

After adequate venous access is obtained, a light sedation with Midazolam 1-2 mg is administered. The patient will be monitored and a selective spinal anesthesia will be performed. After the neuraxial procedure the antalgic block of choice is performed with about 40 mL of long acting local anesthetic.

Magnesium Solfate 1g and Dexametasone 4mg are administered after the block. If the patient wishes, a propofol continuos infusion may be administered for sedation during the surgery. Before the patient leaves the OR, Ketorolac 30mg will be administered.

Pain control after surgery will be achieved with acetaminophen 1g t.i.d., Ketorolac 30mg on demand, and Morphine solfate if NRS >5 after Ketorolac.

Every 6 hours the patient will be monitored by the anesthesia team. After 24 hours the antalgic effect of the nerve block is reasonably thought to be over, so the follow up is interrupted.

Inclusion Criteria:

• Age > 18 y/o
• Total knee replacement elective surgery
• Informed consent

Exclusion Criteria:

• Age < 18 y/o
• Surgery with general anesthesia
• Patients with coagulopaties
• Patients in chronic opioid therapy
• Refuse to sign informed consent form
• Unable to sign informed consent form
• Know allergies to medication used for analgesia

All patients meeting the inclusion criteria