This clinical trial aims to assess the analgesic efficacy of ultrasound-guided FIB using different analgesic combinations administered into the iliac fascia compartment. The main question it aims to answer is:

·What is the total morphine (mg) consumption at 24 hours postoperatively for each of the three groups?

The secondary questions are:

• What is the length of stay in hospital for each group?
• What is the risk of falling associated with the use of fascia iliaca block? Researchers will compare two analgesic combinations of local anesthestic naropin 0,25% versus dextrose 10% administered by fascia iliaca block for postoperative pain after total hip arthroplasty.

The investigators plan to conduct a single-center, prospective, blinded, randomized controlled study of 150 eligible patients undergoing elective THA via a miniinvasive anterior approach starting June 2024. All patients will receive spinal anesthesia and preoperatively FIB for analgesia. The investigators define randomly three patient groups: Group 1, receiving 40 ml naropin 0,25% in saline, Group 2, receiving 40 ml naropin 0,25% in dextrose 5%, and Group 3, receiving 40 ml dextrose 10%. After the regression of spinal anesthesia, all the patients receive the same multimodal pain therapy according to the visual analog scale (VAS), including Paracetamol IV, NSAID, and morphine, according to the pain protocol in our hospital. The primary endpoint of the study is total morphine (mg) consumption at 24 hours postoperatively, and the secondary goals were length of stay and the risk of fall.

Inclusion Criteria:

• Indication of total primary hip arthroplasty
• ASA I-III
• BMI<40 kg/m2

Exclusion Criteria:

• Inability or refusal to sign informed consent
• Known allergies to any of the drugs used in the study
• Hepatic or renal insufficiency
• Gastritis or gastroduodenal ulcer
• Opioid dependency
• Coagulopathy
• Pregnancy
• Scars in the surgery and fascia iliaca block areas
• Clinical evidence of peripheral neuropathies.