This randomized clinical trial aims to evaluate and compare the analgesic efficacy and functional outcomes of the quadro-iliac plane block (QIPB) and the supra-inguinal fascia iliaca compartment block (S-FICB) in patients undergoing total hip arthroplasty.

The primary outcome is the Numeric Rating Scale (NRS) within the first 48 hours after surgery. Secondary outcomes include postoperative total opioid consumption, ıncidence of quadriceps motor block, time to first ambulation, block performance time, falls, length of hospital stay, block- related complications(hematoma,local anesthetic systemic complications, vascular puncture, and infection), patient satisfaction assessed using a Likert scale, and incidence of postoperative nausea and vomiting.

Materials and Methods:

This prospective, randomized clinical trial will include patients aged 18-80 years with American Society of Anesthesiologists (ASA) physical status I-III who are scheduled to undergo elective unilateral primary total hip arthroplasty unde spinal anesthesia. Before enrollment, all patients will be informed about the study protocol and written informed consent will be obtained. Patients will be instructed on the use of the Numeric Rating Scale (NRS) for postoperative pain assessment, where 0 represents no pain and 10 represents the worst pain imaginable. Patients with contraindications to spinal anesthesia, allergy to local anesthetics, coagulopathy, infection at the injection site, chronic opioid use, pre-existing neurological deficits involving the lower extremities, cognitive impairment preventing reliable communication, revision or bilateral hip arthroplasty, and refusal to participate will be excluded from the study. Patients will be randomly allocated to one of two study groups using a computer-generated randomization sequence (https://www.randomizer.org). Randomization will be performed by a team member not involved in patient management or outcome assessment. Allocation concealment will be achieved using sequentially numbered sealed opaque envelopes, which will be opened immediately before block performance. Upon arrival in the operating room, standard monitoring including electrocardiography, non-invasive blood pressure measurement, and pulse oximetry will be applied. Following intravenous access and preloading according to institutional practice, spinal anesthesia will be performed at the L3-L4 or L4-L5 intervertebral space using a 25-gauge Quincke spinal needle under aseptic conditions. After confirmation of free cerebrospinal fluid flow, 12-15 mg of 0.5% hyperbaric bupivacaine will be administered intrathecally. Supplemental sedation with intravenous midazolam and/or propofol may be provided when required for patient comfort.

Following successful spinal anesthesia, patients will receive either ultrasound- guided quadro-iliac plane block (QIPB) or supra-inguinal fascia iliaca compartment block (S-FICB) according to group allocation. All blocks will be performed by anesthesiologists experienced in regional anesthesia and familiar with both techniques.

All patients will receive the same multimodal postoperative analgesic regimen and standardized postoperative rehabilitation protocol. Postoperative pain scores at rest and during movement will be assessed using the NRS during the first 48 postoperative hours. Opioid consumption, incidence of quadriceps motor block, time to first ambulation, patient satisfaction, postoperative nausea and vomiting, falls, length of hospital stay, block performance time, and block-related complications will also be recorded.

Outcome assessments will be performed by investigators who are unaware of group allocation.

Inclusion Criteria:

• Age between 18 and 80 years
• American Society of Anesthesiologists physical status I-III
• Scheduled for elective unilateral primary total hip arthroplasty
• Surgery planned under spinal anesthesia
• Ability to understand and use the Numeric Rating Scale
• Written informed consent provided

Exclusion Criteria:

• Refusal to participate
• Revision total hip arthroplasty
• Bilateral total hip arthroplasty
• Contraindication to spinal anesthesia
• Contraindication to peripheral nerve block
• Known allergy to local anesthetics or study drugs
• Coagulopathy or anticoagulant use incompatible with neuraxial/regional anesthesia
• Infection at the block injection site
• Pre-existing neurological deficit involving the operative lower extremity
• Peripheral neuropathy
• Chronic opioid use
• Cognitive impairment or inability to communicate reliably
• Severe hepatic or renal failure
• Body mass index >35 kg/m²
• Pregnancy