Total hip arthroplasty (THA) causes moderate-to-severe postoperative pain. The PROSPECT guideline recommends the supra-inguinal fascia iliaca compartment block (SI-FICB) for THA, whereas evidence for newer quadratus-lumborum-family blocks is limited. The quadro-iliac plane block (QIPB) is a recently described fascial plane block, and no study has compared QIPB with SI-FICB head-to-head in any surgical context. In this prospective, double-blind, patients undergoing elective THA who receive one of the two routinely used preoperative blocks (SI-FICB or QIPB, chosen by the attending anesthesiologist as part of routine care) are systematically observed and compared. The primary objective is to assess whether the postoperative analgesic efficacy of QIPB is non-inferior to SI-FICB, using the resting NRS pain score at 6 hours postoperatively as the primary endpoint (non-inferiority margin Δ = 1.3).

Inclusion Criteria:

• Adults aged 18-75 years
• Scheduled for elective primary total hip arthroplasty
• ASA physical status I-III
• Able to understand and communicate in Turkish and complete assessment scales
• Completed preoperative anesthesia evaluation and approved for surgery
• Signed written informed consent

Exclusion Criteria:

• Known allergy/contraindication to any local anesthetic, including bupivacaine
• Coagulopathy or anticoagulant/antiplatelet therapy contraindicating block (per ASRA 2022)
• Active infection or skin breakdown at the block site
• Chronic opioid use (≥3 months daily) or history of opioid dependence
• Morbid obesity (BMI > 40 kg/m²)
• Cognitive impairment or communication difficulty precluding reliable NRS/QoR-15 assessment
• Pregnancy or breastfeeding
• Revision THA or emergency THA for fracture
• Intraoperative complications requiring major protocol deviation (e.g., >1000 mL blood loss, cardiac arrest)
• Technically failed block (no sensory change at any region on the T1 cold test)