This study is planned as a single-center, prospective, randomized, controlled, double-blind trial in adult patients undergoing elective primary total hip arthroplasty under spinal anesthesia. Eligible participants will be patients aged 18 years or older, classified as ASA physical status I-III, and able to provide informed consent. Patients with ASA IV-V, serious cardiac, respiratory, hepatic, or renal disease, neuropsychiatric disorders, cognitive impairment preventing reliable NRS assessment, coagulopathy, local anesthetic allergy, infection or scar at the block site, failed block, signs of local anesthetic systemic toxicity, exposure to local anesthetic doses above protocol limits, revision total hip arthroplasty, fracture-related total hip arthroplasty, or refusal to participate will be excluded. Participants will be randomized by sealed-envelope method into two groups. Group 1 will receive PENG block after spinal anesthesia in the supine position using ultrasound guidance and 20 mL of 0.25% bupivacaine. Group 2 will receive PENG block followed by ultrasound-guided PPD block, with 30 mL of 0.25% bupivacaine used for the PPD block. In addition, both groups will receive lateral femoral cutaneous nerve block with 5 mL of 0.25% bupivacaine. The primary objective is to compare postoperative pain intensity between groups using Numeric Rating Scale scores. Secondary evaluations include postoperative analgesic consumption, time to first rescue analgesia, time to first mobilization, and motor function including ankle dorsiflexion strength. An initial pilot phase including 40 patients is planned, and the final sample size will be calculated using G*Power based on pilot data with alpha 0.05 and power 0.80. The study will continue until the target sample size is reached.
