This prospective, randomized, assessor-blinded study will compare serratus posterior superior intercostal plane block and erector spinae plane block in adult female patients undergoing unilateral breast surgery. The primary outcome is chronic postoperative pain at 3 months, assessed using the Brief Pain Inventory-Short Form.

This single-center, prospective, randomized, controlled, assessor-blinded study will include adult female patients scheduled for elective unilateral breast surgery. Participants will be randomized in a 1:1 ratio to receive either serratus posterior superior intercostal plane block or erector spinae plane block before general anesthesia.

The study aims to compare the effects of these two regional anesthesia techniques on chronic postoperative pain at 3 months. Chronic pain will be assessed using the Brief Pain Inventory-Short Form.

Inclusion Criteria:

• Female patients aged 18-65 years
• ASA physical status I-III
• Body mass index (BMI) between 18 and 35 kg/m²
• Scheduled for elective unilateral breast surgery (mastectomy with or without sentinel lymph node biopsy)
• Ability to understand and provide written informed consent

Exclusion Criteria:

• Infection at the site of block application
• Known allergy to local anesthetics
• Coagulopathy or anticoagulant therapy
• Chronic opioid use
• Pregnancy
• Inability to communicate or cooperate
• Refusal to participate
• Failed block
• Requirement of additional intraoperative analgesia outside the study protocol
• Development of serious intraoperative complications

The patient and the outcome assessor will be blinded to group allocation. The anesthesiologist performing the block will not be blinded.