This prospective, randomized, patient- and assessor-blinded, single-center non-inferiority trial will compare the analgesic efficacy of the Shoulder Posterior Pericapsular Nerve Group (SPENG) block with combined posterior suprascapular and axillary nerve blocks in adults undergoing elective shoulder arthroscopy under general anesthesia. Both groups will receive the same total volume and concentration of local anesthetic. The primary outcome will be the highest resting Numeric Rating Scale pain score recorded during the first 24 postoperative hours. Secondary outcomes will include block performance time, sensory block success in suprascapular and axillary nerve territories, opioid consumption, time to rescue analgesia, motor function, diaphragmatic function, postoperative recovery quality, patient satisfaction, and block-related complications.