This prospective observational study aims to determine the incidence and clinical impact of rebound pain after peripheral nerve blocks in patients undergoing total knee arthroplasty. Rebound pain is defined as a sudden, severe pain (NRS ≥7) emerging after block resolution. Primary outcome is the incidence of rebound pain; secondary outcomes include pain severity, rescue analgesia use, nausea, vomiting, sleep quality, and patient satisfaction.

Inclusion Criteria:

• Age between 18 and 70 years
• ASA physical status I to III
• Scheduled for elective unilateral total knee arthroplasty under spinal anesthesia
• Peripheral nerve block (PNB) planned as part of multimodal analgesia
• Ability to understand and provide written informed consent
• Willingness and ability to complete the postoperative pain diary

Exclusion Criteria:

• Known allergy or hypersensitivity to local anesthetics
• Contraindication to regional anesthesia
• ASA physical status IV or higher
• Neurological or psychiatric disorders interfering with study participation or pain reporting
• Use of anticoagulants or presence of coagulopathy
• Use of medications that may alter pain perception or rebound pain response
• Local infection at the block site
• Emergency surgeries
• Inability or unwillingness to complete the postoperative pain diary or follow-up

The study population consists of adult patients aged 18 to 70 years who are scheduled for elective unilateral total knee arthroplasty under spinal anesthesia at a tertiary care hospital. All participants will receive peripheral nerve blocks as part of a standardized multimodal analgesia protocol. Patients must be physically and cognitively able to provide consent and complete a postoperative pain diary. Those with contraindications to regional anesthesia, allergies to local anesthetics, or significant comorbidities (ASA IV and above) will be excluded.

This study does not plan to share individual participant data due to institutional policies and patient confidentiality considerations.