This study compares the analgesic efficacy of single-dose adductor canal block (sACB) versus continuous-dose adductor canal block (cACB) for postoperative pain management in total knee replacement patients. To ensure a high level of clinical accuracy, the investigation specifically focuses on a cACB cohort where ultrasound confirmation ensures the catheter remains correctly positioned for a full 48 hours. Participants are assigned to groups using a 1:1 randomization protocol via computer-generated tables to eliminate selection bias. Clinical consistency is maintained by using identical pharmacological agents across both groups: 0.5% Heavy Bupivacaine for spinal anesthesia and 0.5% ropivacaine with 1:200,000 epinephrine for the nerve block itself. Furthermore, both groups adhere to a standardized multimodal analgesic schedule to control for external variables. In the cACB group, intravenous patient-controlled analgesia (IV PCA) serves as a designated rescue therapy should the catheter fail. The primary technical evaluation occurs 48 hours post-surgery, utilizing ultrasound to verify catheter placement and quantify pain levels. Beyond immediate recovery, the study evaluates long-term success through Patient-Reported Outcome Measures (PROMs) at a 12-week follow-up, focusing on functional restoration and the patient's overall quality of life. By isolating the variable of catheter stability, the research aims to provide a definitive comparison of whether the continuous delivery of local anesthetic offers a statistically significant clinical advantage over a single-dose administration in the context of modern orthopedic recovery protocols.

Inclusion Criteria:

• Age 40-80 yrs
• Scheduled for unilateral total knee arthroplatsy
• ASA I-III
• BMI 18-35 kg/㎡
• Able to read and understand consent form

Exclusion Criteria:

• Allergy to local anesthetics
• Infection at the block site
• History of neuropathy or peripheral nerve disease
• Coagulation disorders or use of anticoagulants (if discontinuation is not possible)
• Communication disorders or cognitive impairment
• Chronic opioid use (≥30 MME/day, 3 months or more)
• Severe chronic pain (NRS ≥7/10, 3 months or more)
• Renal impairment (eGFR <30 mL/min/1.73m²)
• Hepatic impairment (Child-Pugh C)
• Blood coagulation disorders
• Pregnancy