A Randomized Comparison of the Efficacy of the IPACK Block Versus the Popliteal Plexus Block for Posterior Knee Analgesia, in Patients Undergoing a Total Knee Arthroplasty and Receiving a Continuous Distal Femoral Triangle Block

Total knee arthroplasty (TKA) is commonly associated with significant postoperative pain, including pain arising from the posterior aspect of the knee. Regional anesthesia techniques are frequently used as part of a multimodal analgesic strategy to improve pain control, reduce opioid requirements, and facilitate early functional recovery. This prospective, randomized, double-blind, superiority clinical trial will compare the analgesic efficacy of the interspace between the popliteal artery and capsule of the posterior knee (iPACK) block with the popliteal plexus block in adult patients undergoing elective unilateral primary total knee arthroplasty. All participants will receive a continuous femoral triangle block and a standardized multimodal postoperative analgesic regimen. Participants will be randomly assigned to receive either an ultrasound-guided iPACK block or an ultrasound-guided popliteal plexus block. The primary outcome will be cumulative intravenous morphine consumption delivered through a patient-controlled analgesia (PCA) device during the first 24 hours after surgery. Secondary outcomes will include cumulative morphine consumption during the first 12 hours, posterior knee pain at rest and during movement, time to first PCA morphine administration, quality of recovery assessed with the QoR-15 questionnaire, distal motor function, early functional recovery, block performance time, postoperative adverse effects, and neurological symptoms. The study hypothesis is that the popliteal plexus block will provide superior opioid-sparing analgesia compared with the iPACK block when both techniques are combined with a continuous femoral triangle block, while preserving distal motor function and maintaining an acceptable safety profile.

Inclusion Criteria: * Adults aged 18-85 years. * Scheduled for elective unilateral primary total knee arthroplasty for knee osteoarthritis. * American Society of Anesthesiologists (ASA) physical status I-III. * Ability to understand and use the 0-10 Numeric Rating Scale (NRS) for pain assessment. * Ability to understand and use the intravenous patient-controlled analgesia (PCA) device. * Ability to complete the Quality of Recovery-15 (QoR-15) questionnaire. * Ability to provide written informed consent. Exclusion Criteria: * Revision or bilateral total knee arthroplasty. * Patient refusal or inability to provide informed consent. * Contraindication to peripheral nerve block, including infection at the needle insertion site or clinically significant coagulation abnormalities. * Known allergy or contraindication to the local anesthetics or analgesic medications used in the study protocol. * Pre-existing clinically significant sensory or motor neurological deficit affecting the operative lower limb. * Chronic opioid use or opioid dependence that could interfere with postoperative opioid consumption assessment. * Inability to understand or operate the PCA device. * Cognitive impairment or communication difficulty preventing reliable assessment of pain, motor function, or QoR-15. * Any medical condition that, in the investigator's judgment, would make participation unsafe or interfere with assessment of the study outcomes.