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. Effective multimodal analgesia is important to facilitate early mobilization, functional recovery, participation in physical therapy, and patient satisfaction while minimizing opioid consumption and opioid-related adverse effects.

Motor-sparing regional anesthesia techniques are an important component of multimodal analgesia for TKA. The femoral triangle block provides analgesia primarily to the anterior and medial aspects of the knee while aiming to preserve quadriceps motor function. However, additional regional anesthesia techniques are often required to adequately treat pain originating from the posterior aspect of the knee.

The interspace between the popliteal artery and capsule of the posterior knee (iPACK) block is commonly used to provide posterior knee analgesia by targeting terminal articular sensory branches while minimizing blockade of the main tibial and common peroneal nerves. The popliteal plexus block (PPB) is an alternative motor-sparing regional anesthesia technique targeting the neural plexus contributing to the sensory innervation of the posterior knee.

Previous randomized studies suggest that the popliteal plexus block can provide effective posterior knee analgesia while preserving distal motor function. Direct comparison with the iPACK block has demonstrated non-inferior analgesia and shorter block performance time. Nevertheless, uncertainty remains regarding whether the popliteal plexus block provides superior opioid-sparing analgesia compared with the iPACK block when both techniques are incorporated into an otherwise standardized multimodal analgesic regimen.

This prospective, randomized, double-blind, superiority clinical trial will compare ultrasound-guided popliteal plexus block with ultrasound-guided iPACK block in adults 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 allocated to one of two parallel groups. Participants in the active comparator group will receive an ultrasound-guided iPACK block, whereas participants in the experimental group will receive an ultrasound-guided popliteal plexus block. Perioperative anesthetic management, continuous femoral triangle analgesia, postoperative multimodal analgesia, and intravenous patient-controlled analgesia (PCA) settings will otherwise be standardized between groups.

The primary outcome will be cumulative intravenous morphine consumption administered through the PCA device during the first 24 hours after surgery. The study is designed to test the hypothesis that the popliteal plexus block is superior to the iPACK block in reducing 24-hour postoperative morphine consumption.

Secondary opioid-related outcomes will include cumulative intravenous morphine consumption during the first 12 hours after surgery and the time from the end of surgery to the first successful intravenous morphine administration through the PCA device.

Posterior knee pain will be evaluated separately at rest and during movement using an 11-point Numeric Rating Scale (NRS) ranging from 0 to 10, where 0 represents no pain and 10 represents the worst imaginable pain. Posterior knee pain will be assessed at 2, 4, 6, 12, and 24 hours postoperatively.

Quality of postoperative recovery will be evaluated using the 15-item Quality of Recovery questionnaire (QoR-15). The questionnaire will be administered preoperatively and 24 hours after surgery. The 24-hour QoR-15 score will be compared between groups, with the preoperative score used as a baseline measure of recovery status.

Distal motor function will be evaluated by assessing ankle dorsiflexion and plantar flexion strength using the Medical Research Council (MRC) muscle strength scale. Motor function will be assessed preoperatively and at 6 and 24 hours postoperatively to determine whether either posterior knee block results in clinically relevant distal motor impairment.

Early functional recovery will also be assessed during the first postoperative physical therapy evaluation within 24 hours after surgery. The ability to perform an active straight leg raise will be recorded as a binary outcome (Yes/No). The ability to stand and ambulate using the prescribed assistive device, such as a walker or crutches, will also be recorded as a binary outcome (Yes/No). When ambulation is not achieved, the principal reason will be documented when possible, including motor weakness, pain, dizziness or hypotension, nausea, or other causes.

The technical efficiency of the two posterior knee blocks will be evaluated by measuring block performance time. Performance time will be recorded in minutes and defined as the interval from initial placement of the ultrasound transducer for acquisition of the block image until withdrawal of the block needle following completion of local anesthetic injection.

Postoperative adverse effects will include nausea and vomiting, pruritus, and urinary retention. Procedure-related safety outcomes will include accidental vascular puncture, local anesthetic systemic toxicity, and new postoperative neurological symptoms.

Neurological symptoms potentially related to the regional anesthesia procedures, including numbness, paresthesia, dysesthesia, weakness, or other new sensory or motor deficits affecting the operated lower limb, will be assessed during the postoperative period. Participants will additionally undergo a standardized telephone follow-up approximately 7 days after surgery to identify persistent or newly reported neurological symptoms. Participants reporting clinically relevant persistent, progressive, or motor neurological deficits will be referred for further clinical evaluation according to institutional practice.

The study aims to determine whether the popliteal plexus block provides superior opioid-sparing analgesia compared with the iPACK block when both are used as adjuncts to a continuous femoral triangle block for primary total knee arthroplasty. In addition to analgesic efficacy, the study will evaluate posterior knee pain, quality of recovery, distal motor function, early functional recovery, technical efficiency, and the safety profile of both regional anesthesia techniques.