Efficacy of iPACK (Interspace Between the Popliteal Artery and the Capsule of the Posterior Knee) Versus Periarticular Local Infiltration Analgesia After Unilateral Total Knee Arthroplasty: Prospective Randomized Control Trial

Background: Total Knee Arthroplasty (TKA) is one of the most frequent procedures performed by orthopedic surgeons. Research has found that orthopedic surgeries are the most painful procedures.(1) Unrelieved pain post orthopedic surgery is a stressor that can cause altered physiologic changes and negative effects on every organ system of the body. Untreated pain can result in complex pathophysiology than the pain caused by the original injury or disease. This can have both detrimental physical and psychological consequences for patients, as well as a substantial economic impact due to increased costs of health care and lost productivity. (2) The anatomy of sensory supply to the knee joint is complex with contributions from both the lumbar and sacral plexuses. The anterior-medial compartmental innervation consists of branches from the femoral nerve, including the saphenous nerve, the medial femoral cutaneous nerve and the nerve to vastus medialis. The lateral femoral cutaneous nerve, the common peroneal nerve, and the nerves to vastus intermedius and lateralis innervate the knee anterolaterally. The posterior group consists of the popliteal nerve plexus that ramifies around the genicular vasculature in the popliteal fossa. The popliteal nerve plexus is derived from the tibial nerve and the posterior branch of the obturator nerve. The posterior group supplies intra-articular innervation to the menisci, the peri-meniscular joint capsule, the cruciate ligaments, the infra-patellar fat pad, and the posterior part of the fibrous knee capsule.(3) The medial para-patellar arthrotomy performed for total knee arthroplasty, through the anteromedial integument of the knee and the extra-articular medial retinacular complex, evokes pain mediated by the infra-patellar branch of the saphenous nerve, the medial retinacular nerve (the terminal branch of the nerve to vastus medialis), and the anterior branch of the medial femoral cutaneous nerve. This procedure will not affect the extra-articular nerve branches to the anterolateral portion of the knee from the common peroneal nerve, the nerves to vastus intermedius and lateralis, and the lateral femoral cutaneous nerve. The intra-articular excision evokes pain from structures innervated by the posterior group. (4) Ultrasound-guided Femoral Nerve Block (FNB) is one of the most commonly used techniques that has been shown to significantly improve analgesia and reduce postoperative opioid consumption after TKA. However, FNB may lead to quadriceps muscle weakness, limiting ambulation and increasing the risk of falls, making physical rehabilitation results unsatisfactory.(5) Recently, there has been increased interest in the Adductor Canal Block (ACB) for pain relief after total knee arthroplasty. (6) The adductor canal is a pyramidal, musculoaponeurotic tunnel from the apex of the femoral triangle to the adductor hiatus, running between the vastus medialis muscle anterolaterally and the adductor longus and adductor Magnus muscles posteromedially. It is covered in its entire length by the vastoadductor membrane. The contents of the adductor canal include the superficial artery and vein, saphenous nerve, the nerve to vastus medialis, the posterior branch of the obturator nerve, and in some cases, the medial cutaneous nerve and the anterior branch of the obturator nerve. The advantage of this technique rests in the fact that it provides localized motor-sparing analgesia, with similar opioid consumption and side effects when compared with FNB.(7) However, ACB does not provide analgesia to the posterior aspect of the knee, which can be moderate to severe after surgery. This pain may be ameliorated by the addition of the ultrasound-guided local anesthetic infiltration of the Interspace between the Popliteal Artery and the Capsule of the posterior Knee (iPACK). (8) Although this technique seems to provide many advantages, it may present some limitations and risks like intravascular injection and injury due to the presence of the popliteal vessels near the target. Although the use of ultrasound guidance decreases this risk, significant bleeding and serious complications can still occur due to the inability to recognize and compress the source of bleeding. (4)

Methods: In this study we are going to recruit 169 participants to compare them in two groups. group-1 iPACK (n=85) will receive Adductor Canal Block (ACB) + iPACK and group 2 LIA (n=84) ACB+ periarticular Local Infiltration Analgesia (LIA). All participants, care provider (nurses & assistant anesthetists) and outcome assessors (physiotherapist) will be blinded to the group allocation. Only the anesthesiologist responsible for perioperative care performing the ACB and iPACK blocks will be aware of the randomization. All peripheral nerve blocks will be performed with complete aseptic technique and under ultrasound guidance. Periarticular LIA will be performed by the surgeon with the landmark technique base. This study will be conducted in six months' duration. All patients will consent for spinal anesthesia, ACB, and iPACK and they will be instructed how to report pain on a 10 cm long Numerical Rating Scale (NRS) postoperatively.

The primary outcome, severity of pain (NRS) will be evaluated in Post Anesthesia Care Unit (PACU). The secondary outcome, time to mobilization along with pain score will be recorded in the ward after 2 hours of surgery then every 12 hours until the patient discharged home. Quadriceps muscle strength will be evaluated with the knee range of motion (ROM). A completely straight knee joint (extension) will measure 0° and a fully bent knee will have a flexion of at 130° degrees. The Timed-Up-and-Go (TUG) tests to evaluate functional recovery after TKA. The TUG test measures the time it takes a patient to get up from a chair, walk 3 m, and return to the sitting position in the chair.

On arrival to operation room (OR), all eligible participants will have intravenous (IV) cannula in situ and monitors according to the Association of Anesthetists of Great Britain and Ireland (AAGBI). Under complete aseptic technique, spinal anesthesia will be performed with pencil point 25 Gauge (Whitacre) needle with heavy Bupivacaine 0.5% and Fentanyl 15 micrograms (mics) total 3 milliliters (ml). After spinal anesthesia, each participant will receive either ultrasound-guided ACB+iPACK or ACB+ periarticular LIA.

Description of peripheral nerve blocks technique: