Infiltration between the popliteal artery and the capsule of the knee (IPACK) vs. selective tibial nerve block for analgesia after total knee arthroplasty: a triple-blinded randomised controlled trial

Introduction: Infiltration between the popliteal artery and the capsule of the knee (IPACK) and the selective tibial nerve block provide analgesia for the posterior aspect of the knee after total knee arthroplasty. This randomised controlled triple-blinded trial tested the hypothesis that IPACK provides superior analgesia to selective tibial nerve block after total knee arthroplasty. Methods: Patients having total knee arthroplasty under spinal anaesthesia with a femoral triangle block were allocated randomly to receive either IPACK with 19 ml ropivacaine 0.2% or a selective tibial nerve block with 5 ml ropivacaine 0.75%. The postoperative analgesic strategy included paracetamol; ibuprofen; and intravenous morphine patient-controlled analgesia. Primary outcome was cumulative intravenous morphine consumption on postoperative day 1. Secondary analgesic outcomes included pain scores at rest and during movement measured on postoperative days 1, 2 and 3. Functional outcomes were quadriceps strength; walking distance; and range of motion. Results: In total, data from 90 patients were analysed (45 allocated to each group). Cumulative intravenous morphine consumption on postoperative day 1 was similar between the patients allocated to the IPACK and selective tibial nerve block groups (mean (SD) 6 (7) mg vs. 5 (6) mg, respectively; p = 0.36). Four patients (9%) who received selective tibial nerve block had motor block of the common peroneal nerve. No other differences were seen between groups in secondary outcomes. Discussion: The IPACK and selective tibial nerve block provide similar analgesia after total knee arthroplasty under spinal anaesthesia with a femoral triangle block.