Addition of infiltration between the popliteal artery and the capsule of the posterior knee (IPACK) to local infiltration analgesia for total knee arthroplasty: a prospective randomized controlled trial.

BACKGROUND: Local infiltration analgesia (LIA) is a popular analgesic technique commonly administered during total knee arthroplasty (TKA). Recent studies have demonstrated that the infiltration between the popliteal artery and the capsule of the posterior knee (IPACK) can be complementary to analgesic modalities. However, the combined and relative efficacy of LIA and IPACK is unclear. We aimed to evaluate the analgesic and functional outcomes among LIA, IPACK, and LIA+IPACK.

MATERIALS AND METHODS: A total of 120 patients undergoing primary TKA were randomly allocated to 1 of 3 groups: LIA (50 mL of 0.25% ropivacaine and 2.0 μg/mL epinephrine); IPACK (20 mL of 0.25% ropivacaine and 2.0 μg/mL epinephrine); and LIA+IPACK. The primary outcome was the visual analog scale (VAS) pain score. Secondary outcomes were opioid use, knee range of motion (ROM), quadriceps muscle strength, mobilization distance, timed up and go (TUG) test, and postoperative complications.

RESULTS: The mean VAS pain scores were significantly higher after using IPACK alone than after using LIA+IPACK and LIA within 24 hours (all p＜0.05). LIA+IPACK had lower mean VAS pain scores than LIA when the knees were at rest (within 12 hours, p < 0.05) and flexion (within 8 hours, p＜0.05). Patients receiving LIA+IPACK and LIA had significantly lower morphine equivalents (ME) than those receiving IPACK alone within 24 hours (26.3, 28.9 versus 47.8, both p＜0.05) and during hospitalization (98, 101.6, versus 128.4 both p＜0.05). Both LIA+IPACK and LIA had higher ROM (within two days), higher level of muscle strength (within 12 hours), longer mobilization distances (within one day), and shorter TUG time (till discharge) compared with IPACK alone (all p＜0.05), while LIA+IPACK only had a higher knee ROM than LIA on the first postoperative day (p＜0.05). There was no significant difference in any other outcomes.

CONCLUSIONS: This randomized controlled trial demonstrated that there were significantly lower pain scores, less opioid consumption, and better functional results with LIA+IPACK and LIA when compared with IPACK alone, suggesting that IPACK alone was inferior for pain control.