Real-world Opioid-Sparring Effects of Infiltration between the Popliteal Artery and the Capsule of the Knee (IPACK) in Patients Undergoing Anterior Cruciate Ligament Reconstruction

IntroductionPatients undergoing anterior cruciate ligament (ACL) reconstruction experience substantial postoperative pain, which delays recovery and leads to both immediate and long-term opioid use. In other knee procedures, infiltration between the popliteal artery and the capsule of the posterior knee (IPACK) has demonstrated analgesic and opioid reducing effects. However, the effect in patients undergoing ACL reconstruction has not been investigated. We aimed to investigate the real-world effect of IPACK in patients undergoing ACL reconstruction on immediate postoperative opioid consumption. ParticipantsIn this single-centre difference-in-differences cohort study, all patients who underwent ACL reconstruction surgery at Bispebjerg Hospital, Denmark, from 1 February 2024 to 30 June 2025 are included. The study further includes a similar reference cohort, comprising all patients who underwent trochleaplasty, Elmslie-Trillat, or medial patellofemoral ligament reconstruction during the same period, and at the same hospital. InterventionThe primary exposure is the implementation of IPACK as part of perioperative management for ACL reconstruction on 1 January 2025. The IPACK was performed under ultrasound guidance, immediately before surgery, administering 20 mL of ropivacaine 0.5% between the popliteal artery and the posterior knee capsule. OutcomesThe primary outcome is the cumulative opioid consumption from surgical incision to 2 hours postoperatively. Secondary outcomes include the cumulative opioid consumption from incision to 24 hours postoperatively, the worst reported pain score at 0-24h postoperatively, occurrence of postoperative nausea or vomiting (PONV) 0-24h postoperatively, length of PACU stay, length of hospital stay, and nerve injuries. As an exploratory outcome, carbon dioxide emissions will be investigated. Statistical analysisThe main analysis will be a standard two-way fixed effects DiD regression assessing the changes occurring at the time of implementation of IPACK in the ACL cohort, with adjustment for the underlying time trend. Continuous outcomes are reported as mean difference (95% confidence interval [CI]), and binary outcomes as absolute and relative risks (95% CI).