Analgesic Efficacy of Continuous Bupivacaine Infusion versus Liposomal Bupivacaine in Parasacral Ischial Plane Block After Total Knee Arthroplasty: An Open-Label, Randomized, Controlled, Non-Inferiority Study.

BACKGROUND: Effective management of posterior knee pain following total knee arthroplasty (TKA) remains a clinical challenge. Comparative analgesic efficacy of continuous parasacral ischial plane block (CPIPB) and liposomal bupivacaine (LB) is unclear. This study aimed to evaluate whether the analgesic efficacy of a single-shot PIPB using LB is non-inferior to CPIPB in patients undergoing TKA. METHODS: This open-label, randomized, controlled non-inferiority trial enrolled patients scheduled for unilateral TKA who were randomly allocated to either the CPIPB or LB group. Patient-controlled intravenous analgesia (PCA) with sufentanil was provided as rescue analgesia. The primary outcome was postoperative analgesic efficacy, which was indicated by the cumulative area under the curve (AUC) of the Numerical Rating Scale (NRS) scores obtained at rest and activity until 72 h postoperatively after leaving the post-anaesthesia care unit (PACU). A pre-specified non-inferiority margin of 20.7 was established. Other outcomes included NRS scores, rescue opioid consumption, rehabilitation parameters, PIPB outcomes and postoperative adverse events. RESULTS: A total of 100 patients were enrolled and randomly assigned to the CPIPB or LB group. Both per-protocol (n=90) and intention-to-treat (n=100) analyses confirmed non-inferiority, the upper limits of the 95% CI for the differences in cumulative NRS-AUCPACU-72h at rest (PP 18.03, ITT 16.82) and activity (PP 19.82, ITT 18.42) were strictly below the 20.7 margin. NRS differences were found at rest 60h and 72h, or at activity 72h (P<0.05). CPIPB was associated with lower cumulative rescue opioid consumption, a longer time to first rescue analgesia, and more favorable early rehabilitation parameters (including range of motion, 2-minute walking distance, and Western Ontario and McMaster Universities Osteoarthritis Index scores). The catheter-related complications of CPIPB had catheterization failure 4.1%, insertion site leakage 2.2%, catheter dislodgement 4.3% and catheter clogging 6.7%. The CPIPB group had lower rates of postoperative nausea, insomnia. CONCLUSIONS: A single-shot PIPB with LB met the prespecified non-inferiority criterion for pain relief compared with CPIPB after TKA, while CPIPB performs better in opioid consumption and early rehabilitation parameters.