Background and Aims Pain management is the primary concern after total knee arthroplasty (TKA). Popliteal plexus block (PPB) is unclear for contributing to the pain relief of the posterior knee compared with a tibial nerve block (TNB). This research investigated the effect of PPB on postoperative pain outcomes and early achievement for discharge criteria compared to TNB in a non-inferior manner.

Methods We randomly assigned the PPB or TNB group to 136 patients (UMIN40054). We gave each 10 mL of 0.25% levobupivacaine as PPB or TNB combined with adductor canal block. The primary outcome was to achieve the discharge criteria (pain control with oral analgesics, knee flexion >90°, and ambulatory rehabilitation). A noninferiority test was adopted with a margin of 9 hours and outcome variables were analyzed by the two-sided Wilcoxon rank-sum test.

Results The time to accomplish discharge criteria was 45.0 (range: 24–92) hours in the PPB group and 47.5 (39–120) hours in the TNB group, whose difference of -2.0 hours (95% CI: -4.0 to 0 hours, p=0.017) was noninferior and superior to PPB. The postoperative dorsal and plantar strength was significantly lower in the TNB group on postoperative 6 hours; however, it was not different on 24 hours. Pain scores, knee flexion/extension ranges and the necessity of additional analgesics were comparable.

Conclusions PPB is an excellent alternative procedure for posterior knee pain management with a straightforward technique, gives superior postoperative early discharge criteria achievement and preserves foot strength compared with TNB.