Background and objective: An ultrasound-guided anesthetic technique targeting the interspace between the popliteal artery and capsule of the posterior knee (iPACK) can provide posterior knee analgesia with preserved motor function after total knee arthroplasty (TKA). This study compared the peroneal nerve motor-sparing effects of iPACK block and tibial nerve block (TNB) when combined with local infiltration analgesia (LIA) and continuous adductor canal block (CACB).

Methods: In this study, 105 patients scheduled for elective TKA were randomized to receive proximal iPACK block (iPACK1), distal iPACK block (iPACK2), or TNB, along with spinal anesthesia, modified LIA, and CACB. The primary outcome was the incidence of common peroneal nerve (CPN) motor blockade. Secondary outcomes included CPN sensory function, tibial sensorimotor function, posterior knee pain, pain score, intravenous morphine requirement, timed up-and-go test, quadriceps muscle strength, range of motion, length of hospital stay, patient satisfaction, and adverse events.

Results: The incidence of CPN motor blockade was significantly higher in the TNB group than in the iPACK1 (p=0.001) and iPACK2 (p=0.001) groups, but was not significant between the iPACK1 and iPACK2 groups (p=0.76). Tibial nerve motor function was more preserved in the iPACK1 and iPACK2 groups than in the TNB group (p<0.001 and p<0.001, respectively). Complete CPN and tibial sensorimotor blockade were not observed in the iPACK2 group. Posterior knee pain score was significantly higher in the iPACK1 group than in other groups during the 24-hour postoperative period (p=0.001).

Conclusions: Compared with TNB, iPACK1 and iPACK2 preserved CPN and tibial nerve motor function to a greater extent. However, iPACK2 did not demonstrate complete CPN and tibial nerve motor blockade while maintaining effective posterior knee pain relief.