Evaluation of the iPACK block injectate spread: a cadaveric study

Abstract

Background and objectivesUltrasound-guided infiltration of the interspace between the popliteal artery and capsule of the knee (iPACK) block, a new regional analgesic technique, is believed to relieve posterior knee pain, after total knee arthroplasty, by targeting the articular branches innervating posterior aspect of the joint. The extent of injectate spread and the number of articular branches affected is currently unknown. This cadaveric study aimed to compare the area of dye spread and frequency of articular branches staining following a proximal versus distal injection technique.MethodsAn ultrasound-guided iPACK injection (10 mL of methylene blue dye solution) was performed in 14 lightly embalmed specimens: 7 injected using a proximal injection technique (1 fingerbreadth above base of patella) and 7 using a distal injection technique (at the superior border of the femoral condyles). Following injection, dissection, digitization, and 3D modeling were performed to map the area of dye spread and determine the frequency of nerve staining.ResultsBoth injection techniques achieved a similar mean area of injectate spread. Of the four articular branches supplying the posterior knee joint capsule, the genicular branch of posterior division of obturator nerve was stained in all specimens. The proximal injection resulted in staining of superior medial genicular nerve, due to dye spread through the adductor hiatus, whereas superior lateral genicular nerve and anterior branch of common fibular nerve were consistently stained following distal injection. Other articular branches were stained with variable frequency.ConclusionsBoth proximal and distal iPACK injection techniques provided a similar area of dye spread in the popliteal region and extensive staining of the articular branches supplying the posterior capsule. The proximal injection technique promoted greater anteromedial dye spread, while the distal injection had more anterolateral spread. Further clinical study is required to confirm our cadaveric findings.

Evaluation of the proximal adductor canal block injectate spread: a cadaveric study

“…In the previous literature, Runge et al reported extensive dye injectate spread into the popliteal fossa using a distal ACB 12. Similar results were reported using the IPACK block,27 suggesting supplementation of a distal ACB with an IPACK block may be redundant. However, the proximal adductor canal injection, used in the current study, captured posteromedial branch of NVM and SMGN with minimal spread into the popliteal fossa, with the exception of one specimen.…”

Motor-sparing effect of iPACK (interspace between the popliteal artery and capsule of the posterior knee) block versus tibial nerve block after total knee arthroplasty: a randomized controlled trial

“…Moreover, the proximal iPACK block resulted in a significantly greater number of patients with posterior knee pain, possibly due to differences in local anesthetic distribution between the techniques. In the proximal iPACK block, local anesthetic is injected at the femoral shaft level, just above the femoral condyle and the upper border of the posterior capsule of the knee, resulting mainly in the spread of the local anesthetic to the superior medial and lateral genicular nerves (the terminal branches of the femoral and common peroneal nerves) that run along both the medial and lateral sides of the distal femur rather than dissipating to the branches of the sciatic nerve or popliteal plexus 26–28. Therefore, the improvement in postoperative analgesia with the addition of the proximal iPACK block to ACB in previous studies might possibly be due to a synergistic blockade of the sensory innervation of the anteromedial and lateral aspects of the knee, since pain related to different parts of the knee was not observed in these studies 18–20 28.…”

Saphenous nerve and IPACK block

“…We would like to thank Tran et al 1 for their work bringing further knowledge on the spread pattern and nerve branches covered by infiltration between popliteal artery and capsule of the knee (IPACK) block.…”