Stoike, David E.

Objectives Local anesthetic injection into the interspace between the popliteal artery and the posterior capsule of the knee (IPACK) has the potential to provide motor‐sparing analgesia to the posterior knee after total knee arthroplasty. The primary objective of this cadaveric study was to evaluate injectate spread to relevant anatomic structures with IPACK injection. Methods After receipt of Institutional Review Board Biospecimen Subcommittee approval, IPACK injection was performed on fresh‐frozen cadavers. The popliteal fossa in each specimen was dissected and examined for injectate spread. Results Ten fresh‐frozen cadaver knees were included in the study. Injectate was observed to spread in the popliteal fossa at a mean ± SD of 6.1 ± 0.7 cm in the medial‐lateral dimension and 10.1 ± 3.2 cm in the proximal‐distal dimension. No injectate was noted to be in contact with the proximal segment of the sciatic nerve, but 3 specimens showed injectate spread to the tibial nerve. In 3 specimens, the injectate showed possible contact with the common peroneal nerve. The middle genicular artery was consistently surrounded by injectate. Conclusions This cadaver study of IPACK injection demonstrated spread throughout the popliteal fossa without proximal sciatic involvement. However, the potential for injectate to spread to the tibial or common peroneal nerve was demonstrated. Consistent surrounding of the middle genicular artery with injectate suggests a potential mechanism of analgesia for the IPACK block, due to the predictable relationship between articular sensory nerves and this artery. Further study is needed to determine the ideal site of IPACK injection.

ObjectivesTo identify any anatomic barriers to local anesthetic spread between the sciatic nerve (SN) and the posterior femoral cutaneous nerve (PFCN) at the level of the infragluteal crease and to describe a potential technique for an ultrasound (US)‐guided subgluteal PFCN block in a cadaveric model.MethodsBilateral US‐guided subgluteal injections of a colored latex solution were performed around the SN (15 mL) and PFCN (10 mL) in 4 unembalmed cadavers, for a total of 8 cadaver thighs. The specimens were dissected after latex polymerization to observe the spread of the latex solutions.ResultsWith US guidance, the PFCN was visualized deep to the gluteus maximus and slightly superficial or lateral to the SN at the level of the infragluteal crease. The SN and PFCN were found on dissection to be coated with their respective colored latex in all 8 thighs. The SN and PFCN were consistently separated by the deep investing muscular fascia of the thigh, with only 2 thighs showing substantial mixing of latex injectates.ConclusionsThe deep investing muscular fascia of the thigh appears to impede the spread of injectate between the SN and PFCN in a most unembalmed cadaver specimens. A US‐guided subgluteal PFCN blockade may be a feasible technique to complement an SN block when complete anesthesia of the posterior thigh is required.