Abstract
Below-knee surgeries are among the most commonly performed orthopedic or plastic and reconstructive procedures. They are associated with significant postoperative pain despite the use of systemic analgesics. The regional analgesia (RA) technique has been proven beneficial for better patient outcomes when used as an adjunct to multimodal analgesia in the early postoperative period. However, apprehension of an acute compartment syndrome (ACS) can limit the administration of appropriate RA techniques in such surgeries, leading to more opioid consumption to meet the increasing analgesic demands. Many modifications in the RA related to techniques and the local anesthetic type, concentration, and volume have been described to tackle such situations. The ideal RA technique should provide procedure-specific analgesia below the knee joint without affecting motor power and/or causing any delay in diagnosing or treating ACS.The high-volume proximal adductor canal (Hi-PAC) block is a novel RA technique described as motor-sparing and procedure-specific for the below-knee surgeries. The Hi-PAC block, a single-injection technique, is administered in the proximal adductor canal targeting the saphenous nerve and depositing local anesthetics (LA) adjacent to the femoral artery below the vasoadductor membrane (VAM). By directly blocking the saphenous nerve and indirectly the sciatic nerve, it covers the entire innervation of the pain-generating components involved in the below-knee surgeries.This article describes the anatomical and technical considerations of the Hi-PAC block and provides background knowledge of the relevant anatomy and sonoanatomy for a better understanding of its intricacies.
Highlights
The pain management in the lower extremity surgeries is always challenging due to variable severity of the pain depending on the surgical dissection, suboptimal analgesia with only systemic analgesics, and restricted use of regional analgesia (RA) techniques due to concerns about the possibility of developing acute compartment syndrome (ACS)
Upon tracking the ultrasound probe in the craniocaudal direction, the apex of the femoral triangle (FT) can be identified as overlapping medial borders of the adductor longus muscle (ALM) and sartorius muscle (STM), appearing as a figure of "3." The proximal adductor canal (AC) can be located just (2-3 cm) distal to the apex of FT, where a hyperechoic saphenous nerve (SN) can be seen anterolateral to the femoral artery (FA) and nerve to vastus medialis (NVM) over the vasoadductor membrane (VAM) between the VMM and STM
Selective targeting of sensory nerve fibers by using local anesthetics (LA) at low concentration may fail to mask the pain of impending compartment syndrome, making the high-volume proximal adductor canal (Hi-PAC) block an appropriate RA technique in such conditions
Summary
The pain management in the lower extremity surgeries is always challenging due to variable severity of the pain depending on the surgical dissection, suboptimal analgesia with only systemic analgesics, and restricted use of regional analgesia (RA) techniques due to concerns about the possibility of developing acute compartment syndrome (ACS). It is the proximal one-third part of AC that roughly occupies a 2-5 cm area distal to the apex of the FT The sonoanatomy of this region reveals posteromedial ALM, anterolateral VMM, and medial VAM with the STM above (Figure 5, Panel D). Femoral vessels can be seen entering into the adductor hiatus before becoming popliteal vessels The sonoanatomy of this region reveals posteromedial AMM, anterolateral VMM, and medial VAM with STM above (Figure 5, Panel F). Upon tracking the ultrasound probe in the craniocaudal direction, the apex of the FT can be identified as overlapping medial borders of the ALM and STM, appearing as a figure of "3." The proximal AC can be located just (2-3 cm) distal to the apex of FT, where a hyperechoic SN can be seen anterolateral to the FA and NVM over the VAM between the VMM and STM.
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