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.

Introduction: Total knee arthroplasty (TKA) is a life-changing joint surgery that improves health-related quality of life and functional status. Patients in need of this surgery mostly belong to the geriatric age group with limited functional reserves and multiple co-morbidities requiring utmost perioperative care with the most suitable analgesic modalities. Regional analgesia (RA) should provide effective analgesia while allowing early mobility, reduced opioid consumption, and early discharge. Dual subsartorial block (DSB) is a novel procedure-specific, motor-sparing, and opioid-sparing RA technique for TKA surgeries. Our study compared the analgesic efficacy of the two different combinations of volumes used in DSB. Methods: This prospective randomized comparative study included patients between 25-75 years of age of American Society of Anesthesiology (ASA) I-II grades who underwent an elective cemented unilateral total knee replacement performed via medial approaches under neuraxial anesthesia. A total of 104 patients were divided into two equal groups based on the local anesthetic (LA) volumes (Group A 10/20 ml and Group B 20/10 ml) used in the DSB. Postoperative pain scores (using a visual analog scale) and quadriceps strengths (using neurological exam), and opioid consumption were measured at regular intervals till discharge. Results: Most patients (71.2%) remained pain-free and comfortable until discharge, while 28.8% complained of pain within 12 hours of DSB. Mean quadriceps strength remained almost normal (4-5/5) until the discharge with no incidences of buckling or fall in either group. Over time, the postoperative trend between the groups showed a significant difference for dynamic pain (p = 0.002) and quadriceps strength (p = <0.001). There was an insignificant difference (p = 0.161) between the groups regarding opioid consumption, with the median oral morphine equivalent of zero in both groups. Discussion: The effective analgesic coverage of DSB is based on the involvement of all innervations of the procedure-specific pain generators of TKR surgeries. The specific focus on selective sensory innervations and the type/volume of the LA used makes DSB a motor-sparing RA alternative that facilitates early mobility and discharge. It can provide effective postoperative analgesia without compromising the motor strength of the quadriceps muscle when administered in either 10/20 or 20/10 volumes.