Defining the Optimal Location to Place an Adductor Canal Block

The aim of the current project is to address a gap in the existing literature related to optimal placement of local anesthetic for an adductor canal (AC) block. The current study seeks to examine whether placement of the local anesthetic in the AC for knee surgery is more effective at reducing post-operative pain following arthroscopic knee surgery compared to a control. Specifically, if the anesthetic is more beneficial than the control group, the research will determine which location is optimal by comparing groups that receive anesthetic in the midpoint of the thigh, the proximal end of the thigh, or the distal end of the thigh.

Although there has been an abundance of literature highlighting the efficacy of using regional blocks to decrease post-operative pain, the exact location of placement of local anesthetic for anesthetizing the nerves in the AC is unknown for optimal pain relief in patients undergoing knee surgery. The saphenous nerve consistently lies in the AC at various points of local anesthetic deposit, however there are many other nerves that lie in the canal that may branch off proximally or distally from the AC that are important to target in achieving optimal pain relief for patients undergoing knee arthroscopy.1-3 The AC is bounded in a triangular shape by the vastus medialis anterolaterally, the sartorius medially, and the adductor longus/adductor magnus posteriorly. The canal contains the deep femoral artery and the deep femoral vein. The saphenous nerve consistently lies within this canal, a significant sensory contributor to the knee.1-3 Other branches of the femoral nerve can also be found in the AC. The nerve to the vastus medialis (NVM) and the posterior branches of the obtruator nerve (PON) can also be found, although inconsistently, in the AC at various locations.4,5 These nerves are thought to innervate the knee as well and contribute to pain when missed during this block. The course of these nerves is unknown. While some surmise that the NVM branches proximally and the PON branches distally, there is no consensus on this. Currently, an AC block is most often placed in the mid-thigh as measured by visual observation. The investigators seek to investigate where along the tract of the AC would be optimal to place local anesthetic to optimize analgesia on all nerves that innervate the knee without having motor loss as would occur with a femoral nerve block