Location of Injection of Local Anesthetics in the Adductor Canal Block

Location of Injection of Local Anesthetics in the Adductor Canal Block: A Randomized Controlled Trial of the Effect on Postoperative Analgesia and Motor Power

The adductor canal block (ACB) is the standard of care for analgesia after Anterior Cruciate Ligament (ACL) repair. ACB is performed by injecting local anesthetic (freezing) in the subsartorial canal in the thigh which is about 7-10cm long. Preliminary evidence suggests that different injection sites within the canal may produce different degrees of analgesia and quadriceps motor block. This trial seeks to determine the effects of various ACB injection sites on postoperative analgesia and motor power following ACL repair.

Adductor canal block (ACB) is replacing femoral nerve block (FNB) as the peripheral nerve block of choice for knee surgery. The ACB aims to inject local anesthetics (LA) within the neurovascular sheath in the subsartorial adductor canal around the femoral nerve. The point where the sartorius muscle crosses over the femoral artery is generally the accepted site for performing ACB. Clinically, injecting LA in the adductor canal blocks the sensory innervation of the knee and thus offers pain relief that is similar to FNB while conserving motor power around the knee. While these benefits are desirable, the exact location for performing ACB that ensures these benefits, remains debatable. The subsartorial adductor canal itself is 7-10cm long and the anatomical location of the sensory and motor nerves that innervate the knee and its surrounding muscles in this canal may vary. This randomized controlled trial is designed to identify and refine the ACB technique by clinically determining the effects of various ACB injection locations on postoperative analgesia and quadriceps motor power following ACL repair.

Inclusion Criteria:

• Patients booked for anterior cruciate ligament surgery under general anesthesia
• English speaking
• BMI <38 kg/m2

Exclusion Criteria:

• Refusal or inability to provide informed consent
• Allergy to local anesthetics
• Contraindication to regional anesthesia including coagulopathy or bleeding - diathesis
• Infection
• Nerve Injury at the site of the nerve block
• Malignancy at the site of the nerve block
• History of drug and/or alcohol dependence
• History of long term opioid intake or chronic pain disorder
• History of pre-existing neuropathy in the operative leg
• History of significant psychiatric conditions that may affect patient assessment
• Inability to understand the informed consent and demands of the study
• Allergy to any of the components of multi-modal analgesic regimen
• Revision ACL repair