Since study conception and approval in 2018, we have shown that the analgesic benefit of an adductor canal block is not clinically significant in the setting of ACL reconstruction surgery of the knee.

The aim of this multi-centered study is to evaluate the effects of two distinct Adductor Canal Block (ACB) adjuncts, dexamethasone and dexmedetomidine, and their combination, on postoperative analgesia in patients undergoing Anterior Cruciate Ligament (ACL) Repair.

Anterior cruciate ligament repair (ACLR) is a surgical procedure of the knee associated with moderate to severe postoperative pain lasting beyond 24 hours following surgery. Provision of adequate postoperative analgesia is a prerequisite for performing this procedure on outpatient basis. By virtue of their analgesic effects, peripheral nerve blocks (PNBs), such as adductor canal block (ACB), have thus become part of the care standard for this surgical procedure.

Though ACB provides effective pain relief, the duration of analgesia associated with this block is limited to eight hours postoperatively. As a result, patients having outpatient ACLR may experience severe pain following discharge, require additional opioid analgesics to control their pain, and even visit the emergency department for acute pain management. Consequently, perioperative care for the young outpatient population undergoing this procedure is an area where improvement is needed.

Mixing adjuncts with local anesthetics can prolong the duration of analgesia of PNBs; both dexmedetomidine and dexamethasone have been shown to effectively extend the duration of PNB analgesia by 60% and 80% hours, respectively. The use of dexamethasone is wide spread, and dexmedetomidine is progressively gaining popularity.

At Toronto Western Hospital, the use of adjuncts is left to the discretion of the anesthesiologists administering PNB; and dexamethasone is occasionally used to prolong block duration. The alternative approach to prolonging block duration is using ambulatory ACB catheters, but this is an expensive option that is applicable to select patients, and it is not available at the TWH.

Importantly, these adjuncts seem to exert their effect through independent mechanisms; thus there may be an advantage to combining adjuncts together. Further prolongation of the duration of analgesia is desirable, as the prolongation of block duration associated with each of these two adjuncts, alone, falls short of the duration of worst postoperative pain following ACLR. Consequently, the investigators aimed to explore whether the combination of these two adjuncts offers an incremental benefit over either of them alone, by examining their potential additive or synergistic effect.

This randomized controlled trial compares the effect of using perineural dexamethasone, dexmedetomidine, and their combination to Control on the duration of postoperative analgesia in patients having ambulatory ACLR with ACB.

Inclusion Criteria:

• English Speaking
• ASA 1-3 patients
• BMI <40

Exclusion Criteria:

• Refusal or inability to provide informed consent
• Any contraindication to regional anesthesia including coagulopathy or bleeding diathesis, allergy to local anesthetics, infection, nerve injury or malignancy at the site of the block
• History of alcohol/drug dependence
• History of long term opioid intake or chronic pain disorder
• History of preexisting 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 the multimodal analgesic regimen
• Revision of ACL repair
• Diabetes
• Significant bradycardia (baseline heart rate ≤ 40 beats per minute)

Patients who give written informed consent will be randomly assigned on the day of surgery to either of the four study groups using a computer-generated block randomization schedule in blocks of varying sizes. Group allocation will not be disclosed to the anesthesiologist performing the ACB. An anesthesia assistant will receive an opaque envelope containing the result of randomization, and will prepare the block study solution in identical syringes. The patient receiving ACB will also be blinded to the study solution injected. Furthermore, outcome assessment will be performed by a blinded research assistant.