This video demonstrates how to perform an ultrasound-guided single-shot adductor canal block for postoperative pain control in a pediatric patient presenting for anterior cruciate ligament repair.
Equipment needed: linear or curvilinear probe, a 100 mm hyperechoic nerve block needle, ropivacaine 0.2% or bupivacaine 0.25%, a 10 mL syringe, a syringe with normal saline for hydrodissection, ChloraPrep sticks, and sterile gloves. Procedure: After inducing anesthesia and securing the airway, position the patient supine with the surgical leg externally rotated, ideally in a frog-leg position. Sterilize the area with chlorhexidine and drape the procedural area. Position the high-frequency ultrasound transducer over the anteromedial thigh, starting at the mid-thigh. Identify the relevant anatomy: the sartorius muscle is superficial, boat-shaped, and located on the medial mid-thigh, with the superficial femoral artery (SFA) lying immediately deep to it. The saphenous nerve, which appears hyperechoic (bright), is positioned lateral and anterior to the SFA. Scan both proximally and distally until the SFA is clearly visible and centered under the sartorius muscle on your image. Using an in-plane, lateral-to-medial approach, insert the needle aiming towards the 6 o'clock position relative to the artery. Aspirate to check for blood return, then inject normal saline to hydrodissect the tissue. Proceed by injecting the local anesthetic in 5 mL increments, aspirating before each injection to ensure there is no blood return. Ensure adequate spread of the anesthetic by observing how it distributes around and compresses the superficial femoral artery, as both the nerve and artery are in the same fascial plane. Adjust the needle direction as needed to improve the spread of the anesthetic around the artery. Administer a total of 1 mL/kg of local anesthetic, up to a maximum of 10-20 ml. After delivering the appropriate volume, remove the needle.
The adductor canal block targets the saphenous nerve, a terminal sensory branch of the femoral nerve that runs within the adductor canal at the mid-thigh level, alongside the superficial femoral artery. The adductor canal is bordered by several muscles: the vastus medialis anterolaterally, the adductor longus posteromedially, and the sartorius anteromedially. The saphenous nerve is covered by the vasoadductor membrane, a fascial layer connecting the vastus medialis to the adductor longus muscle. For optimal results, the local anesthetic should be injected deep to the vasoadductor membrane. Blocking the saphenous nerve at this site provides analgesia to the anteromedial knee, lower leg, and ankle, while preserving quadriceps motor function, which promotes quicker rehabilitation and faster postoperative recovery. Consequently, the adductor canal block has become a preferred alternative to femoral nerve blocks, as it provides similar analgesia while maintaining quadriceps function. Adductor canal block is commonly supplemented with iPACK (infiltration between the popliteal artery and the knee capsule) block to provide dense analgesia after knee surgeries such as total knee replacement and anterior cruciate ligament repair, or with popliteal sciatic nerve blocks to provide complete analgesia for ankle and foot surgeries. Complications of the adductor canal block, though infrequent, can include nerve injury, bleeding, local anesthetic systemic toxicity (LAST), infection, and quadriceps weakness, particularly if the local anesthetic volume exceeds 20-30 ml. Ultrasound guidance enhances the accuracy of local anesthetic administration and helps minimize these risks by providing clear visualization of the relevant anatomy. Absolute contraindications for the adductor canal block are similar to those for other peripheral nerve blocks and include patient refusal and active infection at the injection site. Relative contraindications include a history of coagulopathy or use of antithrombotic medications, allergies to local anesthetics, and pre-existing neural deficits in the area affected by the block.
Review Pediatric Ultrasound-Guided Adductor Canal Block.