The adductor canal block is a modern technique in regional anesthesia used primarily to manage pain following surgery on the lower extremity. It involves a targeted injection of local anesthetic medication to numb specific sensory nerves that transmit pain signals from the knee and surrounding tissues. This method of pain control has become a standard component of Enhanced Recovery After Surgery (ERAS) protocols. By focusing the anesthetic directly on the pain pathway, the block can significantly reduce the patient’s reliance on systemic pain medications, such as opioids, in the immediate postoperative period. The technique supports a faster recovery and better overall surgical outcome.
Anatomical Target and Nerve Function
The injection targets the adductor canal, also known as Hunter’s Canal, which is a narrow tunnel located in the middle third of the thigh. This canal is an intermuscular passageway, bordered by the sartorius, vastus medialis, and adductor longus or magnus muscles. The primary structure targeted within this canal is the saphenous nerve, which is a sensory-only branch of the larger femoral nerve.
The saphenous nerve provides sensation to the skin on the front and inner side of the knee, as well as the inner aspect of the lower leg down to the ankle. By blocking this nerve, the procedure achieves substantial pain relief for knee surgery without affecting the major motor function of the thigh. The goal is to avoid the more proximal femoral nerve, which controls the quadriceps muscles responsible for extending the knee and allowing a patient to bear weight. This selective targeting addresses the pain while preserving muscle strength necessary for movement.
Steps of the Block Procedure
The adductor canal block is performed using a high-frequency ultrasound device, which allows the specialist to visualize the underlying anatomy and guide the needle in real-time. The patient is typically positioned lying supine, with the leg slightly bent and rotated outward to expose the inner thigh. The skin is thoroughly cleaned with a sterile solution, and a local anesthetic is often injected superficially to numb the skin before the main procedure begins.
The specialist places the ultrasound probe transversely on the inner mid-thigh to locate the femoral artery, which serves as a consistent landmark within the adductor canal. The needle is then inserted in-plane and advanced toward the canal, passing beneath the sartorius muscle. Once the needle tip is positioned near the femoral artery and the saphenous nerve, the local anesthetic is injected slowly (often 10 to 20 milliliters). The specialist observes the spread of the medication on the ultrasound screen, ensuring accurate placement and confirming a safe injection away from blood vessels. For prolonged pain relief, a thin, flexible catheter may be inserted instead of a single injection, allowing for continuous delivery of the anesthetic for several days.
Specific Surgical Uses and Motor Sparing Benefits
The adductor canal block is widely applied in surgeries involving the knee, most notably Total Knee Arthroplasty (TKA), as well as procedures like Anterior Cruciate Ligament (ACL) reconstruction. For many years, the standard approach for postoperative pain was the Femoral Nerve Block, but that technique often resulted in significant temporary weakness of the quadriceps muscle. This weakness presented a safety concern, increasing the risk of falls and delaying the start of physical rehabilitation.
The primary benefit of the adductor canal block is its motor-sparing effect. It delivers comparable pain relief while minimizing the impact on quadriceps muscle strength. By preserving the function of this major thigh muscle, the patient can participate in early physical therapy, safely bear weight, and walk sooner after the operation. This preserved muscle function is a significant advantage in modern recovery pathways, contributing to earlier mobilization and potentially a shorter hospital stay.
Risks and Expected Post-Procedure Sensations
While the adductor canal block is considered a safe procedure, patients should be aware of potential complications, though major issues are uncommon. Risks include localized bleeding, bruising at the injection site, or infection, which is minimized by sterile technique. There is also a slight chance of local anesthetic systemic toxicity (LAST) if the medication is inadvertently injected into a blood vessel, which is mitigated by ultrasound guidance and careful monitoring.
Following the procedure, patients commonly experience temporary numbness or a heavy, tingling sensation along the inner side of the lower leg and foot, corresponding to the distribution of the blocked saphenous nerve. The duration of effective pain relief from a single injection typically lasts between 18 and 24 hours, after which the sensation will gradually return. Patients should contact their care team if they experience prolonged or deep-seated weakness in the thigh muscle that was unexpected, or if they notice signs of infection. Unintended weakness can occur if the local anesthetic spreads more proximally in the thigh, temporarily affecting the motor fibers of the femoral nerve.