An ultrasound-guided adductor canal block is a regional anesthesia technique that precisely targets specific nerves in the thigh to provide pain relief. This procedure involves injecting a local anesthetic near nerves within the adductor canal, a natural tunnel located in the middle third of the thigh. By doing so, it offers effective pain management without significantly affecting muscle strength in the leg.
Why This Block is Used
The adductor canal block is frequently used for pain management following surgical procedures involving the knee and lower leg. It is often applied after total knee arthroplasty (TKA) and anterior cruciate ligament (ACL) reconstruction, significantly reducing pain and the need for opioid medications. This block also proves beneficial for other knee arthroscopic procedures, providing targeted pain relief with minimal impact on quadriceps muscle strength.
This technique plays a role in enhanced recovery protocols, which aim to optimize patient outcomes by accelerating rehabilitation and reducing hospital stays. By minimizing motor blockade, patients can mobilize earlier after surgery, facilitating a quicker return to normal activities and physical therapy. This sparing of motor function helps reduce reliance on systemic opioids, thereby decreasing associated side effects like nausea, constipation, and sedation. The adductor canal block contributes to a more comfortable and efficient recovery process.
Performing the Block with Ultrasound Guidance
Performing an ultrasound-guided adductor canal block begins with careful patient positioning, typically supine with the leg externally rotated, sometimes in a “frog-leg” position. The area is then sterilized and draped. A high-frequency linear ultrasound transducer is placed on the skin over the mid-thigh to visualize the underlying anatomy.
The ultrasound guides the practitioner in identifying key anatomical structures within the adductor canal. The sartorius muscle, a superficial, boat-shaped muscle, serves as a significant landmark, with the superficial femoral artery (SFA) lying immediately deep to it. The saphenous nerve, the primary target for this block, appears as a bright, hyperechoic structure, is typically located lateral and anterior to the SFA. The ultrasound allows for real-time visualization, ensuring accurate identification of these structures.
Once the target structures are clearly identified, a specialized nerve block needle is inserted using an in-plane approach, usually from lateral to medial. The needle is advanced towards the area just anterior to the femoral artery, deep to the sartorius muscle. Before injecting any medication, the practitioner aspirates the syringe to confirm that no blood is drawn, indicating the needle is not within a blood vessel.
A small amount of normal saline may be injected to hydrodissect the tissue, creating a space for the local anesthetic and confirming needle tip placement. Subsequently, the local anesthetic, such as ropivacaine 0.2% or bupivacaine 0.25%, is injected in 5 mL increments, with aspiration performed before each injection to re-confirm proper placement. A total volume typically ranges from 10 to 20 mL, or about 1 mL per kilogram of body weight, ensuring adequate spread around the superficial femoral artery and the saphenous nerve within the fascial plane. The real-time visualization provided by ultrasound is crucial, allowing the practitioner to observe the anesthetic spreading around and compressing the superficial femoral artery, which confirms the correct distribution of the medication.
What Patients Can Expect
Before the adductor canal block procedure, patients typically receive instructions regarding fasting, similar to other surgical procedures, and will be asked to provide informed consent. Upon arrival at the facility, the medical team will review the patient’s medical history and discuss the procedure in detail, addressing any questions or concerns. Patients are usually positioned comfortably on their back, with the leg to be blocked slightly bent and rotated outward, often in a “frog-leg” position.
During the block, the skin at the injection site is cleaned and numbed with a local anesthetic. Patients may feel a sensation of pressure or a mild pinch as the needle is inserted, but significant pain is uncommon due to the numbing medication and the precise ultrasound guidance. Throughout the procedure, the medical team monitors the patient’s comfort and vital signs. The entire process of administering the block usually takes only a few minutes once the patient is positioned and the anatomy is identified.
Immediately after the block, patients will experience numbness in the medial aspect of the knee, lower leg, and possibly the ankle, as the local anesthetic takes effect. A significant advantage of the adductor canal block is its ability to provide pain relief while largely preserving motor function of the quadriceps muscle, meaning patients can often move their leg and bear weight, unlike with some other types of leg blocks. The duration of pain relief varies, but patients can generally expect analgesia for 6 to 12 hours, depending on the specific anesthetic used.
Minor side effects, such as mild bruising or soreness at the injection site, are possible. Serious complications are rare due to the precision offered by ultrasound guidance. The adductor canal block integrates smoothly into the overall recovery process, particularly for knee surgeries, by offering prolonged pain control that facilitates early mobilization and participation in physical therapy. This early engagement in rehabilitation is considered beneficial for a faster and more complete recovery.