Adductor Canal Block - An Overview

Introduction

Following knee surgery, postoperative nerve blocks provide excellent analgesia, allowing early functional rehabilitation. Adductor canal block (ACB) is becoming increasingly common as an analgesic method following knee surgery since it produces equivalent analgesia with the femoral nerve block while preserving quadriceps power. Unfortunately, because the adductor canal (AC) follows the femoral triangle, a local anesthetic (LA) can diffuse to the common femoral nerve, and quadriceps muscle damage has been recorded following ACB.

The adductor canal block (ACB) is an interfascial plane block executed in the thigh. It anesthetizes many branches distal to the femoral nerve, saphenous nerve, and both the sensory and motor branches to the quadricep muscles and components of the obturator nerve. The ACB is designed to offer appropriate analgesia by blocking the saphenous nerve (sensory nerve) and a portion of the obturator nerve as they pass through the adductor canal in the thigh.

Pain is usually worse following complete knee replacement. Adequate postoperative multimodal analgesia promotes early physical therapy to optimize the postoperative range of motion and minimize joint adhesions after knee replacement. It is critical to strike a balance between pain management and the necessity for a patient who is aware and cooperative during physical therapy. The idea of anesthetizing the saphenous nerve within the adductor canal to offer analgesia to the medial aspect of the ankle and foot has long been considered. This adductor canal block is performed by employing a more proximal (mid-thigh) technique and a higher amount of local anesthetic. Compared to conventional field blocks just below the knee and blind trans-sartorial methods, the application of ultrasound (US) guidance enhanced saphenous block effectiveness.

What Are the Indications for the Adductor Canal Block?

• ACB was more effective than femoral nerve block (FNB) for preserving the quadriceps muscle strength, quicker knee function restoration, enhanced range of motion, and lower likelihood of falls.

• When executed correctly, an adductor canal block (ACB) can give comparative analgesia for total knee arthroplasty. With this in mind, orthopedic surgeons increasingly prefer ACB over FNB for primary knee arthroplasty.

• The ACB rapidly replaces the femoral nerve block in primary knee surgery as the usual acute pain control technique.

• Following total knee arthroplasty (TKA), the aim has shifted to retaining motor function, allowing for better physical therapy, rapid recovery, and shorter hospitalization.

What Is the Anatomy of the Adductor Nerve Block?

The adductor canal is composed of vastoadductor membrane, a sturdy aponeurotic layer, that produces a subsartorial fascial tunnel that crosses the anteromedial thigh, reaching from the tip of the femoral triangle to the adductor hiatus, an opening in the adductor Magnus's muscle. The adductor canal contains As a result, adductor canal blockage may result in sensory alterations that extend beyond the saphenous nerve distribution to encompass the anteromedial knee from the superior patellar pole to the proximal tibia.

What Are the Contents of the Adductor Canal?

• Superficial femoral artery and vein.

• Saphenous nerve, afferent sensory nerves.

• Medial femoral cutaneous, and medial retinacular nerve.

• Efferent motor nerve: vastus medialis nerve.

• Nerve terminals of the branch of the posterior obturator nerve.

What Is the Ultrasound Anatomy of the Adductor Canal?

The triangular adductor canal is bounded by the vastus medialis laterally, adductor longus, or Magnus medially muscles, with the sartorius mimicking a trapezoid ‘boat-shaped’ muscle constitutes the roofing of the adductor canal anteromedially.

What Is the Technique to Block the Adductor Canal?

• The patient is positioned lying horizontally with the face and torso facing up, while the Leg on the same side rotated outside and slightly moved away from the body.

• A high-frequency direct array transducer is positioned transversely across the intersection of the distal and the middle third of the anteromedial thigh to acquire a short cross-sectional axis image of the adductor canal.

• The more distant the level, the less probable a motor block of the vastus medialis.

• The adductor canal block is traditionally applied more proximally about midthigh level, roughly midway between the anterior superior iliac spine and the patella.

• The superficial femoral artery is the anatomical component of interest, generally found at a distance of two to three cm, immediately deep into the sartorius muscle.

• It could be hard to observe in some individuals. Locating the femur and advancing the probe toward the medial side of the leg until the pulsatile anechoic femoral artery and the vein can be observed.

• The saphenous nerve can be observed at this level as a tiny hyperechoic structure between the vastus medialis and sartorius muscle, just above and lateral to the femoral artery.

• The ultrasonic probe is used to apply firm pressure to the femoral vein, which lies beneath the artery, reducing the possibility of unintentional intravascular injection.

• The needle is placed in the plane from lateral to medial and moved towards the femoral artery. When stimulation is given to the nerve, numbness in a saphenous distribution may occur.

• After confirming the proper needle tip placement deeply into the sartorius muscle and anterior lateral to the artery, the local anesthetic solution may be placed with suitable distribution throughout the artery using real-time ultrasound vision.

• If a continuous nerve block is proposed, the catheter should be placed anterolateral to the artery to provide sufficient infusion. Single-shot ACB has been demonstrated to offer equivalent analgesia to continuous FNB catheter and has aided in discharge following TKA.

• As a result, implementing a continuous peripheral nerve block in the adductor canal might necessitate an informed clinical judgment that should be considered, the necessary period of analgesia, the responsibility of ACB in improving early recovery, and the use of multimodal analgesics required to facilitate early mobility and discharge.

What Are the Adverse Effects of the Adductor Canal Block?

• Include unsuccessful block, systemic toxicity, and injection into the vessels.

• Any infections, damage to the nerve, and allergic response to local anesthetic.

• Accidental puncture to the vessels.

• Formation of hematoma.

• Quadriceps muscular weakening.

Conclusion

ANB can be used to provide analgesia and anesthesia for any treatment performed below the knee. It has evolved as a unique approach, constantly displaying similar analgesic effectiveness to femoral nerve block for total knee replacement. By inhibiting the main afferent sensory innervation of the leg without affecting quadriceps muscular strength, ACB will replace FNB as the favored regional anesthetic method for pain control after primary total knee arthroplasty.