Adductor Canal Block (ACB)

The Adductor Canal Block (ACB) is a regional anesthesia technique primarily used for postoperative analgesia in knee surgeries (e.g., total knee replacement, ACL reconstruction). It provides sensory blockade while preserving quadriceps strength, making it an excellent alternative to femoral nerve block for early mobilization.

1. Anatomy of the Adductor Canal

The adductor canal (subsartorial or Hunter’s canal) is a musculo-fascial tunnel located in the middle third of the thigh. It serves as a passage for neurovascular structures between the femoral triangle and the popliteal fossa.

A. Boundaries of the Adductor Canal

Boundary	Structure
Anterior	Sartorius muscle
Medial	Vastoadductor membrane
Lateral	Vastus medialis muscle
Posterior	Adductor longus and adductor magnus muscles

B. Contents of the Adductor Canal

✅ Saphenous nerve (sensory branch of femoral nerve)

✅ Nerve to vastus medialis (motor branch, partly spared in ACB)

✅ Femoral artery

✅ Femoral vein

2. Indications of Adductor Canal Block

✅ Total Knee Arthroplasty (TKA) – Provides post-op analgesia while preserving quadriceps function.

✅ ACL Reconstruction – Reduces pain without causing significant weakness.

✅ Medial Meniscus Repair – Covers the medial knee pain pathway.

✅ Knee Arthroscopy – For pain relief in minor knee procedures.

✅ Superficial Femoral Artery Interventions – Can be used for vascular procedures.

3. Contraindications

❌ Patient refusal

❌ Infection at the injection site

❌ Severe coagulopathy

❌ Allergy to local anesthetics

❌ Pre-existing neurological deficit in the lower limb

4. Technique of Adductor Canal Block

A. Patient Positioning

• Supine position with leg slightly externally rotated to expose the medial thigh.

B. Ultrasound-Guided Approach

1️⃣ Probe Placement:

• High-frequency linear probe placed transversely at the mid-thigh level.

2️⃣ Identify Structures:

• Locate femoral artery, saphenous nerve (hyperechoic structure anterolateral to the artery).

3️⃣ Needle Insertion:

• In-plane technique, from lateral to medial, targeting the space adjacent to the artery.

4️⃣ Local Anesthetic Injection:

• 10–20 mL of 0.2–0.5% Ropivacaine or Bupivacaine deposited around the saphenous nerve.

5. Drug Dosage & Choice

Drug	Concentration (%)	Volume (mL)	Duration of Block
Ropivacaine	0.2–0.5%	10–20 mL	6–12 hours
Bupivacaine	0.25–0.5%	10–20 mL	8–16 hours
Lidocaine	1–2%	10–15 mL	2–4 hours

6. Advantages of Adductor Canal Block Over Femoral Nerve Block

Parameter	Adductor Canal Block	Femoral Nerve Block
Motor Block	Minimal	Significant quadriceps weakness
Ambulation	Early mobilization	Delayed mobilization
Fall Risk	Low	High
Pain Relief	Good (medial knee and anterior knee)	Better (entire knee)

7. Complications of Adductor Canal Block

⚠️ Nerve injury – Rare but possible if the saphenous nerve is traumatized.

⚠️ Hematoma – Avoid puncturing the femoral artery/vein.

⚠️ Local anesthetic systemic toxicity (LAST) – Ensure aspiration before injection to prevent intravascular injection.

⚠️ Infection – Use aseptic precautions.

⚠️ Incomplete block – Can occur if local anesthetic is not deposited correctly.

8. MCQs on Adductor Canal Block

1. Which nerve is primarily blocked in an adductor canal block?

A) Sciatic nerve

B) Saphenous nerve

C) Obturator nerve

D) Common peroneal nerve

✅ Answer: B (Saphenous nerve, a sensory branch of the femoral nerve).

2. Which of the following is a major advantage of an adductor canal block over a femoral nerve block?

A) More complete analgesia

B) Less risk of nerve injury

C) Preservation of quadriceps strength

D) Longer duration of analgesia

✅ Answer: C (ACB preserves quadriceps function, allowing early mobilization).

3. What is the best imaging modality to perform an adductor canal block?

A) X-ray

B) Fluoroscopy

C) Ultrasound

D) MRI

✅ Answer: C (Ultrasound is the gold standard for regional blocks).

4. What is the typical site of injection for an adductor canal block?

A) Femoral triangle

B) Medial thigh, mid-point between ASIS and patella

C) Popliteal fossa

D) Lateral thigh

✅ Answer: B (Mid-thigh, along the adductor canal).

5. Which muscle forms the anterior boundary of the adductor canal?

A) Vastus lateralis

B) Sartorius

C) Adductor longus

D) Biceps femoris

✅ Answer: B (Sartorius forms the anterior boundary of the adductor canal).

Viva Questions on Adductor Canal Block

1️⃣ What is the main indication for an adductor canal block?

✅ Postoperative analgesia after total knee replacement (TKA), ACL reconstruction, and knee surgeries.

2️⃣ Why is adductor canal block preferred over femoral nerve block?

✅ It provides effective analgesia while preserving quadriceps strength, allowing early ambulation and reducing the risk of falls.

3️⃣ What are the ultrasound landmarks for an adductor canal block?

✅ Femoral artery, saphenous nerve, sartorius muscle, vastus medialis, adductor longus.

4️⃣ How can complications be avoided?

✅ Use ultrasound guidance, aspirate before injection, and use aseptic technique.

5️⃣ Which local anesthetic is preferred for an adductor canal block?

✅ Ropivacaine 0.2–0.5% (10–20 mL) for prolonged analgesia with minimal motor block.