The adductor canal (a.k.a subsartorial canal, Hunter’s canal) is an about 8-10 cm long aponeurotic tunnel and located distal to the midpoint of the anteromedial thigh from the apex of the femoral triangle to the adductor hiatus.
Located inside the canal are the:
- the (superficial) femoral artery
- the femoral vein
- the saphenous nerve
- a nerve branch to the vastus medialis muscle
- terminal nerve endings of the posterior branch of the obturator nerve are located inside the canal.
Anatomical Target and Coverage
The adductor canal block (ACB) targets the saphenous nerve, which is the sensory terminal branch of the femoral nerve that innervates the skin of the medial, anteromedial, and posteromedial aspects of the lower extremity from the distal thigh to the medial malleolus.
Research indicates that the saphenous nerve also contributes to the innervation of the periost of the medial malleolus and the joint capsula.
The ACB is indicated for anesthesia and analgesia for various lower leg/foot surgeries with antero-medial and postero-medial incisions, especially for a range of knee surgeries. This block is an alternative to the femoral nerve block to preserve quadriceps strength while providing a similar level of analgesia.
Block Technique
The block is performed with a high frequency linear ultrasound probe in a supine patient with slight external rotation of the leg. The probe is placed perpendicular to the long axis of the thigh at the mid-thigh level to obtain the short axis view of the adductor canal. The saphenous nerve is usually located lateral to the femoral artery and the needle is usually inserted in-plane from the lateral side, and the needle tip is advanced lateral to the artery. A single-shot injection or catheter for continuous peripheral nerve infusion can be used.
Dosing
Adult patients >60kg
Single shot: 15-20 ml of 0.2-0.5% ropivacaine
Infusion: 6-8ml/hour 0.2% ropivacaine
Block Duration
The single shot ACB with ropivacaine will provide 8-16 hours of cutaneous analgesia.
When longer analgesia is desired, a catheter-based technique can be used to allow continuous infusion of the local anaesthetic thus providing analgesia for days if needed.
Contraindications
Absolute contraindications: Patient refusal, allergy to local anaesthetics or additives, infection at the injection site.
Relative contraindications: coagulopathy
Side effects / Complications
Infection, hematoma, nerve damage, myositis of the quadriceps muscle3 and local anaesthetic systemic toxicity.
Quadriceps weakness may cause delayed rehabilitation and patient falls.
Farag, Ehab, and Loran Mounir-Soliman. Brown's Atlas of Regional Anesthesia, E-Book, Elsevier, 2020. ProQuest Ebook Central, https://ebookcentral.proquest.com/lib/ucsflib-ebooks/detail.action?docID=6229005.
Clendenen SR, Whalen JL. Saphenous nerve innervation of the medial ankle. Local Reg Anesth. 2013;6:13-16. Published 2013 Mar 6. doi:10.2147/LRA.S42603
Abdallah FW, Whelan DB, Chan VW, Prasad GA, Endersby RV, Theodoropolous J, Oldfield S, Oh J, Brull R. Adductor Canal Block Provides Noninferior Analgesia and Superior Quadriceps Strength Compared with Femoral Nerve Block in Anterior Cruciate Ligament Reconstruction. Anesthesiology. 2016 May;124(5):1053-64. doi: 10.1097/ALN.0000000000001045. PMID: 26938989.
Neal, Joseph M. “Local Anesthetic-Induced Myotoxicity After Continuous Adductor Canal Block.” Reg Anesth Pain Med 41.6 723–727. Web.