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BLOCK AT A GLANCE

Block of the saphenous nerve under the sartorius muscle at the medial aspect of the mid-third thigh. Depending on the injection level and injected volume, it may also block branches of the femoral and obturator nerves.

  • Indications: Anesthesia for foot and ankle surgery in combination with a sciatic nerve block, analgesia for knee surgery in combination with multimodal analgesia, and saphenous vein stripping, or harvesting

  • Goal: Spread of LA around the femoral artery in the fascial compartment between the sartorius, vastus medialis, and adductor muscles

  • Local anesthetic volume: 10 to 20 mL

GENERAL CONSIDERATIONS

Under “subsartorial blocks,” we describe three related, but distinct blocks: subsartorial saphenous nerve, adductor canal, and femoral triangle blocks.

The subsartorial saphenous nerve block is a well-established technique to anesthetize the medial aspect of the leg, ankle, and midfoot. It is commonly performed as an adjunct to the sciatic nerve block for lower leg surgery. The use of ultrasound (US) guidance improves its success rate, by allowing determination of the optimal injection site and monitoring of the LA spread.

The adductor canal block is similar to the subsartorial saphenous nerve block, except that larger volumes of LA are used. It was introduced as an alternative to the femoral nerve block to avoid quadriceps paresis after knee surgery. The adductor canal block is commonly used in the multimodal analgesic regimen of the enhanced recovery after surgery (ERAS) protocols for knee arthroplasty.

The femoral triangle block is an injection of LA proximal to the adductor canal to anesthetize additional terminal branches of the femoral nerve. This results in better analgesia, but also in more motor weakness of the quadriceps muscle.

While the analgesic efficacy of the adductor canal is well-documented, the ideal level at which LA should be injected remains unanswered. Recent anatomical studies suggested that in addition to the saphenous nerve, the medial femoral cutaneous nerve, branches from the nerve to the vastus medialis, and articular branches from the obturator nerve are often present in the adductor canal and contribute to the innervation of the anteromedial aspect of the knee. The level of the injection (proximal-distal) and volume of injectate are factors that determine the block outcomes. For instance, the femoral triangle block with a large volume of LA results in proximal spread to the femoral nerve, and quadriceps weakness. However, a proximal block also confers better analgesia to the anterior knee capsule. While the adductor canal injection does not result in a complete femoral nerve block, recent studies suggest that the LA may spread through the Hunter hiatus into the popliteal fossa. This, in turn, may result in a block of the articular branches to the posterior capsule from the sciatic nerve and obturator nerve (popliteal plexus).

Limitations

The saphenous nerve travels with the femoral artery and vein at the midthigh. ...

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