Sciatic Nerve Block (Anterior Parafemoral Technique)

Combined with femoral or saphenous nerve block, parafemoral approach to anterior sciatic block can be used for surgery on the foot, lower leg, knee or distal thigh. This block also provides a better Tourniquet pain relief than does the classical approach.

Anterior sciatic nerve block is a useful technique in patients who are unable to assume lateral decubitus or lithotomy position. In addition, anterior approach also allows performance of the femoral block in the same position and using the same skin preparation, which shortens the time required to complete both blocks. The advantages of our parafemoral approach to sciatic block over the classical anterior approach (Beck's approach) are:

• The landmarks are very simple and distinct in most patients
• The proximal extent of anesthesia of the thigh is greater than in the classical approach because the nerve is approached more proximally
• The lesser trochanter does not obstruct the path of the needle toward the sciatic nerve

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Combined with femoral or saphenous nerve block, parafemoral approach to anterior sciatic block can be used for surgery on the foot, lower leg, knee or distal thigh.

This block also provides a better Tourniquet pain relief than does the classical approach.

Pain management after operations on the foot, lower leg, knee or distal thigh.

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The patient is positioned supine with the leg extended on the table.

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Standard regional anesthesia tray is used (see Equipment, Block Tray Setup). We use a 15 cm insulated needle connected to Tracer II/ Solostim® nerve stimulator with foot pedal for control of the current output (LifeTech®, Inc., Stafford, TX). Controlling the current output by foot pedal eliminates the need for helpers, provides faster control of the current output and allows unassisted performance of the block.

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As with all other techniques featured on NYSORA, the landmarks for the parafemoral approach to sciatic nerve are quite simple and logical:

1. Femoral crease
2. Femoral artery
3. Insertion point: 1-2 cm lateral to the lateral border of the femoral artery

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The inguinal area is disinfected and the femoral crease, femoral artery and insertion site 1-2 cm lateral to the lateral border to the femoral artery are marked with a pen. Local anesthetic is injected subcutaneously at the anticipated point of the block needle insertion (left figure).

With the palpating hand firmly pressed on the thigh and the middle finger on the femoral artery, a 15-cm 20G needle connected to the nerve stimulator is inserted 1-2 cm lateral to the femoral artery (middle figure).

The initial stimulating current should be set at 1.5 mA. The needle orientation should be almost in a perpendicular plane with a slight inferior and lateral angulation (5-15°) (right figure). As the needle is advanced, stimulation of one of the femoral nerve branches is often elicited at 1-3 cm depth. As the needle is further advanced, the femoral nerve twitches cease. The sciatic nerve is typically stimulated at a depth of 10-12 cm. The needle is advanced until the foot twitches are obtained at 0.5 mA or less at which point 15-20 ml of local anesthetic is injected.

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This is an advanced regional anesthesia technique and it is best practiced by those with a significant experience with basic and intermediate techniques.

This is a deep block and the needle transverses multiple tissue plains. Adequate sedation and analgesia is necessary to decrease the discomfort during the block performance as well as to allow meaningful interpretation of the obtained responses to nerve stimulation.

Avoid multiple reinsertions of the needle as this may result in thigh hematoma. Anterior approach to sciatic nerve block is an advanced regional anesthesia technique and should be performed only by those with significant experience in peripheral nerve blockade.

Anterior approaches to sciatic nerve block should not be used for continuous sciatic nerve block techniques. The catheter advancement is difficult at an angle at which the sciatic nerve is stimulated.

Never use epinephrine for this block when the thigh tourniquet is planned!

Tip

When the needle encounters bone, this usually indicates contact with femoral neck or acetabulum. The possible redirection planes are: 5°-10° degrees INFERIOR and up to 5° MEDIAL to the initial insertion plane.

When stimulation of the sciatic nerve is obtained at less than 0.2 mA, the needle should be slightly withdrawn before injecting the local anesthetic! Reason: nerve stimulation at small current output may indicate intraneuronal placement of the needle.

Rotation of the leg with the parafemoral sciatic block technique is not necessary as this does not have a significant effect on the ability to reach the sciatic nerve.

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