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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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ANTERIOR APPROACH: SCIATIC BLOCK

Position.

Anterior block of the sciatic nerve can be carried out in the supine patient whose leg is in neutral position. The anesthesiologist should be at the patient’s side, similar to positioning during femoral nerve block.

Needle Puncture.

In the supine patient, a line should be drawn from the anterosuperior iliac spine to the pubic tubercle. Another line should be drawn parallel to this line from the midpoint of the greater trochanter inferomedially, as illustrated in Figure 12-6 . The first line is trisected, and a perpendicular line is drawn caudolaterally from the juncture of the medial and middle thirds, as shown in Figure 12-6 . At the point where the perpendicular line crosses the more caudal line, a 22-gauge, 12-cm needle is inserted until it contacts the femur at its medial border. Once the needle has contacted the femur, it is redirected slightly medially to slide off the medial surface of the femur. At approximately 5 cm past the depth required to contact the femur, a paresthesia or motor response should be sought to ensure successful block ( Fig. 12-7 ). Once a paresthesia or motor response is obtained, 20 to 25 mL of local anesthetic is injected.

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Figure 12-6  Sciatic nerve block: anterior technique.


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Figure 12-7  Magnetic resonance image (cross-sectional) at the level of the anterior sciatic nerve.


Potential Problems.

The same problems that exist with the classic approach should be considered with this anterior approach.

Pearls

This block has the advantage of being based on a simple concept, although I am able to produce anesthesia using the anterior approach slightly less often than when using the classic approach to the sciatic nerve. Perhaps with additional experience this difference would not be as apparent. One observation that may help improve one’s success rate with this block is to make sure that the lower extremity to be blocked is maintained in the neutral position and is not allowed to assume either a medially or laterally rotated position. This block may be useful in supine patients who are in significant discomfort and cannot be positioned for the classic approach.

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