What is the anterior approach to sciatic nerve block for pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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Answer

Answer

The sciatic nerve can also be blocked anteriorly in patients who cannot assume the Sims or lithotomy position because of lower extremity trauma. This is also a useful technique when the clinician desires performance of a combination of nerve blocks for the lower extremity, perhaps also including the lateral femoral cutaneous, femoral, and obturator nerves, and in some cases, the lumbar plexus.

The anterior approach requires that the patient is positioned in supine with the leg in a neutral position. The greater trochanter and the crease of the groin on the involved side are identified by palpation. An imaginary line is then drawn parallel to the crease of the groin that runs from the greater trochanter to the center of the thigh. This center point is then identified and prepared with antiseptic solution. A 25-gauge, 3.5-inch needle is then slowly advanced perpendicular to skin until it impinges on the femur. Again, nerve stimulation techniques can be used as described for guidance.

When the needle reaches the bony surface of the femur, it is then walked slightly superiorly and medially off the top of the lesser trochanter. When the sciatic nerve is reached, paresthesia is elicited; if a nerve stimulator is used, dorsiflexion and plantar flexion of the foot is elicited. The patient should be warned prior to stimulation or paresthesia so that they respond immediately. Paresthesia is usually elicited at a depth 1 inch beyond initial body contact. Once the needle elicits paresthesia, it is withdrawn about 1 mm. If paresthesia is not persistent and aspiration is negative, then as much as 20 mL of 1 % preservative-free lidocaine can be slowly infused. Methylprednisolone can be added to treat an inflammatory component, similar to that described with the posterior approach.


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