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Chapter 32F. Ultrasound-Guided Sciatic Nerve Block

When compared to the posterior approach, what is the disadvantage of the anterior approach to a sciatic nerve block?

A. It may be difficult to position a trauma patient in order to perform this block anteriorly.

B. It cannot be performed using ultrasound guidance, but is done with landmarks and nerve stimulation.

C. It is not anatomically well-suited for a placement of continuous infusion catheter.

D. It provides a smaller area of sensory blockade than a block done at the subgluteal level by a posterior approach.

C is correct. Many layers of muscle and soft tissue need to be penetrated with an introducer and this leads to an increased risk of hematoma. It is in the medial thigh, which may be uncomfortable for patients and is likely to be dislodged by patient movement.

A is incorrect. The anterior approach to the sciatic nerve block has the advantage of easy positioning for patients who are unable to lie in the lateral or prone position due to trauma or pain. However, leaving a continuous infusion catheter by this approach is not advised.

B is incorrect. The catheter would have to make a 90 degree (or more) turn from the direction of insertion of the introducer to the path of the nerve. The anterior approach uses the nerve stimulator as well as a curvilinear probe for the ultrasound due to the increased level of depth needed for visualization.

D is incorrect. The sciatic nerve block done at the level of the subgluteal posterior approach as well as the anterior approach both miss the posterior femoral cutaneous nerve, which provides sensation to the posterior thigh.

Which statement is true when comparing the anterior approach to the transgluteal posterior approach for a sciatic nerve block?

A. The anterior approach is better suited than the transgluteal approach for placement of a continuous infusion catheter.

B. The transgluteal approach is done using a linear array probe while the anterior approach uses a curvilinear probe.

C. The transgluteal approach is better suited than the anterior approach for a tibial osteotomy.

D. The transgluteal approach provides more cutaneous coverage than the anterior approach.

D is correct. The anterior vs. posterior approaches to a sciatic nerve block come down to clinical judgment by the anesthesia provider based on the comfort level of the provider and the status of the patient who will be having surgery. The three most common ...

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