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Chapter 32G. Ultrasound-Guided Popliteal Sciatic Block

Which statement is true regarding the ultrasound anatomy of the sciatic nerve in the popliteal fossa?

A. The separation of the tibial nerve and common peroneal nerve is consistently identified at the level of the popliteal crease.

B. The sciatic nerve is visualized at the popliteal fossa deep to the popliteal artery and vein.

C. The scanning technique should focus on identifying the level of division of the nerve and the connective tissue sheath containing both components.

D. The sciatic nerve is typically seen as a hypoechoic, oval structure with a honeycomb pattern.

C is correct. To perform a popliteal block, the ultrasound imaging should focus on identifying the division of the sciatic nerve and the common sheath (Vloka’s sheath) containing both components (tibial and common peroneal nerves). Successful injection will deposit local anesthetic within the common sheath in between the nerves.

A is incorrect. The anatomy of the sciatic nerve in the popliteal fossa is variable, and the division into the tibial nerve (TN) and common peroneal nerve (CPN) occurs at an inconstant distance from the popliteal crease, between 2 and 10 cm.

B is incorrect. At the popliteal fossa, the sciatic nerve typically is visualized superficial and lateral to the popliteal vessels.

D is incorrect. The tibial nerve is seen as a hyperechoic, oval, or round structure with a honeycomb pattern.

If nerve stimulator is used during a popliteal sciatic nerve block (0.5 mA, 0.1 msec), contact of the needle tip with either branch of the nerve is associated with:

A. Flexion of the knee with stimulation of the sciatic nerve proximal to the division

B. Plantar flexion of the foot with stimulation of the tibial nerve

C. Dorsal extension with stimulation of the sural nerve

D. Paresthesia on the medial aspect of the leg with stimulation of the peroneal nerve

B is correct. If nerve stimulation is used (0.5 mA, 0.1 msec), contact of the needle tip with the tibial nerve is associated with a motor response of the calf muscles and plantar flexion of the foot and toes.

A is incorrect. The branches of the sciatic nerve supplying the hamstring muscles, responsible for the flexion of the knee, take off proximally in the posterior thigh. Therefore, they are spared by blockade at the popliteal fossa.

C is incorrect. Stimulation of the sural nerve will result in paresthesia of the ...

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