Popliteal Nerve Block

For procedures below the knee, the sciatic nerve is often blocked (posteriorly or laterally) in the popliteal fossa. It may be necessary to block both the tibial and peroneal nerves separately if the sciatic nerve has already divided (there are variable proximal and distal bifurcation points).


Anatomy

The sciatic nerve terminates by dividing into tibial and common peroneal (fibular) nerves, both contained within the common epineural sheath of the sciatic nerve.
Blockade of both tibial and common peroneal nerves will target the entire leg below the knee except for the area of skin supplied exclusively by the saphenous nerve on the anteromedial ankle and foot. The nerve generally divides into the tibial nerve medially and the common peroneal nerve laterally near the apex of the popliteal fossa (approximately two thirds of the way down the thigh; however, its division is variable and can occur at a more proximal location, anywhere between the piriformis muscle and the popliteal fossa.

Patient Positioning and Surface Anatomy

Position the patient laterally or prone with the operative leg slightly flexed. Ideally, the ankles should be positioned beyond the end of the table so that motor responses to nerve stimulation can be readily observed. The landmarks become more visible when the knee is flexed against resistance.

The puncture site is often located at the tip of a triangle formed by the popliteal crease at the base and the medially located muscles (above) on the sides. Alternatively, drawing lines 8 cm long in the cephalad direction, from the insertion site of the medial and lateral tendons, the puncture point is at the midpoint of a line attaching the two (almost parallel)
lines.