Fig. 1. Short-axis (transverse cross-sectional) ultrasound scans of the posterior thigh in the popliteal fossa with corresponding labeled images during ( A ) dorsiflexion and ( B ) plantarflexion of the foot. On both scans, the sciatic nerve is seen between the semimembranosus/semitendinosus muscle complex ( Semitendinosus ) and the biceps femoris muscle ( Biceps ). ( A ) During dorsiflexion, the tibial component of the sciatic nerve moves towards the posterior surface of the leg. ( B ) During plantarflexion, the common peroneal component moves towards the posterior surface. These antagonistic movements cause a rotation and seesaw-like motion of the sciatic nerve (“seesaw” sign). Tickmarks are spaced 10 mm. Curved arrows indicate the direction of nerve movement (Additional information regarding this is available on the Anesthesiology Web site at http://www.anesthesiology.org).