"Figure of four" position improves the visibility of the sciatic nerve in the popliteal fossa.

Objectives: We studied the influence of patient positioning on the visibility of the sciatic nerve during ultrasound (US) examination in the popliteal region.

Methods: Using a linear broad band 7-12 MHz frequency probe, US examination of 24 sciatic nerves was performed by a blinded operator to obtain the best possible image at the level of the popliteal crease (PC) and at 4 and 8 cm above the PC in the prone position. Examinations were performed in neutral prone (Group N), with a silicone roller under the foot (Group R) and in "figure of four" (Group FOF) positions. "Figure of four" position was described as: the leg to be examined is flexed and abducted to allow the foot to rest on the ankle of the contralateral leg. A visibility score for the sciatic nerve was established as follows: Score I: Nerve is identified, but borders are not clear. Score II: Nerve is identified. Borders of the nerve are clearly distinguished from the surrounding structures. Three or less fascicles are visible. Score III: Nerve is identified. Borders of the nerve are clearly distinguished from the surrounding structures. Four or more fascicles are visible.

Results: The distance of nerve division from the PC was 6.9+/-1.6 cm. A higher visibility score was obtained in Group FOF (2.6+/-0.6 vs 1.7+/-0.8) at the PC and at 4 cm (2.3+/-0.5 vs 1.6+/-0.8) and 8 cm (2.3+/-0.7 vs 1.4+/-0.7) above the PC, compared to Group N (p<0.001).

Conclusion: "Figure of four" position improves the visibility of the sciatic nerve and may have clinical impact.