“Figure of four” position improves the visibility of the sciatic nerve in the popliteal fossa
Yavuz Gürkan1, Hasan Tahsin Sarısoy2, Çiğdem Çağlayan3, Mine Solak1, Kamil Toker1
1Departments Of Anesthesiology, Kocaeli University Hospital, Kocaeli, Turkey
2Departments Of Radiology, Kocaeli University Hospital, Kocaeli, Turkey
3Departments Of Public Health, Kocaeli University Hospital, Kocaeli, Turkey
Keywords: Popliteal block, sciatic nerve; ultrasound.
Abstract
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.