Determination of the optimal position of the lower extremity for femoral nerve block with ultrasonographic measurements: a prospective volunteer-based study.

OBJECTIVE: The aim of the study was to determine the optimal position for femoral nerve block (FNB) under ultrasound guidance.

PATIENTS AND METHODS: We included fifty volunteers between 18-65 years of age in this study. The distances from the skin to the landmarks, which were taken as a reference for the ultrasound-guided FNB (apex point of the femoral artery = F12, lateral point = F9, and lower point = F6), were measured and compared in 3 different positions given to the lower extremity (neutral position: P1, 45° abduction: P2, and flexed knee: P3). The ease of application and the quality of the ultrasound images were evaluated at each measurement by assigning a subjective observer score and comparing them in three positions.

RESULTS: All three measurement points were found to be closest to the skin at position P3. However, the distances from F9 (p = 0.023) and F6 (p = 0.006) to the skin were significant. A significant difference was found between P1 and P3 in terms of the distance from F9 (p = 0.027) and F6 to the skin (p = 0.007). P3 was determined to be the position with the highest score for clarity of the ultrasonography images and ease of detection of the measurement points (p < 0.001). As the scores of ease of access to the femoral nerve (FN) and image clarity increased, the distance from the measurement point to the skin surface decreased, which was statistically significant.

CONCLUSIONS: The ideal position for ultrasound-guided FNB is the P3 position. As an alternative for patients with limited mobility, the P2 position can be used.