Identification of the popliteal sciatic nerve through the above-knee lateral approach provides superior echogenicity and ultrasound visibility: a patient volunteer trial

BACKGROUND

Distinguishing light-echoed nerves from surrounding structures is challenging but may be important in nerve block administration. We evaluated the effect of patient characteristics on the echogenicity or visibility of the popliteal sciatic nerve (PSN).

METHODS

This study included adult patients who presented to the operating room as volunteers. The primary outcome was the success rate of nerve identification by ultrasound using different PSN access paths. The secondary outcome included the PSN visibility score (VIS), scan time, and PSN depth. Logistic regression analysis was used to identify factors associated with the PSN identification success rate. The body mass index (BMI) proximal-based cut-off was used to compare the PSN identification success rate through different access paths.

RESULTS

The PSN was successfully identified in 89.7% of the volunteers. The access paths (P < 0.01) and BMI (P = 0.01) were identified as independent predictors of successful PSN identification. A higher PSN identification success rate (P = 0.01), a higher VIS (P < 0.01), a more superficial PSN depth (P < 0.01), and a shorter scan time (P < 0.01) were observed in the above-knee lateral approach. Among volunteers with BMI ≥ 26.77 kg/m2, the PSN identification success rate through the above-knee lateral approach was significantly higher (P < 0.01), and PSN depth was shallower (P < 0.01) than through the medial approach.

CONCLUSIONS

The ultrasound-guided above-knee lateral approach for PSN block improved the PSN identification success rate, ensured a more superficial nerve location, and provided a clearer image.