Comparison of ultrasound-guided sciatic nerve staining with methylene blue or blue tissue marker.

Objective: To compare the use of methylene blue and blue tissue marker in achieving sciatic nerve staining in cadaveric rats after perineural or intramuscular injection.

Study Design: Experimental, randomized, blinded, crossover cadaveric study.

Animals: A group of 16 fresh-frozen adult Wistar rat cadavers.

Methods: Phase I: ultrasound-guided sciatic nerve injections were performed using either methylene blue (Group Methb, n = 8) or a blue tissue marker (Group Tmarker, n = 8).

Phase Ii: ultrasound-guided biceps femoris intramuscular injections were performed with the same dyes (Group Methb IM, n = 8; Group Tmarker IM, n = 8). Volume of each injection was 0.1 mL, followed by a 5 minute interval before anatomical dissection. Positive staining was measured along the sciatic nerve in millimeters. Data analysis included t tests for parametric data and Wilcoxon and Fisher's exact tests for nonparametric data, with significance set at p < 0.05.

Results: Phase I: both solutions consistently stained the sciatic nerve in all pelvic limbs. However, the length of staining was significantly greater in Group Methb (18 ± 1.9 mm) than in Group Tmarker (4.7 ± 1.3 mm) (p < 0.001).

Phase Ii: sciatic nerve staining was observed in the Group Methb IM (7/7, 100%), with a median spread of 12 mm (interquartile range 11-12 mm), whereas no staining was detected in the Group Tmarker IM (0/8) (p = 0.015).

Conclusions: and clinical relevance Methylene blue achieved greater staining along the sciatic nerve than blue tissue marker. Furthermore, methylene blue diffused through the biceps femoris, effectively staining the sciatic nerve and surrounding tissues. This difference highlights the potential for overestimation in studies that use methylene blue and underscores the importance of selecting appropriate dye solutions.