Ultrasound-guided and ‘blind’ sciatic nerve injection techniques: Comparison in rat cadavers

Abstract

Objective

To compare the success rate and extent of sciatic nerve staining with a bupivacaine–dye solution using two injection techniques: ‘blind’ or ultrasound-guided approach.

Study design

Prospective, experimental, randomized, cadaveric study.

Animals

Adult female Wistar rat cadavers [n = 24, mass 352 g (323–374)].

Methods

Each sciatic nerve was randomly allocated to one of two groups: ‘blind’ (group B) or ultrasound-guided approach (group US) to injection. Following injection of bupivacaine–dye solution (0.1 mL), gross anatomical dissection was performed to visualize nerve staining, categorizing it as either positive or negative. The length of nerve staining was then measured and visual inspection conducted to identify potential nerve damage. Fisher's exact test was used to compare positive or negative nerve staining, and the Wilcoxon signed rank test used to compare the length of nerve staining between groups.

Results

In group B, the bupivacaine–dye solution stained 16/24 sciatic nerves (67% success). In group US, staining was successfully observed in all 24 nerves (100% success, p < 0.004). The length of nerve staining [median (interquartile range)] was 2 (2–3) mm in group B and 5 (4–6) mm in group US (p < 0.001). One sciatic nerve in group B had injectate distributed over 16 mm, suggestive of an intraneural injection. No signs of laceration or nerve damage were visible under 6× magnification in either group.

Conclusions and clinical relevance

The ultrasound-guided approach for sciatic nerve injection demonstrated a higher success rate with superior injectate distribution when compared with the ‘blind’ approach. Ultrasound guidance is recommended over a ‘blind’ approach for sciatic nerve block in rats when possible.