Background: The authors describe a new lateral approach to the sciatic nerve (SN) block in the popliteal fossa by using magnetic resonance imaging (MRI) and assessed its clinical feasibility.

Methods: The authors reviewed the MRI of the SN of 40 patients to compare a new landmark with the classical one. For the modified technique, the landmarks were the upper edge of the patella and the tendon of the biceps femoris. A line was drawn vertically from the upper edge of the patella. The puncture site was located at the intersection of this line with the lower part of the tendon. For the MRI study from the puncture point, the authors determined simulated needle direction to access the neurovascular bundle and measured its depth.

Results: The mean ± standard deviation distance from the skin puncture to the tibial nerve was 48 ± 6 mm in the classic group versus 26 ± 5 mm (P < .0001) and to the common peroneal nerve 42 ± 6 mm in the classic group versus 19 ± 5 mm (P < .0001). The success rate was 94% (95% confidence interval 89-99) in 100 patients. Ten patients required general anesthesia; 4 because of the saphenous nerve failure (not analyzed as a failure) and 6 because of SN block failure.

Conclusions: Based on the MRI images, a needle inserted below the biceps femoris tendon provides an easy access point to the common peroneal and/or the tibial nerve. This modified lateral approach to the SN was easy to perform, had a high success rate, and was without complication in this small cohort.