Is the Double-Injection Technique Really Needed?

Abstract

To the Editor: The recent article by March et al. (1) comparing single and double injection techniques of the sciatic nerve at the popliteal level raises several issues. First, the puncture point is not clearly defined and the time between the two injections in the two stimulation groups is not given. Second, stimulation of the two branches of the sciatic nerve at the popliteal level using a posterior approach and a fixed defined point, (10 cm from the popliteal skin crease) does not take into consideration the anatomical variation between patients. It has been shown in 500 consecutive patients scheduled for a popliteal block, that the distance between the knee crease to the apex of the popliteal fossa—the apex being the ideal puncture point for performing this block because it is the most proximal point from the knee crease (which allows a puncture without interfering with the muscle structure), varies from 6 to 13 cm (2). Third, when the two parts of the sciatic nerve (peroneal and tibial) are still together, the procedure used by the authors is not without risk. In other words, if the second stimulation occurs on a nerve, that is already partially anesthetized, the risk of inadvertent intraneural injection is increased. Finally, we disagree with the author's conclusion, because one stimulation at the apex of the popliteal fossa which elicits inversion (almost) always successfully blocks both components of the sciatic nerve (2). A double stimulation may be indicated, only when inversion is, for any reason, impossible to elicit, meaning that the peroneal and tibial parts of the sciatic nerve are already well separated (3). Markus Risch, MD Stephan Blumenthal, MD Alain Borgeat, MD Department of Anesthesia Balgrist University Hospital Zurich, Switzerland [email protected]