Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space
Toronto, Canada
* E-mail: sherif.abbas{at}uhn.on.ca
Editor—We read with interest the recent manuscript1 on ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space. We are pleased to learn that our previously described technique2 has gained popularity in other centres worldwide. The standard of care at Toronto Western Hospital for patients undergoing total knee arthroplasty is continuous catheter-based femoral nerve block, single-shot sciatic nerve block, and a spinal anaesthetic. Since 2005, we have performed a total of 675 sciatic nerve blocks, of which 207 were done using our ultrasound-guided subgluteal approach.2 We have found excellent reliability with no reported complications.
Karmakar and colleagues have provided a well written, detailed description of their experience with the ultrasound-guided subgluteal sciatic nerve blockade; however, given the similarity with our previously described subgluteal technique, we were disappointed to find no mention of our endeavours.
Hong Kong, China
* E-mail: karmakar{at}cuhk.edu.hk
Editor—We thank Dr Abbas and Brull for their interest in our recent article.1 They suggest that we have reported on a technique that their group has previously described.2 We respectfully disagree with their assertion and would like to offer the following explanation to substantiate our claims.
Their article2 described the sono-anatomy of the sciatic nerve and a technique of performing ultrasound-guided sciatic nerve injection at the infra-gluteal location in volunteers. By definition, ‘infra-gluteal’ is inferior to the gluteal crease.3 Therefore, an infra-gluteal injection for sciatic nerve block is performed inferior to a line joining the greater trochanter and the ischial tuberosity.3 4 Figure 1B in their article illustrates the location at which the infra-gluteal ultrasound scan and injection is performed. In the technique that we describe, the ultrasound scan and needle insertion is performed above the gluteal crease and directly over a line joining the lateral prominence of the greater trochanter and the ischial tuberosity. Although the two techniques may appear similar, because they are both ‘sub-gluteal’ injections, that is, under the gluteus maximus, and both injections are made in relation to the greater trochanter and the ischial tuberosity, there are subtle anatomical differences that make these two techniques different.
In the technique that we describe, the ‘sub-gluteal space’, which is a well-defined anatomical space and contains the sciatic nerve, is initially identified on the ultrasound image as a hypo-echoeic area between the hyper-echoeic perimysium of the gluteus maximus and the quadratus femoris muscle. Distention of the subgluteal space to a test injection of saline through the block needle is then confirmed—‘our end point’, irrespective of whether a motor response to nerve stimulation is elicited in the foot or not, before the local anaesthetic is injected. In contrast, Chan and colleagues perform their ultrasound-guided subgluteal injection in the infra-gluteal position after identifying the sciatic nerve using nerve stimulation. There is no mention by Chan and colleagues as to whether they were able to identify a potential perineural space on the ultrasound image of the infra-gluteal area before the local anaesthetic injection, although they report enlargement of the space after the injection. We were able to identify pulsations of the inferior gluteal artery medial to the sciatic nerve in the ‘subgluteal space’ whereas Chan and colleagues were unable to identify any blood vessel in the vicinity of their injection confirming that our two techniques were performed at different locations. Moreover, local anaesthetic also spreads between different muscles in the two techniques. In our technique, the local anaesthetic spread between the gluteus maximus and the quadratus femoris muscle. In comparison, in the infra-gluteal technique, it spreads between the gluteus maximus and biceps femoris muscle posteriorly5 and the adductor magnus muscle anteriorly.
We agree that the above discussion should have been included in our report and hope that it will help clarify the differences between our technique and the technique of ultrasound-guided subgluteal sciatic nerve block at the infra-gluteal position.
References
1 Karmakar MK, Kwok WH, Ho AM, Tsang K, Chui PT, Gin T. Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space. Br J Anaesth (2007) 98:390–5.
2 Chan VW, Nova H, Abbas S, McCartney CJ, Perlas A, Xu dQ. Ultrasound examination and localization of the sciatic nerve: a volunteer study. Anesthesiology (2006) 104:309–14.[CrossRef][Web of Science][Medline]
3 Franco CD, Tyler SG. Modified subgluteal approach to the sciatic nerve. Anesth Analg (2003) 97:1197.
4 Sukhani R, Candido KD, Doty R Jr, Yaghmour E, McCarthy RJ. Infragluteal-parabiceps sciatic nerve block: an evaluation of a novel approach using a single-injection technique. Anesth Analg (2003) 96:868–73.
5 Gray AT, Collins AB, Schafhalter-Zoppoth I. Sciatic nerve block in a child: a sonographic approach. Anesth Analg (2003) 97:1300–2.
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