Letters to the Editor
Richard Brull, MD, FRCPC Department of Anesthesia and Pain Management, Toronto Western Hospital University of Toronto Toronto, Ontario, Canada
The authors declare no conflict of interest. REFERENCES 1. Bhatt SB, Hofmann JP. Maximum effective needle-nerve distance: what did we really find? Reg Anesth Pain Med. 2014;39:351. 2. Albrecht E, Kirkham KR, Taffe P, et al. The maximum effective needle-to-nerve distance for ultrasound-guided interscalene block: an exploratory study. Reg Anesth Pain Med. 2014; 39:56–60. 3. Spence BC, Beach ML, Gallagher JD, Sites BD. Ultrasound-guided interscalene blocks: understanding where to inject the local anaesthetic. Anaesthesia. 2011;66:509–514. 4. Horlocker TT, O’Driscoll SW, Dinapoli RP. Recurring brachial plexus neuropathy in a diabetic patient after shoulder surgery and continuous interscalene block. Anesth Analg. 2000;91:688–690. 5. Koff MD, Cohen JA, McIntyre JJ, Carr CF, Sites BD. Severe brachial plexopathy after an ultrasound-guided single-injection nerve block for total shoulder arthroplasty in a patient with multiple sclerosis. Anesthesiology. 2008;108: 325–328. 6. Hebl JR, Horlocker TT, Pritchard DJ. Diffuse brachial plexopathy after interscalene blockade in a patient receiving cisplatin chemotherapy: the pharmacologic double crush syndrome. Anesth Analg. 2001;92:249–251.
Questions Regarding a Comparison of Techniques for Piriformis Muscle Injection Accepted for publication: April 15, 2014. To the Editor: y colleagues and I read with great interest the paper on comparison of the efficacy of 2 imaging techniques for injection into piriformis muscle by Fowler et al.1 We have some questions regarding the methodology and statistical analysis techniques used in this study. First, we are unclear about the site of the ultrasound (US)-guided injection from the authors’ description of their technique. The long axis of the piriformis muscle is cephalad to the ischial spine, and we use this landmark routinely during scanning to avoid placement of the probe caudal to the belly of the piriformis. It is easy to confuse the piriformis with the other external rotators of the hip (superior and inferior gemelli and obturator externus) if the US probe is positioned too caudally.2,3 In the
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Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
US diagram, the authors showed the ischial tuberoisty on the medial side. This suggests that the US probe was placed caudal to the ischial spine and the injection may not have been in the piriformis muscle. Second, we are concerned about the large volume (10 mL) of injectate used in this study. The authors discuss this briefly as a limitation of the study, but the piriformis is a fairly thin muscle and it does not accommodate more than 1 to 3 mL of injectate.3,4 Large volume of injections can be associated with spillover to structures in vicinity of the piriformis muscle including the gluteus maximus and the sciatic nerve. Consistent with this, the authors report that 25% of their patients in the fluoroscopy group (3 of 12) had minor leg weakness; this suggests injection around the sciatic nerve. Lastly, the description of sample size calculation is confusing because the authors have not defined any clear primary end point(s). The authors have based their sample size calculation on the basis of a study that evaluated injection of botulinum toxin type A into the piriformis muscle using a single group, crossover study design in only 9 patients.5 We can understand that a mixedeffects model and the Geisser-Greenhouse corrected F test was used to check for violation of assumption of sphericity, but we would like the authors to elaborate on the technique used for sample size calculation. Anuj Bhatia, MBBS, MD, FRCA, FRCPC FIPP, FFPMRCA, EDRA Department of Anesthesia and Pain Management University of Toronto University Health Network-Toronto Western Hospital, Mount Sinai Hospital, and Women’s College Hospital Toronto, Ontario, Canada
The author declares no conflict of interest. REFERENCES 1. Fowler IM, Tucker AA, Weimerskirch BP, Moran TJ, Mendez RJ. A randomized comparison of the efficacy of 2 techniques for piriformis muscle injection: ultrasound-guided versus nerve stimulator with fluoroscopic guidance. Reg Anesth Pain Med. 2014;39:126–132. 2. Peng PW, Narouze S. Ultrasound-guided interventional procedures in pain medicine: a review of anatomy, sonoanatomy, and procedures: part I: nonaxial structures. Reg Anesth Pain Med. 2009;34:458–474. 3. Jankovic D, Peng P, van Zundert A. Brief review: piriformis syndrome: etiology, diagnosis, and management. Can J Anaesth. 2013;60: 1003–1012. 4. Childers MK, Wilson DJ, Gnatz SM, Conway RR, Sherman AK. Botulinum toxin type A use in piriformis muscle syndrome: a pilot study. Am J Phys Med Rehabil. 2002;81:751–759.
5. Blunk JA, Nowotny M, Scharf J, Benrath J. MRI verification of ultrasound-guided infiltrations of local anesthetics into the piriformis muscle. Pain Med. 2013;14: 1593–1599.
Reply to Dr Bhatia Accepted for publication: May 9, 2014. To the Editor: e thank the editor for the opportunity to respond to the excellent questions posed by Dr Bhatia in response to our article.1,2 In regard to the description of our ultrasound-guided procedure, we utilized a technique described by Drs Peng and Narouze3 and were very careful to ensure that the long-axis view of the piriformis muscle was obtained at or just superior to the level of the ischial spine, so that more caudal external of the rotators was not mistakenly injected. In Figure 1 of our article, the osseous structure most medial is indeed the ischial spine and not the ischial tuberosity, and we appreciate Dr Bhatia’s pointing this out. In order to demonstrate the location of the sciatic nerve in relationship to the piriformis muscle, we rotated the transducer 30 degrees laterally and caudad in the direction of the greater trochanter and moved the transducer 2 cm laterally toward the greater trochanter in order to obtain a view of the ischial spine medially and greater trochanter laterally. By performing this rotation, we were able to obtain a cross-sectional view of the sciatic nerve and demonstrate to readers the close relationship of the sciatic nerve to the piriformis muscle. As readers can see in Figure 1 of our article, the sciatic nerve was located just superior to the piriformis muscle. By remaining above or at the level of the ischial spine, in addition to rotating the subject’s hip externally and internally and visualizing a sliding movement of the muscle under ultrasound, we ensured that we were always injecting into the piriformis muscle and not more inferior external rotators such as the gemelli muscles or obturator externus. We also appreciate Dr Bhatia’s concern about the large volume of injectate used for our injections and actually cited this in our article as one of the limitations of our study. However, the volume we used for injections is similar to other authors’ techniques. For example, Benzon et al4 used injection volumes of 12 to 16 mL, and Hanania and Kitain5 used volumes of 10 mL for their piriformis injections. Avolume of 10 mL likely did result in perisciatic spread in some patients as Dr Bhatia
W
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Richard Brull, MD, FRCPC Department of Anesthesia and Pain Management, Toronto Western Hospital University of Toronto Toronto, Ontario, Canada
The authors declare no conflict of interest. REFERENCES 1. Bhatt SB, Hofmann JP. Maximum effective needle-nerve distance: what did we really find? Reg Anesth Pain Med. 2014;39:351. 2. Albrecht E, Kirkham KR, Taffe P, et al. The maximum effective needle-to-nerve distance for ultrasound-guided interscalene block: an exploratory study. Reg Anesth Pain Med. 2014; 39:56–60. 3. Spence BC, Beach ML, Gallagher JD, Sites BD. Ultrasound-guided interscalene blocks: understanding where to inject the local anaesthetic. Anaesthesia. 2011;66:509–514. 4. Horlocker TT, O’Driscoll SW, Dinapoli RP. Recurring brachial plexus neuropathy in a diabetic patient after shoulder surgery and continuous interscalene block. Anesth Analg. 2000;91:688–690. 5. Koff MD, Cohen JA, McIntyre JJ, Carr CF, Sites BD. Severe brachial plexopathy after an ultrasound-guided single-injection nerve block for total shoulder arthroplasty in a patient with multiple sclerosis. Anesthesiology. 2008;108: 325–328. 6. Hebl JR, Horlocker TT, Pritchard DJ. Diffuse brachial plexopathy after interscalene blockade in a patient receiving cisplatin chemotherapy: the pharmacologic double crush syndrome. Anesth Analg. 2001;92:249–251.
Questions Regarding a Comparison of Techniques for Piriformis Muscle Injection Accepted for publication: April 15, 2014. To the Editor: y colleagues and I read with great interest the paper on comparison of the efficacy of 2 imaging techniques for injection into piriformis muscle by Fowler et al.1 We have some questions regarding the methodology and statistical analysis techniques used in this study. First, we are unclear about the site of the ultrasound (US)-guided injection from the authors’ description of their technique. The long axis of the piriformis muscle is cephalad to the ischial spine, and we use this landmark routinely during scanning to avoid placement of the probe caudal to the belly of the piriformis. It is easy to confuse the piriformis with the other external rotators of the hip (superior and inferior gemelli and obturator externus) if the US probe is positioned too caudally.2,3 In the
M
352
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
US diagram, the authors showed the ischial tuberoisty on the medial side. This suggests that the US probe was placed caudal to the ischial spine and the injection may not have been in the piriformis muscle. Second, we are concerned about the large volume (10 mL) of injectate used in this study. The authors discuss this briefly as a limitation of the study, but the piriformis is a fairly thin muscle and it does not accommodate more than 1 to 3 mL of injectate.3,4 Large volume of injections can be associated with spillover to structures in vicinity of the piriformis muscle including the gluteus maximus and the sciatic nerve. Consistent with this, the authors report that 25% of their patients in the fluoroscopy group (3 of 12) had minor leg weakness; this suggests injection around the sciatic nerve. Lastly, the description of sample size calculation is confusing because the authors have not defined any clear primary end point(s). The authors have based their sample size calculation on the basis of a study that evaluated injection of botulinum toxin type A into the piriformis muscle using a single group, crossover study design in only 9 patients.5 We can understand that a mixedeffects model and the Geisser-Greenhouse corrected F test was used to check for violation of assumption of sphericity, but we would like the authors to elaborate on the technique used for sample size calculation. Anuj Bhatia, MBBS, MD, FRCA, FRCPC FIPP, FFPMRCA, EDRA Department of Anesthesia and Pain Management University of Toronto University Health Network-Toronto Western Hospital, Mount Sinai Hospital, and Women’s College Hospital Toronto, Ontario, Canada
The author declares no conflict of interest. REFERENCES 1. Fowler IM, Tucker AA, Weimerskirch BP, Moran TJ, Mendez RJ. A randomized comparison of the efficacy of 2 techniques for piriformis muscle injection: ultrasound-guided versus nerve stimulator with fluoroscopic guidance. Reg Anesth Pain Med. 2014;39:126–132. 2. Peng PW, Narouze S. Ultrasound-guided interventional procedures in pain medicine: a review of anatomy, sonoanatomy, and procedures: part I: nonaxial structures. Reg Anesth Pain Med. 2009;34:458–474. 3. Jankovic D, Peng P, van Zundert A. Brief review: piriformis syndrome: etiology, diagnosis, and management. Can J Anaesth. 2013;60: 1003–1012. 4. Childers MK, Wilson DJ, Gnatz SM, Conway RR, Sherman AK. Botulinum toxin type A use in piriformis muscle syndrome: a pilot study. Am J Phys Med Rehabil. 2002;81:751–759.
5. Blunk JA, Nowotny M, Scharf J, Benrath J. MRI verification of ultrasound-guided infiltrations of local anesthetics into the piriformis muscle. Pain Med. 2013;14: 1593–1599.
Reply to Dr Bhatia Accepted for publication: May 9, 2014. To the Editor: e thank the editor for the opportunity to respond to the excellent questions posed by Dr Bhatia in response to our article.1,2 In regard to the description of our ultrasound-guided procedure, we utilized a technique described by Drs Peng and Narouze3 and were very careful to ensure that the long-axis view of the piriformis muscle was obtained at or just superior to the level of the ischial spine, so that more caudal external of the rotators was not mistakenly injected. In Figure 1 of our article, the osseous structure most medial is indeed the ischial spine and not the ischial tuberosity, and we appreciate Dr Bhatia’s pointing this out. In order to demonstrate the location of the sciatic nerve in relationship to the piriformis muscle, we rotated the transducer 30 degrees laterally and caudad in the direction of the greater trochanter and moved the transducer 2 cm laterally toward the greater trochanter in order to obtain a view of the ischial spine medially and greater trochanter laterally. By performing this rotation, we were able to obtain a cross-sectional view of the sciatic nerve and demonstrate to readers the close relationship of the sciatic nerve to the piriformis muscle. As readers can see in Figure 1 of our article, the sciatic nerve was located just superior to the piriformis muscle. By remaining above or at the level of the ischial spine, in addition to rotating the subject’s hip externally and internally and visualizing a sliding movement of the muscle under ultrasound, we ensured that we were always injecting into the piriformis muscle and not more inferior external rotators such as the gemelli muscles or obturator externus. We also appreciate Dr Bhatia’s concern about the large volume of injectate used for our injections and actually cited this in our article as one of the limitations of our study. However, the volume we used for injections is similar to other authors’ techniques. For example, Benzon et al4 used injection volumes of 12 to 16 mL, and Hanania and Kitain5 used volumes of 10 mL for their piriformis injections. Avolume of 10 mL likely did result in perisciatic spread in some patients as Dr Bhatia
W
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
