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and a meticulous biplanar technique was used to guide an 18-gauge Tuohy needle into the T12/L1 interspace with minimal bony contact. Loss of resistance to saline was met at a depth of 4.5 cm, and a 20-gauge epidural catheter was threaded easily 4 cm into the epidu space. An 18-gauge 2-inch Crawford needle was used to tunnel the catheter subcutaneously. An anteroposterior and lateral epidurogram was performed with 2 mL of iohexol (Omnipaque 300; GE Healthcare, Cork, Ireland). The catheter position was confirmed at T12 with adequate midline vertical spread in a pattern consistent with posterior and anterior epidural spread (Fig. 1). The patient was returned to the supine position, and the epidural catheter was periodically bolused with 0.25% bupivacaine with 1:200,000 epinephrine intraoperatively to maintain analgesia. The operative procedure was uneventful. The patient was extubated and later discharged to the ward. Postoperatively, the patient was placed on patient-controlled epidural analgesia with an epidural infusion containing 0.1% ropivacaine, 2 μg/mL fentanyl, and 0.5 μg/mL clonidine. The basal rate was set at 10 mL/h with 2 mL every 30 minutes demand. Scheduled oral acetaminophen 650 mg every 6 hours was used as a pain adjunct. On postoperative day (POD) 2, the basal rate was increased to 12 mL/h, and analgesia was reported to be excellent. The epidural catheter was removed on POD 4 after successful transition to oral hydrocodone/ acetaminophen 7.5/500 every 4 hours. She was discharged on POD 4. Both patient and family reported superior analgesia and reduced hospital stay compared with earlier admissions for similar orthopedic operations. Successful placement of an epidural catheter can be a challenging task in children with OPPG given the relative fragility of bony structures and high incidence of preexisting vertebral column abnormalities.

However, we suggest that an epidural catheter placed under meticulous fluoroscopic guidance to minimize damage to surrounding tissue may be an appropriate option for children with OPPG undergoing lowerextremity surgery. Indeed, epidural analgesia has been shown to provide postoperative analgesia superior to intravenous patientcontrolled analgesia4 and may also reduce hospital length of stay.5 Inadequately managed acute pain may possibly lead to chronic pain states, and this must be taken into consideration when planning anesthetics for patients with chronic painful diseases such as OPPG. Imaging modalities such as ultrasound and fluoroscopy continue to increase the safety of acute pain management techniques, and the option of regional anesthesia should be considered in all eligible patients to reduce the costs of inadequately treated perioperative pain.

Humphrey Lam, MD Aaron Broman, MD Andrew Franklin, MD Department of Anesthesiology Division of Pediatric Anesthesiology Vanderbilt University School of Medicine and Monroe Carell Jr. Children’s Hospital at Vanderbilt Nashville, TN

The authors declare no conflict of interest. REFERENCES 1. Ai M, Heeger S, Bartels CF, Schelling DK. Clinical and molecular findings in osteoporosis-pseudoglioma syndrome. Am J Hum Genet. 2005;77:741–753. 2. Gong Y, Vikkula M, Boon L, et al. Osteoporosis-pseudoglioma syndrome, a disorder affecting skeletal strength and vision, is assigned to chromosome region 11q12–13. Am J Hum Genet. 1996;59:146–151. 3. Teebi AS, Al-Awadi SA, Marafie MJ, Bushnao RA, Satyanath S. Osteoporosis-pseudoglioma syndrome with congenital heart disease: a new association. J Med Genet. 1988;25:32–36. 4. Wu CL, Cohen SR, Richman JM, et al. Efficacy of postoperative patient-controlled and continuous infusion epidural analgesia versus intravenous patient-controlled analgesia with opioids. Anesthesiology. 2005;103:1079–1088.

FIGURE 1. Anteroposterior epidurogram.

5. Wilson GA, Brown JL, Crabbe DG, Hinton W, McHugh PJ, Stringer MD. Is epidural analgesia associated with an improved outcome following open Nissen fundoplication? Paediatr Anaesth. 2001;11:65–70.

© 2014 American Society of Regional Anesthesia and Pain Medicine

Letters to the Editor

Defining Adductor Canal Block Accepted for Publication: December 4, 2013. To the Editor: e read with great interest the very thorough and well-executed article by Jæger et al concerning the comparison of the adductor canal block (ACB) versus the femoral nerve block for analgesia after total knee arthroplasty.1 However, we believe that some essential anatomical matters need to be addressed and clarified. The technique of the so-called ACB as described by the authors in the present and several previous articles consistently involved needle insertion halfway between the base of the patella and the anterior superior iliac spine (ASIS) under ultrasound to obtain a cross-sectional view of the femoral vessels and the saphenous nerve.1–4 Using an in-plane needle approach, a catheter was inserted via the needle, with the needle tip just lateral to the saphenous nerve lying lateral to the femoral artery, and 30 mL of ropivacaine 0.5% was injected via the catheter while visualizing sonographic expansion of the presumed adductor canal (AC). However, it is an anatomical matter of fact that the needle insertion point defined above is within the femoral triangle proximal to the AC. The AC extends from the apex of the femoral triangle to the adductor hiatus—and the apex of the femoral triangle is defined by the crossing of the medial margin of the adductor longus muscle and the medial margin of the sartorius muscle. The AC is a musculo-aponeurotic tunnel. It is roofed from the apex of the femoral triangle to the adductor hiatus by the vastoadductor membrane (VAM), which is a strong aponeurosis (also known as the anteromedial intermuscular septum or the subsartorial fascia) between the adductor longus and magnus muscles and the vastus medialis muscle. The sartorius muscle extends from the ASIS to the proximal medial surface of the tibia, and it runs anterior to the VAM. The AC is also known as the subsartorial canal, which might contribute to the confusion about the extent of the AC—considering that the sartorius muscle is the longest muscle in the body and much longer than the AC. The AC always contains the femoral vessels, the saphenous nerve, and the nerve to the vastus medialis muscle. The obturator nerve does often (but not always) enter the distal part of the AC and follows the femoral artery through the hiatus of the adductor magnus tendon to the popliteal

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Letters to the Editor

fossa. The obturator nerve pierces the oblique posterior ligament of the knee and supplies the posteromedial capsule of the knee joint and contributes to the innervation of the cruciate ligaments. As Jæger et al1 correctly point out, local anesthetic injected in the AC can be speculated to spread distally inside the canal and block the saphenous nerve as well as the posterior branch of the obturator nerve (if present in the canal). Local anesthetic theoretically might spread as far as the distal part of the AC with the approach described by the authors— reportedly demonstrated with magnetic resonance imaging in only 1 patient.4 Unfortunately, the referred solitary T2-weighted magnetic resonance image does not verify spread of liquid in the AC. Both water and fat are bright on T2weighted images without fat suppression, and the bright signal present in the AC has the same intensity as the fat signal seen around the other vessels and nerves in the image. Consistent distal local anesthetic spread in the AC will most probably require an injection within the AC and not in the femoral triangle as performed by the authors. The injection technique described in the present and the previous ACB studies is more correctly termed a “subsartorial volume block in the femoral triangle” because the position halfway between the base of the patella and the ASIS is well inside the femoral triangle and certainly proximal to the entrance of the AC. To use the term “adductor canal block” with this needle entry point is a misnomer. To locate the AC correctly, we suggest identification of sonographic internal landmarks (VAM, sartorius muscle, adductor longus muscle, vastus medialis muscle, and the femoral vessels) and not based on external surface landmarks and measurements. If the goal of the ACB volume block is to anesthetize the saphenous nerve and the posterior branch of the obturator nerve, then the preferred needle entry point is the distal thigh within the AC where the femoral artery is sonographically seen to descend posteriorly toward the adductor hiatus, as described by Manickam et al5 in 2009. In our opinion, rather than using a large volume of local anesthetic to fill the entire AC, it is more logical to use the subsartorial approach to selectively anesthetize the saphenous nerve in the femoral triangle with a small local anesthetic volume (∼5 mL) and to selectively block the posterior branch of the obturator nerve with an equally small local anesthetic volume in the interfascial plane between the adductor brevis and magnus muscles in the

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subinguinal region.6 Further studies are warranted to compare the usefulness of combined selective blockade of the saphenous nerve subsartorially and the posterior branch of the obturator nerve with the ACB for total knee arthroplasty.

Thomas Fichtner Bendtsen, MD, PhD Department of Anesthesia and Intensive Care Medicine Aarhus University Hospital Aarhus, Denmark

Bernhard Moriggl, MD, PhD Division of Clinical and Functional Anatomy, Department of Anatomy Histology and Embryology Innsbruck Medical University Innsbruck, Austria

Vincent Chan, MD Department of Anesthesia Toronto Western Hospital University of Toronto Toronto, Ontario, Canada

Erik Morre Pedersen, MD, DMSc Department of Radiology Aarhus University Hospital Aarhus, Denmark

Jens Børglum, MD, PhD Department of Anesthesia and Intensive Care Medicine Copenhagen University Hospital Bispebjerg, Denmark

The authors declare no conflict of interest. REFERENCES 1. Jæger P, Zaric D, Fomsgaard JS, et al. Adductor canal block versus femoral nerve block for analgesia after total knee arthroplasty. A randomized, double-blind study. Reg Anesth Pain Med. 2013;38: 526–532. 2. Jæger P, Grevstad U, Henningsen MH, Gottschau B, Mathiesen O, Dahl JB. Effect of adductor canal blockade on established, severe post-operative pain after total knee arthroplasty: a randomised study. Acta Anaesthesiol Scand. 2012;56: 1013–1019. 3. Jenstrup MT, Jæger P, Lund J, et al. Effects of adductor canal blockade on pain and ambulation after total knee arthroplasty: a randomized study. Acta Anaesthesiol Scand. 2012;56:357–364. 4. Lund J, Jenstrup MT, Jæger P, Sorensen AM, Dahl JB. Continuous adductor canal blockade for adjuvant post-operative analgesia after major knee surgery: preliminary results. Acta Anaesthesiol Scand. 2011;55:14–19.

5. Manickam B, Perlas A, Duggan E, Brull R, Chan VW, Ramlogan R. Feasibility and efficacy of ultrasound-guided block of the saphenous nerve in the adductor canal. Reg Anesth Pain Med. 2009;34:578–580. 6. Soong J, Schafhalter-Zoppoth I, Gray AT. Sonographic imaging of the obturator nerve for regional block. Reg Anesth Pain Med. 2007;32:146–151.

Reply to Dr Bendtsen Accepted for Publication: February 3, 2014. To the Editor: e would like to thank our colleagues1 for their interest in our randomized trial2 and especially in our preliminary report of the adductor canal block published in 2011,3 and we appreciate the important questions they raise regarding the anatomical basis of the adductor canal block. Although the issues our colleagues address certainly have an academic interest, it is our belief that they may have limited clinical relevance. Whether the technique is most correctly named an adductor canal block has no impact on the result of our randomized study—that by depositing local anesthetics in the proximity of the femoral artery at the midthigh level with a subsartorial approach—we demonstrated preserved quadriceps strength with an analgesic effect similar to that of the femoral nerve block.2 To address their first set of concerns, we respectfully disagree with their evaluation that “…it is an anatomical matter of fact that the needle insertion point defined above is within the femoral triangle proximal to the adductor canal.” Our colleagues continue with a thorough, but not referenced, anatomical description of the adductor canal and femoral triangle. However, there is nothing in that description contradicting that our needle tip is within the adductor canal. The adductor canal is an aponeurotic tunnel containing the femoral vessels in the middle third of the thigh.4 It runs from the apex of the femoral triangle, which is situated in the proximal third of the thigh.4 A needle insertion in the midpoint of the thigh would per definition be within the adductor canal, rather than in the femoral triangle. This is supported by the boundaries of the 2 regions; the adductor canal is roofed by the sartorius muscle and the underlying fascia, whereas the femoral triangle has no muscular roof.4 Furthermore, the lateral boundary of the femoral triangle is the medial margin of the sartorius muscle.4 This means that any block being

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Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.