REVIEW URRENT C OPINION
Use of ultrasound for lower extremity Daniela Ghisi a, Laurent Delaunay b, and Andrea Fanelli c
Purpose of review To explore the recent advances in the use of ultrasound for lower extremity blocks, including approaches to the lumbar and sacral plexus blocks. Recent findings Procedures of the lower extremity often require blocks of the lumbar and sacral plexuses. The use of ultrasound offers some advantages, including the possibility to directly visualize the distribution of local anesthetics. Summary Lower extremity blocks under ultrasound guidance often require advanced skills because of the depth of target nerves. This review summarizes the recent advances in the use of ultrasound guidance over traditional techniques. Keywords lower extremity, lumbar plexus, nerve blocks, sacral plexus, ultrasound
INTRODUCTION Evidence about the advantages of the ultrasound guidance when applied to lower extremity blocks has been recently growing. Current literature has demonstrated the superiority, or at least the equivalence, of the ultrasound guidance vs. the nerve stimulation technique [1]. When both modalities are used together, the onset is shorter and the procedure time is faster [2], especially for some lower extremity blocks. Although a theoretical reduction of complications has been claimed in the previous literature, more data are needed in terms of safety to be conclusive about the superiority of ultrasound guidance over other techniques [2]. The present review aims at presenting the most recent findings about the application of ultrasound guidance to lower extremity blocks, including sacral and lumbar plexuses and their major branches.
ULTRASOUND FOR SACRAL PLEXUS BLOCK Knowledge of classical anatomic descriptions is essential for regional anesthesia. However, as for the upper limb, it is important to keep in mind that variations are frequent and ‘normal anatomy’ is found in only 50–70% of cases [3]. The sciatic nerve is an oval cross-sectional structure, generally hyperechoic filled with hypoechoic components giving www.co-anesthesiology.com
the classical ‘honeycomb’ aspect. The ratio of connective and neural tissue increases during the trajectory of the nerve from proximal to distal, to the point of creating a thick paraneural sheath around the nerve [4]. This sheath plays an important role in the spread of local anesthetic during sciatic block.
PARASACRAL APPROACH In the parasacral region, the sacral plexus leaves the pelvis and enters the buttock via the greater sciatic foramen. Local anesthetics easily spread to the entire sacral plexus territory, and since the quadratus femoris muscle nerve, which produces a small ramus for the hip joint, this approach is highly recommended in complex hip surgery. However, the needle can theoretically damage the internal iliac vessels, ureter, and rectum if introduced beyond the plexus. Moreover, there is close relation between the sciatic nerve and the superior gluteal a Department of Anaesthesia and Perioperative Medicine, Istituti Ospitalieri, Cremona, Italy, bDepartment of Anaesthesia, Clinique Ge´ne´rale, Annecy, France and cDepartment of Anaesthesia and Intensive Care, Istituto Ortopedico Rizzoli, Bologna, Italy
Correspondence to Laurent Delaunay, MD, Clinique Ge´ne´rale, 4 chemin de la tour la Reine, 74000 Annecy, France. Tel: +33 6 60 41 29 88; fax: +33 9 81 95 65 80; e-mail: [email protected] Curr Opin Anesthesiol 2014, 27:528–537 DOI:10.1097/ACO.0000000000000119 Volume 27 Number 5 October 2014
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KEY POINTS Recent ultrasound and cadaver studies suggest that sciatic nerve block, especially in the popliteal area, are more successful if the local anesthetic is injected between paraneurium and epineurium. Although there is lack of extensive randomized controlled trials, current evidence suggests that the use of ultrasound guidance is preferable to improve the block characteristics of lumbar plexus branches such as performance time, patient procedural comfort and onset time, together with other proven advantages that are often block specific. For lumbar plexus and lumbar paravertebral block, real-time ultrasound guidance allows direct visualization of the anatomy, needle, and local anesthetic distribution. When not feasible, a preprocedural scanning is highly suggested to ascertain the kidney location as well as transverse process and psoas muscle depths. When you choose a block, you have to take into account the likely extension of anesthesia. For a given surgery, when several techniques are possible, you have to choose the one with the best risk and benefit balance.
artery. Two ultrasound-guided approaches have been described [5,6]. The patient is placed in Sim’s position. A curved array low-frequency probe is necessary. In Taha’s approach, the sciatic nerve is localized in its small axe at the posterior border of the ischium. Eisenberg proposes to visualize the nerve in its long axis. The transducer is placed on the Mansour line drawn between posterior iliac spine and ischial tuberosity [7]. The greater sciatic foramen is localized on this line. A light rotation is then performed to align the probe first with the inferior gluteal vessels and then with the sciatic nerve (Fig. 1).
TRANSGLUTEAL APPROACH The sciatic nerve is localized between the greater trochanter and the ischial tuberosity or hamstring muscles [8]. The needle has to pass through the gluteus maximus muscle, that is why we prefer the term ‘transgluteal’ for this approach. In the buttock, the sacral plexus has already fanned out in its different branches. Only the sciatic nerve, the posterior femoral cutaneous and probably the inferior gluteal nerves can be reliably blocked with such an approach. The superior gluteal nerve and the nerve to the quadratus femoris muscle cannot be blocked by this approach. This fact must be considered, especially for hip surgery. Transgluteal approach is safer than the parasacral approach as its major risk is limited to a puncture of the inferior gluteal artery vessels and if the needle misses the nerve, it is stopped by bone. The patient is placed in Sim’s position. A curved array low-frequency probe is necessary. The greater trochanter is located laterally, the ischial tuberosity medially, and the gluteus maximus muscle superficially. The sciatic nerve is located beneath the muscle at mid-distance between the greater trochanter and the ischial tuberosity (Fig. 2). The probe can be moved along the groove formed between the hamstring muscles and the vastus lateralis muscle. A 100 mm needle is inserted parallel and in line with the ultrasound beam. The use of nerve stimulator is very useful for this deep block as image quality is highly variable from one patient to another.
ANTERIOR APPROACH Only the sciatic nerve can be constantly blocked at this level. Extension to the posterior femoral cutaneous nerve is unpredictable. The patient is placed in the supine position. A curved array lowfrequency probe is necessary. The probe is placed in the medial and inguinal region in order to direct the
Sciatic nerve
FIGURE 1. Parasacral approach. The probe is positioned on Mansour’s line. With light probe rotation, we progressively unwound, first the inferior gluteal artery, then the sciatic nerve. 0952-7907 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
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Needle
Hamstring muscles
The lateral approach is interesting as the patient is in the supine position and it is not necessary to mobilize the leg. A 150 mm needle should be used. As the needle trajectory is very close to femoral vessels and nerve, particularly care must be taken in needle progression. The nerve stimulator must be immediately switched on after passing the skin.
Sciatic nerve
SUBGLUTEAL AND POPLITEAL APPROACH Femur
FIGURE 2. Transgluteal approach. Note the nerve position between Hamstring muscle and femur.
ultrasound beam to the femoral shaft [9]. The femoral vessels and the femoral periosteum are easily spotted as well as the muscle structure often surrounded by a hyperechoic fascia corresponding to the hamstring muscles (semitendinosus, semimembranosus, and biceps muscles). The nerve is located between the latter and the femur (Fig. 3). It is recommended to move the probe to the middle of the thigh to find the best image of the nerve. The needle can be introduced in plane laterally or medially. In both cases, nerve stimulation is important and helpful. In the medial approach, the patient is positioned with the hip and knee flexed on the operated side and the leg externally rotated at approximately 458 [10]. A 100 mm long needle is sufficient. This is the safest approach.
Femoral vessels
Semi tendinous/ membranous muscles
Needle
Femoral shaft
Sciatic nerve
In the thigh, the sciatic nerve runs between semitendinosus and semimembranosus muscles medially, and biceps femoris muscle and their tendons laterally. From the middle of the thigh to the popliteal crease the sciatic, the common peroneal and tibial nerves give off branches to the posterior part of the knee joint. Inside the popliteal fossa, the tibial and common peroneal nerves, respectively, provide a medial and a lateral sural cutaneous nerve. The level at which the medial and lateral sural nerves join to form the sural nerve varies widely. Consequently, in this area, the sural nerve block may be incomplete, especially when injection is performed beyond the sciatic bifurcation. For example, in case of surgery for Achille tendon rupture, a subgluteal approach is more interesting than popliteal because there is no risk of defect anesthesia in the sural territory. The specificity of the sciatic nerve at the thigh is thickness of the paraneural sheath surrounding the popliteal sciatic nerve (paraneurium). Its ultrasound aspect is hyperechoic, but it is difficult to distinguish from the fascia of the muscle (epimysium) and the external nerve layer (epineurium; Fig. 4). This sheath is an important feature when a sciatic nerve is dissected. It is well described in the anatomic literature for different nerves [11]. Vloka et al. [12] were the first to highlight its role in the spread of the local anesthetic in a cadaver study. Two recent studies have confirmed these notions and clarified the ultrasound aspect of this space. The first one is a cadaver study combining gross dissection, ultrasound examination, and histologic analysis. Controlled dye injection under the paraneurium allows extensive distal and proximal spread along the nerve. When the injection is performed outside the sheath, the spread is limited without any contact between dye and epineurium. The concordance between macroscopic dissection and ultrasound was excellent [13 ]. The second one is a patient study comparing local anesthetic injection under or outside the paranerve. The spread of local anesthetic along the nerve was quantified by three-dimensional reconstruction after the completion of the block and relation with quality of sensory block was noted. Injection under paraneurium allows better diffusion with a greater length of nerve in contact &
FIGURE 3. Anterior approach. Needle direction is planned to avoid femoral vascular nervous bundle. 530
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1
Epimysium Paraneurium
2
Epineurium
3 4
FIGURE 4. On the left, scheme of a peripheral nerve with the different conjunctival layers: (1) paraneurium, (2) epineurium, (3) perineurium, and (4) endoneurium. On the right, ultrasound images of sciatic nerve in popliteal area after local anesthetic injection where you can identify the different layer surrounding the nerve.
with local anesthetic. The blocks were more effective and had greater success rate than blocks performed outside of the paraneurium layer [14]. In both studies, the authors have shown that it is not an intraneural injection; indeed, no diffusion beyond the epineurium was observed. Recently, Karmakar et al. [15 ] have definitively validated this concept on a small series with a high definition ultrasound device. A linear high-frequency probe is sufficient. When it is possible, we prefer to position the patient in the ventral position. It is more comfortable for the operator and it is easier to move the probe (Fig. 5). The patient can also be in the supine position, but in this case it is better to reverse the ultrasound image on the device. The most important thing is to really inject beneath the paraneurium. There is no optimal level to block the nerve. The best place is where you have the best image. Ultrasound scanning of posterior thigh is useful to choose the puncture &
point. In the course from subgluteal to the popliteal area, the skin–nerve distance varies with the smallest skin–nerve distances at the popliteal crease and up to 5.4 cm distal to the subgluteal fold [16]. The nerve can be approached with in-plane or out-ofplane techniques indifferently. The goal is to obtain a circumferential spread of local anesthetic around the nerve between epineurium and paraneurium. To avoid brutal intraneural penetrance, when the needle passes the sheath, the nerve should be approached tangentially. The operator must feel the needle crossing the sheath as a loss of resistance sensation. As shown in Fig. 6, three aspects of spread are described. The best place is the third, where local anesthetic trends to surround the nerve. It can be useful to renew the same operation on the other side to obtain the classical ‘donut aspect’.
DISTAL AND ANKLE BLOCKS Below the knee, all the branches of the sciatic nerves can be blocked under ultrasound guidance [17]. Figures 7–10 give the position of the probe and classical ultrasound image for all these blocks.
Sciatic nerve
ULTRASOUND FOR LUMBAR PLEXUS BLOCK
Curled catheter Needle
Femur
FIGURE 5. Popliteal approach with catheter introduction. The patient is in the ventral position. As the nerve is approached perpendicularly, we use a special curled catheter (Pajunk, Geisingen, Germany), white arrow.
As for the sacral plexus, comprehension of anatomy is the key for successful blocks of the lumbar plexus as well as for the blocks of all its major branches.
LUMBAR PLEXUS AND LUMBAR PARAVERTEBRAL BLOCK Ultrasound guidance has been first described for the posterior approach to the lumbar plexus block
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(a)
(b)
(c)
FIGURE 6. Different aspects of local anesthetic injection during a sciatic popliteal block. (a) A typical bubble aspect of intramuscular injection, (b) Injection between epimysium and paraneurium, the local anesthetic seems in contact with the nerve but not surrounding it. (c) Correct subparaneurium injection, you can see here that the local anesthetic diffusion trends to surround the nerve without intraneural injection.
in 2001 [18]. The ultrasound guidance can be applied either as a preprocedural scanning or as a real-time guidance, allowing direct view of the needle, the anatomical structures, and the local anesthetic spread. Very few studies have been published regarding the application of the ultrasound guidance for the psoas compartment block in adults [19]. Sonoanatomical studies have shown that it is possible to
visualize the transverse processes, vertebral body, psoas major muscle, erector spinae, quadratus lumborum, lower pole of the kidney, peritoneum, aorta, and vena cava [20,21], whereas direct imaging of the nerve roots is not easy to reproduce because of their depth and the ‘acoustic shadow’ of the transverse processes [22 ]. The plexus can be viewed in a transverse plane with the needle inserted in plane, either from medial to lateral [23] or from lateral to medial [24], or out-of-plane [25], or in a longitudinal scan with the needle inserted in-plane [19]. According to Karmakar et al. [20], a paramedian transverse scan of &
Posterior tibial vessels Achilles tendon
Tibial nerve Anterior tibial artery Extensor digitorum longus muscle
Deep peroneal nerve
FIGURE 7. Tibial nerve at the ankle. At this level, the tibial nerve have motor fibers, a nerve stimulator could be used and helpful. Subcutaneous injection could be performed just over internal malleolus to block distal ramus of saphenous nerve. 532
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FIGURE 8. Deep peroneal nerve at the ankle. Volume 27 Number 5 October 2014
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Superficial personal nerve
Peroneus brevis muscle
Extensor digitorum longus muscle
Fibula
Tibia
FIGURE 9. Superficial peroneal nerve at the mid-leg.
the lumbar region with the ultrasound probe between two adjacent transverse processes and directed medially is preferable because it reduces the ‘acoustic shadow’ (Fig. 11). In our clinical practice, we are performing continuous psoas compartment blocks under real-time ultrasound guidance, preferring the longitudinal scan and the in-plane needle approach. The first subcostal scan is performed to localize the inferior kidney pole. The second scan is dedicated to visualize the sacral promontory in long axis as the sonoanatomical landmark which allows to ascend cranially to L2–L3, counting the shadows of the transverse processes (Fig. 12). A reliable catheterization of the lumbar plexus can be achieved after identifying the transverse processes of L2–L3 and the psoas muscle lying between them. These sonoanatomical landmarks are always reproducible, whereas visualization of the lumbar nerve roots might be challenging in the elderly and obese
Lesser saphenous vein
patients, both with transverse and longitudinal approaches. The aid of a nerve stimulator can help in improving the reliability of the described approaches. When real-time ultrasound guidance is not feasible, a prepuncture ultrasound imaging is suggested. In fact, surface landmarks do not accurately predict neither transverse process nor lumbar plexus depths. Instead, simply placing the ultrasound probe in a parasagittal plane perpendicular to the skin allows direct visualization of the transverse process and prediction of its depth within 1 cm, and therefore estimation of lumbar plexus depth within 1 cm [26]. Epidural spread of the local anesthetic as well as absorption, especially in cases of injection of large volumes, are still possible complications of the technique [27,28].
FEMORAL NERVE BLOCK Femoral nerve block requires a high-frequency linear probe which allows prompt identification of the nerve in a transverse section, as a triangular hyperechoic region which lies lateral to the artery, deep to the fascia lata and to the fascia iliaca, and on the anterior aspect of the iliopsoas muscle. Its identification may sometimes be more challenging and the nerve may also appear as a biconvex or oval hyperechoic structure, because of its location between the fascia iliaca and the iliopsoas muscle (Fig. 13) [27–29]. It seems that ultrasound guidance improves femoral nerve block onset and quality of sensory and motor blocks, reducing local anesthetic requirements, when compared with nerve stimulation technique [30].
Sural nerve Peroneus brevis muscle
Quadratus lumborum muscle
Erector spinae muscle
Lumbar plexus
Psoas muscle Shadow of vertebra
FIGURE 10. Sural nerve at the ankle.
FIGURE 11. Transversal view of lumbar plexus in psoas muscle.
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(a)
(b)
TPL3
TPL2
FIGURE 12. (a) Longitudinal scan of transverse processes of L2–L3 with the psoas muscle bed between them. (b) External view of the block procedure: the needle is inserted in line from the caudal end of the probe in a longitudinal axis.
Recently, many efforts have been directed to investigate whether the local anesthetic distribution, as well as the catheter tip position, may improve femoral nerve block quality, differentiating sensory and motor blocks. In fact, Ilfeld et al. [31] showed that an anterior catheter tip positioning may increase cutaneous sensory block vs. a posterior catheter tip placement, without increasing motor block. A study ˝ cs et al. [32] similarly showed that depositing by Szu the local anesthetic only anteriorly to the nerve results in fewer needle redirections and greater patient satisfaction than trying to surround the neural target circumferentially. According to Marhofer et al. [27], an ‘out-ofplane’ approach is preferable, especially when performing continuous femoral nerve blocks, because it allows catheter advancement parallel to the long axis of the nerve [27]. Nevertheless, Ruiz et al. [33] have shown that needle–nerve contact is more common with the out-of-plane approach, therefore possibly increasing the incidence of traumatic events.
Fascia lata
Fascia iliaca Common femoral artery Femoral nerve
FIGURE 13. Ultrasound view of the femoral nerve: it appears hyperechoic, triangular shaped, at the level of the common femoral artery under fascia iliaca. 534
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In conclusion, it is still debated whether an in-plane vs. out-of-plane needle-probe placement is preferable for femoral perineural catheter. Fredrickson and Danesh-Clough [34] have shown no differences in pain scores, local anesthetic and opioid postoperative consumptions between the two different approaches, suggesting that anesthesiologists should use the needle-probe approach they are more used to.
LATERAL FEMORAL CUTANEOUS NERVE BLOCK Lateral femoral cutaneous nerve block is indicated in surgical procedures involving the anterolateral thigh [35]. The advent of the ultrasound guidance has improved the accuracy of this block over the traditional technique based on the anatomical landmarks [36]. The nerve lies under the inguinal ligament and superficially to the sartorius muscle (Fig. 14). Anatomical variations have been described in 20% of cases [37]. When comparing a subinguinal technique (local anesthetic injected under the inguinal ligament 1–2 cm medial to the anterior superior iliac spine) with a nerve-targeting technique (local anesthetic around the neural target), the former reaches higher success rate [38]. Another way of improving the nerve localization under ultrasound guidance, thus possibly increasing the block success rate and quality, is to apply a high-frequency probe, as done by Zhu et al. [39]. The authors evaluated 240 lateral femoral cutaneous nerves in 120 volunteers, looking for the space between the tensor fasciae latae and the sartorius muscles as initial sonographic landmarks. As a result of its sonographic characteristics and the application of an 18-MHz frequency probe, the nerve was easily identified as an ovoid hypoechoic structure with hyperechoic dots within it [40]. Volume 27 Number 5 October 2014
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Lateral femoral cutaneous nerve
Sartorius muscle
part of adductor magnus muscles. The anterior division of the obturator nerve was identified between the adductor longus and brevis muscles, whereas the posterior division below the adductor brevis (Fig. 15). A more proximal approach to the obturator nerve before its bifurcation has also been proposed by Akkaya et al. [45].
ADDUCTOR CANAL BLOCK
FIGURE 14. Lateral femoral cutaneous nerve divided into two branches. Note that this nerve is highly variable as in its course than by the skin territories supplied.
OBTURATOR NERVE BLOCK Indications for obturator nerve block include major knee surgeries, as an adjuvant in pain therapy to femoral nerve block, and endoscopic transurethral resections of inferolateral bladder tumors, to prevent thigh adductor muscle contraction during the procedure. However, it is difficult to predict whether the block is necessary in urological surgery only on the basis of the tumor site [40]. The feasibility of ultrasound imaging of the obturator nerve has been confirmed in literature [41]. Sinha et al. [42] demonstrated that the injection of half of the local anesthetic solution between the pectineus and adductor brevis muscles, and half between the adductor brevis and adductor magnus muscles under ultrasound guidance provides a mean muscle strength reduction of 82% in 93% of their population (30 patients scheduled for knee surgery). Different approaches have been proposed for ultrasound-guided obturator nerve block, both inplane and out-of-plane, either before or after the bifurcation of the obturator nerve into its anterior and posterior branches. Helayel et al. [43] applied an out-of-plane approach for the anterior branch of the obturator nerve, which appears as a flat, hyperechoic structure between the pectineus, adductor longus, and brevis muscles. Also, Simeoforidou et al. [44] proposed an out-of-plane approach for both obturator nerve branches with dual guidance. After placing the patient in supine position with the thigh externally rotated, a linear high-frequency ultrasound probe was positioned opposite the angle formed by the inguinal crease and adductor longus, perpendicular to the skin to visualize the pectineus muscle, the adductor longus, adductor brevis, and
In the last few years, the adductor canal block (represents a variant of the saphenous nerve block) has been presented as an alternative to the femoral nerve block in patients undergoing total knee replacement. The reason is that ‘it preserves quadriceps function’ in contrast to the claim that femoral nerve block does not [46,47]. This claim is mostly supported by the studies performed in normal volunteers and in patients in whom the femoral nerve block has been performed using a volume and a concentration of local anesthetics established to produce a complete motor block (30 ml of bupivacaine 0.25%) [46,48 ]. The difference between these two blocks is not so clear when the femoral block is performed using a volume and a concentration of local anesthetics allowing early patient mobilization (15 ml of 0.1% ropivacaine). Moreover, sensory supply of the knee is complex. This suggests that total infiltration of the joint could allow a complete sensory block without motor block [49]. However, the use of adductor blocks has spread like fire because it is supported by some orthopedic surgeons, despite the lack of objective evidence related to its true benefit. An ultrasound-guided approach to the saphenous nerve block has been described to the blockade of the saphenous nerve, including the adductor canal. However, it is important to recognize that &
Pectineus muscle
Obturator nerve ant. branch Adductor muscles
Obturator nerve post. branch
FIGURE 15. Obturator nerve aspect immediately after the bifurcation in anterior and posterior branches.
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REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest Sartorius muscle
Superficial femoral artery
Lateral
Medial
FIGURE 16. Saphenous nerve at mid-thigh level: whenever the nerve is not clearly identified, a blind injection of local anesthetic (2 ml) on each side of the femoral artery is suggested (white arrow).
the nerve to the vastus medialis also lies in the proximal portion of the adductor canal, possibly resulting in undesired motor weakness when a more proximal approach to the saphenous nerve is preferred. Kapoor et al. [50] dissected 40 embalmed cadaver thighs and determined that in 72.5% of specimens the most distal visible branch of the nerve to the vastus medialis pierced the muscle proximal to the site, where the saphenous nerve crosses the anterior surface of the superficial femoral artery to become medial to the vessel. These considerations are fundamental when choosing between a transsartorial (more proximal) or a subsartorial and adductor canal (more distal) saphenous nerve block (Fig. 16).
CONCLUSION Ultrasound guidance for lower extremity blocks is gaining more and more popularity because of the need to produce effective anesthesia and analgesia in the perioperative period in the setting of fasttrack surgeries. In conclusion, although there is lack of extensive randomized controlled trials, current evidence supports the use of ultrasound guidance to improve block characteristics such as performance time, patient procedural comfort, and onset time, together with other proven advantages that are often block specific [2]. Acknowledgements None. Conflicts of interest There are no conflicts of interest. 536
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1. Liu SS, Ngeow J, John RS. Evidence basis for ultrasound-guided block characteristics: onset, quality, and duration. Reg Anesth Pain Med 2010; 35:S26–S35. 2. Neal JM, Brull R, Chan VW, et al. The ASRA evidence-based medicine assessment of ultrasound-guided regional anesthesia and pain medicine: executive summary. Reg Anesth Pain Med 2010; 35:S1–S9. 3. Bergman RA, Thompson SA, Afifi AK, Saadeh FA. Compendium of human anatomic variation. Baltimore-Mu¨nich: Urban & Schwarzenberg; 1988. 4. Moayeri N, Groen GJ. Differences in quantitative architecture of sciatic nerve may explain differences in potential vulnerability to nerve injury, onset time, and minimum effective anesthetic volume. Anesthesiology 2009; 111:1128– 1134. 5. Eisernberg E. Bloc du nerf ischiatique par voie parasacre´e. In: Arnette, editor. Echographie en anesthesia re´gionale pe´riphe´rique. 2007. pp. 117–123. 6. Taha AM. A simple and successful sonographic technique to identify the sciatic nerve in the parasacral area. J Can Anesth 2012; 59:263–267. 7. Mansour NY. Reevaluating the sciatic nerve block: another landmark for consideration. Reg Anesth 1993; 18:322–323. 8. Karmakar MK, Kwok WH, Ho AM, et al. Ultrasound-guided sciatic nerve block: description of a new approach at the subgluteal space. Br J Anaesth 2007; 98:390–395. 9. Chan VW, Nova H, Abbas S, et al. Ultra-sound examination and localization of the sciatic nerve. A volunteer study. Anesthesiology 2006; 10:309–314; J Anesth 2011; 25:621–624. 10. Osaka Y, Kashiwagi M, Nagatsuka Y, Miwa S. Ultrasound-guided medial midthigh approach to sciatic nerve block with a patient in a supine position. J Anesth 2011; 25:621–624. 11. Millesi H, Zoch G, Rath T. The gliding apparatus of peripheral nerve and its clinical significance. Ann Chir Main Memb Super 1990; 9:87–97. 12. Vloka JD, Hadzic A, Lesser JB, et al. A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg 1997; 84:387–390. 13. Andersen HL, Andersen SL, Tranulm-Jensen J. Injection inside the paraneural & sheath of the sciatic nerve. Direct comparison among ultrasound imaging, macroscopic anatomy, and histologic analysis. Reg Anesth Pain Med 2012; 37:410–414. This cadavers study confront the anatomical and ultrasound informations. The authors highlight the importance of paraneural sheath in the diffusion of local anesthetic around the sciatic nerve. 14. Missair A, Weisman RS, Suarez MR, et al. A 3-dimensional ultrasound study of local anesthetic spread during lateral popliteal nerve block. What is the ideal end point for needle tip position? Reg Anesth Pain Med 2012; 37:627–632. 15. Karmakar MJ, Shariat AN, Pangthipampai P, Chen J. High-definition ultra& sound imaging defines the paraneural sheath and the fascial compartments surrounding the sciatic nerve at the popliteal fossa. Reg Anesth Pain Med 2013; 38:447–451. The authors have confirmed the results of Andersen [15] and defined the subparaneural space as the target for local anesthetic injection. 16. Bruhn J, Van Geppen GJ, Gielen J, Scheffer J. Visualization of the course of the sciatic nerve in adult volunteers by ultrasonography. Acta Anaesthesiol Scand 2008; 52:1298–1302. 17. Delbos A, Nicholls B, Charest E, et al. Ultrasound-guided nerve blocks: lower limb. Philadelphia: DVD Lippincott Williams & Wilkins; 2013. 18. Kirchmair L, Entner T, Wissel J, et al. A study of the paravertebral anatomy for ultrasound-guided posterior lumbar plexus block. Anesth Analg 2001; 93:477–481. 19. Chin KJ, Perlas A. Ultrasonography of the lumbar spine for neuraxial and lumbar plexus blocks. Curr Opin Anesthesiol 2011; 24:567–572. 20. Karmakar MK, Ho AM, Li X, et al. Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident. Br J Anaesth 2008; 100:533–537. 21. Salviz EA, Gurkan Y, Tekin M, Buluc L. Ultrasound guided psoas compartment block and general anesthesia for arthroscopic knee surgery: a case report. Agri 2014; 26:34–38. 22. Karmakar MK, Li JW, Kwok Wh, et al. Sonoanatomy relevant for lumbar plexus & block in volunteers correlated with cross-sectional anatomic and magnetic resonance images. Reg Anesth Pain Med 2013; 38:391–397. A complete and relevant description of sonoanatomy of the paramedian transverse view of lumbar plexus. 23. Kirchmair L, Entner T, Kapral S, Mitterschiffthaler G. Ultrasound guidance for the psoas compartment block: an imaging study. Anesth Analg 2002; 94:706–710. 24. Morimoto M, Kim JT, Popovic J, et al. Ultrasound-guided lumbar plexus block for open reduction and internal fixation of hip fracture. Pain Pract 2006; 6:124–126.
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Use of ultrasound for lower extremity Ghisi et al. 25. Kirchmair L, Enna B, Mitterschiffthaler G, et al. Lumbar plexus in children. A sonographic study and its relevance to pediatric regional anesthesia. Anesthesiology 2004; 101:445–450. 26. Ilfeld BM, Loland VJ, Mariano ER. Prepuncture ultrasound imaging to predict transverse process and lumbar plexus depth for psoas compartment block and perineural catheter insertion: a prospective, observational study. Anesth Analg 2010; 110:1725–1728. 27. Marhofer P, Harrop-Griffths W, Willschke H, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia. Part 2 – recent developments in block techniques. Br J Anaesth 2010; 104:673–683. 28. Litz RJ, Vicent O, Wiessner D, Heller AR. Misplacement of a psoas compartment catheter in the subarachnoid space. Reg Anesth Pain Med 2004; 29:60–64. 29. Szu˝cs S, Morau D, Iohom G. Femoral nerve blockade. Med Ultrason 2010; 12:139–144. 30. Salinas FV. Ultrasound and review of evidence for lower extremity peripheral nerve blocks. Reg Anesth Pain Med 2010; 35:S16–S25. 31. Ilfeld BM, Loland VJ, Sandhu NS, et al. Continuous femoral nerve block: the impact of catheter tip location relative to the femoral nerve (anterior versus posterior) on quadriceps weakness and cutaneous sensory block. Anesth Analg 2012; 14:721–727. 32. Szu˝cs S, Morau D, Sultan SF, et al. A comparison of three techniques (local anesthetic deposited circumferential to vs. above vs. below the nerve) for ultrasound guided femoral nerve block. BMC Anesthesiol 2014; 14:article 6. 33. Ruiz A, Sala-Blanch X, Martinez-Oco´n J, et al. Incidence of intraneural needle insertion in ultrasound-guided femoral nerve block: a comparison between the out-of-plane versus the in-plane approaches. Rev Esp Anestesiol Reanim 2014; 61:73–77. 34. Fredrickson MJ, Danesh-Clough TK. Ultrasound-guided femoral catheter placement: a randomised comparison of the in-plane and out-of-plane techniques. Anaesthesia 2013; 68:382–390. 35. Shteynberg A, Riina LH, Glickman LT, et al. Ultrasound guided lateral femoral cutaneous nerve (LFCN) block: safe and simple anesthesia for harvesting skin grafts. Burns 2013; 39:146–149. 36. Ng I, Vaghadia H, Choi PT, Helmy N. Ultrasound imaging accurately identifies the lateral femoral cutaneous nerve. Anesth Analg 2008; 107:1070–1074. 37. Damarey B, Demondion X, Boutry N, et al. Sonographic assessment of the lateral femoral cutaneous nerve. J Clin Ultrasound 2009; 37:89–95. 38. Hara K, Sakura S, Shido A. Ultrasound-guided lateral femoral cutaneous nerve block: comparison of two techniques. Anaesth Intensive Care 2011; 39:69–72.
39. Zhu J, Zhao Y, Liu F, et al. Ultrasound of the lateral femoral cutaneous nerve in asymptomatic patients. BMC Musculoskelet Disord 2012; 13:227. 40. Mihara T, Itoh H, Hashimoto K, Goto T. Trans-resectoscope stimulation predicts the need to block adductor response during bladder tumor resection. Anesth Analg 2013; 117:740–744. 41. Soong J, Schafhalter-Zoppoth I, Gray AT. Sonographic imaging of the obturator nerve for regional block. Reg Anesth Pain Med 2007; 32:146–151. 42. Sinha SK, Abrams JH, Houle TT, Weller RS. Ultrasound-guided obturator nerve block: an interfascial injection approach without nerve stimulation. Reg Anesth Pain Med 2009; 34:261–264. 43. Helayel PE, da Conceicao DB, Pavei P, et al. Ultrasound-guided obturator nerve block: a preliminary report of a case series. Reg Anesth Pain Med 2007; 32:221–226. 44. Simeoforidou M, Bareka M, Basdekis G, et al. Peripheral nerve blockade as an exclusive approach to obturator nerve block in anterior cruciate ligament reconstructive surgery. Korean J Anesthesiol 2013; 65:410–417. 45. Akkaya T, Ozturk E, Comert A, et al. Ultrasound-guided obturator nerve block: a sonoanatomic study of a new methodologic approach. Anesth Analg 2009; 108:1037–1041. 46. Kim DH, Lin Y, Goytizolo EA, et al. Adductor canal block versus femoral nerve block for total knee arthroplasty: a prospective, randomized, controlled trial. Anesthesiology 2014; 120:540–550. 47. Jæger P, Zaric D, Fomsgaard JS, et al. Adductor canal block versus femoral nerve block for analgesia after total knee arthroplasty: a randomized, doubleblind study. Reg Anesth Pain Med 2013; 38:526–532. 48. Kwofie MK, Shastri UD, Gadsden JC, et al. The effects of ultrasound-guided & adductor canal block versus femoral nerve block on quadriceps strength and fall risk: a blinded, randomized trial of volunteers. Reg Anesth Pain Med 2013; 38:321–325. In a normal volunteer, the adductor canal block produces less weakness than a femoral nerve block performed using chloroprocaine at an anesthetic dose established to produce a motor blocks. Studies are required to establish whether the adductor canal block has the same advantage compared to a femoral block when analgesic blocks are performed to allow postoperative mobilization. 49. Egeler C, Jayakumar A, Ford S. Adductor canal block is useful but does not achieve a complete block of the knee. Reg Anesth Pain Med 2014; 39:81– 82. 50. Kapoor R, Adhikary SD, Siefring C, McQuillan PM. The saphenous nerve and its relationship to the nerve to the vastus medialis in and around the adductor canal: an anatomical study. Acta Anaesthesiol Scand 2012; 56:365–367.
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Use of ultrasound for lower extremity Daniela Ghisi a, Laurent Delaunay b, and Andrea Fanelli c
Purpose of review To explore the recent advances in the use of ultrasound for lower extremity blocks, including approaches to the lumbar and sacral plexus blocks. Recent findings Procedures of the lower extremity often require blocks of the lumbar and sacral plexuses. The use of ultrasound offers some advantages, including the possibility to directly visualize the distribution of local anesthetics. Summary Lower extremity blocks under ultrasound guidance often require advanced skills because of the depth of target nerves. This review summarizes the recent advances in the use of ultrasound guidance over traditional techniques. Keywords lower extremity, lumbar plexus, nerve blocks, sacral plexus, ultrasound
INTRODUCTION Evidence about the advantages of the ultrasound guidance when applied to lower extremity blocks has been recently growing. Current literature has demonstrated the superiority, or at least the equivalence, of the ultrasound guidance vs. the nerve stimulation technique [1]. When both modalities are used together, the onset is shorter and the procedure time is faster [2], especially for some lower extremity blocks. Although a theoretical reduction of complications has been claimed in the previous literature, more data are needed in terms of safety to be conclusive about the superiority of ultrasound guidance over other techniques [2]. The present review aims at presenting the most recent findings about the application of ultrasound guidance to lower extremity blocks, including sacral and lumbar plexuses and their major branches.
ULTRASOUND FOR SACRAL PLEXUS BLOCK Knowledge of classical anatomic descriptions is essential for regional anesthesia. However, as for the upper limb, it is important to keep in mind that variations are frequent and ‘normal anatomy’ is found in only 50–70% of cases [3]. The sciatic nerve is an oval cross-sectional structure, generally hyperechoic filled with hypoechoic components giving www.co-anesthesiology.com
the classical ‘honeycomb’ aspect. The ratio of connective and neural tissue increases during the trajectory of the nerve from proximal to distal, to the point of creating a thick paraneural sheath around the nerve [4]. This sheath plays an important role in the spread of local anesthetic during sciatic block.
PARASACRAL APPROACH In the parasacral region, the sacral plexus leaves the pelvis and enters the buttock via the greater sciatic foramen. Local anesthetics easily spread to the entire sacral plexus territory, and since the quadratus femoris muscle nerve, which produces a small ramus for the hip joint, this approach is highly recommended in complex hip surgery. However, the needle can theoretically damage the internal iliac vessels, ureter, and rectum if introduced beyond the plexus. Moreover, there is close relation between the sciatic nerve and the superior gluteal a Department of Anaesthesia and Perioperative Medicine, Istituti Ospitalieri, Cremona, Italy, bDepartment of Anaesthesia, Clinique Ge´ne´rale, Annecy, France and cDepartment of Anaesthesia and Intensive Care, Istituto Ortopedico Rizzoli, Bologna, Italy
Correspondence to Laurent Delaunay, MD, Clinique Ge´ne´rale, 4 chemin de la tour la Reine, 74000 Annecy, France. Tel: +33 6 60 41 29 88; fax: +33 9 81 95 65 80; e-mail: [email protected] Curr Opin Anesthesiol 2014, 27:528–537 DOI:10.1097/ACO.0000000000000119 Volume 27 Number 5 October 2014
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KEY POINTS Recent ultrasound and cadaver studies suggest that sciatic nerve block, especially in the popliteal area, are more successful if the local anesthetic is injected between paraneurium and epineurium. Although there is lack of extensive randomized controlled trials, current evidence suggests that the use of ultrasound guidance is preferable to improve the block characteristics of lumbar plexus branches such as performance time, patient procedural comfort and onset time, together with other proven advantages that are often block specific. For lumbar plexus and lumbar paravertebral block, real-time ultrasound guidance allows direct visualization of the anatomy, needle, and local anesthetic distribution. When not feasible, a preprocedural scanning is highly suggested to ascertain the kidney location as well as transverse process and psoas muscle depths. When you choose a block, you have to take into account the likely extension of anesthesia. For a given surgery, when several techniques are possible, you have to choose the one with the best risk and benefit balance.
artery. Two ultrasound-guided approaches have been described [5,6]. The patient is placed in Sim’s position. A curved array low-frequency probe is necessary. In Taha’s approach, the sciatic nerve is localized in its small axe at the posterior border of the ischium. Eisenberg proposes to visualize the nerve in its long axis. The transducer is placed on the Mansour line drawn between posterior iliac spine and ischial tuberosity [7]. The greater sciatic foramen is localized on this line. A light rotation is then performed to align the probe first with the inferior gluteal vessels and then with the sciatic nerve (Fig. 1).
TRANSGLUTEAL APPROACH The sciatic nerve is localized between the greater trochanter and the ischial tuberosity or hamstring muscles [8]. The needle has to pass through the gluteus maximus muscle, that is why we prefer the term ‘transgluteal’ for this approach. In the buttock, the sacral plexus has already fanned out in its different branches. Only the sciatic nerve, the posterior femoral cutaneous and probably the inferior gluteal nerves can be reliably blocked with such an approach. The superior gluteal nerve and the nerve to the quadratus femoris muscle cannot be blocked by this approach. This fact must be considered, especially for hip surgery. Transgluteal approach is safer than the parasacral approach as its major risk is limited to a puncture of the inferior gluteal artery vessels and if the needle misses the nerve, it is stopped by bone. The patient is placed in Sim’s position. A curved array low-frequency probe is necessary. The greater trochanter is located laterally, the ischial tuberosity medially, and the gluteus maximus muscle superficially. The sciatic nerve is located beneath the muscle at mid-distance between the greater trochanter and the ischial tuberosity (Fig. 2). The probe can be moved along the groove formed between the hamstring muscles and the vastus lateralis muscle. A 100 mm needle is inserted parallel and in line with the ultrasound beam. The use of nerve stimulator is very useful for this deep block as image quality is highly variable from one patient to another.
ANTERIOR APPROACH Only the sciatic nerve can be constantly blocked at this level. Extension to the posterior femoral cutaneous nerve is unpredictable. The patient is placed in the supine position. A curved array lowfrequency probe is necessary. The probe is placed in the medial and inguinal region in order to direct the
Sciatic nerve
FIGURE 1. Parasacral approach. The probe is positioned on Mansour’s line. With light probe rotation, we progressively unwound, first the inferior gluteal artery, then the sciatic nerve. 0952-7907 ß 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
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Needle
Hamstring muscles
The lateral approach is interesting as the patient is in the supine position and it is not necessary to mobilize the leg. A 150 mm needle should be used. As the needle trajectory is very close to femoral vessels and nerve, particularly care must be taken in needle progression. The nerve stimulator must be immediately switched on after passing the skin.
Sciatic nerve
SUBGLUTEAL AND POPLITEAL APPROACH Femur
FIGURE 2. Transgluteal approach. Note the nerve position between Hamstring muscle and femur.
ultrasound beam to the femoral shaft [9]. The femoral vessels and the femoral periosteum are easily spotted as well as the muscle structure often surrounded by a hyperechoic fascia corresponding to the hamstring muscles (semitendinosus, semimembranosus, and biceps muscles). The nerve is located between the latter and the femur (Fig. 3). It is recommended to move the probe to the middle of the thigh to find the best image of the nerve. The needle can be introduced in plane laterally or medially. In both cases, nerve stimulation is important and helpful. In the medial approach, the patient is positioned with the hip and knee flexed on the operated side and the leg externally rotated at approximately 458 [10]. A 100 mm long needle is sufficient. This is the safest approach.
Femoral vessels
Semi tendinous/ membranous muscles
Needle
Femoral shaft
Sciatic nerve
In the thigh, the sciatic nerve runs between semitendinosus and semimembranosus muscles medially, and biceps femoris muscle and their tendons laterally. From the middle of the thigh to the popliteal crease the sciatic, the common peroneal and tibial nerves give off branches to the posterior part of the knee joint. Inside the popliteal fossa, the tibial and common peroneal nerves, respectively, provide a medial and a lateral sural cutaneous nerve. The level at which the medial and lateral sural nerves join to form the sural nerve varies widely. Consequently, in this area, the sural nerve block may be incomplete, especially when injection is performed beyond the sciatic bifurcation. For example, in case of surgery for Achille tendon rupture, a subgluteal approach is more interesting than popliteal because there is no risk of defect anesthesia in the sural territory. The specificity of the sciatic nerve at the thigh is thickness of the paraneural sheath surrounding the popliteal sciatic nerve (paraneurium). Its ultrasound aspect is hyperechoic, but it is difficult to distinguish from the fascia of the muscle (epimysium) and the external nerve layer (epineurium; Fig. 4). This sheath is an important feature when a sciatic nerve is dissected. It is well described in the anatomic literature for different nerves [11]. Vloka et al. [12] were the first to highlight its role in the spread of the local anesthetic in a cadaver study. Two recent studies have confirmed these notions and clarified the ultrasound aspect of this space. The first one is a cadaver study combining gross dissection, ultrasound examination, and histologic analysis. Controlled dye injection under the paraneurium allows extensive distal and proximal spread along the nerve. When the injection is performed outside the sheath, the spread is limited without any contact between dye and epineurium. The concordance between macroscopic dissection and ultrasound was excellent [13 ]. The second one is a patient study comparing local anesthetic injection under or outside the paranerve. The spread of local anesthetic along the nerve was quantified by three-dimensional reconstruction after the completion of the block and relation with quality of sensory block was noted. Injection under paraneurium allows better diffusion with a greater length of nerve in contact &
FIGURE 3. Anterior approach. Needle direction is planned to avoid femoral vascular nervous bundle. 530
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1
Epimysium Paraneurium
2
Epineurium
3 4
FIGURE 4. On the left, scheme of a peripheral nerve with the different conjunctival layers: (1) paraneurium, (2) epineurium, (3) perineurium, and (4) endoneurium. On the right, ultrasound images of sciatic nerve in popliteal area after local anesthetic injection where you can identify the different layer surrounding the nerve.
with local anesthetic. The blocks were more effective and had greater success rate than blocks performed outside of the paraneurium layer [14]. In both studies, the authors have shown that it is not an intraneural injection; indeed, no diffusion beyond the epineurium was observed. Recently, Karmakar et al. [15 ] have definitively validated this concept on a small series with a high definition ultrasound device. A linear high-frequency probe is sufficient. When it is possible, we prefer to position the patient in the ventral position. It is more comfortable for the operator and it is easier to move the probe (Fig. 5). The patient can also be in the supine position, but in this case it is better to reverse the ultrasound image on the device. The most important thing is to really inject beneath the paraneurium. There is no optimal level to block the nerve. The best place is where you have the best image. Ultrasound scanning of posterior thigh is useful to choose the puncture &
point. In the course from subgluteal to the popliteal area, the skin–nerve distance varies with the smallest skin–nerve distances at the popliteal crease and up to 5.4 cm distal to the subgluteal fold [16]. The nerve can be approached with in-plane or out-ofplane techniques indifferently. The goal is to obtain a circumferential spread of local anesthetic around the nerve between epineurium and paraneurium. To avoid brutal intraneural penetrance, when the needle passes the sheath, the nerve should be approached tangentially. The operator must feel the needle crossing the sheath as a loss of resistance sensation. As shown in Fig. 6, three aspects of spread are described. The best place is the third, where local anesthetic trends to surround the nerve. It can be useful to renew the same operation on the other side to obtain the classical ‘donut aspect’.
DISTAL AND ANKLE BLOCKS Below the knee, all the branches of the sciatic nerves can be blocked under ultrasound guidance [17]. Figures 7–10 give the position of the probe and classical ultrasound image for all these blocks.
Sciatic nerve
ULTRASOUND FOR LUMBAR PLEXUS BLOCK
Curled catheter Needle
Femur
FIGURE 5. Popliteal approach with catheter introduction. The patient is in the ventral position. As the nerve is approached perpendicularly, we use a special curled catheter (Pajunk, Geisingen, Germany), white arrow.
As for the sacral plexus, comprehension of anatomy is the key for successful blocks of the lumbar plexus as well as for the blocks of all its major branches.
LUMBAR PLEXUS AND LUMBAR PARAVERTEBRAL BLOCK Ultrasound guidance has been first described for the posterior approach to the lumbar plexus block
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(a)
(b)
(c)
FIGURE 6. Different aspects of local anesthetic injection during a sciatic popliteal block. (a) A typical bubble aspect of intramuscular injection, (b) Injection between epimysium and paraneurium, the local anesthetic seems in contact with the nerve but not surrounding it. (c) Correct subparaneurium injection, you can see here that the local anesthetic diffusion trends to surround the nerve without intraneural injection.
in 2001 [18]. The ultrasound guidance can be applied either as a preprocedural scanning or as a real-time guidance, allowing direct view of the needle, the anatomical structures, and the local anesthetic spread. Very few studies have been published regarding the application of the ultrasound guidance for the psoas compartment block in adults [19]. Sonoanatomical studies have shown that it is possible to
visualize the transverse processes, vertebral body, psoas major muscle, erector spinae, quadratus lumborum, lower pole of the kidney, peritoneum, aorta, and vena cava [20,21], whereas direct imaging of the nerve roots is not easy to reproduce because of their depth and the ‘acoustic shadow’ of the transverse processes [22 ]. The plexus can be viewed in a transverse plane with the needle inserted in plane, either from medial to lateral [23] or from lateral to medial [24], or out-of-plane [25], or in a longitudinal scan with the needle inserted in-plane [19]. According to Karmakar et al. [20], a paramedian transverse scan of &
Posterior tibial vessels Achilles tendon
Tibial nerve Anterior tibial artery Extensor digitorum longus muscle
Deep peroneal nerve
FIGURE 7. Tibial nerve at the ankle. At this level, the tibial nerve have motor fibers, a nerve stimulator could be used and helpful. Subcutaneous injection could be performed just over internal malleolus to block distal ramus of saphenous nerve. 532
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FIGURE 8. Deep peroneal nerve at the ankle. Volume 27 Number 5 October 2014
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Superficial personal nerve
Peroneus brevis muscle
Extensor digitorum longus muscle
Fibula
Tibia
FIGURE 9. Superficial peroneal nerve at the mid-leg.
the lumbar region with the ultrasound probe between two adjacent transverse processes and directed medially is preferable because it reduces the ‘acoustic shadow’ (Fig. 11). In our clinical practice, we are performing continuous psoas compartment blocks under real-time ultrasound guidance, preferring the longitudinal scan and the in-plane needle approach. The first subcostal scan is performed to localize the inferior kidney pole. The second scan is dedicated to visualize the sacral promontory in long axis as the sonoanatomical landmark which allows to ascend cranially to L2–L3, counting the shadows of the transverse processes (Fig. 12). A reliable catheterization of the lumbar plexus can be achieved after identifying the transverse processes of L2–L3 and the psoas muscle lying between them. These sonoanatomical landmarks are always reproducible, whereas visualization of the lumbar nerve roots might be challenging in the elderly and obese
Lesser saphenous vein
patients, both with transverse and longitudinal approaches. The aid of a nerve stimulator can help in improving the reliability of the described approaches. When real-time ultrasound guidance is not feasible, a prepuncture ultrasound imaging is suggested. In fact, surface landmarks do not accurately predict neither transverse process nor lumbar plexus depths. Instead, simply placing the ultrasound probe in a parasagittal plane perpendicular to the skin allows direct visualization of the transverse process and prediction of its depth within 1 cm, and therefore estimation of lumbar plexus depth within 1 cm [26]. Epidural spread of the local anesthetic as well as absorption, especially in cases of injection of large volumes, are still possible complications of the technique [27,28].
FEMORAL NERVE BLOCK Femoral nerve block requires a high-frequency linear probe which allows prompt identification of the nerve in a transverse section, as a triangular hyperechoic region which lies lateral to the artery, deep to the fascia lata and to the fascia iliaca, and on the anterior aspect of the iliopsoas muscle. Its identification may sometimes be more challenging and the nerve may also appear as a biconvex or oval hyperechoic structure, because of its location between the fascia iliaca and the iliopsoas muscle (Fig. 13) [27–29]. It seems that ultrasound guidance improves femoral nerve block onset and quality of sensory and motor blocks, reducing local anesthetic requirements, when compared with nerve stimulation technique [30].
Sural nerve Peroneus brevis muscle
Quadratus lumborum muscle
Erector spinae muscle
Lumbar plexus
Psoas muscle Shadow of vertebra
FIGURE 10. Sural nerve at the ankle.
FIGURE 11. Transversal view of lumbar plexus in psoas muscle.
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(a)
(b)
TPL3
TPL2
FIGURE 12. (a) Longitudinal scan of transverse processes of L2–L3 with the psoas muscle bed between them. (b) External view of the block procedure: the needle is inserted in line from the caudal end of the probe in a longitudinal axis.
Recently, many efforts have been directed to investigate whether the local anesthetic distribution, as well as the catheter tip position, may improve femoral nerve block quality, differentiating sensory and motor blocks. In fact, Ilfeld et al. [31] showed that an anterior catheter tip positioning may increase cutaneous sensory block vs. a posterior catheter tip placement, without increasing motor block. A study ˝ cs et al. [32] similarly showed that depositing by Szu the local anesthetic only anteriorly to the nerve results in fewer needle redirections and greater patient satisfaction than trying to surround the neural target circumferentially. According to Marhofer et al. [27], an ‘out-ofplane’ approach is preferable, especially when performing continuous femoral nerve blocks, because it allows catheter advancement parallel to the long axis of the nerve [27]. Nevertheless, Ruiz et al. [33] have shown that needle–nerve contact is more common with the out-of-plane approach, therefore possibly increasing the incidence of traumatic events.
Fascia lata
Fascia iliaca Common femoral artery Femoral nerve
FIGURE 13. Ultrasound view of the femoral nerve: it appears hyperechoic, triangular shaped, at the level of the common femoral artery under fascia iliaca. 534
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In conclusion, it is still debated whether an in-plane vs. out-of-plane needle-probe placement is preferable for femoral perineural catheter. Fredrickson and Danesh-Clough [34] have shown no differences in pain scores, local anesthetic and opioid postoperative consumptions between the two different approaches, suggesting that anesthesiologists should use the needle-probe approach they are more used to.
LATERAL FEMORAL CUTANEOUS NERVE BLOCK Lateral femoral cutaneous nerve block is indicated in surgical procedures involving the anterolateral thigh [35]. The advent of the ultrasound guidance has improved the accuracy of this block over the traditional technique based on the anatomical landmarks [36]. The nerve lies under the inguinal ligament and superficially to the sartorius muscle (Fig. 14). Anatomical variations have been described in 20% of cases [37]. When comparing a subinguinal technique (local anesthetic injected under the inguinal ligament 1–2 cm medial to the anterior superior iliac spine) with a nerve-targeting technique (local anesthetic around the neural target), the former reaches higher success rate [38]. Another way of improving the nerve localization under ultrasound guidance, thus possibly increasing the block success rate and quality, is to apply a high-frequency probe, as done by Zhu et al. [39]. The authors evaluated 240 lateral femoral cutaneous nerves in 120 volunteers, looking for the space between the tensor fasciae latae and the sartorius muscles as initial sonographic landmarks. As a result of its sonographic characteristics and the application of an 18-MHz frequency probe, the nerve was easily identified as an ovoid hypoechoic structure with hyperechoic dots within it [40]. Volume 27 Number 5 October 2014
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Lateral femoral cutaneous nerve
Sartorius muscle
part of adductor magnus muscles. The anterior division of the obturator nerve was identified between the adductor longus and brevis muscles, whereas the posterior division below the adductor brevis (Fig. 15). A more proximal approach to the obturator nerve before its bifurcation has also been proposed by Akkaya et al. [45].
ADDUCTOR CANAL BLOCK
FIGURE 14. Lateral femoral cutaneous nerve divided into two branches. Note that this nerve is highly variable as in its course than by the skin territories supplied.
OBTURATOR NERVE BLOCK Indications for obturator nerve block include major knee surgeries, as an adjuvant in pain therapy to femoral nerve block, and endoscopic transurethral resections of inferolateral bladder tumors, to prevent thigh adductor muscle contraction during the procedure. However, it is difficult to predict whether the block is necessary in urological surgery only on the basis of the tumor site [40]. The feasibility of ultrasound imaging of the obturator nerve has been confirmed in literature [41]. Sinha et al. [42] demonstrated that the injection of half of the local anesthetic solution between the pectineus and adductor brevis muscles, and half between the adductor brevis and adductor magnus muscles under ultrasound guidance provides a mean muscle strength reduction of 82% in 93% of their population (30 patients scheduled for knee surgery). Different approaches have been proposed for ultrasound-guided obturator nerve block, both inplane and out-of-plane, either before or after the bifurcation of the obturator nerve into its anterior and posterior branches. Helayel et al. [43] applied an out-of-plane approach for the anterior branch of the obturator nerve, which appears as a flat, hyperechoic structure between the pectineus, adductor longus, and brevis muscles. Also, Simeoforidou et al. [44] proposed an out-of-plane approach for both obturator nerve branches with dual guidance. After placing the patient in supine position with the thigh externally rotated, a linear high-frequency ultrasound probe was positioned opposite the angle formed by the inguinal crease and adductor longus, perpendicular to the skin to visualize the pectineus muscle, the adductor longus, adductor brevis, and
In the last few years, the adductor canal block (represents a variant of the saphenous nerve block) has been presented as an alternative to the femoral nerve block in patients undergoing total knee replacement. The reason is that ‘it preserves quadriceps function’ in contrast to the claim that femoral nerve block does not [46,47]. This claim is mostly supported by the studies performed in normal volunteers and in patients in whom the femoral nerve block has been performed using a volume and a concentration of local anesthetics established to produce a complete motor block (30 ml of bupivacaine 0.25%) [46,48 ]. The difference between these two blocks is not so clear when the femoral block is performed using a volume and a concentration of local anesthetics allowing early patient mobilization (15 ml of 0.1% ropivacaine). Moreover, sensory supply of the knee is complex. This suggests that total infiltration of the joint could allow a complete sensory block without motor block [49]. However, the use of adductor blocks has spread like fire because it is supported by some orthopedic surgeons, despite the lack of objective evidence related to its true benefit. An ultrasound-guided approach to the saphenous nerve block has been described to the blockade of the saphenous nerve, including the adductor canal. However, it is important to recognize that &
Pectineus muscle
Obturator nerve ant. branch Adductor muscles
Obturator nerve post. branch
FIGURE 15. Obturator nerve aspect immediately after the bifurcation in anterior and posterior branches.
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REFERENCES AND RECOMMENDED READING Papers of particular interest, published within the annual period of review, have been highlighted as: & of special interest && of outstanding interest Sartorius muscle
Superficial femoral artery
Lateral
Medial
FIGURE 16. Saphenous nerve at mid-thigh level: whenever the nerve is not clearly identified, a blind injection of local anesthetic (2 ml) on each side of the femoral artery is suggested (white arrow).
the nerve to the vastus medialis also lies in the proximal portion of the adductor canal, possibly resulting in undesired motor weakness when a more proximal approach to the saphenous nerve is preferred. Kapoor et al. [50] dissected 40 embalmed cadaver thighs and determined that in 72.5% of specimens the most distal visible branch of the nerve to the vastus medialis pierced the muscle proximal to the site, where the saphenous nerve crosses the anterior surface of the superficial femoral artery to become medial to the vessel. These considerations are fundamental when choosing between a transsartorial (more proximal) or a subsartorial and adductor canal (more distal) saphenous nerve block (Fig. 16).
CONCLUSION Ultrasound guidance for lower extremity blocks is gaining more and more popularity because of the need to produce effective anesthesia and analgesia in the perioperative period in the setting of fasttrack surgeries. In conclusion, although there is lack of extensive randomized controlled trials, current evidence supports the use of ultrasound guidance to improve block characteristics such as performance time, patient procedural comfort, and onset time, together with other proven advantages that are often block specific [2]. Acknowledgements None. Conflicts of interest There are no conflicts of interest. 536
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