Original Article. A radiologic and anatomic assessment of injectate spread following transmuscular quadratus lumborum block in cadavers* Summary

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1 Original Article doi: /anae A radiologic and anatomic assessment of injectate spread following transmuscular quadratus lumborum block in cadavers* S. D. Adhikary, 1 K. El-Boghdadly, 2 Z. Nasralah, 3 N. Sarwani, 4 A. M. Nixon 5 and K. J. Chin 6 1 Associate Professor of Anesthesiology, Department of Anesthesiology and Perioperative Medicine, 4 Associate Professor of Radiology, Medical Director, MRI, Department of Radiology, Penn State Hershey Medical Center, Pennsylvania, USA 2 Regional Anesthesia Fellow, 6 Associate Professor of Anesthesia, Department of Anesthesia, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada 3 Assistant Professor, Department of Science Education, Hofstra Northwell School of Medicine, Hempstead, New York, USA 5 Ph.D. Graduate Student in Anatomy, Department of Neurosurgery, Penn State College of Medicine, Pennsylvania, USA Summary We performed bilateral transmuscular quadratus lumborum blocks in six cadavers using iodinated contrast and methylene blue. Computed tomography imaging was performed in four cadavers and anatomical dissection was completed in five. This demonstrated spread to the lumbar paravertebral space in 63% of specimens, laterally to the transversus abdominis muscle in 50% and caudally to the anterior superior iliac spine in 63% of specimens. There was no radiographic evidence of spread to the thoracic paravertebral space. Anatomical dissection revealed dye staining of the upper branches of the lumbar plexus and the psoas major muscle in 70% of specimens. Further clinical studies are required to confirm if the quadratus lumborum block might be a suitable alternative to lumbar plexus block.... Correspondence to: K. J. Chin gasgenie@gmail.com Accepted: 14 April 2016 Keywords: abdominal wall blocks; anatomy; quadratus lumborum; regional anaesthesia; ultrasound-guided technique *Presented in part at the American Society of Regional Anesthesia (ASRA) meeting, New Orleans, LA, USA, April 2016 Introduction Ultrasound-guided quadratus lumborum block is a relatively new regional anaesthetic technique which purports to provide somatic analgesia for abdominal surgery. There are several described approaches which differ in sonographic landmarks, the direction of needle insertion (anterior-to-posterior or posterior-to-anterior), and whether local anaesthetic is injected anterior, lateral or posterior to the quadratus lumborum muscle [1, 2]. In all cases, the assumption is that local anaesthetic injected adjacent to the quadratus lumborum muscle will spread in a medial and cranial direction, under the crura and arcuate ligaments of the diaphragm, into the thoracic paravertebral space [3]. Local anaesthetic might also track medially and caudally along the psoas major muscle to involve the major branches of the lumbar plexus [4]. It is unclear if one pattern of spread predominates over the other with the quadratus lumborum block and, if so, which one. We, therefore, 2016 The Association of Anaesthetists of Great Britain and Ireland 73

2 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block undertook a cadaveric study of the ultrasound-guided transmuscular (anterior) quadratus lumborum block to determine the extent of injectate spread and peripheral nerve involvement using both radiographic imaging and anatomic dissection. Methods The Institutional Review Board of Ethics of Penn State Hershey College of Medicine, Pennsylvania, USA approved the study for exemption from formal review. The study was conducted on six fresh human cadavers in the Multidisciplinary Laboratory of Penn State College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA. Bilateral ultrasound-guided transmuscular (anterior) quadratus lumborum block was performed on each cadaver using a SonoSite M-Turbo TM (SonoSite, Inc., Bothell, WA, USA) ultrasound machine and a curved 2 5 MHz probe with a protective plastic sheath. All blocks were performed by one of two anaesthetists involved in the study (S.A and K.C). Each cadaver was placed in the lateral position. The transducer was placed in a transverse orientation on the flank just cranial to the iliac crest, then slid posteriorly to obtain an image of the quadratus lumborum muscle bordered by the lateral edge of the L3/L4 transverse process medially, psoas major muscle Figure 1 Ultrasound image of the transmuscular quadratus lumborum block. Arrow indicates needle trajectory and injection point between QLM (quadratus lumborum muscle) and PMM (psoas major) muscles. ESM, erector spinae muscle; L3 TP, L3 transverse process; IOM, internal oblique muscle. anteriorly and the erector spinae muscle posteriorly [5, 6] (Fig. 1). An 8-cm, 17-gauge Tuohy needle was then inserted in-plane with the ultrasound beam in a posterior-to-anterior direction through the quadratus lumborum muscle until the ventral fascia of the muscle was penetrated. At this point, 20 ml of an injectate mixture comprising 10 ml of an iodinated contrast material, iohexol (Omnipaque 300, GE Healthcare, Princeton, NJ, USA), diluted in 85 ml of sodium chloride 0.9% with 5 ml of methylene blue dye was deposited in the fascial plane between the quadratus lumborum and psoas major muscles. The same procedure was repeated on the contralateral side of each cadaver. Within 30 min of completing bilateral transmuscular quadratus lumborum blocks, the cadaver was transferred to a computed tomography (CT) scanner where pelvic, abdominal and thoracic imaging was performed in order to radiographically assess distribution of injectate. All CT studies were performed on 128 slice multidetector CT scanners (Siemens Flash CT; Siemens Healthcare, Malvern, PA, USA). Images were acquired using routine clinical imaging protocols from the skull base to the mid-lower leg with the following parameters: kvp 120, effective mas 210, rotation time 0.5 s, pitch 0.8 and detector collimation 1.2 mm. Images were reconstructed using a soft tissue algorithm with 3-mm slice thickness at 3-mm intervals. All images were reviewed by one radiologist (NS). Spread of injectate was assessed primarily upon review of the axial image set supplemented with multiplanar images. The superior extent of spread was correlated with the level of the thoracolumbar vertebra. The lateral extent was described according to the degree to which the injectate spread along the lateral abdominal musculature in the axial plane. The medial extent was described according to the proximity of the injectate to the paravertebral space as well as which muscles were coated with the injectate. The posterior extent of spread was described relative to the muscles and structures coated with the injectate. As the inferior extension of the injectate moved more anteriorly along the fascial planes, the caudal extent of the injectate spread was correlated to the nearest bony landmark of the pelvis rather than a corresponding vertebra The Association of Anaesthetists of Great Britain and Ireland

3 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block Anatomical dissection of the cadavers was subsequently performed by two anatomists (ZN and AN) with the body supine. An abdominal midline incision was made to the superficial fascia from the xiphoid process to the pubic symphysis. This was followed by bilateral transverse incisions from the xiphoid process to the midaxillary line and incisions from pubis to midaxillary line along the iliac crest. The resulting skin flaps were laterally reflected. Thereafter, the superficial fascia was removed to expose the abdominal wall muscles and their aponeuroses which were separated and individually viewed. A midline incision through the muscle layers was then made from xiphoid to pubic symphysis, followed by bilateral supraumbilical transverse incisions to the midaxillary line. The resulting muscle flaps were then reflected laterally to expose the abdominal cavity. The gastrointestinal tract was removed from the gastroesophageal junction to the rectum, and posterior abdominal viscera removed to expose the anterior aspect of the posterior abdominal wall muscles and associated nerves. Radiographic data were evaluated and documented by a radiologist (NS). The extent of methylene blue staining of muscles, nerves, fascial planes and tissues in each hemi-abdomen was photographed and documented by the anatomists (ZN and AN). All data collected were recorded in a standardised spreadsheet and analysed using Microsoft Excel 2016 (Microsoft Corp, Redmond, WA, USA). Results Sonographic landmarks were readily identified and bilateral transmuscular quadratus lumborum blocks performed in all six cadavers. Computed tomography imaging was not performed in two cadavers due to lack of scanner availability, yielding radiographic data from eight hemi-abdominal specimens. Anatomical dissection was performed on all cadavers, although the sixth cadaver exhibited significant decomposition at the time of dissection and it was not possible to accurately determine the extent of dye spread. Anatomical data on dye spread was therefore available for ten hemi-abdominal specimens. There was medial radiographic spread of the injectate involving the psoas muscle in all specimens. Contrast was seen to spread further medially to the lumbar paravertebral space in five (63%) specimens. Lateral spread reached the lateral border of the quadratus lumborum muscle in all cases, and further to the transversus abdominis muscle in 50% of specimens. The caudal spread reached the level of the L4 transverse process in all specimens, the anterior superior iliac spine in five (63%), and extended below the pelvic rim in two specimens. The cephalad extent of radiographic spread reached the L1 transverse process in all specimens, extending to the T12 transverse process in two (25%). There was no visible injectate spread beyond the diaphragm into the thoracic cavity in any specimen (Fig. 2). Methylene blue staining of the quadratus lumborum muscle was seen in all specimens and staining of the psoas major muscle was visible in seven (70%). In two, there was lateral spread to the transversalis fascia plane (deep to transversus abdominis muscle). There was staining of the ilioinguinal and iliohypogastric nerves where they emerged from the lateral edge of psoas major muscle in 100% and 80% of specimens, respectively, and staining of the subcostal nerve in 50% (Table 1; Fig. 3). The lateral femoral cutaneous nerve was stained 30% of the time but in no instance was staining of the femoral nerve observed. It was not possible to freely dissect the lumbar plexus from the psoas muscle to examine it for direct staining, nor was it possible to separate the transversus abdominis from the internal oblique muscle to confirm dye entry into the transversus abdominis plane in any specimen. Discussion To understand the anatomical basis for the quadratus lumborum block, an appreciation of the myofascial compartments of the posterior abdominal wall is necessary. The quadratus lumborum muscle is enclosed within the anterior and middle layers of the thoracolumbar fascia which is a continuous fascial system beginning at the occiput and terminating at the sacrum [7, 8]. The anterior layer of thoracolumbar fascia is contiguous with the investing fascia of the psoas muscle medially [8]. Laterally, this anterior layer of thoracolumbar fascia blends with the transversalis fascia that lines the deep or inner aspect of the entire abdominal wall and the two terms are often used interchangeably when describing the fascial layer that 2016 The Association of Anaesthetists of Great Britain and Ireland 75

4 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block (a) (b) (c) (d) Figure 2 Three-dimensional reconstructions of iodinated contrast injectate in a single cadaver showing spread cranially to T12, caudally to the level of the anterior superior iliac spine, and medially to the lumbar paravertebral area. (a) posterior; (b) right oblique; (c) anterior; and (d) left oblique. invests the anterior (ventral) surface of the quadratus lumborum muscle [8]. The transversalis fascia is also cranially contiguous with the endothoracic fascia and thus the plane between the quadratus lumborum muscle and the transversalis fascia can potentially permit spread from an injection point adjacent to the quadratus lumborum muscle towards both the lumbar and thoracic paravertebral spaces. This posterior and cranial spread to the thoracic paravertebral space has been proposed as the primary mechanism of action for both the quadratus lumborum block and landmarkguided transversus abdominis plane (TAP) block [3, 6, 9]. As the anterior cutaneous branches of the T7-T11 intercostal nerves only emerge into the TAP medial to the anterior axillary line, it is, therefore, unlikely that anterior spread of local anaesthetic within the TAP can account for the extensive anterior abdominal blockade reported with either the quadratus lumborum block or the landmark-guided TAP block [9, 10]. Multiple quadratus lumborum block approaches have been described [2]. The first approach described was derived from the landmark-guided TAP block once it was realised that the Triangle of Petit overlies the zone where the internal oblique and transversus abdominis muscles taper off into an aponeurosis to abut the quadratus lumborum muscle. In fact, this lateral ( QL1 ) approach to the quadratus lumborum block was initially termed a posterior ultrasound-guided TAP block [3, 12], although the injection is not made into the TAP, but into the transversalis fascia plane at the confluence of the quadratus lumborum muscle and terminal aponeurosis of the internal oblique and transversus abdominis muscles. The needle is advanced in an anterior-to-posterior direction and injectate spread occurs over the anterior aspect of the quadratus lumborum muscle. Successful abdominal analgesia has been reported with the lateral (QL1) approach in several case reports [13 16]. Børglum et al. [6] The Association of Anaesthetists of Great Britain and Ireland

5 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block Table 1 Dye staining of nerves, intermuscular fascial planes and muscles. Values are number and proportion. Structure Number of specimens demonstrating dye staining Frequency of dye staining Subcostal (T12) nerve 5 50% Iliohypogastric nerve 8 80% Ilioinguinal nerve % Genitofemoral nerve 2 20% Lateral femoral 3 30% cutaneous nerve EO-IO plane 0 0 IO-TA plane 0 0 TF Plane 2 20% QLM % PMM 7 70% EO, external oblique muscle; IO, internal oblique muscle; TA, transversus abdominis muscle; TF, transversalis fascia; QLM, quadratus lumborum muscle; PMM, psoas major muscle. Figure 3 Right side cadaveric dissection of stained muscles and nerves following transmuscular quadratus lumborum block. Findings demonstrate a stained quadratus lumborum muscle, as well as stained subcostal, iliohypogastric and ilioinguinal nerves. The lateral femoral cutaneous nerve, genitofemoral nerve and psoas major muscle remain unstained. subsequently described the transmuscular quadratus lumborum approach, also called an anterior QL block, in which the plane between quadratus lumborum muscle and transversalis fascia is reached by advancing the needle in a posterior-to-anterior direction through the quadratus lumborum muscle. Again, its efficacy is supported in a case report [17]. Finally, Blanco and McDonnell [9] have recommended a modification of the lateral (QL1) approach (the posterior quadratus lumborum block - which they termed the QL2 quadratus lumborum block, a posterior QL block) in which an injection is made on the posterior (dorsal) aspect of the quadratus lumborum muscle instead of on the ventral aspect. They regard this as safer to perform (Fig. 4). Alternative approaches have and will continue to be suggested [18]; each of which will require further study to determine their merit. The implication of our findings is that, anatomically, the quadratus lumborum block could provide analgesia of the inguinal and hip region and is similar to a lumbar plexus block in this respect. The ilioinguinal and iliohypogastric nerves emerge from the psoas major muscle onto the ventral surface of the quadratus lumborum muscle which is where the majority of these nerves were stained. The lateral femoral cutaneous, obturator and femoral nerves emerge from the lateral aspect of psoas major at a more caudal location. This may explain why they were less consistently stained. The genitofemoral nerve emerges medially and caudally from the psoas major muscle and was, thus, unstained in the majority of specimens. The transmuscular quadratus lumborum approach is, in fact, almost identical to the ultrasoundguided lumbar plexus block approaches described by Sauter et al. [5] and Kirchmair et al. [19]; the main difference being that, in the latter blocks, the needle is advanced beyond the tissue plane between the quadratus lumborum and psoas major muscles to contact the lumbar plexus branches where they pass through psoas major. Although we did not study the other quadratus lumborum block approaches, there is evidence that they may also produce a lumbar plexus block. A small volunteer study of lateral (QL1) quadratus lumborum blocks [3] reported that although there was MRI evidence of thoracic paravertebral spread up to T4, the extent of cutaneous sensory block was quite variable, and only consistently involved the area of injection, groin and upper lateral thigh. This suggests a predominant clinical effect from block of the subcostal, ilioinguinal, iliohypogastric and lateral femoral cutaneous 2016 The Association of Anaesthetists of Great Britain and Ireland 77

6 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block Figure 4 Diagrammatic representation of the key fascial layers of the posterior abdominal wall (left) and the three approaches to the quadratus lumborum block (right). LD, latissimus dorsi; TLF, thoracolumbar fascia; QL, quadratus lumborum. nerves. This pattern of block is further supported by a randomised, controlled trial which compared the lateral (QL1) quadratus lumborum block with femoral nerve block in patients with hip fracture undergoing bipolar hemi-arthroplasty. The authors found both lower pain scores and opioid consumption in patients who received the quadratus lumborum block [4]. Blanco et al. [20] have also recently reported that the posterior (QL2) quadratus lumborum block reduces pain scores and opioid consumption in patients undergoing lower segment caesarean section under spinal anaesthesia with multimodal analgesia (but no intrathecal morphine). Their findings are consistent with somatic analgesia of the surgical site in the T12- L1 dermatomes. Finally, it should be noted that leg weakness has been reported with the transversalis fascia plane block [21], which is very similar to the lateral quadratus lumborum block [22, 23]. This further reinforces the possibility that the branches of the lumbar plexus may be involved by local anaesthetic tracking between the quadratus lumborum muscle and transversalis fascia. The absence of thoracic paravertebral spread in this study does not necessarily rule this out as a mechanism of action in quadratus lumborum block. Case reports and cadaveric studies indicate that fluid can track caudally from the thoracic paravertebral space under the arcuate ligaments of the diaphragm and into the lumbar paravertebral space [24 26]. This is due to the continuity of the endothoracic fascia with the transversalis fascia. It is not clear, however, if there would be preferential spread cranially into the thoracic paravertebral space or medially into the psoas compartment when fluid is injected adjacent to the quadratus lumborum muscle. Nevertheless, a recent study of the posterior (QL2) block approach in laparoscopic ovarian surgery found that all patients had sensory loss between T8 and L1 and more than half had a block up to T7 [11]. These data, together with MRI findings demonstrating contrast spread into the thoracic paravertebral area with lateral (QL1) quadratus lumborum blocks and landmark-guided TAP blocks [3] suggests that injectate spread may be more dynamic and extensive in living subjects than in cadavers. In summary, this first cadaveric study of the transmuscular quadratus lumborum block demonstrates that injectate spreads over the posterior abdominal wall to the psoas major muscle and includes the upper branches of the lumbar plexus. In the light of our findings and those of published clinical trials [4], the quadratus lumborum block may be an acceptable alternative to lumbar plexus block for peri-operative analgesia in surgery involving the hip and inguinal region. The early evidence is also promising for provision of The Association of Anaesthetists of Great Britain and Ireland

7 Adhikary et al. Cadaveric study of the transmuscular quadratus lumborum block more extensive abdominal analgesia [11, 13 16]. Although we did not find direct evidence for this in our cadaveric study, injectate spread may be different in live subjects, and thus research into the value of this technique in abdominal surgery should continue. In addition, we recommend that patients receiving a quadratus lumborum block should be closely evaluated for leg weakness in order to minimise the risk of falls. Acknowledgements We thank Dr Patrick McQuillan, MD, for editorial assistance with the manuscript. Competing interests No external funding or competing interests declared. References 1. Elsharkawy H. Ultrasound-Guided Quadratus Lumborum Block: How Do I Do It? ASRA News 2015; 15: El-Boghdadly K, Elsharkawy H, Short A, Chin KJ. Quadratus lumborum block nomenclature and anatomical considerations. 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