The Anatomical Foundations of Regional Anesthesia and Acute Pain Medicine Macroanatomy Microanatomy Sonoanatomy Functional anatomy

In this chapter, the authors present the most common arrangement of the brachial plexus; its five roots of origin, three trunks, anterior and posterior divisions, three cords, and, finally, its terminal branches. The sensory dermatomal and osteotomal innervation of the spinal roots are discussed, as well as the neurotomal distribution of each peripheral terminal branch. Anatomical dissections of the lateral view of the neck and its posterior triangle are presented, as well as trans-sectional anatomical views at the level of the 6th cervical vertebra. Photographs of anatomical dissections of the five scalene muscles are discussed, especially the crossover of the fibers of the anterior and middle scalene muscles, which forms the paravertebral trough, and the seven most commonly found positional anomalies of the muscles with the roots of the cervical ventral rami. Finally, multiple anatomic sagittal sections of the neck, starting from the spine and ending at the mid-clavicular line, show the supraclavicular brachial plexus. These multiple sections are presented in the form of three figures of strategic positions, and also as a movie where these multiple sections have been added together to play sequentially. The authors discuss the innervation of the five joints around the shoulder girdle in some detail in this chapter.

The aims of this chapter are to explain and present the older and new concepts and understanding around the microanatomy of nerve roots, trunks, and peripheral nerves. More recent work over the past 3 or 4 years looked at nerves with high-definition ultrasound and electron microscopy and illustrated that the paraneural or circumneural sheath is what neurosurgeons for years have been calling the “gliding apparatus” of the nerve. The space just deep to this layer is the subcircumneural (subparaneural) space, which should most probably be the target space for successful and safe single-injection block and catheter placement for continuous nerve block. The different microanatomical features of spinal roots, plexus trunks, and peripheral nerves are discussed and compared, as well as the microanatomical explanation of the different sonographical appearance of these three types of nerves.

With this chapter, the authors discuss the sonoanatomy of the posterior triangle of the neck. The basic sonoanatomy is approached from two angles, the first from a static ultrasound point of view to give the reader the opportunity to study the different structures in detail. Secondly, a video production has been produced to explain the dynamic ultrasound of this area. In both instances, the ultrasound transducer probe is placed so that the initial view is that of a known structure. In the anterolateral approach, the probe is placed on the cricoid cartilage and moved posterior to bring the thyroid gland into view; slightly more posterolateral, the common carotid artery comes into view, followed by the large anterior tubercle of the transverse process of the 6th cervical vertebra. From this known position, the probe is moved cephalad and caudad to identify the other structures of the cervical vertebrae and brachial plexus. In the lateral approach, the probe is placed in the supraclavicular area where the subclavian artery and vein are clearly visible, and from there, the trunks of the brachial plexus are followed cephalad to view the transverse processes of the vertebrae and the spinal nerve roots and trunks as they exit the neuroforamens and form the trunks. The sonoanatomy of the supraclavicular fossa is discussed in detail.

In this chapter, the authors discuss the macro- and microanatomy of the brachial plexus cords below the clavicle. The area below the clavicle is defined, for the purposes of this discussion, as the area from just below the clavicle - the proximal infraclavicular area, to the lateral border of the major pectoral muscle and the deltopectoral groove – the distal infraclavicular area. In the proximal infraclavicular area, the three cords are situated lateral to the axillary artery and vein and all three cords are in a communal circumneural (paraneural) sheath. As the cords track more distally, they spread out around the artery so that the three cords are apart and each is in its own circumneural sheath. The lateral cord is now anterolateral, the medial cord is anteromedial, and the posterior cord is posterior to the axillary artery.

The area below the clavicle is where an infraclavicular block is typically performed. Although a very popular and useful approach for single injection nerve blocks for regional anesthesia, infraclavicular blocks have been met with disappointment as far as continuous nerve blocks are concerned. The most likely reason is probably because infraclavicular blocks are usually performed in the area of the deltopectoral groove, where the three cords are arranged around the axillary artery and are relatively far apart. A better option for continuous nerve block catheter placement would probably be more proximal, directly under the clavicle, where all three the cords are together just after crossing the first rib with the vein most medial, the artery more lateral, and the bundle of brachial plexus cords most lateral (very similar to the femoral nerve). This chapter outlines these differences ultrasonographically. The ultrasoundassisted approach to the lateral and medial pectoral nerves, the so-called “PEC 1” block,” is also discussed. The proximal and distal infraclavicular nerves, as well as the pectoralis approach to the lateral and medial pectoral muscles, are discussed in this chapter with the help static images and video productions.

Counting the axillary nerve, which is not truly in the axilla, there are seven peripheral nerves in the axilla that arise from the brachial plexus. These are the medial cutaneous nerves to the arm and the forearm, the ulnar nerve, which arises from the medial cord, the median nerve, which comes from the medial and lateral cords, the radial nerve, which arises from the posterior cord, and the musculocutaneous nerve, which originates from the lateral cord. These nerves and their areas of sensory distributions are discussed in this chapter. The intercostobrachial nerve, which does not originate from the brachial plexus, arises from the first and second thoracic spinal root and innervates the skin in the medial upper arm and axilla. The motor functions of these nerves are discussed in Chapter 9.

In this chapter, the author combines the established views of the microstructure of the ulnar nerve as an example of a singe peripheral nerve, with some newer concepts that have emerged only recently. The position and importance of the circumneural (paraneural) sheath and subcircumneural (subparaneural) space are discussed, as well as the other membranes and compartments surrounding this peripheral nerve, namely, the endoneurium, perineurium, epineurium, and epimysium. The subepimyseal space is discussed in the context of peripheral nerve block.

Ultrasound is a dynamic process whereby structures can and should be followed to their origins and destinations for optimal identification. Because of this, it is not always satisfactory to study static ultrasound images. When studying sonoanatomy, the authors strongly advise readers to first study the macro- and microanatomy and then to view the accompanying video production that illustrates the dynamic sonoanatomy (Movie 1). In this chapter, the authors explain the static sonoanatomy of the axilla and the rest of the arm, and with the aid of a video production, the dynamic sonoanatomy of these structures and areas.

All or most of the nerves of interest to regional anesthesiologists or acute pain physicians are mixed nerves with autonomic, sensory, motor, and proprioception functions. Each function is conducted by a specific type of nerve axon. We have provided an overview of these axons and their functions in Chapter 2 (Table 1 of Chapter 2). For the purposes of this chapter, the authors focus on the sensory and motor functions of each of the nerves. To create the video productions that accompany this chapter, Mary Bryson painted the muscles and nerves on a model and we used percutaneous nerve mapping as described by Bösenberg and his colleagues to illustrate the motor function of each nerve (Movies 1 to 11). With the aid of a peripheral nerve stimulator, the path of many superficial peripheral nerves can be “mapped” prior to skin penetration by stimulating the motor component of the peripheral nerve percutaneously with 1.5- to 2.5-mA current output.

There are four areas of interest to the regional anesthesiologist and acute pain physician in the anterior thigh. These include three nerves and their branches and one specific area. These nerves are the femoral nerve with its seven branches, the obturator nerve with its two branches, and the lateral cutaneous nerve of the thigh. The adductor canal is the anatomical area of interest, as an adductor canal block, although much debated and its true value questioned, has been popularized in recent years. These nerves and their areas of sensory distributions and the adductor canal are discussed in this chapter. A fourth nerve, the genitofemoral nerve, and more specifically, its femoral branch, also features in this area and is discussed in this chapter.

In this chapter, the author combines the established views of the microstructure of the femoral nerve as an example of a combined peripheral nerve or bundle of nerves with newer concepts that have emerged only recently. The position and importance of the circumneural (paraneural) sheath and subcircumneural (subparaneural) space are discussed, as well as the other membranes and compartments around a peripheral nerve, namely, the endoneurium, perineurium, epineurium, and epimysium. The subepimyseal space is discussed in the context of peripheral nerve block.

Ultrasound is a dynamic procedure whereby structures can and should be followed to their origins and destinations for optimal identification. Because of this, it is not always satisfactory to study static ultrasound images. When studying sonoanatomy, the authors strongly advise readers to first study the macro- and microanatomy and then to view the accompanying video productions that illustrates the dynamic sonoanatomy (Movies 1-4). In this chapter, the authors explain the static sonoanatomy of the femoral and obturator nerves and that of the lateral cutaneous nerve of the thigh and the adductor canal, and with the aid of video productions, the dynamic sonoanatomy of these structures and areas.

There are five areas of interest to the regional anesthesiologist and acute pain physician concerning where the sciatic nerve can be approached. These include the parasacral, the transgluteal, the subgluteal, the mid-femoral, and the popliteal areas. These areas and the relationships of the sciatic nerve to other structures in those specific areas, as well as the areas of sensory distributions of the sciatic nerve and its branches are discussed in this chapter. Other nerves, not part of the sciatic nerve but originating from the sacral plexus, such as the posterior cutaneous nerve of the thigh and the pudendal nerve, are also discussed in this chapter.

In this chapter, the author combines the established views of the ultrastructure of the sciatic nerve as an example of a combined peripheral nerve or bundle of nerves with newer concepts that have emerged only recently. The position and importance of the circumneural (paraneural) sheath and subcircumneural or subparaneural space are discussed, as well as the other membranes and compartments around a peripheral nerve, namely, the endoneurium, perineurium, epineurium, and epimysium. The subepimyseal space is discussed in the context of peripheral nerve block.

Ultrasound is a dynamic process whereby structures can and should be followed to their origins and destinations for optimal identification. Because of this, it is not always satisfactory to study static ultrasound images. When studying sonoanatomy, the authors strongly advise readers to first study the macro- and microanatomy and then to view the accompanying video productions that illustrates the dynamic sonoanatomy (Movies 1-3). In this chapter, the authors explain the static sonoanatomy of the sciatic nerve at the parasacral, the subgluteal, mid-femoral and the popliteal areas, and with the aid of a video production, the dynamic sonoanatomy of these structures and areas.

To ensure a successful ankle block, it is important to realize that there are two nerves that are deep to the fascia layer and three nerves that are superficial to it. An electrical current can readily cross fascia layers, but local anesthetics cannot, therefore, it is important to deposit the local anesthetic on the correct side of the fascia. The deep nerves are the posterior tibial and deep peroneal nerves. The superficial nerves are the sural, saphenous, and superficial peroneal nerves. If the name of the nerve starts with an “s,” it lies superficial to the fascia. The macroanatomy, which includes the trans-sectional anatomy and surface anatomy, and the sonoanatomy of all the nerves around the ankle are discussed in this chapter, as well as the sensory areas that these nerve innervate and the innervation of the ankle joint.

All or most of the nerves of interest to regional anesthesiologists or acute pain physicians are mixed nerves with autonomic, sensory, motor, and proprioception functions. Each function is conducted by a specific type of nerve axon. We provided an overview of these axons and their functions in Chapter 2 (Table 1 of Chapter 2). For the purposes of this chapter, the authors focus on the sensory and motor function of each of the nerves. To create the video productions that accompany this chapter, Mary Bryson painted the muscles and nerves on a model and we used percutaneous nerve mapping as described by Bösenberg and his colleagues to illustrate the motor function of each nerve (Movies 1 to 6). With the aid of a peripheral nerve stimulator, the path of many superficial peripheral nerves can be “mapped” prior to skin penetration by stimulating the motor component of the peripheral nerve percutaneously with 1.5- to 2.5-mA current output.

From superficial to deep, the external oblique, internal oblique, and transversus abdominis muscles anterolaterally and the rectus abdominis muscles medially form the abdominal wall. Deep to these muscles, the transversalis fascia separates the abdominal visceral contents from the muscles that form the abdominal wall. The nerves that innervate the abdominal wall musculature and supply sensory innervation to its overlying skin and peritoneum are derived from the ventral rami of the intercostal nerves from the 6th to 12th thoracic spinal nerves (T6 to T12) and the 1st lumbar spinal root (L1). The anterior and lateral cutaneous branches of the ventral rami of the intercostal nerves travel in the plane between the internal oblique muscle and the transversus abdominis muscle (known as the TA plane - TAP). There is a thin fascial sheet between the internal oblique muscle and transversus abdominis muscle in which the nerves lay between the fascia and the transversus abdominis muscle. The cutaneous branches of the T6 to T12 nerves branch and communicate with adjacent nerves within the TA plane, forming an extensive network that results in three plexuses: the intercostal plexus anterolaterally, the TAP plexus running with the deep circumflex iliac artery, and the rectus sheath plexus running with the deep inferior epigastric artery. The macroanatomy and sonoanatomy (static and dynamic) of these muscles and nerves are discussed in this chapter.

The thoracic paravertebral space (TPVS) is a wedge-shaped space of which the anterior boundary is the parietal pleura of the lung. The superior costotransverse ligament (SCTL) and the internal intercostal membrane (IIM) form the posterior boundary, while the posterolateral aspect of the vertebra, the intervertebral disc, and the intervertebral foramen form the medial border. Superior and inferior the boundaries are the heads and necks of the ribs. The TPVS contains spinal nerve roots, the posterior rami of the thoracic nerves, the anterior rami, which comprises the intercostal nerves, the gray and white rami communicantes to the sympathetic chain and the sympathetic chain itself, the spinal rami from the aorta, and an intervertebral veins that form a vascular plexus. The TPVS communicates superiorly and inferiorly with the adjacent TPVS above and below, medially with the spinal epidural space, and laterally with the intercostal space. The macro- and microanatomy and sonoanatomy (static and dynamic) of these spaces and its nerve roots and relationships to other structures are discussed in this chapter.

The positioning of the lumbar plexus within the psoas muscle is somewhat controversial. Winnie, for example, described the plexus as lying between the psoas and quadratus lumborum muscles. From this description, “psoas compartment block” was termed for the lumbar plexus block. Other names for the same thing are “lumbar plexus block”, “lumbar paravertebral block”, “quadratus lumborum block” and “fascia iliaca block” to name a few. Most authors described the plexus and its nerve branches within the psoas muscle between its anterior and posterior masses. The ventral rami of the first three and the major part of the fourth lumbar spinal roots (L2, L3, and L4) form the lumbar plexus. A contribution from the 1st lumbar nerve (L1) is common. As soon as the ventral rami of these spinal nerve roots exit the intervertebral foramina, they become embedded in the psoas muscle, anterior to the transverse processes. At the L4 to L5 level, however, the lumbar plexus branches are still medial and close to the transverse processes. The distance of the lumbar plexus to the skin varies with body habitus and gender. Capdevila and his colleagues described the distances as varying from 57 to 93 mm in women and from 61 to 101 mm in men.

The macro-, microanatomy, and sonoanatomy (static) of the lumbar plexus, its nerve roots, and relationships to other structures are discussed in this chapter.

The spinal column has 33 vertebrae: seven cervical, twelve thoracic, five lumbar, five sacral (fused), and four coccygeal. There are four curves in the spinal column: the cervical and lumbar curve convex anteriorly, whereas the thoracic and sacral curves convex posteriorly. The macro-, microanatomy, and sonoanatomy (static) of neuraxium, its content and relationships to other structures are discussed in this chapter. Special attention is given to the ligaments of the spine, and the ligamentum flavum in particular, paying special attention to the shapes that the spinal canal takes in certain regions, and the structure and consistency of the ligamentum flavum. Two further questions are specifically addressed in detail in this chapter. The first questions are why an epidural block is “segmental” and does not, like subarachnoid anesthesia, block the entire spinal cord distal to the site of injection. The second question answered in this chapter is why elderly people are less prone than their younger counterparts to developing postdural puncture headache following accidental dural puncture during attempted epidural block. Both of these questions are comprehensively addressed in this chapter on microanatomical grounds.

The abdominal and pelvic sympathetic nervous system mediates visceral sensation and vasomotor tone to the abdominal organs and vessels, as well as sudomotor, vasomotor, and pilomotor function of the lower extremities. Pain sensation that is sympathetically maintained or mediated can be treated by a targeted block of the abdominal sympathetic ganglia or plexuses. A comprehensive understanding of the relevant physical anatomy and fluoroscopic or sonographic anatomy is a prerequisite for safely and effectively performing a sympathetic blockade.

The trigeminal ganglion gives off three branches. One of them is the ophthalmic nerve, which again splits into three branches: the lacrimal, the frontal, and the nasociliary nerves. The other two branches are the maxillary and mandibular nerves. In this chapter the authors discuss all the branches of these nerves as well as the nerves of the cervical plexus. The innervation of the skin of the head, the eye, nose, mouth, teeth, tongue, ear and larynx are discussed in detail. Finally the authors outline the sonoanatomy of infraorbital and greater occipital nerves, the superficial cervical plexus and that of the eye and orbit.