Nerve Blocks

32 Nerve Blocks

Steven Gabel

Summary

Local anesthesia can be done by field blocks, ring blocks, or localized nerve blocks. Nerve blocks can be used alone or in combination with other forms of anesthesia. Benefits of nerve blocks are the following: longer-lasting anesthesia; more effective anesthesia when field or ring blocks fail; less volume of local anesthesia needed, making procedure safer; and less of a painful anesthetic experience. Not all areas lend themselves to easy nerve blocks. The area being treated must be within a zone fed by a specific nerve. One must have an understanding of sensory enervation and anatomy of different nerves. Care must be taken not to damage the nerve with intraneural injection. In hair transplantation, supraorbital and trochlear nerve blocks for the frontal part of the scalp are common and consistently effective. Occipital nerve blocks for anesthetizing the occipital scalp can be used but are not consistent and therefore used less frequently. For transplants of beard and mustaches, some use submental nerve blocks, but it has to be used in combination with ring or field blocks because it does not usually cover the entire area being transplanted.

Keywords: supraorbital nerve block supraorbital nerve supratrochlear nerve supraorbital notch supraorbital foramen anatomy anesthesia pain

Key Points

•Nerve blocks can be useful by increasing the level of anesthesia, prolonging the time anesthesia, and decreasing the volume of anesthesia.

•Nerve block can be useful in the frontal are for patients who seem resistant to standard ring blocks.

•Supraorbital nerve blocks for the frontal recipient area are the most common nerve blocks used in hair transplantation.

•The supraorbital nerve block can be done by both a direct and a superior approach.

32.1 Introduction

The supraorbital nerve block is a relatively easy technique to perform and reduces the overall pain of anesthetic injections into the scalp for the hair restoration patient. Since the patient is awake throughout the entire procedure, it is incumbent upon the physician to use methods that that can minimize their discomfort and control their pain. Although most hair restoration cases utilize a ring blockade of local anesthetic adjacent to the frontal hairline, studies have shown that by employing supraorbital nerve blocks, patients have significantly less pain associated with the procedure, resulting in a better experience and less anxiety if a second procedure is required.1

32.2 Anatomy of the Supraorbital Nerve

A complete understanding of the anatomy of the supraorbital region and distribution of the supraorbital nerve is critical in successfully blocking the nerve and achieving satisfactory anesthesia. The supraorbital nerve is the primary cutaneous nerve innervating the forehead and the frontal half of the scalp. The supraorbital and supratrochlear nerves are branches of the frontal nerve, which originate from the ophthalmic division of the trigeminal nerve.² The supraorbital nerve, which is the larger of the two, exits the frontal bone between the medial one-third and the lateral two-thirds of the supraorbital rim. The supraorbital vessels accompany the nerve. The morphology of the supraorbital region has been critically investigated to understand the relationship between the supraorbital nerve and how it exits the frontal bone. In one study of 83 adult skulls, a supraorbital notch (SON), which measures on average of 5.1 to 5.5 mm in transverse diameter, was observed more frequently (68.87%) than a supraorbital foramen (SOF) (28.91%). Studies have also shown that a SON is converted into a SOF in approximately 25% of cases secondary to ossification of the periosteal ligaments bridging the gap. Additionally, accessory SOF were observed in 66.25% of specimens studied, and these were found both medial and lateral to the SON/SOF.³ In some cases, the foramen was located 15 mm above the supraorbital margin of the frontal bone.⁴

The distance between the midline of the forehead and the SON/SOF is quite variable and studies have shown a range between 22 and 32.02 mm.⁴^,⁵ This distance also varies between ethnic groups and in a study of South Indian skulls, the mean distance between the SOF and the midline was 30.18 mm on the right and 29.51 mm on the left.⁶ In a study of 110 Asian skulls, the distance between the SOF and the midline was 23.9 and 24.6 mm on the right and 24.2 and 25.6 mm on the left in men and women, respectively.⁷ The Korean population demonstrated a much longer distance of 29 mm between the midline of the forehead and the SOF.⁸ The clinical significance of these observations aids the surgeon in identifying the exact location of the supraorbital nerve complex, and it is important to understand the significant variability of the location where the supraorbital nerve and accessory branches exit the frontal bone.

As the supraorbital nerve exits the skull through a SON/SOF, it is deep to the periorbital and frontalis muscles. It divides into superficial (medial) and deep (lateral) branches (Fig. 32.1). The superficial branch of the supraorbital nerve pierces the frontalis muscle, fans out over the anterior surface of the forehead, and innervates the frontal scalp.⁹ Nerve block studies specifically targeting the superficial branch demonstrated anesthesia of the forehead into the frontal hairline and scalp. The deep division of the supraorbital nerve ascends laterally between the galea and the periosteum toward the temporal fusion line. Once it reaches the level of the coronal suture line, it divides into smaller branches penetrating the galea to enter the frontoparietal scalp with its terminal branches. Selective nerve block studies of the lateral division of the supraorbital nerve demonstrated frontoparietal anesthesia from approximately the posterior portion of the frontal scalp (behind the hairline) to the lambdoid suture on the ipsilateral side of the block. Combined, the medial and lateral divisions of the supraorbital nerve innervate the scalp from the midline of the forehead medially to the temporal fusion line laterally and posteriorly to the vertex of the scalp (Fig. 32.2). Understanding the anatomical relationship of the supraorbital nerve is crucial as one must anesthetize both the superficial and deep branches for complete blockage of the nerve.

Fig. 32.1 The supraorbital nerve exits the frontal bone via a supraorbital notch or supraorbital foramen (red arrow) and divides into the superficial (medial) division and deep (lateral) division (*). The supratrochlear nerve exits the frontal bone approximately 1 cm medial to the supraorbital nerve (blue arrow).

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