Technique of Radiofrequency Denervation

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CHAPTER 24 Technique of Radiofrequency Denervation

Sara Haspeslagh, Maarten Van Kleef

INTRODUCTION

History

The use of electrical current to create lesions for the treatment of pain began in 1931, when Kirschner introduced it for the treatment of trigeminal neuralgia.¹ In 1965, Mullan used direct current to perform percutaneous lateral cordotomy for unilateral malignant pain.² Later that year, Rosomoff modified this technique and used radiofrequency (RF) current for this treatment.³ An RF current was found to produce more predictable, circumscribing lesions. Several years later, Sweet and Wepsic described their technique for the use of RF lesions of the Gasserian ganglion in the treatment of trigeminal neuralgia.⁴ In spinal pain, the use of RF current was reported in a series of cases by Shealy (1975).⁵ He described RF lesioning of the medial branch to treat lumbar facet joint pain. Subsequently, more options for the use of RF lesioning in various spinal pain syndromes were introduced into clinical practice.⁶^–⁸ The introduction of a small-diameter (22-gauge) temperature monitoring electrode system by Sluijter and Mehta in 1981⁹ increased the safety of the current method used.¹⁰ Since then, RF procedures have been widely adopted by many pain practitioners. In addition there have been many new technical developments, such as the improvement of the quality of C-arm image intensifiers. All these developments have contributed to a widespread use of RF lesioning.

Recently, a modification of the traditional RF method was introduced by Sluijter et al.¹¹ They used the same output setting of the lesion generator that was used for making heat lesions as in RF lesioning, but they interrupted this output to allow generated heat to be washed out by thermal conductivity and circulation. This technique is called ‘pulsed radiofrequency’ (PRF) and is claimed to be nondestructive. Until now, there are no reports of any sensory or motor loss following this procedure. However, it is too soon to categorically recommend this technique because the mechanism of action is still unknown. Until several double-blind, randomized, controlled trials are conducted this new approach should not be routinely employed.

Physics

Radiofrequency current

An RF current is applied by an RF lesion generator through an electrode, which is insulated except for the most distal part. This exposed region is the active portion of the electrode. The RF current flows from the electrode tip to the dispersive ground plate, which is placed on the arm or leg of the patient and leads the current back to the RF lesion generator. RF current flows through tissue and results in an electric field. This electric field places an electric force on the ions within tissue electrolytes, causing them to oscillate at a high rate (i.e. 300 000 times per second).¹² Tissue heating is created by frictional dissipation of the ionic current within the fluid medium, which heats the electrode.

Lesion size

The size of the lesion not only depends on the diameter of electrode and the length of the uninsulated electrode tip, but also depends on tip temperature. This was confirmed in animal studies by Cosman et al. in 1984.¹³ Bogduk et al. studied not only the size of the lesions, but also the shape of the lesion.¹⁴ They performed experimental lesions in egg white and fresh meat. They found that RF lesions do not extend distal to the tip of the electrode, but extend radially around the active electrode tip in a spheroidal shape. Based on these observations, Bogduk suggested that the best placement of the electrode tip was parallel to the target structure.

Other research methods involving computerized or mathematical modeling of similar experiments have been used. For example, Moringlane et al. studied experimental RF coagulation with a computer-based on-line monitoring of temperature and power.¹⁵ Vinas et al. also studied lesion size in vivo using fresh eggs and in vitro using the subcortical white matter of rabbits.¹⁶ Both investigators obtained results that were similar to those reported by Bogduk et al. Once equilibrium temperature is reached (after 20–40 seconds), the size of the lesion does not increase. However, some variables such as circulation effect and the tissue heat conductivity may also produce a variation in lesion size, but are unpredictable.¹³ Consequently, the lesion size may therefore be variable at different locations within the body.

Radiofrequency lesion generator

The modern RF lesion generating system has different functions, including a pulsed RF mode. There is continuous on-line impedance measurement to confirm continuity of the electrical circuit and to detect any short circuits. One of the key components of the system is nerve stimulator function. It is used to confirm the proper position of electrode tip (it indicates the electrode-to-nerve distance) and to permit minor adjustments. To ensure the proximity of the active tip to the sensory fibers, stimulation is performed at 50 Hz. The 2 Hz stimulation is carried out to detect extraspinal muscle contractions that occur when the needle is placed too close to a nerve root motor fiber. Voltage, current, and wattage during an RF procedure are also monitored. Finally, a generator monitors temperature using a thermocouple. This is an important lesion parameter, but the temperature is only measured at the tip of the electrode and not in the more peripheral zones of the lesion area. The usefulness of tip temperature to monitor the lesion size is minimized because the lesion size is dependent on local blood circulation. There is a rapid drop in temperature over the first few millimeters from the electrode tip.^13,¹⁷

Effect of radiofrequency current on nerve tissue

The effect of RF lesions on nerve tissue is controversial. Letcher and Goldring, in 1968, investigated the effect of RF current and heat on the nerve action potential of the saphenous nerve in cats.¹⁸ Delta and C-fibers were blocked before the alpha-beta group by both RF current and heat. Uematsu,¹⁹ and subsequently Smith et al.,²⁰ reported quite disparate results. Smith et al. created RF lesions of different temperatures by placing an electrode into the lumbar intervertebral foramina of dogs.²⁰ Indiscriminate damage of both small and large fibers by RF current was observed. Uematsu conducted a histological analysis of feline sciatic nerves that sustained RF thermocoagulation.¹⁹ These studies have been criticized because large, 14-gauge electrodes were used; in addition, they were placed close to the dorsal root ganglion during open surgery. However, these methods are not comparable to the technique which is commonly used in clinical practice today, since 22-gauge needles where not available at that time.²¹ In response to this critique, de Louw et al., in 2001, tried to investigate morphological effects of RF lesions as they develop in normal clinical situations.²¹ A percutaneous RF lesion adjacent to the dorsal root ganglion (DRG) of goats was created with a 22-gauge electrode at a tip temperature of 67°C. Immunocytochemical changes indicative of proliferation and regeneration was observed 2 weeks after the RF lesion was created. These alterations occurred outside the DRG, without interfering with the function of large myelinated fibers.

Effect of pulsed radiofrequency current on nerve tissue

Recently, the importance of heat as the definitive mechanism of action RF lesioning has been questioned.¹¹ In 1998, Sluijter et al. investigated isothermic RF lesioning also termed pulsed RF (PRF) treatment.¹¹ Ostensibly, PRF generates its therapeutic effects independent of thermal factors. The pulses are given at a rate of 2 Hz and last 20 msec. The rest period is 480 msec, and this allows the generated heat to be washed out by thermal conductivity and circulation.

The mechanism by which pulsed RF treatment effects symptom relief remains unknown. In 2002, Higuchi et al. undertook a study to elucidate this mechanism. They attempted to identify spinal cord neuron activation following the exposure of the dorsal ganglion of rats to PRF currents.²² A significant increase in the number of cFos-immunoreactive neurons in the superficial laminae of the dorsal horn was observed. This finding indicates that PRF current activates pain-processing neurons in the dorsal horn and that this effect is not mediated by tissue heating.

This technique is considered to be a safer method of treatment because until now the observations showed no signs of neurodestruction and thus neurological side effects.^11,²³ Cahana et al., in 2003, compared the acute effects of pulsed versus continuous RF energy on impulse propagation and synaptic transmission in hippocampal slice cultures and on cell survival in cortical cultures of rats.²⁴ In both systems, they found an induction of distance-dependent tissue destruction under the stimulating needle (namely, an inhibition of evoked synaptic activity), but this was more pronounced in the continuous RF group. Thus, they concluded that the acute effects of PRF are more reversible and less destructive in nature than the acute effects of classic continuous RF mode.

Nevertheless, the safety, efficacy, and the mechanism of action of pulsed RF current remains unresolved at the present time. Clinical trials still are needed to prove its potential efficacy.

RADIOFREQUENCY DENERVATION IN THE CERVICAL REGION

Cervical percutaneous radiofrequency denervation of the facet joints

Relevant anatomy

The cervical zygapophyseal joints are innervated in the same way as the lumbar zygapophyseal joints (Fig. 24.1). The cervical segmental nerves divide into the primary anterior ramus and the primary posterior ramus on exiting the neuroforamen. Immediately, the posterior branch divides into a lateral and a medial branch in the cervical intertransverse space. The medial branches of C4 to C8 run dorsally and medially through the ‘waist’ of their respective articular pillars. They innervate the facet joints at the level of the exiting segmental nerve and at the level below. Because of this multilevel innervation of the facet joints, usually the medial branch procedure is performed at several levels. Furthermore, the medial branches give deep branches to multifidus muscles and superficial branches to semispinal cervical muscles.

Fig. 24.1 Anatomy of cervical facet joints and their innervation. The medial branches of the posterior primary rami of the segmental nerves C3, C4, and C5 are indicated by red lines, the vertebral artery by the blue line

The anatomy of the innervation of the C2–3 facet joint is distinct from the lower cervical joints. It receives innervation by branches of the greater occipital nerve, which is the continuation of the posterior primary ramus of the C2 segmental nerve. The C3 posterior primary ramus of the segmental nerve gives a medial branch that innervates the C2–3 facet joint, but also gives a branch that forms the third occipital nerve that runs cranially to innervate the skin of the lower part of the occipital region. There is no facet joint between the C1 and the C2 vertebrae.

Procedure

Sedation is not employed because of the need for continuous communication between practitioner and patient. Several approaches to reach the medial branch of the dorsal ramus at the upper and middle cervical area can be used.

The most commonly used approach by these authors is the posterolateral approach.²⁵ For this technique, the patient is positioned supine on the operating table, which is tolerated well. The occiput is placed on a headrest and the cervical spine is slightly extended. The C-arm is positioned in a moderately oblique (±30°) location to secure a safe distance between the electrode tip and the exiting segmental nerve. In this position the gantry angle is parallel to the axis of the intervertebral foramen that is upward and slightly caudal. In this position the segmental nerves exit in a plane approximately perpendicular to the monitor screen. The degree of obliquity should be such that the projection of the pedicles is seen a little anterior to 50% of the vertebral body (Fig. 24.2). In the frontal plane, there should be a small angle of the C-arm with the transverse plane. This provides clear visibility of the intervertebral discs and the neuroforamina. In this projection, the medial branch runs over the base of the superior articular process, which is easily viewed. Entry points are marked on the skin, somewhat posterior and caudal to the target points as seen on the monitor, i.e. dorsal from the posterior border of the facet column and slightly caudal. Care should be taken to ensure that the entry point is not too anterior in the neck to avoid important vascular structures such as the carotid artery. The first needle (preferably the most cranial) is inserted in a horizontal plane and in a slightly cranial direction not deeper than 2 cm, so that the needle point is in line with the target point. Then the needle is carefully advanced anteriorly and cranially until bone contact is made with the facet column at the target point (see Fig. 24.2).

Fig. 24.2 Oblique fluoroscopic view of cervical facet joints with three needles aiming for the medial branches of the C3–4, C4–5, and C5–6 facet joints. The red line indicates the position of the pedicles projection a little anterior to 50% of the vertebral body. The green dots indicate the target points.

During the first step of the procedure, several things can go wrong. The needle tip may be projecting over or anterior to the target point without any bone contact. Should the needle then be introduced further and more anteriorly to an imaginary line connecting the posterior aspects of the neural foramina it could make contact with the segmental nerve or even with the vertebral artery. To avoid this, each advancement of the needle should be checked and, if necessary, should be redirected more posteriorly. As the needle is advanced it becomes increasingly difficult to reposition the needle tip to an accurate location. If the needle tip is projecting posterior to the bone of the facet column and is advanced further, there is the possibility that it will pass between the laminae and make contact with the spinal cord. This can occur if the entry point of the needle is too far posterior in the neck. To avoid this, an anteroposterior (AP) check should be made to confirm an ideal starting point.

The position of the C-arm in the AP direction should confirm the position of the needle tip adjacent to the concavity (‘waist’) of the articular pillars of the cervical spine at the corresponding level (Fig. 24.3). Once the first needle is in the proper position, the other needles are introduced in the same way as described above. The authors prefer to take advantage of the first needle serving as an indicator for the direction and depth for subsequent needles, which accounts for their recommendation of placing all needles before applying RF rather than lesioning a single medial branch and then placing the next needle. The technique is identical for the facet joints from C3–4 until C6–7. The direction of the needle at the C2 level is different. It should be oriented toward the small branches that innervate the C2–3 facet joint and not toward the medial branch, which is the greater occipital nerve. For the RF treatment of this facet joint, the needle should be placed at the arch of C2 at the level of the upper border of foramen C3.

Fig. 24.3 Antero-posterior fluoroscopic view of the needles aiming for the medial branches of the cervical facet joints C3–4, C4–5, and C5–6. The target points are indicated with green dots. Notice that the needle aiming for the C3–4 medial branch has to be redirected more cranially.

When optimal anatomical localization of the needles transpires, an electrical stimulation is performed to confirm correct needle position, i.e. parallel to the medial branch. This can be accomplished by identifying the stimulation thresholds. First, an electrical stimulation rate of 50 Hz should be given and should elicit a response (tingling sensation) in the neck at less than 0.5 volts. Next, a stimulation at 2 Hz is performed to confirm accurate needle position. Contractions of the paraspinal muscles will be noticed. Muscle contractions in the arm indicate needle placement too close to the exciting nerve root. In that case the needle should be repositioned more posteriorly. Once proper positioning of the needle is confirmed, the medial branch of the dorsal ramus is anesthetized with 1–2 mL local anesthetic solution (lidocaine 1–2%). An 80°C radiofrequency thermal lesion is made for 60 seconds at each level. To date, there have been no reported complications from cervical facet joint denervation when the procedure is methodically performed.²⁶

Some postoperative burning pain is described in >30% of patients.²⁷ It disappears spontaneously after 1–3 weeks. One should always bear in mind that there is risk of puncture of the vertebral artery when the needle is positioned anterior to the foramen in the posterolateral approach.

A second approach, which is more popular in the United States, is the posterior approach of the facet joint. This was first introduced by Lord et al. in 1995.²⁸ In this technique, the patient is positioned prone on the operating table, with the head flexed (about 5–10°) and with the face resting on a padded ring. This is a ‘tunnel vision’ technique, in which the target points are the posterior aspects of the waists of the articular pillars at the levels to be blocked and are the same as the entry points. The needle is introduced from posterior of the neck to make contact with each of the two nerves supplying the painful joints. When bone contact is made, the C-arm is turned to give a lateral view in which the needle tip should be seen in the posterior aspect of the waist of the articular pillar. A deviation toward the midline should be avoided because of risk of penetration into the epidural and subarachnoid space. Subsequently, the needle is incrementally advanced until the tip is projecting at the center of the pedicle. Then, a slightly lateral deviation should be made so that the needle tip is in the most lateral aspect of the articular pillar in the posteroanterior view. When this position is confirmed, stimulation is performed as described above to determine the 50 Hz and 2 Hz thresholds. If these are acceptable, local anesthetic is injected and an RF lesion (80°C for 60 sec) is made. At each location two lesions are made: the second one after a rotation of the RF needle over 90° from its first position.

Cervical radiofrequency lesioning of the dorsal root ganglion

Relevant anatomy

The segmental nerves of C3 to C8 exit through the lower parts of the neuroforamina on the transverse processes just below the level of the facet joints. They pass obliquely forward and downwards and posterior to the vertebral arteries and veins in grooves formed by the anterior and posterior tubercles of the corresponding transverse processes. In these grooves, they lie on the medial parts. Just anterior and inferior to them lie the small ventral roots. The first cervical nerve passes between the posterior arch of C1 and the vertebral artery. The dorsal ramus of the first spinal nerve becomes the suboccipital nerve and supplies the suboccipital muscles. This first cervical nerve has almost exclusively motor fibers and only seldom any significant sensory component. Thus, there is usually no need to block this nerve. The second cervical nerve passes transversely behind the C1–2 joint, and the large dorsal ramus forms the greater occipital nerve, which innervates the posterior scalp.

Procedure

Again, this technique is performed without any sedation because of the need of cooperation of the patient. The radiofrequency lesioning of the dorsal root ganglion (RF-DRG) is only performed after a positive diagnostic segmental nerve block (usually several diagnostic blocks are performed). For this procedure, the patient is lying supine on the operating table with a slight extension of the neck. Firstly, the C-arm should be positioned obliquely so that the first three contralateral pedicles are projecting just posteriorly to the anterior line of the vertebral bodies. Secondly, the intervertebral discs should be clearly visible. To do so, the C-arm is orientated in the frontal plane. One should adapt C-arm positioning to have an optimal view of the intervertebral foramen of the level one wants to treat. The axis of the intervertebral foramen points 25–35° anteriorly and 10° caudally. The inclination of the C-arm in the frontal plane should be such that there is no double contour in the caudal aspect of the foramen. Then the target point is identified: it is posterior in the neuroforamen between the caudal and the middle third. This dorsal position is chosen in order to avoid possible damage to the motor fibers of the segmental nerve and to the vertebral artery, which runs anterior to the ventral part of the foramen. The entry point is marked on the skin and is the same as the target point. This technique is a ‘tunnel vision’ technique what means that the entry of the needle is in the direction of the X-rays.³² The needle is than projected on the screen like a dot and the field of vision can theoretically be narrowed down to a tunnel-like diameter (Fig. 24.4). After injection of local anesthetic (lidocaine 1%) into the skin with a 22-gauge subcutaneous needle, a 22-gauge spinal needle or, preferably, a needle with a connecting tube is inserted into the superficial layers of the skin, in the direction of the X-rays so that the electrode is projected on the screen as a dot. Subsequently, the needle is advanced carefully and every step is checked with fluoroscopy. There is the possibility of inadvertent puncture of the segmental nerve. That is why an early check in the anteroposterior (AP) view is done. In this view, the endpoint is the point where the tip of the needle is projecting 1–2 mm lateral to the lateral border of the facet column. Thereafter, only 0.2–0.5 mL of water-soluble dye (Iohexol 240 mg/mL; Omnipaque® 240) is injected to confirm the proper position of the needle tip close to the segmental nerve and to exclude an accidental intradural or intravascular position of the electrode. When this is confirmed, 0.5 mL of local anesthetic (lidocaine 1–2%) is injected. Alternatively, to perform a radiofrequency lesion, the cannula is advanced until the tip projects into the middle of the facet column (Fig. 24.5). Then the stylet is removed and 0.2–0.5 mL of dye is injected to confirm proximity to the targeted nerve root. The RF probe is now inserted through the cannula. After checking the impedance, electrical stimulation is started at a rate of 50 Hz. The patient should feel a tingling sensation. If the stimulation threshold is felt under 0.4 volts, the needle is withdrawn until the threshold is between >0.4 and <0.65 volts. At the C2 level, a suboccipital tingling has to be confirmed by the patient. Next, the frequency is changed to 2 Hz, and the patient is observed for muscle contractions in the arm and/or hand. These should not occur below a voltage of 1.5 times the 50 Hz threshold. When the thresholds are acceptable, 0.5–1.0 mL of local anesthetic (lidocaine 1–2%) is injected. Subsequently, an RF current is led through the electrode in order to increase the temperature at the tip slowly to 67°C for 60 seconds. As mentioned above, there is the tendency toward using pulsed RF current when treating the DRG because it is believed to be less destructive. With this technique, the stimulation at 50 Hz is started when the needle tip is projecting 2 mm medially to the lateral border of the facet column. An ideal threshold is obtained at <0.3 Hz. Then, a conventional 2 × 20 msec/sec, 45 volt and 120 sec. pulsed RF procedure is performed. The pulsed RF treatment can be repeated a second time if the 50 Hz threshold is lower than the initial threshold after a slight repositioning of the needle.

Fig. 24.4 Oblique fluoroscopic view of blocking the C6 segmental nerve. Notice the needle in tunnel vision (projecting as a dot) posterior in the C6 foramen between caudal and middle third of this foramen.

Fig. 24.5 Antero-posterior fluoroscopic view of RF lesioning of the DRG of the C6 segmental nerve. Notice that the needle tip still has to be inserted more until it is projecting at the middle of the facetal column (target point is indicated with a red dot).

To perform a diagnostic block and (pulsed) RF procedure of the C2 DRG, the C-arm is positioned straight lateral because of the different anatomy at this level. There is no facet joint and there are no major blood vessels in the direct neighborhood that should be considered. The target point of the DRG of C2 is about 3 mm posterior to the tip of the dome-shaped space between the laminae of the C1 and C2 vertebrae (Fig. 24.6). After injection of a local anesthetic, the needle is inserted and advanced in a tunnel vision technique. The depth of the needle is checked in the AP position (Fig. 24.7) and the needle tip should be projecting halfway across and posterior to the C1–2 joint using a through-the-mouth view. The next steps are identical to those described above for the C3 to C7 DRG.

Fig. 24.6 Lateral fluoroscopic view of the block of the C2 segmental nerve. The target point is the same as the entry point (tunnel vision technique), namely approximately 3 mm posterior to the tip of the dome-shaped space between the laminae of the C1 and C2 vertebrae.

Fig. 24.7 Antero-posterior fluoroscopic view of the block of the C2 segmental nerve, where the tip is projecting halfway across and posterior to the C1–2 joint (atlantoaxial joint) (indicated by a red line). Notice the course of the nerve shown by the injected dye. Notice also that this isn’t a ‘through-the-mouth’ view, but an AP view with hyperextension of the cervical spine.

The radiofrequency lesioning of the C8 DRG should be avoided because of the high tendency to develop neuritis and even deafferentation pain. The reason for this occurrence has not been discovered. The pulsed RF technique could be an alternative to avoid this complication.

Equipment

For a diagnostic block, it is recommended to use a needle with a connecting tube (for example: an RCN-needle, Radionics), so that once proper positioning of the needle has been attained, contrast medium and local anesthetics can be given without displacement of the needle. For an RF lesioning, either the SMK-50 mm with a 4 mm active tip or the SMK-100 mm with a 5 mm active tip can be used. For the pulsed RF technique, a SMK-C5 with a 4 mm active tip is used.

Postprocedure care

The patient can be discharged 1–2 hours postprocedure. Driving or operating dangerous machinery during the first 24 hours after the procedure is prohibited. A side effect that is often seen (40–60%) is a mild burning sensation (some deep neck soreness) in the treated dermatome that subsides spontaneously after 1–3 weeks.³³ Some sensory changes, such as a slight hypoesthesia, may occur but invariably disappears within 3–4 months.^34,³⁵

Case study

A 44-year-old female attending the authors’ pain clinic with a 6-month history of pain in her neck radiating to her shoulder, arm, index and middle fingers. The pain in her arm was the most disabling. Physical examination revealed a diminished anteflexion of the cervical spine and paravertebral tenderness over cervical facet joints C3–4, C4–5, and C5–6 on the right side. Neurological examination revealed a positive Spurling test on the right side. Physical examination of both shoulders was normal and radiography of cervical spine showed some minor degenerative abnormalities; in addition, electromyography was also normal. Conservative management (medication, physical therapy, and TENS) gave no meaningful pain relief. In different sessions, the C5, C6, and C7 segmental nerves on the right side were tested. Because of an important decrease (about 50%) of the pain after diagnostic block of the C6 segmental nerve, DRG of C6 was treated with a PRF current for 120 seconds. Two months after the treatment there was an improvement of the pain of 60%. Seven months after treatment there was still the same level of pain relief.

RADIOFREQUENCY DENERVATION IN THE THORACIC REGION

Thoracic percutaneous radiofrequency denervation of the facet joints

Relevant anatomy

In contrast to the lumbar facet joints, the thoracic facet joints are more vertically oriented and almost parallel to the coronal plane (Fig. 24.8). They are oriented perpendicular to the sagittal plane and face directly anterior. The thoracic facet joints are innervated by medial branches of the posterior primary rami of the segmental nerves. Each thoracic facet joint is bisegmentally innervated by the medial branch of the same level and the medial branch of the level above. The thoracic medial branches pass through the intertransverse space and touch the superolateral corner of the transverse process. Then they run medially and inferiorly across posterior surfaces of the transverse processes before entering the posterior compartment of the back and innervating the multifidus muscles.³⁶ In that location they give ascending articular branches to the facet joint. An exception to this pattern occurs at the midthoracic levels (T5–8). Although the curved course remains essentially the same, inflection occurs at a point superior to the superolateral corner of the transverse process. This course is different than that seen with the lumbar medial branches which are fixed at the junction of the superior articular process and the transverse process.³⁷ The T11 and T12 medial branches have the same course as the lumbar medial branches.³⁷ Obtaining a fluoroscopic view is quite difficult for a variety of reasons. In this region one has to contend with overprojection of the ribs, the prominent transverse process that is directed slightly cranial and markedly posterior, and the size and orientation of the pedicles that can make them difficult to visualize. In addition, the orientation of the thoracic facet joints impedes the operator’s ability to differentiate between superior and inferior articular process.

Fig. 24.8 Anatomy of the thoracic facet joints and their innervation. Notice that the thoracic facet joints are more vertical and orientated almost parallel to the coronal plane in comparison to the cervical facet joints. The medial branches of the posterior primary rami make their inflection of the curved course at the superolateral corner of the transverse process (indicated by the red lines) and touching it.

Procedure

Sedation is avoided as communication between operator and patient must be maintained at all times. In contrast to diagnostic thoracic intra-articular block, which has been well described,³⁸ expert opinion varies on RF lesioning of median branches in the thoracic vertebrae. Nonetheless, the authors describe how they perform an RF lesion of the median branches at the thoracic level. Although the authors embrace this technique some authors have suggested that the needle tip is actually ‘too far anterior’ to the medial branch to result in denervation. The authors use the junction between the superior articular process and the superior border of the transverse process as a target point for thoracic medial branch neurotomy, Stolker et al. reported that with this target site the medial branch of the dorsal ramus was never within reach of the electrodes.³⁹ Based on Stolker’s work, the authors suggest exercising caution regarding categorical acceptance of the technique described here.

The C-arm is positioned in the transverse plane and an external radiopaque object such as a clamp is used to identify the proper level. A straight-on AP view of the vertebra at the anticipated target level is obtained. The endplates of the vertebra should be parallel without any visible endplate double contours. Then the C-arm is axially and slightly obliquely rotated in the sagittal plane. This should facilitate the access to the target point that is the junction of the superior articular process and the transverse process. A proposed entry point is marked on the skin and local anesthetics (lidocaine 1%) with a 23-gauge needle are injected. The RF needle is then inserted parallel with the gantry angle (angle of the C-arm beam) until bone contact is reached at the junction of the superior articular process and the transverse process (Fig. 24.9). Subsequently, the needle is redirected slightly more cranially and laterally until it is just loses osseous contact. Then the needle position is checked in the lateral view. The needle tip should be just posterior to a line connecting the posterior aspects of the neuroforamina (Fig. 24.10). Stimulation at 50 Hz is now performed. A paravertebral tingling sensation should be perceived with a current with a voltage of less than 0.5 volts. Next, stimulation at 2 Hz should provoke paravertebral muscle contractions at a voltage of ≤1. Stimulation should be negative for anterior nerve root stimulation, which would be perceived as muscle contraction and/or pain in the anterior chest wall or abdominal region depending on the level undergoing RF. When proper needle positioning has been confirmed with fluoroscopic imaging and electrical stimulation, 0.5 mL of lidocaine 1–2% is administered at each level. After local anesthesia has taken effect, RF lesioning is conducted for 60 sec at 20 V. The authors typically RF three levels because of the multisegmental innervation of the facet joints.

Fig. 24.9 Slightly oblique fluoroscopic view of the RF denervation of the medial branches of the T3–4, T4–5, T5–6, and T6–7 facet joints on the right side. The needles make bone contact at the junction of the superior articular process and the transverse process.

Fig. 24.10 Lateral fluoroscopic view of needle tips at the medial branches of the T3–4, T4–5, T5–6, and T6–7 facet joints. The needle tips should be projecting just posterior to a line connecting the posterior aspects of the neuroforamina.

As was alluded to earlier, the authors use this technique and are attempting to refine it.

Equipment

For a diagnostic block a 10 cm CMK needle (with a connecting tube) is used. For an RF lesioning, a SMK-C10 cannula with a 5 mm active tip can be used. Alternatively, a 10 cm with 10 mm active tip Racz-Finch radiofrequency thermocoagulation (RFTC) needle can be used. When using the latter needle, a 20-gauge angiocatheter and an RFTC electrode are necessary.

Postprocedure care

As with any RF procedure there is always the possibility of postprocedure exacerbation of pain. A complication unique to the thoracic region is a pneumothorax. Proper technique and the use of fluoroscopic guidance for the placement of the needle will minimize the risk of this complication. The patient must be warned of the possibility of the development of a pneumothorax and should return to the hospital if shortness of breath or pain with inspiration develops. The patient can be discharged home a few hours after the procedure provided the vital parameters are normal.

Thoracic radiofrequency lesioning of the dorsal root ganglion

Relevant anatomy

In the higher thoracic segments, it is difficult to reach the dorsal root ganglia because of overlying anatomical structures. Among the obstacles are the wide facet column, articulations of the transverse processes with the ribs and, most importantly, the lungs. The pulmonary structures prevent adopting a very lateral approach, which would have been ideal to allow one to get under the posterior osseous barriers. In successive lower thoracic segments, the anatomy gradually resembles the anatomy of the lumbar spine. This change creates an opportunity for lower thoracic DRG to be reached as if it were a lumbar DRG.

Procedure

Two or more diagnostic blocks at different levels must be performed to identify the segment involved, because of the frequent overlapping of thoracic segmental pain from one segment to another. An intercostal block can be used as a test block of a thoracic segmental nerve.⁴⁰ The level which provides the best temporary pain reduction is then selected for RF lesioning of the dorsal root ganglion. As described above, in the upper thoracic spine, the classic approach (posterolateral) is not possible because the foraminae face more anteriorly and accurate positioning of the needle is hindered by the angle of the ribs. Therefore, an alternative technique is used to reach the DRG of T7 and above. The patient is placed in a prone position and a dorsal approach is used. The target point is the craniodorsal part of the intervertebral foramen and is thus the same as the target point in the classic dorsolateral approach. The entry point is the midpoint of the pedicle in the posteroanterior view (Fig. 24.11). This entry point is checked in a lateral view where it should aim for the superior dorsal quadrant of the foramina where the DRG should be situated. A small hole is drilled through the lamina of the vertebra under fluoroscopic guidance in the posteroanterior view using a 16-gauge Kirschner wire and local anesthesia. A potential danger is the piercing of the facet joint. Then, an RF cannula is inserted through the burr hole into the proper position, which is checked in the lateral view and should be in the craniodorsal part of the intervertebral foramen (Fig. 24.12). The stylet of the cannula is replaced with an RF probe and stimulation at 50 Hz is carried out. The patient should feel tingling sensations in the selected dermatome using a 0.4–1.0 V stimulus. Stimulation at 2 Hz should not give contractions of the intercostal muscles at a stimulation threshold below 1.5 times the sensory threshold. After satisfactory placement is achieved, 0.4 mL of contrast medium (Omnipaque) is injected to exclude intradural or intravascular spread. When correct position has been confirmed, 1–2 mL of lidocaine 1–2% is injected and a 60 second, 67°C lesion is made. One could consider performing PRF lesioning (pulses of 2 Hz and 20 msec during 120 seconds), but this technique has not yet been proven to be less destructive or as effective as RF lesioning.

Fig. 24.11 Antero-posterior fluoroscopic view of a RF lesioning of the T8 DRG. The entry point is the midpoint of the pedicle (indicated by a green line; the pedicle is indicated by a red line) in the posteroanterior view. Notice the introduction needle is in tunnel vision.

Fig. 24.12 Lateral view of the RF lesioning of the T8 DRG where the proper position of the RF cannula is the craniodorsal part of the intervertebral foramen. Notice the introducer needle (indicated with a red line).

At the lower levels the same approach can be used as at the lumbar level. The needle position, the stimulation, and the lesion parameters are identical. This technique is described under RF denervation in the lumbar region.

Equipment

A 10 cm SMK 22-gauge cannula with 5 mm active tip and an RF probe can be used. This needle can be manually curved to perform the parasagittal approach. For the dorsal approach, a 16-gauge Kirschner wire can be used the make a burr hole into the lamina.

Postprocedure care

One of the most important complications is the possibility of damage to the nerve root or spinal cord during needle placement. Another common complication is neuritis. Again, there is a slight possibility of a pneumothorax and/or hemothorax. These particular complications should be described in detail to any prospective candidate for RF lesioning. Other possible complications include infection, increased pain, bleeding, and bruising. The authors typically discharge patients a few hours after undergoing procedures. It cannot be overemphasized that the absence of a pneumothorax should be clinically determined. If any doubt remains, radiographs are mandatory.

Case study

A 55-year-old woman was referred by the neurology service to the authors’ pain clinic. She worked for a cleaning company. For almost 2 years she had progressive, continuous pain which began in the upper thoracic region and referred symptoms to just under the right breast.

Neurological examination and MRI scan from the thoracic region were normal. There were mild degenerative changes of the midthoracic vertebrae. A trial of medication was tried with little in the way of success. These included gabapentin, amitriptylline and venlafaxin. Other therapies included transcutaneous nerve stimulation and physical therapy. These were equally ineffectual.

Diagnostic blocks were performed at the T6, T7, and T8 levels with each block performed during a separate visits. Diagnostic block at the level T7 on the right side provided complete relief of pain. A radiofrequency lesion of the T7 dorsal root ganglion was performed using a standard orthopedic drill (AO drill). There was complete relief of pain after this procedure for 4 months. Four months later the patient underwent an identical procedure with excellent pain relief.

RADIOFREQUENCY DENERVATION IN THE LUMBAR REGION

Lumbar percutaneous radiofrequency denervation of the facet joints

Relevant anatomy

The lumbar facet joints are all almost vertically oriented (Fig. 24.13). The upper lumbar facet joints are more oriented in the sagittal plane and they rotate to a more oblique angle in the lower lumbar region. The upper facet joints are more curved than the lower joints, which are more flat. The facet joint is innervated by the medial branch of the posterior ramus of the spinal nerve. As it exits from the intervertebral foramen, the spinal nerve divides into an anterior primary ramus and a posterior primary ramus. At approximately 5 mm from its origin, the posterior primary ramus divides into medial, lateral, and intermediate branches. The medial branch supplies the facet joint at its own level and the next lower level. The medial branch runs in a dorsal and caudal direction and lies in a groove on the base of the superior articular process in direct contact with the base of the superior surface of the transverse process. Each medial branch also supplies the multifidius, interspinales, and intertransversarii mediales muscles and the ligaments and periosteum of the neural arch.

Fig. 24.13 Anatomy of the lumbar facet joints and their innervation. The medial branches of the posterior primary rami of the segmental nerves L1, L2, and L3 are indicated by red lines.

The anatomy of the L5–S1 facet joint is different. The transverse process of S1 is replaced by the ala of the sacrum and thus the median branch of L5 runs at the junction between the sacral articular process and the upper sacral border. Also, in some circumstances there is a branch from the S1 nerve exiting the posterior opening of the first sacral foramen. It courses cephalad and innervates the L5–S1 facet joint. Consequently, in certain patients the only way to completely denervate the L5–S1 facet joint would be to conduct RF at three locations, affecting the medial branches of L4, L5, and S1.

Procedure

Since continuous verbal feedback from the patient is required during the stimulation and heating phases, sedation is not employed.

The patient assumes a prone position on the fluoroscopic table. A pillow is placed under the abdomen to diminish the physiological lumbar lordosis. Firstly, targeted levels are identified and a straight AP projection is obtained. Then, the C-arm is axially rotated until there are no visible double contours of the caudal endplate of the middle vertebra. The middle vertebra of the levels to be treated is used as the reference point prior to the searching for the optimal position of the C-arm. Subsequently, the C-arm is rotated to an approximately 15° oblique view until the spinous processes are projecting off the midline but well inside the contralateral facet joints. Then, the entry point should be marked over the target point, which is the point at the junction of the superior articular process and transverse process. To perform a diagnostic block, the target point should be approximately 1 mm under this junction to avoid inadvertent spread of local anesthetic to segmental nerves, thereby creating the potential for a false-positive result. After injection of local anesthetic (lidocaine 1%) into the skin, the needle is inserted at the entry point and slowly advanced using a tunnel vision technique until the tip makes osseous contact. For a diagnostic block, the position of the needle is then checked in the lateral view, which should be at the level of the inferior part of the intervertebral foramen in line with the facet joint column. When accurate positioning is confirmed and following a negative aspiration, 1 mL of local anesthetic (lidocaine 1%) is injected at each level. To perform an RF lesioning of the medial branch, after making bone contact with the needle tip, the needle is redirected slightly more cephaled until bone contact is lost and immediately the target point is reached (Fig. 24.14). Then, the C-arm is rotated into the lateral view to check the position of the needle tip, which should be in line with the facet joint column and at the level of the inferior part of the intervertebral foramen about 1 mm dorsal to the level of the line connecting the posterior aspects of the intervertebral foramina (Fig. 24.15). It should be a little deeper and more cranial than the position of the needle for the diagnostic block. When this position is confirmed, the impedance is checked and, if acceptable, stimulation at 50 Hz is conducted. The patient should feel new pressure or tingling in the back at a voltage of <0.5 V. If sensations are felt in the ipsilateral extremity, the needle tip is too close to the segmental nerve. It is imperative the needle be slightly withdrawn and stimulation at 50 Hz checked again. Subsequently, settings are changed so that stimulation occurs at 2 Hz. The patient should experience localized contractions of the multifidus muscle and not of muscles of the leg. These local contractions can be palpated by the operator. Similarly, any contractions that occur in the leg may be detected by the operator or the assistant if a hand is placed over the muscles innervated by the exiting nerve root. If the patient perceives pain and/or contractions in the extremity or if muscular contractions are detected by an operator then the needle must be repositioned. After accurate positioning of the needle tip is attained and a negative aspiration is demonstrated, 1 mL of local anesthetic (lidocaine 1%) is injected at each level. RF lesioning of 20 V (approximately 67°C) is performed for 60 seconds.

Fig. 24.14 Oblique fluoroscopic view of two needles in tunnel vision, aiming for the medial branches of the L3–4 and L4–5 facet joints on the left side.

Fig. 24.15 Lateral fluoroscopic view of RF lesioning of the medial branches of the L3–4, L4–5 and L5–S1 facet joints. Notice that the tips of the needles are in line with the facet joint column and are projecting at the level of the inferior part of the intervertebral foramen about 1 mm dorsal to the level of the line connecting the posterior aspects of the intervertebral foramina.

The fluoroscopic view for the L5–S1 facet joint and thus the median branch of the L5 is different from the other lumbar levels because of the difference in anatomy. The L5 medial branch lies at the junction between the superior sacral articular process and the upper border of the sacrum. Since there is no pedicle at this level to use as a radiological landmark, the C-arm is positioned so that the junction is seen as a round, curved transition. The C-arm is rotated slightly obliquely (about 15°). The identified target point is the curve of the transition and is the same as the entry point. The needle is thus placed in tunnel vision (Fig. 24.16). The depth of the needle is checked in the lateral position and the tip must project over the posterior border of the facetal column. Thereafter, the rest of the procedure is the same as described before.

Fig. 24.16 More anteroposterior fluoroscopic view while aiming for the medial branch that innervates the L5–S1 facet joint. Notice that the needle aiming at the nerve of this joint is in tunnel vision and that the upper needles (aiming for the medial branches of the L3–4 and L4–5 facet joints) are not.

Equipment

A 22-gauge, 10 cm SMK needle with a 5 mm active tip can be used to perform an RF lesioning. Another possibility is to use a 10 cm, 20-gauge blunt RFTC needle with a 10 mm active tip and a 16-gauge angiocatheter as an introducer. However, no clinical studies have been published using the latter mentioned equipment.

For a diagnostic procedure, a needle with tubing is preferred (for example: a 10 cm 22-gauge pole RC needle). When a PRF lesioning is performed, a 10 cm SMK cannula and a SMK-TC 10 RF probe can be used.

Postprocedure care

The patient is allowed to go home immediately after the procedure. Driving a car or handling dangerous machinery is proscribed for the first 24 hours. In some instances there will be a transient numbness of the ipsilateral extremity because of overflow of local anesthetics into the intervertebral foramen. The overall incidence of minor complications per radiofrequency site was found to be only 1%.⁴¹ For up to 2 weeks after the procedure there may be burning pain perceived in the lower extremity (neuritic pain) or there can be more localized pain lasting in excess of 2 weeks. Invariably, these are short-lived side effects and will resolve spontaneously. Other possible side effects include infection, bruising, and muscle spasms.

Case study

A 64-year-old man presented to the authors’ pain clinic with a major complaint of low back pain with radiation into the bilateral inguinal region and into the dorsal thighs. These symptoms had been present for 2 years with failure to improve with classic rehabilitation measures including medication and physical therapy. Physical examination revealed limited extension of the lumbar spine and pain on extension. Furthermore, there was pain elicited with paravertebral pressure to the lower lumbar region. Neurological examination was normal. Radiography of the lumbar spine revealed a facet arthrosis of the right L4–5 and L5–S1 facet joint and less so on the left side. Diagnostic block of the median branches of the right L4, L5, and S1 posterior primary rami was performed with 1 mL of lidocaine 1% at each level. Thirty minutes after the procedure, the patient reported approximately 70% pain intensity relief. One week later, an RF lesion of these median branches was performed. At 8-weeks follow-up the patient reported complete relief of pain.

Lumbar radiofrequency lesioning of the dorsal root ganglion

Relevant anatomy

The lumbar dorsal root ganglion (DRG) is situated in the cranial part of the intervertebral foramen. The DRG lies more dorsally in the upper lumbar levels compared to the lower lumbar levels.

Procedure

Sedation is not employed. The procedure is performed with the patient in prone position on a fluoroscopic table with a pillow under the abdomen to diminish the physiological lumbar lordosis and facilitate the approach. A straight AP view is secured and the targeted segmental level is identified using a radiopaque object such as a clamp. Then, the C-arm is axially rotated to give a view of the targeted vertebra without any double contour of the endplate. Subsequently, the C-arm is rotated obliquely, approximately 20–25°, so that the spinous processes are projecting just medially to the contralateral facet column. Then, the entry point is marked and is the same as the target point (Fig. 24.17). The target point is different for a diagnostic segmental block in comparison to an RF of the DRG. For a diagnostic block, the target point is 1–2 cm distal to the DRG. The target point for an RF lesioning of the DRG is approximately 1 mm caudad to an imaginary line that bisects the pedicle. After infiltration of the skin with local anesthetics (lidocaine 1%), the needle is inserted and slowly advanced using a tunnel vision technique. The depth of the needle should be checked following each advancement. This is best viewed using a lateral projection. If this is not done, the root can be inadvertently irritated or even injured. In this lateral view, the needle tip should rest within the cranial part of the intervertebral foramen and only 1 mm past the posterior aspect of this foramen (Fig. 24.18). To do a diagnostic block of the segmental nerve, which is always performed before any RF lesioning, the needle should also be in the cranial part of the intervertebral foramen, but at the ventral border. Even using meticulous technique does not guarantee that the root will not be touched by an advancing needle. The authors routinely warn the patient that this may happen and that they should not be concerned. If the patient experiences a sudden jolt of pain in the ipsilateral radicular dermatome the needle should be immediately withdrawn a millimeter or two. The next step is to check the needle position by injecting contrast medium. Turn the C-arm in an AP projection, where the needle tip should be projecting within the contours of the vertebra and inject a small volume of dye. Only the exiting nerve should be seen and there should be no flow of contrast into the epidural space (Fig. 24.19). For a diagnostic block, more than 1 mL of local anesthetic (lidocaine 1%) is injected. To perform an RF or PRF lesioning of the DRG, stimulation at 50 Hz is first conducted. It should give a tingling sensation in the leg in the appropriate dermatome at a threshold <0.5 V. Subsequently, the 2 Hz threshold is searched for and should occur at less than 150% of the previously established 50 Hz threshold. In the lumbar region, the PRF lesioning of the DRG is preferred as it may be less destructive than RF lesioning. The authors create a lesion over 120 seconds using pulses of 2 × 20 msec/sec at 45 V. If the impedance is >400 Ohms, 1 mL of lidocaine 1% should be injected before the lesioning. The tip temperature should not exceed 42°C. If this occurs, the voltage should be lowered to 40°C.

Fig. 24.17 Oblique fluoroscopic view (approximately 20–25°) to perform an RF lesioning of the L5 DRG on the left side. Notice that the spinous processes are projecting just medially to the contralateral facet column. The target point (indicated by a red dot) is approximately 1 mm caudal to an imaginary line that bisects the pedicle (indicated by a blue line).

Fig. 24.18 Lateral fluoroscopic view of the needle tip while performing an RF lesioning of the L5 DRG. The needle tip should be projecting in the cranial part of the intervertebral foramen and only 1 mm past the posterior aspect of this foramen.

Fig. 24.19 Antero-posterior fluoroscopic view of an RF lesioning of the L5 DRG. Notice that the needle tip is projecting within the contours of the vertebra. A small volume of dye is injected and is revealing the L5 exiting nerve.

Prior to performing this intervention, the spine clinician should be aware that there is level two evidence that RF lesioning of a lumbar DRG is not effective.⁴²

Equipment

For a diagnostic block, a 10 cm 22-gauge needle can be used. An example is the pole RC needle. To perform an RF lesioning, a 100 mm SMK cannula and SMK-TC 10 RF probe can be used.

Postprocedure care

Patients should be warned that local anesthesia can create a temporary weakness of the lower extremity following a diagnostic block. Consequently, standing or walking for 45–60 minutes after the procedure is potentially dangerous. At 15–30 minutes after the diagnostic block, its analgesic effect should be tested. If there is pain relief of >50%, a PRF treatment can be planned. The patient can go home immediately after an RF lesioning. Patients should be warned that there can be a burning pain for a few weeks and that the beneficial effect of the treatment may be delayed for several weeks (6–8 weeks).

THE SYMPATHETIC SYSTEM

Stellate ganglion block

Relevant anatomy

The cervical paravertebral sympathetic trunks consists of preganglionic fibers originating in the anterolateral horn of the first and second thoracic spine segments (Fig. 24.20). They innervate the head and the neck. These preganglionic fibers travel with the ventral roots of T1 and T2 as white communicating rami and then join the sympathetic chain cephalad and synapses either at the inferior or middle or superior cervical ganglion. The inferior cervical ganglion is called the stellate ganglion and all preganglionic fibers either synapse here or pass through this ganglion. Then the postganglionic fibers run cranially following a course along the carotid arteries or go to the cervical plexus or upper cervical nerves as gray communicating rami to innervate neck structures.

Fig. 24.20 Anatomy of the stellate ganglion, indicated by a red line.

The preganglionic fibers that will innervate the upper extremity originate in the T2 and T8 or T9 spine segments and travel with the ventral roots of T2–8 as white communicating rami to join the sympathetic chain. Subsequently they pass cephalad and make synapses at the second thoracic, the first thoracic, the stellate, or the middle cervical ganglion (occasionally). Some of the postganglionic fibers form the subclavian perivascular plexus. However, most of these fibers travel to the anterior spinal nerves of C5–T1 as gray communicating rami and join the anterior spinal nerves to form the brachial plexus.

Often, the inferior cervical ganglion and the upper thoracic ganglion are fused to form the stellate ganglion. Sometimes the middle cervical ganglion is also fused with the stellate ganglion. The stellate ganglion usually lies on the lateral border of the longus colli muscle anterior in the neck between the base of the seventh cervical transverse process and the first rib. The classic approach to block the stellate ganglion is at the C6 level, namely at the Chaussignac’s tubercle. The ganglion is limited medially by the longus colli muscle, laterally by the scalene muscles, inferiorly by the pleura, anteriorly by the subclavian artery, and posteriorly by the transverse processes.⁴³

Sympathetic innervation of the upper extremity is provided by the stellate ganglion through gray communicating rami of C7, C8, and T1 and occasionally from C5 and C6. However, the T2 and T3 gray communicating rami also can innervate the upper extremity but don’t always pass through the stellate ganglion (they are then called ‘Kuntz’s nerves’) and thus aren’t blocked by blocking the stellate ganglion. That is often the reason why the stellate ganglion block fails to provide adequate relief of the sympathetically mediated pain of the upper extremity.

Procedure

There is no need for sedation of the patient. On the contrary, it is not recommended to perform this procedure on a sedated patient because it can be catastrophic. Every sudden, uncontrolled movement of the patient can dislocate the needle and can cause unintentional injection in the important nearby structures such as the carotid artery or the spinal canal.

An intravenous line can be provided before starting the blockade to have a safe access for injection of resuscitative drugs if needed.

The use of the C-arm is optional, but practical to check and confirm proper needle positioning.

The anterior approach at C6 is the most commonly used approach, but it can give an insufficient block of the sympathetic innervation of the upper extremity (see above). The patient is lying supine on a fluoroscopic table with a pillow under the shoulders to slightly hyperextend the neck. In this manner, the landmarks are easier to locate and the esophagus on the left side will be located more medially and thus away from the needle insertion point. The target point is the same as the entry point and is the Chaussignacs’ tubercle (C6) approximately 1–2 cm from the midline. This tubercle can be palpated and is located at the medial border of the sternocleidomastoid muscle lateral to the cricoid cartilage. Palpation of the tubercle is best done with the index finger, and most of the time this finger is also used to retract the carotid artery laterally away from the needle entry point. Then the needle is inserted just medially to the index finger towards the junction between the tubercle and the C6 vertebral body. Local injection of the skin is done with lidocaine 1%. The needle is aimed downwards perpendicular to the fluoroscopic table until bone contact is made. This bony contact is expected at a depth of 2.0–2.5 cm. Pneumothorax can be avoided with careful placement of the needle: control the direction and advance the needle gradually. The needle position can then be checked with fluoroscopy in the anteroposterior position (Fig. 24.21) and in the lateral view after injection of water-soluble dye. Of course, this injection of dye is only performed when the aspiration test has proven to be negative: i.e. no aspiration of cerebrospinal fluid or blood. When proper needle position is confirmed following the spread of the contrast medium, local anesthetic (lidocaine 1%) can be injected gradually using 0.5 mL as a test injection. After every 3–4 mL of local anesthetic, careful re-aspiration should be done to exclude dislocation of the needle point. At least 5 mL of local anesthetic fluid is needed to block the stellate ganglion, but this volume does not guarantee that Kuntz’s nerves (T2 and T3) will be blocked. A volume of at least 10 mL is probably needed to block all the sympathetic innervation of the upper extremity including the anomalous Kuntz’s nerves.

Fig. 24.21 Antero-posterior fluoroscopic view of a diagnostic block of the right stellate ganglion after injecting dye.

To provide a long-lasting blockade, radiofrequency thermocoagulation can be used. When the stellate ganglion block is performed as a diagnostic block to predict the effect of an RF lesioning, only 2–3 mL of local anesthetic solution should be used, otherwise it is not a good predictor. After correct placement of the electrode tip, stimulation is performed at 2 Hz and at 50 Hz to exclude close proximity to the phrenic nerve, the recurrent laryngeal nerve, or the segmental nerve of C7. When no stimulation of these nerves occurs and the injection of contrast dye reveals the characteristic spread, 2 mL of lidocaine 1% is injected and a 60-second, 80°C lesion is made.

An alternative method to the C6 anterior approach is the C7 anterior approach. These two methods are comparable, however the C7 anterior approach is more technically challenging because the C7 transverse process is not easily palpable. It is due to this anatomic issue that the authors recommend the use of fluoroscopy. Nevertheless, the advantage of this approach is the fact that a smaller volume (only 4–6 mL) of local anesthetic can be used to provide complete blockade of the sympathetic innervation of the upper extremity. The disadvantage of this technique is that the risk of pneumothorax is much greater.

Equipment

To perform a stellate ganglion block, a 23- or 24-gauge 4–6-cm needle can be used. A side line tubing is recommended because it guarantees the stability of the needle tip during the aspiration and the injection (for example: a 60 mm 24-gauge Pole RC needle). A 22-gauge SMK needle of 50 mm with a 4 mm active tip can be used to perform a radiofrequency thermolesion.

Postprocedure care

Correct placement of the block can be confirmed when an ipsilateral Horner’s syndrome is seen: miosis, ptosis, and enophthalmia. Conjunctival injection, nasal congestion, and facial anhidrosis are also signs that can be seen. The blockade of the sympathetic innervation of the upper extremity will reveal temperature differences between the blocked arm and the contralateral arm (raised skin temperature in the ipsilateral arm) and visible engorgement of the veins on the ipsilateral hand and forearm.

Ten to fifteen minutes after a diagnostic block, the effect can be evaluated and the patient can go home with an accompanying person.

Thoracic sympathetic block

Relevant anatomy

The preganglionic fibers of the thoracic sympathetic chain originate from the anterolateral horn of the respective thoracic spine segments and travel with the thoracic segmental nerves through the intervertebral foramen.⁴⁴ As white communicating rami, they synapse with postganglionic fibers in the thoracic sympathetic ganglia. Most often, there are 10 pairs of thoracic sympathetic ganglia lying paravertebrally and at the posterolateral surface of the thoracic vertebral bodies. Sometimes 11 pairs of ganglia can be found. Some of the postganglionic fibers return to their respective somatic nerves as gray communicating rami and go to the regional vasculature, the sweat glands, and the pilomotor muscles of the skin. Some of them go to the cardiac plexus and go up or down the sympathetic trunk to end in more distant ganglia. As mentioned above, the first thoracic ganglion is fused with the lower cervical ganglion to form the stellate ganglion.

The difficulty in blocking the thoracic sympathetic chain is related to, on one hand, the proximity of the pleura directly lateral and anterior to the ganglia and, on the other hand, the proximity of the segmental nerves.

Procedure ⁴⁵

There is no need for sedation.

The patient is lying on a fluoroscopic table in a prone position. Ideally, there should be a pillow under the chest so that the thoracic spine is slightly flexed. The C-arm can be used to check the needle position. The entry point of the needle should be just below and approximately 4 cm to the spinous process of the vertebra one level above the level to be blocked. The needle is inserted and a local anesthetic (lidocaine 1%) skin wheal is made. The needle tip is directed towards the lamina until bone contact is made. Then the needle is laterally ‘walked off’ the lamina until a loss of resistance is observed. This is the sensation one should expect while passing through the costotransverse ligament. After this loss of resistance, the needle should be advanced another 0.5–1.0 cm. There are several possible complications at this point. First, there is the possibility to enter the pleura and in doing so causing a pneumothorax. This should be avoided by keeping the needle tip medially as close as possible to the vertebral body. Secondly, it is possible to enter the intraspinal space when the needle tip is positioned too medially. Thirdly, the needle tip could be making contact with the segmental vertebral nerve and causing paresthesia in the respective dermatome. When this occurs, the needle should be withdrawn and redirected a little bit more cephalad. When the aspiration test is negative for blood, cerebrospinal fluid, or air, approximately 5 mL of local anesthetics (lidocaine 1–2%) can be injected.

Longer-lasting pain relief can be provided by radiofrequency lesioning. Until now, no randomized, controlled trials have been performed to prove the efficacy of the radiofrequency lesioning of the thoracic sympathetic chain.

Equipment

A 23- or 24-gauge, 4–6 cm needle can be used (for example: a 60 mm 24-gauge Pole RC needle).

Postprocedure care

After the procedure with local anesthetics, the patient should be observed for several hours and vital parameters should be checked. When these parameters are stable, the patient can go home but has to be instructed to come back to the hospital within half an hour if shortness of breath should occur because of the possibility of a developing and evolving pneumothorax.

Lumbar sympathetic block

Relevant anatomy

The lumbar sympathetic chain consists of two paravertebral trunks that are connected segmentally by preganglionic neurons (Fig. 24.22). These preganglionic fibers follow their corresponding nerves as white communicating rami and communicate in the paravertebral ganglia with postganglionic efferents and with efferents to the pelvic viscera. Some postganglionic fibers directly pass the ganglia and go to the ganglia in the aortic plexus and the superior and inferior hypogastric plexuses. The postganglionic fibers leave the sympathetic chain as gray communicating rami. Some go to the L1 nerve (iliohypogastric and genitofemoral nerve), others go to the L2–5 nerves, and the rest go to the upper three sacral nerves and end in the lumbosacral plexus.

Fig. 24.22 Anatomy of the lumbar sympathetic chain. This is a cross-sectional view where the two paravertebral sympathetic trunks are seen (indicated with a black line).

There is a great variation in number and position of the ganglia of the sympathetic chain. Most often four ganglia on each side are found. Often, there is a fusion of the L1 and L2 ganglia.

Procedure

Sedation should not be employed.

The patient lies in a prone position on a radioscopic table. A straight AP projection is obtained. Next, the obliqueness is adjusted. The spinous processes should project over the contralateral facet column, which is usually at about a 35° oblique angle. The target point is approximately 1 mm lateral to and a little caudal to the middle of the concavity of the vertebral body (Fig. 24.23). This point is often obstructed by the transverse process. Therefore, the C-arm is rotated axially to move the transverse process upwards so that visualization of the target point is unobstructed. After local infiltration of the skin with lidocaine 1%, the needle is inserted and advanced using a tunnel vision technique. The depth is checked on the lateral view. The needle tip should be at the anterior border of the vertebra (Fig. 24.24). In the AP view, the needle tip should be projecting within the lateral border of the vertebra and over the facet column (see Fig. 24.24). During the procedure, the patient is asked to report paresthesias, especially when the L4 level is treated, because of the possibility of making contact with the L3 ramus and thus the genitofemoral nerve. When the needle is in the right position, 1–2 mL of water-soluble contrast medium is injected and should spread cranially and caudally. A lateral spread of the dye at the L4 level suggests dispersal within the psoas muscle. When this happens, the needle should be redirected more anteriorly or medially. In the lateral view, the dye should spread at the anterolateral border of the vertebra in a linear fashion (Fig. 24.25). For an RF lesion, the next step is to perform sensory stimulation at 50 Hz. The patient should only feel a little pressure or warmth in the back, but not in the inguinal region or groin because this suggests the proximity of the needle tip to the genitofemoral nerve. Using motor stimulation of up to 2 or 3 volts should not trigger fasciculations or induce inguinal or groin pain. When the correct position is confirmed and a negative aspiration obtained, then 1–2 mL of local anesthetic (lidocaine 1%) is injected and an RF lesion (90 seconds, 67°C) is performed.