Cervical spine pain related to the facet joints

Cervical spine pain related to the facet joints

TE C H N I Q U E S I N R E G I O N A L A N E S T H E S I A A N D P A I N M A N A G E M E N T ] (]]]]) ]]]–]]] Available online at www.scien...

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Available online at www.sciencedirect.com

www.elsevier.com/locate/trap

Cervical spine pain related to the facet joints Kenneth D. Candido, MDn, Bryant England, MD Advocate Illinois Masonic Medical Center-Chicago, University of Illinois College of Medicine-Chicago, 836 W Wellington Ave, Suite 4815, Chicago, Illinois 60657

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Keywords:

Neck pain is a common diagnostic entity, with a lifetime prevalence of between 65% and

Cervicalgia

80%. Appreciation of the role of the cervical facet joints in the etiology of cervical spine pain

Cervical facet syndrome

is paramount to providing sustained pain relief for individuals suffering from degenerative and posttraumatic neck pain. Studies have demonstrated that approximately 60% of patients who sustain whiplash-type rear-end motor vehicle collisions would have pain that results from the facet joints alone, or in conjunction with the cervical intervertebral disks. An appreciation of the anatomical foundation for the development of these painful conditions includes knowledge of the dual, overlapping innervation of each cervical facet joint with contributions from levels at, and above the joint. Medial branch nerves invest the joints; are held closely adherent to the articular pillars by tendons of the semispinalis capitis muscles; and can be treated using local anesthetic nerve blocks followed by radiofrequency (RF) procedures for prolonged benefit. Nerves in facet joints contain modified nociceptors, including silent nociceptors, low-threshold mechanoreceptors, and mechanically sensitive nociceptors. Nerves within facet joints are both free and encapsulated and contain Substance P and calcitonin gene–related peptide. Treatment approaches must address these diverse anatomical and physiological phenomena to provide the highest level of interventional therapy. Large, well-conducted studies have demonstrated the efficacy and safety of providing short-term symptomatic pain relief using cervical facet medial branch nerve blocks. Continuous-energy thermal lesioning RF ablation techniques of the cervical medial branches may produce pain relief that persists for up to 12 months in two-thirds of patients so treated. A systematic review of well-conducted studies recently published confirmed that the evidence in favor of using RF ablation is level II for the longterm effectiveness of RF neurotomy and facet joint nerve blocks in managing cervical facet joint pain. Imaging for performing these procedures is mandatory to assure success and to minimize adverse events from occurring. Fluoroscopy is a standard imaging technique, but ultrasound and even computed tomography scan guidance have been documented to be satisfactory in properly trained interventionalists. The cervical facet joints with their medial branches represent a reliable target for directing interventional therapies aimed at addressing nociceptive type pain, albeit with a neurogenic component. Future studies would reflect our evolving appreciation of these intricate anatomical networks of innervation and their role in the etiology of chronic headache and neck pain. & 2015 Elsevier Inc. All rights reserved.

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Correspondence author. E-mail address: [email protected] (K.D. Candido)

http://dx.doi.org/10.1053/j.trap.2016.10.002 1084-208X/& 2015 Elsevier Inc. All rights reserved.

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Introduction Neck pain and cervical spine pain are common pain management issues faced not only in the United States but also on a global scale. For example, Great Britain has a yearly incidence of roughly 12 cases per 1000 persons, Canada estimates a lifetime prevalence of 67%, and the Netherlands describes 2% of primary care visits being related to pain emanating from the cervical spine.1,2 Multiple studies have demonstrated a lifetime prevalence of cervical pain of 65%-80% with a chronicity prevalence of 26%-44% that affects patients in the United States.3 This leads to many millions of dollars not only in medical expenses but also in lost wages from nonattendance to work, unemployment or underemployment, and disability. It is worth mentioning that neck pain is nearly as prevalent as low back or lumbar spine pain, may be underrepresented and underreported, and moreover both cervical and lumbar spinal pain can occur concomitantly. A number of structures can contribute to spinal pain including the cervical intervertebral disks, the dorsal root ganglia, fascia, ligaments, muscles, and the zygapophyseal or facet joints, which are present from C2-C3 caudally. Indeed, pain from C0-C1 (atlanto-occipital joint) or C1-2 (atlanto-axial joint) (Figures 1 and 2) can be sources of headache and neck pain, but have been considered to be somewhat controversial sources of pain as well owing to the absence of a true joint capsule or a true neural target. Increasing evidence points to the zygapophyseal joint as a major contributor to spinal pain. This is represented in the cervical spine by 54%-60% of patients with chronic spinal pain and by 15%-45% of patients with chronic lumbar spine pain.4 Patients most frequently develop cervical spine pain after an inciting event, including whiplash injury or posttraumatic arthropathy, or postspinal surgical pain; however, degenerative changes are a recognized etiology as well. With whiplash injury when the patient has the forceful hyperextension followed by acute flexion the zygapophyseal joint can be disrupted or injured. Studies have shown in this scenario that the zygapophyseal joint can be fractured, can develop intra-articular hemorrhage, or undergo rupture of the joint capsule.5 Degenerative models attempt to

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hypothesize the zygapophyseal cascade involving a 3 joint complex structure of 2 vertebral bodies, the intervertebral disk and the zygapophyseal joints, in an aging and structural description.3 Furthermore, there are 3 distinct types of nociceptors (specialized pain receptors) found within the joint capsule of the true zygapophyseal joints. These include silent nociceptors, low-threshold mechanoreceptors, and mechanically sensitive nociceptors.6 Nerves found here are both free and encapsulated and contain Substance P (SP) and calcitonin gene–related peptide (CGRP). CGRP is produced in both peripheral and central neurons. It is a potent peptide vasodilator and can function in the transmission of pain. CGRP is derived mainly from the cell bodies of motor neurons when synthesized in the ventral horn of the spinal cord and may contribute to the regeneration of nervous tissue after injury. SP is an undecapeptide member of the tachykinin neuropeptide family. It is a neuropeptide, acting as a neurotransmitter and as a neuromodulator. SP can be released from the peripheral terminals of sensory nerve fibers in the skin, muscle, and joints. It is proposed that this release is involved in neurogenic inflammation, which is a local inflammatory response to certain types of infection or injury occurring to the cervical facet joints. These then are the 2 primary chemical mediators of nociception involved in cervical facet joint–mediated pain and dysfunction. Pain related to the cervical zygapophyseal joints and the A-O and A-A joints is typically described as being dull and achy, continual, and located in the suboccipital and posterior neck regions.7 Indeed, Bogduk et al have carefully mapped out the overlapping innervation on the head, neck, and shoulders related to the cervical zygapophyseal joints using a provocation maneuver involving neural stimulation.7

Anatomy The cervical spine is an intricate structure of soft tissue and bony structures that allow for stability and mobility of the head and neck. The cervical spine is composed of 7 vertebrae with intervertebral foramina found at every level to accommodate exiting spinal nerves, excluding the atlas (C1) and

Fig. 1 – (A and B) Skeletal anatomy of atlanto-occipital (A-O) and atlanto-axial (A-A) joints. The A-A joint flexes, extends, and laterally rotates the head up to 601. (Photo courtesy: Kenneth D. Candido, MD) (Color version of figure is available online.)

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Fig. 2 – (A) Anterior-posterior fluoroscopic view of two needles placed into both the atlanto-occipital and atlanto-axial joints (Photo courtesy: Kenneth D. Candido, MD). (B) Lateral fluoroscopic view of same two needles as noted earlier (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.) axis (C2) (Figures 3-8). The vertebrae of the cervical spine are unique in that structurally they have variations for a given level. The atlas articulation with the base of the skull is not a true zygapophyseal jointlacking joint capsule or synovium, and without an intervertebral foramen to accommodate an exiting nerve root. Additionally, the atlas and axis share a special articulation between the odontoid of the axis and

anterior arch of the atlas, but there is no posterior articulation of C1-C2. The exiting roots of C1 also lack neural foramina. The articular (not a true zygapophyseal, or “Z” type joint) joint is superior and anterior in orientation for the atlas and axis, with an anterior (the inferior articular facet) to posterior (the superior articular facet) orientation. The vertebral artery exists the foramen magnum medial to the A-O

Fig. 3 – Relationship of vertebral artery, exiting the foramen magnum, medial to A-O joint, and lateral to A-A joint (Figure courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

Fig. 4 – Targets for facet joint-related medial branch injections, middle of the waist line of the articular pillars, and center of the trapezoid (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

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Fig. 5 – Red “dots” denotes the target for needle tip placement for cervical medial branch nerve injections (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

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Fig. 7 – Medial branch nerves of the dorsal rami have been drawn in red ink denoting targets for cervical nerve block injections and lateral oblique view (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

joint and swings laterally to the A-A joint. This has implications (discussed later) for needle placement when contemplating A-O or A-A blocks. Additionally, there are uncinate processes beginning at cervical vertebra 4 (C4) to prevent lateral translation. The posterior cervical spine has 12 muscles that allow for the various ranges of motions one can do from rotary, to flexion and extension of the cervical spine. Attachment sites of these muscles include the base of the cranium, cervical vertebra, spine of the scapula, and the thoracic spine. There are 15 anterior and posterior ligaments that contribute to the stability of the cervical spine itself. The tendon of the splenius capitis muscle is important as the medial branch nerves are held in place along the lateral margins of the vertebral bodies by these structures. With all these structures, there is an additional intricate sensory and motor innervation to the cervical spine. There

are 8 primary cervical nerve roots, with the anterior primary rami of C5-T1 comprising the brachial plexus. A “prefixed” brachial plexus has contributions from C4 as well, whereas a “postfixed” plexus has a contribution from T2 in addition to T-1. The dorsal rami of the superior and inferior spinal nerves give rise to the medial branches, which supply the articular nerve branches to each facet joint. It is the dorsal ramus that provides the sensory information with the ventral ramus serving as the motor branch. In the cervical spine the Cruveilhier plexus, or the posterior cervical plexus, is a network of dorsal primary rami found in the upper cervical posterior spine. The third cervical nerve exits and forms an anastomosis with the first and second cervical nerve.8 C2 and C3 give rise to the greater and lesser occipital nerves, often cited as frequent sources of headache with the greater occipital nerve (GON)—formed from the posterior primary rami of C-2 and the lesser occipital nerve formed from the anterior primary rami of C2 and C3. In cadavers that were examined, the Cruveilhier plexus was found to be deep to the semispinalis capitis muscle, with the suboccipital nerve (C1 dorsal ramus) looping to communicate with the GON (C2 dorsal ramus) being the most frequent variant 65% of sides

Fig. 6 – Lateral oblique view of the targets for needle tip placement for cervical medial branch injections (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

Fig. 8 – Medial branch nerves of the dorsal rami have been drawn in red ink denoting targets for cervical nerve block injections; and posterior view (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

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studied.8 Additionally, 54% of sides had C2 dorsal ramus and the third occipital nerve (TON) (C3 dorsal ramus) interconnection. Communications were found to include the C4 dorsal ramus as well at a lower rate with connections between the semispinalis capitis muscle posteriorly and the semispinalis cervicis muscle anteromedially, but never extending beyond to C5 or more caudally.8 Based on cadaveric analysis, most of the cervical dorsal rami gave off 1 medial branch; however, the cervical dorsal rami gave off 2 medial branches in 27%, 15%, 2%, and 0% at the vertebral level C4, C5, C6, and C7, respectively. The diameters of the medial branches varied from 1.0-1.2 mm, and the average distance from the notch of inferior articular process to the medial branches was approximately 2 mm. Most of the bifurcation sites were located at the medial side of the posterior tubercle of the transverse process. On the analysis of 3-dimensional computed tomography reconstruction images, cervical medial branches (C4-C6) passed through the upper 49%-53% of a line between the tips of 2 consecutive superior articular processes (anterior line). Also, cervical medial branches passed through the upper 28%-35% of a line between the midpoints of 2 consecutive facet joints (midline).9 The medial branch of the dorsal rami courses along the lateral aspect of the vertebral lamina wrapping around to innervate its respective zygapophyseal joint. The medial nerve has a fascial layer that houses it against the vertebra. This is a reason why it is imperative to identify bone during the performance of diagnostic or therapeutic medial branch blocks, and to assure needle-bony contact throughout the procedure(s).

Diagnosis and confounders Multiple structures can be injured resulting in pathologic processes manifesting as cervical spine or neck pain. As a consequence, there is a range of presentations exhibited clinically with pain originating from the zygapophyseal joints of the cervical spine. These patterns of referred pain have been extensively studied, and a firm understanding has been established between pain from the joint and pain from the intervertebral cervical disk. In a classic study conducted by Bogduk et al,10 56 patients who were involved in motor vehicle collisions and who developed neck pain were studied to determine the etiology of their pain. Each patient underwent provocation discography of the cervical intervertebral disks and diagnostic cervical zygapophyseal joint blocks using local anesthetics. They found that the etiology of pain was roughly divided as follows: 1/5 of patients had pain emanating from the intervertebral disks alone, 1/5 had pain emanating from the facet joints alone, 2/5 had pain that was referable to both the disk and the joint, and approximately 1/5 had pain that was not identified as being referable to either the disk or joint. This means that up to 60% (1/5 þ 2/5) of patients manifesting with neck pain after a manual vacuum aspiration would have some involvement of the cervical facet joints.10 The various referred pain patterns and responsible zygapophyseal joint and dorsal rami include occipital C2-C3 joints and C3 dorsal ramus, upper posterior cervical, upper posterolateral or retromandibular C0-C3 joints (C0 represents the atlanto-occipital articulation), middle

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posterior cervical C3-C5 joints and C4 dorsal ramus, lower posterior cervical C4-C6 joints and C5 dorsal ramus, suprascapular C4-C6 joints and C4 dorsal ramus, superior scapular C6-C7 joints and C7 dorsal ramus, midscapular C6-T1 joints and C7 dorsal ramus, shoulder, and upper arm regions11 (Figures 7-9). With these referred pain patterns, a patient may present with cervicogenic headaches that can be suboccipital or temporal in distribution, cervical neck pain, and shoulder girdle pain and which is typically rated as being continual, dull, and achy and of moderate-to-severe intensity (44/10 on a numeric pain rating scale). The distribution can be unilateral or bilateral, but most typically is bilateral with a rate as high as 70% observed.4 Additionally, there is a high prevalence of multiple zygapophyseal levels being involved for a given patient. The most commonly represented facet joints involved in facet joint and medial branch mediated pain appear to be the C3-C4 and C5-C6 levels12 (Figure 11). The first step in establishing a diagnosis involves a thorough history and more importantly a comprehensive physical examination to corroborate subjective patient information. Paravertebral tenderness elicited, in addition to performing passive range of motion maneuvers, and strength testing have a high rate of sensitivity and variable specificity for identifying the zygapophyseal joint that is the source of pain. The most commonly involved joints are C3-C4 and C5-C6 with a lower prevalence of symptomatic C2-C3, C4-C5, and C6-C7.12 In the hands of a more experienced examiner sensitivity and specificity diagnosis increases with the high probability of symptomatic joints being limited to C3-C4 and C5-C6.11,12 It was found that the sensitivity (sensitivity is the proportion of patients with disease who test positive) is 89%-100% with specificity (specificity is the proportion of patients without disease who test negative) being significantly lower and more unreliable.13 Historically, facet joint injections had been used to diagnose zygapophyseal joint pain. Under direct fluoroscopy, targeted joints are injected with small volumes (0.25 mL) of water-soluble, iodine-based contrast dye, which should reproduce the patient’s pain. After that, the joint is then injected with local anesthetic which is typically 1% plain (no added epinephrine) lidocaine that would again reproduce the pain, but if the provocation test with local anesthetic proves

Fig. 9 – The third occipital nerve demonstrated between C2 and C3 (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.)

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Fig. 10 – Needles in place for medial branch injections at C3, C4, and C5 for blockade of segments C3-4 and C4-5 (Photos courtesy: Kenneth D. Candido, MD). positive the patient should have a reduction in pain, and an observed response to a different local anesthetic (“doublediagnostic” type block), perhaps using 0.25% plain bupivacaine should occur as well on repeat confirmation testing.14,15 However, careful analysis has shown that facet joint (interarticular) injections do not confer any advantage in efficacy when compared with medial branch nerve blocks. Furthermore, translating results from an articular injection to determining candidacy for therapeutic radiofrequency (RF)

ablation (RFA) neurotomy is difficult, at best. The results attained from medication bathing the intra-articular structures are likely irrelevant in assuring a given neural target has been anesthetized external to the joint. As such, in light of the potential for needles placed into a cervical facet joint being misplaced into the spinal epidural or subarachnoid spaces, or into the substance of the spinal cord itself, most authorities now advocate for medial branch block injections in favor of the articular joint injections. For determining efficacy, a patient should exhibit a minimum of 80% pain reduction with 1% lidocaine in preinjection painful movements that lasts 2 hours or longer. This is confirmed with a 0.25% bupivacaine injection that must either outlast the duration of the lidocaine injection, or last 3 hours or more with 80% reduction in pain. Patients who fulfill both of these respective criteria represent candidates for advanced therapeutic modalities to prolong analgesia. A false-positive result occurs when a patient has a response to a diagnostic lidocaine injection, but fails to have an appropriate response based on those criteria when a diagnostic bupivacaine block is performed. The false-positive rate was found to be as high as 45% for the cervical spine4 (Figures 10-12).

Pain management interventions: The benefits of RFA

Fig. 11 – Total 5 needles (C2, TON, C3, C4, and C5) each placed through a single local anesthetic skin wheal, stars denote segments most commonly affected by cervical facet joint degeneration (C3-C4 and C5-C6), and TON ¼ third occipital nerve site (Photo courtesy: Kenneth D. Candido, M. D.). (Color version of figure is available online.)

There are multiple cervical spine etiologic pain syndromes that can effectively be treated with different interventional pain relieving modalities. Meta-analysis of the various treatment interventions, however, has yielded suboptimal evidence of efficacy, but the study design may significantly factor into this.16 This is a direct result of most studies being small randomized samples; being retrospective or prospective using small populations of patients; instead of consisting of large prospective, randomized, blinded, and placebo-controlled

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Fig. 12 – Optimal C-arm fluoroscopy angle with steep cephalo-caudal tilt to minimize shadow imposed by mandible for P-A (posterior-anterior) viewing (Photo courtesy: Kenneth D. Candido, MD). (Color version of figure is available online.) studies. Depending on the etiology of pain the interventionalist can use different approaches to provide short term as well as sustained pain relief. It should be pointed out that there appears to be no unique role for the addition of steroids to local anesthetics injected for diagnostic or therapeutic medial branch blocks. In an elegant study, Manchikanti et al17 studied 60 patients with pain on examination believed to be related to the cervical facet joints. In all, 4 groups were created with one group received bupivacaine medial branch blocks alone; a second group of 15 patients received bupivacaine plus sarapin (a spreading agent identified from the Pitcher plant); the third group received bupivacaine plus betamethasone (a glucocorticoid steroid), and the fourth group received all 3 agents administered simultaneously (bupivacaine, betamethasone, and sarapin). There was no difference in efficacy among any of the groups regarding analgesia, which would tend to indicate that steroids (and indeed, sarapin as well) confer no additional advantage to cervical medial branch blocks in pain relief. Before considering interventional therapy, patients typically need to fail conservative treatments including, but not limited to physical therapy, chiropractor treatment, and medicines including nonsteroidal antiinflammatory drugs, membrane stabilizers, local anesthetic creams, gels or patches, or opioids. Evidence is most supportive of medial branch blockade and RFA for patients with diagnosed zygapophyseal joint pain to the exclusion of other confounding diagnoses. Indications for intervention include patients with whiplash injury including both acute and chronic neck pain in a cape-like distribution, neck pain associated with postspinal surgery syndrome, symptomatic degenerative cervical spine changes, cervicogenic headaches, and shoulder pain not related to direct shoulder joint or structural involved. In the acute whiplash injury, setting steroids have been shown to be very effective in reducing the duration of pain, but are likely equally effective given systemically as perineurally. Medial branch blocks are an effective intervention that can be used in cases of neck pain and headache that is refractory

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to conservative measures. As with diagnostic injections noted earlier, therapeutic injections are done with local anesthetics, but with a higher volume employed (0.5 mL vs 0.25 mL per nerve) compared with that used for diagnostic blocks. Steroids like methylprednisolone or betamethasone are regularly used by some practitioners in conjunction with local anesthetics, primarily for their anti-inflammatory properties, but there is no evidence supporting such use. Furthermore, there is always a possibility of engendering some consequence or side-effect owing to corticosteroid use, and as such, the present authors do not advocate for their use for medial branch blocks. Being that 2 spinal level dorsal rami supply sensory innervation for a given zygapophyseal joint, the interventionalist would need to target the symptomatic level in addition to 1 spinal level above. The situation is rather simple at all levels aside from the space between C2 and C3 where the TON resides. For example, to denervate the C3-C4 facet joint, one would need to place 2 needles, one at C3 along the articular pillar in the center of the trapezoid, and another placed at C4, before injection of local anesthetic solution. Imaging during these procedures is mandatory, and can include use of ultrasound, fluoroscopy, or computed tomography scan guidance.16 The gold standard for imaging is use of fluoroscopy to confirm needle placement. The interventionalist can place and maneuver the needle as desired with the added confirmation of using contrast dye to ensure intravascular injection is avoided. The disadvantages compared to use of ultrasound are ionizing radiation exposure, inability to visualize soft tissues, and possible an added expense incurred by use of the contrast. As an alternative ultrasound can be used; this offers the added benefit of using continual imaging and visualization of soft tissues, including most importantly blood vessels. The foramen transversarium houses the vertebral artery, which is situated immediately ventral to the target for performing medial branch blocks. It must be reconciled during the performance of either diagnostic medial branch blocks or therapeutic RF neurotomy. The downside of ultrasound use is the necessity of having an assistant to help guide the injection or adjust the settings on the ultrasound machine, and one may not consistently reliably identify if an intravascular injection has or has not occurred; and ultrasound has been cited as being more technically challenging than fluoroscopy with a steeper learning curve associated with its use.18 However, ultrasound has been found to be as efficacious as fluoroscopy when performing medial branch blockade.19 Patients are positioned in the lateral decubitus position with the affected side upper most with ultrasound-guided techniques as compared with being placed prone with fluoroscopic-guided methods; either of which can be used for unilateral or bilateral joint involvement. A 22-guage 1.53.5-in. sharp-cutting beveled needle with a 301 curve at its distal tip is frequently used in injecting the medial branch of the dorsal rami. The use of a curved-tip needle has, according to the present authors, simplified the ability to direct the needle tip away from an obstruction without the requirement to retract the needle to the skin surface and redirecting, as one would need to do when employing a straight needle. The needle should be advanced until the lamina is engaged (typically at approximately 2-3 cm from the skin surface), at

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which time the interventionalist should guide the needle toward the center of the articular pillar in the trapezoid, while advancing along the vertebra. The structures that are traversed are the skin, fascial layer, muscles, and the various ligaments until the vertebra is reached. As noted, placing a slight angle to the tip of the needle can aid in adding a better access point to the medial branch nerve and also to assure that the needle shaft “hugs” the rounded body of the vertebra. At this point with fluoroscopy use, contrast dye needs to be injected and observed for runoff, indicating the needle as being intravascular that would necessitate needle repositioning. Ultrasound does not require contrast use as the vascular structures are continuously being visualized as hypoechoic structures that can be traced using Doppler ultrasound. After low-volume injection, some patients would have complete resolution of their pain, whereas others may require repeat injections (typically up to 2 sets as discussed earlier). It is recommended by some authorities to not exceed more than 6 injections on an annual basis. For cervicogenic headaches, the TON and GONs should be targeted at C2-C3. The atlanto-occipital joint, which does not have a true facet joint capsule, has also been shown to be a source of cervicogenic headaches. Reproducible pain with contrast dye injection supports the concept that the atlanto-occipital joints contribute to the source of headaches in many individuals. The long-term alternative to repeated local anesthetic injection is continual energy, RFA of the medial branch nerve (neurotomy or rhizotomy). Steps involved are the same as for injections with use of either ultrasound or fluoroscopy (preferred) with the needle attached to an energy source and with an electrode placed into the Teflon-coated needle. Typical needles are 22-gauge, 5 cm long (with a 5 mm active [uncovered by Teflon] tip) or 10 cm long (with a 10 mm active tip). In most individuals, the 5-cm long needle (2 in. long) suffices when using the posterior approach. The present authors favor the posterior approach to needle placement for 2 main reasons. First, the dense posterior neck musculature (semispinalis capitis, splenius capitis,and longissimus capitis) offer superior “holding” capacity for needles placed from posterior-to-anterior than do the lateral neck muscles that need to be traversed to reach the lateral mass targets (sternocleidomastoid and levator scapulae). This has potential implications particularly if one elects to perform provocative motor stimulation before lesioning; the dense musculature minimizes needle displacement from muscle contraction, which is a typical event when the lateral approach is used. Secondly, the approach to the target from posterior-to-anterior places the greatest length of active tip against the vertebral body compared with a lateral approach that only permits the exposed needle tip to contact bone. As such, and as the electrical energy is expressed approximately 2 mm in each direction from the needle shaft and tip, more complete lesioning is assured with a greater surface contact area with the posterior approach than the mere 2 mm exposure to the target afforded by the lateral approach. Needles typically have curves placed by the manufacturer at the distal tip, with the curves facing the open bevel. The use of RFA relies on Ohm’s Law; V ¼ IR, where V ¼ voltage, I ¼ current, and R ¼ resistance. The RFA generator relies on

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assessment of impedance as a surrogate for resistance. Standard impedance levels are measured once the needles are placed on the target, and it is incumbent on the proceduralist to assure that these values are within a certain standard value (generally speaking, o100 Ω; no 41000 Ω). When the medial branch sensory nerve is isolated during the sensory stimulation portion of the procedure, the patient’s pain would be reproduced, which would decrease the likelihood of targeting the incorrect nerve or a large, mixed spinal nerve, for example. During motor stimulation, there needs to be a lack of upper extremity movement, although muscle fasciculation may be seen before moving forward with the ablation at a low set energy (typical values are to set the generator to deliver 801C 490 seconds). Typical contemporary generators may perform multiple lesions at a single time, which drastically improves operating room efficiency by reducing procedure-related time requirements. At this point, the frequency is increased and the exposed (active) tip of the needle is the conduit for ablation of the nerve, RFA is believed to involve modulation of c-fos and mindbomb homolog (MIB-1), although this remains of some considerable theoretical concern and some have suggested that these genes are modulated more by pulsed RF (PRF) more than in continual energy RFA. PRF techniques have also been described, and there is a body of literature favoring its use. PRF is nontissue destructive, in contradistinction with conventional (thermal) RFA. However, in the United States of America, the used of PRF has not evolved into a reimbursable procedure, and hence its use has fallen into disfavor. Patients who undergo RFA (continuous energy-thermal lesioning) treatment do very well with reductions in pain on the order of at least 60%-80% observed and increased effectiveness with repeat treatments.20 Individuals previously unemployed, disabled, or employed, but below baseline were found to have a significant improvement in employment. Reliance on oral medications has been found to be reduced as well with successfully treated cervicogenic headaches.14 Psychiatric diagnoses significantly improved with reduction in pain that included somatization, depression, and anxiety.15 Patients respond very well to both medial branch block injections and RFA, although data are conflicting.16 Studies by Bogduk and Lord were independently conducted and found that an expected duration of RFA of the cervical medial branches should approach 40 weeks when successes are considered and failures are eliminated from statistical consideration.20,21 Even so, it is not uncommon for a patient to require multiple injections or RFA procedures to adequately keep zygapophyseal joint–mediated pain controlled. There are favorable results with decreased frequency of headaches posttreatment allowing for improved functionality on the order of monthly and weekly rates.22 A recent article23 confirmed the essential findings of Bogduk and Lord noted earlier. In that retrospective medical record review of 44 patients who had undergone RFA of cervical medial branches, it was found that at 12 months 63.64% of patients were pain free. Furthermore, the median duration of complete pain relief was 52 weeks. Patients who experienced pain relief had ceased using prescription analgesia by their 6 week review. There were no repeat cervical RF rhizotomies, procedurerelated infections, or unplanned hospital admissions.23

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In New Zealand, a total of 104 patients presenting to 2 pain practices with neck pain were prospectively studied to determine efficacy of one-time and repeat cervical RFA.24 In 74% and 61% of patients there was a successful outcome lasting 17-20 months for the first RFA. Allowing for a repeat RFA, patients maintained relief for a median duration of 20-26 months, with about 60% still having relief at follow-up.24 This would support the prospect of performing repeat RFA treatment in partial responders, or in those who had non-sustained benefit from a first series of procedures. The success of repeated cervical RFA in instances where a first procedure resulted in success has been found in a systematic review to range from 67%-95%.25 A single posterior-lateral approach, similar to that employed by the present authors and demonstrated in the figures given, has been formally studied in the Netherlands. The authors studied 65 patients meeting inclusion criteria and found that this approach resulted in 55.4% of patients deriving relief from the RFA, persisting for 2 months. At a 3-year follow-up, 30% of patients remained symptom free.26 A systematic review of well-conducted studies recently published confirmed that the evidence in favor of using RFA is level II for the long-term effectiveness of RF neurotomy and facet joint nerve blocks in managing cervical facet joint pain.27 Concomitant cervical and lumbar zygapophyseal pain commonly occur as well and outcomes are favorable if they are treated in a staggered fashion. It has been suggested that a failed medial branch block or RFA is considered to be a complication of the procedure, albeit benign, that can occur. Failed RFA can be owing to an incomplete or inadequate RF lesion, to a posterior Cruvelhier plexus innervation of a symptomatic facet joint, or to an unrelated, but co-existing symptomatic pain process. More serious adverse outcomes could occur with accidental intravascular delivery of the local anesthetic and if steroids are added to a local anesthetic, steroid-induced toxicity may be observed.28 It is mandatory to employ an imaging modality to avoid other preventable complications such as intrathecal injection of local anesthetics leading to direct central nervous system toxicity. The interventionalist should always be prepared to properly treat situations involving systemic local anesthetic toxicity. Even under ideal conditions, ablationinduced neuralgia may occur. In a group of 64 patients undergoing RFA of the TON, the incidence of post-RFA neuritis was reported to be 19%, averaging 2.6 months but including one patient having symptoms persisting for 1 year.29

Conclusion Cervical spinal pain is a widespread medical issue, the treatment of which continues to evolve. Although the zygapophyseal joint as a source of pain in the neck and head,30 on an anatomical and neurosensory level is becoming better understood, there remain many with recalcitrant cervical pain. As with any medical interventions there would be patients who tend to do better or worse than others, but having a greater understanding of the zygapophyseal joint would further advance diagnosis and treatment. Both medial nerve

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blockade and more long-term RFA are extremely viable treatment selections that offer outstanding benefits in carefully selected patients. The most recent data collected from retrospective medical record reviews show that approximately two-thirds of patients can expect 12 months of pain-free experiences after RFA of the cervical medial branches.23 The level of evidence in favor of RFA extracted from a large systematic review is II.27 These have been established as the interventions of choice as they have been shown to significantly improve quality of life and functionality in addition to being successful at reducing pain.

refere nces

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