Zygapophysial Joint Blocks and Radiofrequency Ablation
Marzena Buzanowska
William Bonner
Yejia Zhang
Christopher T. Plastaras
Zygapophysial joints (z-joints, also known as facet joints) are true synovial joints in the spine that are part of the three-joint spinal motion complex—paired zygapophysial joints and the intervertebral disk. Although the disk is the primary load-bearing structure, biomechanical studies have shown that the zygapophysial joints can carry up to 33% of the load in a healthy three-joint complex and that this increases when the spine is in an extended position.1 Osteoarthritis (OA) of the zygapophysial joints is related to degenerative disease of the disk, and subsequent disk space narrowing may increase the axial loading carried by the zygapophysial joints up to 70%.2 The prevalence of cervical zygapophysial joint OA has been estimated to be 19% in adults aged 45 to 64 years and 57% in adults aged over 65 years.3 In the lumbar spine, moderate or severe lumbar spine zygapophysial joint OA was present in 36% of adults aged below 45 years, 67% of adults aged 45 to 64 years, and 89% of adults older than 65.4 The earliest pathophysiologic changes in a zygapophysial joint with OA involve the articular cartilage, synovium, and capsule. These changes include pitting of the cartilage, followed by fissuring, fibrillations, and erosions down to the subchondral bone. Progressive cartilage thinning results in joint space narrowing. In the later stages there is involvement of the subchondral bone, which develops bony sclerosis, subchondral cysts, and osteophyte formation at the joint margins.5,6 Each zygapophysial joint and its capsule is innervated by two medial branches of the dorsal primary rami of the spinal nerves, which carry pain signals from the osteoarthritic joints.7 As the correlation between the radiographic presence of OA and pain has not been established,8 a detailed clinical evaluation usually leads to the correct diagnosis. Treatment of pain due to zygapophysial joint OA includes conservative measures such as physical therapy and topical and oral medications. If these modalities fail to relieve pain, interventional options include steroid injection directly into the joint to reduce inflammation, or radiofrequency nerve ablation (RFA). Prior to any RFA procedure, the painful joints are identified by a thorough history and physical exam, and confirmatory injections of anesthetic agents into an awake and alert patient. RFA for the treatment of zygapophysial joint-mediated pain involves the application of high-frequency electric current that heats the tip of a specialized needle and leads to selective destruction of the medial branch nerves that innervate the particular joint.9 The efficacy of RFA has been shown to be improved if two separate diagnostic medial branch blocks provided 85% pain relief for the duration of the anesthetic that was used.10
PROCEDURAL TECHNIQUE
Cervical Zygapophysial Joint Radiofrequency Ablation
Relevant Anatomy
The cervical zygapophysial joints are paired, planar, synovial joints, formed between the inferior articular processes of one cervical vertebra and the superior articular processes of the next.
Zygapophysial joints are formed between the C2 through C7 cervical vertebrae and are located posterior to the intervertebral foramina. The synovial joints between the occiput and C1 and between C1 and C2 are not zygapophysial joints, because they lie in front of the plane of the spinal nerves, and are beyond the scope of this chapter.
Figure 7.1 Illustration of the anatomy of the cervical medial branches: C4, C5, and C6.
The cervical zygapophysial joints angle in a posterocaudal direction in the sagittal plane about 45 degrees.10,11
Cervical zygapophysial joints are innervated by the medial branches of the dorsal primary rami. Each joint receives innervation from two medial branches, which correlate to the levels that make up the joint (i.e., C5-C6 z-joint is innervated by the C5 and C6 medial branches). The typical cervical medial branches wrap around the articular pillar. The C3 medial branch lies along the superior edge of the lateral mass. The C4 and C6 medial branches run along the superior one-third division of their respective lateral masses. The C5 medial branch is located in the middle of the lateral mass. The C7 medial branch is located at the top of the C7 superior articular process. The C1 dorsal ramus has no cutaneous or articular branches. The C2 dorsal ramus has a large medial branch, called the greater occipital nerve, which innervates the posterior scalp. The C3 medial branch splits into a smaller branch, which provides partial innervation to the C3-C4 joint, and a larger branch (the third occipital nerve) that connects with the C2 dorsal ramus and solely innervates the C2-C3 z-joint (see Fig. 7.1).
Step-by-Step Technique
Medial branch block: This diagnostic procedure is performed twice on separate occasions to reduce the false positive rate of a single block paradigm and to improve likely efficacy of an RFA procedure. When the skin is cleansed and draped in a sterile manner, the patient is positioned in either a side-lying or a prone position. The fluoroscope is aligned so that a true lateral view of the cervical spine is obtained, with the desired level being centered in the middle of the screen. The right and left lateral masses and z-joints must be lined up. The target is identified by finding a “centroid” of each lateral mass. A centroid is the location on the lateral mass that is created by connecting the angles of the trapezoid (lateral mass as seen in lateral view under x-ray). A spinal needle is
then placed under x-ray guidance so that the tip of the needle is positioned at the target location. An anteroposterior (AP) view is obtained to confirm that the needle tip is not medial to the lateral border of the articular pillar. Contrast medium is then injected to confirm needle placement. Next, the local anesthetic is injected.10
Radiofrequency ablation: This nerve ablation procedure is performed usually with the patient in a prone position, and with a grounding pad secured to the skin of the leg. The goal is to position the RF needle along the course of the nerve to ensure that the nerve is ablated, while taking into account anatomic variations. When the skin is cleansed and draped in a sterile manner, the fluoroscope is aligned so that an AP view of the cervical spine is obtained. The image intensifier is then tilted caudally and the waist of the articular pillar is visualized. The image intensifier is then placed obliquely toward the symptomatic side in order to create a trajectory view along the lateral mass of the articular pillar. A spinal RF cannula is then inserted, and a lateral x-ray view obtained to confirm that the needle tip is not too anterior and not past the anterior border of the lateral mass. A contralateral oblique view ensures that the tip does not extend into the neural foramen. The cannula is advanced to rest on bone in the anatomic region of the medial branch nerve (see Fig. 7.2). As a practice option, sensory and motor stimulation is performed (by applying electrical stimulation at 50 and 2 Hz, respectively) to ensure that a motor branch of the nerve root is not close to the needle tip. A small amount of anesthetic is injected and the stylet is replaced with the RF probe. The RF machine is then turned on and the needle tip heats up to the desired temperature. The ablation procedure is then performed by maintaining the probe tip at the final temperature of 80°C for 90 seconds. If using the cooled RFA system, the setting is 60°C for 150 seconds. When the process is complete, the needles are removed. The patient is then taken to a recovery area for observation and is subsequently discharged.10
Complications: This procedure is relatively safe when performed following established technique guidelines. The most serious complications arise if the needle is placed incorrectly, for example, into a blood vessel, the intervertebral foramen, or the intrathecal space. A grounding pad must be correctly placed on the patient’s skin to avoid burns. RFA is contraindicated in patients with an active local or systemic infection, a bleeding diathesis, where other joint blocks have been indeterminate or negative, or in the setting of pregnancy. Relative contraindications include anatomic derangements that compromise the safety of the procedure, severe coexisting disease producing significant respiratory or cardiovascular compromise, immunosuppression, and unrealistic patient expectations.
Figure 7.2 X-ray images (A: Lateral view and B: Posterior-anterior view) of the cervical spine depicting the final needle tip in the superior aspect of the C3 and C4 lateral masses where the medial branches course.
Outcome: The patient may have some soreness at the site of injection for the first 24 hours, but afterward will often experience improvement in pain for months to sometimes as long as 2 years.Related posts:
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