Fig. 16.1
Posterior view of the L3–L4 zygapophysial joints. (Arrow) straight surface of the right joint, (AC) articular cartilage, (I) inferior articular process L3, (S) superior articular process L4
Fig. 16.2
Varieties of orientation and curvature of the lumbar zygapophysial joints. (a) Flat joint orientated 60° (L3–L4), (b) curved joint (C shaped) orientated 30° (L2–L3), (c) flat joint orientated 25° (L3–L4), (d) flat joint orientated 75° (L5–S1)
The orientation of a lumbar zygapophysial joint is, by convention, defined by the angle made by the average plane of the joint with respect to the sagittal plane (Fig. 16.2) [31]. Smaller angles (less than 45°) are found more often in the upper lumbar spine. The levels L3–4 to L5–S1 usually show angles about 45–50° [34]. The extent to which a joint can resist forward displacement or rotatory displacement depends on the shape and orientation of the joint. The smaller the angle and the closer the joint is orientated toward the sagittal plane, the less the vertebra can resist forward displacement [31].
In the case of joints with curved articular surfaces, particular portions of the surface are involved in resisting different movements. During rotation the entire articular surface is in contact. Therefore, rotation is well resisted [31].
16.2.1.2 Capsule
Each lumbar zygapophysial joint is enclosed by a fibrous capsule that is about 1 mm thick. At the superior and inferior ends of the joint, the capsule is long and relatively lax and attaches somewhat away from the articular margin [31, 34]. Its laxity accommodates the superior and inferior displacements of the articular process during flexion of the lumbar spine (Fig. 16.3). In a joint in its neutral position, this lax capsule creates subcapsular recesses that extend over the surface of the articular process, at the superior and inferior poles of the joint. In some patients, the anterior synovial recess may extend into the ligamentum flavum. The posterior synovial recess of the lumbar zygapophysial joint often extends beyond the articulating surfaces of the lumbar facets into the posterior fibrous capsule [35]. In both the superior and inferior parts of the capsule, there is a tiny hole that permits the passage of fat during movements of the joint [31]. Anteriorly, the fibrous capsule is replaced by the ligamentum flavum [36].
Fig. 16.3
L4–L5 zygapophysial joint in a spine in an intact cadaver and frozen in situ. The extension causes the tip of the inferior articular process to come in contact with the pars interarticularis of L5 (arrow). The joint capsule is elongated and severely compressed against the pars interarticularis. A richly vascularized meniscoid (*) is projecting into the opening of the superior joint space (Courtesy of W. Rauschning)
16.2.1.3 Intra-articular Structures
Articular cartilage assumes the same concave or convex curvature as the underlying facet. It is thickest over the center of each facet, rising to a height of about 2 mm [31, 37]. The articular cartilage rests on a thickened layer of bone known as the subchondral bone. Age changes and degenerative changes affect the articular cartilage and also the subchondral bone.
There are no particular features of the synovium of the lumbar zygapophysial joints that distinguish it from the synovium of any typical synovial joint. It attaches along the entire peripheral margin of the articular cartilage on one facet and extends across the joint to attach to the margin of the opposite articular cartilage [31].
Two more intra-articular structures are present. These are fat and a structure referred to as meniscoid. The fat fills all leftover space underneath the capsule. It communicates with the fat outside the joint through the foramen in the capsule [31]. From their histology, it is clear that meniscoids are not comparable to a meniscus in the knee. They resemble more the intra-articular structures found in the small joints of the hand [38, 39]. There have been many different interpretations of the meniscoid structures. The most comprehensive study identifies three types [31, 40, 41]. The smallest structure is the connective tissue rim, a thickening of the internal surface of the capsule. The second type of structure is an adipose tissue pad (Fig. 17.3), consisting of a fold of synovium, fat, and blood vessels. The largest structure is fibroadipose meniscoids which also consist of synovium, fat collagen, and blood vessels. The adipose tissue pads and the fibroadipose meniscoids have been interpreted as serving a protective function [31, 40].
16.2.2 Innervation
The zygapophysial joints of the lumbar spine have a dual nerve supply from the medial branches of the dorsal rami of the spinal nerves at the same level and from the level above. The numbering of the spinal nerve and the bone that it crosses is different. The spinal nerve of a particular segment issues from below the vertebra with the same segmental number as the spinal nerve, but the spinal nerve then crosses the superior articular process of the next vertebra.
The medial branch of the dorsal ramus in the lumbar spine courses over the base of the transverse process at the junction of the superior articulating process (Fig. 16.4) [18]. The lumbar dorsal rami carry the same segmental number as the vertebra from which they originate. In their subsequent course, these nerves cross structures and innervate joints below their segment of origin [43]. The course of the medial branches L1–L4 is similar. Each nerve runs in the groove formed by the junction of the transverse process and the superior articular process. Subsequently, each medial branch runs under the mamillo-accessory ligament [44]. This ligament is responsible for the reliable location. It can be large and sometimes ossified, particularly at lower levels [44]. Beyond the ligament, the medial branch sends branches to innervate the zygapophysial joint, multifidus muscle, interspinal muscles, and the interspinous ligaments [45]. There are three branches of the medial branch. The proximal branch hooks around the articular process to supply the facet above. The medial descending branch courses in inferomedial manner to innervate the superior and medial portions of the capsule below plus muscle and skin. The ascending branch supplies the joint above [46]. As a consequence, each zygapophysial joint has a dual nerve supply. For example, the L2 and L3 medial branches innervate the L3–L4 joint. In addition to the joints, the medial branch also innervates the multifidus muscle, the interspinous muscle, and the periosteum [45, 47–49].
Fig. 16.4
Lumbar medial branch anatomy. Left anterior oblique illustration. (L3–S1) spinous processes, (mal) mamillo-accessory ligament, (nr) nerve root, (I) inferior articular process, (S) superior articular process, (sb) superior branch from medial branch, (ib) inferior branch of medial branch, (dr) dorsal ramus, (mb) medial branch (Reproduced from Klessinger [42])
The L5 dorsal ramus crosses the ala of the sacrum. There is no medial branch for L5. The target is the dorsal ramus itself. The medial branch does not arise until the dorsal ramus reaches the caudal region of the L5–S1 joint [49].
The joint capsules and the surrounding structures are richly innervated by encapsulated, unencapsulated, and free nerve endings. Nociceptors fire when the capsule is stretched or subjected to compressive forces [47, 50]. The presence of low-threshold, rapidly adapting mechanosensitive neurons suggests that in addition to transmitting nociceptive information, the facet capsule also serves a proprioceptive function [51]. Nerve fibers have also been found in subchondral bone and intra-articular inclusions of zygapophysial joints, signifying that facet-mediated pain may originate in structures other than the joint capsule [52, 53].
16.3 Physiology
The zygapophysial joints are involved in all principal movements of the spine. Possible movements are axial compression/distraction, flexion/extension, axial rotation, and lateral flexion. Horizontal translation does not occur as isolated movement [36].
In the reflection of the joints as a possible pain source, the applied loads and the restriction of movements are particularly important.
16.3.1 Axial Compression/Distraction
The interbody joints (i.e., the intervertebral disks) are designed as the principal weight-bearing components of the spine. The importance of the zygapophysial joints is discussed controversially. Studies reported that all the compressive force is resisted by the disk [54]. Others found that the zygapophysial joints can bear 28 % or more of vertically applied load [55].
Three conditions lead to a remarkable load to the zygapophysial joints: First, with axial load in combination with a backward movement, the articular facets are driven into each other, and load can be transmitted through the joints [36]. Second, with severe or sustained axial compression, the inferior articular processes can be lowered until their tips impact the laminae of the vertebrae below [56]. Axial loads can be transmitted through the inferior articular process to the laminae. Third, in prolonged standing with a lordotic spine, the joints at each segmental level bear an average of some 16 % of the axial load [54, 57].
In contrast, in a neutral position, the articular surfaces run parallel to the direction of axially applied load. Thus, in a neutral position, they cannot sustain the load. Also, in the conditions of erect sitting, the zygapophysial joints are not impacted [36].
16.3.2 Flexion/Extension
Flexion involves a combination of anterior sagittal rotation and anterior translation. Anterior translation is resisted by the impaction of the superior and inferior facets. In curved joints, the load is concentrated on the anteromedial portions of the facets [59], where commonly age changes are seen. The sagittal rotation component involves tension in the joint capsule. The capsules of the joints contribute about 39 % of the resistance during flexion.
Extension involves posterior sagittal rotation and posterior translation together with the downward movement of the inferior articular process and the spinous process. This movement is limited by bony impaction between the spinous processes [36, 60]. The interspinous ligament buckles and becomes trapped.
16.3.3 Axial Rotation
The zygapophysial joints protect the intervertebral disk from excessive torsion. The inferior articular facets of the upper vertebra will be impacted against its opposing superior articular facet. Because the joint space is quite narrow, the range of movement before impaction occurs is quite small. The capsule of the opposite joint is being stretched. Experimental studies have established that the zygapophysial joints contribute between 42 and 54 % of the torsional stiffness of a segment [36, 61]. The zygapophysial joints provide a substantial buffer during the first 3° of rotation. They must be severely compressed before rotation exceeds the critical range of 3° [36].
16.3.4 Lateral Flexion
Lateral flexion involves a complex and variable combination of lateral bending and rotatory movements [36].
16.3.5 Rotation in Flexion
This is a common movement associated with the onset of back pain. However, studies offer conflicting results and opinions that stem from the complexities of this movement [36].
16.4 Pathological Changes
16.4.1 Degeneration
During life, changes occur to the intervertebral disk and to the zygapophysial joints called spondylosis or osteoarthrosis. These changes are not per se a disease but an expression of the morphological consequences of stress applied to the disk and the joints during life. The incidence of osteoarthrosis is just as great in patients with symptoms as in patients without symptoms [62, 63]. Additional factors must be present to make the zygapophysial joints a pain source.
The degenerative changes are more advanced in the concave superior articular process than in the inferior articular process. It is the backward-facing portion of the facet that resists the forward shear stresses applied to the intervertebral joint during weight-bearing and flexion movements [64]. After the fifth decade, the subchondral bone of the zygapophysial joint gets thinner [65]. The articular cartilage exhibits focal changes. Vertical fibrillation of the cartilage, which reflects the repeated stress, and sclerosis of the subchondral bone plate are common [66]. Severe or repeated pressure may result in erosions and focal thinning of the cartilage (Fig. 16.5). Other regions might exhibit swelling of the cartilage. Where cartilage is lost, fibrofatty intra-articular inclusions may increase in size [66].
Fig. 16.5
Sagittal section through the neuroforamina of a severely degenerated lower lumbar spine of a 70-year-old man. The zygapophysial joints are in a subluxated position due to the loss of segmental height. The pars interarticularis of L5 is being eroded superiorly by the inferior articular process of L4 and inferiorly by the superior articular process of S1 (*). Such pars erosion is a prerequisite for the development of degenerative spondylolisthesis. There is no cartilage in the L5–S1 zygapophysial joint (arrow heads) (Courtesy of W. Rauschning)
Older joints exhibit gross thickening (Fig. 16.6a). The development of osteophytes along the attachment sites of the joint capsule and ligamentum flavum to the superior articular process increases. As a result of repeated stress during rotatory movements, the articular cartilage spreads out to cover and protect the edges of the bony articular process [64].
Fig. 16.6
Examples of magnetic resonance imaging findings concerning the zygapophysial joints. (a) Degenerative changes, (b) synovial cyst of the zygapophysial joint and increased joint volume, (c) asymmetric joint gap, (d) increased joint volume (Reproduced from Klessinger [42])
A progressive decrease of range in movement with age is evident in the entire lumbar spine and in individual intervertebral joints [67, 68].
Zygapophysial joints are frequently affected by osteoarthritis. The arthritis is usually secondary to disk degeneration or spondylosis [69], but in 20 % of cases, it can be totally independent [70]. This condition is believed to be a possible cause of zygapophysial joint pain [71–74].
Inflammatory mediators, such as cytokines, prostaglandins, and neuropeptides, increase within the joint and the dorsal root ganglion in joint inflammation and arthritis [75–77]. Specifically, prostaglandin E2 (PGE2) has been identified as a key mediator of inflammation-induced behavioral sensitivity and increased neuronal excitability [78–80]. Overexpression of MMP-1, induced by interleukin-1β, plays an important role in the inflammatory process of lumbar zygapophysial joint degeneration [81].
16.4.2 Degenerative Disk Disease
The intervertebral disk and the paired zygapophysial joints form a functional unit, and therefore, changes in the disk height are relevant for the load of the zygapophysial joints. The pressure between the facets increases significantly with the narrowing of the disk space [59]. Increased pressure may be a source of pain in patients with reduced disk spaces [59]. Maintenance of disk height is the normal feature of aging. Overt disk narrowing invites the consideration of some process other than aging [64].
One possible process is internal disk disruption. It may lead to disk degradation and disk resorption and is independent of degenerative changes [82]. Degradation of the nucleus of the disk is initiated by an endplate fracture that progressively destroys the nucleus pulposus [2]. Less able to bind water, the nucleus is less able to sustain pressure. In time, the annulus buckles under the load, and the disk loses height, which compromises the function of all joints in the affected segment [2]. As a result, reactive changes occur in the form of osteophyte formation in the zygapophysial joints. Disk narrowing may also predispose zygapophysial joint disease. When the disk becomes narrowed, up to 70 % of the compressive force usually applied to the disk is transferred to the zygapophysial joints [54].
Another reason for a loss of disk height is herniation of disk material. The material that is extruded into the spinal canal can no longer contribute to the disk height. In contrast to degenerative changes, the loss of disk material and disk height occurs within a short time. A gradual adaptation of the involved structures to the new situation is hardly possible. In addition, in case of surgery, sometimes not only the extruded disk material but also parts of the annulus and the central portion of the nucleus are removed. Therefore, patients with a herniated disk and compression of the nerve root suffer not only from radicular pain but also often from zygapophysial pain, which can exacerbate after surgery.
Degeneration and loss of structural integrity of the intervertebral disks have been shown to result in concomitant degenerative changes in the zygapophysial joints [83–85]. The reverse is also true. Degeneration and motion abnormalities at the zygapophysial joints can induce and accelerate degeneration of the intervertebral disks [57, 86, 87]. In a magnetic resonance imaging (MRI) study evaluating the relation between facet joint osteoarthritis and degenerative disk disease, facet joint osteoarthritis was rarely found in the absence of disk degeneration but tended to be most pronounced at spinal levels associated with advanced degenerative disk disease [88].
16.4.3 Synovial Cysts
The term synovial cyst refers to cysts that arise from the zygapophysial joint capsule of the lumbar spine (Fig. 16.6b) [89]. They can be lined with synovium and contain serous, gelatinous, or hemorrhagic fluid [90]. The development is linked to degenerative spondylosis, segmental instability, and perhaps trauma [90, 91]. They are a cause of back pain and radiculopathy, with zygapophysial joint degeneration being the most common cause for cyst formation [81].
16.4.4 Asymmetric Load
A temporary one-sided load is often found in the context of knee or hip problems with appropriate gait disturbance or when walking with crutches. These patients develop often zygapophysial joint pain without structural changes. The reason is unusual strain or overuse of the joint. The treatment prognosis is good.
Facet tropism (asymmetry of the facet angles) may have a relationship to degenerative changes in the spine, either as the cause of degenerative changes or as the result of abnormal forces produced by degeneration [96]. These degenerative changes can be a potential cause of back pain [96]. The clinical significance of facet tropism is not yet well established [96–101]. A difference of facet angles of more than 7° (Fig. 16.6c) is found in 77 % of men and 66 % of women [96]. Facet tropism is a predisposing factor for degenerative changes [102, 103] but does not seem to be associated with zygapophysial joint osteoarthritis [96].
However, there is a positive association between the sagittal orientation of the facets and osteoarthritis [96]. Severe osteoarthritis is associated with back pain, independent of sociodemographics and the narrowing of disk height [104].
Scoliosis is a further condition with asymmetric load. Asymmetric degeneration leads to increased asymmetric load and therefore to a progression of the degeneration and deformity, as either scoliosis or kyphosis. The destruction of zygapophysial joints, joint capsules, disks, and ligaments may create mono- or multisegmental instability and, eventually, spinal canal stenosis [105]. In primary degenerative scoliosis, the degeneration ends up with zygapophysial joint arthritis with hypertrophic capsules, calcification, and osteophytes [105]. The most frequent clinical problem of adult scoliosis is back pain. At the site of the curve, it can be localized either at the apex or in its concavity, and zygapophysial joint pain can be localized in the countercurve from below the curve to above the curve [105].
16.4.5 Spondylolisthesis
Arthritis of the zygapophysial joints with loss of their normal structural support is the major local reason that probably leads to the development of degenerative vertebral slippage [106, 107]. It seems to be evident that morphological abnormalities of zygapophysial joints in the lumbar spine are a significant cause of low back pain and segmental instability and a predisposing factor in the development of degenerative spondylolisthesis [108–110]. One of the most probable sources of pain related to degenerative spondylolisthesis is degenerated and subluxated zygapophysial joints and segmental instability that causes tension in the zygapophysial joint capsule and ligaments [106, 109]. Patients with degenerative spondylolisthesis have more sagittally orientated zygapophysial joints and more significant zygapophysial joint tropism than normal control subjects [109]. The cephalad portion of the zygapophysial joints is more sagittally oriented, and the caudad portion of the zygapophysial joints is more coronally oriented in patients with degenerative spondylolisthesis [111]. Often, an increased joint volume indicates spinal instability [112], or synovial cysts associated with degenerative spondylolisthesis and zygapophysial joint osteoarthritis can be found [113]. Exaggerated fluid in the facets seen on axial MRI (Fig. 16.6d) is significantly suggestive of spondylolisthesis [114].
It is well known, though, that patients with degenerative spondylolisthesis might have sources of pain other than the zygapophysial joints [115]. In particular, the often additionally present spinal canal stenosis causes symptoms. The second pathology often interlinked with degenerative spondylolisthesis is disk degeneration [106, 107].
Spondylolisthesis is a characteristic example of concurrent pain sources in the same patient at the same time. The proportion by which the zygapophysial joints are involved in the complex symptoms is often difficult to diagnose [116].
16.4.6 Injuries
Extension of the spine is limited by the impaction of the inferior articular process on the lamina below. Under this condition, the continued application of an extension force results in a rotation around the impacted articular process and draws the contralateral zygapophysial joint backward. A rupture of the joint capsule is possible [2]. Rotation is also limited by the impaction of the zygapophysial joint. Further rotation also can result in a rupture of the contralateral capsule.
Zygapophysial joint pain is likely to occur with repetitive, chronic strains as might be seen in the elderly or, less frequently, after an acute event such as tearing the joint capsule by stretching it beyond its physiologic limits. This hypothesis is supported by clinical studies indicating a higher prevalence of facet arthropathy in elderly patients [117–119] and numerous cases of lumbar facet arthropathy after high-energy trauma [120]. There are more than two dozen reported cases of lumbar facet dislocation after rapid deceleration injuries [120–123]. The mechanism of injury in these cases is purported to be a combination of hyperflexion, distraction, and rotation [120, 121, 124].
Both in biomechanical studies and in postmortem studies, capsular tears, capsular avulsion, subchondral fractures, intra-articular hemorrhage, and fractures of the articular process have been found [2, 125–129]. Fractures of the zygapophysial joints cannot be detected on plain radiographs and might be too small to be seen in computer tomography (CT) scans [128, 129]. Lesions such as capsular tears cannot be detected by radiography, CT, or MRI. It may be that these lesions underlie zygapophysial joint pain [2].
16.4.7 Other Conditions
16.5 Symptoms
Pain originating from the zygapophysial joints is a lumbar spinal pain [137]. This means that the pain is arising in an area between the lateral borders of the erector spinae at any lumbar level. The pain results from noxious stimulation and is therefore a somatic pain. Somatic pain must be distinguished from visceral pain and from neurogenic pain. Neurogenic pain results from damage or irritation of the axons or cell bodies of a peripheral nerve. Radicular pain is a typical example of neurogenic pain. Zygapophysial joint pain is often associated with pain in the buttock or in the leg. However, in this case, it is a somatic referred pain and not a radicular pain. Referred pain is perceived in a region innervated by nerves other than those that innervate the actual source of pain [2, 36]. Referred pain occurs because of a misperception of the region of the signal that reaches the brain by a convergent sensory pathway [2]. Somatic referred pain is perceived deeply. It is diffuse and hard to localize and it is aching in quality [138].
The joint capsule seems to be more likely to generate pain than the synovium or articular cartilage. There is considerable overlap between all lumbar facet joints, with the referral pattern being more widespread and variable in patients with chronic pain than in asymptomatic volunteers [1].
The zygapophysial joints meet all requirements that are necessary to be a possible pain source: They are well innervated by the medial branches, and free nerve endings are found in the joint capsules (see Sect. 16.2.2). In both patients and volunteers, mechanical stimulation or chemical stimulation of the joints with injection of hypertonic saline or with a contrast medium produces back pain and referred pain identical to that commonly seen in patients [47, 70, 139]. Pain can be relieved by anesthetizing one or more of the lumbar zygapophysial joints. Therefore, like other synovial joints in the human body, the zygapophysial joints represent a potential pain generator in patients with chronic low back pain.
Often, the patient can localize the center of zygapophysial joint pain at a specific level, unilateral or bilateral. Sometimes tenderness is evident over the affected joint [140]. Additionally, referred pain with diffuse borders is present. It occurs predominantly in the buttock and in the thigh in a nondermatomal distribution. Radiation below the knee can occur, even as far as the foot [70, 141]. All of the lumbar facet joints are capable of producing pain that can be referred into the groin, although this is more common with lower facet joint pathology [1]. Pain emanating from upper facet joints tends to extend into the flank, hip, and upper lateral thigh, whereas pain from the lower facet joints is likely to penetrate deeper into the thigh, usually laterally and/or posteriorly [1].
Pain at the beginning of a movement is typical for pain of joint origin. Therefore, the zygapophysial joints often hurt when moving from a sitting to a standing position or while sleeping when turning from one side to the other. Morning stiffness with difficulty to put on socks in a standing position and pain early in the morning that is relieved during the next hours and with walking will be reported often. The considerations of the normal movements (Sect. 16.3) allow one to form opinions regarding the movements that cause pain. Twisting or rotational movements, extension, and rotation in flexion are more likely to increase pain. Sitting with a round back and a relaxed musculature results in a substantial load for the joints. Also the monotonous seating position in a car might be a strain on the joints.
An acute onset of a sharp, penetrating low back pain with immobilization of the lumbar spine (acute locked back) is called Hexenschuss (witch’s shot) in German. This term illustrates the medieval idea that diseases are inflicted to people through an arrow shot (Fig. 16.7) by supernatural beings (e.g., witches, elves). Even today, the pain sometimes comes so unexpectedly out of a normal movement that an explanation seems to be difficult.
Fig. 16.7
Illustration of a Hexenschuss on a print by Johann Zainer around the year 1489/1490. Woodcut from the Tractatus von den bösen Weibern, die man Hexen nennt by Ulrich Molitor
And indeed, the cause remains speculative. However, theories have been advanced involving the concept of meniscal entrapment [2]. Upon flexion, these meniscoid structures (Sect. 16.2.1) are trapped in the subcapsular pockets of the joint [142]. This condition might be amenable to manipulative therapy.
The description of the pathological changes of the zygapophysial joints (Sect. 16.4) makes it clear that zygapophysial joint pain is often only one component of a more complex syndrome. Spinal canal stenosis is often symptomatic with neurogenic claudication and radiculopathy and, at the same time, pain deriving from the zygapophysial joints. However, back pain from the zygapophysial joints can occur together with radicular pain or even with a radiculopathy if the spinal nerve is irritated or compressed by an additional pathology, like a herniated disk, neuroforaminal stenosis, or a synovial cyst.
16.6 Diagnosis
16.6.1 Clinical Findings
No historic or physical examination variables exist to identify a zygapophysial joint as the pain source [143, 144]. Target joints might be identified by the pain pattern, local tenderness over the area, and provocation of pain with deep pressure. The neurological examination is usually normal. When performing the straight leg rise test (Lasègue’s sign), the patient often experiences back pain. However, there should be no sciatic pain.
Revel et al. [118] identified seven variables associated with a positive response to facet joint anesthesia: age greater than 65 years and pain not exacerbated by coughing, not worsened by hyperextension, not worsened by forward flexion, not worsened when rising from forward flexion, not worsened by extension-rotation, and well relieved by recumbency. However, subsequent investigations have also failed to corroborate the findings of Revel et al. [118].
Of course, the clinical examination serves to delineate zygapophysial joint pain from other pain sources. As shown above (Sect. 16.5), zygapophysial joint pain appears often in combination with other pathologies (e.g., spinal canal stenosis, spondylolisthesis, or a herniated disk).
16.6.2 Radiologic Findings
The prevalence of abnormal zygapophysial joint changes on radiologic imaging depends on the age and presence of symptoms in the study population, the imaging modality used, and the threshold use for rendering a diagnosis of abnormal. In studies conducted in patients with low back pain, the incidence of degenerative facet disease on computed tomographic scanning ranges from around 40 % in some studies [73, 145] to upward of 85 % in others [146]. MRI is considered to be somewhat less sensitive than CT imaging in detecting degenerative facet changes [146–148], although several studies conducted in chronic low back pain patients found both the sensitivity and specificity of MRI to be more than 90 % compared with those of CT [88, 147].
On plain radiographs, osteoarthrosis (Fig. 16.8) appears as commonly in asymptomatic individuals as in patients with back pain [63, 149]. In addition, CT scans do not have a diagnostic value for lumbar zygapophysial joint pain [150].
Fig. 16.8
Plain radiography with severe osteoarthrosis L4–L5
Particularly striking results in MRI (Fig. 16.6) can be helpful to identify the level of the pain source. An increased joint volume indicates spinal instability [112].
In summary, the evidence in the literature does not support the routine use of radiologic imaging to diagnose zygapophysial joint pain.
16.6.3 Medial Branch Blocks
A detailed description of the technique of medial branch blocks (Fig. 16.9), the evaluation of results, and the validity is given in Chap. 33.
Fig. 16.9
AP view of needles in position for an L4 medial branch block and L5 dorsal ramus block after application of a contrast medium (Reproduced from Klessinger [151])
Medial branch blocks are a diagnostic tool. They are used to test if the pain stems from a zygapophysial joint because the medial branch innervates the joint. For this reason medial branch blocks are also referred to as zygapophysial joint blocks or facet joint blocks. The fundamental indication for medial branch blocks is the desire to know if the zygapophysial joints are the pain source. Diagnostic lumbar zygapophysial joint nerve blocks are recommended in patients with suspected zygapophysial joint pain. Of course, the response must affect the management. The only validated treatment for pain mediated by the medial branches is radiofrequency neurotomy [152].
Because the singular reason for performing diagnostic medial branch blocks is to obtain information, the evaluation of the patient’s response is essential. A positive response to a block is complete relief of that part of the pain that the blocks are expected to provide relief for the duration commensurate with the expected duration of the local anesthetic’s effect. If more than one pain source is known, only a proportion of the pain will be relieved [151].
Lumbar medial branch blocks are the most thoroughly validated of all spinal interventional procedures [153, 154]. Single diagnostic blocks are not valid because they carry an unacceptable high false-positive rate of 25–45 % [8, 155–159]. In order to reduce the likelihood of responses being false positive, controlled blocks are mandatory [152]. Uncontrolled blocks or intra-articular blocks lack validity [8]. In addition, false-negative results after medial branch blocks are reported [160]. For a detailed discussion on false-positive and false-negative blocks, see Chap. 33.
The degree of relief that should occur after medial branch blocks remains contentious [161]. Ideally, diagnostic blocks should produce complete relief of pain or near-complete relief. This would occur only when the patient’s sole or principal source of pain lies in the joints innervated by the nerves blocked. Some investigators, however, use a more liberal criterion, such as >50 % relief of pain. This criterion allows medial branch neurotomy to be used to provide substantial, but not necessarily complete, relief of pain, which is nevertheless clinically worthwhile [8]. Adopting lesser diagnostic criteria admits more patients for treatment, but the outcomes are poorer. The implication is that physicians will be treating more patients but not achieving optimal outcomes. Adopting more stringent diagnostic criteria admits fewer patients for treatment, but the outcomes achieved are of greater quality (see discussion in Chap. 33).
16.6.4 Arthrography
Arthrography is the demonstration of the internal contours of the joint by injecting a contrast medium [162]. Although various interesting features of a zygapophysial joint can be demonstrated, none of these features has been shown to be diagnostic of any disorder, and none has been shown to determine if the joint is a source of pain. Consequently, lumbar zygapophysial arthrography has no established diagnostic value [162].
16.6.5 Intra-articular Blocks
In this procedure, a local anesthetic is injected into the joint. The objective is to test if anesthetizing a particular joint relieves the patient’s pain. The validity of intra-articular blocks of the lumbar zygapophysial joints has never been tested and has never been established [8, 163, 164]. For intra-articular blocks, there is no consequent treatment [163].
Moreover, several advantages of medial branch blocks exist [152]: Medial branch blocks are easier to perform. Entering a narrow joint space can be difficult. Sometimes osteophytes or degenerative changes may block the entry. Medial branches are safer because bone prevents overpenetration of the needle and entering the spinal canal. Target nerves can be anesthetized with different agents whose duration of effect is known. If the response to medial blocks is positive, radiofrequency neurotomy is a therapeutic utility with predictive validity [151].
16.7 Therapy
16.7.1 Conservative Treatment
No specific conservative treatment for zygapophysial joint pain exists. Patients with zygapophysial joint pain are treated in the same way as patients with low back pain emerging from a different pain source. There are no clinical studies specifically assessing pharmacotherapy or noninterventional treatment for lumbar arthropathy [1].
The treatment of low back pain (and also of zygapophysial joint pain) consists of a multimodal approach comprising conservative therapy, medical management, procedural interventions, and, if indicated, psychotherapy. Nonsteroidal antiinflammatory drugs are widely considered first-line drugs for the treatment of low back pain, with little evidence to support one particular drug over another [165–167].
16.7.2 Radiofrequency Denervation
Guidelines only exist for radiofrequency denervation of the zygapophysial joints, published by the International Spine Intervention Society [43]. Radiofrequency denervation is the direct consequence after the diagnosis of zygapophysial joint pain was validated by controlled medial branch blocks, and it is the only validated treatment for pain mediated by the medial branches [152].
Percutaneous denervation procedures offer pain relief by denervation of the nerves that innervate painful joints. It is a percutaneous therapeutic procedure in which a radiofrequency electrode is used to coagulate one or more of the medial branches of the lumbar dorsal rami, or the L5 dorsal ramus, in order to relieve back pain mediated by these nerves.
For medial branch neurotomy to be anatomically accurate and effective, the electrodes should be placed parallel to the target nerve. Also, lesions should be placed along the maximal available length of the nerve to optimize duration effect [8]. Therefore, exact anatomic knowledge is essential.
Medial branch neurotomy is performed in patients experiencing pain for at least 3 months and in those who did not respond to conservative treatment. Controlled medial branch blocks are mandatory as a diagnostic test to prove that the target nerve is responsible for the pain. Radiofrequency neurotomy provides good evidence-based results whenever patients have been selected correctly and when anatomically accurate surgical techniques have been used.
Thermal radiofrequency neurotomy is a procedure distinct from pulsed radiofrequency or dorsal root ganglion radiofrequency. Thermal radiofrequency deliberately produces a lesion in the target nerve by denaturing its constituent proteins at the site at which the electrode is applied. The other procedures do not do so [43].
16.7.2.1 Patient Selection
The optimal patient for medial branch neurotomy is one who has been experiencing pain for at least 3 months and whose pain did not respond to conservative treatment. The patient should have a realistic expectation. Previous surgery does not preclude neurotomy [168, 169]. Repeat radiofrequency neurotomy after recurrence of pain is possible [170]. It is quite safe to coagulate one or two nerves, but it is not known how many more nerves can be coagulated with safety.
For various reasons, medial branch blocks are the only acceptable and validated diagnostic test as an indication for radiofrequency neurotomy [8]. Medial branch blocks have been validated for validity [171], target specificity [172], and construct validity [173]. Patients with positive responses to controlled blocks can expect to have substantial and lasting responses to medial branch neurotomy [173]. Uncontrolled blocks or intra-articular blocks lack validity [8].
16.7.2.2 Contraindications
Absolute contraindications for radiofrequency exist in patients unwilling or unable to consent to the procedure, patients with systemic infection or bleeding diathesis, or those on anticoagulants with a high risk of bleeding and pregnancy. Relative contraindications exist in patients using pacemaker equipment, after immunosuppression, in patients with unrealistic expectations, and in uncooperative patients [43].
16.7.2.3 Technique
For radiofrequency neurotomy, a high-frequency electrical current is alternating between a large surface area on a ground plate and a small area on the uninsulated tip of the electrode. The electrical field becomes denser at the electrode tip, and therefore, charged molecules around the tip start to oscillate [174]. Where the current is strong enough, this oscillation heats the tissues sufficiently to coagulate them. The volume of the tissue assumes the form of a spheroid. Coagulation occurs principally in a radial direction perpendicular to the long axis of the electrode [175, 176]. The dimensions of the lesions generated are proportional to the length and the width of the electrode. As a rule, in the radial direction, tissues up to 1.6 or 2.3 electrode-widths away from the electrode surface are coagulated [43, 175]. For practical implication, it is important to know that the electrode does not reliably coagulate in the distal direction. Therefore, electrodes that are placed perpendicular to the nerve may miss coagulating the nerve. Consequently, the electrode must be placed parallel to the target nerve [175, 176]. Because the lesion size is proportional to the width of the electrode, small-gauge electrodes should be avoided.
The size of the lesion also depends on the temperature and duration of coagulation. Coagulation starts at a temperature of 65 °C [175, 176]. The volume of the lesion expands as the temperature increases to 80 °C. The optimal duration of coagulation lies between 60 and 90 s at 80 °C. During neurotomy, the temperature should be increased slowly [177].
Several ways exist in which radiofrequency neurotomy is currently practiced [178]. In this overview the technique recommended by the International Spine Intervention Society is described [43]. A steep caudocephalad axial tilt of the fluoroscopy beam along with a 20° lateral tilt is used [43]. The cannula can be positioned precisely parallel to the target nerve. However, the appearance of the vertebral structures might be unusual. A spinal needle inserted primarily as a guide might be needed. The distance from skin to the target nerve might be long (Fig. 16.10).
Fig. 16.10
Illustration of a lateral view of the lumbar spine. The optimal trajectory of the electrode with an insertion point below the target area. (L3–L5) vertebral body, (I) inferior articular process, (S) superior articular process (Reproduced from Klessinger [42])
Lumbar medial branch neurotomy is performed as an outpatient procedure. The patient is placed prone on a radiolucent fluoroscopy table. The patient’s back is prepared and draped in a sterile manner. An adhesive grounding pad is placed on the upper back and connected to the radiofrequency generator. Generally, no sedation, systemic analgesia, or premedication is required. The procedure can be performed under local anesthesia.
The technique is analogous in all lumbar levels. Only the terminology is different. The L5 dorsal ramus is itself targeted where it crosses the ala of the sacrum instead of its medial branch. One way to find the medial branch is to perform a medial branch block using a standard technique (Sect. 16.6.3 and Chap. 36) and leave the block needle in place. It can be used for the administration of local anesthetics. The tip of the needle will always be pointing to where the target nerve lies irrespective of the type of fluoroscopic views used. The target point is the lateral surface of the superior articular surface just above its junction with the root of the transverse process. The tip of the electrode must be placed proximally from the mamillo-accessory ligament (Fig. 16.5). At the sacrum, the mamillo-accessory ligament is rudimentary.
At all levels, the electrode needs to be as closely parallel to the nerve as possible. Typically, it needs to be 15–20° oblique to the sagittal plane and it must be inserted somewhere below the target level (Fig. 16.10). Sometimes multiple parallel placements of the electrode are necessary to coagulate the nerve properly. As a larger gauge electrode makes larger lesions, an 18-G electrode with a 10-mm tip is recommended.
The accurate placement of the needle and the electrode must be documented with hard copy films, images on paper, or digital storage (Fig. 16.11). Now the nerve and the surrounding tissue can be anesthetized. The lesion is made by increasing the temperature slowly until it reaches 80 °C. This temperature is maintained for 60–90 s.
Fig. 16.11
Different views of an electrode placed for an L4 medial branch neurotomy. (a) Anteroposterior view, (b) corresponding oblique view, (c) anteroposterior view of an electrode placed for an L5 medial branch neurotomy
The radiofrequency electrode includes the possibility of nerve stimulation, with sensory and motor capabilities, which allows the precise localization of the target nerve. However, in the guidelines of the International Spine Intervention Society, electrical stimulation is considered unnecessary [43].
For lumbar radiofrequency medial branch neurotomy, several theoretical risks apply. These include hematoma, infection, and allergic reactions to local anesthetics. Provided that the electrodes are placed correctly, they penetrate only the skin and posterior back muscle. The spinal nerve and the ventral ramus lie more anterior. Skin burns should not be a risk when a correct ground plate is used. In the literature, no reports of adverse effects can be found [179, 180]. Examples from medicolegal proceedings are known.
16.7.2.4 Results
A comprehensive narrative review of lumbar medial branch neurotomy was presented by Bogduk et al. [8]. Two main problems in the assessment of studies were described: (1) a technique without parallel needle placement and (2) an inconsistent patient selection [8].
Considering the historical development of radiofrequency neurotomy (Sect. 16.1.1), it is obvious that different techniques were used, which cannot be compared with one another. The position of the electrode plays an essential role. The earliest studies with the technique described by Shealy in 1974–1976 [14–17, 181] claimed good success even if it was not possible to coagulate the nerve with the described technique. In the later study of Leclaire et al. [182], the operative technique was not described. The outcome was poor. Negative results were also found in the study of van Wijk et al. [183]. Again, an inaccurate surgical technique was used [184].
In other studies, patient selection was questionable. Van Kleef et al. [185] did not select patients on the basis of controlled medial branch blocks but did require 50 % pain relief after single diagnostic blocks. A low success rate with a short duration was the result. Nevertheless, active treatment was superior to placebo treatment. Nath et al. [186] included patients with different pain sources. Controlled blocks and a correct technique were used. Complete and enduring pain relief was not reported because patients still had other sources of persisting pain. However, for the pain for which patients were treated, the study showed significant improvements after radiofrequency neurotomy compared with sham treatment. Another study [187] designed to test pulsed radiofrequency showed that conventional radiofrequency neurotomy was significantly more effective than sham treatment.
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