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Interventional pain and spine specialist

The facet joints are a pair of joints in the posterior aspect of the spine. Although these joints are most commonly called the facet joints, they are more properly termed the zygapophyseal joints (abbreviated as Z-joints), a term derived from the Greek roots zygos, meaning yoke or bridge, and physis, meaning outgrowth. The term facet joint is a misnomer because the joint occurs between adjoining zygapophyseal processes, rather than facets, which are the articular cartilage lining small joints in the body (eg, phalanges, costotransverse and costovertebral joints). This joint is also sometimes referred to as the apophyseal joint or the posterior intervertebral joint.

As is true of any synovial joint, the facet-joint is a potential source of pain. In fact, the facet-joint is one of the most common sources of low back pain (LBP). The first discussion of the facet-joint as a source of LBP was by Goldwaith in 1911. (1) In 1927, Putti (2) illustrated osteoarthritic changes of facet-joints in 75 cadavers of persons older than 40 years. In 1933, Ghormley(3)  coined the term facet syndrome, suggesting that hypertrophic changes secondary to osteoarthritis of the zygapophyseal processes led to lumbar nerve root entrapment, which caused LBP. In the 1950s, Harris and Mcnaz (4) and McRae (5) determined that the etiology of facet-joint degeneration was secondary to intervertebral disc degeneration. Hirsch et al were later able to reproduce LBP with injections of hypertonic saline solution into the facet-joints, thus affirming the role of the facet-joints as a source of LBP (6)

Functional Anatomy

The spine is composed of a series of functional units. Each unit consists of an anterior segment, which is made up of 2 adjacent vertebral bodies and the intervertebral disc between them, and the posterior segment, which consists of the laminae and their processes. One joint is formed between the 2 vertebral bodies, whereas the other 2 joints, known as the facet-joints, are formed by the articulation of the superior articular processes of one vertebra with the inferior articular processes of the vertebra above. Thus, the facet-joints are part of an interdependent functional spinal unit consisting of the disc-vertebral body joint and the 2 facet-joints, with the facet-joints paired along the entire posterolateral vertebral column.(7)

Facet joints are well innervated by the medial branches of the dorsal rami. In the thoracic and lumbar spine, the facet joints are in­nervated by medial branches of the dorsal rami of the spinal nerves except at L5 lev­el (8). After the medial branch splits off from the dorsal ramus, it courses caudally around the base of the superior articular process of the level below toward that level's Z-joint (e.g., the L2 medial branch wraps around the L3 superior articular process to approach the L2-L3 facet-joint). The medial branch then continues in a groove between the superior articular process and transverse process (or, in the case of the L5 medial branch, between the superior articular process of S1 and the sacral ala of S1, which is the homologous structure to the transverse processes of the lumbar vertebrae). As it makes this course, the medial branch is held in place by a ligament joining the superior articular process and the transverse process, termed the mamillo-accessory ligament (MAL).

The MAL is so named because it adjoins the mamillary process of the superior articular process to the accessory process of the transverse process. The MAL is clinically important because it allows precise location of the medial branch of the dorsal ramus using only bony landmarks, which is essential for fluoroscopically guided procedures.

After passing underneath the MAL, the medial branch of the dorsal ramus gives off 2 branches to the nearby facet-joints. One branch innervates the facet-joint of that level, and the second branch descends caudally to the level below. Therefore, each medial branch of the dorsal ramus innervates 2 joints—that level and the level below (e.g., the L3 medial branch innervates the L3-L4 and L4-L5 facet-joints). Similarly, each facet-joint is innervated by the 2 most cephalad medial branches (e.g., the L3-L4 facet-joint is innervated by the L2 and L3 medial branches). Medial branch also innervates the multifidus, interspinales, and intertransversarii mediales muscles, the interspinous ligament, and, possibly, the ligamentum flavum. (9)

This has several important clinical implications. First, pain relief from anesthetizing the medial branch does not necessarily implicate the facet-joints as the primary pain generator, because one of the other structures innervated by the medial branch may have been the pain generator. Second, denervation of the medial branch by RFA may affect the nerve supply to the multifidus muscle. This is important because lumbosacral radiculopathy is often another consideration in the differential diagnosis of LBP.

The L5 dorsal ramus divides into me­dial and lateral branches, with the medi­al branch continuing medially, innervat­ing the lumbosacral joint.

Pathogenesis

As with any synovial joint, degener­ation, inflammation and injury of facet joints can lead to pain upon joint motion. Pain leads to restriction of motion, which eventually leads to overall physical decon­ditioning. Irritation of the facet joint in­nervation in itself also leads to secondary muscle spasm. It has been assumed that degeneration of the disc would lead to as­sociated facet joint degeneration and sub­sequent spinal pain. These assumptions were based on the pathogenesis of degen­erative cascade in the context of a three joint complex that involves the articula­tion between two vertebrae consisting of the intervertebral disc and adjacent fac­et joints, as changes within each mem­ber of this joint complex will result in changes in others (10, 11). It was also the view of Vernon-Roberts and Pi­rie (12) that disc degeneration causes os­teophyte formation and facet joint chang­es, because facet joints at relatively normal disc levels are either normal or only slight­ly degenerate.

The Facet joint is a common pain generator in the lower back. The 2 common mechanisms for this generation of pain are either (1) direct, from an arthritic process within the joint itself, or (2) indirect, in which overgrowth of the joint (e.g., facet joint hypertrophy or a synovial cyst) impinges on nearby structures. (13)

The Facet-joints are diarthrodial joints with a synovial lining, the surfaces of which are covered with hyaline cartilage, which is susceptible to arthritic changes and arthropathies. Repetitive stress and osteoarthritic changes to the facet joint can lead to zygapophyseal hypertrophy. Like any synovial joint, degeneration, inflammation, and injury can lead to pain with joint motion, causing restriction of motion secondary to pain and, thus, deconditioning. In addition, facet-joint arthrosis, particularly trophic changes of the superior articular process, can progress to narrowing of the neural foramen. In addition, as is the case for any synovial joint, the synovial membrane can form an outpouching and, thus, a cyst. Facet-joint cysts are most commonly seen at the L4-L5 level (65%), but they are also seen at the L5-S1 (31%) and L3-L4 (4%) levels. These synovial cysts can be clinically significant, particularly if they impinge on nearby structures (e.g., the exiting nerve root).

Facet-joint hypertrophy or a synovial cyst can also contribute to lateral and central lumbar stenosis, which can lead to impingement on the exiting nerve root. Thus, facet-joint pain can occasionally produce a pain referral pattern that is indistinguishable from disc herniation.

Numerous other causes, including rheumatoid arthritis, ankylosing spondy­litis and capsular tears, etc., also have been described as sources of facet joint pain (14).

Facet joints have been implicated as responsible for spinal pain in 15% to 45% of patients with low back pain (15), 54% to 67% of patients with neck pain and 48% of patients with thoracic pain in controlled stud­ies. These figures were based on respons­es to controlled diagnostic blocks of these joints, in accordance with the criteria es­tablished by the International Associa­tion for the Study of Pain

Diagnosis

Clinical

Establishing a diagnosis of lumbosacral facet syndrome is difficult because the findings are nonspecific and correlation between the history and physical examination findings is poor. However, obtaining a detailed history and performing a physical examination help rule out other entities and assist with guiding the examiner in establishing the diagnosis of facet-joint–mediated LBP.

Although no single sign or symptom is diagnostic, Jackson et al demonstrated that the combination of the following 7 factors was significantly correlated with pain relief from an intra-articular facet-joint injection (16):

1. Older age

2. Previous history of LBP

3. Normal gait

4. Maximal pain with extension from a fully flexed position

5. The absence of leg pain

6. The absence of muscle spasm

7. The absence of exacerbation with a Valsalva maneuver

Facet-joint pathology should be considered if the patient describes nonspecific LBP with a deep and achy quality that is usually localized to a unilateral or bilateral Paravertebral area.

The common referral areas for facet-joint–mediated pain are flank pain, buttock pain (often extending into the posterior thigh, but rarely below the knee), pain overlying the iliac crests, and pain radiating into the groin.

The pain is often exacerbated by twisting the back, by stretching, by lateral bending, and in the presence of a torsional load. Some patients describe their pain as worse in the morning, aggravated by rest and hyperextension, and relieved by repeated motion. Often, this lumbosacral facet syndrome may occur after an acute injury (e.g., extension and rotation of the spine), or it may be chronic in nature.

Unlike other lumbar spine pathologies such as disc herniation, facet-joint–mediated pain likely will not worsen with an increase in intra-abdominal and thoracic pressure. Therefore, worsening of pain with coughing, laughing, or a Valsalva maneuver is suggestive that the facet-joint is not the primary pain generator.

Examination

Sensory examination: Sensory examination (i.e., light touch and pinprick in a dermatomal distribution) findings are usually normal in persons with facet-joint pathology.

Muscle stretch reflexes: Patients with facet-joint–mediated LBP usually have normal muscle stretch reflexes. Radicular findings are usually absent unless the patient has nerve root impingement from bony overgrowth or a synovial cyst.

Straight leg–raise test: This maneuver is usually normal for facet-joint–mediated pain. However, if facet-joint hypertrophy or a synovial cyst encroaches on the intervertebral foramen, causing nerve root impingement, this maneuver may elicit a positive response.

Diagnostic blocks

It has been postulated that for any structure to be deemed a cause of back pain, the structure should have been shown to be a source of pain in patients, using diagnostic techniques of known reliability and validity (25). The diagnostic blockade of a structure with a nerve supply with the ability to generate pain can be performed to test the hypothesis that the target structure is a source of a patient’s pain

The choice between intraarticular blocks and medial branch blocks is to some extent preference and training of the physician. However, various considerations apply in choosing either intraarticular injection or medial branch. Intraarticular injections are more difficult and time consuming than nerve blocks because they require accurate placement of the needle within the joint cavity with care not to over distend the joint. In contrast, medial branch blocks are expeditious and carry no risk of over distention. Furthermore, at times joint entry may be impossible because of the severe age related changes or post traumatic arthropathy; no such processes affect access to the nerves .Significant leakage of intraarticular injected fluid into epidural space and spillage over to the nerve roots has been described. With appropriate care this is minimal with medial branch blocks. Finally, intraarticular blocks are appropriate if intraarticular therapy is proposed but if radiofrequency therapy is proposed, medial branch blocks become the diagnostic procedure of choice. In addition, in the past only intraarticular injections were considered as therapeutic. However, recent evidence has shown that medial branch blocks have better evidence for the therapeutic effectiveness than intraarticular blocks (17).

 

Valid information is only obtained by performing controlled blocks, either in the form of placebo injections of normal saline or comparative local anesthetic blocks, in which on two separate occasions, the same joint is anesthetized using local anesthetics with different durations of action. . In a double-block protocol, the patient is given an injection with a short-acting anesthetic (e.g., lidocaine) and records the duration of pain relief in a diary. On a follow-up visit (typically 1-2 wk later), a second injection is performed, using an anesthetic with a different duration of action (e.g., bupivacaine, which has a longer half-life than lidocaine), and the patient again should chart pain relief in a diary. A patient is diagnosed as having a positive block if they receive pain relief (typically >80%) for both injections for a length of time corresponding to the duration of action of the medication. (18, 19,20) Given the dual innervation of each Z-joint, one must anesthetize or block the cephalad and subadjacent medial branches (eg, anesthetize the L3 and L4 medial branches for the L4-L5 Z-joint). Injections are diagnostic if patients report significant relief of symptoms, usually at least a 50% reduction in pain.

Lab Studies

Laboratory studies are not generally necessary for the diagnosis of lumbosacral facet joint syndrome.

Imaging Studies

Plain radiography

• Plain radiographs are traditionally ordered as the initial step in the workup of lumbar spine pain. The main purpose of plain films is to determine underlying structural pathologic conditions. These studies are not generally recommended in the first month of symptoms in the absence of red flags. An exception to this would be if the low back symptoms are related to a sports injury and a fracture is suggested.
• Three views are commonly obtained, including an anteroposterior (AP), lateral, and oblique; however, the utility of oblique views has been questioned.
• Plain radiographs may reveal degenerative changes, but these findings have not been found to correlate with facet-joint–mediated pain.

Bone scanning

• Bone scanning can be helpful when a tumor, infection, or fracture (occult or traumatic) is suggested.
• Bone scanning is not usually indicated in the initial workup, and the results are normal in persons with lumbosacral facet joint syndrome.
• Bone scan findings have not been found to correlate with facet-joint–mediated pain.

Computed tomography (CT) scanning

• Generally, CT scanning is not necessary unless other bony pathology (eg, fracture) must be excluded.
• A CT scan of the lumbosacral spine provides excellent anatomic imaging of the osseous structures of the spine, especially to rule out fractures or arthritic changes. Single-photon emission CT (SPECT) images may offer better resolution if spondylolysis is suggested.
• With facet-joint pathology, one may find arthritic changes in the facet-joints and degenerative disc disease; however, facet-joint pathology is also frequently seen in asymptomatic patients, and, therefore, abnormal findings on a CT scan are not diagnostic.
• Despite the excellent imaging of the bony anatomy of the facet-joint, CT scans are not useful for the diagnosis of the facet-joint as a pain generator. For example, Schwarzer et al found no correlation between facet-joint pathology on a CT scan and those patients who responded to diagnostic facet-joint blocks. (21) .Therefore, the correlation of an abnormal facet-joint anatomy as observed on CT scans with true facet -joint–mediated pain is poor.

Magnetic resonance imaging (MRI)

• In general, MRI is not indicated for the evaluation of nonradicular LBP.
• The main utility of MRI is for excluding pathologies other than facet-joint arthropathy, because many degenerative changes in the facet-joint are asymptomatic. Similarly, true facet-joint–mediated pain may be present despite a normal MRI examination.
• MRI provides detailed anatomic images of the soft structures of the spine, such as the intervertebral discs, which often show degenerative changes before facet-joint pathology. (22)
• MRI also may illustrate nerve root entrapment secondary to facet-joint hypertrophy or a synovial cyst and may help visualize the intervertebral foramen; however, facet-joint pathology may be present despite normal imaging study findings.
• MRI is particularly useful for the evaluation of a synovial cyst emanating from a facet-joint and for distinguishing a synovial cyst from other abnormalities. Gadolinium enhancement is useful in the evaluation of a potential synovial cyst. Also helpful is to make the radiologist aware that a synovial cyst is part of the differential diagnosis because this entity is often overlooked.

Other Tests

Electrodiagnosis

• Electro diagnostic studies, such as nerve conduction studies and needle EMG, are not usually indicated for possible lumbosacral facet syndrome. However, these studies should be considered if the history and physical examination findings suggest nerve root impingement or if the diagnosis remains unclear.
• Persons with facet-joint pathology typically present with normal sensory and motor examination findings; however, some patients describe the pain as radiating in nature and others report a positive straight leg–raise test result. Thus, electro diagnostic testing may be helpful for excluding other causes of pain, such as radiculopathy.

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