Laboratory and Imaging Studies
Laboratory studies
Laboratory studies are not generally necessary for the diagnosis of lumbosacral facet joint syndrome.
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 Z-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 Z-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 Z-joint pathology, one may find arthritic changes in the Z-joints and degenerative disc disease; however, Z-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 Z-joint, CT scans are not useful for the diagnosis of the Z-joint as a pain generator. For example, Schwarzer et al found no correlation between Z-joint pathology on a CT scan and those patients who responded to diagnostic Z-joint blocks. [8] Therefore, the correlation of an abnormal Z-joint anatomy as observed on CT scans with true Z-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 Z-joint arthropathy, because many degenerative changes in the Z-joint are asymptomatic. Similarly, true Z-joint–mediated pain may be present despite a normal MRI examination. [19]
MRI provides detailed anatomic images of the soft structures of the spine, such as the intervertebral discs, which often show degenerative changes before Z-joint pathology. [20]
MRI also may illustrate nerve root entrapment secondary to Z-joint hypertrophy or a synovial cyst and may help visualize the intervertebral foramen; however, Z-joint pathology may be present despite normal imaging study findings.
MRI is particularly useful for the evaluation of a synovial cyst emanating from a Z-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.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the Medscape Reference topic Nephrogenic Systemic Fibrosis.
NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see Medscape.
Other Tests
Electrodiagnosis
Electrodiagnostic 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 Z-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, electrodiagnostic testing may be helpful for excluding other causes of pain, such as radiculopathy.
RFA of the medial branch of the dorsal ramus affects the innervation of not only the Z-joint, but also the multifidus muscle. Normally, denervation potentials in the multifidus muscles in the setting of LBP are most commonly associated with lumbosacral radiculopathy. In the setting of a patient who has had previous RFA, however, the denervation potential is likely secondary to denervation from the procedure and not a radiculopathy.
Procedures
Medial branch block
Given that no historical or physical examination maneuver is unique or specific to Z-joint–mediated LBP, fluoroscopically guided medial branch nerve injections are often used for diagnostic purposes to determine whether the Z-joint in question is responsible for LBP. Once the Z-joint is established as the pain generator, more definitive treatment options, such as radiofrequency ablation, are offered. A Z-joint injection may also be used for therapeutic purposes, but many consider this procedure more challenging to perform.
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. Although the optimal number of blocks prior to radiofrequency denervation is uncertain, most guidelines, including the Spine Intervention Society (SIS) and the North American Spine Society (NASS), recommend a positive response to 2 screening medial branch blocks with at least 80% relief on 2 occasions for radiofrequency ablative denervation to be done. [21]
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Dorsal ramus innervation (medial and lateral branches). MAL23 = mamillo-accessory ligament bridging the mamillary and accessory processes of L2 and L3; Z-joint = zygapophyseal joint.
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Mamillary process anatomy.
