Applied Radiology

Dr. Cherukuri is a third-year Radiology Resident at The University of Pittsburgh Medical Center. He received both his undergraduate and medical degrees from The University of Pennsylvania. He plans to pursue a fellowship in Musculoskeletal Radiology at The University of Pittsburgh in 2003.

Radiologists are playing an expanding role in the management of spinal pain through the application of discography, image-guided injection therapy, and percutaneous vertebroplasty. Discography demonstrates the source of pain in patients who are suspected of having discogenic disease, but who have normal or equivocal findings on MRI. Image-guided injection therapy is a safe and simple way to deliver steroids to the epidural space, nerve roots, or facet joints to relieve symptoms from radiculopathy or degenerative facet disease. Despite widespread clinical use, however, controversy regarding its efficacy remains. Finally, vertebroplasty is proving to be an effective treatment for painful and debilitating vertebral compression fractures by delivering methylmethacrylate cement percutaneously into the vertebral body.

Spinal pain is an extremely common cause of morbidity in the United States and is the second most common reason patients seek medical attention. It is a challenging and multifactorial disease that is best managed by a cross-disciplinary approach involving spine surgeons, radiologists, anesthesiologists, and rehabilitative medicine specialists, among others. Recent advances in several image-guided percutaneous therapies have expanded the role of the procedural radiologist in the treatment of spinal pain.

This article discusses three rapidly growing radiologic approaches to the care of these patients--discography, percutaneous vertebroplasty, and image-guided injection therapy. The focus will be on the clinical indications and efficacy of these procedures with only brief discussions of their technical aspects, which have been detailed in several excellent review articles. ^1-11

Discography

Diagnostic imaging has long played a central role in determining the etiology of back pain, especially with the wide availability of high-quality magnetic resonance imaging (MRI). In general, MRI has a high sensitivity for delineating morphologic derangements that can lead to spinal pain such as degenerative disc disease, facet arthropathy, annular tears, herniations, and spinal stenoses. However, MRI is less sensitive for the detection of disc pathology in the cervical and thoracic spines than in the lumbar spine; although false negatives do occur even in the lumbar spine. ^1,12,13 Furthermore, studies have shown that many normal, asymptomatic volunteers have disc herniations that are found on MRI. ¹⁴ It is, therefore, crucial that careful clinical correlation be made when trying to understand the significance of both positive and negative MRI findings and that correlative studies such as discography be considered.

For these reasons, discography is playing an expanding role in localizing discogenic back pain and in identifying occult annular tears and other internal disc derangements. It is a provocative test that involves the injection of contrast material into the suspected pathologic disc and measuring the clinical response in terms of reproducing the patient's symptoms. Patients may be referred for discography regardless of what the imaging findings reveal, especially in cases of suspected cervical and thoracic disc problems without obvious disc herniations. The clinical goals of discography include clearly identifying the intervertebral disc as a source of the patient's back pain and determining which levels are involved. When performed in a standardized, reproducible manner, this technique can result in improved outcomes for surgical therapy--first, by confidently demonstrating that a patient contemplating spinal surgery does indeed have discogenic pain, and, second, by identifying the precise disc levels that are pathologic. Discography also plays a role in identifying candidates who would benefit from intradiscal electrotherapy (IDET).

Before a discogram is performed, it is important to review the patient's previous imaging studies to identify the patient's overall anatomy and likely sites of pathology. Spinal cord and nerve root compression are also important to identify, as these may be contraindications to discography. ¹ This is because distension of a disc that is already severely compressing the spinal cord or nerve roots may worsen the compression and exacerbate the patient's symptoms. Other contraindications include active infection anywhere in the body, uncorrected bleeding disorders, and the inability to lie still for the duration of the study. Generally, the procedure can be performed safely with conscious sedation.

Technique

The technical aspects of performing discography vary among practitioners and depend upon the spinal level being evaluated. ^1,2 High-resolution C-arm fluoroscopy or CT-fluoroscopy is mandatory for adequate visualization of bony landmarks during needle placement and for the detection of annular tears during contrast injection. Twenty-two- or 25-gauge spinal needles (Beckton-Dickinson, Franklin Lakes, NJ) of varying lengths are used depending on patient size. Both coaxial- and single-needle approaches to the disc have been described and can be used depending upon operator preference. Post-discography CT is sometimes performed for better delineation of the size and locations of annular disruptions but is not routinely used by all authors.

After the patient has been positioned on the table appropriately, the skin is cleansed with an iodine-based disinfectant (Betadine, Purdue Pharma, Stamford, CT), followed by an alcohol rinse. Sterile technique must be carefully applied during all percutaneous spinal procedures, particularly during discography, as discitis is a potentially serious, albeit rare, complication occurring in <0.01% of cases. ¹ For cervical discography, the patient is placed in a supine position and the needle is inserted from an anterolateral approach. For lumbar and thoracic discography, the patient is placed in the prone position and the needle is inserted from a dorsolateral approach.

Once the patient has been prepped and local anesthesia has been administered, the fluoroscope is aligned in the plane of the target disc. The needle is advanced toward the inferior margin of the disc with intermittent fluoroscopy to observe needle position. Care must be taken in the cervical region to avoid the carotid arteries branches and jugular veins. When the needle tip reaches the outer part of the annular disc, slight resistance will be felt, and the needle is then advanced through the outer annulus into the center of the disc, where the needle tip position is confirmed by anteroposterior and lateral fluoroscopy. As the needle tip approaches the annular margin of the disc, it is not uncommon for contact to occur with a nerve root, resulting in discomfort or pain that requires repositioning of the needle. The patient is warned of this possibility during needle insertion.

Once the needle tip is in the center of the disc, contrast is injected while the radiologist watches under fluoroscopy. Typically, 2 to 4 mL of nonionic contrast (Omnipaque 240, Amersham Health, Princeton, NJ) should be injected to achieve full distension of the nucleus pulposus, which is crucial to provoking a pain response. ^1,2 Endpoints for injection include detection of an annular tear, severe pain, or resistance of the disc to accepting further contrast (figure 1). The patient's description of elicited symptoms and particularly whether or not his or her clinical symptoms were reproduced (ie, concordant versus nonconcordant pain) are recorded carefully, along with the symptom severity and the presence of annular pathology. When a painful disc is encountered, injection of preservative-free local anesthetic such as lidocaine into the disc is useful for temporary pain relief to allow for completion of the study. This is important for reducing pain that may confuse the evaluation of adjacent disc levels. After discography, patients are monitored for 1 to 3 hours prior to discharge. Discharge instructions should include advising the patient to expect some pain and discomfort for a few days after the procedure and to return for medical attention promptly should he/she experience signs and symptoms of developing discitis, such as worsening back pain, severe point tenderness, fever, or chills. Progression of discitis into an epidural abscess or vertebral osteomyelitis are other thoretical complications.

Percutaneous vertebroplasty

First developed in the mid-1980s by Deramond and colleagues ⁶ in France, percutaneous vertebroplasty has become an increasingly utilized and effective way of treating painful vertebral compression fractures from benign and malignant diseases. It was originally applied successfully to vertebral hemangiomas and osteolytic metastatases, although its primary application in North America has become the treatment of osteoporotic compression fractures. ⁸ Compression fractures can be devastating complications of osteoporosis leading to severe back pain and complications of immobility such as progressive bone demineralization, thromboembolic disease, pneumonia, depression, and markedly decreased functional status. The incidence of compression fractures will undoubtedly increase as the U.S. population ages. To date, conventional therapy for compression fractures has centered upon conservative measures such as bed rest, nonsteriodal anti-inflammatory drugs and narcotics for pain control, and bracing devices.

Percutaneous vertebroplasty consists of injecting polymethylmethacrylate (PMMA), an exothermic semi-liquid cement, into the vertebral body under radiologic guidance through a percutaneously inserted cannula. This method of internally casting the vertebral body results in enhanced vertebral body stability and loss of micromotion across fracture planes. ¹¹ These factors, along with the possible thermal damage that the PMMA cement does to vertebral body pain receptors, are thought to be the mechanisms behind the dramatic pain relief this procedure can provide, although the exact mechanism is not known. Several published series have shown at least moderate-to-complete pain relief in approximately 63% to 90% of patients undergoing vertebroplasty at intermediate-term (approximately 6 months) follow-up. ^6,7 Other benefits of vertebroplasty include decreased use of analgesics and increased mobility. ^6,15 Large series documenting the long-term effectiveness of percutaneous vertebroplasty are pending. To maximize effectiveness, this procedure should be part of a comprehensive medical regimen directed by an osteoporosis specialist.

Other crucial factors in promoting successful outcomes for vertebroplasty are appropriate patient selection and work-up. Vertebral compression fractures clinically present with pain that is aggravated by flexion of the spine, such as the motion incurred when moving to a sitting position. It is usually described as a deep, midline pain that is nonradiating and relieved by lying in bed. Radicular symptoms should alert one to the possibility that the pain may be due to other causes, such as disc disease or spinal or neural foraminal stenoses. A careful physical examination should be performed, including assessment and documentation of the patient's baseline neurological status to evaluate for weakness or radicular symptoms, which may indicate spinal stenosis or nerve root compromise. On physical examination, every attempt must be made to correlate the site of the vertebral body collapse with the patient's symptoms. This can be done by heavily palpating the patient's back along the midline under fluoroscopy until the patient's symptoms are reproduced. This type of localization is critical in selecting candidates who will benefit from the procedure. When many months or years have passed since the patient's onset of pain or when there are multiple affected vertebral bodies with associated degenerative changes, as there often are, identifying the culprit of the patient's pain can be difficult. One should keep in mind that in cases of multilevel collapse, the most morphologically abnormal vertebral body is not necessarily the cause of the patient's pain, and that pain can be referred to adjacent levels.

Relative contraindications to vertebroplasty include extreme collapse of the vertebral body (ie, vertebra plana) and >20% stenosis of the spinal canal. ^7,8,10 While the optimal timing of vertebroplasty is a controversial and evolving topic, most practitioners advocate some trial of medical therapy before performing vertebroplasty. ⁷ This varies with the severity of pain and the aggressiveness of the medical therapy. For example, patients who require hospitalization with heavy narcotic requirements may be considered for vertebroplasty earlier than others. Improvement of pain on medical therapy is another relative contraindication to percutaneous vertebroplasty, and active infection and uncorrected bleeding diatheses are absolute contraindications. A recent report by Kaufmann et al ¹⁵ suggests that the likelihood of clinical benefit from vertebroplasty is not related to the age of the fracture.

Ideally, preprocedural evaluation of vertebroplasty candidates is performed by MRI, although some rely on plain films (figure 2A) and bone scintigraphy with SPECT imaging (figure 2B). When reviewing the MR images (figures 2C and 2D), radiologists should identify the size and location of the fracture cleft, the presence of bone edema, the integrity of the posterior cortical margin, and the presence or absence of spinal canal or neural foraminal stenoses. T2-weighted or short tau inversion recovery sequences are particularly useful in identifying areas of bone marrow edema, which indicate acute fractures to help localize the source of the patient's pain.

Technique

The technical aspects of percutaneous vertebroplasty have been well described in several recent reviews. ^6-11 The procedure can generally be done under conscious sedation with the appropriate physiologic monitoring, such as pulse oximetry and heart rate monitoring by a nurse. General anesthesia is rarely required except for patients with high levels of anxiety or pain. Once the patient has been prepared and draped in the prone position and local anesthesia has been administered to the skin and periosteum, the vertebral body is accessed from a transpedicular approach with an 11-gauge bone biopsy needle through a small skin incision (figures 2E and 2F). The tip of the needle is advanced to the anterior third of the vertebral body near the midline, which is confirmed by biplane fluoroscopy at our institution. A vertebrogram can be performed prior to PMMA injection to exclude the possibility that the needle communicates with major venous structures, although not all authors perform this step routinely. The PMMA powder is then prepared with an organic solvent and a sterile opacifying barium agent (approximately 30% wt/vol) (Bryan Corporation, Woburn, MA) and instilled into the vertebral body under careful biplane fluoroscopic visualization. The injection is terminated when there has been filling of the fracture cleft, extension to the posterior vertebral margin, or evidence of extraosseous cement leakage. It is important to note that the percentage of vertebral body filling has no relationship to pain relief; therefore, overaggressive filling of the vertebral body, which can increase the chance of leak or extravasation, should be avoided. ⁹

At the end of the procedure, the patient is monitored for 1 to 2 hours, at which time he or she is encouraged to ambulate to evaluate for pain improvement. The patient is discharged home the same day with instructions for limited progressive activity and reduction of narcotic use as tolerated to judge response to therapy.

Complications from vertebroplasty are relatively low, occurring in 1% to 10% of patients. ^8,9 They include the following: failure of pain relief or worsening of pain; spinal cord or nerve root compression; rib fractures from lying in the prone position; paravertebral hematomas; swallowing difficulty from esophageal compression; and pulmonary embolism from venous cement extravasation. ^8,16 Complications are associated with poor visualization of cement flow during injection, poor needle positioning, inadequate aseptic technique, and inability of the patient to cooperate. They may occur somewhat more frequently in patients with neoplastic disease due to the higher incidence of cortical destruction. The value of careful attention to cement flow with strict lateral fluoroscopy, as well as meticulous needle positioning to prevent paraspinal cement leaks and venous extravasation, cannot be overemphasized. The small associated risk of spinal cord or nerve root compression from cement leaks requires the availability of a spine surgeon in case emergent decompressive surgery should become necessary.

Epidural steroid injections, nerve root injections, and facet injections

Although it has been in use for several decades and many clinical trials have been performed, the therapeutic efficacy of steroid injection therapy for spinal pain remains controversial. ^17-21 While the basic pathophysiologic mechanisms of spinal pain and sciatica are incompletely understood, Nygaard et al ²² and Lee et al ²³ have suggested that disc herniations are associated with an abnormal inflammatory response mediated by phospholipases and other compounds, resulting in nerve root irritation. These irritant effects are thought to be countered by the anti-inflammatory effects of epidural steroids. ²³ Nelemans and colleagues ¹⁹ recently published a comprehensive review of 21 randomized, controlled trials of injection therapies, and found that the overall methodologic quality of these studies was poor; only three of the trials were performed in a well-designed, placebo-controlled manner. These three trials showed a trend toward short-term and long-term pain relief, but this trend was not statistically significant in the pooled data. Despite the numerous clinical trials published, the authors concluded that there remains a paucity of high-quality data either to support the use of steroid injection therapy or to recommend abandoning its use, and that further clinical trials need to be undertaken.

Notwithstanding the controversies regarding its efficacy, clinicians continue to refer patients to radiologists for these procedures. Many of the trials evaluating steroid injection therapies, especially the earlier ones, have been criticized for their lack of needle position documentation. In clinical practice, injection therapies are often performed blindly by nonradiologists without imaging guidance. However, Stitz and Sommer ²⁴ have shown that blind needle placement results in inappropriate positioning of the needle tip approximately 25% of the time, thus supporting the use of imaging guidance. As for their current clinical role, injection therapies, such as nerve root blocks and facet joint injections, may have diagnostic and therapeutic value in identifying or confirming the source of spinal pain when surgery is being considered. ^17,21 The temporary relief of pain that steroid injections provide may also allow more aggressive and effective physical rehabilitative measures.

Technique

Image-guided steroid injections can be performed from a transforaminal approach for selective nerve root blocks, from a midline interlaminar approach for epidural injections, and directly into the facet joint for facet injections. Recently, Silbergleit et al ⁵ presented a well-written review of the technical details of these three types of injection therapy. Selective nerve root injections are used for patients with radicular symptoms, often due to acute disc pathology that is resistant to conservative therapy or is due to degenerative neural foraminal stenosis.

Fluoroscopy, CT, or CT-fluoroscopy can be used for guidance during selective nerve root blocks depending on operator preference, although CT is believed by many to be more accurate, as it images the nerve root target directly. ^3,5 The needle is usually inserted from an oblique dorsolateral approach (figures 3 and 4), and as the tip approaches the target nerve root, the patient's radicular symptoms may be reproduced. The nerve root sleeve is injected with a standard mixture of a long-acting corticosteroid such as betamethasone (Schering Corporation, Kenilworth, NJ) or methylprednisolone (Pharmacia & Upjohn, Kalamazoo, MI) and a local anesthetic (0.5% bupivocaine). Facet joint injections can also be accomplished under either CT or fluoroscopic guidance with the same injection mixture as that used for nerve root blocks. Fluoroscopic guidance is adequate for epidural steroid injections, which are usually performed with an interlaminar approach, but can also be performed with a sacral hiatal or transforaminal approach. ⁵

Needle tip position in the epidural space is suggested by sudden loss of resistance during needle advancement and is confirmed by epidurography with 2 to 3 mL of nonionic iodinated contrast material (Omnipaque 240, Amersham Health, Princeton, NJ) (figure 5). A standard dose of corticosteroid (eg, 1 to 2 mL of methylprednisolone acetate [40 mg/mL]) and a local anesthetic (0.5% bupivocaine) is injected. Complications from epidural steroid injections are extremely uncommon and are usually minor, including small epidural hematomas and vasovagal responses. ²⁵ Infectious complications and inadvertent intrathecal administration of medication are theoretical risks as well.

Future applications

Percutaneous spinal interventions will continue to evolve rapidly in the near future. The application of percutaneous vertebroplasty may expand to include the delivery of bioresorbable bone-strengthening polymers, antibiotic-impregnated materials, osteogenic growth factors, and even antitumoral agents. Ongoing research will undoubtedly result in the development of cements that have higher tensile strengths and are easier to use. Cement delivery systems will also become easier to use and more widely available. Beyond vertebroplasty, newer techniques (such as kyphoplasty, which involves treating compression fractures by inserting a balloon inflation device into the vertebra to restore vertebral body height), are currently under evaluation. ²⁶ Intradiscal electrotherapy (IDET) and radiofrequency neurotomy are two other developing image-guided treatments for discogenic and facet-related back pain. ²⁷ Magnetic resonance guidance systems and combined CT-fluoroscopic devices may bring additional improvements in safety, speed, and efficacy of injection procedures. Before these promising techniques achieve wider clinical use, a clearer definition of long-term outcomes, complications, and effect upon patients' quality of life must be determined by large randomized prospective clinical trials.

Conclusion

Percutaneous spinal interventions have become integral components in the multidisciplinary approach to the management of spinal pain, which is a serious and costly healthcare problem debilitating millions of Americans each year. Procedural radiologists are ideally suited to perform these exciting procedures safely and accurately due to their skill in image-guided intervention and intimate knowledge of anatomy. Competition from spine physicians and anesthesiologists to perform these procedures will likely continue as future applications broaden this rapidly growing field and as clinical indications and efficacy are defined more clearly.

Acknowledgments

The author would like to thank Dr. William E. Rothfus, Dr. Stephen Grahovac, and Dr.Vibhu Kapoor of The University of Pittsburgh Medical Center, for reviewing this manuscript and providing the clinical images.