DOI: 10.1148/rg.276065509
RadioGraphics 2007;27:1751-1771
© RSNA, 2007
Management of Chronic Low Back Pain: Rationales, Principles, and Targets of Imaging-guided Spinal Injections1
Jan Fritz, MD,
Thomas Niemeyer, MD,
Stephan Clasen, MD,
Jakub Wiskirchen, MD,
Gunnar Tepe, MD,
Bruno Kastler, MD,
Thomas Nägele, MD,
Claudius W. König, MD,
Claus D. Claussen, MD, and
Philippe L. Pereira, MD
1 From the Departments of Diagnostic Radiology (J.F., S.C., J.W., G.T., C.W.K., C.D.C., P.L.P.), Orthopedic Surgery (T. Niemeyer), and Neuroradiology (T. Nägele), Eberhard-Karls-University, Hoppe-Seyler-Str 3, Tübingen, Germany; and Department of Radiology, Université de Franche Comté, CHU Minjoz, Besancon, France (B.K.). Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received February 13, 2006; revision requested June 14; final revision received March 23, 2007; accepted March 23. All authors have no financial relationships to disclose.
Address correspondence to J.F., Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 600 N Wolfe St, Baltimore, MD 21287 (e-mail: jfritz4{at}jhmi.edu).
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Abstract
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If low back pain does not improve with conservative management, the cause of the pain must be determined before further therapy is initiated. Information obtained from the patient’s medical history, physical examination, and imaging may suffice to rule out many common causes of chronic pain (eg, fracture, malignancy, visceral or metabolic abnormality, deformity, inflammation, and infection). However, in most cases, the initial clinical and imaging findings have a low predictive value for the identification of specific pain-producing spinal structures. Diagnostic spinal injections performed in conjunction with imaging may be necessary to test the hypothesis that a particular structure is the source of pain. To ensure a valid test result, diagnostic injection procedures should be monitored with fluoroscopy, computed tomography, or magnetic resonance imaging. The use of controlled and comparative injections helps maximize the reliability of the test results. After a symptomatic structure has been identified, therapeutic spinal injections may be administered as an adjunct to conservative management, especially in patients with inoperable conditions. Therapeutic injections also may help hasten the recovery of patients with persistent or recurrent pain after spinal surgery.
© RSNA, 2007
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Describe the indications and rationales for diagnostic and therapeutic spinal injections.
- Identify the most likely anatomic sources of nonspecific chronic low back pain.
- Discuss ways of maximizing the accuracy of diagnostic spinal injection results.
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Introduction
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Low back pain is one of the most frequently reported symptoms in the industrialized world (1). In most cases, the symptom is due to a benign nonemergent condition involving some degree of spinal degeneration (2). Pain that continues for more than 7–12 weeks despite conservative management is described as chronic (3). The estimated prevalence of nonspecific chronic low back pain in adults is 15% but increases with increasing age, to 44% at the age of 70 years (4,5).
If chronic low back pain does not improve with conservative management, the cause must be identified before the most appropriate therapy can be determined. The sheer number of spinal structures that are potential sources of low back pain results in a broad differential diagnosis and represents a major challenge to identifying the cause of pain (6). A precise medical history and thorough physical examination, along with tailored laboratory testing and noninvasive imaging, are important steps toward establishing a working diagnosis (7). These measures should suffice to identify or to rule out underlying disease processes (fracture, malignancy, visceral or metabolic abnormality, deformity, inflammation, and infection), neurologic disorders requiring surgical intervention (cauda equina syndrome, myelopathy), and social or psychological distress that may amplify or prolong pain (8).
However, in most cases, the initial clinical and imaging findings are nonspecific or are insufficient for diagnosis (6). Chronic low back pain is described as nonspecific when the clinical and imaging findings have insufficient predictive values for the identification of symptomatic spinal structures (9–20). Among patients with chronic low back pain and without a demonstrated neurologic deficit or a disk herniation visible at imaging, a spinal cause was identifiable in only 15% (21).
In such patients, 
spinal injections allow a functional assessment of the anatomic structures that are suspected to be sources of pain. Diagnostic spinal injections are performed to test the hypothesis that a specific spinal structure is symptomatic (22). Indications for diagnostic spinal injections are listed in Table 1.
After a symptomatic structure has been identified, spinal injections may be used for pain management. Indications for therapeutic spinal injections are summarized in Table 2.
The classification of low back pain according to whether it is radicular or nonradicular allows a systematic approach to diagnosis and helps guide the interventional radiologist toward the most likely pain generators (23) (Fig 1). Radicular pain is most often associated with spinal nerve root irritation due to compression and inflammation. Annular fissure with leakage of nucleus pulposus material to the spinal nerve root is another possible causal mechanism for radicular pain (24). Nonradicular pain is typically produced by abnormalities in the facet joints, sacroiliac joints, and intervertebral disks. Less frequently, abnormal facet joints and sacroiliac joints may produce leg pain (13,22,25).
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Figure 1. Flow diagram shows a dynamic, adaptable algorithm for performing diagnostic spinal injections that are appropriate to the individual clinical situation. Initial targets for injection are selected according to whether pain is radicular or nonradicular. On the basis of initial clinical and imaging findings, the sacroiliac joints or the facet joints may be tested first; alternatively, in cases in which there is evidence of disk abnormalities, diskography may be performed before the joints are tested. Selective epidural injections may be performed last in cases of nonradicular pain. At each stage of diagnostic testing, a positive test result (eg, relief of chronic low back pain after the injection of a joint, or provocation of typical pain at diskography) leads to identification of the targeted structure as a significant source of pain. Diagnostic injections with a positive result may be followed by therapeutic injections.
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In various studies, facet joints, intervertebral disks, sacroiliac joints, and spinal nerves have been identified as the most common sources of chronic low back pain (22,23,26–30). Although bones, muscles, and ligaments also may account for short-lived episodes of low back pain, they have not been identified as frequent primary causes (23,30,31). The criteria for identifying an anatomic structure as a potential source of chronic low back pain are detailed in Table 3.
The remainder of the article describes in greater detail the rationales for, and the underlying principles of, lumbar facet joint injection, selective spinal nerve root injection, sacroiliac joint injection, and diskography for the management of chronic low back pain.
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Diagnostic and Therapeutic Uses of Spinal Injections
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The basic assumptions that underlie the diagnostic and therapeutic uses of spinal injections are derived from theories of pain causation (22). These assumptions are as follows: (a) Selective infiltration of the pain-generating structure with a local anesthetic relieves the patient’s typical pain by temporarily blocking the activity of stimulated nociceptors. Relief of pain is the most important information that may be obtained from diagnostic injections of sacroiliac joints, facet joints, and nerve roots. (b) Irritation of a symptomatic structure by the injectant or the needle stimulates nociceptors and thereby provokes or aggravates the patient’s typical pain. Pain provocation is the most important diagnostic information that may be obtained from diskography but is less reliable as an identifier of symptomatic sacroiliac joints, facet joints, and nerve roots (32–34). (c) Nociceptor stimulation associated with inflammatory processes such as the phospholipase A2 pathway may be interrupted by locally delivered steroids, with a resultant therapeutic benefit.
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Principles of Diagnostic Testing with Spinal Injections
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The accuracy of a clinical test is defined by its specificity (the relative prevalence of false-positive test results) and its sensitivity (the relative prevalence of false-negative results). Accuracy is ideally determined by comparison with the best available test, the reference standard. However, for diagnostic spinal injection procedures, accuracy is difficult to ascertain because there is no available reference standard. Surgeries such as spinal fusion vary in type and in degree of success, and the results of surgery may not be indicative of the role of a particular structure in preoperative pain generation (35). The adherence to general testing principles and specific principles related to diagnostic spinal injections helps maximize the objectivity, reliability, and validity of the procedures and, thus, the accuracy of the results.
To obtain accurate diagnostic test results and to determine the short- and long-term effects of treatment procedures, the quality and quantity of the patient’s pain must be assessed. It is important to explain to the patient that the procedure should result in relief of the typically experienced back pain, which is referred to as concordant pain relief. If multiple levels are tested, the most objective results may be obtained by testing each implicated level during a separate session. Pain responses may be assessed while the patient is at rest or performing a typically painful maneuver and usually are quantified by using some form of a numeric rating scale. Pain relief of 50%–80% may be regarded as an indication that the targeted structure is a significant source of pain.
Accurate drug delivery to the appropriate anatomic target is a major prerequisite for obtaining a valid test result. For diagnostic testing, only a small volume (with the amount depending on the targeted structure) is injected to ensure exclusive infiltration of the targeted structure and avoid false-positive results due to the effects of the injectant on potential pain generators nearby. This is a fundamental difference with therapeutic spinal injections, in which larger volumes are used. The injection of a minimal amount of a diluted contrast agent before drug delivery enables assessment of the accuracy of needle tip placement. If the contrast agent is injected with the drug, distribution of the injectant can be monitored as well. However, the routine use of a contrast agent for these purposes may be controversial (36).
To ensure the reliability of a positive test result (pain relief), testing should be repeated in the same target. Onetime testing generally is associated with a higher rate of false-positive results (27,37). One of two methods may be used to increase the precision of test results by administering two separate injections (ideally, 1 week apart) in the targeted structure: (a) controlled injections, one a placebo (saline) and the other an anesthetic; or (b) comparative injections, one a short-acting anesthetic (eg, lidocaine) and the other a long-acting anesthetic (eg, ropivacaine). The second injection should confirm the results of the initial injection either by reproducing them exactly with an identical protocol or by producing an expected modification (eg, with controlled injections, no pain relief because of the use of a placebo such as saline; with comparative injections, more prolonged pain relief because of the use of a long-acting anesthetic).
The use of controlled injections may invoke a conflict of ethics because saline injections cannot be expected to result in a therapeutic benefit. With the use of comparative injections, a long-acting steroid may be added as a therapeutic component to the last injection (38). Comparative and controlled injections have been successfully used to increase the reliability of test results in facet joint injections (39) and sacroiliac joint injections (27,30).
The reliability and validity of the procedure are important conditions for obtaining conclusive test results, but procedural validity is the most important of the two because according to test theory, reliability is a necessary but insufficient condition for validity. In clinical practice, this means that if target-specific drug delivery is not achieved and therefore the targeted structure is not tested or a nontargeted structure is tested, the results may still be reproducible, and reliability therefore may be judged acceptable; however, the test results may still be false-positive. Furthermore, accurate results of diagnostic injection are fundamental to ensure benefits from subsequent therapeutic injections.
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Imaging Guidance
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To maximize test accuracy and minimize complications, spinal injections are best performed with imaging guidance (36,40–42). Fluoroscopy and CT may be used for the whole spectrum of spinal injections, and both modalities are capable of providing equivalent results. Fluoroscopy is fast and relatively cost-effective, but CT may be preferred for guidance of injections in the sacroiliac joints, in joints where access is hindered by osteophytes, or in structures adjacent to the spinal cord. Interventional MR imaging also offers cross-sectional multiplanar imaging capabilities without the risk of ionizing radiation. The technique was tested in feasibility studies and in several spinal injection procedures performed in a clinical setting (43–45). In accordance with the principle of keeping exposure to ionizing radiation as low as reasonably achievable, MR imaging is of particular value for imaging guidance in younger patients and in serial therapeutic injections.
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Lumbar Facet Joint Injections
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Diagnostic and therapeutic injections of the facet joints involve the imaging-guided delivery of various agents in various volumes to the joints and the nerves that innvervate them.
Rationale and Utility for Diagnosis
The facet joints are paired true synovium-lined joints with a cavity and are formed by the superior and inferior articular processes of adjacent vertebrae. Facet joints are well innervated; they receive bisegmental innervations from the medial branches of the dorsal rami as well as autonomic fibers ending in the joint capsule and synovial membrane (46). Facet joints were proven to be sources of chronic low back pain during provocation testing in healthy volunteers (47). Facetogenic pain may result from various pathologic states, including degenerative changes and segmental instability of variable degrees and causes, inflammation (eg, arthritis), synovial cysts, trauma, and occupational injury (48). Noninvasive diagnostic procedures (eg, imaging) provide no significant indicators of facet joint involvement in chronic low back pain, especially in the presence of degenerative disease (16). Comparative facet joint blocks currently represent the most valid and reliable test for the diagnosis of symptomatic facet joints. In one study, controlled facet joint blocks led to the identification of symptomatic facet joints in 30% of patients with chronic low back pain (39).
Rationale and Utility for Therapy
Systemic drug therapy and physiotherapy play an important role in reducing facetogenic pain, but not all patients experience a satisfactory response to these therapies (49). Surgical procedures such as spinal fusion are a more invasive form of intervention with outcomes that may vary widely (50). Steroid facet joint injections are a minimally invasive option for treatment of facetogenic pain and may decrease nociceptor activity (51). Neurolysis of the pain-conducting nerves is an alternative that may result in the complete cessation of pain (52). Currently, the therapeutic effect of intraarticular or paraarticular steroid injections to the medial branch is not clear (31), while periarticular (extracapsular) facet joint infiltration may be less effective than intraarticular injection (53). Medial branch neurotomy has been shown to result in long-term benefit in patients with chronic low back pain who have been evaluated with comparative diagnostic blocks (52).
Principles and Targets
Facet joint anesthesia can be achieved with the injection of a local anesthetic into the joint or directly to the site of the medial branches of the dorsal rami. Complete facet joint anesthesia by using a medial branch block requires targeted drug delivery to both supplying medial branches, which is best performed at the ipsilateral transverse process of the same lumbar vertebral level and at the level below (Fig 2). Several standard fluoroscopy-guided techniques have been described (42) (Fig 3). The use of CT may allow a more individualized approach (40,42) (Fig 4). Facet joint injections also may be performed with MR imaging for guidance (Fig 5).
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Figure 2a. Innervation of the lumbar spine. (a) Diagram shows the innervation of the facet joints at the levels of lumbar vertebrae (LV) 1 through 5 (arrows) by inferior and superior articular segments (thin yellow lines) of two adjacent medial nerve branches (thick yellow lines). The thick yellow line ending in the red asterisk denotes the dorsal primary ramus of the L5 nerve. Each of the T12 through L4 medial nerve branches courses under the pedicle at the same level and crosses the transverse process one level below the neural foramen; these points of crossing (*) are the targets for medial nerve branch injections. Thus, to anesthetize the L2-3 facet joint, which is innervated by medial branches of the L1 and L2 spinal nerves, the anesthetic must be injected into the transverse process at the levels of L2 and L3. (b) Diagram shows the course of the dorsal primary ramus of L5 (yellow line), which directly innervates the L5-S1 facet joint (black arrow) after crossing the ala of the sacrum at a point (*) adjacent to the root of the S1 superior articular process; this point is the target for anesthesia of the primary dorsal ramus of L5. The red arrow denotes the inferior articular segment of the medial branch of the L4 nerve. (c) Diagram provides an anterior view of the lumbar spine and medial branches of nerves T12 (a), L1 (b), L2 (c), L3 (d), and L4 (e), each of which courses immediately above the transverse process one level below the vertebra with which it is numerically identified, and the dorsal primary ramus of the L5 nerve (f), which traverses the ala of the sacrum.
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Figure 2b. Innervation of the lumbar spine. (a) Diagram shows the innervation of the facet joints at the levels of lumbar vertebrae (LV) 1 through 5 (arrows) by inferior and superior articular segments (thin yellow lines) of two adjacent medial nerve branches (thick yellow lines). The thick yellow line ending in the red asterisk denotes the dorsal primary ramus of the L5 nerve. Each of the T12 through L4 medial nerve branches courses under the pedicle at the same level and crosses the transverse process one level below the neural foramen; these points of crossing (*) are the targets for medial nerve branch injections. Thus, to anesthetize the L2-3 facet joint, which is innervated by medial branches of the L1 and L2 spinal nerves, the anesthetic must be injected into the transverse process at the levels of L2 and L3. (b) Diagram shows the course of the dorsal primary ramus of L5 (yellow line), which directly innervates the L5-S1 facet joint (black arrow) after crossing the ala of the sacrum at a point (*) adjacent to the root of the S1 superior articular process; this point is the target for anesthesia of the primary dorsal ramus of L5. The red arrow denotes the inferior articular segment of the medial branch of the L4 nerve. (c) Diagram provides an anterior view of the lumbar spine and medial branches of nerves T12 (a), L1 (b), L2 (c), L3 (d), and L4 (e), each of which courses immediately above the transverse process one level below the vertebra with which it is numerically identified, and the dorsal primary ramus of the L5 nerve (f), which traverses the ala of the sacrum.
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Figure 2c. Innervation of the lumbar spine. (a) Diagram shows the innervation of the facet joints at the levels of lumbar vertebrae (LV) 1 through 5 (arrows) by inferior and superior articular segments (thin yellow lines) of two adjacent medial nerve branches (thick yellow lines). The thick yellow line ending in the red asterisk denotes the dorsal primary ramus of the L5 nerve. Each of the T12 through L4 medial nerve branches courses under the pedicle at the same level and crosses the transverse process one level below the neural foramen; these points of crossing (*) are the targets for medial nerve branch injections. Thus, to anesthetize the L2-3 facet joint, which is innervated by medial branches of the L1 and L2 spinal nerves, the anesthetic must be injected into the transverse process at the levels of L2 and L3. (b) Diagram shows the course of the dorsal primary ramus of L5 (yellow line), which directly innervates the L5-S1 facet joint (black arrow) after crossing the ala of the sacrum at a point (*) adjacent to the root of the S1 superior articular process; this point is the target for anesthesia of the primary dorsal ramus of L5. The red arrow denotes the inferior articular segment of the medial branch of the L4 nerve. (c) Diagram provides an anterior view of the lumbar spine and medial branches of nerves T12 (a), L1 (b), L2 (c), L3 (d), and L4 (e), each of which courses immediately above the transverse process one level below the vertebra with which it is numerically identified, and the dorsal primary ramus of the L5 nerve (f), which traverses the ala of the sacrum.
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Figure 3a. Fluoroscopy-guided diagnostic injection of a lumbar facet joint in a 62-year-old man with a new onset of nonradicular back pain after fusion of the L5 and S1 vertebrae for treatment of spinal instability. (a, b) Right anterior oblique radiographs show the position of the needle tip (arrow in a) in the joint space of the L4-5 left facet joint. The needle tip position is demonstrated by the intraarticular distribution of a small volume of a mixture of lidocaine and iodinated contrast material. In b, obtained after bilateral injection of 0.8 mL of the mixture, there is intraarticular enhancement on the left (black arrow) and extraarticular enhancement on the right (white arrow). (c) Axial CT image shows narrowing of the joint space (arrow) of the right L4-5 facet joint, a condition that impeded intraarticular drug delivery. Subsequent medial branch blocks helped identify the L4-5 facet joints as sources of pain due to deterioration of the segment adjacent to the fused vertebrae.
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Figure 3b. Fluoroscopy-guided diagnostic injection of a lumbar facet joint in a 62-year-old man with a new onset of nonradicular back pain after fusion of the L5 and S1 vertebrae for treatment of spinal instability. (a, b) Right anterior oblique radiographs show the position of the needle tip (arrow in a) in the joint space of the L4-5 left facet joint. The needle tip position is demonstrated by the intraarticular distribution of a small volume of a mixture of lidocaine and iodinated contrast material. In b, obtained after bilateral injection of 0.8 mL of the mixture, there is intraarticular enhancement on the left (black arrow) and extraarticular enhancement on the right (white arrow). (c) Axial CT image shows narrowing of the joint space (arrow) of the right L4-5 facet joint, a condition that impeded intraarticular drug delivery. Subsequent medial branch blocks helped identify the L4-5 facet joints as sources of pain due to deterioration of the segment adjacent to the fused vertebrae.
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Figure 3c. Fluoroscopy-guided diagnostic injection of a lumbar facet joint in a 62-year-old man with a new onset of nonradicular back pain after fusion of the L5 and S1 vertebrae for treatment of spinal instability. (a, b) Right anterior oblique radiographs show the position of the needle tip (arrow in a) in the joint space of the L4-5 left facet joint. The needle tip position is demonstrated by the intraarticular distribution of a small volume of a mixture of lidocaine and iodinated contrast material. In b, obtained after bilateral injection of 0.8 mL of the mixture, there is intraarticular enhancement on the left (black arrow) and extraarticular enhancement on the right (white arrow). (c) Axial CT image shows narrowing of the joint space (arrow) of the right L4-5 facet joint, a condition that impeded intraarticular drug delivery. Subsequent medial branch blocks helped identify the L4-5 facet joints as sources of pain due to deterioration of the segment adjacent to the fused vertebrae.
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Figure 4a. CT-guided intraarticular facet joint injections performed for diagnosis of nonspecific chronic low back pain in a 55-year-old woman with hip dysplasia. (a) Axial image shows correct placement of the needle (arrow), with a posterolateral approach and with angulation of 45°, in the left L4-5 facet joint. (b) Axial image shows appropriate intraarticular distribution of the injectant (0.2 mL of an iodinated contrast material and 0.8 mL of lidocaine), with bulging of the anterior and posterior joint capsule (arrows) and with no evidence of extraarticular leakage. After bilateral injections, the woman reported pain relief of 80%.
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Figure 4b. CT-guided intraarticular facet joint injections performed for diagnosis of nonspecific chronic low back pain in a 55-year-old woman with hip dysplasia. (a) Axial image shows correct placement of the needle (arrow), with a posterolateral approach and with angulation of 45°, in the left L4-5 facet joint. (b) Axial image shows appropriate intraarticular distribution of the injectant (0.2 mL of an iodinated contrast material and 0.8 mL of lidocaine), with bulging of the anterior and posterior joint capsule (arrows) and with no evidence of extraarticular leakage. After bilateral injections, the woman reported pain relief of 80%.
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Figure 5a. MR imaging–guided intraarticular facet joint injections performed for therapy of chronic low back pain in a 32-year-old woman. The pain source had been identified at previous diagnostic facet joint injections as the L4-5 facet joints. An open 0.2-T MR imaging system was used for guidance of therapeutic injections. (a) Axial oblique gradient-echo image, acquired with a two-dimensional fast low-angle shot sequence (repetition time [TR] msec/echo time [TE] msec, 66/9; matrix, 256 x 256), shows the positioning of an MR-compatible 20-gauge needle (arrow) at the L4-5 level. Subsequently, 0.8 mL of a long-acting steroid (triamcinolone) was injected bilaterally. (b) Axial MR image, obtained with a short inversion time inversion-recovery sequence (turbo inversion recovery magnitude, or TIRM) (4425/48; matrix, 256 x 256), depicts the injectant as bilateral areas of increased intraarticular signal intensity (arrows). After a course of four bilateral injections administered over an 8-week period, the woman was pain free for 8 months.
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Figure 5b. MR imaging–guided intraarticular facet joint injections performed for therapy of chronic low back pain in a 32-year-old woman. The pain source had been identified at previous diagnostic facet joint injections as the L4-5 facet joints. An open 0.2-T MR imaging system was used for guidance of therapeutic injections. (a) Axial oblique gradient-echo image, acquired with a two-dimensional fast low-angle shot sequence (repetition time [TR] msec/echo time [TE] msec, 66/9; matrix, 256 x 256), shows the positioning of an MR-compatible 20-gauge needle (arrow) at the L4-5 level. Subsequently, 0.8 mL of a long-acting steroid (triamcinolone) was injected bilaterally. (b) Axial MR image, obtained with a short inversion time inversion-recovery sequence (turbo inversion recovery magnitude, or TIRM) (4425/48; matrix, 256 x 256), depicts the injectant as bilateral areas of increased intraarticular signal intensity (arrows). After a course of four bilateral injections administered over an 8-week period, the woman was pain free for 8 months.
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For diagnostic testing of a specific facet joint, the use of 1 mL or less of an anesthetic allows localized injection during medial branch blocks and avoidance of capsular rupture during intraarticular injections. Local diffusion of the anesthetic to the spinal nerves is associated with increased rates of false-positive test results (54), which were found in 38% of lumbar medial branch block procedures in one study (37). The addition of a contrast agent to the anesthetic injectant helps detect any unintended distribution to nontargeted structures (eg, vascular uptake because of an unintended intravascular injection) (54).
Intraarticular injections and medial branch blocks may produce comparable diagnostic results (55). However, for comparative facet joint injections, medial branch blocks may be preferable because of the greater predictability of the duration of anesthesia with direct application of the anesthetic to the nerve site (Fig 6); when the anesthetic is applied within the relatively avascular environment of the joint capsule, by contrast, the duration of local anesthesia is less predictable (22).
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Figure 6a. CT-guided dorsal primary ramus block. (a) Image obtained after the injection of 0.3 mL of diluted iodinated contrast material shows the needle tip positioned at the lateral aspect of the dorsal facet of the right L5-S1 facet joint, with contrast material backflow along the needle track (arrow). The L5 dorsal primary ramus was not reached because the needle tip location was too medial and the tip did not penetrate the fascia of the spinalis thoracis muscle. (b) Image shows repositioning of the needle tip at a deeper and more lateral location that allows localized distribution of contrast material at a site lateral to the L5-S1 facet joint and sufficient infiltration of the dorsal primary ramus (arrow) of the L5 nerve without affecting the anteriorly located spinal nerve.
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Figure 6b. CT-guided dorsal primary ramus block. (a) Image obtained after the injection of 0.3 mL of diluted iodinated contrast material shows the needle tip positioned at the lateral aspect of the dorsal facet of the right L5-S1 facet joint, with contrast material backflow along the needle track (arrow). The L5 dorsal primary ramus was not reached because the needle tip location was too medial and the tip did not penetrate the fascia of the spinalis thoracis muscle. (b) Image shows repositioning of the needle tip at a deeper and more lateral location that allows localized distribution of contrast material at a site lateral to the L5-S1 facet joint and sufficient infiltration of the dorsal primary ramus (arrow) of the L5 nerve without affecting the anteriorly located spinal nerve.
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Therapeutic injections of facet joints may be performed with a mixture of a long-acting anesthetic and a steroid, which is administered in the amount of 1–1.5 mL in intra- and paraarticular locations (Fig 7) or in the amount of 1–2 mL at the site of the medial nerve branch. Neurolysis of the medial branch may be performed with an alcohol injection (40) or with radiofrequency ablation (52). A series of injections might be necessary to control the patient’s pain.
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Figure 7a. CT-guided facet joint injections in a 39-year-old man with nonspecific nonradicular back pain for more than 2 years. (a) CT myelogram shows moderate left-sided disk protrusion (arrow) without evidence of nerve root compression. Results of diskography were negative, but comparative bilateral intraarticular facet joint injections helped identify the L4-5 facet joints as pain generators. (b, c) Axial CT images show the right facet joint (arrow) after intraarticular (b) and paraarticular (c) therapeutic injections with a mixture of 0.8 mL of a long-acting local anesthetic (ropivacaine) and a steroid (triamcinolone acetonide). Bilateral injections resulted in a pain reduction of 50% for a period of 6 months.
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Figure 7b. CT-guided facet joint injections in a 39-year-old man with nonspecific nonradicular back pain for more than 2 years. (a) CT myelogram shows moderate left-sided disk protrusion (arrow) without evidence of nerve root compression. Results of diskography were negative, but comparative bilateral intraarticular facet joint injections helped identify the L4-5 facet joints as pain generators. (b, c) Axial CT images show the right facet joint (arrow) after intraarticular (b) and paraarticular (c) therapeutic injections with a mixture of 0.8 mL of a long-acting local anesthetic (ropivacaine) and a steroid (triamcinolone acetonide). Bilateral injections resulted in a pain reduction of 50% for a period of 6 months.
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Figure 7c. CT-guided facet joint injections in a 39-year-old man with nonspecific nonradicular back pain for more than 2 years. (a) CT myelogram shows moderate left-sided disk protrusion (arrow) without evidence of nerve root compression. Results of diskography were negative, but comparative bilateral intraarticular facet joint injections helped identify the L4-5 facet joints as pain generators. (b, c) Axial CT images show the right facet joint (arrow) after intraarticular (b) and paraarticular (c) therapeutic injections with a mixture of 0.8 mL of a long-acting local anesthetic (ropivacaine) and a steroid (triamcinolone acetonide). Bilateral injections resulted in a pain reduction of 50% for a period of 6 months.
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Sacroiliac Joint Injections
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Diagnostic and therapeutic sacroiliac joint injections involve the imaging-guided delivery of a local anesthetic, a steroid, or both to the synovial and fibrous compartments of the sacroiliac joint.
Rationale and Utility for Diagnosis
The sacroiliac joint is extensively innervated by the ventral rami of the L4 and L5 nerves, the superior gluteal nerve, and the dorsal rami of the L5 and S2 nerves (56). Provocation injections in sacroiliac joints in healthy volunteers have helped identify the sacroiliac joints as possible sources of spinal pain (57). Chronic sacroiliac joint pain may occur after traumatic or cumulative shear injuries (eg, in gait disorders), inflammatory changes (eg, spondylarthritis), or lumbar fusion, or may be idiopathic (58). In chronic low back pain, there are no significant predictors for the identification of symptomatic sacroiliac joints because of significant overlap of the joints with other potentially painful spinal structures (17,19). Controlled and comparative intraarticular sacroiliac joint blocks currently represent the most valid and reliable tests for the diagnosis of symptomatic sacroiliac joints in patients with nonspecific chronic low back pain (59). With the use of controlled sacroiliac joint blocks, the prevalence of sacroiliac joint pain was found to range from 10% to 19% (27,30).
Rationale and Utility for Therapy
Nonspecific chronic low back pain of sacroiliac origin may not respond to conservative management (eg, drug therapy and pelvic stabilization exercises), and sacroiliac fusion surgery is not a generally accepted method for treating chronic sacroiliac pain (60). Inflammatory back pain due to noninfectious sacroiliitis rarely responds to widely available long-term treatment (61). Therapeutic sacroiliac joint injections resulted in long-term benefits in patients in whom the sacroiliac joint was identified as the source of nonspecific chronic low back pain after controlled or comparative diagnostic sacroiliac joint blocks (62,63) and in patients with noninfectious sacroiliitis diagnosed at MR imaging (42,64). Serial therapeutic injections may be necessary for pain management.
Principles and Targets
The sacroiliac joint consists of a synoviumlined cartilaginous compartment and a fibrous compartment (Fig 8). The synovial compartment of the sacroiliac joint borders the sacroiliac groove dorsally and may be accessed most easily with a posteroinferior approach; with a posterosuperior approach, by contrast, the needle must be inserted through the fibrous compartment of the joint.
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Figure 8a. Sacroiliac joint anatomy. Three-dimensional axial CT reconstructions at superior (a) and inferior (b) levels of the sacroiliac joints depict the synovial (solid lines) and fibrous (dotted lines) compartments. Intraarticular needle placement is possible at both levels by using a dorsal approach. Needle placement at the superior level may be preferred when cross-sectional imaging is used for guidance, whereas the inferior level is easily accessible with fluoroscopic guidance.
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Figure 8b. Sacroiliac joint anatomy. Three-dimensional axial CT reconstructions at superior (a) and inferior (b) levels of the sacroiliac joints depict the synovial (solid lines) and fibrous (dotted lines) compartments. Intraarticular needle placement is possible at both levels by using a dorsal approach. Needle placement at the superior level may be preferred when cross-sectional imaging is used for guidance, whereas the inferior level is easily accessible with fluoroscopic guidance.
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The three-dimensional structure of the joint, with its curved surfaces, ridges, and depressions, varies from person to person. According to the results of one study, the desired intraarticular drug delivery was achieved in only 22% of "blind" (non–imaging-guided) injections of sacroiliac joints, whereas 24% of such injections resulted in inadvertent epidural puncture, a complication with potentially serious adverse effects (65).
Several fluoroscopy-guided techniques have been described (42) (Fig 9). However, CT is the preferred modality for guidance of injections of sacroiliac joints with a complex three-dimensional configuration or with osteophytosis (40) (Fig 10). MR imaging also is especially valuable for guidance in patients with sacroiliitis due to spondylarthropathy, who typically present between the ages of 20 and 30 years (43) (Fig 11).
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Figure 9a. Fluoroscopy-guided diagnostic sacroiliac joint injection. (a) Right anterior oblique radiograph shows apparently correct positioning of the needle tip at an inferior level within the left sacroiliac joint (arrow). A test injection with 0.1 mL of diluted iodinated contrast material demonstrated extraarticular distribution of the injectant, a finding indicative of incorrect positioning of the needle tip. (b) Radiograph obtained after repositioning of the needle tip in an intraarticular location (verified with several small test injections) and injection of 1 mL of lidocaine mixed with iodinated contrast material in a ratio of 1:20 shows the expected intraarticular distribution of injectant (arrows).
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Figure 9b. Fluoroscopy-guided diagnostic sacroiliac joint injection. (a) Right anterior oblique radiograph shows apparently correct positioning of the needle tip at an inferior level within the left sacroiliac joint (arrow). A test injection with 0.1 mL of diluted iodinated contrast material demonstrated extraarticular distribution of the injectant, a finding indicative of incorrect positioning of the needle tip. (b) Radiograph obtained after repositioning of the needle tip in an intraarticular location (verified with several small test injections) and injection of 1 mL of lidocaine mixed with iodinated contrast material in a ratio of 1:20 shows the expected intraarticular distribution of injectant (arrows).
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Figure 10a. CT-guided diagnostic sacroiliac joint injection in a 37-year-old man with chronic low back pain but without correlative imaging findings. Before the diagnostic injection, the patient rated the intensity of pain at 7 on a 10-point scale. (a) Axial CT image obtained at the level of the superior sacroiliac joint shows positioning of the needle tip (arrow) at the junction of the fibrous and synovial compartments, approximately 2.5 cm from the entrance to the sacroiliac groove. (b) Image obtained after the injection of 1 mL of a mixture of lidocaine and iodinated contrast material (ratio, 1:10) shows infiltration of both compartments (arrows), with dorsal bulging of the posterior sacroiliac ligament (arrowhead) and without evidence of extraarticular distribution. After the injection, the patient reported a significant decrease in pain intensity (rating of 2).
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Figure 10b. CT-guided diagnostic sacroiliac joint injection in a 37-year-old man with chronic low back pain but without correlative imaging findings. Before the diagnostic injection, the patient rated the intensity of pain at 7 on a 10-point scale. (a) Axial CT image obtained at the level of the superior sacroiliac joint shows positioning of the needle tip (arrow) at the junction of the fibrous and synovial compartments, approximately 2.5 cm from the entrance to the sacroiliac groove. (b) Image obtained after the injection of 1 mL of a mixture of lidocaine and iodinated contrast material (ratio, 1:10) shows infiltration of both compartments (arrows), with dorsal bulging of the posterior sacroiliac ligament (arrowhead) and without evidence of extraarticular distribution. After the injection, the patient reported a significant decrease in pain intensity (rating of 2).
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Figure 11a. MR imaging–guided therapeutic sacroiliac joint injection in a 17-year-old girl with intense chronic low back pain (intensity rating of 9) after a 6-week course of nonsteroidal anti-inflammatory drug therapy, which was complicated by gastritis, and a 3-month course of sulfasalazine therapy without control of symptoms of sacroiliac inflammation. (a) Coronal oblique MR image obtained with a short inversion time inversion-recovery sequence (7000/ 120) before a therapeutic injection of 40 mg of triamcinolone shows bilateral subchondral regions of the sacroiliac joints with marked signal hyperintensity due to T2 prolongation (arrows), features indicative of acute sacroiliitis. (b) Gradient-echo MR image obtained for guidance of the left sacroiliac joint injection shows the tip of a commercially available MR-compatible 20.5-gauge needle (arrow) that was inserted through the fibrous compartment and into the synovial joint space. (c) MR image obtained 3 months later with the same sequence as a shows near-complete resolution of the subchondral inflammatory changes (arrows). The patient was pain free.
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Figure 11b. MR imaging–guided therapeutic sacroiliac joint injection in a 17-year-old girl with intense chronic low back pain (intensity rating of 9) after a 6-week course of nonsteroidal anti-inflammatory drug therapy, which was complicated by gastritis, and a 3-month course of sulfasalazine therapy without control of symptoms of sacroiliac inflammation. (a) Coronal oblique MR image obtained with a short inversion time inversion-recovery sequence (7000/ 120) before a therapeutic injection of 40 mg of triamcinolone shows bilateral subchondral regions of the sacroiliac joints with marked signal hyperintensity due to T2 prolongation (arrows), features indicative of acute sacroiliitis. (b) Gradient-echo MR image obtained for guidance of the left sacroiliac joint injection shows the tip of a commercially available MR-compatible 20.5-gauge needle (arrow) that was inserted through the fibrous compartment and into the synovial joint space. (c) MR image obtained 3 months later with the same sequence as a shows near-complete resolution of the subchondral inflammatory changes (arrows). The patient was pain free.
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Figure 11c. MR imaging–guided therapeutic sacroiliac joint injection in a 17-year-old girl with intense chronic low back pain (intensity rating of 9) after a 6-week course of nonsteroidal anti-inflammatory drug therapy, which was complicated by gastritis, and a 3-month course of sulfasalazine therapy without control of symptoms of sacroiliac inflammation. (a) Coronal oblique MR image obtained with a short inversion time inversion-recovery sequence (7000/ 120) before a therapeutic injection of 40 mg of triamcinolone shows bilateral subchondral regions of the sacroiliac joints with marked signal hyperintensity due to T2 prolongation (arrows), features indicative of acute sacroiliitis. (b) Gradient-echo MR image obtained for guidance of the left sacroiliac joint injection shows the tip of a commercially available MR-compatible 20.5-gauge needle (arrow) that was inserted through the fibrous compartment and into the synovial joint space. (c) MR image obtained 3 months later with the same sequence as a shows near-complete resolution of the subchondral inflammatory changes (arrows). The patient was pain free.
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To achieve adequate diagnostic specificity, the injectant must be localized within the joint. The injection of a small volume (1 mL or less) helps lower the risk of capsular rupture and leakage of the injectant beyond the joint. Distribution of the anesthetic to spinal nerves or to the facet joints and their medial nerve branches leads to false-positive results (Fig 12). The administration of comparative blocks may be useful for identifying initial false-positive results, which have been found in as many as 20% of cases (27). The addition of a contrast agent to the injectant not only helps ensure intraarticular localization but also helps identify inadvertent intravascular injection, which could lead to false-negative results (65).
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Figure 12a. Incorrect needle placement during CT-guided sacroiliac joint injection for diagnosis of chronic low back pain. (a) Axial CT image shows the needle tip location (arrow) after insertion through the dorsal aspect of the fibrous compartment of the left sacroiliac joint. Penetration was insufficiently deep to achieve intraarticular delivery of the anesthetic. (b, c) CT images obtained after the injection of 1 mL of a mixture of iodinated contrast material and anesthetic show enhancement indicative of unintended extraarticular distribution of the injectant: in b, at the S1 nerve root (arrow); in c, at the dorsal ramus of the L5 nerve (arrowhead) and adjacent to the capsule of the L5-S1 facet joint (arrow). Unintended distribution, if undetected at imaging, would lead to false-positive test results.
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Figure 12b. Incorrect needle placement during CT-guided sacroiliac joint injection for diagnosis of chronic low back pain. (a) Axial CT image shows the needle tip location (arrow) after insertion through the dorsal aspect of the fibrous compartment of the left sacroiliac joint. Penetration was insufficiently deep to achieve intraarticular delivery of the anesthetic. (b, c) CT images obtained after the injection of 1 mL of a mixture of iodinated contrast material and anesthetic show enhancement indicative of unintended extraarticular distribution of the injectant: in b, at the S1 nerve root (arrow); in c, at the dorsal ramus of the L5 nerve (arrowhead) and adjacent to the capsule of the L5-S1 facet joint (arrow). Unintended distribution, if undetected at imaging, would lead to false-positive test results.
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Figure 12c. Incorrect needle placement during CT-guided sacroiliac joint injection for diagnosis of chronic low back pain. (a) Axial CT image shows the needle tip location (arrow) after insertion through the dorsal aspect of the fibrous compartment of the left sacroiliac joint. Penetration was insufficiently deep to achieve intraarticular delivery of the anesthetic. (b, c) CT images obtained after the injection of 1 mL of a mixture of iodinated contrast material and anesthetic show enhancement indicative of unintended extraarticular distribution of the injectant: in b, at the S1 nerve root (arrow); in c, at the dorsal ramus of the L5 nerve (arrowhead) and adjacent to the capsule of the L5-S1 facet joint (arrow). Unintended distribution, if undetected at imaging, would lead to false-positive test results.
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Therapeutic sacroiliac injections are usually performed in intraarticular locations (63,64). However, in a recent controlled trial, a reduction of back pain was reported after periarticular injections, probably because of the anesthetic effect on the richly innervated posterior ligamentous apparatus (62). A larger volume (3–5 mL) of the long-acting anesthetic-steroid mixture may be used to achieve infiltration of all the innervated sacroiliac structures, since the goal of pain management is more important than the avoidance of capsular leakage in therapeutic injections.
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Selective Nerve Root and Epidural Injections
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Diagnostic and therapeutic selective nerve root injections involve the imaging-guided delivery of drugs (a local anesthetic, a
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Abstract
LEARNING OBJECTIVES FOR TEST...
