Selective Interventional Spinal Techniques: Injections and Ablations
Selective spinal and joint injections are being performed with increasing frequency in the management of acute and chronic disorders of the musculoskeletal system. Effective treatment of chronic spine and joint pain requires accurate identification of the correct pain source. Interventional pain specialists play a critical role in the selective provision of spinal injection techniques to diagnose and treat musculoskeletal pain disorders.
One of the most common pain disorders seen by interventional pain specialists is spine and sacroiliac joint (SIJ) pain. The facet (zygapophyseal) joints can be significant source of spinal and extremity pain.1-4 These joints, and the nerves innervating them, can produce cervical, thoracic, lumbar, and referred pain (head, shoulder, scapula, buttock, thigh, and leg). The SIJ, which also is innervated, has been shown to be a significant source of referred pain in the buttocks, hip, and posterior thigh.
This article will review the benefits of spinal injections in the diagnosis and management of spinal joint pain and discuss specific treatment techniques for SIJ pain.
Injection techniques have obvious diagnostic and therapeutic value—they are extremely useful tools for precisely diagnosing and localizing the spinal pain generator(s). Therefore, the goal of diagnostic selective nerve or joint injections is to differentiate the qualitative and quantitative contributions of discogenic, radicular, and posterior element axial pain sources. This is especially true in the setting of multilevel spine and joint disease and in situations where imaging or electromyographic tests show no obvious abnormalities.
The injections can be directed at specific target sites in and around the spine. Because of the precise needle localization needed and the technical difficulty of performing these procedures, the use of fluoroscopy and contrast dye are essential. Epidural injections frequently are performed without radiographic guidance, but incorrect needle placement into subcutaneous, intraligamentous, and intravenous locations occurs in up to 25% of cases. Therefore, fluoroscopic visualization with an epidurogram, perisheathogram, or arthrogram is highly recommended, especially in postoperative cases in which anatomical boundaries are disrupted and imaging studies are difficult to interpret accurately.
Sometimes diagnostically reproducing the pain trigger during these procedures facilitates accurate identification of the painful structure. Typically, non-affected nerve roots will not trigger a severe pain response when they are mechanically irritated by a spinal needle or contrast dye. In addition, when combined with a local anesthetic or corticosteroid solution, spinal injections can provide temporary pain relief—which would indicate a therapeutic benefit and a positive response to the procedure.
Comparison of pain levels before and after the injections—by patient verbalization, pain procedure diaries, and visual analog scales (VAS)—helps the practitioner gauge the response to the anesthetic procedures. Afterwards, provocative maneuvers, such as assessment of spinal range of motion, straight leg raises, and ambulatory capabilities before and after the injections also may help the practitioner determine the contribution of that particular site as the actual painful source. Exaggerated or extreme pain behaviors during these assessments provides information about nonphysiologic causes of pain—usually provided from before and after procedures such as that noted on pain procedures diaries or VAS pain scores comparisons. 5-9
Indication for Procedures
These selective spinal and joint injections are indicated specifically for medically stable patients and are considered outpatient, minimally invasive, minor surgical procedures. For patients with failed back surgical syndrome and for those considering operative interventions (eg, spinal fusion, microdiscectomy, or laminectomy and decompression), combining injection procedures with an accurate history and physical exam and appropriate imaging and/or electrophysiologic studies can help the interventional pain specialist and/or the spinal surgeon develop a more directed and efficient treatment program. Spinal injections also can be used as an adjunct to rehabilitation and physical therapy, proving pain relief, increasing range of motion before and/or during the rehabilitative process, and allowing the patient to participate more fully in the therapy program.
Before performing any diagnostic and/or therapeutic procedures for spinal and joint pain, the interventional pain specialist must understand the radiographic anatomy of the facet and larger joints, most importantly the nerves involved (Figures 1 and 2). Each of the facet and larger joints have a dual nerve supply. For example, the facet joints are innervated by the medial branch of the dorsal ramus, one from the level above the target joint and one from the level below the target joint.
Although numerous interventional procedures are used to treat spinal-related pain conditions, a few of the most common types of diagnostic and therapeutic spinal injections are listed in Table 1.10-15
Sacroiliac Intra-articular Joint
The sacroiliac joint (SIJ) can be a primary or secondary source of lower back pain or dysfunction that should be thoroughly investigated and considered. Studies using controlled blocks to identify the pain generator have shown that the prevalence of SIJ pain in those with lower back and buttock pain is approximately 15%.16,17 The importance of the SIJ often is overlooked because its anatomical location makes it difficult to examine in isolation, and many SIJ clinical tests place mechanical stresses on contiguous structures. In addition, many other structures may refer pain to the SIJ.
Before 1934, the SIJ was felt to be the primary cause of lower back pain. However, a study by Mixter and Barr focused attention on the disc as the primary cause of lower back pain.18 Recently, attention has been refocused on the SIJ as a primary or secondary cause of lower back pain and disability. SIJ dysfunction is first suspected when a patient presents with a suggestive mechanism of injury (direct fall on the buttocks, rear-end motor vehicle accident with ipsilateral foot on the brake at the moment of impact; fall into a hole with one leg in the hole and the other leg extended outside). Pain diagrams, which document a predominant pain zone extending from the posterosuperior iliac spine to the caudal portion of the joint, can accurately predict which patients with suspected discogenic or posterior element pain have symptomatic SIJs on provocative injection.