Chronic back pain

The disciplined investigation of chronic low back pain is predicated on the relative prevalence of various possible sources and causes of pain. In younger patients and in patients with a history of injury, the most common lesion is internal disk disruption. It accounts for at least 40 percent of cases.130 Next most common is sacroiliac joint pain, which accounts for some 20 percent of cases.96,97 The prevalence of lumbar zygapophysial joint pain is not more than 15 percent,131 and is probably less than 5

132, 133

percent in these patients. , In contrast, in elderly, uninjured patients, the prevalence of lumbar zygapophysial joint pain can be as high as 40 percent.134

These data influence the diagnostic strategy that might be assumed. The choice lies between pursuing discogenic pain or a source of pain in the synovial joints (Figure 12.2). The former would be indicated in younger injured patients and the latter in older patients with no history of trauma.

Another factor bears on this initial consideration. An MR image of the lumbar spine is an appropriate screening test before undertaking any invasive investigations for low back pain. Not only will it reveal any occult lesions not evident on or suspected from history, it also streamlines invasive investigations, preventing them from being undertaken arbitrarily or routinely.

If the MR image is absolutely normal and shows no changes in the intervertebral disks, the disks are unlikely to be the source of pain. Although disk stimulation may be positive in disks of normal appearance, this is an uncommon event (Table 12.9). Moreover, the available data are derived from studies conducted before contemporary manometric criteria were applied. Therefore, they may overstate the yield of disk stimulation in disks with normal appearance on MR imaging.

Consequently, in the interests of efficiency, the pursuit of discogenic pain should be avoided, in the first instance, in patients with pristine disks on MR imaging. Whether or not the disks should be investigated later is a practical and ethical question that can be considered once the diagnostic algorithm is otherwise exhausted. The pursuit of pain from the synovial joints is the option more likely to be productive in younger patients with normal disks, and in elderly patients with no evident source of pain.

DISK ALGORITHM

The MR image may show a high intensity zone (HIZ) in an annulus fibrosus. This sign should not be confused with fissure or unremarkable spots in the annulus. It consists of a bright signal, seen on carefully acquired T2-weighted images, with a brightness greater than that of the nucleus, and at least equivalent to that of the cere-brospinal fluid.138, 139 140 141 When present in patients with back pain, it implicates the affected disk as the source of the patient's pain, with a positive likelihood ratio of 6.138142 The sign is not common, being found in fewer than 30 percent of patients.138, 139 140 141 However, when present, its high likelihood ratio renders it a diagnostic sign. For the diagnosis of internal disk disruption, a likelihood ratio of 6 converts the pretest likelihood of 40 percent to a diagnostic confidence of 80 percent. In that event, internal disk disruption can be diagnosed on the basis of MR imaging alone, and further investigation may not be necessary if all that is required is a diagnosis. Confirmation of discogenic pain by discography would be required only if destructive treatment is being entertained.

If the MR image does not show an HIZ, a critical consideration is if multiple disks are degraded. If that is the case, pursuit of discogenic pain is questionable, for if multiple disks are likely to be symptomatic there is no available, efficient treatment for multilevel disk disease.

If, however, only one or perhaps two, disks are abnormal, it is potentially profitable to establish a diagnosis of discogenic pain. This can be done by disk stimulation complemented by post-discography CT scanning.108 Disk stimulation establishes if the disk is symptomatic. CT scanning established the internal morphology of the disk, and whether or not a fissure characteristic of internal disk disruption is present.

If disk stimulation is negative, investigating the sacroiliac and zygapophysial joint blocks should be considered (Figure 12.2). These may or may not be the source of pain despite the appearance of the disks on MR imaging, but having excluded the disks as the source of pain the chances are greater that the sacroiliac joint or the zygapophysial joints are the source of pain.

Figure 12.2 An algorithm for the investigation of low back pain.

SYNOVIAL JOINT ALGORITHM

If the synovial joint strategy is initiated, certain clinical decisions need to be taken before blocks are commenced (Figure 12.3). Rarely, if at all, have invasive tests been able to establish the source of pain in patients who have pain restricted to the midline, i.e. with no lateral radiation. Therefore, operators should carefully consider pursuing diagnostic blocks in such patients. Similarly, in patients with bilateral pain, operators should carefully consider if it is feasible and likely that the patient has bilateral sacroiliac joint pain. If not, it would be more efficient to pursue zygapophysial joint pain as the source, because these joints are far more likely to have suffered injuries bilaterally. Third, it is conspicuous from the research literature that sacroiliac joint pain does not project rostrally

Table 12.9 A contingency table correlating the results of magnetic resonance imaging against the results of provocation discography as the criterion standard for a symptomatic lumbar disk.

Magnetic resonance imaging

Disk stimulation

Symptomatic Asymptomatic

Abnormal

201 152

Normal

50 234

Based on the pooled data of Osti and Fraser,135 Horton and Daftari,136 and Simmons et a/.137

Sensitivity = 0.80; specificity = 0.60; positive predictive value = 0.57; negative predictive value = 0.82.

Based on the pooled data of Osti and Fraser,135 Horton and Daftari,136 and Simmons et a/.137

Sensitivity = 0.80; specificity = 0.60; positive predictive value = 0.57; negative predictive value = 0.82.

above L5.96,98 So, if the patient's pain is restricted to below this level, the sacroiliac joint becomes the more likely target. Conversely, if the pain extends above L5, the zygapophysial joints (or the disks) are the more likely source.

None of these clinical indicators is diagnostic of the source of pain in a positive sense; they do not predict that the chosen investigation will be positive. Their utility works in reverse. They render the competing source of pain as less likely, and serve to choose which investigation is less likely to be productive.

If the sacroiliac joint is selected as the target, this joint can be blocked using well-defined, established techni-ques.95 If the response to a first block is negative, sacroiliac joint pain is excluded, and the investigations can turn to the zygapophysial joints (Figure 12.4). If the response to a first block is positive, that response is not diagnostic, because it could be false-positive. A control block must subsequently be performed. If the control block is negative, the diagnosis of sacroiliac joint pain is refuted, and the operator should carefully consider their next steps. They need to be confident that the placebo response to the first block was an isolated event, and not a sign that the patient is confused about their pain and its investigation. If the response to the control block is positive, a diagnosis of sacroiliac joint pain is established, and no further investigations are required.

A similar process applies to the investigation of zyga-pophysial joint pain. It is inefficient to investigate one joint at a time. The prevalence of zygapophysial joint pain is low, and the chances of negative responses are high. If joints are investigated one at a time, the chances are that multiple blocks will prove negative. This constitutes a waste of resources. It is more efficient to conduct a screening block, targeting multiple levels, in the first instance. If a screening block of multiple levels proves negative, further investigations are not warranted. Thereby, patients who do not have zygapophysial joint pain are identified with one test, and resources are not wasted performing multiple tests with negative results.

The lower two segmental levels are the most commonly affected. So, the screening blocks should target these levels. Operators should have good cause to target joints at higher levels.

The appropriate procedure for screening blocks are medial branch blocks at L5, L4, and L3.99 These are preferred over intraarticular blocks because they have been validated and are prognostic of the only proven treatment for lumbar zygapophysial joint pain, which is lumbar medial branch neurotomy.

If a patient proves negative to screening blocks, the operator needs to consider what next steps are justified. Sacroiliac joint blocks might be entertained, or investigations might cease.

If a patient has a positive response to screening blocks, further blocks should be undertaken in order to pinpoint the actual source of pain. For an accurate diagnosis, joints should be anesthetized one segment at a time, and the diagnosis confirmed by controlled blocks. Some operators elect to block multiple joints at a time, largely on the grounds that they are not reimbursed for multiple, sequential blocks. It should be recognized that this amounts to an idiosyncrasy of the reimbursement system, which does not reflect optimal practice.

If confirmatory blocks prove positive, a diagnosis of zygapophysial joint pain is established. If confirmatory blocks are negative, the operator should carefully consider if further investigations are justified.

Back Pain Revealed

Back Pain Revealed

Tired Having Back Pains All The Time, But You Choose To Ignore It? Every year millions of people see their lives and favorite activities limited by back pain. They forego activities they once loved because of it and in some cases may not even be able to perform their job as well as they once could due to back pain.

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