Decision making in surgical treatment of chronic low back pain: The performance of prognostic tests to select patients for lumbar spinal fusion

Abstract

Chronic low back pain (CLBP) is one of the main causes of disability in the western world with a huge economic burden to society. As yet, no specific underlying anatomic cause has been identified for CLBP. Imaging often reveals degenerative findings of the disc or facet joints of one or more lumbar motion segments. These findings, however, can also be observed in asymptomatic people. It has been suggested that pain in degenerated discs may be caused by the ingrowth of nerve fibers into tears or clefts of the annulus fibrosus or nucleus pulposus, and by reported high levels of pro-inflammatory mediators. As this so-called discogenic pain is often exacerbated by mechanical loading, the concept of relieving pain by spinal fusion to stabilise a painful spinal segment, has been developed. For some patients lumbar spinal fusion indeed is beneficial, but its results are highly variable and hard to predict for the individual patient. To identify those CLBP patients who will benefit from fusion, many surgeons rely on tests that are assumed to predict the outcome of spinal fusion. The three most commonly used prognostic tests in daily practice are immobilization in a lumbosacral orthosis, provocative discography and trial immobilization by temporary external transpedicular fixation.Aiming for consensus on the indications for lumbar fusion and in order to improve its results by better patient selection, it is essential to know the role and value of these prognostic tests for CLBP patients in clinical practice. The overall aims of the present thesis were: 1) to evaluate whether there is consensus among spine surgeons regarding the use and appreciation of prognostic tests for lumbar spinal fusion; 2) to verify whether a thoracolumbosacral orthosisis (TLSO) truly minimises lumbosacral motion; 3) to verify whether a TLSO can predict the clinical outcome of fusion for CLBP; 4) to assess whether provocative discography of adjacent segments actually predicts the long-term clinical outcome fusion; 5) to determine the incidence of postdiscography discitis, and whether there is a need for routine antibiotic prophylaxis; 6) to assess whether temporary external transpedicular fixation (TETF ) can help to predict the outcome of spinal fusion; 7) to determine the prognostic accuracy of the most commonly used tests in clinical practice to predict the outcome of fusion for CLBP. The results of a national survey among spine surgeons in the Netherlands were presented in Study I. The surgeons were questioned about their opinion on prognostic factors and about the use of predictive tests for lumbar fusion in CLBP patients.The comments were compared with findings from the prevailing literature. The survey revealed a considerable lack of uniformity in the use and appreciation of predictive tests. Prognostic factors known from the literature were not consistently incorporated in the surgeons decision making process either. This heterogeneity in strategy is most probably caused by the lack of sound scientific evidence for current predictive tests and it was concluded that currently there is not enough consensus among spine surgeons in the Netherlands to create national guidelines for surgical decision making in CLBP. In Study II, the hypothesized working mechanism of a pantaloon cast (i.e., minimisation of lumbosacral joint mobility) was studied. In patients who were admitted for a temporary external transpedicular fixation test (TETF), infrared light markers were rigidly attached to the protruding ends of Steinman pins that were fixed in two spinal levels. In this way three-dimensional motion between these levels could be analysed opto-electronically. During dynamic test conditions such as walking, a plaster cast, either with or without unilateral hip fixation, did not significantly decrease lumbosacral joint motion.Although not substantiated by sound scientific support, lumbosacral orthoses or pantaloon casts are often used in everyday practice as a predictor for the outcome of fusion. A systematic review of the literature supplemented with a prospective cohort study was performed (Study II) in order to assess the value of a pantaloon cast in surgical decisionmaking. It appeared that only in CLBP patients with no prior spine surgery, a pantaloon cast test with substantial pain relief suggests a favorable outcome of lumbar fusion compared to conservative treatment. In patients with prior spine surgery the test is of no value. It is believed by many spine surgeons that provocative discography, unlike plain radiographs or magnetic resonance imaging, is a physiologic test that can truly determine whether a disc is painful and relevant in a patient's pain syndrome, irrespective of the morphology of the disc. It has been suggested that in order to achieve a successful clinical outcome of lumbar fusion, suspect discs should be painful and adjacent control discs should elicit no pain on provocative discography. For this reason, a cohort of patients in whom the decision to perform lumbar fusion was based on an external fixation (TETF) trial, was analysed retrospectively in Study IV. The results of preoperative discography of solely the levels adjacent to the fusion were compared with the clinical results after spinal fusion. It appeared that in this select group of patients the discographic status of discs adjacent to a lumbar fusion did not have any effect on the clinical outcome. Copyright © Informa Healthcare Ltd 2013.