Radiologic Criteria for the Diagnosis of Spinal Stenosis: Results of a Delphi Survey 1

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1 Note: This copy is for your personal non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, contact us at Original Research n Musculoskeletal Imaging Nadja Mamisch, MD Martin Brumann Juerg Hodler, MD, MBA Ulrike Held, PhD Florian Brunner, MD, PhD Johann Steurer, MD For the Lumbar Spinal Stenosis Outcome Study Working Group Zurich Radiologic Criteria for the Diagnosis of Spinal Stenosis: Results of a Delphi Survey 1 Purpose: Materials and Methods: To develop a list of radiologic criteria for describing lumbar spinal stenosis, to learn from experts which parameters they consider to be most important, and to assess the strength of agreement among experts on the most relevant criteria. An expert panel of 41 radiologists (musculoskeletal experts and neuroradiologists from Europe and the United States) was formed. A three-round Delphi survey was conducted. Twenty-seven of the 41 nominated experts agreed to participate; 21 completed all three rounds. In the first round, experts were asked to complete a list of suggested parameters and cutoff values to describe lumbar spinal stenosis. In the second round, panelists rated the diagnostic relevance of each parameter (visual analog scale, 0 10). In the third round, panelists were provided with the group results (median and range) and their own answers and had the opportunity to adapt their judgments from round 2. To assess the degree of consensus among experts, the Cronbach a was calculated. Results: Conclusion: The qualitative criteria disk protrusion and perineural intraforaminal fat were rated as the most important diagnostic indicators, with median scores of 9 (range, 2 10). The highest rated quantitative criterion was the anteroposterior diameter of the osseous canal, with a median score of 8; however, there was a wide range of scores (range, 0 10). The median Cronbach a of all panelists within the group was 0.81 after the third round. Results of the survey suggest that there are no broadly accepted quantitative criteria and only partially accepted qualitative criteria for the diagnosis of lumbar spinal stenosis. The latter include disk protrusion, lack of perineural intraforaminal fat, hypertrophic facet joint degeneration, absent fluid around the cauda equine, and hypertrophy of the ligamentum flavum. q RSNA, From the Department of Diagnostic and Interventional Radiology (N.M., J.H.) and Horten Centre for Patient Oriented Research and Knowledge Transfer (M.B., U.H., F.B., J.S.), University Hospital Zurich, Raemistrasse 100, 8091 Zurich, Switzerland. Received September 9, 2011; revision requested October 26; revision received January 30, 2012; accepted February 7; final version accepted February 14. Address correspondence to N.M. ( Supplemental material: /suppl/doi: /radiol /-/dc1 q RSNA, radiology.rsna.org n Radiology: Volume 264: Number 1 July 2012

2 Spinal stenosis is the most frequent indication for lumbar surgery in people older than 65 years (1). The correct diagnosis remains a challenge for clinicians and radiologists (2 4). Lumbar spinal stenosis has been defined as buttock or lower extremity pain, which may occur with or without low back pain, associated with diminished space available for the neural and vascular elements in the lumbar spine (5). This definition covers both the anatomic anomaly narrowing of the spinal canal and the clinical manifestations neurogenic claudication. As the term stenosis implies, radiologic criteria are essential for the correct diagnosis of lumbar spinal stenosis. The North American Spine Society states in their guidelines that imaging is the key noninvasive test for lumbar spinal stenosis, but they provide no radiologic criteria for stenosis (5). Vague or indefinite diagnostic criteria represent a problem for physicians, patients, and researchers. In a recently published review, Genevay et al (6) reported that various criteria are used for describing lumbar spinal stenosis and that criteria are not always clearly defined and may prevent a reliable diagnosis. Imprecise inclusion criteria represent a major problem for researchers. Unclear definitions may seriously limit the interpretation of trial results and render the synthesis of trial results in systematic reviews and meta-analyses difficult or even impossible (7). Advances in Knowledge nn A more often used quantitative indicator (median score of 8 on a scale of 0 10) for the presence of lumbar spinal stenosis is the anteroposterior diameter of the osseous spinal canal, with a cutoff value of 12 mm at the level of the endplate. nn Cutoff values for the highest rated quantitative parameters given by the experts were 12 mm for the midsagittal diameter of the dural sac, 3 mm for the diameter of the foramen, and 3 mm for the lateral recess height. In a previously published study, a list of quantitative radiologic criteria published in the literature to describe lumbar spinal stenosis has been compiled (8). This study was performed to develop a list of radiologic criteria for describing lumbar spinal stenosis, to learn from experts which parameters they consider to be most important, and to assess the strength of agreement among experts on the most relevant criteria. Materials and Methods A three-round, based Delphi survey (9,10) was used to obtain a comprehensive and weighted list of radiologic criteria for lumbar spinal stenosis. Selection of Panelists Two musculoskeletal radiologists (N.M. and J.H.) generated a list of 41 international experts in the field of spine radiology (26 musculoskeletal radiologists and 15 neuroradiologists). All panelists have authored at least one article concerned with spinal radiology in a peer-reviewed journal. The panelists were contacted by , informed about the aims of the study, and asked to participate in the survey. Twentyseven experts agreed to participate; 23 completed the first round and 21 each completed the second and third rounds. The 21 participating experts are listed at the end of the article in the acknowledgments. Delphi Items A list of 10 quantitative radiologic criteria, measurement points, or parameters Implication for Patient Care nn Accepted qualitative criteria for the diagnosis of lumbar spinal stenosis are the presence of disk protrusion, lack of perineural intraforaminal fat, presence of hypertrophic facet joint degeneration, absence of fluid around the cauda equine, and hypertrophy of the ligamentum flavum; quantitative measurements do not appear to be accepted by our surveyed authorities. to describe lumbar spinal stenosis was prepared. These items were compiled from the results of a systematic literature review (8). In previously published articles, seven parameters for central, two for lateral, and one for foraminal stenosis had been identified. A scientific illustrator prepared drawings of the lumbar spine with markings of the measurement points. These drawings were sent together with the list of parameters to the panelists to minimize misunderstandings and reduce uncertainties about the measurement points. The detailed sequence of steps of the survey is shown in Figure 1. The detailed list is shown in Table E1 (online), and the drawings for clarification are shown in Figures 2 and 3. In the first round, participants were given the following instructions: We ask you to check thoroughly if the list with the sites of measurement, specific measurement points, and cutoff values is complete. If not, please add missing measurement points and cutoff values. We also encourage you to add qualitative criteria, which in your opinion are relevant for the diagnosis of lumbar spinal stenosis. The quantitative and qualitative parameters used to describe lumbar spinal stenosis and cutoff values, as reported by the panelists, were added to update the original list. In the second round, each panelist evaluated in the updated list each of the 17 items (10 quantitative and seven qualitative) for their relevance to the Published online before print /radiol Content code: Radiology 2012; 264: Author contributions: Guarantors of integrity of entire study, N.M., J.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, N.M., M.B., J.H., U.H., J.S.; clinical studies, N.M., F.B., J.S.; statistical analysis, M.B., U.H., J.S.; and manuscript editing, N.M., J.H., U.H., F.B., J.S. Potential conflicts of interest are listed at the end of this article. See also the editorial by Friedly and Jarvik in this issue. Radiology: Volume 264: Number 1 July 2012 n radiology.rsna.org 175

3 radiologic diagnosis and reported cutoff values for the quantitative parameters. They were asked to answer two questions: In your opinion, what is the relevance of the following measurements in the radiologic diagnosis of lumbar spinal stenosis? and Which cutoff values at different measurement points do you apply and recommend? A visual analog scale, with the anchors not relevant at all (score, 0) and extremely important (score, 10), was used to record the responses to the first question. Boxes with different cutoff values identified in the literature or reported by panelists in the first round of this Delphi survey were added to the questionnaire. For each parameter, an empty box to enter another value was added. In the third round, the pooled results of the group as to the relevance of each measurement point, presented as medians and ranges, were sent to the 21 panelists who responded. We asked them to look at the group results and their own answers from round 2 and gave them the opportunity to change values if they considered it appropriate. Owing to the fact that some panelists would not answer the questions about cutoff values and some wrote that radiologic findings could or should only be interpreted in connection with clinical information, we refrained from asking them again about cutoff values in the third round. Statistical Analysis The median and interquartile range for each parameter was calculated to demonstrate the importance that was assigned to single items. To evaluate consistency and consensus among a group of panelists, the Cronbach a was used. If the panelists responses are highly correlated, then findings are considered to be consistent and the Cronbach a will be high (close to 1) (11). We calculated the Cronbach a after rounds 2 and 3, aiming to improve it by giving the panelists information about the group s decision in round 3. The Cronbach a was calculated over all items and for the quantitative and qualitative items separately. The Cronbach a can be interpreted as a correlation coefficient of this group s evaluation with another Figure 1 Figure 1: Flowchart shows the sequence of steps in the Delphi process. random sample of panelists evaluation of the items. When the Cronbach a is close to 1, there seems to be agreement among and consistency in the responses of the panelists, which will likely be observed similarly in a different sample of panelists. For statistical analysis, R 2.13 software (R Foundation for Statistical Computing, Vienna, Austria; was used. Results Twenty-seven of the 41 contacted panelists agreed to participate. Twenty-three panelists returned the questionnaire after round 1, and 21 each returned the questionnaire after rounds 2 and 3. Thirteen experts were from Switzerland, six were from the United States, three were from Germany, two each were from Austria and England, and one was from France. The panelists had a median of 15 years (range, 4 25 years) of experience in the field of musculoskeletal radiology or neuroradiology. In the first round of the survey, participants completed the list of potential parameters by adding seven additional measurement points, all of them qualitative items: disk protrusion, extrusion, or sequestration; perineural intraforaminal fat; hypertrophic facet joint degeneration; absent fluid around the cauda equine; hypertrophy of the ligamentum flavum; serpentine and/or redundant nerve roots; and epidural lipomatosis. Second Round The medians for the diagnostic relevance of the quantitative parameters ranged from 3 to 8 (interquartile range, 1 4), and medians for the qualitative parameters ranged from 6 to 9 (interquartile 176 radiology.rsna.org n Radiology: Volume 264: Number 1 July 2012

4 Figure 2 Figure 2: Schematics provide axial view of lumbar vertebra. (a) Arrows indicate measurements of anteroposterior (1) and transverse (3) diameters of the osseous spinal canal as well as the ligamentous interfacet distance (2). (b) Determination of anteroposterior diameter of dural sac (4), height of lateral recess (2), and lateral recess angle (6). (c, d) Cross-sectional areas of dural sac (7) and contrast material column (8) are shown in red. Figure 3 Figure 3: Schematic provides sagittal view of two lumbar vertebrae. Arrows indicate measurements of anteroposterior diameter of osseous spinal canal (1), midsagittal diameter of dural sac (9 ), and anteroposterior diameter of foramen (10 ). range, 1 3). The Cronbach a for all items was 0.76 after the second round. The quantitative items alone led to a Cronbach a of 0.72, and the qualitative items Table 1 Results of Cronbach a Analysis Expert No. Round 2 Round Group Note. Data are median Cronbach a values. The Cronbach a improved from round 2 to round 3 for 19 of the 21 panelists. led to a Cronbach a of Results are shown in Table 1. Only four of the panelists reported cutoff values for all 10 quantitative parameters. Two panelists gave no values at all and disclosed that they never use quantitative values for the diagnosis of lumbar spinal stenosis. Five members of the expert panel argued that setting and interpretation of cutoff values is only reasonable in connection with clinical information. Sixteen panelists specified cutoff values for the anteroposterior diameter of the osseous canal and the diameter of intervertebral foramen, and 14 panelists specified cutoff values for the midsagittal diameter of the dural sac. Quantitative details about the five most often reported measurement points are given in Table 2. A detailed list of all results is shown in Table E2 (online). Third Round We received answers from 21 panelists (16 musculoskeletal radiologists and five neuroradiologists) in round 3. Six participants made no changes in their assessment of the relevance of the parameters, whereas 15 made changes (median, five parameters; range, 2 11 parameters). All but one of the six highest ranked radiologic criteria, with median values of 8 or 9, were qualitative parameters. The only highly rated quantitative parameter is the anteroposterior diameter of the osseous spinal canal. Details about the values of attributed relevance are shown in Table 3. After the third round, the Cronbach a improved to 0.81 (from 0.76). Radiology: Volume 264: Number 1 July 2012 n radiology.rsna.org 177

5 Table 2 Cutoff Values for the Five Highest Rated Quantitative Parameters for Measurement at MR Imaging Parameter or Measurement Point Midvertebral Level Endplate Disk Level Anteroposterior diameter of osseous spinal canal, L3 and L4 (mm),11 (,11 14) [2/5],12 (,10 15) [2/5] Midsagittal diameter of dural sac (mm),12 (,10 12) [4/4],12 (,10 12) [6/6] Diameter of foramen (mm),3 (,2 3) [8/8] Lateral recess height (mm),3 (,2 4) [12/13] Cross-sectional area of dural sac (mm 2 ),100 (,69 100) [2/2],100 (,69 100) [9/9] Note. Data are the most often cited values. Numbers in parentheses are ranges of answers given by the experts. Numbers in brackets are numbers of experts citing the most often noted values. The Cronbach a improved to 0.78 (from 0.72) for quantitative items alone and to 0.79 (from 0.77) for qualitative items. Details are shown in Table 1. Discussion Experts in musculoskeletal radiology mainly use qualitative criteria for the diagnosis of lumbar spinal stenosis. Five of the six parameters that were rated as most relevant refer to these qualitative criteria. The measurement of the anteroposterior diameter of the osseous spinal canal was the only quantitative criterion included often by the experts. Homogeneity among panelists responses for qualitative parameters was fairly high. However, no consensus for the highest ranked parameters was achieved in this survey. The results indicate that most of the participating experts rated qualitative parameters as highly relevant, whereas others rated them as more or less irrelevant. Heterogeneity in the cutoff values for the various measurement points was also observed. One of the strengths of the Delphi design used in this survey is the anonymity of panelists (12). This reduces the influence of strong opinion leaders on other participants and, thereby, the results of the survey. We have put together an international panel including neuroradiologists and musculoskeletal radiologists to include a broad range of experts from different countries. We are aware that the selection of participants has an influence on the results of the survey and that different results Table 3 Scores for Quantitative and Qualitative Criteria after the Third Round Parameter Median IQR Range Quantitative criteria Anteroposterior diameter of osseous spinal canal Cross-sectional area of dural sac Midsagittal diameter of dural sac Diameter of the foramen Lateral recess height Cross-sectional area of contrast material column Ligamentous interface distance Transverse diameter of osseus spinal canal Cross-sectional area of dural sac: stenosis ratio Lateral recess angle Qualitative criteria Disk protrusion/extrusion/sequestration Perineural intraforaminal fat Hypertrophic facet joint degeneration Absent fluid around the cauda equine Hypertrophy of the ligamentum flavum Serpine and/or redundant nerve roots Epidural lipomatosis Note. Relevance of quantitative and qualitative criteria: minimum = 0, maximum = 10. IQR = interquartile range. might have been obtained with another panel of experts. To minimize this potential bias, we invited experts from different countries in Europe and different areas of the United States. A further advantage of the Delphi method is the small number of experts that must participate to obtain useful results. As various experiments have shown, 13 participants seem to be sufficient for a Delphi study (13). With 21 panelists, we are above this limit. One of the goals of a Delphi survey is to seek consensus among experts about uncertain issues. Although no consensus about the most relevant parameters was achieved, as the wide ranges demonstrate, the survey was stopped after the third round. We assume that additional rounds would have shown similar results but that some outliers would have changed their mind to please the surveyors, which would lead to social desirability bias (14). The absence of broadly accepted standards for defining lumbar spinal stenosis may have an impact on medical practice and clinical research. 178 radiology.rsna.org n Radiology: Volume 264: Number 1 July 2012

6 Physicians caring for patients complaining about symptoms compatible with lumbar spinal stenosis expect to get the following information from radiologists: First, they need to know if stenosis is present. If stenosis is present, physicians need detailed information about the location of the stenosis and want to know which anatomic structure(s) (disk, ligamental, osseous) is causing the narrowing. This information is necessary to inform patients about their disorder and to recommend adequate treatment options for each individual patient (2). For a diagnostic criterion to be useful in clinical practice there should be a high degree of consensus among experts, with a reliability coefficient, like the Cronbach a, higher than 0.9 (15,16). Although no such high degree of consensus was reached in this survey, and in the absence of more reliable criteria, we recommend the use of at least one of the highest rated parameters, such as the presence of a disk protrusion and the presence of perineural intraforaminal fat, as well as the anteroposterior diameter of osseous canal in clinical practice and in clinical studies. However, we are aware that further effort and research is needed to develop broadly accepted classification criteria for lumbar spinal stenosis. A potential limitation of our study is that the list of criteria is incomplete. To reduce the number of missing criteria, we explicitly asked the panel members to add every criterion they are aware of. In conclusion, the results of the survey suggest that there are no broadly accepted quantitative criteria and only partially accepted qualitative criteria for the diagnosis of lumbar spinal stenosis. Acknowledgments: We thank all the participants of the expert panel: G. Andreisek, Zurich, Switzerland; K. Barath, Zurich, Switzerland; J. Bencardino, New York, NY; A. Berlis, Augsburg, Germany; J. Carrino, Baltimore, Md; C. Chung, San Diego, Calif; J.L. Drapé, Paris, France; J. Hodler, Zurich, Switzerland; S. Kollias, Zurich, Switzerland; J. Kramer, Linz, Austria; K. Lövblad, Geneva, Switzerland; E. Mc- Nally, Oxford, England; M. Pathria, San Diego, Calif; C. Pfirrmann, Zurich, Switzerland; F. Roemer, Augsburg, Germany; W. Palmer, Boston, Mass; S. Sartoretti, Winterhtur, Switzerland; U. Studler, Basle, Switzerland; D. Weishaupt, Zurich, Switzerland; M. Zanetti, Zurich, Switzerland; and V. Zubler, Zurich, Switzerland. We also thank Peter Roth, scientific illustrator at the University Hospital Zurich, for the creation of the schematic drawings. Disclosures of Potential Conflicts of Interest: N.M. No potential conflicts of interest to disclose. M.B. No potential conflicts of interest to disclose. J.H. Financial activities related to the present article: none to disclose. Financial activities not related to the present article: institution has a grant or grant pending from Siemens, GE, Guerbet, and Bayer; institution received partial support of travel of residents and junior staff. Other relationships: none to disclose. U.H. No potential conflicts of interest to disclose. F.B. No potential conflicts of interest to disclose. J.S. No potential conflicts of interest to disclose. References 1. Deyo RA, Gray DT, Kreuter W, Mirza S, Martin BI. United States trends in lumbar fusion surgery for degenerative conditions. Spine 2005;30(12): ; discussion Haig AJ, Tomkins CC. Diagnosis and management of lumbar spinal stenosis. JAMA 2010;303(1): Suri P, Rainville J, Kalichman L, Katz JN. Does this older adult with lower extremity pain have the clinical syndrome of lumbar spinal stenosis? JAMA 2010;304(23): Katz JN, Harris MB. Clinical practice: lumbar spinal stenosis. 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Am J Public Health 1984; 74(9): Graham B, Regehr G, Wright JG. Delphi as a method to establish consensus for diagnostic criteria. J Clin Epidemiol 2003; 56(12): Milholland AV, Wheeler SG, Heieck JJ. Medical assessment by a Delphi group opinion technic. N Engl J Med 1973;288(24): Dalkey N. The Delphi method: an experimental study of group opinion. Santa Monica, Calif: Rand, Fisher R, Katz J. Social-desirability bias and the validity of self-reported values. Psychol Mark 2000;17(2): Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull 1979;86(2): Bland JM, Altman DG. Cronbach s alpha. BMJ 1997;314(7080): Radiology: Volume 264: Number 1 July 2012 n radiology.rsna.org 179