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Response: Perceived threat to PAIVM validity?
Author's Response: Perceived threat to PAIVM validity?
Validity of spine accessory motion assessment not threatened by results of this study
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J. Haxby Abbott, Senior Research Fellow University of Otago
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haxby.abbott{at}otago.ac.nz J. Haxby Abbott
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I thank Landel et al1 for their reply. But I believe that the old "careful reading will reveal that his arguments, in fact, support our findings" line is code for "he's got us; quick, bring out the smoke and mirrors!" The response by Landel et al does not address the key flaw in their research design, which is that the reference standard they used was not a valid match for the intent of the clinical test. Therefore, their results cannot support the concluding sentence of their abstract: "This finding calls into question the validity of the [posterior-anterior] PA procedure for assessing intervertebral lumbar spine motion."2(p43) Landel et al have responded that "we did not state that...the [postero-anterior intervertebral motion] PAIVM test['s]...worth is in question" and that "we fail to see how our findings could be perceived as a threat to the validity of the PAIVM test." However, the concluding sentence of their abstract (above) and the next-to-last sentence of their conclusion state "This finding calls into question the validity of the PA procedure as a method for assessing intervertebral motion of the lumbar spine."2(p49) These inconsistent statements are grounds enough, I would think, for me to request an apology for their accusation that one of my factual statements was "disingenuous." It was not. Clinicians do believe the PAIVM tells them something about segmental movement: sagittal translation, not rotation.3-5 We asked a very large number of clinicians in 2 different countries, and they told us.3 I agree that there is need and scope for more research to clarify the biomechanical concurrent validity, and clinical predictive validity, of these tests; however, the authors are incorrect when they state that "prior to our report, there were no studies showing that the PAIVM test can reliably assess either motion or stiffness."1 There are several, some of which the authors referred to in their research report.2 In addition, and more pertinently, there have been 2 concurrent validity studies of the PAIVM tests.4,5 These independently found very consistent results in support of the validity of PAIVMs for assessing sagittal translation, as summarized by Abbott.6 The study by Landel et al is 1 of 3 studies to investigate the concurrent validity of the PAIVM test.2,4,5 It is the one with the smallest number of subjects and the smallest number of testing clinicians. Although use of magnetic resonance imaging (MRI) allowed the investigation to be truly concurrent, a strength of the present study,2 the method for measuring motion was unsophisticated, and the choice of the biomechanical parameter measured was inappropriate for the intent of the clinical PAIVM test; therefore, we agree with the authors when they state that "We fail to see how our findings could be perceived as a threat to the validity of the PAIVM test." References 1 Landel R, Kulig K, Fredericson M, et al. Author's response: perceived threat to PAIVM validity? Available at: http://www.ptjournal.org/cgi/eletters/88/1/43. 2 Landel R, Kulig K, Fredericson M, et al. Intertester reliability and validity of motion assessments during lumbar spine accessory motion testing. Phys Ther. 2008;88:43-49. 3 Abbott JH, Flynn TW, Fritz J, et al. Manual physical assessment of spinal segmental motion: intent and validity. Man Ther. doi:10.1016/j.math.2007.09.011. 4 Abbott JH, McCane B, Herbison P, et al. Lumbar segmental instability: a criterion-related validity study of manual therapy assessment. BMC Musculoskelet Disord. 2005;6:56. 5 Fritz JM, Piva SR, Childs JD. Accuracy of the clinical examination to predict radiographic instability of the lumbar spine. Eur Spine J. 2005;14:743–750. 6 Abbott JH. Passive intervertbral motion tests for diagnosis of lumbar instability. Aust J Physiother. 2007;53:66. |
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Rob Landel University of Southern California, Kornelia Kulig, Michael Fredericson, Bernard Li, and Christopher M. Powers
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rlandel{at}usc.edu Rob Landel, et al.
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We wish to thank J Haxby Abbott for his comments concerning our study1 and appreciate the opportunity to address the points that he has raised. Despite his apparent disagreement with parts of our report, careful reading will reveal that his arguments, in fact, support our findings. In his comments, Abbott states that clinicians place more importance on stiffness than motion, citing a November 2007 survey.2 In the Discussion section of our study, we state, "The possibility that the examiners' judgments were influenced by perceived stiffness instead of motion could explain the poor agreement between the manual assessments and the [magnetic resonance imaging] MRI measurements."1(p48) The concluding statement of the article reads, "It is possible that clinicians are basing their manual [posterior-anterior] PA assessments on perceived stiffness instead of intervertebral motion; however, further research is needed to test this hypothesis."1(p49) Our conclusions are in agreement with what clinicians report in the "intent of assessment" survey by Abbott et al.2 The ability to manually distinguish mechanical stiffness has been demonstrated, although this is not true on human spines.3 Maher and Adams4 suggest that the perception of posteroanterior stiffness may be multidimensional, influenced for example by visual cues, and our findings suggest that the amount of sagittal plane motion is not one of those dimensions. Our conclusions regarding stiffness can only be inferred from our data, because (as we pointed out) we did not measure the force applied. One must ask, however, what the 2 clinicians perceived when they agreed on the least mobile segment even when the segmental rotation occurring at those segments was rarely the least. We hypothesize that the clinicians were assessing something other than motion. A reasonable conclusion is that the clinicians were able to feel how the motion ended better than they were able to feel the motion itself, because they did not agree on the most mobile segment. It is plausible that they felt an increase in the resistance to the force applied, which of course is the definition of stiffness. With regard to the "threat" to the postero-anterior intervertebral motion (PAIVM) test, we disagree that the "validity of the spine accessory motion assessment is not threatened [emphasis added]," at least in the sagittal plane. It cannot be clearer that the intent of the test, as suggested by its name, is to assess motion. This is true regardless of what clinicians have subsequently redefined the test to mean. Indeed, this would suggest that clinicians, in advance of supporting research, have already abandoned the concept of motion testing using the PAIVM test in favor of assessments of pain and stiffness. Perhaps, to reflect this apparent change of intent by clinicians, the name of the test should be changed to Passive Pain Provocation and Stiffness Test (PPPAST). It is disingenuous to state that "clinicians use [the PAIVM test] primarily to assess pain response, but in terms of biomechanical parameters clinicians primarily assess quality of resistance (stiffness, greater or lesser resistance to therapist-applied pressure), quantity of sagittal translation, and quality of the path of vertebral motion." The primary finding of the cited survey was that the "majority of respondents (65.9%; 95% CI 61.5%, 70.0%) believed that PAIVMs are 'somewhat accurate' or 'very accurate' for estimating the quantity of movement present at a lumbar segment (for example identifying restricted, normal, excessive movement)."2 It is clear from Abbott et al2 that clinicians believe the test tells them something about segmental movement. In any case, we did not state that the PAIVM test should be abandoned or that its worth is in question. Indeed, we stated that there are uses for the examination, for example, as part of the clinical prediction rule for manipulation of the lumbar spine. The appearance of threat to the test is in the eye of the beholder. Our point is that if the intent of the test is to assess motion, as the name of the test suggests, then the test is likely not very useful. We fail to see how our findings could be perceived as a threat to the validity of the PAIVM test when, prior to our report, there were no studies showing that the PAIVM test can reliably assess either motion or stiffness. Discussing validity in the absence of reliability is a futile exercise. Therefore, if it were not for our determination that using a dichotomous within-subject scale allows for reliable identification of the least mobile segment, we could not even begin to have this discussion. Our results provide more, not less, reason to continue to examine this assessment. Finally, we disagree with the use of the term "meaningless." It is hardly meaningless to state that what clinicians are assessing during the performance of the PAIVM test is not segmental rotation. This information furthers our understanding of the biomechanics behind the test. Furthermore, careful reading of the text will reveal that we cited our study's limitations, including the lack of force measurement (in order to calculate stiffness), and the method’s inability to capture linear displacement. We thank Dr Abbott for reiterating our paper's call for this type of research to be done, again in order to more fully understand the biomechanics underlying this clinical test. References 1 Landel R, Kulig K, Fredericson M, et al. Intertester reliability and validity of motion assessments during lumbar spine accessory motion testing. Phys Ther. 2008;88:43-49. 2 Abbott JH, Flynn TW, Fritz J, et al. Manual physical assessment of spinal segmental motion: intent and validity. Man Ther. doi: 10.1016/j.math.2007.09.011.
3 Maher C, Adams R. Is the clinical concept of spinal stiffness multidimensional? Phys Ther. 1995;75:854-860; discussion 861-854. 4 Maher CG, Adams RD. Stiffness judgments are affected by visual occlusion. J Manipulative Physiol Ther. 1996;19:250-256. |
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J.Haxby Abbott, Senior Research Fellow University of Otago
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haxby.abbott{at}otago.ac.nz J.Haxby Abbott
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The validity of a test or measure is the extent to which that test or measure actually assesses what it is intended to assess. The research design for investigating the validity of a test or measure requires that all subjects undergo both the clinical test or measure and a reference standard assessment that reflects as closely as possible the true state of what the clinical test or measure being studied is intended to assess. The key word in both of these statements is "intend." In order for the research design to have internal validity, it is crucial that there is a match between intent of the clinical test or measure and what the reference standard can measure. No match—the research design is faulty and the result is meaningless. In this study by Landel et al,1 the clinical test under investigation is the postero-anterior intervertebral motion test (PAIVM). So far so good. What is the PAIVM test intended to measure? Recent research informs us that clinicians use it primarily to assess pain response, but in terms of biomechanical parameters clinicians primarily assess quality of resistance (stiffness, greater or lesser resistance to therapist-applied pressure), quantity of sagittal translation, and quality of the path of vertebral motion.2 The reference standard chosen in the present study is not appropriate because it measures quantity of intervertebral sagittal rotation. Clinicians do not intend to assess quantity of sagittal rotation with the PAIVM test.2 Barely 2% of the members of two national manual therapy organizations who responded to our "intent of assessment" survey ranked quantity of rotation as an important assessment using the PAIVM test. Of all the biomechanical parameters measurable, rotation was reported by clinicians as that they had least intention of assessing.2 The reference standard chosen by the researchers is not a match to the intent of the clinical test. No match—the research design is faulty and the result is meaningless. What biomechanical parameters should the researchers have used as the reference standard? According to the clinicians who use these assessments, they intend to assess stiffness, translation, and the path of the vertebrae during motion2; therefore, I suggest the researchers should include both force and displacement to measure stiffness, and measure sagittal translation and the finite center of rotation. References 1 Landel R, Kulig K, Fredericson M, et al. Intertester reliability and validity of motion assessments during lumbar spine accessory motion testing. Phys Ther. 2008;88:43-49. 2 Abbott JH, Flynn TW, Fritz JM, et al. Manual physical assessment of spinal segmental motion: intent and validity. Man Ther. doi:10.1016/j.math.2007.09.011. |
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