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Letters and Responses |
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 for 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 posteroanterior 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 (eg, 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.
R Landel, PT, DPT, OCS, CSCS, is Assistant Professor, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, Calif
 | Footnotes |
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How did Abbott reply to the response from Landel et al? Visit www.ptjournal.org/cgi/eletters/88/1/43 to find out.
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