Journal of Manipulative and Physiological Therapeutics
Volume 27, Issue 8 , Pages 533-534, October 2004

The Reliability of Quantifying Upright Standing Postures as a Baseline Diagnostic Clinical Tool

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Article Outline

 

To the Editor:

We read with interest the article by Dunk et al1 regarding poor reliability of a type of postural analysis. We have identified significant methodological flaws that challenge the validity of their conclusions.1

To begin, this investigation used only 1 examiner, and it is possible that this examiner could have made gross mistakes from one examination to the next, causing poor intraexaminer reliability. Conversely, he/she could have been unusually good from one examination to the next and provide artificially high intraexaminer reliability. Statistically, therefore, multiple examiners are needed to average any artificially low or high intraexaminer data and give a more reasonable mean. It is generally accepted that a minimum of 3 examiners, each performing an analysis at least twice, is needed for any conclusions to be drawn about interexaminer and intraexaminer reliability.2, 3

Second, their use of only 14 study subjects is a questionable sample size for reliability studies.1 Traditionally, depending on the ICC type of equations used, between 30 and 60 subjects would be necessary for a conclusion of reliability to be made.2, 3 A proper statistical power analysis is necessary for this conclusion to be valid. Perhaps Dunk et al1 could provide a power analysis demonstrating significance based on their small number of subjects.

Third, the authors omitted several references that contradict their conclusions because they show that posture is highly repeatable in both the sagittal and coronal planes.4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 For example, in a study of 160 men and women, Raine and Twomey4 found no significant differences for each group with repeated measures of head and shoulder postures. Using postural photographs in 18 subjects, Zonnenberg et al5 found good to excellent ICCs for 2 examiners and 2 trials 7 days apart. Using more sophisticated computerized analysis, Swinkles and Dolan6, 7 showed that healthy individuals are capable of accurate postural repositioning both within and between day sessions and that this is independent of spinal movements between recordings.

The information from the above studies4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 indicates that 1 or more serious flaws exist with the methods and design used by Dunk et al.1 For example, Dunk et al1 used fins at C7, T12, and L5. These fins may magnify errors in postural repositioning. Further, Dunk et al1 used landmarks “taped to the skin”; however, they claim to have used the occipital protuberance but fail to mention that they placed this over the hair of the subject without shaving this region (their Fig 1B). Additionally, after taping these landmarks to the skin, the subjects walked 20 meters. Walking could have caused the fins to shift or tilt slightly, and Dunk et al1 make no mention of accounting for this variable. Finally, Dunk et al1 did not control for subject positioning at the feet in a standardized manner; they simply let the subject reposition themselves for each session. If the subject stood slightly oblique (lateral view) to the wall and the camera on 1 session or further to the left or right (anteroposterior and posteroanterior views) compared with the next, this artificially would create errors in analysis and affect reliability of repositioning. In fact, looking at Fig 1 on page 93,1 the subject is absolutely standing different distances from the vertical line attached to the wall. These types of projection errors with photographs have been detailed by earlier investigations5, 20 and it needs to be stated that the subject's posture may not have been different from session to session, only the position relative to the reference frame.

Lastly, we draw attention to the inappropriate extrapolation of their data to the performance of other posture analysis software. For example, the BioTonix system does not require digitization of photographically captured reflective points; this system is a web-based computation of the center of reflective markers placed on different body landmarks. A mathematical algorithm reads the respective coordinates of the reflectors. Further, the BioTonix system does not merely compare angles to vertical as was performed by Dunk et al.1 The BioTonix system calculates distances and angles and provides measurements of body parts relative to the part immediately below. This minimizes the effect of sway or shift at the lower extremities. Therefore, the results from Dunk et al1 only apply to their design.

The lack of a sufficient number of examiners, the small sample size of 14 subjects, the omission of several relevant references, the errors in subject and marker positioning, and the extrapolation of their findings to entirely different postural systems create considerable concern with validity of this publication. We look forward to an explanation from the authors concerning these methodological flaws, omissions, and inappropriate extrapolations.

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References 

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  19. Vernon H. An assessment of the intra- and inter-reliability of the posturometer. J Manipulative Physiol Ther. 1983;6:57–60
  20. Zonnenberg AJJ, Van Maanen CJ, Oostendorp RAB, Elvers JWH. Body posture photographs as a diagnostic aid for musculoskeletal disorders related to temporomandibular disorders (TMD). J Craniomandibular Pract. 1996;14:225–232

PII: S0161-4754(04)00166-6

doi:10.1016/j.jmpt.2004.08.009

Journal of Manipulative and Physiological Therapeutics
Volume 27, Issue 8 , Pages 533-534, October 2004

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