Cervical Spine Geometry Correlated to Cervical Degenerative Disease in a Symptomatic Group

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To the Editor:

Wiegand et al¹ used a cross-sectional approach to show a correlation between cervical spine alignment and cervical degenerative joint disease (DJD) when each was assessed via plain film radiography. The authors' final conclusion states that if further work supports this correlation, “the opportunity to predict risk factors for cervical degenerative joint disease is available using cervical radiography.”

We would like to point out what we perceive are 2 shortcomings of this study. First, there is lack of clarity regarding the data analysis of certain subjects. Second, we feel the data presented do not support the above conclusion and that assessing the issue of risk for degenerative joint disease would require more than a correlation in a cross-sectional study.

On our first point, the radiographic inclusion criteria allowed degenerative joint disease as well as other pathologies. The authors describe 11 subjects with pathologies other than degenerative joint disease, including diffuse idiopathic skeletal hyperostosis (DISH), congenital block, fracture, surgical fusion, and other. However, the way these subjects were treated in the data analysis is ambiguous. It is unclear if they were included in the DJD pathology group, the nonpathology group, or were omitted. Including these patients in the study group would make it difficult to accurately describe the relationship between geometric abnormalities and DJD alone (the goal of the study), and results obtained in such a manner must be viewed with extreme skepticism.

Our second point regards the authors' final conclusion on the subject of risk. This study showed that a group of symptomatic subjects exhibited contemporaneous signs of degenerative pathology and misalignment on plain film radiographs. However, the time-order relationship is unknown. There is no indication that the identified cervical geometric abnormalities even preceded-let alone contributed to the development of−the observed degenerative pathology.

This is an inherent limitation of cross-sectional studies; there is usually no way of knowing which of the correlated findings occurred first, so attributing risk is very problematic.² In the Weigand et al¹ study, this problem is compounded because the proposed risk factor is actually a feature of the disease. Nonuniform loss of joint space and altered joint alignment are 2 of the characteristic radiographic features of degenerative joint disease.^3., ^4. It is possible that the subjects in question were misaligned because they were degenerated and not degenerated because they were misaligned. In other words, it may be that cervical degenerative joint disease is a risk factor for cervical spine geometric abnormalities and not vice-versa.

A more appropriate approach to assess risk for degenerative joint disease would be a case-control design measuring characteristics of individuals that predate the onset of disease.² In this case, it would require having prior radiographs of all subjects before degenerative pathology was evident and then noting if subjects with geometric abnormalities in the past were more likely to exhibit degenerative pathology at the time of investigation. Even better would be a prospective cohort design^2., ^5. where 2 groups–one with and the other without geometric abnormalities but both without degenerative joint disease–could be followed to see if there was a difference in the rate of developing the disease at a later date.

While these designs may require more time and resources, they are better suited than cross-sectional approaches to provide evidence of risk. We look forward to the results of these types of studies to begin to understand the role that spinal misalignment may play in the development of degenerative joint disease.

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References 

1. Wiegand R, Kettner NW, Brahee D, Marquina N. Cervical spine geometry correlated to cervical degenerative disease in a symptomatic group. J Manipulative Physiol Ther. 2003;26:341–346
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2. Gelbach SH. In: Interpreting the medical literature. New York: McGraw-Hill, Inc; 1993;p. 57–66
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3. Resnick D. Degenerative disease of the spine. In:  Resnick D editors. Bone and joint imaging. 2nd ed. Philadelphia: WB Saunders; 1996;p. 355–377
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4. Rowe LJ, Yochum TR. Arthritic disorders. In:  Yochum TR,  Rowe LJ editor. Essentials of skeletal radiology. 2nd ed. Baltimore: Williams & Wilkins; 1996;p. 795–817
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5. Sackett DL, Richardson WS, Rosenberg W, Haynes RB. Critically appraising the evidence. In:  Sackett DL,  Richardson WS,  Rosenberg W,  Haynes RB editor. Evidence-based medicine: how to practice and EBM teach. Edinburgh: Churchill Livingstone; 1997;p. 85–90
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