J Manipulative Physiol Ther. 1997 May; 20(4): 246-56.

Evaluation of the assumptions used to derive an ideal normal cervical spine model.

Harrison DD, Janik TJ, Troyanovich SJ, Harrison DE, Colloca CJ.

Department of Mathematical Sciences, University of Alabama, Huntsville 35899, USA.

OBJECTIVES: To evaluate the accuracy of anatomical assumptions made to derive a geometrical, ideal, normal model of the upright, static, sagittal cervical spine, to make comparisons with other spinal models and to discuss the implications of a normal cervical model. BACKGROUND: Anatomical assumptions were made based on observations to assist in the development of a computerized geometrical model of the ideal upright, static, sagittal cervical spine. These assumptions address the magnitudes of the contribution made by the vertebral bodies and intervertebral discs to the overall magnitude and geometric shape of the cervical lordosis. STUDY DESIGN: (a) Data were collected from 400 lordotic lateral cervical radiographs and compared with the predictions of a geometric normal cervical lordotic model. Angels of intersecting tangent lines, drawn at posterior vertebral body margins, were measured at each disc space and between C2 and C7. Height-to-length ratios and an anterior weight-bearing distance were measured. (b) Literature reviews were obtained through Medline and Chirolars. RESULTS: (a) Modeling: the 400 sample subjects varied from the geometric model by approximately 5%. Subgroup averages, from partitioning the C2-C7 angle into 5 degrees intervals, were less than 8% in error to model predictions. (b) Literature review: lordosis is the normal configuration for the cervical spine and many chiropractic empirical models are similar. CONCLUSIONS: The anatomical assumptions used to derive our normal geometric model of the cervical lordosis seem to be supported by the average values and literature reviewed. Two typical geometric configurations of the cervical spine were identified as a normal circular lordotic arc of 34 degrees and an ideal normal of 42 degrees. Literature reviewed establishes cervical lordosis as a desirable clinical outcome of care.