Introducing the External Link Model for Studying Spine Fixation and Misalignment: Part 2, Biomechanical Features☆
Received 22 April 2006; received in revised form 26 September 2006; accepted 9 December 2006.
Abstract
Objectives
The purpose of this study was to characterize intervertebral stiffness and alignment changes in the external link model and evaluate it as an experimental mimic for studying the chiropractic subluxation.
Method
A controlled test-retest design was used to evaluate rats with spine segments linked in 3 alignment configurations and controls that were never linked. Dorsal-to-ventral spine stiffness was measured with a load platform, and flexion/extension misalignment was assessed on lateral radiographs obtained with a spine extension jig. Descriptive statistics were computed for study groups, and multiple linear regression models were used to examine all potential explanatory variables for the response variables “stiffness” and “joint position.”
Results
Rats tested with links in place had significantly higher dorsal-to-ventral stiffness in the neutral configuration than rats in the flexed configuration. This difference remained after the links were removed. Stiffness after link removal was greater for longer linked periods. Surprisingly, stiffness after link removal was also greater with longer unlinked periods. Longer linked periods also produced greater misalignments during forced spine extension testing. Although link configuration was not a statistically significant predictor of misalignments, longer times after link removal did produce greater misalignments.
Conclusions
This study suggests that the external link model can be a valuable tool for studying the effects of spine fixation and misalignment, 2 cardinal features of what has been historically described as the chiropractic subluxation. Significant residual stiffness and misalignment remained after the links were removed. The progressive course of this lesion is consistent with subluxation theory and clinical chiropractic experience.
aAssociate Professor, Palmer Center for Chiropractic Research, Davenport, Iowa
bProfessor, Department of Research, National University of Health Sciences, Lombard, Illinois
dDirector of Community Health Services, Ingham County Health Department, Lansing, Michigan
Submit requests for reprints to: Charles N.R. Henderson, 741 Brady St, Davenport, IA 52803, USA.
☆ This study was supported by grant 97-10-18 from the National Chiropractic Mutual Insurance Company administered by the Foundation for Chiropractic Education and Research. At the Palmer Site, this investigation was conducted in a facility constructed with support from the Research Facilities Improvement grant C06 RR15433 from the National Center for Research Resources, National Institutes of Health, Washington, D.C.
ABSTRACT