Objective: Traditional forms of chiropractic treatment methods have attempted to restore alignment of vertebrae to proposed "normal" positions. Although this approach has existed throughout chiropractic's 100-yr history, little has been written in the scientific literature in support of this approach. The objective of this review is to study further the rationale behind this approach and evaluate some of the mechanical, anatomical and physiological evidence upon which this chiropractic approach is based.
Study selection: Articles and studies were selected that discuss analysis of stress and strains in spinal tissues from gravitational loading and experimental deformation in human and animal models. Studies that included radiographic measurements and classifications of spinal configuration in the sagittal plane were reviewed for their relevance to the chiropractic concept of a typical, usual or normal spinal configuration against which to compare patients.
Conclusion: The usual, typical or normal configuration of the cervical spine in the sagittal dimension is a lordosis with a range of 16.5-66 degrees when measured as tangent lines along the cervical curve of the posterior vertebral body margins of C2 and C7. An analysis of stresses and strains supports this claim, as do studies from the scientific literature that attempt to measure and classify average cervical configuration from large population bases. The use of normative data as a gauge against which to measure patients' structural health and as an outcome of the degree of success or failure of chiropractic interventions seem to be logical consequences of these findings.