OBJECTIVE: To compare the current knowledge of 3-D spinal mechanics and abnormal equilibrium states with chiropractic motion theories, chiropractic vertebral letter listing theories, and chiropractic technique theories.

DATA COLLECTION: A manual search of available reference texts and a computer search of literature from Index Medicus were collected with an emphasis on 3-D studies of human spinal movements, segmental instability, Euler buckling of the spine, and chiropractic theories concerning vertebral movements.

RESULTS: Previous spinal coupling results based upon two-dimensional radiographic studies are inadequate and inaccurate. Therefore, the validity of any chiropractic technique procedure, listing, motion analysis or adjusting style based on the two-dimensional radiograph and coupling studies must be questioned. We have identified four types of spinal subluxations (displacements) in the biomechanical literature: (a) posture main motion and associated segmental coupling, (b) Euler buckling viewed in the anteroposterior view, (c) snap through viewed in the lateral view and (d) segmental instability.

CONCLUSIONS: Full three-dimensional investigations of spinal coupling patterns have shown that the vertebrae rotate and translate in all three axes and that previous theories of spinal coupling based upon two-dimensional studies are inaccurate and invalid. Previous chiropractic letter listings (e.g., PRI, PLS, etc.) of spinal displacements are inadequate and invalid. Only one of the four types of biomechanical displacements, segmental instability, is consistent with the traditional chiropractic theory of segmental spinal displacements; in general, this does not respond well to care. In general, vertebrae displacement must be viewed in the context of equilibrium configurations and one vertebra can not be displaced as an individual misalignment. Validity questions arise for any technique methods that use letter listings of displacement taken from motion palpation or two-dimensional radiographic analysis.

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