Subject: The Activator® Adjusting Instrument – Biomechanical

Title: Evaluating Mechanical Force Manually Assisted Short lever adjusting using an anthropomorphic model

Reference: Sridhar Venkataraman, BS. Gary T. Yamaguchi, PhD, Paul J. Osterbauer, DC. And Arlan W. Fuhr, DC. Arizona State University Tempe, The National Institute of Chiropractic Research, Phoenix, AZ; Evaluating Mechanical Force Manually Assisted Short lever adjusting using an anthropomorphic model; In: The Proceedings of the FCER’s Fourth Annual International Conference on Spine Manipulation, Chicago, IL, May 15-17, 1992, page 136

Abstract:
Background and Objectives: Little is known about the dynamics of spinal manipulation in general and mechanical force manually assisted short lever adjustments in particular. The purpose of this study is to quantify the biomechanical response to impulsive loads applied over the cervical and lumbar spine. This would enable the estimation of the internal motion and loading that occurs due to the instrument delivered short lever chiropractic adjustment.

Method: An anthropomorphic model of the human body has been constructed for this study. The Activator Adjusting Instrument, a product of Activator Methods Inc., is used to produce the impulsive loads. The mechanical construction of the model involves the fabrication and testing of bones, ligaments, intervertebral discs and muscles using composite materials that closely mimic the passive properties of the physiological system. Electronic instrumentation in the model includes transducers which measure displacements and accelerations of the vertebrae and intervertebral pressures in the cervical and lumbar spine.

Results: An anthropomorphic model using similar mechanical construction techniques has been used to study neck pressures and motion while affixed to a halo orthosis. This previous model has been found to provide a reasonable substitute for the human spine, in terms of the mechanical responses to forces and/or torques. While no experiments have yet been completed for testing the model using the Activator adjusting instrument, the following provides an idea of what could be expected in this ongoing project:

• Measurement of the range of motion of the spinal elements due to spinal manipulation and an analysis of the effects of vertebral displacements.
• Measurement of the disk pressures for analysis of the effects of impulsive force applied by the Activator instrument.
• Measurement of the acceleration of spinal elements to deduce the relative bone movements and their implications.
• Testing for the mechanical compression of the vertebral artery due to cervical spine adjustment.

Conclusions: Anthropomorphic modeling may prove useful in understanding the dynamics of spine manipulation, particularly when integrated with computer modeling and in vivo studies.