OBJECTIVE: The purpose of this study was to quantify and compare the three-dimensional intersegmental motions among three commonly used chiropractic adjusting instruments.
SETTING: Operating theatre, Institute for Medical and Veterinary Science, Adelaide, Australia
METHODS: Six adolescent Merino sheep were examined. In all animals, tri-axial accelerometers were attached to intraosseous pins rigidly fixed to the L1 and L2 lumbar spinous processes under fluoroscopic guidance. Three hand-held mechanical force chiropractic adjusting instruments (Chiropractic Adjusting Tool [CAT], Activator Adjusting Instrument IV [Activator IV], and the Impulse Adjusting Instrument [Impulse]) were used to randomly apply posteroanterior spinal manipulative thrusts to the spinous process of T12. Three force settings (low, medium, and high) and a fourth setting (Activator IV only) were applied in a randomized repeated measures design. Acceleration responses in adjacent segments (L1, L2) were recorded at 25 kHz, and the three-dimensional intersegmental segmental (L1-L2) acceleration transfer at each force setting was computed and compared among devices using a repeated measures analysis of variance (ANOVA, á = .05).
RESULTS: Intersegmental acceleration responses mirrored the peak force magnitude produced by each adjusting instrument. For all devices, intersegmental accelerations were greatest for axial, followed by posteroanterior and medial-lateral measurement axes for the data examined. Compared to the mechanical (spring) adjusting instruments (CAT, Activator IV), the electromechanical Impulse Adjusting Instrument was found to produce the most linear increase in both force and intersegmental motion response. Intersegmental motions were similar when comparing the spring-loaded devices, Activator IV and CAT for most force settings and axes examined. Significantly larger magnitude intersegmental motions were observed for Activator IV over CAT at the medium setting and setting 4 (p<.05). Significantly larger magnitude posteroanterior and medial-lateral intersegmental motion responses were consistently observed for Impulse over Activator IV and CAT for nearly all medium and high force settings examined (p<.05) measuring nearly 2 to 3-fold larger in some cases.
CONCLUSIONS: Larger magnitude 3D intersegmental motion responses were observed for spinal manipulative thrusts delivered with Impulse for nearly all force settings examined. Knowledge of the vertebral motion responses produced by hand-held chiropractic adjusting instruments assists in understanding biomechanical responses and supports the clinical rationale for patient treatment using instrument-based adjustments. Our results indicate that the force-time characteristics of impulsive-type adjusting instruments significantly affects spinal motion, and suggests that instruments can and should be tuned to provide optimal force delivery.
This abstract is reproduced with the permission of the publisher.