The effect of duration and amplitude of spinal manipulative therapy (SMT) on spinal stiffness

Abstract

The aim of this study was to determine the effect of spinal manipulation therapy (SMT) force magnitude and force duration on the spinal stiffness of a feline preparation. A mechanical device performed simulated SMTs at the L6 spinous process in 22 anesthetised felines. Subjects were divided into four groups. Two groups (no preload, preload) received SMT having maximal displacements of 1.0mm, 2.0mm and 3.0mm of total displacement (displacement control). In two other groups (preload, no preload), SMTs were applied with maximal loads of 25%, 55% and 85% body weight (force control). Each of the SMTs were applied in order of increasing displacement or force amplitudes, at increasing durations ranging from 25 to 250 ms. Spinal stiffness was quantified by applying an indentation load to external surface of the back. Linear mixed effects models were fit for post-SMT stiffness variables. When SMT was applied under displacement control with and without a preceding preload, a significant interactive effect occurred between force magnitude and force duration (p≤0.05) for some of the stiffness variables. The findings from this experiment demonstrate that spinal stiffness in a feline model was affected by the interaction of the force amplitude and force duration parameters but the exact nature of this interaction remains unclear. This study provides guidance for further investigation given other SMT parameters not tested here may facilitate the ability of SMT to alter spinal stiffness.

Neural responses to the mechanical characteristics of high velocity, low amplitude spinal manipulation: Effect of specific contact site

“…Because the thrust of an HVLA-SM is intended to impart movement to a vertebra (Bergmann, 2005) we first applied a preload force beyond which the L 6 vertebra would be expected to move during the thrust using methods previously described (Vaillant et al, 2012; Reed et al, 2013; Cao et al, 2013). Thrust duration was fixed at 100ms based upon clinical findings (Hessell et al, 1990; Herzog et al, 1993; Triano, 2001) where thrust durations in the thoracic and lumbar spines are typically less than 150ms and upon animal studies (Pickar and Kang, 2006; Pickar et al, 2007; Reed et al, 2013) where 100ms represents the threshold duration at which a non-linear increase in muscle spindle discharge occurred.…”

“…While preload magnitude and duration interact to modulate muscle spindle activity during the thrust (Reed et al, 2014), preload, thrust duration, and thrust amplitude all appear to have minimal effect on changing the responsiveness of muscle spindles to spinal movement following the thrust (Cao et al, 2013; Reed et al, 2014). Also using a feline model Kawchuk and colleagues found that thrust duration interacts with thrust amplitude toward changing spinal stiffness (Vaillant et al, 2012). In addition, the specific contact site through which the thrust is applied determines whether spinal stiffness changes (Edgecombe et al, 2013).…”

Effect of Spinal Manipulation Thrust Duration on Trunk Mechanical Activation Thresholds of Nociceptive Specific Lateral Thalamic Neurons

“…Hypotheses for HVLA-SM's mechanism of action have begun to focus on central neurophysiological interactions due to the nonlocalized nature of HVLA-SM-induced alterations in somatic pain that have been reported. 15,38,40 Determining both underlying neurophysiological HVLA-SM mechanisms and how clinician-controlled mechanical parameters of HVLA-SM delivery may ultimately optimize changes in central somatosensory pain modulation has become a priority in both basic 4,5,8,14 and clinical 6,7,9,10 studies of spinal manipulation. Therefore, we undertook this study as a first step in determining whether there is a relationship between HVLA-SM, thrust duration, and changes in mechanical activation thresholds of thalamic neurons.…”

“…4,5 Basic and clinical studies aimed at determining the relationship between these various mechanical delivery parameters of spinal manipulation and their effects on neurophysiological, biomechanical, and/or patient outcome measures are just beginning to be reported in the literature. [4][5][6][7][8][9][10][11][12][13][14] Once delineated, these findings could markedly improve and eventually optimize the utilization and effectiveness of spinal manipulation.…”

“…4,5 Basic and clinical studies aimed at determining the relationship between these various mechanical delivery parameters of spinal manipulation and their effects on neurophysiological, biomechanical, and/or patient outcome measures are just beginning to be reported in the literature. [4][5][6][7][8][9][10][11][12][13][14] Once delineated, these findings could markedly improve and eventually optimize the utilization and effectiveness of spinal manipulation.Numerous studies show that high-velocity, low-amplitude spinal manipulation (HVLA-SM) immediately increases mechanical pressure pain thresholds (ie, decreases sensitivity) in both symptomatic and asymptomatic individuals. [15][16][17][18][19][20][21][22][23][24] These hypoalgesic effects occur both unilaterally and bilaterally as well as proximally and distally to the manipulation site.…”