Abstract
BackgroundPrevious studies observed that the intervertebral disc experiences the greatest forces during spinal manipulative therapy (SMT) and that the distribution of forces among spinal tissues changes as a function of the SMT parameters. However, contextualized SMT forces, relative to the ones applied to and experienced by the whole functional spinal unit, is needed to understand SMT’s underlying mechanisms.AimTo describe the percentage force distribution between spinal tissues relative to the applied SMT forces and total force experienced by the functional unit.MethodsThis secondary analysis combined data from 35 fresh porcine cadavers exposed to a simulated 300N SMT to the skin overlying the L3/L4 facet joint via servo-controlled linear motor actuator. Vertebral kinematics were tracked optically using indwelling bone pins. The functional spinal unit was then removed and mounted on a parallel robotic platform equipped with a 6-axis load cell. The kinematics of the spine during SMT were replayed by the robotic platform. By using serial dissection, peak and mean forces induced by the simulated SMT experienced by spinal structures in all three axes of motion were recorded. Forces experienced by spinal structures were analyzed descriptively and the resultant force magnitude was calculated.ResultsDuring SMT, the functional spinal unit experienced a median peak resultant force of 36.4N (IQR: 14.1N) and a mean resultant force of 25.4N (IQR: 11.9N). Peak resultant force experienced by the spinal segment corresponded to 12.1% of the total applied SMT force (300N). When the resultant force experienced by the functional spinal unit was considered to be 100%, the supra and interspinous ligaments experienced 0.3% of the peak forces and 0.5% of the mean forces. Facet joints and ligamentum flavum experienced 0.7% of the peak forces and 3% of the mean forces. Intervertebral disc and longitudinal ligaments experienced 99% of the peak and 96.5% of the mean forces.ConclusionIn this animal model, a small percentage of the forces applied during a posterior-to-anterior SMT reached spinal structures in the lumbar spine. Most SMT forces (over 96%) are experienced by the intervertebral disc. This study provides a novel perspective on SMT force distribution within spinal tissues.
Highlights
Spinal manipulative therapy (SMT) is a conservative intervention commonly used to treat spinal pain and other musculoskeletal conditions (Hurwitz, 2012; Beliveau et al, 2017)
As the objective of this study was to describe the SMT force distribution between spinal tissues in terms of percentage relative to the applied SMT force and the total forces experienced by the spine segment, the resultant force magnitude (Fres) was calculated using Equation 1, where Fx corresponds to the force in the mediolateral direction, Fy is the force in the anterioposterior direction and Fz is the force in the superioinferior direction
Our results show that it is only a small percentage of the applied SMT forces that reaches spinal structures [median peak force 36.4N (14.1 interquartile range (IQR)) of applied 300N] and that, among these, the majority of force is experienced by the intervertebral disc, which is in accordance with previous studies (Kawchuk et al, 2010; Funabashi et al, 2016, 2017a,b, 2018)
Summary
Spinal manipulative therapy (SMT) is a conservative intervention commonly used to treat spinal pain and other musculoskeletal conditions (Hurwitz, 2012; Beliveau et al, 2017). SMT thrust loading rate has been observed to influence vertebral displacements and muscle spindle response (Reed et al, 2013; Nougarou et al, 2016) In addition to these force-time characteristics, other input parameters, such as location of applied force has been investigated and reported to influence vertebral displacements, spinal stiffness, paraspinal muscle activity and muscle spindle discharge frequency (Colloca and Keller, 2001; Keller et al, 2003; Colloca et al, 2004; Edgecombe et al, 2013; Reed et al, 2015; Reed and Pickar, 2015). Contextualized SMT forces, relative to the ones applied to and experienced by the whole functional spinal unit, is needed to understand SMT’s underlying mechanisms
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