Paraspinal soft tissue layer differential movement from spinal manipulative therapy preload forces

Abstract

Introduction: Implicit within spinal manipulative therapy is the assumption that treatment loads are effectively transcribed to actuate consistent mechanisms for expected clinical results. There is conflicting evidence between the mechanistic understandings and the physiologic responses from experimental evidence. Greater clarity on how loads are transferred through tissues to the target sites would be useful in enhancing utilization and efficacy of spinal manipulative procedures. Purpose: Directly monitor displacement of tissue in strata at sequential depths between the load application site and target articulation in the thoracic spine. Tissue displacement served as a surrogate for evidence of load transmission. Methods: Ultrasound elastography techniques monitored displacement in sequential strata while electromyographic signals, force, kinematic motions were monitored synchronously. Volunteers were placed prone on a treatment table, while a typical spinal manipulative pre-load maneuver was applied in the thoracic spine. Results: When applying a therapeutic load to the skin the results demonstrate with increasing depth of tissue there is a sequentially decreasing rank order in the mean cumulative displacement with each layer being significantly greater than the deeper adjacent layer. Superficial loose connective tissue layer (0.34 mm ± 0.15) vs. intermediate muscle layer (0.28 mm ± 0.11), p=0.004. Intermediate muscle layer (0.28 mm ± 0.11) vs. deep muscle layer (0.16 mm ± 0.6), p<0.0001. Filtered myoelectric signals were linearly correlated with tissue strata cumulative displacements, but the relationship was not strong (-0.23 < r < 0.46). Conversely, Pearson correlation analysis revealed strong and relatively stable correlations (0.74 < r < 0.90) for the association between displacement at the load application site and tissue layers. Conclusion: The sequential tissue motion demonstrates that some degree of load transfer through layers occurs. Both direct and indirect stimulation of tissues across both depth and breadth is feasible, to an extent consistent with the stimulation of mechanoreceptors.