title: Differential displacement of soft tissue layers from manual therapy loading.
abstract: BACKGROUND
  Understanding the biomechanics of spinal manipulative therapy requires knowing how loads are transmitted to deeper structures. This investigation monitored displacement at sequential depths in thoracic paraspinal tissues parallel with surface load directions.
  
  
  METHODS
  Participants were prone and a typical preload maneuver was applied to thoracic tissues. Ultrasound speckle tracking synchronously monitored displacement and shear deformation of tissue layers in a region of interest adjacent to load application to a depth of 4 cm. Cumulative and shearing displacements along with myoelectric activity were quantitatively estimated adjacent to loading site.
  
  
  RESULTS
  The cephalocaudal cumulative displacement in layers parallel to the surface were, in order of depth, 1.27 (SD=0.03), 1.18 (SD=0.02), and 1.06 (SD=0.01) mm (P<0.000), respectively. The superficial/intermediate shear was 2.1 ± 2.3% whereas the intermediate/deep shear was 4.4% (SE=3.7, P=0.014). Correlation of tissue layers was stronger with application site displacement at the surface (0.87<r<0.89) than with muscle activation (0.65<r<0.67).
  
  
  CONCLUSIONS
  Surface loading of the torso in combined posteroanterior and caudocephalic directions result in both displacement of tissues anteriorly and in shearing between tissue layers in the plane of the tissues strata to depths that could plausibly affect spinal tissues. Displacements of tissues more likely arise passively, consistent with load transmitted by the retinacula cutis and epimuscular force pathways. Displacements are similar in magnitude to those known to evoke biologically relevant responses in both animal and human studies.
authors.affiliation: Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Shawn
authors.initials: S
authors.lastname: Engell
authors.affiliation: Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada; Graduate Education and Research, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada. Electronic address: Jtriano@cmcc.ca.
authors.forename: John J
authors.initials: JJ
authors.lastname: Triano
authors.affiliation: Department of Neurological Sciences, College of Medicine, University of Vermont, Burlington, VT, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Fox
authors.affiliation: Department of Neurological Sciences, College of Medicine, University of Vermont, Burlington, VT, USA; Osher Center for Integrative Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: Helene M
authors.initials: HM
authors.lastname: Langevin
authors.affiliation: Biomedical Engineering and Radiology, Columbia University, New York, NY, USA.
authors.forename: Elisa E
authors.initials: EE
authors.lastname: Konofagou
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003238:Connective Tissue / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D008297:Male; D020393:Manipulation, Spinal; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D016684:Prone Position; D013904:Thoracic Vertebrae; D055815:Young Adult
keywords: Biomechanics; Cumulative displacement; Elastography; Electromyography; Shear displacement; Spinal manipulation