title: Effects of follower load and rib cage on intervertebral disc pressure and sagittal plane curvature in static tests of cadaveric thoracic spines.
abstract: The clinical relevance of mechanical testing studies of cadaveric human thoracic spines could be enhanced by using follower preload techniques, by including the intact rib cage, and by measuring thoracic intervertebral disc pressures, but studies to date have not incorporated all of these components simultaneously. Thus, this study aimed to implement a follower preload in the thoracic spine with intact rib cage, and examine the effects of follower load, rib cage stiffening and rib cage removal on intervertebral disc pressures and sagittal plane curvatures in unconstrained static conditions. Intervertebral disc pressures increased linearly with follower load magnitude. The effect of the rib cage on disc pressures in static conditions remains unclear because testing order likely confounded the results. Disc pressures compared well with previous reports in vitro, and comparison with in vivo values suggests the use of a follower load of about 400N to approximate loading in upright standing. Follower load had no effect on sagittal plane spine curvature overall, suggesting successful application of the technique, although increased flexion in the upper spine and reduced flexion in the lower spine suggest that the follower load path was not optimized. Rib cage stiffening and removal both increased overall spine flexion slightly, although with differing effects at specific spinal locations. Overall, the approaches demonstrated here will support the use of follower preloads, intact rib cage, and disc pressure measurements to enhance the clinical relevance of future studies of the thoracic spine.
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Boston, MA, USA; Department of Orthopedic Surgery, Harvard Medical School, Boston, MA, USA. Electronic address: danders7@bidmc.harvard.edu.
authors.forename: Dennis E
authors.initials: DE
authors.lastname: Anderson
authors.affiliation: Department of Mechanical Engineering, The University of Kansas, Lawrence, KS, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Mannen
authors.affiliation: Bioengineering Graduate Program, The University of Kansas, Lawrence, KS, USA.
authors.forename: Hadley L
authors.initials: HL
authors.lastname: Sis
authors.affiliation: Bioengineering Graduate Program, The University of Kansas, Lawrence, KS, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Wong
authors.affiliation: Bioengineering Graduate Program, The University of Kansas, Lawrence, KS, USA.
authors.forename: Eileen S
authors.initials: ES
authors.lastname: Cadel
authors.affiliation: Bioengineering Graduate Program, The University of Kansas, Lawrence, KS, USA; Department of Mechanical Engineering, The University of Kansas, Lawrence, KS, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Friis
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Boston, MA, USA; Department of Orthopedic Surgery, Harvard Medical School, Boston, MA, USA.
authors.forename: Mary L
authors.initials: ML
authors.lastname: Bouxsein
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D011187:Posture; D011312:Pressure; D000070602:Rib Cage / Q000502:physiology*; D013904:Thoracic Vertebrae / Q000502:physiology*
keywords: Follower load; Intervertebral disc pressure; Mechanical testing; Rib cage; Thoracic spine