title: In situ deformation of growth plate chondrocytes in stress-controlled static vs dynamic compression.
abstract: Longitudinal bone growth in children/adolescents occurs through endochondral ossification at growth plates and is influenced by mechanical loading, where increased compression decreases growth (i.e., Hueter-Volkmann Law). Past in vivo studies on static vs dynamic compression of growth plates indicate that factors modulating growth rate might lie at the cellular level. Here, in situ viscoelastic deformation of hypertrophic chondrocytes in growth plate explants undergoing stress-controlled static vs dynamic loading conditions was investigated. Growth plate explants from the proximal tibia of pre-pubertal rats were subjected to static vs dynamic stress-controlled mechanical tests. Stained hypertrophic chondrocytes were tracked before and after mechanical testing with a confocal microscope to derive volumetric, axial and lateral cellular strains. Axial strain in hypertrophic chondrocytes was similar for all groups, supporting the mean applied compressive stress's correlation with bone growth rate and hypertrophic chondrocyte height in past studies. However, static conditions resulted in significantly higher lateral (p<0.001) and volumetric cellular strains (p≤0.015) than dynamic conditions, presumably due to the growth plate's viscoelastic nature. Sustained compression in stress-controlled static loading results in continued time-dependent cellular deformation; conversely, dynamic groups have less volumetric strain because the cyclically varying stress limits time-dependent deformation. Furthermore, high frequency dynamic tests showed significantly lower volumetric strain (p=0.002) than low frequency conditions. Mechanical loading protocols could be translated into treatments to correct or halt progression of bone deformities in children/adolescents. Mimicking physiological stress-controlled dynamic conditions may have beneficial effects at the cellular level as dynamic tests are associated with limited lateral and volumetric cellular deformation.
authors.affiliation: Department of Mechanical Engineering, École Polytechnique de Montréal, Montréal, Canada; Research Center at Sainte-Justine University Hospital, Montréal, Canada.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Zimmermann
authors.affiliation: Department of Mechanical Engineering, École Polytechnique de Montréal, Montréal, Canada.
authors.forename: Séréna
authors.initials: S
authors.lastname: Bouguerra
authors.affiliation: Research Center at Sainte-Justine University Hospital, Montréal, Canada.
authors.forename: Irene
authors.initials: I
authors.lastname: Londoño
authors.affiliation: Research Center at Sainte-Justine University Hospital, Montréal, Canada; Department of Dental Medicine, University of Montréal, Montréal, Canada.
authors.forename: Florina
authors.initials: F
authors.lastname: Moldovan
authors.affiliation: Department of Mechanical Engineering, École Polytechnique de Montréal, Montréal, Canada; Research Center at Sainte-Justine University Hospital, Montréal, Canada.
authors.forename: Carl-Éric
authors.initials: CÉ
authors.lastname: Aubin
authors.affiliation: Department of Mechanical Engineering, École Polytechnique de Montréal, Montréal, Canada; Research Center at Sainte-Justine University Hospital, Montréal, Canada. Electronic address: isabelle.villemure@polymtl.ca.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Villemure
mesh_terms: D000818:Animals; D001846:Bone Development; D019902:Chondrocytes / Q000502:physiology*; D006132:Growth Plate / Q000166:cytology*; D008297:Male; D011312:Pressure; D017207:Rats, Sprague-Dawley; D013314:Stress, Mechanical; D013977:Tibia
keywords: Cyclic loading; Growth plate; Hypertrophic chondrocytes; Viscoelastic cellular deformation