title: Ratio between mature and immature enzymatic cross-links correlates with post-yield cortical bone behavior: An insight into greenstick fractures of the child fibula.
abstract: As a determinant of skeletal fragility, the organic matrix is responsible for the post-yield and creep behavior of bone and for its toughness, while the mineral apatite acts on stiffness. Specific to the fibula and ulna in children, greenstick fractures show a plastic in vivo mechanical behavior before bone fracture. During growth, the immature form of collagen enzymatic cross-links gradually decreases, to be replaced by the mature form until adolescence, subsequently remaining constant throughout adult life. However, the link between the cortical bone organic matrix and greenstick fractures in children remains to be explored. Here, we sought to determine: 1) whether plastic bending fractures can occur in vitro, by testing cortical bone samples from children's fibula and 2) whether the post-yield behavior (ωp plastic energy) of cortical bone before fracture is related to total quantity of the collagen matrix, or to the quantity of mature and immature enzymatic cross-links and the quantity of non-enzymatic cross-links. We used a two-step approach; first, a 3-point microbending device tested 22 fibula machined bone samples from 7 children and 3 elderly adults until fracture. Second, biochemical analysis by HPLC was performed on the sample fragments. When pooling two groups of donors, children and elderly adults, results show a rank correlation between total energy dissipated before fracture and age and a linear correlation between plastic energy dissipated before fracture and ratio of immature/mature cross-links. A collagen matrix with more immature cross-links (i.e. a higher immature/mature cross-link ratio) is more likely to plastically deform before fracture. We conclude that this ratio in the sub-nanostructure of the organic matrix in cortical bone from the fibula may go some way towards explaining the variance in post-yield behavior. From a clinical point of view, therefore, our results provide a potential explanation of the presence of greenstick fractures in children.
authors.affiliation: Institute of Movement Science (ISM), CNRS, UMR 7287, Aix-Marseille University, av. de, Luminy, F-13288 Marseille France; Laboratory of Mechanics and Acoustics (LMA), CNRS, UPR 7051, Aix-Marseille University, Centrale Marseille, 31 chemin Joseph-Aiguier, F-13402 Marseille cedex 20, France; Department of Physical Therapy, College of Staten Island, City University of New York, NY 10314, United States. Electronic address: jph.berteau@gmail.com.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Berteau
authors.affiliation: INSERM, UMR 1033, F-69008 Lyon, France; Université de Lyon, F-69008 Lyon, France.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Gineyts
authors.affiliation: Institute of Movement Science (ISM), CNRS, UMR 7287, Aix-Marseille University, av. de, Luminy, F-13288 Marseille France.
authors.forename: Martine
authors.initials: M
authors.lastname: Pithioux
authors.affiliation: Institute of Movement Science (ISM), CNRS, UMR 7287, Aix-Marseille University, av. de, Luminy, F-13288 Marseille France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Baron
authors.affiliation: Department of Physical Therapy, College of Staten Island, City University of New York, NY 10314, United States; INSERM, UMR 1033, F-69008 Lyon, France.
authors.forename: Georges
authors.initials: G
authors.lastname: Boivin
authors.affiliation: Laboratory of Mechanics and Acoustics (LMA), CNRS, UPR 7051, Aix-Marseille University, Centrale Marseille, 31 chemin Joseph-Aiguier, F-13402 Marseille cedex 20, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lasaygues
authors.affiliation: Institute of Movement Science (ISM), CNRS, UMR 7287, Aix-Marseille University, av. de, Luminy, F-13288 Marseille France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Chabrand
authors.affiliation: INSERM, UMR 1033, F-69008 Lyon, France; Université de Lyon, F-69008 Lyon, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Follet
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001857:Bone Matrix / Q000737:chemistry / Q000254:growth & development* / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D002851:Chromatography, High Pressure Liquid; D005360:Fibula / Q000502:physiology; D050723:Fractures, Bone / Q000503:physiopathology*; D006801:Humans; D013314:Stress, Mechanical
keywords: Children's bone; Collagen cross-links; Mechanical properties; Post-yield behavior