title: Increased intra-cortical porosity reduces bone stiffness and strength in pediatric patients with osteogenesis imperfecta.
abstract: Osteogenesis imperfecta (OI) is a heritable disease occurring in one out of every 20,000 births. Although it is known that Type I collagen mutation in OI leads to increased bone fragility, the mechanism of this increased susceptibility to fracture is not clear. The aim of this study was to assess the microstructure of cortical bone fragments from patients with osteogenesis imperfecta (OI) using polarized light microscopy, and to correlate microstructural observations with the results of previously performed mechanical compression tests on bone from the same source. Specimens of cortical bone were harvested from the lower limbs of three (3) OI patients at the time of surgery, and were divided into two groups. Group 1 had been subjected to previous micro-mechanical compression testing, while Group 2 had not been subjected to any prior testing. Polarized light microscopy revealed disorganized bone collagen architecture as has been previously observed, as well as a large increase in the areal porosity of the bone compared to typical values for healthy cortical bone, with large (several hundred micron sized), asymmetrical pores. Importantly, the areal porosity of the OI bone samples in Group 1 appears to correlate strongly with their previously measured apparent Young's modulus and compressive strength. Taken together with prior nanoindentation studies on OI bone tissue, the results of this study suggest that increased intra-cortical porosity is responsible for the reduction in macroscopic mechanical properties of OI cortical bone, and therefore that in vivo imaging modalities with resolutions of ~100 μm or less could potentially be used to non-invasively assess bone strength in OI patients. Although the number of subjects in this study is small, these results highlight the importance of further studies in OI bone by groups with access to human OI tissue in order to clarify the relationship between increased porosity and reduced macroscopic mechanical integrity.
authors.affiliation: Institut de Biomécanique Humaine Georges Charpak, Arts et Metiers ParisTech (ENSAM), 151 Boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: V
authors.initials: V
authors.lastname: Vardakastani
authors.affiliation: Institut de Biomécanique Humaine Georges Charpak, Arts et Metiers ParisTech (ENSAM), 151 Boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: D
authors.initials: D
authors.lastname: Saletti
authors.affiliation: Institut de Biomécanique Humaine Georges Charpak, Arts et Metiers ParisTech (ENSAM), 151 Boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: W
authors.initials: W
authors.lastname: Skalli
authors.affiliation: Service de Chirurgie Orthopédique et Réparatrice de l'enfant, Hôpital Armand Trousseau, 26, avenue du Docteur Arnold Netter, 75571 Paris Cedex 12, France.
authors.forename: P
authors.initials: P
authors.lastname: Marry
authors.affiliation: Laboratoire de Mécanique des Solides, CNRS UMR7649, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
authors.forename: J M
authors.initials: JM
authors.lastname: Allain
authors.affiliation: Institut de Biomécanique Humaine Georges Charpak, Arts et Metiers ParisTech (ENSAM), 151 Boulevard de l'Hôpital, 75013 Paris, France; School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, GPO Box 2434, 2 George St, Brisbane, Australia. Electronic address: clayton.adam@ensam.eu.
authors.forename: C
authors.initials: C
authors.lastname: Adam
mesh_terms: D001842:Bone and Bones / Q000473:pathology* / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D019245:Compressive Strength; D055119:Elastic Modulus; D005260:Female; D006801:Humans; D008297:Male; D008859:Microscopy, Polarization; D010013:Osteogenesis Imperfecta / Q000473:pathology* / Q000503:physiopathology*; D016062:Porosity
keywords: Bone mechanics; Bone microstructure; Collagen alignment; Intra-cortical porosity; Osteogenesis imperfecta