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In Vivo Assessment of Elasticity of Child Rib Cortical Bone Using Quantitative Computed Tomography 时间:2017-07-18 23:52   来源:未知   作者:admin   点击: 次 Abstract:Elasticity of the child rib cortical bone is poorly known due to the difficulties in obtaining specimens to perform conventional tests. It was shown on the femoral cortical bone that elasticity is strongly correlated with density for both children and adults through a unique relationship. Thus, it is assumed that the relationships between the elasticity and density of adult rib cortical bones could be expanded to include that of children. This study estimated in vivo the elasticity of the child rib cortical bone using quantitative computed tomography (QCT). Twenty-eight children (from 1 to 18 y.o.) were considered. Calibrated QCT images were prescribed for various thoracic pathologies. The Hounsfield units were converted to bone mineral density (BMD). A relationship between the BMD and the elasticity of the rib cortical bone was applied to estimate the elasticity of children’s ribs in vivo. The estimated elasticity increases with growth (7.1 ± 2.5 GPa at 1 y.o. up to 11.6 ± 1.9 GPa at 18 y.o.). This data is in agreement with the few previous values obtained using direct measurements. This methodology paves the way for in vivo assessment of the elasticity of the child cortical bone based on calibrated QCT images.
1. Introduction
The knowledge of the mechanical properties of the child rib cortical bone could be useful for ribcage models. Such models could be used to assess mechanical loading on the thorax (e.g., for brace treatment or car crash accidents). However, the mechanical properties of pediatric thoracic tissues have been poorly studied due to difficulties in obtaining specimens to perform conventional tests [1, 2]. Regarding specifically the rib cortical bone of children, mechanical data are extremely limited [1]. To the authors’ knowledge, only a handful of studies exploring pediatric rib mechanical properties can be found in the existing literature [3–5]. Some other studies did not focus specifically on children, but the population included donors younger than 18 years [6–9].
   Compared to the few studies on children’s ribs, a significant number of studies performed three-point bending tests on adult rib segments or tensile loading tests on rib coupons to investigate the mechanical properties [9–16], while other studies performed anteroposterior loading tests on the whole ribs [8, 17, 18]. These studies provided detailed knowledge on the human rib mechanical properties of adults. The only existing studies on children’s ribs used cadaveric bones or bone tissues collected during surgery but are limited by the number of collected samples. Thus, noninvasive techniques could be extremely valuable to overcome the limitation.
It has been shown previously that variations in trabecular bone properties produced a negligible influence on the mechanical response of a rib model [19]. Therefore, this study focuses on the rib cortical bone. Our group showed recently that quantitative ultrasound can be used to derive rib mechanical properties ex vivo [13], but this technique cannot yet be applied in vivo. It is well known that mechanical properties are related to bone density (physical measurement) [5, 20, 21]. Some studies also showed that the mechanical properties of the femur or tibia bone can be measured by bone mineral density (BMD) using quantitative computed tomography (QCT) [22–26].
  The mechanical properties of child and adult cortical bone tissue were found to differ, but the relationship between mechanical properties and ash density is the same for both child and adults [27]. Ash density was previously shown to be strongly related to BMD [25]. Thus, it is assumed that the relationships between elasticity and BMD on the adult rib cortical bone could be expanded to include that of children. Currently, no relationship exists between mechanical properties and BMD of the child rib cortical bone. The current study was designed to fill this gap. Thus, the main goal of this study is to estimate in vivo the elasticity (Young’s modulus E) of the child rib cortical bone, using calibrated clinical QCT images.