Christine Chappard

The status of strontium in biological apatites: an XANES/EXAFS investigation

Osteoporosis represents a major public health problem through its association with fragility fractures. The public health burden of osteoporotic fractures will rise in future generations, due in part to an increase in life expectancy. Strontium-based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk but the molecular mechanisms of the action of these Sr-based drugs are not totally elucidated. The local environment of Sr(2+) cations in biological apatites present in pathological and physiological calcifications in patients without such Sr-based drugs has been assessed. In this investigation, X-ray absorption spectra have been collected for 17 pathological and physiological calcifications. These experimental data have been combined with a set of numerical simulations using the ab initio FEFF9 X-ray spectroscopy program which takes into account possible distortion and Ca/Sr substitution in the environment of the Sr(2+) cations. For selected samples, Fourier transforms of the EXAFS modulations have been performed. The complete set of experimental data collected on 17 samples indicates that there is no relationship between the nature of the calcification (physiological and pathological) and the adsorption mode of Sr(2+) cations (simple adsorption or insertion). Such structural considerations have medical implications. Pathological and physiological calcifications correspond to two very different preparation procedures but are associated with the same localization of Sr(2+) versus apatite crystals. Based on this study, it seems that for supplementation of Sr at low concentration, Sr(2+) cations will be localized into the apatite network.

Synchrotron Ultraviolet Microspectroscopy on Rat Cortical Bone: Involvement of Tyrosine and Tryptophan in the Osteocyte and Its Environment

Alcohol induced osteoporosis is characterized by a bone mass decrease and microarchitecture alterations. Having observed an excess in osteocyte apoptosis, we aimed to assess the bone tissue biochemistry, particularly in the osteocyte and its environment. For this purpose, we used a model of alcohol induced osteoporosis in rats. Bone sections of cortical bone were investigated using synchrotron UV-microspectrofluorescence at subcellular resolution. We show that bone present three fluorescence peaks at 305, 333 and 385 nm, respectively corresponding to tyrosine, tryptophan and collagen. We have determined that tyrosine/collagen and tryptophan/collagen ratios were higher in the strong alcohol consumption group. Tryptophan is related to the serotonin metabolism involved in bone formation, while tyrosine is involved in the activity of tyrosine kinases and phosphatases in osteocytes. Our experiment represents the first combined synchrotron UV microspectroscopy analysis of bone tissue with a quantitative biochemical characterization in the osteocyte and surrounding matrix performed separately.

Chondrocalcinosis of Femoro-Tibial and Proximal Tibio-Fibular Joints in Cadaveric Specimens: A High-Resolution CT Imaging Study of the Calcification Distribution

Objectives To analyze calcium deposits by computed tomography (CT) in femoro-tibial compartments and proximal tibio-fibular joints; to assess the relationship with CT-assessed osteoarthritis (OA). Methods 68 (34 pairs) cadaveric knees (mean age of 84) were scanned at high resolution CT. Menisci and hyaline cartilage calcifications in the femoro-tibial and proximal tibio-fibular joints were analyzed. OA was CT-assessed by the Kellgren and Lawrence score. Gross appearance of OA was evaluated on 29 left knees after dissection and India ink staining of tibial plateaus. Results In femoro-tibial joints, meniscal calcifications (MC) and hyaline cartilage calcifications (HCC) were detected in 23(34%) and 14(21%) knees respectively. Calcifications mainly involved the three meniscal segments and were mainly observed in all thirds of the femoro-tibial compartments. In proximal tibio-fibular joints, HCC were detected in 19(28%) knees. The association HCC-MC in femoro-tibial joints and between calcifications in femoro-tibial and proximal tibio-fibular joints was strong (p<0.0001). Femoro-tibial and proximal tibio-fibular CT-assessed OA were respectively found in 23(34%) and 19(28%) knees. HCC were significantly associated with femoro-tibial OA (p = 0.04) while MC were not (p = 0.34). OA macroscopic evaluation showed a mean surface of cartilage lesions of 35% (range 0.13–0.55). No significant difference was demonstrated regarding the CT-detection of MC, HCC or CT-assessed OA. Conclusions This is the first study to report a strong association of chondrocalcinosis between femoro-tibial and tibio-fibular joints in addition to a strong association between MC and HCC in femoro-tibial compartments. No significant relationship between chondrocalcinosis and OA was demonstrated.

Influence of anisotropic bone properties on the biomechanical behavior of the acetabular cup implant: a multiscale finite element study

Abstract Although the biomechanical behavior of the acetabular cup (AC) implant is determinant for the surgical success, it remains difficult to be assessed due to the multiscale and anisotropic nature of bone tissue. The aim of the present study was to investigate the influence of the anisotropic properties of peri-implant trabecular bone tissue on the biomechanical behavior of the AC implant at the macroscopic scale. Thirteen bovine trabecular bone samples were imaged using micro-computed tomography (μCT) with a resolution of 18 μm. The anisotropic biomechanical properties of each sample were determined at the scale of the centimeter based on a dedicated method using asymptotic homogenization. The material properties obtained with this multiscale approach were used as input data in a 3D finite element model to simulate the macroscopic mechanical behavior of the AC implant under different loading conditions. The largest stress and strain magnitudes were found around the equatorial rim and in the polar area of the AC implant. All macroscopic stiffness quantities were significantly correlated (R2 > 0.85, p < 6.5 e-6) with BV/TV (bone volume/total volume). Moreover, the maximum value of the von Mises stress field was significantly correlated with BV/TV (R2 > 0.61, p < 1.6 e-3) and was always found at the bone-implant interface. However, the mean value of the microscopic stress (at the scale of the trabeculae) decrease as a function of BV/TV for vertical and torsional loading and do not depend on BV/TV for horizontal loading. These results highlight the importance of the anisotropic properties of bone tissue.

Ultrasound Speed of Sound Measurements in Trabecular Bone Using the Echographic Response of a Metallic Pin.

Bone quality is an important parameter in spine surgery, but its clinical assessment remains difficult. The aim of the work described here was to demonstrate in vitro the feasibility of employing quantitative ultrasound to retrieve bone mechanical properties using an echographic technique taking advantage of the presence of a metallic pin inserted in bone tissue. A metallic pin was inserted in bone tissue perpendicular to the transducer axis. The echographic response of the bone sample was determined, and the echo of the pin inserted in bone tissue and water were compared to determine speed of sound, which was compared with bone volume fraction. A 2-D finite-element model was developed to assess the effect of positioning errors. There was a significant correlation between speed of sound and bone volume fraction (R(2) = 0.6). The numerical results indicate the relative robustness of the measurement method, which could be useful to estimate bone quality intra-operatively.

High resolution volume quantification of the knee joint space based on a semi-automatic segmentation of computed tomography images

Osteoarthritis (OA) is a joint disorder that causes pain, stiffness and decreased mobility. Knee OA presents the greatest morbidity. The main characteristic of OA is the cartilage loss inducing joint space (JS) narrowing. Usually, the progression of OA is monitored by the minimum JS measurement on 2D X-rays images. New dedicated systems based on cone beam computed tomography, providing enough image quality and with favourable dose characteristics are under development. With these new systems, it would be possible to follow the 3D JS changes. High resolution peripheral computed tomography (HR-pQCT) usually used for assessing the trabecular and cortical bone mineral density have been performed on specimen knees with an isotropic voxel of 82 microns. We present here a new semi-automatic segmentation method to measure the 3D local variations of JS. The experiments have been done on HR-pQCT data set and the results have been extended to other computed tomography images with low resolution and/or with cone beam geometry.

Graph Structuring of Skeleton Object for Its High-Level Exploitation

Skeletonization is a morphological operation that summarizes an object by its median lines while preserving the initial image topology. It provides features used in biometric for the matching process, as well as medical imaging for quantification of the bone microarchitecture. We develop a solution for the extraction of structural and morphometric features useful in biometric, character recognition and medical imaging. It aims at storing object descriptors in a re-usable and hierarchical format. We propose graph data structures to identify skeleton nodes and branches, link them and store their corresponding features. This graph structure allows us to generate CSV files for high level analysis and to propose a pruning method that removes spurious branches regarding their length and mean gray level. We illustrate manipulations of the skeleton graph structure on medical image dedicated to bone microarchitecture characterization.

Three-dimensional Simulation of Quantitative Ultrasound in Cancellous Bone Using the Echographic Response of a Metallic Pin

Degenerative discopathy is a common pathology that may require spine surgery. A metallic cylindrical pin is inserted into the vertebral body to maintain soft tissues and may be used as a reflector of ultrasonic wave to estimate bone density. The first aim of this paper is to validate a three-dimensional (3-D) model to simulate the ultrasonic propagation in a trabecular bone sample in which a metallic pin has been inserted. We also aim at determining the effect of changes of bone volume fraction (BV/TV) and of positioning errors on the quantitative ultrasound (QUS) parameters in this specific configuration. The approach consists in coupling finite-difference time-domain simulation with X-ray microcomputed tomography. The correlation coefficient between experimental and simulated speed of sound (SOS)—respectively, broadband ultrasonic attenuation (BUA)—was equal to 0.90 (respectively, 0.55). The results show a significant correlation of SOS with BV/TV (R = 0.82), while BUA values exhibit a nonlinear behavior versus BV/TV. The orientation of the pin should be controlled with an accuracy of around 1° to obtain accurate results. The results indicate that using the ultrasonic wave reflected by a pin has a potential to estimate the bone density. SOS is more reliable than BUA due to its lower sensitivity to the tilt angle.

Three-dimensional mapping of the joint space for the diagnosis of knee osteoarthritis based on high resolution computed tomography: Comparison with radiographic, outerbridge, and meniscal classifications: 3D JOINT SPACE MAPPING

One of the most important characteristic of knee osteoarthritis (OA) is the joint space (JS) width narrowing. Measurements are usually performed on two dimensional (2D) X‐rays. We propose and validate a new method to assess the 3D joint space at the medial knee compartment using high resolution peripheral computed tomography images. A semi‐automated method was developed to obtain a distance 3D map between femur an tibia with the following parameters: volume, minimum, maximum, mean, standard deviation, median, asymmetry, and entropy. We analyzed 71 knee specimens (mean age: 85 years), radiographs were performed for the Kellgren Lawrence (KL) score grading. In a subgroup of 41 specimens, the histopathological Outerbridge and meniscal classifications were performed and then cores were harvested from the tibial plateau in three different positions (posterior, central, and peripheral) and imaged at 10 µm of resolution to measure the cartilage thickness. Minimum, maximum, mean, and median were statistically lower and entropy higher between knee specimens classified as KL = 0 and KL = 3–4. Gr1 and 2 were statistically different from Gr3‐4 for minimum, asymmetry, entropy using the Outerbridge classification and Gr1 was statistically different from Gr3–4 using the meniscal classification. Asymmetry, minimum, mean, median and entropy were significantly correlated with cartilage thickness. Parameters extracted from a 3D map of the medial joint space indicate local variations of JS and are related to local measurements of tibial cartilage thickness, and could be consequently useful to identify early OA.

SAT0551 Location Dependence of the Microstructure of Cartilage and of Subchondral Cortical and Trabecular Bone Microstructure in Knees with NO or Mild OA Assessed by High Resolution Micro-Computed Tomography

Background Loss of articular cartilage and alterations in subchondral bone architecture with the thickening of the cortical subchondral plate and trabeculae are important characteristics of osteoarthritis (OA). The local heterogeneity of these structures in knees with no or mild OA is unknown. Its quantification could help to better understand the changes induced in osteoarthritis. Objectives To determine whether in non OA knees the relationship among cartilage volume, subchondral plate volume and porosity and structural parameters of the subchondral trabecular bone are location dependent. Methods Twenty two left cadaveric knees, with no or mild medial femoro-tibial osteoarthritis (Kellgren-Lawrence grading scale <2) were selected based on radiographs from 13 women and 9 men (mean age 80.9±10.0 years). After dissection, 3 vertical cores (7mm in diameter, 10 mm in length) were extracted in the posterior (S1), inner (S2) and lateral (S3) region of the medial tibial plateau. S1 and S3 were located under the meniscus. The cores were imaged twice with micro-CT (Skyscan 1172®, voxel size 10.23 mm): first using the native extracted cores to characterize cartilage and again after defatting to characterize cortical and trabecular bone architecture. The following parameters were assessed: cartilage volume (CartVol, mm3) and for the cortical subchondral bone: bone volume (BV_sub_chonPl, mm3) and porosity (PoV/TV_sub_chonPl, %). In the subchondral trabecular bone, the following structural parameters were measured in the first 7 mm beneath the subchondral plate: Bone Volume/Total Volume (BV/TV, %), trabecular number (Tb.N, 1/mm), trabecular thickness (Tb.Th, mm), trabecular separation (Tb.Sp, mm), and degree of anisotropy (DA). One-way analysis of variance (ANOVA, Kruskal-Wallis), followed by post-hoc analysis for multiple range test (Tukey-Kramer), and Pearson correlation coefficients r (Spearman in case of non normality, r) were used to investigate group differences in cartilage and bone structure. Results The table shows mean ± SD values for the analyzed parameters and ANOVA results. In addition for all groups, correlations between BV/TV and CartVol were not significant. Correlations between BV/TV and BV_sub_chonPl were significant for S2 and S3 (r=0.60 (p<0.003), r=0.45 (p<0.03), respectively) but not for S1. BV/TV and PoV/TV_sub_chonPl were significantly correlated r=-0.73 (p<10–4) for S3 but not for S1 and S2. CartVol was significantly correlated with with BV_sub_chonPl r=0.72 (p<10–4) and PoV/TV_sub_chonPl r=-0.51 (p<0.01) for S1 but not for S2 or S3. Conclusions In non OA knees, the relationships between CartVol, BV_sub_chonPl and porosity with subchondral trabecular bone volume are location dependent. In an inner position (S2), which is never covered by the meniscus, CartVol, BV_sub_chonPl, and the trabecular bone parameters BV/TV and Tb.Th were higher and DA was lower compared to the lateral (S3) and posterior (S1) locations, which are usually covered by the meniscus. We conclude that the location in the tibial medial plateau and the presence of the meniscus play an important role on the surrounding structures such as cartilage, subchondral plate and trabecular subchondral bone. Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.4404