Monique Arlot

Contribution of Trabecular and Cortical Components to Biomechanical Behavior of Human Vertebrae: An Ex Vivo Study

Whereas there is clear evidence for a strong influence of bone quantity (i.e., bone mass or bone mineral density) on vertebral mechanical behavior, there are fewer data addressing the relative influence of cortical and trabecular bone microarchitecture. The aim of this study was to determine the relative contributions of bone mass, trabecular microarchitecture, and cortical thickness and curvature to the mechanical behavior of human lumbar vertebrae. Thirty‐one L3 vertebrae (16 men, 15 women, aged 75u2009±u200910 years and 76u2009±u200910 years, respectively) were obtained. Bone mineral density (BMD) of the vertebral body was assessed by lateral dual energy X‐ray absorptiometry (DXA), and 3D trabecular microarchitecture and anterior cortical thickness and curvature was assessed by micro‐computed tomography (µCT). Then compressive stiffness, work to failure, and failure load were measured on the whole vertebral body. BMD was correlated with compressive stiffness (ru2009=u20090.60), failure load (ru2009=u20090.70), and work to failure (ru2009=u20090.55). Except for the degree of anisotropy, all trabecular and cortical parameters were correlated with mechanical behavior (ru2009=u20090.36 to 0.58, pu2009=u2009.05 to .001, and ru2009=u20090.36 to 0.61, pu2009=u2009.05 to .0001, respectively). Stepwise and multiple regression analyses indicated that the best predictor of (1) failure load was the combination of BMD, structural model index (SMI), and trabecular thickness (Tb.Th) (Ru2009=u20090.80), (2) stiffness was the combination of BMD, Tb.Th, and curvature of the anterior cortex (Ru2009=u20090.82), and (3) work to failure was the combination of anterior cortical thickness and BMD (Ru2009=u20090.68). Our data imply that measurements of cortical thickness and curvature may enhance prediction of vertebral fragility and that therapies that improve both vertebral cortical and trabecular bone properties may provide a greater reduction in fracture risk.

Role of Trabecular Microarchitecture and Its Heterogeneity Parameters in the Mechanical Behavior of Ex Vivo Human L3 Vertebrae

Low bone mineral density (BMD) is a strong risk factor for vertebral fracture risk in osteoporosis. However, many fractures occur in people with moderately decreased or normal BMD. Our aim was to assess the contributions of trabecular microarchitecture and its heterogeneity to the mechanical behavior of human lumbar vertebrae. Twenty‐one human L3 vertebrae were analyzed for BMD by dual‐energy X‐ray absorptiometry (DXA) and microarchitecture by high‐resolution peripheral quantitative computed tomography (HR‐pQCT) and then tested in axial compression. Microarchitecture heterogeneity was assessed using two vertically oriented virtual biopsies—one anterior (Ant) and one posterior (Post)—each divided into three zones (superior, middle, and inferior) and using the whole vertebral trabecular volume for the intraindividual distribution of trabecular separation (Tb.Sp*SD). Heterogeneity parameters were defined as (1) ratios of anterior to posterior microarchitectural parameters and (2) the coefficient of variation of microarchitectural parameters from the superior, middle, and inferior zones. BMD alone explained up to 44% of the variability in vertebral mechanical behavior, bone volume fraction (BV/TV) up to 53%, and trabecular architecture up to 66%. Importantly, bone mass (BMD or BV/TV) in combination with microarchitecture and its heterogeneity improved the prediction of vertebral mechanical behavior, together explaining up to 86% of the variability in vertebral failure load. In conclusion, our data indicate that regional variation of microarchitecture assessment expressed by heterogeneity parameters may enhance prediction of vertebral fracture risk.

Microarchitecture Influences Microdamage Accumulation in Human Vertebral Trabecular Bone

It has been suggested that accumulation of microdamage with age contributes to skeletal fragility. However, data on the age‐related increase in microdamage and the association between microdamage and trabecular microarchitecture in human vertebral cancellous bone are limited. We quantified microdamage in cancellous bone from human lumbar (L2) vertebral bodies obtained from 23 donors 54–93 yr of age (8 men and 15 women). Damage was measured using histologic techniques of sequential labeling with chelating agents and was related to 3D microarchitecture, as assessed by high‐resolution μCT. There were no significant differences between sexes, although women tended to have a higher microcrack density (Cr.Dn) than men. Cr.Dn increased exponentially with age (r = 0.65, p < 0.001) and was correlated with bone volume fraction (BV/TV; r = −0.55; p < 0.01), trabecular number (Tb.N; r = −0.56 p = 0.008), structure model index (SMI; r = 0.59; p = 0.005), and trabecular separation (Tb.Sp; r = 0.59; p < 0.009). All architecture parameters were strongly correlated with each other and with BV/TV. Stepwise regression showed that SMI was the best predictor of microdamage, explaining 35% of the variance in Cr.Dn and 20% of the variance in diffuse damage accumulation. In addition, microcrack length was significantly greater in the highest versus lowest tertiles of SMI. In conclusion, in human vertebral cancellous bone, microdamage increases with age and is associated with low BV/TV and a rod‐like trabecular architecture.

Effects of preexisting microdamage, collagen cross-links, degree of mineralization, age, and architecture on compressive mechanical properties of elderly human vertebral trabecular bone.

Previous studies have shown that the mechanical properties of trabecular bone are determined by bone volume fraction (BV/TV) and microarchitecture. The purpose of this study was to explore other possible determinants of the mechanical properties of vertebral trabecular bone, namely collagen cross‐link content, microdamage, and mineralization. Trabecular bone cores were collected from human L2 vertebrae (nu2009=u200949) from recently deceased donors 54–95 years of age (21 men and 27 women). Two trabecular cores were obtained from each vertebra, one for preexisting microdamage and mineralization measurements, and one for BV/TV and quasi‐static compression tests. Collagen cross‐link content (PYD, DPD, and PEN) was measured on surrounding trabecular bone. Advancing age was associated with impaired mechanical properties, and with increased microdamage, even after adjustment by BV/TV. BV/TV was the strongest determinant of elastic modulus and ultimate strength (r2u2009=u20090.44 and 0.55, respectively). Microdamage, mineralization parameters, and collagen cross‐link content were not associated with mechanical properties. These data indicate that the compressive strength of human vertebral trabecular bone is primarily determined by the amount of trabecular bone, and notably unaffected by normal variation in other factors, such as cross‐link profile, microdamage and mineralization.

Calcium-vitamin D3 supplementation is cost-effective in hip fractures prevention.

OBJECTIVEnTo assess the cost implications for a preventive treatment strategy for institutionalised elderly women with a combined 1200 mg/day calcium and 800 IU/day vitamin D(3) supplementation in seven European countries.nnnDESIGNnRetrospective cost effectiveness analysis based on a prospective placebo-controlled randomised clinical trial.nnnDATA SOURCESnRecently published cost studies in seven European countries. Clinical results from Decalyos, a 3-year placebo-controlled study in elderly institutionalised women.nnnTRIALSnDecalyos study, with 36 months follow-up of 3270 mobile elderly women living in 180 nursing homes, allocated to two groups. One group received 1200 mg/day elemental calcium in the form of tricalcium phosphate together with 800 IU/day (20 microg) of cholecalciferol (vitamin D(3)), the other placebo.nnnRESULTSnIn the 36 months analysis of the Decalyos study, 138 hip fractures occurred in the group of 1176 women, receiving supplementation and 184 hip fractures in the placebo group of 1127 women. The mean duration of treatment was 625.4 days. Adjusted to 1000 women, 46 hip fractures were avoided by the calcium and vitamin D(3) supplementation. For all countries, the total costs in the placebo group were higher than in the group receiving supplementation, resulting in a net benefit of 79000-711000 per 1000 women.nnnCONCLUSIONnThis analysis suggests that the supplementation strategy is cost saving. The results may underestimate the net benefits, as this treatment has also shown to be effective in decreasing the incidence of other non-vertebral fractures in elderly institutionalised women.

Radiologic assessment of age-related knee joint space changes in women: A 4-year longitudinal study

OBJECTIVEnTo analyze a population-based cohort of women in order to establish normal values of joint space width (JSW) and to evaluate the existence of age-related joint space loss (JSL).nnnMETHODSnKnee radiographs were performed 4 years apart in women from the OFELY (Os des Femmes de Lyon) Cohort. Posteroanterior radiographs of both knees were taken in semiflexion with a standardized fluoroscopically assisted protocol. Radiographs were qualitatively evaluated using a scoring system based on the Altman score that assessed joint space narrowing, osteophytes, and sclerosis for each tibiofemoral compartment and each side. For quantitative assessment, radiographs were digitized using a video camera, and specific software was used to measure JSW in every compartment.nnnRESULTSnWe evaluated the radiographs of 606 women (ages 39-90 years, mean 62 years) and found that in all subjects, JSW significantly decreased with age in every compartment (r = -0.12 to -0.16, P < 0.001), including in 358 subjects without any radiographic abnormality related to osteoarthritis (OA) at baseline. The longitudinal analysis confirmed a significant loss over 4 years of approximately 0.30 mm (6%) for the medial compartment. Multiple regression analysis did not identify significant predictors of JSL among clinical risk factors and biochemical markers of bone and cartilage turnover.nnnCONCLUSIONnIn this first longitudinal study of a population-based cohort of women, we have established normal values of JSW and shown that JSW decreases with aging, especially at the medial compartment, even in subjects without any radiographic abnormalities related to OA.

Influence of Blinding Sequence of Radiographs on the Reproducibility and Sensitivity to Change of Joint Space Width Measurement in Knee Osteoarthritis

To investigate whether knowledge of the sequence of radiographs impacts inter‐ and intraobserver reproducibility and sensitivity to change for measuring joint space width (JSW) in patients with knee osteoarthritis (OA).

Determinants of the Mechanical Behavior of Human Lumbar Vertebrae After Simulated Mild Fracture

The ability of a vertebra to carry load after an initial deformation and the determinants of this postfracture load‐bearing capacity are critical but poorly understood. This study aimed to determine the mechanical behavior of vertebrae after simulated mild fracture and to identify the determinants of this postfracture behavior. Twenty‐one human L3 vertebrae were analyzed for bone mineral density (BMD) by dual‐energy X‐ray absorptiometry (DXA) and for microarchitecture by micro–computed tomography (µCT). Mechanical testing was performed in two phases: initial compression of vertebra to 25% deformity, followed, after 30u2009minutes of relaxation, by a similar test to failure to determine postfracture behavior. We assessed (1) initial and postfracture mechanical parameters, (2) changes in mechanical parameters, (3) postfracture elastic behavior by recovery of vertebral height after relaxation, and (4) postfracture plastic behavior by residual strength and stiffness. Postfracture failure load and stiffness were 11%u2009±u200919% and 53%u2009±u200918% lower than initial values (pu2009=u2009.021 and pu2009<u2009.0001, respectively), with 29% to 69% of the variation in the postfracture mechanical behavior explained by the initial values. Both initial and postfracture mechanical behaviors were significantly correlated with bone mass and microarchitecture. Vertebral deformation recovery averaged 31%u2009±u20097% and was associated with trabecular and cortical thickness (ru2009=u20090.47 and ru2009=u20090.64; pu2009=u2009.03 and pu2009=u2009.002, respectively). Residual strength and stiffness were independent of bone mass and initial mechanical behavior but were related to trabecular and cortical microarchitecture (|r|u2009=u20090.50 to 0.58; pu2009=u2009.02 to .006). In summary, we found marked variation in the postfracture load‐bearing capacity following simulated mild vertebral fractures. Bone microarchitecture, but not bone mass, was associated with postfracture mechanical behavior of vertebrae.

Evaluation and Development of Automatic Two-Dimensional Measurements of Histomorphometric Parameters Reflecting Trabecular Bone Connectivity: Correlations with Dual-Energy X-Ray Absorptiometry and Quantitative Ultrasound in Human Calcaneum

In osteoporosis, bone fragility results from both bone loss and changes in trabecular microarchitecture, which can be quantified by bone histomorphometric parameters. Twenty human calcaneum were collected after necropsy. All measurements were performed at the same anatomical location. Bone histomorphometric parameters were measured on histological slides with an automatic image analyzer. The aims of our study were (1) to develop automatic measurements of four additional parameters reflecting trabecular network connectivity and complexity, i.e., trabecular bone pattern factor (TBPf), Euler number/tissue volume (Euler) according to the three definitions previously reported and to a fourth one established in the laboratory (Eulerstrut.cavity), marrow star volume, and interconnectivity index, and to determine their usefulness in microarchitecture characterization; and (2) to validate these parameters by evaluating their relationship with dual-energy X-ray absorptiometry and quantitative ultrasound (QUS) measurements performed on the same samples. The statistical analysis showed that TBPf and Eulerstrut.cavity appeared to be the most significant connectivity parameters, independently of bone quantity (bone mineral density, apparent density, cancellous bone volume). For QUS, after adjustment for bone quantity, only speed of sound (SOS) was significantly and negatively correlated to Eulerstrut.cavity. Broadband ultrasound attenuation depends only on bone quantity. In conclusion, TBPf (a strut analysis parameter extrapolable in three dimensions) and Eulerstrut.cavity (the only bone connectivity parameter reflecting SOS) are two valid bone microarchitecture parameters. These new parameters were significantly correlated to the established trabecular structure parameters: trabecular thickness or trabecular spacing, being weakly correlated with SOS.

Staining procedure for the detection of microcracks: application to ewe bone.

Microcracks are one of the determinants of the bone strength and their accumulation may contribute to increased fracture risk. They are detected after bulk staining with various dyes, including basic fuschin, calcein and xylenol orange. The duration of staining usually varies across types of bone and species. The ewe is a large animal with a bone remodeling similar to humans, used as an animal model in bone histomorphometry studies. The aim of the present study was to determine the optimal conditions for bulk staining with xylenol orange of ewe bone. Xylenol orange 5mM in 70% ethanol was applied to iliac crest and vertebral biopsies for 2 or 15 days or 1, 2 or 3 months. After embedding, sections of 40, 50 and 80 μm thick were cut with either a precision diamond wire saw or a microtome. The staining was not visible after 2 or 15 days and was heterogeneous after 1 or 2 months. The quality of 40 and 50 μm thick sections was not preserved compared with those of 80 μm. Microcracks were suitably observed on ewe bone after bulk staining with xylenol orange for 3 months, in 80 μm thick sections. We conclude that the staining procedures should differ when examining ewe or human bone. This may be due to differences in bone matrix composition.