Measurement of the bone endocortical region using clinical CT

The reduced cortical bone density in vertebral bodies: risk for osteoporotic fractures? Insights from CT analysis

BACKGROUND

There is a corresponding increase in the prevalence of osteoporosis and related fractures with the aging population on the rise. Furthermore, osteoporotic vertebral compression fractures (OVCF) may contribute to higher patient mortality rates. It is essential to conduct research on risk factors for OVCF and provide a theoretical basis for preventing such fractures.

METHODS

We retrospectively recruited patients who had spine CT for OVCF or back pain. Demographic and CT data were collected. Quantitative computed tomography (QCT) software analyzed the CT data, using subcutaneous fat and paraspinal muscles as reference standards for BMD processing. BMD of cortical and cancellous bones in each patient's vertebral body was determined.

RESULTS

In this study, 144 patients were divided into non-OVCF (96) and OVCF (48) groups. Non-OVCF patients had higher cortical BMD of 382.5 ± 52.4 to 444.6 ± 70.1 mg/cm3, with T12 having the lowest BMD (p < 0.001, T12 vs. L2). Cancellous BMD ranged from 128.5 ± 58.4 to 140.9 ± 58.9 mg/cm3, with L3 having the lowest BMD. OVCF patients had lower cortical BMD of 365.0 ± 78.9 to 429.3 ± 156.7 mg/cm3, with a further decrease in T12 BMD. Cancellous BMD ranged from 71.68 ± 52.07 to 123.9 ± 126.2 mg/cm3, with L3 still having the lowest BMD. Fractured vertebrae in OVCF patients (T12, L1, and L2) had lower cortical bone density compared to their corresponding vertebrae without fractures (p < 0.05).

CONCLUSIONS

T12 had the lowest cortical BMD and L3 had the lowest cancellous BMD in OVCF patients, with T12 also having the highest incidence of osteoporotic fractures. These findings suggest that reduction in cortical BMD has a greater impact on OVCF than reduction in cancellous BMD, along with biomechanical factors.

Preventing stress singularities in peri-implant bone - a finite element analysis using a graded bone model

In finite element analysis bone is often treated as two-layered material that has a discontinuity between the cortical and cancellous bone, which leads to a singularity and incorrect stresses. The goal of this study was to eliminate this singularity and to create a more realistic representation of bone which also considers the transition zone between cortical and cancellous bone as observed in natural bone. This was achieved by modelling bone as a graded material and inserting node-specific values for Young's modulus in the finite element simulation, whereas the transition zone thickness was derived from a CT scan. The modelling was performed semi-automatically, and the maximum principal stresses of the new approach were compared to those of a conventional approach. The new approach was found to effectively avoid singularities and provides more accurate predictions of stress in areas of the bone transition zone. As the approach is automatable and causes rather small overhead it is recommended for use in future work, when the problem at hand requires evaluating stresses close to the former singularity.

Systematic measuring cortical thickness in tibiae for bio-mechanical analysis

BACKGROUND AND OBJECTIVE

Measuring the thickness of cortical bone tissue helps diagnose bone diseases or monitor the progress of different treatments. This type of measurement can be performed visually from CAT images by a radiologist or by semi-automatic algorithms from Hounsfield values. This article proposes a mechanism capable of measuring thickness over the entire bone surface, aligning and orienting all the images in the same direction to have comparable references and reduce human intervention to a minimum. The objective is to batch process large numbers of patients' CAT images obtaining thicknesses profiles of their cortical tissue to be used in many applications.

METHODS

Classical morphological and Deep Learning segmentation is used to extract the area of interest, filtering and interpolation to clean the bones and contour detection and Signed Distance Functions to measure the cortical Thickness. The alignment of the set of bones is achieved by detecting their longitudinal direction, and the orientation is performed by computing their principal component of the center of mass slice.

RESULTS

The method processed in an unattended manner 67% of the patients in the first run and 100% in the second run. The difference in the thickness values between the values provided by the algorithm and the measures done by a radiologist was, on average, 0.25 millimetres with a standard deviation of 0.2.

CONCLUSION

Measuring the cortical thickness of a bone would allow us to prepare accurate traumatological surgeries or study their structural properties. Obtaining thickness profiles of an extensive set of patients opens the way for numerous studies to be carried out to find patterns between bone thickness and the patients' medical, social or demographic variables.

Intrinsic Cortical Property Analysis of the Medial Column of Proximal Humerus

OBJECTIVE

Adequate mechanical support of the medial column is paramount to maintain fracture reduction in locking plating of proximal humerus fractures. However, intrinsic cortical properties of the medial column are rarely discussed. The purpose of the study is to describe regional variation of cortex in the medial column.

METHODS

A total of 147 healthy participants were eligible for enrollment between December 2016 and December 2018. Subjects were divided into three groups: group A (20-39 years), group B (40-59 years), and group C (>60 years). For each individual, a color 3D thickness map for proximal humerus was created by cortical bone mapping (CBM) technique after bilateral shoulders were imaged by computed tomography. Measurement Indices including the cortical thickness (CTh), cortical mass surface density (CM) and the endocortical trabecular density (ECTD) were determined, after six regions of interest (ROI) were defined in metaphyseal region. Regional parameter variations were analyzed by one-way ANOVA.

RESULTS

The CTh, CM and ECTD values were approximately equivalent between genders in the proximal part of the medial column across all ages (P > 0.05).The greatest difference between sexes was found in CTh and CM values of middle and distal part (P < 0.05). The CTh and CM within medial column were negatively associated with age (P < 0.05). The proximal cortical bone of the medial column was thicker and more dense, compared to the lateral column (P < 0.05). Significant regional variation was found in all measured parameters in group A, but not in groups B and C.

CONCLUSION

Our finding proved that regional differences in the distribution of cortical bone in the medial column The attenuation of cortical bone heterogeneity in the medial column was found after the age of 40 years.

Multiparametric 3-D analysis of bone and joint space width at the knee from weight bearing computed tomography

OBJECTIVE

Computed tomography (CT) can deliver multiple parameters relevant to osteoarthritis. In this study we demonstrate that a 3-D multiparametric approach at the weight bearing knee with cone beam CT is feasible, can include multiple parameters from across the joint space, and can reveal stronger relationships with disease status in combination.

DESIGN

33 participants with knee weight bearing CT (WBCT) were analysed with joint space mapping and cortical bone mapping to deliver joint space width (JSW), subchondral bone plate thickness, endocortical thickness, and trabecular attenuation at both sides of the joint. All data were co-localised to the same canonical surface. Statistical parametric mapping (SPM) was applied in uni- and multivariate models to demonstrate significant dependence of parameters on Kellgren & Lawrence grade (KLG). Correlation between JSW and bony parameters and 2-week test-retest repeatability were also calculated.

RESULTS

SPM revealed that the central-to-posterior medial tibiofemoral joint space was significantly narrowed by up to 0.5 mm with significantly higher tibial trabecular attenuation up to 50 units for each increment in KLG as single features, and in a wider distribution when combined (p<0.05). These were also more strongly correlated with worsening KLG grade category. Test-retest repeatability was subvoxel (0.37 mm) for nearly all thickness parameters.

CONCLUSIONS

3-D JSW and tibial trabecular attenuation are repeatable and significantly dependent on radiographic disease severity at the weight bearing knee joint not just alone, but more strongly in combination. A quantitative multiparametric approach with WBCT may have potential for more sensitive investigation of disease progression in osteoarthritis.

Focal osteoporosis defect is associated with vertebral compression fracture prevalence in a bone mineral density-independent manner

Introduction

Focal osteoporosis defect has shown a high association with the bone fragility and osteoporotic fracture prevalence. However, no routine computed tomography (CT)-based vertebral focal osteoporosis defect measurement and its association with vertebral compression fracture (VCF) were discussed yet. This study aimed to develop a routine CT-based measurement method for focal osteoporosis defect quantification, and to assess its association with the VCF prevalence.

Materials and Methods

A total of 205 cases who underwent routine CT scanning, were retrospectively reviewed and enrolled into either the VCF or the control group. The focal bone mineral content loss (focal BMC loss), measured as the cumulated demineralization within bone void space, was proposed for focal osteoporosis defect quantification. Its scan-rescan reproducibility and its correlation with trabecular bone mineral density (BMD) and apparent microarchitecture parameters were evaluated. The association between focal BMC loss and the prevalence of VCF was studied by logistic regression.

Results

The measurement of focal BMC loss showed high reproducibility (RMSSD = 0.011 mm, LSC = 0.030 mm, ICC = 0.97), and good correlation with focal bone volume fraction (r = 0.79, P < 0.001), trabecular bone separation (r = 0.76, P < 0.001), but poor correlation with trabecular BMD (r = 0.37, P < 0.001). The focal BMC loss was significantly higher in the fracture group than the control (1.03 ± 0.13 vs. 0.93 ± 0.11 mm; P < 0.001), and was associated with prevalent VCF (1.87, 95% CI = 1.31-2.65, P < 0.001) independent of trabecular BMD level.

Discussion

As a surrogate measure of focal osteoporosis defect, focal BMC Loss independently associated with the VCF prevalence. It suggests that focal osteoporosis defect is a common manifestation that positively contributed to compression fracture risk and can be quantified with routine CT using focal BMC Loss.

Romosozumab Enhances Vertebral Bone Structure in Women With Low Bone Density

Romosozumab monoclonal antibody treatment works by binding sclerostin and causing rapid stimulation of bone formation while decreasing bone resorption. The location and local magnitude of vertebral bone accrual by romosozumab and how it compares to teriparatide remains to be investigated. Here we analyzed the data from a study collecting lumbar computed tomography (CT) spine scans at enrollment and 12 months post-treatment with romosozumab (210 mg sc monthly, n = 17), open-label daily teriparatide (20 μg sc, n = 19), or placebo (sc monthly, n = 20). For each of the 56 women, cortical thickness (Ct.Th), endocortical thickness (Ec.Th), cortical bone mineral density (Ct.bone mineral density (BMD)), cancellous BMD (Cn.BMD), and cortical mass surface density (CMSD) were measured across the first lumbar vertebral surface. In addition, color maps of the changes in the lumbar vertebrae structure were statistically analyzed and then visualized on the bone surface. At 12 months, romosozumab improved all parameters significantly over placebo and resulted in a mean vertebral Ct.Th increase of 10.3% versus 4.3% for teriparatide, an Ec.Th increase of 137.6% versus 47.5% for teriparatide, a Ct.BMD increase of 2.1% versus a -0.1% decrease for teriparatide, and a CMSD increase of 12.4% versus 3.8% for teriparatide. For all these measurements, the differences between romosozumab and teriparatide were statistically significant (p < 0.05). There was no significant difference between the romosozumab-associated Cn.BMD gains of 22.2% versus 18.1% for teriparatide, but both were significantly greater compared with the change in the placebo group (-4.6%, p < 0.05). Cortical maps showed the topographical locations of the increase in bone in fracture-prone areas of the vertebral shell, walls, and endplates. This study confirms widespread vertebral bone accrual with romosozumab or teriparatide treatment and provides new insights into how the rapid prevention of vertebral fractures is achieved in women with osteoporosis using these anabolic agents. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

An experimental procedure to perform mechanical characterization of small-sized bone specimens from thin femoral cortical wall

The cortical shell of the femoral neck plays a role in determining the overall neck strength. However, there is a lack of knowledge about the mechanical properties of cortical tissue of the femoral neck due to challenges in implementing accurate testing protocols for the thin shell. Indeed, mechanical properties are commonly derived from mechanical testing performed on tissue samples extracted from the femoral diaphysis, i.e. assuming tissue homogeneity along the femur. The aim of this work was to set up a reliable methodology to determine mechanical properties of bone samples extracted from thin cortical shell of the femoral neck. A three-point bending test was used to determine elastic and post-elastic properties of cortical bone samples extracted from the inferior and superior femoral neck. An optical system was used to monitor the sample deflection. Accuracy was preliminarily evaluated by determining the elastic modulus of an aluminium alloy. A good intra- and inter-sample variability was found on determining aluminium elastic modulus: 1.6% and 3.6%, respectively. Additionally, aluminium elastic modulus value was underestimated by less than 1%. A pilot trial was performed on a human femoral neck to assess the procedure feasibility. A total of 22 samples were extracted from the inferior and superior femoral neck and successfully tested. Preliminary results suggest that mechanical properties of cortical bone tissue extracted from human femoral neck might be side dependent, the superior tissue seems to exhibit better mechanical properties than the inferior one, at least in terms of yield stress and maximum strain. This supposedly different mechanical competence must be further investigated. The proposed procedure makes it feasible to carry out such studies.

Cortical bone mapping improves finite element strain prediction accuracy at the proximal femur

Despite evidence of the biomechanical role of cortical bone, current state of the art finite element models of the proximal femur built from clinical CT data lack a subject-specific representation of the bone cortex. Our main research hypothesis is that the subject-specific modelling of cortical bone layer from CT images, through a deconvolution procedure known as Cortical Bone Mapping (CBM, validated for cortical thickness and density estimates) can improve the accuracy of CT-based FE models of the proximal femur, currently limited by partial volume artefacts. Our secondary hypothesis is that a careful choice of cortical-specific density-elasticity relationship may improve model accuracy. We therefore: (i) implemented a procedure to include subject-specific CBM estimates of both cortical thickness and density in CT-based FE models. (ii) defined alternative models that included CBM estimates and featured a cortical-specific or an independently optimised density-elasticity relationship. (iii) tested our hypotheses in terms of elastic strain estimates and failure load and location prediction, by comparing with a published cohort of 14 femurs, where strain and strength in stance and fall loading configuration were experimentally measured, and estimated through reference FE models that did not explicitly model the cortical compartment. Our findings support the main hypothesis: an explicit modelling of the proximal femur cortical bone layer including CBM estimates of cortical bone thickness and density increased the FE strains prediction, mostly by reducing peak errors (average error reduced by 30%, maximum error and 95th percentile of error distribution halved) and especially when focusing on the femoral neck locations (all error metrics at least halved). We instead rejected the secondary hypothesis: changes in cortical density-elasticity relationship could not improve validation performances. From these improved baseline strain estimates, further work is needed to achieve accurate strength predictions, as models incorporating cortical thickness and density produced worse estimates of failure load and equivalent estimates of failure location when compared to reference models. In summary, we recommend including local estimates of cortical thickness and density in FE models to estimate bone strains in physiological conditions, and especially when designing exercise studies to promote bone strength.

Cortical Bone Mapping: Measurement and Statistical Analysis of Localised Skeletal Changes

PURPOSE OF REVIEW

Cortical bone mapping (CBM) is a technique for measuring localised skeletal changes from computed tomography (CT) images. It can provide measurements with accuracy surpassing the underlying imaging resolution. CBM can detect changes in several properties of the cortex, with no prior assumptions about the likely location of said changes. This paper summarises the theory behind CBM, discusses its strengths and limitations, and reviews some studies in which it has been applied.

RECENT FINDINGS

CBM has revealed associations between fracture risk and cortical properties in specific regions of the proximal femur which present feasible therapeutic targets. Analyses of several pharmaceutical and exercise interventions quantify effects that are distinct both in location and in the nature of the micro-architectural changes. CBM has illuminated age-related changes in the proximal femur and has recently been applied to other bones, as well as to the assessment of cartilage. The CBM processing pipeline is designed primarily for large cohort studies. Its main impact thus far has not been in the realm of clinical practice, but rather to improve our fundamental understanding of localised bone structure and changes.