Investigation of the failure behaviour of vertebral trabecular architectures under uni-axial compression and wedge action loading conditions

A systematic review of the Irish osteoporotic vertebral fracture literature

INTRODUCTION

Vertebral fractures (VF) are the most common osteoporotic fracture. They are associated with significant morbidity and mortality and are an important predictor of future fractures. The epidemiology of VF in Ireland is limited and a greater understanding of their scale and impact is needed. Therefore, we conducted a systematic review of publications on osteoporotic VF in Ireland.

METHODS

Systematic searches were conducted using PubMed, Medline, Embase, Scopus and Cochrane electronic databases to identify eligible publications from Ireland addressing osteoporotic VF.

RESULTS

Twenty studies met the inclusion criteria out of 1558 citations. All studies were published since 2000. Data was obtained on 182,771 patients with fractures. Nine studies included more than 100 subjects and three included more than 1000. Females accounted for 70% with an overall mean age of 65.2 years (30-94). There was significant heterogeneity in study design, methods and outcome measures including the following: use of administrative claims data on public hospital admissions, surgical and medical interventions, the impact of a fracture liaison service and the osteoporosis economic burden. The prevalence of VF was difficult to ascertain due to definitions used and differences in the study populations. Only two studies systematically reviewed spine imaging using blinded assessors and validated diagnostic criteria to assess the prevalence of fractures in patient cohorts.

CONCLUSIONS

Several studies show that VF are common when addressed systematically and the prevalence may be rising. However, there is a deficit of large studies systematically addressing the epidemiology and their importance in Ireland.

Long noncoding RNA LINC00958 accelerates the proliferation and matrix degradation of the nucleus pulposus by regulating miR-203/SMAD3

Emerging evidence suggests that long noncoding RNAs (lncRNAs) play important roles in the development of intervertebral disc degeneration (IDD). LncRNA LINC00958 has recently been shown to play crucial roles in the development of tumors. However, the role of LINC00958 in IDD remains unclear. We showed that the expression of lncRNA LINC00958 was upregulated in degenerative NP samples, and LINC00958 expression increased gradually along with the grade of exacerbation of disc degeneration. Ectopic expression of LINC00958 promoted nucleus pulposus (NP) cell proliferation, inhibited aggrecan and Col II expression and promoted MMP-2 and MMP-13 expression. In addition, we showed that miR-203 expression was downregulated in degenerative NP samples, and miR-203 expression reduced gradually along with the grade of exacerbation of disc degeneration. Moreover, we demonstrated that the expression of miR-203 was inversely related with LINC00958 expression in NP samples. Ectopic expression of miR-203 inhibited NP cell growth and inhibited ECM degradation. Furthermore, we showed that ectopic expression of miR-203 suppressed the luciferase activity of the wild-type LINC00958 3'-UTR but not the mutant LINC00958 3'-UTR. Elevated expression of LINC00958 inhibited the expression of miR-203 and promoted the expression of SMAD3. In addition, we demonstrated that lncRNA LINC00958 exerted its function by targeting miR-203 in the NP cells. These data suggested that dysregulated lncRNA LINC00958 expression might play an important role in the development of IDD.

Spinal fractures incurred by a fall from standing height

OBJECTIVE

Falls from standing are common, particularly amongst the aging population, due to declining mobility, proprioception and vision. They are often complicated by fragility fractures, including vertebral fractures, that are associated with significant morbidity and may represent a pre-terminal condition with high one-year mortality rates.

PATIENTS AND METHODS

A retrospective review of the Trauma Audit and Research Network database for a major trauma centre was conducted for all patients admitted between January 2011 and December 2016. Patients with a spinal fracture and a confirmed fall from standing height were eligible for inclusion. Case notes were reviewed for demographics, Injury Severity Score, Charlson co-morbidity score, treatment, complications and outcomes.

RESULTS

Of 1408 patients with a spine fracture admitted during the study period, 229 (16.3%) were confirmed to be secondary to a fall from standing height. The average age of this cohort was 76.6 ± 14.5 years and 134 (58.5%) cases were female. The average ISS score was 9.7 ± 5.4. The 229 patients sustained 283 fractures with a distribution of: cervical (n = 140), thoracic (n = 65) and lumbar (n = 78) spine. Fifty-six (24.5%) patients underwent surgical intervention. Forty-three patients (18.7%) died within 6 months of admission and all-cause mortality was significantly higher in patients with increasing age and Charlson co-morbidity score.

CONCLUSION

Spinal fractures due to a fall from standing height represent one sixth of the fracture workload of the emergency spinal service at a major trauma centre. Whilst the majority of patients can be managed conservatively there are still considerable implications for hospital bed usage and patient mortality.

Assessment of vertebral wedge strength using cancellous textural properties derived from digital tomosynthesis and density properties from dual energy X-ray absorptiometry and high resolution computed tomography

The purpose of this study was to examine the potential of digital tomosynthesis (DTS) derived cancellous bone textural measures to predict vertebral strength under conditions simulating a wedge fracture. 40 vertebral bodies (T6, T8, T11, and L3 levels) from 5 male and 5 female cadaveric donors were utilized. The specimens were scanned using dual energy X-ray absorptiometry (DXA) and high resolution computed tomography (HRCT) to obtain measures of bone mineral density (BMD) and content (BMC), and DTS to obtain measures of bone texture. Using a custom loading apparatus designed to deliver a nonuniform displacement resulting in a wedge deformity similar to those observed clinically, the specimens were loaded to fracture and their fracture strength was recorded. Mixed model regressions were used to determine the associations between wedge strength and DTS derived textural variables, alone and in the presence of BMD or BMC information. DTS derived fractal, lacunarity and mean intercept length variables correlated with wedge strength, and individually explained up to 53% variability. DTS derived textural variables, notably fractal dimension and lacunarity, contributed to multiple regression models of wedge strength independently from BMC and BMD. The model from a scan orientation transverse to the spine axis and in the anterior-posterior view resulted in highest explanatory capability (R²_adj = 0.91), with a scan orientation parallel to the spine axis and in the lateral view offering an alternative (R²_adj = 0.88). In conclusion, DTS can be used to examine cancellous texture relevant to vertebral wedge strength, and potentially complement BMD in assessment of vertebral fracture risk.

Modeling the Mechanical Consequences of Age-Related Trabecular Bone Loss by XFEM Simulation

The elderly are more likely to suffer from fracture because of age-related trabecular bone loss. Different bone loss locations and patterns have different effects on bone mechanical properties. Extended finite element method (XFEM) can simulate fracture process and was suited to investigate the effects of bone loss on trabecular bone. Age-related bone loss is indicated by trabecular thinning and loss and may occur at low-strain locations or other random sites. Accordingly, several ideal normal and aged trabecular bone models were created based on different bone loss locations and patterns; then, fracture processes from crack initiation to complete failure of these models were observed by XFEM; finally, the effects of different locations and patterns on trabecular bone were compared. Results indicated that bone loss occurring at low-strain locations was more detrimental to trabecular bone than that occurring at other random sites; meanwhile, the decrease in bone strength caused by trabecular loss was higher than that caused by trabecular thinning, and the effects of vertical trabecular loss on mechanical properties were more severe than horizontal trabecular loss. This study provided a numerical method to simulate trabecular bone fracture and distinguished different effects of the possible occurrence of bone loss locations and patterns on trabecular bone.

The role of patient-mode high-resolution peripheral quantitative computed tomography indices in the prediction of failure strength of the elderly women's thoracic vertebral body

The correlations between the failure load of 20 T12 vertebral bodies, their patient-mode high-resolution peripheral quantitative computed tomography (HR-pQCT) indices, and the L1 areal bone mineral density (aBMD) were investigated. For the prediction of the T12 vertebral failure load, the T12 HR-pQCT microarchitectural parameters added significant information to that of L1 aBMD and to that of cortical BMD, but not to that of T12 vertebral BMD and not to that of T12 trabecular BMD.

INTRODUCTION

HR-pQCT is a new in vivo imaging technique for assessing the three-dimensional microarchitecture of cortical and trabecular bone at the distal radius and tibia. But little is known about this technique in the direct measurement of vertebral body.

METHODS

Twenty female donors with the mean age of 80.1 (7.6) years were included in the study. Dual X-ray absorptiometry of the lumbar spine and femur was performed. The spinal specimens (T11/T12/L1) were dissected, scanned using HR-pQCT scanner, and mechanically tested under 4° wedge compression. The L1 aBMD, T12 patient-mode HR-pQCT indices, and T12 vertebral failure loads were analyzed.

RESULTS

For the prediction of vertebral failure load, the inclusion of BV/TV into L1 aBMD was the best model (R (2) = 0.52), Tb.N and Tb.Sp added significant information to the L1 aBMD and to the cortical BMD, but none of the vertebral microarchitectural parameters yielded additional significant information to the trabecular BMD (or BV/TV) and to the vertebral BMD.

CONCLUSION

Vertebral microarchitectural parameters obtained from the patient-mode HR-pQCT analysis provide significant information on bone strength complementary to that of aBMD and to that of cortical BMD, but not to that of vertebral BMD and not to that of trabecular BMD.

Prediction of the vertebral strength using a finite element model derived from low-dose biplanar imaging: benefits of subject-specific material properties

STUDY DESIGN

A finite element analysis on osteoporotic vertebrae.

OBJECTIVE

This study aims to validate subject-specific finite element models (FEMs) derived from a low-dose imaging system (EOS, Biospace Med, France) for the prediction of vertebral strength. The vertebrae are submitted to an eccentric compression force leading to compression and anterior bending.

SUMMARY OF BACKGROUND DATA

Given the aging population, osteoporosis and vertebral fractures are a major public health issue. A low bone mineral density (BMD) does not always explain incident fractures, and multifactorial analyses are required. In this context, FEMs based on quantitative computed tomography (QCT) have been proposed to predict vertebral strength in vitro or quantify effects of treatments. However, the clinical use of such a model for the in vivo follow-up of the whole spine is limited by the high-radiation dose induced by QCT and the lying position, which does not allow postural assessment with the same modality.

METHODS

Fourteen vertebrae were modeled using a parametric meshing method. The mesh was subject-specific using geometric parameters computed on the 3-dimensional (3D) reconstructions obtained from the EOS biplanar radiographs. The contribution of cortical bone was taken into account by modeling a cortico-cancellous shell whose properties were derived from experimental data. The effect of subject-specific bone Young's moduli derived from EOS vertebral areal BMD was quantified. The 3D position of the point-of-load application and the 3D orientation of the force was faithfully reproduced in the model to compare the predicted strength and experimental strength under the same loading conditions.

RESULTS

The relative error of prediction decreased from 43% to 16% (2.5 times) when subject-specific mechanical properties, derived from EOS areal BMD, were implemented in the FEM compared with averaged material properties. The resulting subject-specific FEMs predicted vertebral strength with a level of significance close to the QCT-based models (r adjusted = 0.79, root mean square error = 367 N).

CONCLUSION

This work underlines the potential of low-dose biplanar x-ray devices to make subject-specific FEMs for prediction of vertebral strength.