Breaking strength and bone microarchitecture in osteoporosis: a biomechanical approximation based on load tests in 104 human vertebrae from the cervical, thoracic, and lumbar spines of 13 body donors

Gender differences in L1 vertebral strength in adults 50+ using automated CT-based finite element analysis

Osteoporosis is usually diagnosed using a Bone Mineral Density test using dual-energy X-ray Absorptiometry. However, it is limited by low testing rates and the inability to directly measure bone strength. Finite Element Analysis allows for a more detailed assessment of bone strength. However, its modeling complexity and high computational time requirements pose challenges. This study aims to develop customized MATLAB programs to automate the creation of heterogeneous bone models, streamlining preprocessing to reduce time, computational costs, and minimize variability from manual processes. The focus is on establishing a prediction model for the structural strength of the L1 vertebral body using patient-specific CT data, thereby aiding in the prediction of vertebral fracture risk. The CT images are stacked into a 3D array, and the pixel values are converted by Hounsfield units based on CT image. The bone segment and elasticity values are established based on the Hounsfield units. After modeling, strain and stress analysis were performed through the solver LS-DYNA. The compression force was distributed vertically on the upper endplate of the vertebral body. All nodes in the subvertebral plane were fully constrained. For comparison, vertebral models were automatically established and analyzed from recruited subjects. This study collected spine CT imaging datasets from 52 subjects, comprising 28 males and 24 females aged between 50 and 95 years. Preprocessing and mechanical analysis for each subject took an average of approximately 579.6 seconds. Analysis of the results indicated that women over 50 years of age exhibited higher strain and stress values in their vertebral models compared to men under the same applied force, highlighting gender-specific differences in biomechanical characteristics. This study effectively employed a practical approach to identify and select specific spinal segments from CT images, facilitating the automated creation of 3D models for subsequent finite element analysis. The predictive model generated results consistent with previous studies involving mechanical testing on actual human bones. Notably, the implementation of our predictive model substantially decreased processing time for Finite Element Analysis, rendering it more suitable for clinical use and easier to extend for future application.

Impact of different 3D regions of interest on quantifying dynamic lumbar vertebral microstructure in ovariectomized rats-a micro-CT study

Introduction

The selection of regions of interest (ROIs) is crucial for accurate microcomputed tomography (micro-CT) analysis. Distinct ROI selection methods exist for lumbar vertebras in osteoporotic animal model research. However, whether different ROIs directly affect the results of quantitative micro-CT-based microarchitectural data is still unknown. This study aimed to compare the diagnostic accuracy of two commonly used ROIs of lumbar vertebras in ovariectomized (OVX) rats at different time points.

Methods

Rats were randomly divided into the baseline group, the sham/OVX-operated groups, with 12- or 24-weeks sham (Sham 12w or Sham 24w)/12- or 24-weeks (OVX 12w or OVX 24w)-operated group (n = 6 in every group). The fifth lumbar vertebras were collected and scanned using micro-CT. Quantitative analyses of bone microarchitecture parameters were conducted separately for the central ROI (ROI 1) and overall ROI (ROI 2).

Results

The results indicated that the Tb.N of baseline group rats for ROI 1 was significantly lower than that for ROI 2. The Tb.Th of rats of the Sham 12w and Sham 24w groups was significantly increased compared to that of the baseline group rats using the ROI 2 analysis. The bone mineral density (BMD) and bone volume fraction (BV/TV) were significantly lower by the ROI 1 than by the ROI 2 in all groups. The BMD and BV/TV also showed a significant reduction at 24 weeks postoperatively compared with those at 12 weeks postoperatively. Bland-Altman analysis showed good consistency between the two different ROI selection methods.

Conclusion

This study found that capturing peripheral trabeculas (overall ROI) does not explain the increased Tb.Th in healthy mice and decreased Tb.N in OVX mice; both findings indicate that this is evident in both ROI. Moreover, this study suggested the potential value of the central ROI (effective and quicker) for evaluating osteoporosis of the lumbar vertebras in OVX rats and provides a basis for analyzing the morphological changes of lumbar trabecular.

Opportunistic Osteoporosis Assessment and Fracture Risk Determination Using Cancellous Density Measurement in Hounsfield Units of Native Lumbar Computed Tomography Images-A Comparative Study with Conventional Bone Density Evaluation

Background/Objectives: Osteoporosis is a global problem that will increase as the population increases and ages, requiring prevention, early detection, and appropriate treatment. An increasing loss in bone mineral density (BMD) is the hallmark of osteoporosis, leading to an increased risk for insufficiency fractures. We aimed to investigate and analyze the applicability of native lumbar spine computed tomography (CT) scans for the evaluation of bone density compared with standard bone density measurements with quantitative computed tomography (QCT) and computed tomography X-ray absorptiometry of the hip (CTXA). Methods: Patients who were referred to our institution for diagnostic investigations and underwent CT imaging of the lumbar spine, as well as standard osteoporosis assessments including QCT and CTXA, were included in the study, resulting in a total of 240 patients (mean age: 65.9 years, range: 24-91). An ANOVA test was used to compare patient groups without a fracture, with one fracture, with more than one fracture, and with additional sacral fractures. An ROC analysis was performed to assess the predictive power of fracture risk estimation considering HU, QCT, and CTXA values. Results: At least one fracture was detected in 42.9% of these patients. For the lumbar spine, the median HU was 89.9 (range 67.9-126.9) and the median BMD was 73.7 (range 57.1-104.2) mg/cm3. With a correlation coefficient of 0.98 (p < 0.001), the HU values obtained from native lumbar CT scans can be calculated using the following formula: BMDspine = 0.84 + (0.81 × HU). With HU values < 80 and a BMD of the lumbar spine < 66 mg/cm3, a significantly increased number of osteoporotic vertebral fractures were found in the mid-thoracic, thoracolumbar, and sacral regions with an effect size of 0.89. In 32 patients (13.3%), additional sacral fractures were found; these patients showed the lowest density values with a median HU value of 31.8 (12.7-58.2). An ROC analysis of HU revealed a 93% sensitivity for the coincidence of a vertebral fracture. There was no significant difference compared with the AUC of QCT (p = 0.395) for concomitant vertebral body fractures. CTXA values also allowed for risk assessment but showed a significantly lower AUC. We found a negative correlation of BMD with age and a positive correlation of BMD with body mass index. Conclusions: Cancellous density measurements in HU values can be effectively converted into quantitative BMD values in mg/cm3, enabling a reliable assessment of osteoporosis severity and fracture risk prediction. Further quantitative density evaluation of the hip does not add value to fracture risk assessment for the axial skeleton. Based on this study's findings, using HU values in native CT of the lumbar spine alone offers a viable, opportunistic approach towards fracture risk evaluation of the spine.

Textural and geometric measures derived from digital tomosynthesis discriminate women with and without vertebral fracture

Vertebral fractures are a common and debilitating consequence of osteoporosis. Bone mineral density (BMD), measured by dual energy x-ray absorptiometry (DXA), is the clinical standard for assessing overall bone quantity but falls short in accurately predicting vertebral fracture. Fracture risk prediction may be improved by incorporating metrics of microstructural organization from an appropriate imaging modality. Digital tomosynthesis (DTS)-derived textural and microstructural parameters have been previously correlated to vertebral bone strength in vitro, but the in vivo utility has not been explored. Therefore, the current study sought to establish the extent to which DTS-derived measurements of vertebral microstructure and size discriminate patients with and without vertebral fracture. In a cohort of 93 postmenopausal women with or without history of vertebral fracture, DTS-derived microstructural parameters and vertebral width were calculated for T12 and L1 vertebrae, as well as lumbar spine BMD and trabecular bone score (TBS) from DXA images. Fracture patients had lower BMD and TBS, while DTS-derived degree of anisotropy and vertebral width were higher, compared to nonfracture (p < 0.02 to p < 0.003) patients. The addition of DTS-derived parameters (fractal dimension, lacunarity, degree of anisotropy and vertebral width) improved discriminative capability for models of fracture status (AUC = 0.79) compared to BMD alone (AUC = 0.67). For twelve additional participants who were imaged twice, in vivo repeatability errors for DTS parameters were low (0.2 % - 7.3 %). The current results support the complementary use of DTS imaging for assessing bone quality and improving the accuracy of fracture risk assessment beyond that achievable by DXA alone.

Hounsfield Unit Utilization in Cervical Spine for Bone Quality Assessment: A Scoping Review

Bone mineral density (BMD) is an essential indicator of bone strength and plays a crucial role in the clinical management of various spinal pathologies. Hounsfield units (HUs) calculated from computed tomography (CT) scans are a well-established, effective, and non-invasive method to determine bone density in the lumbar spine when juxtaposed to dual-energy X-ray absorptiometry (DEXA) scans, the gold standard for assessing trabecular bone density. Only recently have studies begun to investigate and establish HUs as a reliable and valid alternative for bone quality assessment in the cervical spine as well. In addition, multiple recent studies have identified cervical HUs as an accurate predictor of cage subsidence, an undesired complication of anterior cervical discectomy and fusion (ACDF) of anterior cervical corpectomy and fusion (ACCF) procedures. Subsidence involves migration of the spinal fusion cage into vertebral bodies, causing a loss of disk space, negatively altering spine alignment, and possibly necessitating further unwanted surgical intervention. Using the PRISMA-ScR checklist and the registered scoping review protocol (INPLASY2024100126), this review explores the current research on the use of cervical spine HU measurements as both a determinant of BMD and as a prognosticator of postoperative subsidence following cervical spine procedures (i.e., ACDFs and ACCFs) with the aim of improving clinical and surgical outcomes.

[Comparative evaluation of trabecular bone density in Hounsfield units in the lumbar native CT cross-section for osteoporosis diagnosis and fracture risk determination by different examiners]

BACKGROUND

An increasing loss of bone mineral density (BMD) in the axial skeleton leads to osteoporosis and fractures, with an increase found in the thoracic and thoracolumbar regions.

RESEARCH QUESTION

The extent to which an examiner-independent assessment of the extent of osteoporosis and fracture risk determination is possible by determining the trabecular density in Hounsfield units (HU) in the spine should be examined. The next question was whether quantitative BMD values can be calculated from the HU values.

PATIENTS AND METHODS

225 patients (pt.) with an average age of 64.9 ± 13.1 years and a body-mass-index (BMI) of 26.8 ± 6.8 kg/m2, of which 37 were men and 188 were women, were examined to determine whether they had osteoporosis. The BMD was determined in mg/cm3 using quantitative computed tomography (QCT) in the lumbar region. After anonymization by three experienced radiologists, an additional measurement of the trabecular bone density in HU, was carried out in the same vertebral bodies (a total of 675 vertebral bodies), each using a region of interest (ROI) positioned in the midvertebral cancellous space in the sagittal reformed CT image. In additional lateral X‑rays of the thoracic and lumbar spine, vertebral fractures were detected and graded. Sacral insufficiency fractures that occurred at the same time were also recorded.

RESULTS

The median BMD was 73.2 (57.05-104.17) mg/cm3 and the median HU was 89.93 (67.90-126.95). With a correlation of 0.988 (p < 0.001), quantitative values in mg/cm3 can be calculated using the following formula: Xq = 12.1 + 0.68 × HU. With HU values less than 69.84 and a BMD of the lumbar spine below 59.54 mg/cm3, there was a significantly increased number of OVF. At least one OVF was found in 137/225 pt. In 17/137 pt., sacral fractures were also found; these patients showed the significantly lowest values with a median BMD of 41.81 (16.2-53.7) mg/cm3. Comparable HU values were determined independently of the examiners (p > 0.05).

DISCUSSION

The trabecular density measurements in HU values can be converted into quantitative BMD values in mg/cm3, which enables a good assessment of osteoporosis and fracture risk. Taking the results obtained into account, an opportunistic evaluation using HU values in native CT alone seems quite possible. Experienced examiners have arrived at comparable results.

The Fracture Phenotypes in Women and Men of 50 Years and Older with a Recent Clinical Fracture

PURPOSE OF REVIEW

We review the literature about patients 50 years and older with a recent clinical fracture for the presence of skeletal and extra-skeletal risks, their perspectives of imminent subsequent fracture, falls, mortality, and other risks, and on the role of the fracture liaison service (FLS) for timely secondary fracture prevention.

RECENT FINDINGS

Patients with a recent clinical fracture present with heterogeneous patterns of bone-, fall-, and comorbidity-related risks. Short-term perspectives include bone loss, increased risk of fractures, falls, and mortality, and a decrease in physical performance and quality of life. Combined evaluation of bone, fall risk, and the presence of associated comorbidities contributes to treatment strategies. Since fractures are related to interactions of bone-, fall-, and comorbidity-related risks, there is no one-single-discipline-fits-all approach but a need for a multidisciplinary approach at the FLS to consider all phenotypes for evaluation and treatment in an individual patient.

Diagnosis of newly developed multiple myeloma without bone disease detectable on conventional computed tomography (CT) scan by using dual-energy CT

Objective

To evaluate the diagnostic utility of fat (hydroxyapatite) density [DFat (HAP)] on dual-energy computed tomography (DECT) for identifying clinical diagnosed multiple myeloma without bone disease (MNBD) that is not visible on conventional CT scans.

Material and Methods

In this age-gender-examination sites matched case control prospective study, Chest and/or abdominal images on Revolution CT of MNBDs and control subjects were consecutive enrolled in a 1:2 ratio from October 2022 to November 2023. Multiple myeloma was clinical diagnosed according to criteria of the International Myeloma Working Group. Regions of interest (ROIs) were drawn separately for all thoracolumbar vertebrae in the scanning range by two radiologists. Additionally, a radiologist specializing in musculoskeletal imaging supervised the process. DFat (HAP) was extracted from each ROI. The spine was divided into upper thoracic (UPT), middle and lower thoracic (MLT), thoracolumbar (TL), and middle and lower lumbar (MLL) vertebrae. The area under the receiver operating characteristic curve (AUC) was calculated to evaluate the diagnostic performance of DFat (HAP) in diagnosing multiple myeloma, and the sensitivity, specificity, and accuracy under the optimal cut-off were determined by Youden index (sensitivity + specificity -1).

Results

A total of 32 and MNBD patients and 64 control patients were included. The total number of ROIs outlined included MNBD group (n = 493) and control group (n = 986). For all vertebrae, DFat(HAP) got average performance in the diagnosis of MNBD (AUC = 0.733, p < 0.001) with a cut-off value of 958 (mg/cm3); the sensitivity, specificity, and accuracy were 58.8 %, 77.8 %, and 71.7 %, respectively. Regarding segment analysis, the diagnostic performance was good for all (AUC, 0.803-0.837; p < 0.001) but the UPT segment (AUC = 0.692, p = 0.002). The optimal diagnostic cut-off values for the MLT, TL, and MLL vertebrae were 955 mg/cm3, 947 mg/cm3, and 947 mg/cm3, respectively; the sensitivity, specificity, and accuracy were 80.0 %-87.5 %, 71.9 %-82.6 %, and 77.1 %-81.6 %, respectively.

Conclusion

DECT was effective for detecting MNBD, and better diagnostic results can be obtained by grouping different spine segments.

Investigation of the Role of Osteoporotic Vertebra Degeneration on the Stability of the Lumbar Spine: In Silico Modelling under Compressive Loading

An evaluation of the impact of osteoporosis on loss of spinal stability, with or without intervertebral disc degeneration, using computational analysis is presented. The research also investigates the correlation between osteoporosis and intervertebral disc degeneration. Three-dimensional finite element models of human lumbar spine segments were used to assess the influence of osteoporosis on spinal stability. Five different models of age-related degeneration were created using various material properties for trabecular bone and intervertebral discs. Calculation results indicate that in a spine with osteoporosis, the deformation of the intervertebral discs can increase by more than 30% when compared to a healthy spine. Thus, intervertebral disc deformation depends not only on the degree of degeneration of the discs themselves, but their deformation is also influenced by the degree of osteoporosis of the vertebrae. Additionally, the load-bearing capacity of the spine can decrease by up to 30% with osteoporosis, regardless of the degree of intervertebral disc deformation. In conclusion, osteoporosis can contribute to intervertebral disc degeneration.

Interobserver variability in the determination of bone mineral density in Hounsfield units from differently configured fields of measurement in the cancellous bone of vertebral bodies from elderly body donors

Background

Due to the absence of suitable diagnostic procedures, osteoporosis (OP) is frequently detected late or not at all. Many elderly persons undergo computed tomographies (CT). The routine determination of Hounsfield units (HU) in bone as a part of these examinations could close a gap here.

Methods

Spines were extracted from 22 body donors, fixed in a PVC water phantom, and subjected to a high-resolution CT investigation. Cancellous bone was examined and its bone mineral density measured in HU from cervical vertebra 3 to lumbar vertebra 5 (484 vertebral bodies). On sagittal sections, a circular and a rectangular region of interest (ROI) were defined in mid-vertebral cancellous bone, positioned manually, and the measurements were performed by three experienced radiologists. Bone mineral density (BMD), measured in mg/cm3, was used to determine the presence of OP.

Results

All of the spines were osteoporotic. In the presence of a BMD below 60 mg/cm3 and HU values below 63.36 in lumbar vertebrae, there were significantly more vertebral body fractures in the thoracic and thoracolumbar spine. No difference was observed between the manually positioned circular and rectangular regions of interest (ROI) on the sagittal CT section (p > 0.05). Similar HU counts were obtained by the individual examiners (p > 0.05). The following formula was used to determine QCT values on a non-contrasted CT of the spine: QCT = 0.6 × HU + 13.7.

Conclusions

Measurement of the density of cancellous bone in HU can be used to determine BMD for estimating demineralization. Quantitative BMD values in mg/cm3, which can be calculated from the HU data, concur well with QCT values.

Open the pores - Polydimethylsiloxane influences the porous structure of cancellous bone surrogates for biomechanical testing of osteosyntheses

Synthetic materials used for valid and reliable implant testing and design should reflect the mechanical and morphometric properties of human bone. Such bone models are already available on the market, but they do not reflect the population variability of human bone, nor are they open-celled porous as human bone is. Biomechanical studies aimed at cementing the fracture or an implant cannot be conducted with them. The aim of this study was to investigate the influence of a cell stabilizer on polyurethane-based cancellous synthetic bone in terms of morphology, compressive mechanics, and opening of the cancellous bone structure for bone cement application. Mechanical properties of cylindrical specimens of the bone surrogates were determined by static compression tests to failure. Furthermore, a morphometric analysis was performed using microcomputed tomography. To prove the open-cell nature of the bone surrogates, an attempt was made to apply bone cement. Effects on the mechanical properties of the polyurethane-based bone surrogates were observed by the addition of polydimethylsiloxane. All mechanical parameters like Young's modulus, ultimate stress and yield stress increased statistically significantly with increasing amounts of cell stabilizer (all p > 0.001), except for yield stress. The analysis of morphometric parameters showed a decrease in trabecular thickness, spacing and connectivity density, which was accompanied by an increase in trabecular number and an increase in pore size. The open-cell nature was proven by the application and distribution of bone cement in specimens with stabilizer, which was visualized by X-ray. In conclusion, the results show that by adding a cell stabilizer, polyurethane-based cancellous bone substrates can be produced that have an open-cell structure similar to human bone. This makes these bone surrogates suitable for biomechanical testing of osteosyntheses and for osteosynthesis cementation issues.

Regional Variations in the Intra- and Intervertebral Trabecular Microarchitecture of the Osteoporotic Axial Skeleton with Reference to the Direction of Puncture

BACKGROUND

Trabeculae in vertebral bodies are unequally distributed within the cervical spine (CS), the thoracic spine (TS), and lumbar spine (LS). Such structures are also unequally distributed within the individual vertebrae. Exact knowledge of the microstructure of these entities could impact our understanding and treatment of fractures caused by osteoporosis and possibly improve surgical approaches. Appropriate investigations could help clarify the pathomechanisms of different forms of osteoporotic vertebral fractures, as well as different changes in morphological findings like the trabecular bone score (TBS). In the present study, we applied punctures to the craniocaudal and ventrocaudal directions and obtained cylinders of cancellous bone from the central portions and marginal regions of cervical vertebrae 5 and 6, thoracic vertebrae 8 and 12, and lumbar vertebrae 1 and 3. We systematically analyzed these samples to determine the bone volume fraction, trabecular thickness, separation, connectivity density, degree of anisotropy, and structure model index.

METHODS

Using an 8-gauge Jamshidi needle, we obtained samples from three quadrants (Q I: right margin; Q II: central; Q III: left margin) in the frontal and transverse plane and prepared these samples with a moist cloth in a 1.5 mL Eppendorf reaction vessel. The investigations were performed on a micro-CT device (SKYSCAN 1172, RJL Micro & Analytic Company, Karlsdorf-Neuthard, Germany). All collected data were analyzed using the statistical software package SPSS (version 24.0, IBM Corp., Armonk, NY, USA). Student's t test, the Wilcoxon-Mann-Whitney test, the Chi-squared test, and univariate analysis were used for between-group comparisons. The selection of the test depended on the number of investigated groups and the result of the Shapiro-Wilk test of normal distribution. In the case of statistically significant results, a post hoc LSD test was performed.

RESULTS

In total, we obtained 360 bone samples from 20 body donors. The craniocaudal puncture yielded data of similar magnitudes for all investigated parameters in all three quadrants, with the highest values observed in the CS. Comparisons of the ventrodorsal and craniocaudal microstructure revealed a significantly lower trabecular density and a significantly higher degree of anisotropy in the craniocaudal direction.

CONCLUSIONS

The results presented different distributions and behaviors of trabecular density, with lower density in the mid-vertebral region over the entire breadth of the vertebrae. Reduced trabecular density caused a higher degree of anisotropy and was, therefore, associated with a lower capacity to sustain biomechanical loads. Fractures in fish vertebrae were easily explained by this phenomenon. The different changes in these structures could be responsible, in part, for the changes in the TBS determined using dual-energy X-ray absorptiometry. These results confirm the clinical relevance of the TBS.

Characterization of mechanical stiffness using additive manufacturing and finite element analysis: potential tool for bone health assessment

BACKGROUND

Bone health and fracture risk are known to be correlated with stiffness. Both micro-finite element analysis (μFEA) and mechanical testing of additive manufactured phantoms are useful approaches for estimating mechanical properties of trabecular bone-like structures. However, it is unclear if measurements from the two approaches are consistent. The purpose of this work is to evaluate the agreement between stiffness measurements obtained from mechanical testing of additive manufactured trabecular bone phantoms and μFEA modeling. Agreement between the two methods would suggest 3D printing is a viable method for validation of μFEA modeling.

METHODS

A set of 20 lumbar vertebrae regions of interests were segmented and the corresponding trabecular bone phantoms were produced using selective laser sintering. The phantoms were mechanically tested in uniaxial compression to derive their stiffness values. The stiffness values were also derived from in silico simulation, where linear elastic μFEA was applied to simulate the same compression and boundary conditions. Bland-Altman analysis was used to evaluate agreement between the mechanical testing and μFEA simulation values. Additionally, we evaluated the fidelity of the 3D printed phantoms as well as the repeatability of the 3D printing and mechanical testing process.

RESULTS

We observed good agreement between the mechanically tested stiffness and μFEA stiffness, with R2 of 0.84 and normalized root mean square deviation of 8.1%. We demonstrate that the overall trabecular bone structures are printed in high fidelity (Dice score of 0.97 (95% CI, [0.96,0.98]) and that mechanical testing is repeatable (coefficient of variation less than 5% for stiffness values from testing of duplicated phantoms). However, we noticed some defects in the resin microstructure of the 3D printed phantoms, which may account for the discrepancy between the stiffness values from simulation and mechanical testing.

CONCLUSION

Overall, the level of agreement achieved between the mechanical stiffness and μFEA indicates that our μFEA methods may be acceptable for assessing bone mechanics of complex trabecular structures as part of an analysis of overall bone health.

Regional variations in the intra- and intervertebral trabecular microarchitecture of the osteoporotic axial skeleton

Trabecular structures in vertebral bodies are unequally distributed in the cervical, thoracic and lumbar spine, and also within individual vertebrae. Knowledge of the microstructure of these entities could influence our comprehension and treatment of osteoporotic fractures, and even surgical procedures. Appropriate investigations may clarify the pathomechanisms of various osteoporotic fractures (fish, wedge-shaped, and flat vertebrae). We obtained three cancellous bone cylinders from the centers and margins of cervical vertebra 3 to lumbar vertebra 5, and investigated these in regard of bone volume fraction, trabecular thickness, separation, trabecular number, trabecular bone pattern factor, connectivity density, and degree of anisotropy. Using a Jamshidi needle^®, we obtained samples from three quadrants (QI: right-sided edge, QII: central, QIII: left-sided edge) of 242 prepared vertebrae, and investigated these on a micro-CT device. In all, 726 bone samples were taken from eleven body donors. Bone volume fraction, trabecular thickness, and the degree of anisotropy were significantly lower in QII than in QI and QIII. Trabecular pattern factor, however, was significantly higher in QII than in QI and QIII. The results helped to explain fish vertebrae. Wedge fractures and flat vertebrae are most likely caused by the complex destruction of trabecular and cortical structures. The higher bone volume fraction in the cervical spine compared to the thoracic and lumbar spine accounts for the small number of fractures in the cervical spine. The marked trabecular pattern factor in the center of thoracic and lumbar vertebrae could be a reason for the surgeon to use different screw designs for individual vertebrae.

Is human bone matrix a sufficient augmentation method revising loosened pedicle screws in osteoporotic bone? - A biomechanical evaluation of primary stability

INTRODUCTION

Despite good screw anchorage and safe screw trajectory, screw loosening occurs in several cases, especially in osteoporotic individuals. The aim of this biomechanical analysis was to evaluate the primary stability of revision screw placement in individuals with reduced bone quality. Therefore, revision via enlarged diameter screws was compared to the use of human bone matrix as augmentation to improve the bone stock and screw coverage.

METHODS

11 lumbar vertebral bodies from cadaveric specimens with a mean age of 85.7 years (± 12.0 years) at death were used. 6.5 mm diameter pedicle screws were inserted in both pedicles and hereafter loosened using a fatigue protocol. Screws were revised inserting a larger diameter screw (8.5 mm) in one pedicle and a same diameter screw with human bone matrix augmentation in the other pedicle. The previous loosening protocol was then reapplied, comparing maximum load and cycles to failure between both revision techniques. Insertional torque was continuously measured during insertion of both revision screws.

FINDINGS

The number of cycles and the maximum load until failure were significantly greater in enlarged diameter screws than in augmented screws. The enlarged screws' insertional torque was also significantly higher than of the augmented screws.

INTERPRETATION

Human bone matrix augmentation does not reach the same ad-hoc fixation strength as enlarging the screw's diameter by 2 mm and is therefore biomechanically inferior. Regarding the immediate stability, a thicker screw should therefore be prioritised.

Histomorphometric analysis of osteocyte density and trabecular structure of 92 vertebral bodies of different ages and genders

BACKGROUND

Knowledge of the histomorphometric structure of the vertebral body and factors influencing the structure is essential for a fundamental understanding of osteoporosis and osteoporotic fractures. The present study is focused on osteocyte density - a parameter seldom investigated so far - and trabecular width as well as bone area over tissue area in human vertebral bodies.

METHODS

Ninety-two vertebral body specimens (C5, C6, Th8, Th12, L1, L2) from 12 males and seven females were studied (Ethics Application Number A 2017-0072). The prepared vertebral specimens were extracted from the ventral aspect with a Jamshidi needle®. The punches were decalcified and subsequently H&E stained. Using the Fiji/Image J program (version 1.53 f, Wayne Resband, National Institute of Mental Health, USA), osteocyte numbers were counted per calcified bone surface, and the trabecular width and bone area of trabecular bone were measured. The collected data were analyzed using the statistical software package SPSS, version 23.0 (SPSS Inc., Chicago, USA). Pearson's correlation coefficient was used for correlation analyses. Multiple linear regression analyses were also performed.

RESULTS

Osteocyte density did not differ significantly in comparisons based on gender and age (≤65 years; ≥66 years). Men had wider trabeculae (p < 0.001) and a higher bone area over tissue area (BA/TA, %) (p = 0.025) than women. Individuals over 65 years of age had thinner trabeculae (p < 0.001) and a smaller BA/TA (%) (p < 0.001) than younger individuals. Multiple linear regression analyses were performed to determine the influence of 'gender' and 'age' on trabecular width and bone area over tissue area. The R² was 0.388 for trabecular width and 0.227 for BA/TA (%). Per year of life, trabecular width decreases by 0.368 µm (β < 0.001) and BA/TA (%) by 0.001% (β = 0.001). Men have on average 8.2 µm wider trabeculae than women (β = 0.035). A negative correlation (r = -0.275) was observed between trabecular width and osteocyte density. The wider the trabeculae, the fewer osteocytes per mm² (p = 0.008).

CONCLUSIONS

Surprisingly, we found no difference in osteocyte density with reference to age or gender. However, we did register significant age- and gender-related differences in bone area over tissue area and trabecular thickness. The age-related differences were more pronounced, implying that age-dependent loss of bone structure may be more important than differences between genders.