Biomechanical properties of human thoracic spine disc segments

The I-PREDICT 50th Percentile Male Warfighter Finite Element Model: Development and Validation of the Thoracolumbar Spine

Military personnel are commonly at risk of lower back pain and thoracolumbar spine injury. Human volunteers and postmortem human subjects have been used to understand the scenarios where injury can occur and the tolerance of the warfighter to these loading regimes. Finite element human body models (HBMs) can accurately simulate the mechanics of the human body and are a useful tool for understanding injury. In this study, a HBM thoracolumbar spine was developed and hierarchically validated as part of the Incapacitation Prediction for Readiness in Expeditionary Domains: an Integrated Computational Tool (I-PREDICT) program. Constitutive material models were sourced from literature and the vertebrae and intervertebral discs were hexahedrally meshed from a 50th percentile male CAD dataset. Ligaments were modeled through attaching beam elements at the appropriate anatomical insertion sites. 94 simulations were replicated from experimental PMHS tests at the vertebral body, functional spinal unit (FSU), and regional lumbar spine levels. The BioRank (BRS) biofidelity ranking system was used to assess the response of the I-PREDICT model. At the vertebral body level, the I-PREDICT model showed good agreement with experimental results. The I-PREDICT FSUs showed good agreement in tension and compression and had comparable stiffness values in flexion, extension, and axial rotation. The regional lumbar spine exhibited "good" biofidelity when tested in tension, compression, extension, flexion, posterior shear, and anterior shear (BRS regional average = 1.05). The validated thoracolumbar spine of the I-PREDICT model can be used to better understand and mitigate injury risk to the warfighter.

Development and evaluation of sex-specific thoracolumbar spine finite element models to study spine biomechanics

Musculoskeletal disorders and low back pain (LBP) are common global afflictions, with a higher prevalence observed in females. However, the cause of many LBP cases continues to elude researchers. Current approaches seldom consider differences in male and female spines. Thus, this study aimed to compare the load distribution between male and female spines through finite element modeling. Two finite element models of the spine, one male and one female, were developed, inclusive of sex-specific geometry and material properties. The models consisted of the vertebrae, intervertebral discs (IVD), tendons, surrounding spinal muscles, and thoracolumbar fascia and were subjected to loading conditions simulating flexion and extension. Following extensive validation against published literature, intersegmental rotation, IVD stress, and vertebral body stress were evaluated. The female model demonstrated increased magnitudes for rotation and stresses when compared to the male model. Results suggest that the augmented stresses in the female model indicate an increased load distribution throughout the spine compared to the male model. These findings may corroborate the higher prevalence of LBP in females. This study highlights the importance of using patient- and sex-specific models for patient analyses and care.

Defining and measuring objective and subjective spinal stiffness: a scoping review

PURPOSE

Examine and identify the breadth of definitions and measures of objective and subjective spinal stiffness in the literature, with a focus on clinical implications.

METHODS

A scoping review was conducted to determine what is known about definitions and measures of the specific term of spinal stiffness. Following the framework by Arksey and O'Malley, eligible peer-reviewed studies identified using PubMed, Ebsco health, and Scopus were included if they reported definitions or measures of spinal stiffness. Using a data abstraction form, the studies were classified into four themes: biomechanical, surgical, pathophysiological, and segmental spinal assessment. To identify similarities and differences between studies, sixteen categories were generated.

RESULTS

In total, 2426 records were identified, and 410 met the eligibility criteria. There were 350 measures (132 subjective; 218 objective measures) and 93 indicators of spinal stiffness. The majority of studies (n = 69%) did not define stiffness.

CONCLUSION

This review highlights the breadth of objective and subjective measures that are both clinically and methodologically diverse. There is no consensus regarding a standardised definition of stiffness in the reviewed literature.

Biomechanical evaluation of the thoracolumbar spine comparing healthy and irregular thoracic and lumbar curvatures

BACKGROUND

The geometric alignment of the spine plays an integral role in stability, biomechanical loading, and consequently, pain, and a range of healthy sagittal curvatures has been identified. Spinal biomechanics when sagittal curvature is outside the optimal range remains a debate and may provide insight into the load distribution throughout the spinal column.

METHOD

A thoracolumbar spine model (Healthy) was developed. Thoracic and lumbar curvatures were adjusted by 50% to create models with varying sagittal profiles: hypolordotic (HypoL), hyperlordotic (HyperL), hypokyphotic (HypoK), and hyperkyphotic (HyperK). In addition, lumbar spine models were constructed for the former three profiles. The models were subjected to loading conditions simulating flexion and extension. Following validation, intervertebral disc stresses, vertebral body stresses, disc heights, and intersegmental rotations were compared across all models.

RESULTS

Overall trends demonstrated that HyperL and HyperK models had a noticeable reduction in disc height and greater vertebral body stresses compared to the Healthy model. In comparison, the HypoL and HypoK models displayed opposite trends. Considering the lumbar models, the HypoL model had reduced disc stresses and flexibility, while the contrary was observed in the HyperL model. Results indicate that the models with excessive curvature may be subjected to greater stress magnitudes, while the straighter spine models may reduce these stresses.

CONCLUSIONS

Finite element modeling of spine biomechanics demonstrated that variations in sagittal profiles influence the load distribution and range of motion of the spine. Considering patient-specific sagittal profiles in finite element modeling may provide valuable insight for biomechanical analyses and targeted treatments.

Impact of the Amyotrophic Lateral Sclerosis Disease on the Biomechanical Properties and Oxidative Stress Metabolism of the Lung Tissue Correlated With the Human Mutant SOD1G93A Protein Accumulation

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease, and ALS incidence is increasing worldwide. Patients with ALS have respiratory failure at the disease’s end stages, leading to death; thus, the lung is one of the most affected organs during disease progression. Tissue stiffness increases in various lung diseases because of impaired extracellular matrix (ECM) homeostasis leading to tissue damage and dysfunction at the end. According to the literature, oxidative stress is the major contributor to ECM dysregulation, and mutant protein accumulation in ALS have been reported as causative to tissue damage and oxidative stress. In this study, we used SOD1^G93A and SOD1^WT rats and measured lung stiffness of rats by using a custom-built stretcher, where H&E staining is used to evaluate histopathological changes in the lung tissue. Oxidative stress status of lung tissues was assessed by measuring glucose 6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6-PGD), glutathione reductase (GR), glutathione s-transferase (GST), catalase (CAT), and superoxide dismutase 1 (SOD1) levels. Western blot experiments were performed to evaluate the accumulation of the SOD1^G93A mutated protein. As a result, increased lung stiffness, decreased antioxidant status, elevated levels of oxidative stress, impaired mineral and trace element homeostasis, and mutated SOD1^G93A protein accumulation have been found in the mutated rats even at the earlier stages, which can be possible causative of increased lung stiffness and tissue damage in ALS. Since lung damage has altered at the very early stages, possible therapeutic approaches can be used to treat ALS or improve the life quality of patients with ALS.

3D Bioprinted Implants for Cartilage Repair in Intervertebral Discs and Knee Menisci

Cartilage defects pose a significant clinical challenge as they can lead to joint pain, swelling and stiffness, which reduces mobility and function thereby significantly affecting the quality of life of patients. More than 250,000 cartilage repair surgeries are performed in the United States every year. The current gold standard is the treatment of focal cartilage defects and bone damage with nonflexible metal or plastic prosthetics. However, these prosthetics are often made from hard and stiff materials that limits mobility and flexibility, and results in leaching of metal particles into the body, degeneration of adjacent soft bone tissues and possible failure of the implant with time. As a result, the patients may require revision surgeries to replace the worn implants or adjacent vertebrae. More recently, autograft - and allograft-based repair strategies have been studied, however these too are limited by donor site morbidity and the limited availability of tissues for surgery. There has been increasing interest in the past two decades in the area of cartilage tissue engineering where methods like 3D bioprinting may be implemented to generate functional constructs using a combination of cells, growth factors (GF) and biocompatible materials. 3D bioprinting allows for the modulation of mechanical properties of the developed constructs to maintain the required flexibility following implantation while also providing the stiffness needed to support body weight. In this review, we will provide a comprehensive overview of current advances in 3D bioprinting for cartilage tissue engineering for knee menisci and intervertebral disc repair. We will also discuss promising medical-grade materials and techniques that can be used for printing, and the future outlook of this emerging field.

Compounded topographical and physicochemical cueing by micro-engineered chitosan substrates on rat dorsal root ganglion neurons and human mesenchymal stem cells

Given the intertwined physicochemical effects exerted in vivo by both natural and synthetic (e.g., biomaterial) interfaces on adhering cells, the evaluation of structure-function relationships governing cellular response to micro-engineered surfaces for applications in neuronal tissue engineering requires the use of in vitro testing platforms which consist of a clinically translatable material with tunable physiochemical properties. In this work, we micro-engineered chitosan substrates with arrays of parallel channels with variable width (20 and 60 μm). A citric acid (CA)-based crosslinking approach was used to provide an additional level of synergistic cueing on adhering cells by regulating the chitosan substrate's stiffness. Morphological and physicochemical characterization was conducted to unveil the structure-function relationships which govern the activity of rat dorsal root ganglion neurons (DRGs) and human mesenchymal stem cells (hMSCs), ultimately singling out the key role of microtopography, roughness and substrate's stiffness. While substrate's stiffness predominantly affected hMSC spreading, the modulation of the channels' design affected the neuronal architecture's complexity and guided the morphological transition of hMSCs. Finally, the combined analysis of tubulin expression and cell morphology allowed us to cast new light on the predominant role of the microtopography over substrate's stiffness in the process of hMSCs neurogenic differentiation.

Spine biomechanical testing methodologies: The controversy of consensus vs scientific evidence

Biomechanical testing methodologies for the spine have developed over the past 50 years. During that time, there have been several paradigm shifts with respect to techniques. These techniques evolved by incorporating state-of-the-art engineering principles, in vivo measurements, anatomical structure-function relationships, and the scientific method. Multiple parametric studies have focused on the effects that the experimental technique has on outcomes. As a result, testing methodologies have evolved, but there are no standard testing protocols, which makes the comparison of findings between experiments difficult and conclusions about in vivo performance challenging. In 2019, the international spine research community was surveyed to determine the consensus on spine biomechanical testing and if the consensus opinion was consistent with the scientific evidence. More than 80 responses to the survey were received. The findings of this survey confirmed that while some methods have been commonly adopted, not all are consistent with the scientific evidence. This review summarizes the scientific literature, the current consensus, and the authors' recommendations on best practices based on the compendium of available evidence.

Febio finite element models of the human cervical spine

Finite element (FE) analysis has proven to be useful when studying the biomechanics of the cervical spine. Although many FE studies of the cervical spine have been published, they typically develop their models using commercial software, making the sharing of models between researchers difficult. They also often model only one part of the cervical spine. The goal of this study was to develop and evaluate three FE models of the adult cervical spine using open-source software and to freely provide these models to the scientific community. The models were created from computed tomography scans of 26-, 59-, and 64-year old female subjects. These models were evaluated against previously published experimental and FE data. Despite the fact that all three models were assigned identical material properties and boundary conditions, there was notable variation in their biomechanical behavior. It was therefore apparent that these differences were the result of morphological differences between the models.

Development of a finite element biomechanical whole spine model for analyzing lumbar spine loads under caudocephalad acceleration

Background:Spine injury risk due to military conflict is an ongoing concern among defense organizations throughout the world. A better understanding of spine biomechanics could assist in developing protection devices to reduce injuries caused by caudocephalad acceleration (+Gz) in under-body blasts (UBB). Although some finite element (FE) human models have demonstrated reasonable lumbar spine biofidelity, they were either partial spine models or not validated for UBB-type loading modes at the lumbar functional spinal unit (FSU) level, thus limiting their ability to analyze UBB-associated occupant kinematics.Methods:An FE functional representation of the human spine with simplified geometry was developed to study the lumbar spine responses under +Gz loading. Fifty-seven load curves obtained from post mortem human subject experiments were used to optimize the model.Results:The model was cumulatively validated for compression, flexion, extension, and anterior-, posterior-, and lateral-shears of the lumbar spine and flexion and extension of the cervical spine. The thoracic spine was optimized for flexion and compression. The cumulative CORrelation and Analysis (CORA) rating for the lumbar spine was 0.766 and the cervical spine was 0.818; both surpassed the 0.7 objective goal. The model's element size was confirmed as converged.Conclusions:An FE functional representation of the human spine was developed for +Gz lumbar load analysis. The lumbar and cervical spines were demonstrated to be quantitatively biofidelic to the FSU level for multi-directional loading and bending typically experienced in +Gz loading, filling the capability gap in current models.

Silk fibroins in multiscale dimensions for diverse applications

Silk biomaterials in different forms such as particles, coatings and their assemblies, represent unique type of materials in multiple scales and dimensions. Herein, we provide an overview of multi-scale silk fibroin materials including silk particles, silk coatings and silk assemblies, each of which represents a unique type of material with wide range of applications. They feature tunable structures and mechanical properties with excellent biocompatibility, which are essentially required for various biomedical and drug delivery applications. The review focuses on bringing a new perspective on the utilization of regenerated silk fibroins in modern biomedicine by beginning with the fabrication of silk in multiscale dimensions and their state-of-the-art applications in various biomedical and bioelectronic fields. It covers the fundamentals of processing silk fibroins in multi-dimensions (sizes and shapes) with a specific emphasis on its structural tunability at various length scales (nano-micro) by using the latest fabrication methods/mechanisms and advanced fabrication technologies, followed by their recent applications in diverse fields of biomedicine.

Tantalum: the next biomaterial in spine surgery?

Tantalum is a porous metal, whose elastic modulus, high frictional properties and biocompatibility make it an ideal construct to facilitate adequate bony fusion in spine surgery. Since 2015, the published literature on clinical outcomes of tantalum in spine surgery has more than doubled. A review of the literature was performed on the PubMed (MEDLINE) database on January 27, 2019, for papers pertinent to the use of tantalum metal in spine surgery. Thirteen studies were included in this review. For cervical spine, we found increased fusion rates in autograft alone compared to tantalum standalone (92.8% vs. 89.0%, P=0.001) and tantalum cages plus autograft (92.8% vs. 64.8%, P<0.0001). Complication rates in cervical fusion were lower in patients treated with tantalum standalone versus those treated with autograft (7.4% vs. 13.7%, P<0.0001), and autograft and anterior plate (7.4% vs. 33%, P=0.001). Autograft patients had higher rates of revision surgery compared to tantalum standalone (12.8% vs. 2.8%, P<0.0001) and tantalum ring with autograft (12.8% vs. 7.7%, P<0.001). For lumbar spine, we found autograft had lower fusion rate compared to tantalum standalone (80.0% vs. 93.4%, P<0.0001). Use of tantalum metal in spine fusion surgery shows promising results in fusion, complication and revision rates, and clinical outcomes compared to autograft. Although, fusion rates in short-term studies evaluating tantalum in the cervical spine are conflicting, long-term series beyond 2 years show excellent results. This early finding may be related difficulties in radiographic evaluation of fusion in the setting of tantalum cage use. Further studies are needed to further delineate the timing of fusion with the implementation of tantalum in the cervical and lumbar spine.

F.E.M. Stress-Investigation of Scolios Apex

BACKGROUND

In scoliosis, kypholordos and wedge properties of the vertebrae should be involved in determining how stress is distributed in the vertebral column. The impact is logically expected to be maximal at the apex.

AIM

To introduce an algorithm for constructing artificial geometric models of the vertebral column from DICOM stacks, with the ultimate aim to obtain a formalized way to create simplistic models, which enhance and focus on wedge properties and relative tilting.

MATERIAL/METHODS

Our procedure requires parameter extraction from DICOM image-stacks (with PACS,IDS-7), mechanical FEM-modelling (with Matlab and Comsol). As a test implementation, models were constructed for five patients with thoracal idiopathic scoliosis with varying apex rotation. For a selection of load states, we calculated a response variable which is based upon distortion energy.

RESULTS

For the test implementation, pairwise t-tests show that our response variable is non-trivial and that it is chiefly sensitive to the transversal stresses (transversal stresses where of main interest to us, as opposed to the case of additional shear stresses, due to the lack of explicit surrounding tissue and ligaments in our model). Also, a pairwise t-test did not show a difference (n = 25, p-value≈0.084) between the cases of isotropic and orthotropic material modeling.

CONCLUSION

A step-by-step description is given for a procedure of constructing artificial geometric models from chest CT DICOM-stacks, such that the models are appropriate for semi-global stress-analysis, where the focus is on the wedge properties and relative tilting. The method is inappropriate for analyses where the local roughness and irregularities of surfaces are wanted features. A test application hints that one particular load state possibly has a high correlation to a certain response variable (based upon distortion energy distribution on a surface of the apex), however, the number of patients is too small to draw any statistical conclusions.

Biomechanical tolerance of whole lumbar spines in straightened posture subjected to axial acceleration

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12-L5) were dynamically loaded using a custom-built drop tower. Twenty-three specimens were tested at sub-failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p < 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty-percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9-5.2 kN), and 16 (13-19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2-L5 spinal levels. In general, force-based tolerance was consistent with previous shorter-segment lumbar spine testing (3-5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:1747-1756, 2018.

Elastic modulus in the selection of interbody implants

BACKGROUND

The modulus of elasticity of an assortment of materials used in spinal surgery, as well as cortical and cancellous bones, is determined by direct measurements and plotting of the appropriate curves. When utilized in spine surgery, the stiffness of a surgical implant can affect its material characteristics. The modulus of elasticity, or Young's modulus, measures the stiffness of a material by calculating the slope of the material's stress-strain curve. While many papers and presentations refer to the modulus of elasticity as a reason for the choice of a particular spinal implant, no peer-reviewed surgical journal article has previously been published where the Young's modulus values of interbody implants have been measured.

METHODS

Materials were tested under pure compression at the rate of 2 mm/min. A maximum of 45 kilonewtons (kN) compressive force was applied. Stress-strain characteristics under compressive force were plotted and this plot was used to calculate the elastic modulus.

RESULTS

The elastic modulus calculated for metals was more than 50 Gigapascals (GPa) and had significantly higher modulus values compared to poly-ether-ether-ketone (PEEK) materials and allograft bone.

CONCLUSIONS

The data generated in this paper may facilitate surgeons to make informed decisions on their choices of interbody implants with specific attention to the stiffness of the implant chosen.

Whiplash-Associated Disorders: Occupant Kinematics and Neck Morphology

Synopsis Despite considerable research effort, the incidence of whiplash injury during automotive collisions has continued to rise. This is due, at least in part, to a limited recognition of biomechanical injury mechanisms and factors influencing injury risk. While automotive safety modifications reduced injury risk in some cases, impact on the overall whiplash incidence was limited. This is likely attributable to significant occupant-related differences that have a profound impact on injury risk. Many of those differences were outlined in research studies, and examples include female sex and the associated sex-based anthropometrical variation that can affect seating orientation; cervical spinal posture; and anatomical attributes, including cervical column slenderness and neck muscle morphometry. This review highlights these anatomical attributes and explains, based on biomechanical concepts, the method by which these attributes may alter cervical spine response during automotive rear impacts to affect injury risk. The biomechanical explanations are based on existing studies that have incorporated postmortem human subjects, computational models, and anthropomorphic test devices (ie, crash test dummies), as well as medical imaging in human volunteers. These biomechanical explanations may provide improved understanding of injury risk. J Orthop Sports Phys Ther 2016;46(10):834-844. doi:10.2519/jospt.2016.6846.

The role of obesity in the biomechanics and radiological changes of the spine: an in vitro study

OBJECT

The effects of obesity on lumbar biomechanics are not fully understood. The aims of this study were to analyze the biomechanical differences between cadaveric L4–5 lumbar spine segments from a large group of nonobese (body mass index [BMI] < 30 kg/m2) and obese (BMI ≥ 30 kg/m2) donors and to determine if there were any radiological differences between spines from nonobese and obese donors using MR imaging.

METHODS

A total of 168 intact L4–5 spinal segments (87 males and 81 females) were tested using pure-moment loading, simulating flexion-extension, lateral bending, and axial rotation. Axial compression tests were performed on 38 of the specimens. Sex, age, and BMI were analyzed with biomechanical parameters using 1-way ANOVA, Pearson correlation, and multiple regression analyses. MR images were obtained in 12 specimens (8 from obese and 4 from nonobese donors) using a 3-T MR scanner.

RESULTS

The segments from the obese male group allowed significantly greater range of motion (ROM) than those from the nonobese male group during axial rotation (p = 0.018), while there was no difference between segments from obese and nonobese females (p = 0.687). There were no differences in ROM between spines from obese and nonobese donors during flexion-extension or lateral bending for either sex. In the nonobese population, the ROM during axial rotation was significantly greater for females than for males (p = 0.009). There was no significant difference between sexes in the obese population (p = 0.892). Axial compressive stiffness was significantly greater for the obese than the nonobese population for both the female-only group and the entire study group (p < 0.01); however, the difference was nonsignificant in the male population (p = 0.304). Correlation analysis confirmed a significant negative correlation between BMI and resistance to deformation during axial compression in the female group (R = −0.65, p = 0.004), with no relationship in the male group (R = 0.03, p = 0.9). There was also a significant negative correlation between ROM during flexion-extension and BMI for the female group (R = −0.38, p = 0.001), with no relationship for the male group (R = 0.06, p = 0.58). Qualitative analysis using MR imaging indicated greater facet degeneration and a greater incidence of disc herniations in the obese group than in the control group.

CONCLUSIONS

Based on flexibility and compression tests, lumbar spinal segments from obese versus nonobese donors seem to behave differently, biomechanically, during axial rotation and compression. The differences are more pronounced in women. MR imaging suggests that these differences may be due to greater facet degeneration and an increased amount of disc herniation in the spines from obese individuals.

Fundamental biomechanics of the spine--What we have learned in the past 25 years and future directions

Since the publication of the 2nd edition of White and Panjabi׳s textbook, Clinical Biomechanics of the Spine in 1990, there has been considerable research on the biomechanics of the spine. The focus of this manuscript will be to review what we have learned in regards to the fundamentals of spine biomechanics. Topics addressed include the whole spine, the functional spinal unit, and the individual components of the spine (e.g. vertebra, intervertebral disc, spinal ligaments). In these broad categories, our understanding in 1990 is reviewed and the important knowledge or understanding gained through the subsequent 25 years of research is highlighted. Areas where our knowledge is lacking helps to identify promising topics for future research. In this manuscript, as in the White and Panjabi textbook, the emphasis is on experimental research using human material, either in vivo or in vitro. The insights gained from mathematical models and animal experimentation are included where other data are not available. This review is intended to celebrate the substantial gains that have been made in the field over these past 25 years and also to identify future research directions.

Impaired extracellular matrix structure resulting from malnutrition in ovariectomized mature rats

Bone loss is a symptom related to disease and age, which reflects on bone cells and ECM. Discrepant regulation affects cell proliferation and ECM localization. Rat model of osteoporosis (OVX) was investigated against control rats (Sham) at young and old ages. Biophysical, histological and molecular techniques were implemented to examine the underlying cellular and extracellular matrix changes and to assess the mechanisms contributing to bone loss in the context of aging and the widely used osteoporotic models in rats. Bone loss exhibited a compromised function of bone cells and infiltration of adipocytes into bone marrow. However, the expression of genes regulating collagen catabolic process and adipogenesis was chronologically shifted in diseased bone in comparison with aged bone. The data showed the involvement of Wnt signaling inhibition in adipogenesis and bone loss due to over-expression of SOST in both diseased and aged bone. Further, in the OVX animals, an integrin-mediated ERK activation indicated the role of MAPK in osteoblastogenesis and adipogenesis. The increased PTH levels due to calcium and estrogen deficiency activated osteoblastogenesis. Thusly, RANKL-mediated osteoclastogenesis was initiated. Interestingly, the data show the role of MEPE regulating osteoclast-mediated resorption at late stages in osteoporotic bone. The interplay between ECM and bone cells change tissue microstructure and properties. The involvement of Wnt and MAPK pathways in activating cell proliferation has intriguing similarities to oncogenesis and myeloma. The study indicates the importance of targeting both pathways simultaneously to remedy metabolic bone diseases and age-related bone loss.

CT morphometry of adult thoracic intervertebral discs

PURPOSE

Despite being commonly affected by degenerative disorders, there are few data on normal thoracic intervertebral disc dimensions. A morphometric analysis of adult thoracic intervertebral discs was, therefore, undertaken.

METHODS

Archival computed tomography scans of 128 recently deceased individuals (70 males, 58 females, 20-79 years) with no known spinal pathology were analysed to determine thoracic disc morphometry and variations with disc level, sex and age. Reliability was assessed by intraclass correlation coefficients (ICCs).

RESULTS

Anterior and posterior intervertebral disc heights and axial dimensions were significantly greater in men (anterior disc height 4.0±1.4 vs 3.6±1.3 mm; posterior disc height 3.6±0.90 vs 3.4±0.93 mm; p<0.01). Disc heights and axial dimensions at T4-5 were similar or smaller than at T2-3, but thereafter increased caudally (mean anterior disc height T4-5 and T10-11, 2.7±0.7 and 5.4±1.2 mm, respectively, in men; 2.6±0.8 and 5.1±1.3 mm, respectively, in women; p<0.05). Except at T2-3, anterior disc height decreased with advancing age and anteroposterior and transverse disc dimensions increased; posterior and middle disc heights and indices of disc shape showed no consistent statistically significant changes. Most parameters showed substantial to almost perfect agreement for intra- and inter-rater reliability.

CONCLUSIONS

Thoracic disc morphometry varies significantly and consistently with disc level, sex and age. This study provides unique reference data on adult thoracic intervertebral disc morphometry, which may be useful when interpreting pathological changes and for future biomechanical and functional studies.

High Rotation Rate Behavior of Cervical Spine Segments in Flexion and Extension

Numerical finite element (FE) models of the neck have been developed to simulate occupant response and predict injury during motor vehicle collisions. However, there is a paucity of data on the response of young cervical spine segments under dynamic loading in flexion and extension, which is essential for the development or validation of tissue-level FE models. This limitation was identified during the development and validation of the FE model used in this study. The purpose of this study was to measure the high rotation rate loading response of human cervical spine segments in flexion and extension, and to investigate a new tissue-level FE model of the cervical spine with the experimental data to address a limitation in available data. Four test samples at each segment level from C2–C3 to C7–T1 were dissected from eight donors and were tested to 10 deg of rotation at 1 and 500 deg/s in flexion and extension using a custom built test apparatus. There was strong evidence (p < 0.05) of increased stiffness at the higher rotation rate above 4 deg of rotation in flexion and at 8 deg and 10 deg of rotation in extension. Cross-correlation software, Cora, was used to evaluate the fit between the experimental data and model predictions. The average rating was 0.771, which is considered to demonstrate a good correlation to the experimental data.

Change of mechanical vertebrae properties due to progressive osteoporosis: combined biomechanical and finite-element analysis within a rat model

For assessing mechanical properties of osteoporotic bone, biomechanical testing combined with in silico modeling plays a key role. The present study focuses on microscopic mechanical bone properties in a rat model of postmenopausal osteoporosis. Female Sprague-Dawley rats were (1) euthanized without prior interventions, (2) sham-operated, and (3) subjected to ovariectomy combined with a multi-deficiencies diet. Rat vertebrae (corpora vertebrae) were imaged by micro-CT, their stiffness was determined by compression tests, and load-induced stress states as well as property changes due to the treatment were analyzed by finite-element modeling. By comparing vertebra stiffness measurements with finite-element calculations of stiffness, an overall microscopic Young's modulus of the bone was determined. Macroscopic vertebra stiffness as well as the microscopic modulus diminish with progression of osteoporosis by about 70 %. After strong initial changes of bone morphology, further decrease in macroscopic stiffness is largely due to decreasing microscopic Young's modulus. The micromechanical stress calculations reveal particularly loaded vertebra regions prone to failure. Osteoporosis-induced changes of the microscopic Young's modulus alter the fracture behavior of bone, may influence bone remodeling, and should be considered in the design of implant materials.

Biomechanics of human thoracolumbar spinal column trauma from vertical impact loading

Recent studies suggest that dorsal spine injuries occur in motor vehicle crashes to restrained occupants. Compression/compression-flexion injuries occur in frontal crashes due to seat pan and vertical loading. While injuries, mechanisms and tolerances for neck injuries have been determined, thoraco-lumbar spine data are very limited. The objective of the study was to determine the biomechanical characteristics associated with such spinal injuries due to vertical loading. Upper thoracic (T2-T6), lower thoracic (T7-T11) and lumbar (T12-L5) columns from post mortem human surrogates were procured, fixed at the ends and dropped from three heights: the first two impacts designed as non-failure tests and the final was the failure test. Intermittent evaluations consisted of palpations and x-rays. Injuries were assessed using posttest x-rays and computed tomography scans. The age, stature, total body mass and body mass index of three PMHS were: 50 years, 164 cm, 66.9 kg, and 24.7 kg/m(2). The mean peak forces from 24 tests for the upper and lower thoracic and lumbar spines for varying drop heights ranged from 1.6 to 4.3, 1.3 to 5.1, and 1.3 to 6.7 kN, respectively. All peak forces increased with increasing drop heights. Injuries to the three spines included unstable vertebral body and posterior element (bipedicular and lamina) compression fractures and posterior complex disruptions. Logistic regression analysis indicated that peak forces of 3.4 and 3.7 kN are associated with 50% probability of fracture. These results indicate the initial tolerance limits of dorsal spines under vertical loading.