Stress In Bone Tissue Research Articles

Intertrochanteric fracture: Association between the coronal position of the lag screw and stress distribution

The best position of the lag screw in the femoral head for the fixation of intertrochanteric fracture is controversial. Traditional view suggests that it should be positioned in the central axis of the femoral neck with a tip-apex distance (TAD) of <25mm, but the mechanical properties have not been reported yet. Herein, we aimed to investigate internal fixation with the lag screw placed in different positions on the femoral coronal plane by performing a finite element analysis and to identify a reasonable lag screw position after the internal stress distributions at the femoral head. A three-dimensional finite element model of a healthy male's femur was set up, on which the intertrochanteric fracture model with proximal femoral nail antirotation (PFN-A) was based. Nine modalities of the model were established in accordance with different lag screw positions in the femoral head. Three-dimensional finite element calculations were conducted, and the distribution trends of characteristic high-stress concentration points were observed. The area of high-stress concentration was distributed from the top of the femoral head to the medial cortex of the trochanteric region. Four characteristic high-stress concentration points were observed, and the following trends indicated that the lower the position of the lag screw, the greater its length. A longer and lower lag screw may make the fixation sustain greater stress, reduce bone tissue stress correspondingly in intertrochanteric fractures fixated with PFN-A, and sustain greater stress and more cyclic load at the same bone density.

Вiomechanical rationale for the choice of surgical tactic for treatment of distal femur fractures consolidation disturbances

Objective: to study stress-strain distribution in osteosynthesis model with non-union of distal femoral fracture and to define the most effective ways of injury fixation. Methods: finite ele­ment model of distal femur with different length are created, which is determined by distance (3 and 10 cm) from the top edge to the fracture line of lateral condyle. To fix the fracture used: blocked intramedullary rod, LCP-plate and 95° bladed plate. The area of contact between the fragments was 50 %. To load the appropriate models applied in the natural two-limb standing and flexion of knee joint with rotatory displacement. Results: it is revealed that for all model rotary load is critical in terms of stress in bone tissue, locking elements and structures in general and displacement of fragments of bones. In a case of fracture localization in the epiphyseal part of the femur, safer fixation of short distal fragment provides LCP-plate, so it should be used in such cases. Given the non-union location in the distal diaphy­ses of the femur bone stress are smallest and largest system sta­bility «bone – fixation device» to load strains provides model with blocked intramedullar nail. Therefore, for fixation of frac­ture consolidation problems in the distal femur blocked nail is recommend. Conclusions:the obtained results allow to jus­tify the method of surgical treatment of patients with impaired consolidation of the distal femur fracture, ie. to select fixation device depending on the injury level and the length of distal fragment.

Bone density and anisotropy affect periprosthetic cement and bone stresses after anatomical glenoid replacement: A micro finite element analysis

Glenoid loosening is still a main complication for shoulder arthroplasty. We hypothesize that cement and bone stresses potentially leading to fixation failure are related not only to glenohumeral conformity, fixation design or eccentric loading, but also to bone volume fraction, cortical thickness and degree of anisotropy in the glenoid. In this study, periprosthetic bone and cement stresses were computed with micro finite element models of the replaced glenoid depicting realistic bone microstructure. These models were used to quantify potential effects of bone microstructural parameters under loading conditions simulating different levels of glenohumeral conformity and eccentric loading simulating glenohumeral instability. Results show that peak cement stresses were achieved near the cement–bone interface in all loading schemes. Higher stresses within trabecular bone tissue and cement mantle were obtained within specimens of lower bone volume fraction and in regions of low anisotropy, increasing with decreasing glenohumeral conformity and reaching their maxima below the keeled design when the load is shifted superiorly. Our analyses confirm the combined influences of eccentric load shifts with reduced bone volume fraction and anisotropy on increasing periprosthetic stresses. They finally suggest that improving fixation of glenoid replacements must reduce internal cement and bone tissue stresses, in particular in glenoids of low bone density and heterogeneity.

Study of Bone Tissue Stress and Strain State Aimed at Development of Intelligent Biomaterials for Osteoimplantation

This article studies the stress and strain state of simulated microvolumes of compact bone tissue under uniaxial compression, having different orientation of collagen-mineral fibers, different porosity and mineral content. The purpose of the study is to work out recommendations on development of artificial mechanically compatible biomaterials for osteoimplants. It has been found out that it is necessary to take into account the effective mechanical parameters defining the distribution of the bone tissue stress and strain when making individual implants.

Quantification of fluid shear stress in bone tissue engineering scaffolds with spherical and cubical pore architectures.

Recent studies have shown that mechanical stimulation, in the form of fluid perfusion and mechanical compression, can enhance osteogenic differentiation of mesenchymal stem cells and bone cells within tissue engineering scaffolds in vitro. The precise nature of mechanical stimulation within tissue engineering scaffolds is not only dictated by the exogenously applied loading regime, but also depends on the geometric features of the scaffold, in particular architecture, pore size and porosity. However, the precise contribution of each geometric feature towards the resulting mechanical stimulation within a scaffold is difficult to characterise due to the wide range of interacting parameters. In this study, we have applied a fluid-structure interaction model to investigate the role of scaffold geometry (architecture, pore size and porosity) on pore wall shear stress (WSS) under a range of different loading scenarios: fluid perfusion, mechanical compression and a combination of perfusion and compression. It is found that scaffold geometry (spherical and cubical pores), in particular the pore size, has a significant influence on the stimulation within scaffolds. Furthermore, we observed an amplified WSS within scaffolds under a combination of fluid perfusion and mechanical compression, which exceeded that caused by individual fluid perfusion or mechanical compression approximately threefold. By conducting this comprehensive parametric variation study, an expression was generated to allow the design and optimisation of 3D TE scaffolds and inform experimental loading regimes so that a desired level of mechanical stimulation, in terms of WSS is generated within the scaffold.

ASSESSMENT OF STRAIN AND DEFORMATION OF THE «BONE – FIXATEUR» SYSTEM IN OSTEOSYNTHESIS OF THE LATERAL MALLEOLAR FRACTURES

Injuries of the ankle joint is one of the main causes of disability and poor outcomes which are caused by inadequate reposition, imperfect osteosynthesis and secondary displacement of fragments. Qualitative and reliable stabilization of the lateral malleolar bone fragments essentially depends on the design of the fixateur. Objective: based on the analysis of the stress-strain state of the system «bone – fixateur» to evaluate the effectiveness of the proposed fixateur for osteosynthesis of infrasyndesmotic lateral malleolar fractures. Methods: The finite element analysis with ANSYS software complex and model of the system «bone – fixateur» that limited by the fibula the shape of which was simplified for the construction being symmetric in the frontal plane. Models were built in the program AUTOCAD. Geometry of sections of bone meets the real size of the adult. The criterion for evaluation of the efficiency of plate-fixateur selected values of stresses in bone tissue and movement of the fragment points — opening of the fracture. An additional criterion was the value of stresses in the plate. Results revealed that the greatest amounts in bone tissue are normal stresses σ acting in the direction of the fibular axis. They occur in cortical bone at the edges of the holes for the screws. Stressed state of bone turned significantly heterogeneous. For heavy loads (half from critical for syndesmotic ligaments breakage) stresses in the plate are dangerous. However, they occur in the areas of concentration but the actual loads will be lower. The most significant deviations of the stress state of the bone occur at the edges of the holes for the screws, in the joints cortical and spongiosal bone tissue and in the areas of the load application. The largest loads were normal tension and compressive stresses in the plate due to its curve with maximum performance at the edge the hole for the third top screw from the internal part of the plate. The value of expansion of the fracture was not significant. Conclusions: The proposed fixateur has shown its high efficiency. It is important to consider the characteristics associated with the nature of the maximum stresses arising in areas of concentration, and not to produce constructs for osteosynthesis of brittle materials.

Effect of the parafunctional occlusal loading and crown height on stress distribution.

The aim of this study was to assess, by the three-dimensional finite element method, the influence of crown-to-implant ratio and parafunctional occlusal loading on stress distribution in single external hexagon implant-supported prosthesis. Computer-aided design software was used to confection three models. Each model was composed of a block bone and an external hexagon implant (5x10.0 mm) with screw-retained implant prostheses, varying the height crown: 10, 12.5 and 15 mm. Finite element analysis software was used to generate the finite element mesh and to establish the loading and boundary conditions. Normal (200 N axial and 100 N oblique load) and parafunctional forces (1,000 N axial and 500 N oblique load) were applied. The results were visualized by von Mises and maximum principal stress. In comparison with the normal occlusal force, the parafunctional occlusal force induced an increase in stress concentration and magnitude on implant (platform and first threads) and screw (neck). The cortical bone showed the highest tensile stress under parafunctional force (oblique load). The stress concentration increased as the crown height increased. It was concluded that: increasing the C/I increased stress concentration in both implant components and cortical bone; parafunctional loading increased between 4-5 times the value of stresses in bone tissue compared with functional loading; the type of loading variation factor is more influential than the crown-to-implant factor.

Effect of attachment types and number of implants supporting mandibular overdentures on stress distribution: A computed tomography-based 3D finite element analysis

The objective of this study was to calculate stresses in bone tissue surrounding uncoupled and splinted implants that are induced by a bite force applied to the mandible and to determine whether the number of mandibular overdenture supporting implants in mandibular bone influence the stress distribution. A human adult edentulous mandible retrieved from a formalin fixed cadaver was used to define the geometry of finite element (FE) model and the FE model was verified with experimental measurements. Following the FE model validation, three different biting situations were simulated for the 2-, 3- and 4-implant retentive anchor as well as bar attachment overdentures under vertical loading of 100N. As a result of the analyses, it was concluded that an increment in implant number and the splinted attachment type tended to cause lower stresses and the use of two single attachments seems to be a safe and sufficient solution for the treatment of mandibular edentulism with overdentures.

The Effect of Selenium and Lycopene on Oxidative Stress in Bone Tissue in Rats Exposed to Cadmium

This study examined the effect of selenium (Se) or lycopene (Lyc) and their combination on oxida- tive stress in bone following cadmium (Cd) exposure in vivo. Cd exposure enhanced accumulation of Cd in femur with subsequent increase in LPO and PC and decreased antioxidative enzyme activ- ities in rat femur, along with significant decreases in body and femur bone weights. Subcutaneous (s.c.) injection of Se or Lyc reduced Cd accumulation in bone and increased body and femur weights, when given individually or concomitantly. Antioxidant enzyme activities maintained and/or in- creased following Se and Lyc supplementation when given individually or concomitantly. However, lycopene dose of 10 mg/kg of body weight alone or selenium alone provided better protection to bone tissues of rats against oxidative stress compared to treatment with their combination. Sele- nium and lycopene could be used as a dietary supplement to protect against bone oxidative stress in areas exposed to Cd pollution.

Investigation of mechanical behavior of CPC/bone specimens by finite element analysis

Calcium phosphate cement (CPC), as an important injectable biomaterial, is extensively used for bone repair in clinical application. If mechanical properties of CPC match well with that of bone tissue, it can create an appropriate mechanical environment for bone repair. In our study, the objective was to investigate the responses of bone tissue to CPC in different series of elastic modulus combinations. Finite element analysis (FEA) was applied to calculate the stress/strain on CPC-bone specimens and to further forecast the potential risky area. The predicted results indicated that CPC materials and bone tissue had different stress distribution patterns under the same loading condition. For CPC material, the Von Mises Stress peak occurred in the bone–cement joint area; while for bone tissue, the risky area was located at the bridge area among trabecular bones. The porous and loose structure of cancellous bone induced a greater Von Mises Stress in bone tissue. Quantitative analysis indicated that stress/strain distribution was directly correlated with the elastic modulus of material. When Young's modulus of bone and CPC was 1GPa and 6.10GPa respectively, the optimal stress matching between bone and CPC was achieved. In sum, this work confirmed that FE modeling was the ideal method for predicting fracture behavior of bone–CPC specimen both qualitatively and quantitatively.

Cytoplasmic reactive oxygen species and SOD1 regulate bone mass during mechanical unloading

Oxidative stress contributes to the pathogenesis of age-related diseases as well as bone fragility. Our previous study demonstrated that copper/zinc superoxide dismutase (Sod1)-deficient mice exhibit the induction of intracellular reactive oxygen species (ROS) and bone fragility resulting from low-turnover bone loss and impaired collagen cross-linking (Nojiri et al. J Bone Miner Res. 2011;26:2682-94). Mechanical stress also plays an important role in the maintenance of homeostasis in bone tissue. However, the molecular links between oxidative and mechanical stresses in bone tissue have not been fully elucidated. We herein report that mechanical unloading significantly increased intracellular ROS production and the specific upregulation of Sod1 in bone tissue in a tail-suspension experiment. We also reveal that Sod1 loss exacerbated bone loss via reduced osteoblastic abilities during mechanical unloading. Interestingly, we found that the administration of an antioxidant, vitamin C, significantly attenuated bone loss during unloading. These results indicate that mechanical unloading, in part, regulates bone mass via intracellular ROS generation and the Sod1 expression, suggesting that activating Sod1 may be a preventive strategy for ameliorating mechanical unloading-induced bone loss.

Individual-specific multi-scale finite element simulation of cortical bone of human proximal femur

We present an innovative method to perform multi-scale finite element analyses of the cortical component of the femur using the individual’s (1) computed tomography scan; and (2) a bone specimen obtained in conjunction with orthopedic surgery. The method enables study of micro-structural characteristics regulating strains and stresses under physiological loading conditions. The analysis of the micro-structural scenarios that cause variation of strain and stress is the first step in understanding the elevated strains and stresses in bone tissue, which are indicative of higher likelihood of micro-crack formation in bone, implicated in consequent remodeling or macroscopic bone fracture. Evidence that micro-structure varies with clinical history and contributes in significant, but poorly understood, ways to bone function, motivates the method’s development, as does need for software tools to investigate relationships between macroscopic loading and micro-structure. Three applications – varying region of interest, bone mineral density, and orientation of collagen type I, illustrate the method. We show, in comparison between physiological loading and simple compression of a patient’s femur, that strains computed at the multi-scale model’s micro-level: (i) differ; and (ii) depend on local collagen-apatite orientation and degree of calcification. Our findings confirm the strain concentration role of osteocyte lacunae, important for mechano-transduction. We hypothesize occurrence of micro-crack formation, leading either to remodeling or macroscopic fracture, when the computed strains exceed the elastic range observed in micro-structural testing.

A dynamic finite element analysis of stress distribution in bone tissue surrounding solely or splinted implant-borne fixed partial denture

To study the distribution patterns of stresses induced in bone tissue surrounding solely and splinted implants under dynamic loads. Three dimensional finite-element models were created of two 765 sections of the mandible with solely or splinted implants embedded in. Vertical and oblique dynamic loads were applied in a circle of mastication (0.875 s). The stress distribution was analyzed to study the biomechanical behavior of bone tissue surrounding solely or splinted implants. As loading on the solely implant 5, the maximum von Mises value in the surrounding bone tissue under oblique loads at 0.300 s was 4.2 times as much as that under vertical loads at 0.150 s. Meanwhile, as coincidently loading on the splinted implants, the maximum von Mises value at 0.300 s was 1.2 times as much as that at 0.150 s. As loading on the solely implant 5, the maximum stress value was 48.393 MPa at 0.300 s. As separately loading on the splinted implant 5, the maximum stress value of the whole model was 9.541 MPa in the same loading course, and the maximum stress was located at the distal cervical of the indirectly loaded implant 7. When loading on the pontic, the stress in bone tissue surrounding implant 7 was more than that of implant 5. Stress in the bone-interface of the splinted implants is evenly distributed at the cervical level, which may also reduce disadvantages from oblique loads.

Ultimate Masticatory Force as a Criterion in Implant Selection

Osseointegrated implants often fail because of excessive masticatory forces that cause extremely large stresses in bone tissue. We hypothesized that a proper dental implant could be selected by comparing the ultimate masticatory forces of a wide range of commercially available implants. We determined ultimate oblique masticatory forces for different cylindrical implants, taking into consideration the biomechanical correlation between implant dimensions and stresses in supporting bone. For this purpose, we used the finite element (FE) method and studied von Mises stresses in implant-bone interface areas to evaluate the influence of implant dimensions on stress concentration and on the value of an implant’s ultimate masticatory load. Geometric models of a mandibular segment were generated from computed tomography (CT) images and were analyzed with osseointegrated cylindrical implants. Masticatory forces were applied in their natural direction. All materials were assumed to be linearly elastic and isotropic. Critical point in the peri-implant area of bone was determined. The ultimate value of the masticatory load, which generates ultimate stresses at the critical point, was calculated for each implant. These findings provide correct selection of implant dimensions in clinical cases, because corresponding ultimate values of masticatory force were used as a criterion for assessment of their load-carrying capacity and applicability.

Residual stress distribution in rabbit limb bones

The presence of the residual stresses in bone tissue has been noted and the authors have reported that there are residual stresses in bone tissue. The aim of our study is to measure the residual stress distribution in the cortical bone of the extremities of vertebrates and to describe the relationships with the osteon population density. The study used the rabbit limb bones (femur, tibia/fibula, humerus, and radius/ulna) and measured the residual stresses in the bone axial direction at anterior and posterior positions on the cortical surface. The osteons at the sections at the measurement positions were observed by microscopy. As a result, the average stresses at the hindlimb bones and the forelimb bones were 210 and 149 MPa, respectively. In the femur, humerus, and radius/ulna, the residual stresses at the anterior position were larger than those at the posterior position, while in the tibia, the stress at the posterior position was larger than that at the anterior position. Further, in the femur and humerus, the osteon population densities in the anterior positions were larger than those in the posterior positions. In the tibia, the osteon population density in the posterior position was larger than that in the anterior position. Therefore, tensile residual stresses were observed at every measurement position in the rabbit limb bones and the value of residual stress correlated with the osteon population density ( r=0.55, P<0.01).

Residual Stress Distribution in the Bovine Femoral Diaphysis Measured by Synchrotron

The presence of residual stresses in bone tissue has been noted, and the authors have reported that there are residual stresses in bone tissue. The tensile residual stresses in the bone axial direction on the cortical surface of the bovine femoral diaphyses were measured by X-ray diffraction method with characteristic Mo-Kα X-rays. However, then the residual stresses inside the cortical bone could not be accurately determined. The study here used synchrotron white X-rays obtained from the BL28B2 beam line at SPring-8 and was able to measure the residual stresses in the bovine femoral diaphysis in depth. The measurement positions in the diaphysis specimen were at 1 mm intervals from the outer surface to the inner surface of the specimen in four parts of the diaphysis: anterior, posterior, lateral, and medial. The results showed that the residual stresses in the bone axial direction at the outer cortical surface were tensile and the stresses in the inner positions of the cortical bone were compressive. In the anterior part, the residual stress at the surface was 24.7 MPa. From 2 mm to 10 mm depths inside the diaphysis, compressive residual stresses were measured and the average of these stresses was -9.0 MPa.

Biomechanical grounds for fixing an endoprosthesis of the temporomandibular joint to the mandible

The article deals with biomechanical grounds for using a new Ukrainian total endoprosthesis of the temporomandibular joint in bilateral ankylosis of the temporomandibular joints. With help of the finite-element method, a stress-deformed state of the bone tissue was studied in the region, where the mandibular part of the endoprosthesis was fixed. It was proved that though the above stress significantly increased, its value did not exceed any permissible bone tissue stresses.

Residual Stress Around the Cortical Surface in Bovine Femoral Diaphysis

Residual stress in living tissue plays an important role in mechanical strength. We have reported that residual stress exists in the bone tissue of a rabbit's tibiofibula. The purpose of this study is to measure the residual stress around the outer cortical region of bovine femoral diaphysis and to discuss the distribution of the stress. This work proposed the sin(2) psi method of X-ray diffraction to the measurement of residual stresses in bone tissue. In this method, residual stress can be estimated from the variation in the interplanar spacings orientated to a number of directions without the lattice strain in the stress direction. Four-point bending tests of strip specimens taken from bovine femoral diaphysis were carried out during X-ray irradiation in advance. In the proximal, middle, and distal sections of bovine femoral diaphyses, the residual stresses at the cortical surface were measured using characteristic Mo-Kalpha X-rays. The bending tests of strip specimens with X-ray irradiation showed that the method could reliably estimate residual stresses in the bone tissue. The residual stress of the bone axial direction was larger than that of the circumferential direction. The stresses in the middle part of five diaphyses along the bone axial direction were tensile. The maximum stress was 162 MPa at the lateral position and the minimum was 78 MPa at the posterior position. The residual stress in the bone axial direction varies around the circumferential region. In addition, the bone axial distributions of residual stresses were different in the proximal, middle, and distal sections of the individual femur. Furthermore, it was confirmed that residual stress in the bone tissue was released by the cutting out of the specimen. The residual stresses in bone tissue could be measured by this method. The results show that residual stress in the bone axial direction at the cortical surface in bovine femoral diaphysis is tensile and varies around the circumferential region.

Single-trabecula building block for large-scale finite element models of cancellous bone.

Recent development of high-resolution imaging of cancellous bone allows finite element (FE) analysis of bone tissue stresses and strains in individual trabeculae. However, specimen-specific stress/strain analyses can include effects of anatomical variations and local damage that can bias the interpretation of the results from individual specimens with respect to large populations. This study developed a standard (generic) 'building-block' of a trabecula for large-scale FE models. Being parametric and based on statistics of dimensions of ovine trabeculae, this building block can be scaled for trabecular thickness and length and be used in commercial or custom-made FE codes to construct generic, large-scale FE models of bone, using less computer power than that currently required to reproduce the accurate micro-architecture of trabecular bone. Orthogonal lattices constructed with this building block, after it was scaled to trabeculae of the human proximal femur, provided apparent elastic moduli of approximately 150 MPa, in good agreement with experimental data for the stiffness of cancellous bone from this site. Likewise, lattices with thinner, osteoporotic-like trabeculae could predict a reduction of approximately 30% in the apparent elastic modulus, as reported in experimental studies of osteoporotic femora. Based on these comparisons, it is concluded that the single-trabecula element developed in the present study is well-suited for representing cancellous bone in large-scale generic FE simulations.

Damage-based finite-element vertebroplasty simulations.

The objectives of this study were to quantify the efficacy of vertebroplasty according to: (1) damage and (2) cement quantity (fill) and modulus. Vertebral body damage was numerically simulated using a previously validated two-dimensional finite-element model coupled with an elasto-plastic modulus reduction (EPMR) scheme. The effects of cement fill (% marrow replaced by cement, % MRC) and cement modulus on vertebral apparent modulus and trabecular bone tissue stress concentrations were parametrically assessed for four EPMR damage models (19%, 33%, 60%, and 91% modulus reduction). For this analysis, the elastic modulus of the trabecular bone tissue and marrow elements were assumed to be 10 GPa and 10 kPa, respectively. The effect of cement modulus (varied in the range 1 GPa to 9 GPa) on vertebral apparent modulus was also examined for partial fill (39% MRC) and complete fill (100% MRC) using the 33% modulus reduction damage model. In the case of polymethylmethacrylate (PMMA cement modulus = 2.16 GPa), restoration of the thoracic vertebral body (T10) apparent modulus to undamaged levels required 71% and 100% cement fill for the 19-33% and 60-91% modulus reduction damage models, respectively. Variations in cement modulus had no appreciable effect on the recovery of vertebral apparent modulus to undamaged levels for simulations of partial cement fill (39% MRC). For complete cement fill, however, a PMMA cement modulus produced approximately a 2-fold increase (82%) in vertebral apparent modulus relative to the undamaged vertebral body. Increasing the cement modulus to 9 GPa increased the vertebral apparent modulus over 2.5-fold (158%) relative to the undamaged state. The EPMR damage scheme and repair simulations performed in this study will help clinicians and cement manufacturers to improve vertebroplasty procedures.