Bone Strain Research Articles

Impact of periprosthetic femoral fracture fixation plating constructs on local stiffness, load transfer, and bone strains

Secondary femoral fractures after the successful plate-screw fixation of a primary Vancouver type B1 periprosthetic femoral fracture (PFF) have been associated with the altered state of stress/strain in the femur as the result of plating. The laterally implanted condyle-spanning plate-screw constructs have shown promises clinically in avoiding secondary bone and implant failures as compared with shorter diaphyseal plates. Though the condyle-spanning plating has been hypothesized to avoid stress concentration in the femoral diaphysis through increasing the working length of the plate, biomechanical evidence is lacking on how plate length may impact the stress/strain state of the implanted femur. Through developing and experimentally validating finite element (FE) models of 3 cadaveric femurs, this study investigated the impact of plating on bone strains, load transfer and local stiffness, which were compared between FE models of 2 different plating systems that each had a diaphyseal configuration and a condyle-spanning configuration. Under simulated gait-loading, the condyle-spanning constructs of both plating systems were shown to lower the bone strains around the distal fixation screws (up to 24.8% reduction in maximum principal strain and 26.6% reduction in minimum principal strain) and in the distal metaphyseal shaft of the femur (up to 15.9% and 25.7% reductions in maximum and minimum principal strains, respectively), where secondary bone fractures have been typically reported. In the distal diaphyseal and metaphyseal shaft of femur, FE models of the condyle-spanning constructs were shown to increase the local compressive stiffness (up to 152.9% increases under simulated gait-loading) and decrease the transfer of compressive load (37.1% decreases under simulated gait-loading), which may be indicative of the lowered risks of bone damage.

Bone Strain Index predicts fragility fracture in osteoporotic women: an artificial intelligence-based study

BackgroundWe applied an artificial intelligence-based model to predict fragility fractures in postmenopausal women, using different dual-energy x-ray absorptiometry (DXA) parameters.MethodsOne hundred seventy-four postmenopausal women without vertebral fractures (VFs) at baseline (mean age 66.3 ± 9.8) were retrospectively evaluated. Data has been collected from September 2010 to August 2018. All subjects performed a spine x-ray to assess VFs, together with lumbar and femoral DXA for bone mineral density (BMD) and the bone strain index (BSI) evaluation. Follow-up exams were performed after 3.34 ± 1.91 years. Considering the occurrence of new VFs at follow-up, two groups were created: fractured versus not-fractured. We applied an artificial neural network (ANN) analysis with a predictive tool (TWIST system) to select relevant input data from a list of 13 variables including BMD and BSI. A semantic connectivity map was built to analyse the connections among variables within the groups. For group comparisons, an independent-samples t-test was used; variables were expressed as mean ± standard deviation.ResultsFor each patient, we evaluated a total of n = 6 exams. At follow-up, n = 69 (39.6%) women developed a VF. ANNs reached a predictive accuracy of 79.56% within the training testing procedure, with a sensitivity of 80.93% and a specificity of 78.18%. The semantic connectivity map showed that a low BSI at the total femur is connected to the absence of VFs.ConclusionWe found a high performance of ANN analysis in predicting the occurrence of VFs. Femoral BSI appears as a useful DXA index to identify patients at lower risk for lumbar VFs.

Correlation between insertion torque and peri-implant bone strain during placement of orthodontic mini-implants: A finite element study

Insertion torque is the amount of torque exerted on the implant to tighten into the bone. We investigated whether insertion torque values could be correlated with the strain level in the peri-implant cortical bone resulting from mini-implant insertion. The insertion of a standard size mini-implant (φ1.4mm×7mm) into maxillary alveolar bone was simulated using the finite element method. A total of 3600 calculation steps were employed to numerically reproduce the mini-implant insertion process and analyze the insertion torque and strain distribution in bone. Special attention was given to the relationship between insertion torque values and strain level in the cortical bone at the final tightening. The strain level was quantified using the following 3 strain parameters: (1) average insertion strain, (2) peak insertion strain recorded near the mini-implant thread tips, and (3) the size of the damage zone in the cortical bone. Correlations between the insertion torque values and these 3 parameters were analyzed using linear regression. Direct proportionality and strong correlation were found between the insertion torque values and each of the 3 strain parameters: average insertion strain (r2=0.91), peak insertion strain (r2=0.91), and the size of damage zone (r2=0.90) in the peri-implant cortical bone. The results of this finite element method study demonstrated that insertion torque could serve as a reliable indicator of the strain level in the peri-implant cortical bone resulting from mini-implant insertion.

Assessment of the primary stability of revision tibial trays augmented with a cementless sleeve in AORI Type III defects

BackgroundPrevious studies have evaluated the initial stability of uncemented tibial components in revision total knee replacement (rTKR) in the presence of an Anderson Orthopaedic Research Institute (AORI) Type II tibial defect. This study sought to evaluate similar metrics in the severe Type III (AORI TIII) defects with combined uncemented stem and sleeve fixation, specifically, the effect of varying the stem’s length and tibial canal engagement upon stability and bone strain. MethodFinite element models generated from the CT scans of 4 tibias with Type III defects were used to investigate the primary stability, in terms of the bone–implant composite peak micromotion (CPM) and microstrains (CPS), achieved after virtual implantations with and without stems. ResultsA stemless rTKR had increased metaphyseal CPM and CPS compared to all stemmed implants. Significant area of the bone supporting the stemless rTKR had CPS greater than bone yield (7000 με). Short engaging stems (≤150 mm construct length), could not achieve reliable engagement in the diaphysis (canal fill ≤ 50%), leading to insufficient reduction of CPS (≥5000 με). Longer engaging stems (170–220 mm construct length), were able to reliably engage the diaphysis (fill ratio ≥ 75%) resulting in CPS ≤ 5000 με. Although, non-engaging stems resulted in increased CPM and CPS compared to engaging stems, long non-engaging stems (170–220 mm construct) appeared to provide additional stability to the rTKR compared to stemless rTKR. ConclusionThe results indicate a likely correlation between uncemented stem engagement and metaphyseal CPS in Type III defects. Excessive strain within the supporting metaphyseal bone is likely to lead to rTKR migration and loosening.

Structural analysis of bone by segmentation and finite element analysis in patients with osteoporosis

In bioengineering, mechanical properties related to the stress and stiffness of the materials can be determined by evaluating the bone density obtained from medical images. Diseases such as osteoporosis involve the decrease in bone mass and average bone density, inducing a high risk of fracture and the decrease in mechanical properties. This work proposes the use of numerical methods and medical imaging to evaluate biomarkers related to bone stress and strain affected by osteoporosis. The digital twin of bones is made from the segmentation of the bones associated with the femoral group diagnosed with osteoporosis. The material model for the bone tissue is defined as a functionally graded material with elastic properties obtained from computed tomography numbers. The results show that the proposed method allows monitoring of the disease and the evaluation of the risk of fracture, considering the functional mechanical load. In this sense, the use of radiomics takes advantage of the potential of personalized medicine to improve the lives of patients.

Proximal tibial bone loss in the first 2 years after unicondylar knee arthroplasty: Anatomical pattern, predictors and clinical correlation

BackgroundTibial stress fracture, anteromedial bone pain, and early subsidence could occur after unicondylar knee arthroplasty (UKA). The change in metaphyseal tibial bone density (MTBD) in the coronal and sagittal planes after UKA might be a contributing factor, but this has rarely been investigated. The aim of this study was to assess the regional and temporal change in MTBD in the coronal and sagittal planes in the first 2 years after UKA. MethodsPatients with fixed-bearing medial UKA were recruited. The change in MTBD in the first 24 months after UKA using digital radiological densitometry (DRD) was measured. Potential predictors and clinical correlations were analyzed. ResultsEighty-four cases (female 60%) were selected for review. The follow up time was 63 (±17) months. Anterior and medial regions had the largest proportion of cases with MTBD reduction (90–97%, P < 0.05). Reduction was largest at anterior and medial regions (21–29%, P < 0.05) and smallest at posterior and lateral regions (5–15%, P < 0.05). Maximal reduction occurred at 12 months for the medial region and 24 months for the anterior region. MTBDs of both regions were not significantly influenced by any confounding factors. Significant correlation was found between medial MTBD and Function Score at 6 months. ConclusionsBone loss in a zonal pattern occurs in the first 2 years after UKA with the largest loss in the anterior region below the tibial tray. It is not affected by body mass index, perioperative alignment, or angle of correction. This suggests a physiological response to trauma other than a mechanical response to the change in bone strain.

A taper-fit junction to improve long bone reconstruction: A parametric In Silico model

PurposeCritical size long bone defects represent a clinical challenge in orthopaedic surgery. Various grafting techniques have been developed through the years, but they all present several downsides. A key requirement of all grafting techniques is the achievement of a continuous interface between host bone and graft to enhance both biological processes and mechanical stability. This study used a parametric in silico model to quantify the biomechanical effect of the inaccuracies inherent to current osteotomy techniques, and to test a new concept of accurate taper-fit junction that may improve the biomechanical parameters of the reconstruction under load. MethodsA population-based in-silico 3D model of the reconstruction of a long bone defect was built to represent a defect of the femoral mid-diaphysis. To fix the reconstruction a titanium plate was placed on the lateral aspect of the reconstruction. The model was modified to (i) quantify the biomechanical consequences of actual inaccuracies in the realization of a flat host-graft interface, (ii) compare the contact behaviour and bone strains among different taper angles of the new design and the current host-graft flat interface, (iii) evaluate the robustness of the taper-fit design to inter-subject variability in bone geometry and defect length. ResultsThe influence of 2° single-plane misalignments of the host-graft interface is highly dependent on the misalignment orientation with respect to the metal plate. For some misalignment orientations, tangential micromotions of contact interfaces exceeded alert thresholds. When the angle of the taper-fit host-graft junction is changed from 10° to 30° and the results obtained are compared with the planar case, the overall stiffness is almost preserved, the bone strains are almost unchanged with safety factors higher than five, and full contact closure around the host-graft junction is achieved at 20°. Similarly, contact pressures decrease almost linearly with a 20% decrease at 30°. The host-graft micro motions are almost unchanged in both value and distribution up to 20° and never exceed the warning threshold of 50 μm. ConclusionsThe present in silico study developed quantitative biomechanical evidence that an osteotomy performed with attention to the perpendicularity of the cut planes is needed to reduce the risk of mismatch and possible complications of long bone reconstructions, and that a new concept of a taper-fit junction may improve the biomechanical environment of the interface between the graft and the host bone. The optimal taper-fit configuration is suggested to be around a 20° taper angle. These results will serve as an input to conduct exvivo experiments to further corroborate the proposed taper-fit junction concept and to refine its surgical implementation.

17. Understanding proximal junctional kyphosis: New way of evaluating adjacent segment strain and vulnerability to failure after long segment instrumentation

<h3>BACKGROUND CONTEXT</h3> Proximal junctional kyphosis (PJK) is a common and devastating complication of long segment fusions. Presumably, PJK occurs due to excessive or altered strain distribution at the proximal level above a fusion construct; however, this has not been previously studied or proven experimentally. <h3>PURPOSE</h3> Evaluate the patterns of proximal junction discoligamentous and bone strain distribution following long-segment pedicle screw fixation in a cadaveric model. <h3>STUDY DESIGN/SETTING</h3> Human cadaveric biomechanical testing. <h3>PATIENT SAMPLE</h3> Seven human cadaver specimens (T2-T12). <h3>OUTCOME MEASURES</h3> Range of motion (ROM), posterior rod strain (RS), as well as intervertebral disc (IVD), endplate and bone surface strains at the proximal junction. <h3>METHODS</h3> Nondestructive flexibility tests (4.0 Nm) were performed on 7 specimens (T2-T12) to compare range of motion (ROM), posterior rod strain (RS), as well as intervertebral disc (IVD), endplate and bone surface strains at the proximal junction during flexion, extension, axial rotation (AR) following pedicle screw fixation (PSR) from T4 to T12. Specimens were coated with a high contrast speckle pattern for optical tracking of movements using digital image correlation (DIC) with conversion to principle strain measured at the proximal junction disc and vertebral body bone surfaces. Data were analyzed using a two-way ANOVA followed by post hoc comparisons. <h3>RESULTS</h3> PSR resulted in significantly greater mobility at the proximal free level (T3-4) in flexion compared to intact (p=0.005), but not extension (p=0.3). PSR resulted in significantly lower ROM in flexion and extension across the instrumented T5-T12 levels (p<0.001) compared to intact. In flexion, PSR resulted in decreased strain at the posterior T3 inferior endplate compared to intact (p=0.038). In extension, PSR resulted in decreased strain at the anterior aspect of the disc (p=0.014), but increased strain at the posterior aspect of the disc (p=0.026) compared to intact. In AR, PSR resulted in elevated strain at the T3 inferior endplate (p=0.02), and reduced strain at the T4 superior endplate (p=0.028). Average T4 surface bone strain was lower with PSR compared to intact in flexion (p=0.039) and extension (p=0.028), and lower in the inferior anterior vertebral body in left AR (p=0.045). <h3>CONCLUSIONS</h3> This represents the first cadaveric biomechanical study of bone and soft tissue strain following long segment spinal instrumentation. Our results suggest that instrumentation alters the normal anterior-posterior and cranial-caudal strain profile across the proximal disc and vertebral body—the most common failure points in PJK. This study provides a foundation for understanding the biomechanics underlying PJK and will allow for the development of more targeted prevention strategies. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

P13. Biomechanical effects of proximal PEEK rod extension on the upper instrumented and adjacent levels in a human long segment construct: A cadaveric model

<h3>BACKGROUND CONTEXT</h3> Proximal junctional kyphosis (PJK) is a sequela of spinal fusion that is potentially related to mechanical failure and revision surgery. The high mechanical stress zone, created by the sudden transition from a rigid to a flexible region, is involved in PJK physiopathology. <h3>PURPOSE</h3> We evaluated the biomechanical performance of polyetheretherketone (PEEK) rods used as a semi-rigid transition from a long-segment metallic rod construct to a non-fused thoracic spine. <h3>STUDY DESIGN/SETTING</h3> Cadaveric biomechanical study. <h3>PATIENT SAMPLE</h3> Seven human cadaveric specimens. <h3>METHODS</h3> Seven cadaveric specimens (T2-pelvis with intact rib cage) were used for this study. Standard pure moment range of motion (ROM) tests (7.5 Nm) were performed in flexion, extension, lateral bending (LB), and axial rotation (AR) followed by compression (200 N). Specimens were tested 1) intact, 2) after instrumentation with T10-S1 pedicle screws and S2 alar-iliac screws and metallic rods (PSR), 3) and after extending the proximal construct to T6 using PEEK rods (PSR+PEEK). T10-T11 rod strain, T9 anterolateral bone strain, and T10 screw bending moments were analyzed using paired t test or repeated measures analysis of variance. <h3>RESULTS</h3> PSR decreased T10-T11 ROM in all loading directions (mean 80%), but the decrease was statistically significant only during flexion (70%, P=0.003). PSR+PEEK significantly decreased ROM during flexion (68%, P=0.04) compared with PSR. Compared with PSR, PSR+PEEK significantly decreased T9-T10 ROM in flexion (115%, P=0.003), extension (104%, P=0.006), left LB (46%, P=0.01), and right LB (63%, P=0.02). Compared to the intact condition, PSR+PEEK significantly decreased T9-T10 ROM in flexion (111%, P=0.01) and extension (105%, P=0.003). For PSR+PEEK versus PSR, T5-T6 ROM decreased in all directions (mean 27%) but only significantly during extension (44%, P=0.03) and left AR (40%, P=0.048). The reduction in T9 anterior column bone strain was statistically significant with PSR+PEEK versus PSR during right LB (P=0.02). Compared with PSR, PSR+PEEK significantly reduced the contralateral T10 screw bending moment by 37% (left AR, P=0.03), while the mean ipsilateral decrease was not significant at 14% (right AR, P=0.53). Rod strain polarities reversed with PEEK rods in all loading directions except compression. <h3>CONCLUSIONS</h3> Extending a long-segment construct using PEEK rods redistributed the strain on the upper instrumented and adjacent levels, and caused a decrease in adjacent-level hypermobility, which might contribute to the physiopathology of PJK. Further studies are necessary to observe the clinical outcome of this technique. <h3>FDA DEVICE/DRUG STATUS</h3> PEEK rods (Approved for this indication).

Differences in Fracture Healing Between Female and Male C57BL/6J Mice.

BackgroundMice are increasingly used in fracture healing research because of the opportunity to use transgenic animals. While both, male and female mice are employed, there is no consensus in the literature whether fracture healing differs between both sexes. Therefore, the aim of the present study was to analyze diaphyseal fracture healing in female and male C57BL/6J mice, a commonly used mouse strain in bone research.MethodsFor that purpose, 12-week-old Female (17–20 g) and Male mice (22–26 g) received a standardized femur midshaft osteotomy stabilized by an external fixator. Mice were euthanized 10 and 21 days after fracture and bone healing was analyzed by biomechanical testing, μCT, histology, immunohistochemistry and qPCR.ResultsTen days after fracture, Male mice displayed significantly more cartilage but less fibrous tissue in the fracture callus compared to Female mice, whereas the amount of bone did not differ. At day 21, Male mice showed a significantly larger fracture callus compared to Female mice. The relative amount of bone in the fracture callus did not significantly differ between both sexes, whereas its tissue mineral density was significantly higher in Male mice on day 21, indicating more mature bone and slightly more rapid fracture healing. These results were confirmed by a significantly greater absolute bending stiffness of the fractured femurs of Male mice on day 21. On the molecular level, Male mice displayed increased active β-catenin expression in the fracture callus, whereas estrogen receptor α (ERα) expression was lower.ConclusionThese results suggest that Male mice display more rapid fracture healing with more prominent cartilaginous callus formation. This might be due to the higher weight of Male mice, resulting in increased mechanical loading of the fracture. Furthermore, Male mice displayed significantly greater activation of osteoanabolic Wnt/β-catenin signaling, which might also contribute to more rapid bone regeneration.

Effects of tissue heterogeneity on trabecular micromechanics examined by microCT-based finite element analysis and digital volume correlation

Trabecular bone is natural material with heterogeneous tissue properties. The effect of tissue heterogeneity on the micromechanical behavior of trabecular bone is commonly evaluated by microCT-based finite element (microFE) analysis. Results from prior work remain inconclusive and lack of experimental validation. To address these issues, we combined microFE analysis with mechanical testing and microCT-based digital volume correlation (DVC), as a validation for the microFE approach. Porcine trabecular specimens were tested in compression as sequential microCT scans were taken. DVC was performed to extract “realistic” boundary conditions that were applied to microFE models, and to measure microstructural deformation and strain of the trabecular specimens. Heterogeneous and homogeneous microFE models of each trabecular specimen were created and compared with the experimentally measured microstructural displacement and strains. Results showed strong correlations between DVC-measured and microFE-predicted trabecular displacement and strain fields (R2 ​> ​0.9, p ​< ​0.05), regardless of heterogeneous or homogeneous material assignments. The heterogeneous and homogeneous models predicted similar magnitudes for maximum or minimum principal strains (R2 ​= ​1, p ​< ​0.05). However, incorporation of tissue heterogeneity decreased more than 16.5% in the overall stress level of the trabecular tissues. Regardless, very strong correlations were found between the heterogeneous and homogeneous model-predicted principal strains or stresses. These results together suggest that tissue heterogeneity may have little effect on microFE modeling of typical elastic displacement and strains in the trabecular bone, suggesting that homogeneous material models might be sufficient to predict general trabecular micromechanics.

Commentaries on Viewpoint: Fragile bones of elite cyclists: to treat or not to treat?

Commentaries on Viewpoint: Fragile bones of elite cyclists: to treat or not to treat?

Biomechanical Analysis of Functionally Graded Root Analog Implants on Alveolar Bone: A 3D Finite Element Study

This study aimed to investigate whether axial or radial functionally graded root analog implants can optimize the stress and strain distribution near the implant-bone interface in alveolar bone models under static loads using finite element analysis (FEA). The 3D profile of the root analog implant was captured from a natural tooth in CBCT data. The implant was separated into different layers (3, 5, and 10 layers) to vary the Young modulus axially or radially. The variation in Young modulus was designed to be linear, exponential, or parabolic. Different occlusal loads were applied. The von Mises stress and strain were used to evaluate the system risk of failure. The difference in the numbers of layers had no significant effect on the alveolar bone. In the radial functionally graded implant models, the maximum von Mises stress of the alveolar bone decreased as the outer layer's elastic modulus increased; however, in the vertical functionally graded implants, this stress varied little. The maximum von Mises stress of the cancellous bone changed only slightly, from 2 to 5 MPa in all models. The maximum strain of the alveolar bone varied from 0.001478 mm to 0.003999 mm. Those FEA results were in line with previous findings. The functionally graded root analog implants show no significant biomechanical advantages over dense zirconia implants. Radial functionally graded root analog implants should optimize the peri-implant stresses and are biomechanically favorable for design.

Finite Element Analysis of Fracture Fixation.

Fracture fixation aims to provide stability and promote healing, but remains challenging in unstable and osteoporotic fractures with increased risk of construct failure and nonunion. The first part of this article reviews the clinical motivation behind finite element analysis of fracture fixation, its strengths and weaknesses, how models are developed and validated, and how outputs are typically interpreted. The second part reviews recent modeling studies of the femur and proximal humerus, areas with particular relevance to fragility fractures. There is some consensus in the literature around how certain modeling aspects are pragmatically formulated, including bone and implant geometries, meshing, material properties, interactions, and loads and boundary conditions. Studies most often focus on predicted implant stress, bone strain surrounding screws, or interfragmentary displacements. However, most models are not rigorously validated. With refined modeling methods, improved validation efforts, and large-scale systematic analyses, finite element analysis is poised to advance the understanding of fracture fixation failure, enable optimization of implant designs, and improve surgical guidance.

Finite element analysis of different titanium miniplates: Evaluation of three-dimensional designs applied on condylar neck fractures

IntroductionThe fixation of condylar neck fractures is raising difficulties and for this reason, many plate designs have been developed. The current study compares the performance of four miniplates used in the condylar neck. Material and MethodsA virtual condylar neck fracture in a mandible obtained from a CT scan was fixed with four miniplates (two straight miniplates, lambda, strut, and trapezoidal). Using finite element analysis, we examined the fragments' displacements and stress distribution in the titanium material and bone. The models were analyzed under two loading conditions: a reduced bite force of 135 N and a force of 500 N. ResultsNo risk of material failure was observed. For a load of 135 N, all four plates offer an adequate fixation. For 500 N of applied loading, the lambda and strut plates showed the best rigidity and lowest bone strains. The two parallel plates showed the lowest rigidity and the trapezoidal plate the highest bone strains around all screws. DiscussionThese findings imply that three-dimensional miniplates (lambda, strut) perform better when higher loads are applied. On the other hand, the trapezoidal plate has an increased risk of screw loosening and the two straight plates higher mobility of the fragments.

Biomechanical analyses of one-piece dental implants composed of titanium, zirconia, PEEK, CFR-PEEK, or GFR-PEEK: Stresses, strains, and bone remodeling prediction by the finite element method.

This work aimed to assess the biomechanics, using the finite element method (FEM), of traditional titanium Morse taper (MT) dental implants compared to one-piece implants composed of zirconia, polyetheretherketone (PEEK), carbon fiber-reinforced PEEK (CFR-PEEK), or glass fiber-reinforced PEEK (GFR-PEEK). MT and one-piece dental implants were modeled within a mandibular bone section and loaded on an oblique force using FEM. A MT implant system involving a Ti6Al4V abutment and a cp-Ti grade IV implant was compared to one-piece implants composed of cp-Ti grade IV, zirconia (3Y-TZP), PEEK, CFR-PEEK, or GFR-PEEK. Stress on bone and implants was computed and analyzed while bone remodeling prediction was evaluated considering equivalent strain. In comparison to one-piece implants, the traditional MT implant revealed higher stress peak (112 MPa). The maximum stresses on the one-piece implants reached ~80 MPa, regardless their chemical composition. MT implant induced lower bone stimulus, although excessive bone strain was recorded for PEEK implants. Balanced strain levels were noticed for reinforced PEEK implants of which CFR-PEEK one-piece implants showed proper biomechanical behavior. Balanced strain levels might induce bone remodeling at the peri-implant region while maintaining low risks of mechanical failures. However, the strength of the PEEK-based composite materials is still low for long-term clinical performance.

Novel CT-Based Bone Strength Assessment By Finite Element Analysis for Monitoring Bone Involvement in Myeloma: a Proof of Concept Study

IntroductionMyeloma (MM) is characterized by osteolytic bone disease, detected in up to 80% of patients, increasing the risk for skeletal related events (SREs), causing morbidity, undermining quality of life and impairing survival. Current imaging modalities provide qualitative measures of bone involvement, often after irreversible damage has occurred.Bone strains are a biomechanical measure of bone strength which quantifies bone relative deformation in response to applied force. As a result of load on bone strains develop which may lead to fracture, once strain magnitude reaches the yield strain. Lytic bone lesions cause local weakening expressed by an increase in local strains.We developed CT-based finite element analysis (CTFEA), a novel measure designed to accurately estimate bone strains based on conventional CT scans. We hypothesize this tool may enable quantifying changes in bone strength over time, by monitoring strain. In this concept study we explore the sensitivity and responsiveness of CTFEA in myeloma patients to detect bone-disease progression and treatment response, and explore clinical correlates.MethodsPatients: A pilot retrospective study. After approval by the institutional ethics committee, 16 MM patients, with at least 2 consecutive CT scans including the spine and at least the proximal 1/3 of the femur since 2010 were identified. Demographic, clinical and radiographic data were abstracted from medical records.CTFEA: Femurs of interest were segmented from the CT scan, and a computational model was created with “stiffness” changing from point to point according to CT's gray values. The computational model was loaded virtually with a physiological stance position contact hip force (2.5 X body weight) applied on the femur's head. An elastic finite element analysis was performed that predicts the displacements and strains at any point within the bone (Figure 1). The locations of interest where the larger change in material properties may occur between consecutive CT scans were determined by computing the relative difference in Hounsfield unit (HU) radio-density along bone's axis. At these locations the principal strains were extracted and monitored. A monotonic increase in strains implies deterioration of bone strength, and vice versa. For patients with lytic lesions, bone strength is quantified by monitoring the principal strains in lesions vicinity. Healing is quantified by a decrease in strains. The CTFEA results were compared to conventional radiographic and laboratory measures.ResultsTable 1 summarizes individual patient clinical data at the time points of each of the CT-scans as well as the calculated CTFEA strain values at the location of maximum HU change of the initial 7 patients. Complete analysis of femur and vertebral strain for 16 patients will be presented at the meeting. Indeed no visible change in strain is demonstrated for smoldering MM (SMM) patients (Pts 15 and 16), whereas a monotonic increase is seen for patient 3, RRMM, with successive relapses without visible tumor identified in the femur in CT scans.Patient 17 (RRMM) with a lytic tumor at the distal femur, shows an initial deterioration of bone strength followed by a monotonic improvement until almost full regain of strength after 19 months.Patient 10 (NDMM) with a lytic tumor in the vicinity of the lesser trochanter, achieved a partial response of MM following anti-myeloma induction within 6 weeks, and as well as a significant increase in bone strength. Patient 13 had a rapid MM response but parallel worsening strain in the right femur, patient 18 had a MM partial response over 5 months with slight worsening of strain.ConclusionsPromising trends were found between CTFEA strain prediction and MM clinical course. SMM patients had minimal changes whereas a patient with progressive disease had a monotonic increase in strains. A decrease in strain was seen in some but not all who responded to therapy. The preliminary study is to be enhanced by considering vertebrae, analyzing further patients as well as prospective validation against SREs, to refine calibrate and tailor this measurement. By providing a quantitative metric of bone strain, this tool may allow monitoring bone strength throughout myeloma evolvement, prior to development of SREs. This may support physicians making personalized medical and surgical treatment decisions and provide a useful surrogate endpoint for clinical drug development. [Display omitted] DisclosuresYosibash:PerSimiO: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Trabelsi:PerSimiO: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Biomechanical evaluation of 3-unit fixed partial dentures on monotype and two-piece zirconia dental implants

This study aimed to evaluate the biomechanical behavior, stress distributions and bone microstrain of fixed partial dentures (FPD) with ceramic abutments supported on monotype zirconia implants, titanium implants and two-piece zirconia implants, using finite element analysis. A three-dimensional model of the jaw was simulated containing 1.0 mm thick cortical bone and cancellous bone tissue. A FPD and implant models (4.1 x 10 mm) were modeled containing a cement-retained implant abutment. These models were replicated in three groups with similar geometries: Titanium Implant and Zirconia Abutment (Ti-Zr); Zirconia Implant and Zirconia Abutment (Zr-Zr) and Monotype Zirconia Implant (Zr-S). An axial load of 300 N was applied to the center of the first premolar. The microstrain (με) and the Von-Mises stress (MPa) were assumed as failures criteria. For the three groups, a higher stress concentration was observed in the region of FPD connectors. The Ti-Zr group showed a higher stress concentration in the prosthesis and implant when compared to the other groups. However, the smaller elastic modulus of the titanium implant, in relation to the zirconia, provided a lower stress in the abutment and in the prosthetic screw. The monotype implant system allowed a more homogeneous stress distribution and its strain were predominantly located in the cervical region of the peri-implant bone tissue. Monotype or two-piece zirconia implants can be used for rehabilitation with FPD. However, the absence of separation between implant and abutment in the monotype system avoids the stress concentration in the prosthetic screw and reduced the peri-implant bone strain.

Lattice implants that generate homeostatic and remodeling strains in bone.

Bone remodeling is mediated by several factors including strain. An increase in strain between 1% and 10% compared to homeostasis can trigger bone formation. We aim to create an orthopedic implant using clinically established imaging and manufacturing methods that induces this strain control in human bone. Titanium scaffolds were manufactured with multiaxial apparent modulus tailored to the mechanical properties of bone defined from computed tomography scans of cadaver human tibiae. Five bone cubes were tested with corresponding titanium scaffolds by loading under compression, which is similar to the implanted tibia loading condition. Bone strain was precisely controlled by varying the scaffold modulus, from 0% to 15% bone strain increase. This strain increase is the magnitude reported to invoke bone's positive remodeling. Axial modulus was closely matched between titanium scaffolds and bone, ranging from 48-728 and 81-800 MPa, respectively, whereby scaffold axial modulus was within 2% of nominal target values. Fine control of multiaxial moduli resulted in transverse modulus that matched bone well; ranging from 42-648 and 47-585 MPa in scaffolds and bone respectively. The scaffold manufacturing material and method are already used in the orthopedic industry. This study has significant clinical implications as it enables the design of implants which positively harness bone's natural mechanoresponse and respect bone's mechanical anisotropy and heterogeneity.

Time-resolved in situ synchrotron-microCT: 4D deformation of bone and bone analogues using digital volume correlation

Digital volume correlation (DVC) in combination with high-resolution micro-computed tomography (microCT) imaging and in situ mechanical testing is gaining popularity for quantifying 3D full-field strains in bone and biomaterials. However, traditional in situ time-lapsed (i.e., interrupted) mechanical testing cannot fully capture the dynamic strain mechanisms in viscoelastic biological materials. The aim of this study was to investigate the time-resolved deformation of bone structures and analogues via continuous in situ synchrotron-radiation microCT (SR-microCT) compression and DVC to gain a better insight into their structure-function relationships. Fast SR-microCT imaging enabled the deformation behaviour to be captured with high temporal and spatial resolution. Time-resolved DVC highlighted the relationship between local strains and damage initiation and progression in the different biostructures undergoing plastic deformation, bending and/or buckling of their main microstructural elements. The results showed that SR-microCT continuous mechanical testing complemented and enhanced the information obtained from time-lapsed testing, which may underestimate the 3D strain magnitudes as a result of the stress relaxation occurring in between steps before image acquisition in porous biomaterials. Altogether, the findings of this study highlight the importance of time-resolved in situ experiments to fully characterise the time-dependent mechanical behaviour of biological tissues and biomaterials and to further explore their micromechanics under physiologically relevant conditions. Statement of significanceTime-resolved synchrotron X-ray tomography in combination with in situ mechanical testing provided the first four-dimensional analysis of the mechanical deformation of bone and bone analogues. To unravel the interplay of damage initiation and progression with local deformation, digital volume correlation was used to map the local strain field while microstructural changes were tracked with high temporal and spatial resolution. The results highlighted the importance of fast imaging and time-resolved in situ experiments to capture the real deformation of complex porous materials to fully characterize the local strain-damage relationship. The findings are notably improving the understanding of time-dependent mechanical behaviour of bone tissue, with the potential to be extend to highly viscoelastic biomaterials and soft tissues.