Cortical Bone Strains Research Articles

Cortical Bone Strains Around Straight and Angulated Immediate Orthodontic Microimplants

To measure strains around orthodontic implants upon torque tightening and loading and to assess correlations between factors influencing primary stability. Self-drilling implants were placed into bovine iliac crest blocks after CT assessments. Upon bonding of strain gauges on bone adjacent to the implants, strain measurements were performed using a data acquisition system during torque tightening and 250 g orthodontic force application by elastic chains. The torque required to place straight implants (12.16 N.cm) was higher than 30- to 40-degree angulated implants (9.31 N.cm) (P < 0.05). Cortical bone strain amplitudes of both implant placements were comparable (P > 0.05). Strains during torque tightening of straight (196 με) and tilted (114 με) implants were higher than those obtained during orthodontic loading (20-30 με). Despite the positive and direct relationship found between torque and torque strain output, strong correlations between other parameters could not be detected. Vertically aligned and 30- to 40-degree angulated immediate orthodontic microimplants are associated with low amplitude strains upon torque tightening and orthodontic loading.

The influence of acetabular cup material on pelvis cortex surface strains, measured using digital image correlation

Acetabular cup loosening is a late failure mode of total hip replacements, and peri-prosthetic bone deterioration may promote earlier failure. Preservation of supporting bone quality is a goal for implant design and materials selection, to avoid stress shielding and bone resorption. Advanced polymer composite materials have closer stiffness to bone than metals, ceramics or polymers, and have been hypothesised to promote less adverse bone adaptation. Computer simulations have supported this hypothesis, and the present study aimed to verify this experimentally.A composite hemi-pelvis was implanted with Cobalt Chromium (CoCr), polyethylene (UHMWPE) and MOTIS®carbon-fibre-reinforced polyether etherketone (CFR-PEEK) acetabular cups. In each case, load was applied to the implanted pelvis and Digital Image Correlation (DIC) was used for surface strain measurement. The test was repeated for an intact hemi-pelvis. Trends in implanted vs. intact bone principal strains were inspected to assess the average principal strain magnitude change, allowing comparison of the potential bone responses to implantation with the three cups.The CFR-PEEK cup was observed to produce the closest bone strain to the intact hip in the main load path, the superior peri-acetabular cortex (+12% on average, R2=0.84), in comparison to CoCr (+40%, R2=0.91) and UHWMPE cups (−26%, R2=0.94). Clinical observations have indicated that increased periacetabular cortex loading may result in reduced polar cancellous bone loading, leading to longer term losses in periprosthetic bone mineral density. This study provides experimental evidence to verify previous computational studies, indicating that cups produced using materials with stiffness closer to cortical bone recreate physiological cortical bone strains more closely and could, therefore, potentially promote less adverse bone adaptation than stiffer press-fitted implants in current use.

Three-dimensional finite element analysis of the deformation of the human mandible: a preliminary study from the perspective of orthodontic mini-implant stability

ObjectiveThe aims of this study were to investigate mandibular deformation under clenching and to estimate its effect on the stability of orthodontic mini-implants (OMI).MethodsThree finite element models were constructed using computed tomography (CT) images of 3 adults with different mandibular plane angles (A, low; B, average; and C, high). An OMI was placed between #45 and #46 in each model. Mandibular deformation under premolar and molar clenching was simulated. Comparisons were made between peri-orthodontic mini-implant compressive strain (POMI-CSTN) under clenching and orthodontic traction forces (150 g and 200 g).ResultsThree models with different mandibular plane angles demonstrated different functional deformation characteristics. The compressive strains around the OMI were distributed mesiodistally rather than occlusogingivally. In model A, the maximum POMI-CSTN under clenching was observed at the mesial aspect of #46 (1,401.75 microstrain [µE]), and similar maximum POMI-CSTN was observed under a traction force of 150 g (1,415 µE).ConclusionsThe maximum POMI-CSTN developed by clenching failed to exceed the normally allowed compressive cortical bone strains; however, additional orthodontic traction force to the OMI may increase POMI-CSTN to compromise OMI stability.

Full and surface tibial cementation in total knee arthroplasty: A biomechanical investigation of stress distribution and remodeling in the tibia

Background: Aseptic tibial component loosening remains a major cause of total knee arthroplasty failure. The cementation technique used to achieve fixation may play a major role in loosening. Despite this, the optimum technique remains unanswered. This study aims to investigate stress and strain distributions in the proximal tibia for full cementation and surface cementation of the Genesis II tibial component.Methods: Principal cortical bone strains were measured experimentally in intact, surface cemented and fully cemented synthetic tibiae using strain gauges. Both axial and 15° flexion loading were considered. Finite element models were used to assess both cortical and cancellous bone stresses and strains. Using a bone remodeling algorithm potential sites of bone formation and resorption were identified post-implantation.Findings: Principal cortical bone strain results demonstrate strong correlations between the experimental and finite element analyses (R2≥0.81, RMSE(%)≤17.5%). Higher cortical strains are measured for surface cementation, as full cementation creates a stiffer proximal tibial structure. Simulations reveal that both cementation techniques result in lower cancellous stresses under the baseplate compared to the intact tibia, with greater reductions being computed for full cementation. The surface cementation model displays the closest cancellous stress distribution to the intact model. In addition, bone remodeling simulations predict more extensive bone resorption under the baseplate for full cementation (43%) than for surface cementation (29%).Interpretation: Full cementation results in greater stress reduction under the tibial baseplate than surface cementation, suggesting that surface cementation will result in less proximal bone resorption, thus reducing the possibility of aseptic loosening.

Parametric convergence sensitivity and validation of a finite element model of the human lumbar spine

The primary objective of this study was to generate a finite element model of the human lumbar spine (L1–L5), verify mesh convergence for each tissue constituent and perform an extensive validation using both kinematic/kinetic and stress/strain data. Mesh refinement was accomplished via convergence of strain energy density (SED) predictions for each spinal tissue. The converged model was validated based on range of motion, intradiscal pressure, facet force transmission, anterolateral cortical bone strain and anterior longitudinal ligament deformation predictions. Changes in mesh resolution had the biggest impact on SED predictions under axial rotation loading. Nonlinearity of the moment-rotation curves was accurately simulated and the model predictions on the aforementioned parameters were in good agreement with experimental data. The validated and converged model will be utilised to study the effects of degeneration on the lumbar spine biomechanics, as well as to investigate the mechanical underpinning of the contemporary treatment strategies.

Effect of Screw Fixation on Temporomandibular Joint Condylar Prosthesis

The objective of the present study was to evaluate the effect of the number of screws on the stress and stability of the temporomandibular joint (TMJ) condylar prosthesis and on the strain distribution in the bone. Three-dimensional, finite element models of the mandible and a TMJ condylar prosthesis with fixations involving different numbers of screws in 8 configurations were established to investigate the effect of the number of fixed screws on the stress and stability of the implant and strain in cortical and cancellous bone. The simulations showed that increasing the number of screws beyond 3 only slightly enhanced the implant stability and reduced the implant stress. The position of the inserted screws significantly affected the strain distributions in cortical and cancellous bone tissues. The results of our study have shown that 3 staggered screws can provide optimal implant stability and bone stress and strain distributions in a TMJ condylar prosthesis.

Measurement of Cortical Bone Strain Distribution by Image Correlation Techniques and from Fracture Toughness

Bone fracture toughness has been well studied, however, it is also important to investigate the effect of preservative treatment on the mechanical properties of bones. It is necessary to evaluate crack initiation and propagation after fracture because this process may be different in the case of injured bone tissues. In this study, we attempted to analyze the strain distribution on bone tissue surface by using image correlation techniques in order to elucidate the relationship between microscopic bone damage and strain distribution. Bovine femoral cortical bone was employed as the bone specimen and the three-point bend test method was used to determine the fracture toughness, in accordance with the ASTM E399 guidelines. An Instron type machine was used in the fracture toughness test and the loading rate was set to 1 mm/min. Black and white spray paint was applied in a random pattern to the surface of the specimens, and the specimens were loaded until they were ruptured. Bone surface strain analysis was performed using image correlation techniques and the changes were recorded in a digital image. In order to evaluate the effects of preservative treatment on the mechanical properties of bone, we categorized the specimens into 4 groups: the control group included the specimens that were submitted for testing immediately after machining and the preservation group comprised specimens that were analyzed after preservative treatment with different method (formalin, ethanol and physiological saline solution). A strain analysis performed using image correlation techniques allowed the visualization of the increased strain at the forward end of the slit of the specimens. The strain value at the forward end of the slit (the longitudinal direction of specimens) measured at the time of rupture in the control group was approximately 4 times larger than that in the formalin preservation group, thereby suggesting the embrittlement of bone organic constituents due to preservative treatment. [doi:10.2320/matertrans.M2010426]

Internal strain gradients quantified in bone under load using high-energy X-ray scattering

High-energy synchrotron X-ray scattering (>60 keV) allows noninvasive quantification of internal strains within bone. In this proof-of-principle study, wide angle X-ray scattering maps internal strain vs position in cortical bone (murine tibia, bovine femur) under compression, specifically using the response of the mineral phase of carbonated hydroxyapatite. The technique relies on the response of the carbonated hydroxyapatite unit cells and their Debye cones (from nanocrystals correctly oriented for diffraction) to applied stress. Unstressed, the Debye cones produce circular rings on the two-dimensional X-ray detector while applied stress deforms the rings to ellipses centered on the transmitted beam. Ring ellipticity is then converted to strain via standard methods. Strain is measured repeatedly, at each specimen location for each applied stress. Experimental strains from wide angle X-ray scattering and an attached strain gage show bending of the rat tibia and agree qualitatively with results of a simplified finite element model. At their greatest, the apatite-derived strains approach 2500 με on one side of the tibia and are near zero on the other. Strains maps around a hole in the femoral bone block demonstrate the effect of the stress concentrator as loading increased and agree qualitatively with the finite element model. Experimentally, residual strains of approximately 2000 με are present initially, and strain rises to approximately 4500 με at 95 MPa applied stress (about 1000 με above the strain in the surrounding material). The experimental data suggest uneven loading which is reproduced qualitatively with finite element modeling.

Biomechanical consequences of first metatarsal osteotomy in treating hallux valgus

Background Among the numerous osteotomies for correction of hallux valgus, the modified chevron is known for its good intrinsic stability and the scarf for its large corrective potential. An intermediate design, the reversed-L osteotomy, has been developed to combine these competing biomechanical objectives. The purpose of this in vitro study was to compare the structural and local biomechanical performance of these three designs. Methods Stiffness, cortical bone strains (a factor relevant to bone remodeling), strength and failure mode of the scarf, modified chevron and reversed-L osteotomies were measured on human specimens in two different loading configurations. Findings The scarf osteotomy caused significant changes in stiffness and cortical bone strains with the proximal apex being at the origin of bone failure. The chevron and reversed-L had a generally comparable response to the intact bone. The chevron specimens failed by pivoting of the distal fragment, and the reversed-L by pivoting or fracture. Interpretation This is the first study to investigate the cortical bone strain changes induced by these invasive osteotomies. Alterations from the intact bone response could be directly related to the design of the osteotomy. Notably, the critical weakening proximal apex of the scarf is avoided in the reversed-L, leading to results comparable to the chevron. This study provides support in favor of the intermediate design of the reversed-L as an effective compromise between the competing biomechanical objectives of corrective potential and mechanical stability.

S0201-3-2 ウシ大腿骨海綿骨における骨梁内HAp結晶の配向と変形挙動(骨再生と骨再建のためのバイオマテリアル(3),社会変革を技術で廻す機械工学)

Bone tissue is a composite material composed of hydroxyapatite (HAp) and collagen fiber. The interplanar spacing of HAp crystals can be measured using the X-ray diffraction method, and HAp crystal strain is calculated from the deformation of the interplanar spacing. Previous studies have shown that HAp crystal strain in cortical bone is almost proportional to the tissue strain in the bone axial and circumferential directions. The aim of this study is to measure the HAp crystal strain under tensile loading and the orientation of c-axis of HAp crystals in femoral trabeculae. The experiments in the study used the trabeculae specimens taken from the cancellous bone in a bovine femur. As a result, the c-axis of HAp crystals oriented to the longitudinal direction in the trabeculae. Furthermore, the HAp crystal strain increased with the tissue strain under tensile loading, and the HAp crystal strains were not uniform between the specimens.

Strain shielding in distal femur after patellofemoral arthroplasty under different activity conditions

Strain shielding, a mechanical effect occurring in structures combining stiff with more flexible materials, is considered to lead to a reduction of density in bone surrounding the implant. This effect can be related to the weakness of the implant fixation, which can promote implant loosening. Several studies describe a significant decrease in postoperative bone mineral density adjacent to joint implants, which can compromise their long-term fixation. The aim of the present study was to quantify the strain shielding effect on the distal femur after patellofemoral arthroplasty. For this purpose three activities of daily living were considered: level walking, stair climbing and deep bending at different angles of knee flexion. To determine the strain shielding effect, cortical bone strains were measured experimentally with triaxial strain gauges in synthetic femurs before and after patellofemoral arthroplasty for each of the different daily activities. The results showed that the patellofemoral arthroplasty in general reduced the strains in the medial and distal regions of the femur when deep bending activity occurred, consequently, strain shielding in these regions, with strain decreases of −72.0% and −67.5% were measured. On the other side, higher values of strain were found in the anterior region after patellofemoral replacement for this activity with an increase of +182.0%. The occurrence of strain shielding seems to be more significant when the angle of knee flexion and applied load increases. Strain shielding and over-loading may have relevant effects on bone remodeling surrounding the patellofemoral implant, suggesting a potential effect of later bone resorption in the medial and distal femur regions in case of regular deep bending activity.

Rib fractures under anterior–posterior dynamic loads: Experimental and finite-element study

The purpose of this study was to investigate whether using a finite-element (FE) mesh composed entirely of hexahedral elements to model cortical and trabecular bone (all-hex model) would provide more accurate simulations than those with variable thickness shell elements for cortical bone and hexahedral elements for trabecular bone (hex–shell model) in the modeling human ribs. First, quasi-static non-injurious and dynamic injurious experiments were performed using the second, fourth, and tenth human thoracic ribs to record the structural behavior and fracture tolerance of individual ribs under anterior–posterior bending loads. Then, all-hex and hex–shell FE models for the three ribs were developed using an octree-based and multi-block hex meshing approach, respectively. Material properties of cortical bone were optimized using dynamic experimental data and the hex–shell model of the fourth rib and trabecular bone properties were taken from the literature. Overall, the reaction force–displacement relationship predicted by both all-hex and hex–shell models with nodes in the offset middle-cortical surfaces compared well with those measured experimentally for all the three ribs. With the exception of fracture locations, the predictions from all-hex and offset hex–shell models of the second and fourth ribs agreed better with experimental data than those from the tenth rib models in terms of reaction force at fracture (difference <15.4%), ultimate failure displacement and time (difference <7.3%), and cortical bone strains. The hex–shell models with shell nodes in outer cortical surfaces increased static reaction forces up to 16.6%, compared to offset hex–shell models. These results indicated that both all-hex and hex–shell modeling strategies were applicable for simulating rib responses and bone fractures for the loading conditions considered, but coarse hex–shell models with constant or variable shell thickness were more computationally efficient and therefore preferred.

Human versus sheep vertebral cortical bone strain and intervertebral disc mechanical properties

Human versus sheep vertebral cortical bone strain and intervertebral disc mechanical properties

Effects of prosthesis design and impression techniques on human cortical bone strain around oral implants under load

Purpose The purpose of this study was to evaluate the effects of two different prosthetic designs (screw-retained versus cement-retained) and two impression techniques (open versus closed tray) on bone-level strains around implants. Materials and methods Two Ø 4.1 mm × 10 mm Straumann implants were placed in the bilateral fibulas of six fresh cadavers; bone segments were removed en bloc. Twelve implant-level and six abutment-level (18 total) working casts were made to fabricate fixed partial dentures, resulting in three test groups: Group 1: closed-tray technique/implant-level model/screw-retained prostheses; Group 2: closed-tray technique/abutment-level model/cement-retained prostheses; Group 3: open-tray technique/implant-level model/screw-retained prostheses. Linear strain-gauges were bonded to the cortical bone between implants and the lateral wall of the fibula in close proximity to the implant necks in each bone fragment. Strain-gauge signals were digitized by a data acquisition system and corresponding software at a sample rate of 10 KHz, simultaneously monitored from the computer during application of an external static load of 150 N on the middle of the pontic, using a loading frame. Results The approximal and lateral strains were extremely similar in both prosthetic groups ( p > 0.05). Within-group comparisons for the indirect impression technique showed that approximal and lateral strains in screw- and cement-retained prostheses were similar ( p > 0.05). Neither the prostheses design nor the impression technique had any discernable effect on bone-level strain. Conclusion Strains on the cortical bone around two implant supported, 3-unit screw- or cement-retained fixed prostheses, fabricated either by direct or indirect impression techniques on Straumann dental implants, are similar under a 150 N static load.

Finite element analysis of cortical bone strain induced by self-drilling placement of orthodontic microimplant

Finite element analysis of cortical bone strain induced by self-drilling placement of orthodontic microimplant

Understanding site-specific residual strain and architecture in bovine cortical bone

Living bone is considered as adaptive material to the mechanical functions, which continually undergoes change in its histological arrangement with respect to external prolonged loading. Such remodeling phenomena within bone depend on the degree of stimuli caused by the mechanical loading being experienced, and therefore, are specific to the sites. In the attempts of understanding strain adaptive phenomena within bones, different theoretical models have been proposed. Also, the existing literatures mostly follow the measurement of surface strains using strain gauges to experimentally quantify the strains experienced in the functional environment. In this work, we propose a novel idea of understanding site-specific functional adaptation to the prolonged load in bone on the basis of inherited residual strains and structural organization. We quantified the residual strains and amount of apatite crystals distribution, i.e., the degree of orientation, using X-ray diffraction procedures. The sites of naturally existing hole in bone, called foramen, are considered from bovine femur and metacarpal samples. Significant values of residual strains are found to exist in the specimens. Trends of residual strains noted in the specimens are mostly consistent with the degree of orientation of the crystallites. These features explain the response behavior of bone to the mechanical loading history near the foramen sites. Preferential orientation of crystals mapped around a femoral foramen specimen showed furnished tailored arrangement of the crystals around the hole. Effect of external loading at the femoral foramen site is also explained by the tensile loading experiment.

Lateral Insertion Points in Antegrade Femoral Nailing and Their Influence on Femoral Bone Strains

Insertion of rigid uniplane bent femoral nails through the piriform fossa has been reported to cause neurovascular complications. New nails were designed for more lateral entry points. However, these may be associated with a higher risk of iatrogenic fractures. This study investigated if two differently bent nails with more lateral entry points induce higher cortical bone strains than a uniplane bent nail introduced through the piriform fossa. Three groups of 8 cadaveric femurs were instrumented using the following nail systems and entry points: Cannulated Femoral Nail, piriform fossa; Antegrade Femoral Nail, trochanteric tip; and helical nail, lateral of the trochanteric tip. During insertion, the maximum principal bone strains were recorded at 9 locations at the proximal femur and the diaphysis. The occurrence of iatrogenic fractures or fissures was documented. The highest strains recorded were between 2000 and 4500 mum/m and mainly located at the posterior aspect of the greater trochanter and at the medial side of the entry point. In most of these cases fissures or fractures occurred, the number of which was higher for the trochanteric tip group as compared with the other groups. This was thought to be due to the thin cortical walls as a result of the larger reamer diameter in this group. Low strains (below 2000 microm/m) occurred at the medial cortex where the laterally inserted nails were expected to impinge. Bone strains at the medial impingement location were low for all nails. Entry portals with thin cortical walls due to, for example, larger reamer diameters and a small greater trochanter seem to be more susceptible to insertion accuracy, which may influence strain and fissure or fracture occurrence. Furthermore, we do not recommend determination of the entry point of laterally inserted nails based solely on anatomic landmarks of the greater trochanter because this may influence insertion accuracy. This implies that biplanar imaging is important for accurate and safe insertion of laterally started nails.

A novel in vivo mouse model for mechanically stimulated bone adaptation – a combined experimental and computational validation study

To facilitate the investigation of bone formation, in vivo, in response to mechanical loading a caudal vertebra axial compression device (CVAD) has been developed to deliver precise mechanical loads to the fifth caudal vertebra (C5) of the C57BL/6 female mouse. A combined experimental and computational approach was used to quantify the micro-mechanical strain induced in trabecular and cortical components following static and dynamic loading using the CVAD. Cortical bone strains were recorded using micro-strain gages. Finite element (FE) models based on micro-computed tomography were constructed for all C5 vertebrae. Both theoretical and experimental cortical strains correlated extremely well (R 2>0.96) for a Young's modulus of 14.8 GPa, thus validating the FE model. In this study, we have successfully applied mechanical loads to the C5 murine vertebrae, demonstrating the potential of this model to be used for in vivo loading studies aimed at stimulating both trabecular and cortical bone adaptation.

Cortical bone strain during the placement of orthodontic microimplant studied by 3D finite element analysis

Cortical bone strain during the placement of orthodontic microimplant studied by 3D finite element analysis

Experimental Evaluation of Strain Shielding in Distal Femur in Revision TKA

Theoretical concerns about the use of cemented and press-fit stems in revision total knee arthroplasty (TKA) include stress shielding with adverse effects on prosthesis fixation. Radiological studies have showed distal femoral bone resorption after revision TKA. The revision with use of stems can place abnormal stresses. These stresses can promote the effect of bone stress shielding and may contribute to bone loss. Experimental quantification of strain shielding in the distal synthetic femur following TKA is the main purpose of the present study. Three different constructs of TKA were assessed. The first construct included a stemless femoral component. The other two included a press-fit and a cemented femoral stem. Cortical bone strains were measured experimentally with tri-axial strain gauges in synthetic femurs before and after in-vitro knee surgery. The difference between principal strains of implanted and intact femur was calculated for each strain gauge position. This study indicates that the use of stems in distal femur changes the distribution and magnitude of bone strains. The press-fit stem provoked relevant bone area (stem length) subjected to strain shielding and also originated the highest reduction of strains in the distal region, which can potentially induce bone resorption. The stemless implanted femur produced minor bone strain changes relatively to the intact femur. The use of distal femur stems increases initial stability in the bone, but the observed reduction of strains in this region, relative to the intact femur, provokes strain shielding that can induce bone resorption and may compromise the long term implant stability.