Search

Contains fulltext : 300108.pdf (Publisher’s version ) (Open Access), BACKGROUND: Medial patellofemoral ligament (MPFL) reconstruction is associated with high complication rates because of graft overloading from incorrect graft positioning. To improve clinical outcomes, it is crucial to gain a better understanding of MPFL elongation patterns. PURPOSE: To assess MPFL length changes in healthy knees from 0° to 90° of dynamic flexion and their relationship with anatomic parameters of the patellofemoral joint. STUDY DESIGN: Descriptive laboratory study. METHODS: Dynamic computed tomography scans of an active flexion-extension-flexion movement in 115 knees from 63 healthy participants were evaluated to construct knee joint models. Using these models, the MPFL length was measured as the shortest wrapping path from the Schöttle point on the femur to 3 insertion points on the superomedial border of the patella (proximal, central, and distal). MPFL length changes (%) relative to the length in full extension were calculated, and their correlations with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination were analyzed. RESULTS: The proximal fiber was the longest in full extension and progressively decreased to a median length of -6.0% at 90° of flexion. The central fiber exhibited the most isometric pattern during knee flexion, showing a median maximal decrease of 2.8% relative to the full extension length and no evident elongation. The distal fiber first slightly decreased in length but increased at deeper flexion angles. The median overall length changes were 4.6, 4.7, and 5.7 mm for the proximal, central, and distal patellar insertion, respectively. These values were either not or very weakly correlated with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination when the anatomic parameters were within the healthy range. CONCLUSION: The median MPFL length changed by approximately 5 mm between 0° and 90° of flexion. Proximally, the length c, 01 december 2023

Contains fulltext : 249592.pdf (Publisher’s version ) (Open Access), Recently, it was shown that fracture risk assessment in patients with femoral bone metastases using Finite Element (FE) modeling can be performed using a calibration phantom or air-fat-muscle calibration and that non-patient-specific calibration was less favorable. The purpose of this study was to investigate if phantomless calibration can be used instead of phantom calibration when different CT protocols are used. Differences in effect of CT protocols on Hounsfield units (HU), calculated bone mineral density (BMD) and FE failure loads between phantom and two methods of phantomless calibrations were studied. Five human cadaver lower limbs were scanned atop a calibration phantom according to a standard scanning protocol and seven additional commonly deviating protocols including current, peak kilovoltage (kVp), slice thickness, rotation time, field of view, reconstruction kernel, and reconstruction algorithm. The HUs of the scans were calibrated to BMD (in mg/cm3) using the calibration phantom as well as using air-fat-muscle and non-patient-specific calibration, resulting in three models for each scan. FE models were created, and failure loads were calculated by simulating an axial load on the femur. HU, calculated BMD and failure load of all protocols were compared between the three calibration methods. The different protocols showed little variation in HU, BMD and failure load. However, compared to phantom calibration, changing the kVp resulted in a relatively large decrease of approximately 10% in mean HU and BMD of the trabecular and cortical region of interest (ROI), resulting in a 13.8% and 13.4% lower failure load when air-fat-muscle and non-patient-specific calibrations were used, respectively. In conclusion, while we observed significant correlations between air-fat-muscle calibration and phantom calibration as well as between non-patient-specific calibration and phantom calibration, our sample size was too small to prove that either of these calibration app

Contains fulltext : 245177.pdf (Publisher’s version ) (Open Access), PURPOSE: Accurate identification of metastatic lesions is important for improvement in biomechanical models that calculate the fracture risk of metastatic bones. The aim of this study was therefore to assess the inter- and intra-operator reliability of manual segmentation of femoral metastatic lesions. METHODS: CT scans of 54 metastatic femurs (19 osteolytic, 17 osteoblastic, and 18 mixed) were segmented two times by two operators. Dice coefficients (DCs) were calculated adopting the quantification that a DC˃0.7 indicates good reliability. RESULTS: Generally, rather poor inter- and intra-operator reliability of lesion segmentation were found. Inter-operator DCs were 0.54 (± 0.28) and 0.50 (± 0.32) for the first and second segmentations, respectively, whereas intra-operator DCs were 0.56 (± 0.28) for operator I and 0.71 (± 0.23) for operator II. Larger lesions scored significantly higher DCs in comparison with smaller lesions. Of the femurs with larger mean segmentation volumes, 83% and 93% were segmented with good inter- and intra-operator DCs (> 0.7), respectively. There was no difference between the mean DCs of osteolytic, osteoblastic, and mixed lesions. CONCLUSION: Manual segmentation of femoral bone metastases is very challenging and resulted in unsatisfactory mean reliability values. There is a need for development of a segmentation protocol to reduce the inter- and intra-operator segmentation variation as the first step and use of computer-assisted segmentation tools as a second step as this study shows that manual segmentation of femoral metastatic lesions is highly challenging.

Radboud University, 18 december 2019, Promotor : Verdonschot, N.J.J. Co-promotores : Tanck, E.J.M., Linden, Y.M. van der, Contains fulltext : 212651.pdf (publisher's version ) (Open Access)

Radboud University, 17 april 2018, Promotor : Verdonschot, N.J.J. Co-promotores : Tanck, E.J.M., Linden, Y.M. van der, Contains fulltext : 187343.pdf (publisher's version ) (Open Access)

Radboud Universiteit Nijmegen, 19 november 2015, Promotores : Verdonschot, N.J.J., Jonkers, I. Co-promotores : Tanck, E.J.M., Linden, Y.M. van der, Contains fulltext : 145312.pdf (publisher's version ) (Open Access)

Contains fulltext : 154438.pdf (publisher's version ) (Open Access), BACKGROUND: Exams in anatomy courses are traditionally summative. Formative testing induces retrieval practice, provides feedback and enhances learning results. We investigated the optimal frequency for retrieval practice during an anatomy course. METHOD: During a first-year course, students were offered four online daily quizzes a week that assessed thoracic anatomy. Once a week they received a quiz about abdominal anatomy. Students immediately received feedback afterwards. In the fourth course week, a survey about participation and satisfaction was taken. 424 students participated in the final summative exam. Trunk wall questions were used as a control. Relationship between participation and test results was investigated with a one-way ANOVA. RESULTS: More frequent participation in formative tests was correlated to higher scores in the summative exam with no difference between daily and weekly quizzes. This effect was found for thorax-abdomen and 'control' trunk wall questions. Participation in weekly quizzes was higher (p < 0.001). All survey responses showed a significant difference in favour of the weekly quiz (p < 0.001). DISCUSSION AND CONCLUSION: Participation in formative quizzes was correlated to summative exam scores. This correlation was not specific for the material tested, probably because of diligence. Student participation and preference were much higher in weekly quizzes.

Item does not contain fulltext, Femoral fractures are a major health issue. Most experimental and finite element (FE) fracture studies use polymethylmethacrylate cups on the greater trochanter (GT) to simulate fall impact loads. However, in vivo fall studies showed that the femur is loaded distally from the GT. Our objective was to incorporate in vivo fall data in FE models to determine the effects of loading position and direction, and size of simulated impact site on the fracture load and fracture type for a healthy and an osteoporotic femur. Twelve sets of loading position and angles were applied through 'near point loads' on the models. Additional simulations were performed with 'cup loads' on the GT, similar to the literature. The results showed no significant difference between fracture loads from simulations with near point loads distally from the GT and those with cup loads on the GT. However, simulated fracture types differed, as near point loads distally from the GT generally resulted in various neck fractures, whilst cup load simulations predicted superior neck and trochanteric fractures only. This study showed that incorporating in vivo fall assessments in FE models by loading the models distally from the GT results in prediction of realistic fracture loads and fracture types.

Contains fulltext : 133899.pdf (publisher's version ) (Open Access), Many students in Biomedical Sciences have difficulty understanding biomechanics. In a second-year course, biomechanics is taught in the first week and examined at the end of the fourth week. Knowledge is retained longer if the subject material is repeated. However, how does one encourage students to repeat the subject matter? For this study, we developed 'two opportunities to practice per day (TOPday)', consisting of multiple-choice questions on biomechanics with immediate feedback, which were sent via e-mail. We investigated the effect of TOPday on self-confidence, enthusiasm, and test results for biomechanics. All second-year students (n = 95) received a TOPday of biomechanics on every regular course day with increasing difficulty during the course. At the end of the course, a non-anonymous questionnaire was conducted. The students were asked how many TOPday questions they completed (0-6 questions [group A]; 7-18 questions [group B]; 19-24 questions [group C]). Other questions included the appreciation for TOPday, and increase (no/yes) in self-confidence and enthusiasm for biomechanics. Seventy-eight students participated in the examination and completed the questionnaire. The appreciation for TOPday in group A (n = 14), B (n = 23) and C (n = 41) was 7.0 (95 % CI 6.5-7.5), 7.4 (95 % CI 7.0-7.8), and 7.9 (95 % CI 7.6-8.1), respectively (p < 0.01 between A and C). Of the students who actively participated (B and C), 91 and 80 % reported an increase in their self-confidence and enthusiasm, respectively, for biomechanics due to TOPday. In addition, they had a higher test result for biomechanics (p < 0.01) compared with those who did not actively participate (A). In conclusion, the teaching method 'TOPday' seems an effective way to encourage students to repeat the subject material, with the extra advantage that students are stimulated to keep on practising for the examination. The appreciation was high and there was a positive association between active participation

Item does not contain fulltext, There is an urgent need to improve the prediction of fracture risk for cancer patients with bone metastases. Pathological fractures that result from these tumors frequently occur in the femur. It is extremely difficult to determine the fracture risk even for experienced physicians. Although evolving, fracture risk assessment is still based on inaccurate predictors estimated from previous retrospective studies. As a result, many patients are surgically over-treated, whereas other patients may fracture their bones against expectations. We mechanically tested ten pairs of human cadaveric femurs to failure, where one of each pair had an artificial defect simulating typical metastatic lesions. Prior to testing, finite element (FE) models were generated and computed tomography rigidity analysis (CTRA) was performed to obtain axial and bending rigidity measurements. We compared the two techniques on their capacity to assess femoral failure load by using linear regression techniques, Student's t-tests, the Bland-Altman methodology and Kendall rank correlation coefficients. The simulated FE failure loads and CTRA predictions showed good correlation with values obtained from the experimental mechanical testing. Kendall rank correlation coefficients between the FE rankings and the CTRA rankings showed moderate to good correlations. No significant differences in prediction accuracy were found between the two methods. Non-invasive fracture risk assessment techniques currently developed both correlated well with actual failure loads in mechanical testing suggesting that both methods could be further developed into a tool that can be used in clinical practice. The results in this study showed slight differences between the methods, yet validation in prospective patient studies should confirm these preliminary findings.

Radboud Universiteit Nijmegen, 2 juli 2013, Promotor : Verdonschot, N.J.J. Co-promotores : Homminga, J.J., Tanck, E.J.M., Contains fulltext : 112258.pdf (publisher's version ) (Open Access)

Item does not contain fulltext, Sideways falls onto the hip are a major cause of femoral fractures in the elderly. Martial arts (MA) fall techniques decrease hip impact forces in sideways falls. The femoral fracture risk, however, also depends on the femoral loading configuration (direction and point of application of the force). The purpose of this study was to determine the effect of fall techniques, landing surface and fall height on the impact force and the loading configuration in sideways falls. Twelve experienced judokas performed sideways MA and Block ('natural') falls on a force plate, both with and without a judo mat on top. Kinematic and force data were analysed to determine the hip impact force and the loading configuration. In falls from a kneeling position, the MA technique reduced the impact force by 27%, but did not change the loading configuration. The use of the mat did not change the loading configuration. Falling from a standing changed the force direction. In all conditions, the point of application was distal and posterior to the greater trochanter, but it was less distal and more posterior in falls from standing than from kneeling position. The present decrease in hip impact force with an unchanged loading configuration indicates the potential protective effect of the MA technique on the femoral fracture risk. The change in loading configuration with an increased fall height warrant further studies to examine the effect of MA techniques on fall severity under more natural fall circumstances.

Item does not contain fulltext, Although asymmetric yielding in bone is widely shown in experimental studies, previous case-specific non-linear finite element (FE) studies have mainly adopted material behaviour using the Von Mises yield criterion (VMYC), assuming equal bone strength in tension and compression. In this study, it was verified that asymmetric yielding in FE models can be captured using the Drucker-Prager yield criterion (DPYC), and can provide better results than simulations using the VMYC. A sensitivity analysis on parameters defining the DPYC (i.e. the degree of yield asymmetry and the yield stress settings) was performed, focusing on the effect on bone failure. In this study, the implementation of a larger degree of yield asymmetry improved the prediction of the fracture location; variations in the yield stress mainly affected the predicted failure force. We conclude that the implementation of asymmetric yielding in case-specific FE models improves the prediction of femoral bone strength.

Contains fulltext : 96432.pdf (publisher's version ) (Closed access), STUDY DESIGN: In vitro biomechanical study. OBJECTIVE: To measure the effect that off-axis vertebral loading has on the stiffness and failure load of vertebrae. SUMMARY OF BACKGROUND DATA: Adjacent level vertebral fractures not only are common in patients who received a vertebroplasty treatment but also occur in patients with conservatively treated wedge fractures. The wedge-like deformity, which is present in both groups, changes the spinal alignment. The load of vertebrae adjacent to the fractured vertebra will change from perpendicular to the endplate to a more shearing, off-axis, load. This change may induce a higher fracture risk for vertebrae adjacent to wedge-like deformed vertebrae. METHODS: Twenty vertebrae, harvested from one osteopenic cadaver spine and three osteoporotic cadaver spines, were loaded until failure. The vertebrae were loaded either perpendicular to the upper endplate, representing vertebrae in a spine without wedge fractures (0 degrees group, n = 10), or at an angle of 20 degrees , representing vertebrae adjacent to a wedge fracture (20 degrees groups, n = 10). Vertebral failure load and stiffness were the most important outcome measures. RESULTS: The failure load was significantly higher (P 5 0.028) when tested at 0 degrees (2854 N, SD 5 622 N), compared with vertebrae tested at 20 degrees (2162 N, SD 5 670 N). Vertebrae were also significantly stiffer (P, 0.001) when tested at 0 degrees (4017 N/mm, SD 5 970 N/mm) than those tested at 20 degrees (2478 N/mm, SD 5 453 N/mm). CONCLUSION: The failure load of osteopenic/osteoporotic vertebrae was 24% lower under off-axis loads (20 degrees ) than under axial loads (0 degrees ). This study may lead to a better understanding of the etiology of adjacent vertebral fractures after wedge-like deformities and demonstrates the importance of height reconstruction of wedge fractures in order to normalize the loading conditions on adjacent vertebrae.

Contains fulltext : 88094.pdf (Publisher’s version ) (Open Access), Bone specific, CT-based finite element (FE) analyses have great potential to accurately predict the fracture risk of deteriorated bones. However, it has been shown that differences exist between FE-models of femora scanned in a water basin or scanned in situ within the human body, as caused by differences in measured bone mineral densities (BMD). In this study we hypothesized that these differences can be reduced by re-creating the patient CT-conditions by using an anatomically shaped physical model of the lower body. BMD distributions were obtained from four different femora that were scanned under three conditions: (1) in situ within the cadaver body, (2) in a water basin and (3) in the body model. The BMD of the three scanning protocols were compared at two locations: proximally, in the trabecular bone of the femoral head, and in the cortical bone of the femoral shaft. Proximally, no significant differences in BMD were found between the in situ scans and the scans in the body model, whereas the densities from the water basin scans were on average 10.8% lower than in situ. In the femoral shaft the differences between the three scanning protocols were insignificant. In conclusion, the body model better approached the in situ situation than a water basin. Future studies can use this body model to mimic patient situations and to develop protocols to improve the performance of the FE-models in actual patients.

Item does not contain fulltext

Contains fulltext : 81864.pdf (publisher's version ) (Closed access), PURPOSE: In clinical practice, there is an urgent need to improve the prediction of fracture risk for cancer patients with bone metastases. The methods that are currently used to estimate fracture risk are dissatisfying, hence affecting the quality of life of patients with a limited life expectancy. The purpose of this study was to assess if non-linear finite element (FE) computer models, which are based on Quantitative Computer Tomography (QCT), are better than clinical experts in predicting bone strength. MATERIALS AND METHODS: Ten human cadaver femurs were scanned using QCT. In one femur of each pair a hole (size 22, 40, or 45 mm diameter) was drilled at the anterior or medial side to simulate a metastatic lesion. All femurs were mechanically tested to failure under single-limb stance-type loading. The failure force was calculated using non-linear FE-models, and six clinical experts were asked to rank the femurs from weak to strong based on X-rays, gender, age, and the loading protocol. Kendall Tau correlation coefficients were calculated to compare the predictions of the FE-model with the predictions of the clinicians. RESULTS: The FE-failure predictions correlated strongly with the experimental failure force (r(2)=0.92, p<0.001). For the clinical experts, the Kendall Tau coefficient between the experimental ranking and predicted ranking ranged between tau=0.39 and tau=0.72, whereas this coefficient was considerably higher (tau=0.78) for the FE-model. CONCLUSION: This study showed that the use of a non-linear FE-model can improve the prediction of bone strength compared to the prediction by clinical experts.

Contains fulltext : 79634.pdf (publisher's version ) (Open Access)

Contains fulltext : 69065.pdf (publisher's version ) (Closed access), The process of bone remodeling is carried out by 'basic multicellular units' of osteoclasts and osteoblasts. Osteoclasts excavate a resorption space that is subsequently filled with new bone by osteoblasts. In cortical bone osteoclasts dig tunnels through solid bone, in cancellous bone they dig trenches across the trabecular surface. Osteoblasts fill these tunnels and trenches, creating osteons and hemi-osteons, respectively. Both the osteons of cortical bone and the trabeculae of cancellous bone are aligned to the dominant loading direction, indicating that BMU's are mechanically regulated. How mechanical forces guide these cells is still uncertain. We hypothesize that strain-induced osteocyte signals inhibit osteoclast activity and stimulate osteoblast activity. This hypothesis was implemented in a finite element-based bone adaptation model, that was extended with a cell simulation model. This allowed us to examine tunneling and trenching by osteoclasts. We found that our simulations capture key features of BMU-based remodeling: (1) cortical BMU's create load-aligned osteons; (2) cancellous BMU's move across the surface of trabeculae instead of piercing them; (3) resorption-formation coupling occurs in response to strains around resorption sites; and (4) resorbing osteoclasts target nearby regions of osteocyte death, thus providing a mechanism for bone repair.

Contains fulltext : 69732.pdf (publisher's version ) (Closed access), Bone densitometry measurements are performed to predict the fracture risk in bones. However, the sensitivity of these predictions are not satisfactory. One of the explanations is that densitometry ignores the (architectural) structural aspects of the bone. The effects of varying architectural parameters on the densitometry parameters can be effectively assessed by considering a 3-D image of a bone and vary the bone structure parameters in a controlled manner and determine the consequence of these changes on a simulated (virtual) densitometry analysis. In this paper we present such a computer simulation of densitometry analysis of bone. The simulation allows quantification of densitometry parameters, such as BMD and BMC, on the basis of computed tomography bone scans. The aim of the presented study is the evaluation of our method by comparing its results to the results from real densitometry (DEXA) tests. For the evaluation we selected three femoral bones. These items were CT scanned and individual computer models were created. In addition, the densitometry parameters of these items were assessed by a clinical DEXA scanner. The densitometry parameters obtained from the simulations were very close to the results from the DEXA densitometry measurements. We therefore conclude that our method can be employed in the research on the influence of changes in bone structure on densitometry test results.

Contains fulltext : 49817.pdf (publisher's version ) (Closed access), The paradigm that bone metabolic processes are controlled by osteocyte signals have been the subject of investigation in many recent studies. One hypothesis is that osteoblast formation is enhanced by these signals, and that osteoclast resorption is enhanced by the lack of them. Reduced, or absent, osteocyte signaling can be an effect of reduced mechanical loading (disuse) or of defects in the canalicular network, due to microcracks. This would mean that bone is resorbed precisely there where it is mostly needed. In our study, we addressed this apparent contradiction. The purpose was to investigate how alternative strain-based local stimuli for osteoclasts to resorb bone would affect remodeling and adaptation of the trabecular architecture. For this purpose, a computer-simulation model was used, which couples morphological and mechanical effects of local bone metabolism to changes in trabecular architecture and density at large. Six resorption characteristics were studied in the model: (I) resorption occurs spatially random, (II) resorption is enhanced or (III) strongly enhanced where there is disuse, (IV) resorption is enhanced or (V) strongly enhanced where there are high strains, i.e. overload, and (VI) resorption is enhanced where there is disuse and where there are high strains. Results showed that the rates of structural adaptation to alternative loading were higher for disuse-controlled resorption than for overload-controlled resorption. Architecture and mass remained stable for all cases except (V) in which the structure deteriorated as in osteoporotic bone. We conclude that, given the potential of osteoblasts to form bone in highly strained areas, based on signals from osteocytes, osteoclast resorption can normally be compensated for.

Contains fulltext : 50729.pdf (publisher's version ) (Closed access), INTRODUCTION: Osteoporosis (OP) and osteoarthritis (OA) are both common diseases in the elderly, but remarkably seldom coexist. The bone defects that are related to both diseases develop with increasing age, which suggests that they are related to some form of imperfect bone remodeling. Current opinion holds that the bone remodeling process is supervised by bone cells that respond to mechanical stimuli. An imperfect response of bone cells to mechanical stimuli might thus relate to imperfect bone remodeling, which could eventually lead to a lack bone mass and strength, such as in OP patients. MATERIALS: To investigate whether the cellular response to mechanical stress differs between OP and OA patients, we compared the response of bone cells from both groups to fluid shear stress of increasing magnitude. Bone cells from 9 female OP donors (age 60-90 year) and 9 female age-matched OA donors were subjected to pulsating fluid flow (PFF) of low (0.4+/-0.1 Pa at 3 Hz), medium (0.6+/-0.3 Pa at 5 Hz), or high shear stress (1.2+/-0.4 at 9Hz), or were kept under static culture conditions. RESULTS: We found subtle differences in the shear-stress response of the two groups, measured as nitric oxide (NO) and prostaglandin E2 (PGE2) production. The NO-response to shear stress was higher in the OP than the OA cells, while the PGE2-response was higher in the OA cells. CONCLUSIONS: Assuming that NO and PGE2 play a role in cell-cell communication during remodeling, these results suggest that slight differences in mechanotransduction might relate to the opposite bone defects in osteoporosis and osteoarthritis.

Contains fulltext : 51270.pdf (publisher's version ) (Closed access)

Contains fulltext : 51134.pdf (publisher's version ) (Closed access), Longitudinal growth of long bones takes place at the growth plates. The growth plate produces new bone trabeculae, which are later resorbed or merged into the cortical shell. This process implies transition of trabecular metaphyseal sections into diaphyseal sections. We hypothesize that the development of cortical bone is governed by mechanical stimuli. We also hypothesize that trabecular and cortical bone share the same regulatory mechanisms for adaptation to mechanical loads. To test these hypotheses, we monitored the development of the tibial cortex in growing pigs, using micro-computer tomography and histology. We then tested the concept that regulatory mechanisms for trabecular bone adaptation can also explain cortical bone development using our mechanical stimulation theory, which could explain trabecular bone (re)modelling. The main results showed that, from the growth plate towards the diaphysis, the pores of the trabecular structure were gradually filled in with bone, which resulted in increased density and cortical bone. The computer model largely predicted this morphological development. We conclude that merging of metaphyseal trabeculae into cortex is likely to be governed by mechanical stimuli. Furthermore, cortex development of growing long bones can be explained as a form of trabecular bone adaptation, without the need for different regulatory mechanisms for cortical and trabecular bone.

Contains fulltext : 48714.pdf (publisher's version ) (Closed access), Mechanical loading is thought to provoke a cellular response via loading-induced flow of interstitial fluid through the lacuno-canalicular network of osteocytes. This response supposedly leads to an adaptation of local bone mass and architecture. It has been suggested that loss of estrogen during menopause alters the sensitivity of bone tissue to mechanical load, thereby contributing to the rapid loss of bone. The present study aimed to determine whether estrogen modulates the mechanoresponsiveness of bone cells from osteoporotic women. Bone cell cultures from nine osteoporotic women (aged 62-90 years) were pre-cultured for 24 h with 10(-11) mol/l 17beta-estradiol (E2) or vehicle, and subjected to 1 h of pulsating fluid flow (PFF) or static culture. E2 alone enhanced prostaglandin E(2) (PGE(2)) and nitric oxide (NO) production by 2.8-fold and 2.0-fold, respectively, and stimulated endothelial nitric oxide synthase protein expression by 2.5-fold. PFF, in the absence of E2, stimulated PGE(2) production by 3.1-fold and NO production by 3.9-fold. Combined treatment with E2 and PFF increased PGE(2) and NO production in an additive manner. When expressed as PFF-treatment-over-control ratio, the response to fluid shear stress was similar in the absence or presence of E2. These results suggest that E2 does not affect the early response to stress in bone cells. Rather, E2 and shear stress both promote the production of paracrine factors such as NO and PGE(2) in an additive manner.

Contains fulltext : 59366.pdf (publisher's version ) (Closed access), The purpose of this study was to examine the effect of mineralization on the mechanical properties of embryonic bone rudiments. For this purpose, four-point bending experiments were performed on unmineralized and mineralized embryonic mouse ribs at 16 and 17 days of gestational age. Young's modulus was calculated using force-displacement data from the experiment in combination with finite element analysis (FEA). For the unmineralized specimens, a calculated average for the Young's modulus of 1.11 (+/- 0.62) MPa was established after corrections for sticking to the four-point bending device and aspect ratio, which is the ratio between the length of the bone and its diameter. For the mineralized specimens, the value was 117 (+/- 62) MPa after corrections. Hence, Young's moduli of embryonic bone rudiments increase by two orders of magnitude within 1 day, during endochondral ossification. As an effect, the hypertrophic chondrocytes in the calcifying cartilage experience a significant change in their mechanical environment. The chondrocytes are effectively stress shielded, which means that they do not carry stresses since stresses are supported by the stiffest parts of the tissue, which are in this case the diaphyseal cortex and the calcified matrix. The deformability of the hypertrophic chondrocytes is, therefore, severely reduced. Since the transition is so sudden and enormous, it can be seen as a process of 'catastrophic' proportion for the hypertrophic chondrocytes. The subsequent resorption of calcified cartilage and the expansion of the marrow cavity could be consequential to stress shielding.

Item does not contain fulltext, In this study, we investigate how morphological parameters and mechanical properties derived from microcomputed tomography (microCT) are affected by small errors in threshold value when variable bone structures and different bone volume fractions are involved. For this purpose, biopsies of vertebrae of 6-, 23-, and 230-week-old female pigs were scanned using microCT. For each specimen, five threshold values were determined within the range of thresholds that an observer could select realistically, in steps of 0.5%. The scans were converted to microfinite-element (microFE) models, used to determine the elastic moduli. A variation of 0.5% in threshold resulted in a 5% difference in bone volume fraction and 9% difference in maximal stiffness for bone cubes with a volume fraction of <0.15. When the volume fraction was >0.2, these differences were only 2% and 3%, respectively. For all bone cubes, the differences for trabecular thickness and bone surface density were <3%. The effects on morphological anisotropy and trabecular number were negligible for threshold variations of 0.5%. These findings suggest that threshold selection is important for the accurate determination of volume fraction and mechanical properties, especially for low bone volume fractions; the architectural directionality is less sensitive to changes in threshold.

Item does not contain fulltext, In mature trabecular bone, both density and trabecular orientation are adapted to external mechanical loads. Few quantitative data are available on the development of architecture and mechanical adaptation in juvenile trabecular bone. We studied the hypothesis that a time lag occurs between the adaptation of trabecular density and the adaptation of trabecular architecture during development. To investigate this hypothesis we used ten female pigs at 6, 23, 56, 104, and 230 weeks of age. Three-dimensional morphological and mechanical parameters of trabecular bone samples from the vertebra and proximal tibia were studied using microcomputed tomography and micro-finite element analysis. Both bone volume fraction and stiffness increased rapidly in the initial growth phase (from 6 weeks on), whereas the morphological anisotropy started increasing only after 23 weeks of age. In addition, the anisotropy reached its highest value much later in the development than did bone volume fraction. Hence, the alignment of trabeculae was still progressing at the time of peak bone mass. Therefore, our hypothesis was supported by the time lag between the increase in trabecular density and the adaptation of the trabecular architecture. The rapid increase of bone volume fraction in the initial growth phase can be explained by the enormous weight increase of the pigs. The trabeculae aligned at later stages when the increase in weight, and thus the loading, was slowed considerably compared with the early growth stage. Hence, the trabecular architecture was more efficient in later years. We conclude that density is adapted to external load from the early phase of growth, whereas the trabecular architecture is adapted later in the development.

KUN, 11 juni 2001, Promotores : Huiskes, R., Burger, E.H., Contains fulltext : 144673.pdf (publisher's version ) (Open Access)

Item does not contain fulltext

Item does not contain fulltext

Item does not contain fulltext

Item does not contain fulltext