1,721,212 research outputs found
Strain
No full textStrain is a long-standing international journal that contains leading-edge research on the measurement of the mechanical behavior of structures and systems. The journal includes publications from all engineering disciplines that deal with material behavior and degradation under load, structural design, and measurement methodologies in the field of experimental mechanics. Although the thrust of the journal is experimental, numerical simulations and validation are included in the coverage.
Strain welcomes contributions on novel work in the following areas:
experimental mechanics
non-destructive evaluation techniques
numerical analysis, simulation and validation
residual stress measurement techniques
design of composite structures and components
impact behaviour of materials and structures
signal and image processing
transducer and sensor design
structural health monitoring
biomechanics
extreme environment
micro- and nano-scale testing
Strain has been founded by and is associated to the British Society of Strain Measurements (www.BSSM.org)
A critical analysis of stress shielding evaluation of hip prostheses
No full textIn vitro evaluation of the load transfer of hip prostheses has been performed in recent years for the purpose of understanding the stress shielding phenomena. Over 200 papers were reviewed to determine if a standard exists to evaluate and compare the performance of hip stems. Surprisingly, it was found that little agreement exists in the testing protocol. This makes it very difficult to compare the results reported in different investigations. In several cases very incomplete data are reported about the testing conditions, thus making it impossible to compare the results. This article focuses on: (1) how the loading conditions should be chosen based on physiological loading in a way to give a reproducible setup; (2) how the femur should be constrained; (3) how to generate the same system of loads in the intact and the implanted femur; (4) how to define a reference system: (5) how the specimen type and sample size are chosen. (6) the advantages and limitations of the different strain measurement techniques; (7) how the testing parameters have been chosen in the literature; and (8) how the accuracy of the results has been reported in the literature
Standardization of hemipelvis alignment for in vitro biomechanical testing
Full text linkAlthough in vitro biomechanical tests are regularly performed, the definition of a suitable reference frame for hemipelvic specimens is still a challenge. The aims of the present study were to: (i) define a reference frame for the human hemipelvis suitable for in vitro applications, based on robust anatomical landmarks; (ii) identify the alignment of a hemipelvis based on the alignment of a whole pelvis (including right/left and male/female differences); (iii) identify the relative alignment of the proposed in vitro reference frame with respect to a reference frame commonly used in gait analysis; (iv) create an in vitro alignment procedure easy, robust and inexpensive; (v) quantify the intra-operator repeatability and inter-operator reproducibility of the procedure. A procedure to univocally identify the anatomical landmarks was created, exploiting the in vitro accessibility of the specimen's surface. Through the analysis on 53 CT scans (106 hemipelvises), the alignment of the hemipelvis based on the alignment of a whole pelvis was analyzed: differences between male/female and right/left hemipelvises were not statistically significant To overcome the uncertainty in the identification of the acetabular rim, a standard acetabular plane was defined. An alignment procedure was developed to implement such anatomical reference frame. The intra-operator repeatability and the inter-operator reproducibility were quantified with four operators, on male and female hemipelvises. The intra-operator repeatability was better than 1.5°. The inter-operator reproducibility was better than 2.0°. Alignment in the transverse plane was the most repeatable. The presented procedure to align hemipelvic specimens is sufficiently robust, standardized, and accessible. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1645–1652, 2018
The Size of Simulated Lytic Metastases Affects the Strain Distribution on the Anterior Surface of the Vertebra
No full textMetastatic lesions of the vertebra are associated with risk of fracture, which can be disabling and life-threatening. In the literature, attempts are found to identify the parameters that reduce the strength of a metastatic vertebra leading to spine instability. However, a number of controversial issues remain. Our aim was to quantify how the strain distribution in the vertebral body is affected by the presence and by the size of a simulated metastatic defect. Five cadaveric thoracic spine segments were subjected to non-destructive presso-flexion while intact, and after simulation of metastases of increasing size. For the largest defect, the specimens were eventually tested to failure. The full-field strain distribution in the elastic range was measured with digital image correlation (DIC) on the anterior surface of the vertebral body. The mean strain in the vertebra remained similar to the intact when the defects were smaller than 30% of the vertebral volume. The mean strains became significantly larger than in the intact for larger defects. The map of strain and its statistical distribution indicated a rather uniform condition in the intact vertebra and with defects smaller than 30%. Conversely, the strain distribution became significantly different from the intact for defects larger than 30%. A strain peak appeared in the region of the simulated metastasis, where fracture initiated during the final destructive test. This is a first step in understanding how the features of metastasis influence the vertebral strain and for the construction of a mechanistic model to predicted fracture
Does cement curing cause concerning increase of the temperature when delivered in the human humerus?
No full textFor the treatment of humeral fractures, numerous strategies exist to improve the clinical outcome of the reconstruction and to reduce the incidence of fixation failure. Injection of acrylic-based cements to reinforce the bone and/or augment the screws is one option. The heat generated during cement polymerization raises some concerns, as it could cause tissue damage. The first aim of this study was to measure the temperature over time during polymerization when acrylic cements are delivered inside the bone to treat fracture. The second aim was to assess if the ISO-5833:2002 standard can predict what happens in a real bone. Different tests were performed using two acrylic-based cements (Mendec and Cal-Cemex): (i) the ISO-5833:2002 standard (Annex C); (ii) tests on human bones (humeral diaphysis and humeral head) injected with cement to simulate fracture treatment. In the humeri, the highest temperature was measured in the diaphysis (68.6 °C for Mendec, 62.7°C for Cal-Cemex). These values are comparable with the temperature reached in other consolidated applications (vertebroplasty). Exposure to high temperature was shorter for the diaphysis than for the head. For both cements, in both the diaphysis and the head, temperatures exceeded 48°C for less than 10min. This is within the threshold for tissue necrosis. The ISO-5833:2002 yielded significantly different results in terms of maximum temperature (difference exceeding 15°C) and exposure to temperature above 48°C and 45°C. This discrepancy is probably due to a combination of factors affecting the amount of heat produced and dissipated (e.g., amount and shape of the cement, thermal conductivity)
Experimental errors in the application of photoelastic coatings on human femurs with uncemented hip stems
No full textThe investigation of the stress distribution in the proximal femur is of primary relevance when testing hip prostheses. Most of the in‐vitro research to date, has been conducted with strain gauges. However, the photoelastic coatings provide a field vision of the state of strain and of the most stressed points. The purpose of this work was to validate the application of photoelastic coatings to intact and implanted human femurs. Coatings of various thickness were bonded to two regions: the surface of the diaphysis, and the resection surface of the neck. A theoretical study was conducted on a geometrical model of the diaphysis to quantify some of the experimental errors. The reinforcing effect was found to be far the most important source of error for the coating of the diaphysis. Other possible sources of error such as Poisson's coefficient mismatch, incorrect light incidence angle and uneven coating thickness were also examined. Due to the uneven distribution of such errors, any correction seems impossible. The results must therefore be considered only qualitatively, as a complement to the strain gauging. The coating of the resection surface of the neck of the femur suffers much less from the reinforcing effect, but the coating is more sensitive to Poisson's coefficient mismatch. In this second application, quantitative results can be satisfactorily obtained. © 1994 Blackwell Publishing Lt
Accuracy of the planned vs achieved position of a cementless hip stem: a finite element study
No full textEditorial: Special Issue of the Italian Chapter of the European Society of Biomechanics dedicated to “Biomechanics for in silico clinical trials”
No full textThe 9th Meeting of the Italian Chapter of the European Society of Biomechanics (Bologna, 30 September - 1 October 2019) included a Thematic Symposium on “Biomechanics for in silico clinical trials”. Despite being a meeting of the National Chapter, it always has an international audience. This edition, also thanks to the Thematic Symposium, had a high number of papers with international authors (more than 20 papers out of 72), and international keynote speakers. We felt it was the right time to have a Thematic symposium on in silico trials, as this is definitely an emerging field, not quite mature yet for extensive deployment, and for this reason posing every day new challenges to scientists and to engineers. The choice of the topic is linked to the growing reliability and improved performance of computational models that are changing the approach to clinical tests. New pharmacological treatments, new devices and new surgical techniques can be tested through virtual models by means of numerical simulations. In this context, the understanding of the biomechanical mechanisms plays a fundamental role, since tissue mechanics is linked in a direct and indirect way to the evolution of physiological and pathological conditions. Although the road seems to be marked to favour the exit of the in silico world from laboratories to the clinical side, still a number of open challenges in the field of basic research, industrial developments and regulatory needs remain. The scientific community is then called for applied and interdisciplinary research efforts. The aim of this Special Issue is to collect to-date and advanced results in the field. Interestingly, this is collecting the effort not only of groups working in the field of numerical simulations, but also experimental ones, for the possible synergies. In particular, this Special Issue collect the best papers that were shortlisted by the Scientific Committee and by the Award Committees for the different awards assigned during the meeting
Reconstruction of proximal humeral fractures with a reduced number of screws and a reinforced bone substitute
Full text linkMulti-fragmented fractures of the proximal humerus are difficult to treat, especially in the case of osteoporotic bone. Intra-operative risks include cartilage damage when inserting multiple screws. A common post-operative complication is distal-varus collapse of the head. The aim of this study was to investigate if an Innovative technique (reduced number of screws and injection of a beta-TCP additivated partially resorbable cement) provides the same or better stability of the reconstructed head compared to the Standard technique (using more screws). A four-fragment fracture was simulated in six pairs of humeri, with partial removal of the cancellous bone to simulate osteoporotic “eggshell” defect. One humerus of each pair was repaired with a Standard (locking plate, 2 cortical and 6 locking screws), and the other with the Innovative technique (same plate, 2 cortical and only 3 locking screws, plus cement injection). The reconstructed specimens were subjected to a biomechanical test where a cyclic force of increasing amplitude was applied axially until failure. The Innovative reconstructions withstood a force 3.49 times larger than the contralateral Standard reconstructions before failure started. The maximum force before final collapse for the Innovative reconstructions was 4.24 times larger than the contralateral Standard reconstructions. These differences were statistically significant. The Innovative reconstructions, based on fewer screws and beta-TCP additivated acrylic cement, showed positive results, demonstrating better biomechanical properties compared to the Standard reconstructions. These laboratory findings, along with the advantages of a reduced number of screws, may help perform a surgically safer, and more effective procedure in osteoporotic patients
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