Different Levels Of Constraint Research Articles

Biomechanical analysis of different levels of constraint in TKA during daily activities

BackgroundNumerous total knee prosthetic implants are currently available on the orthopedic market, and this variety covers a set of different levels of constraint: among the various models available, a significant role is covered by mobile bearing cruciate-retaining design with an ultra-congruent insert, mobile bearing cruciate-retaining design, fixed-bearing posterior stabilized prosthesis and fixed-bearing constrained condylar knee. A biomechanical comparative study among them could therefore be helpful for the clinical decision-making process. This study aimed to compare the effect of these different levels of constraint in the knee biomechanics of a patient, in three different configurations representing the typical boundary conditions experienced by the knee joint during daily activities.MethodThe investigation was performed via finite element analysis with a knee model based on an already published and validated one. Four different types of prosthesis designs were analyzed: two mobile-bearing models and two fixed-bearing models, each one having a different level of constraint. The different designs were incorporated in to the 3D finite element model of the lower leg and analyzed in three different configurations reproducing the landing and the taking-off phases occurring during the gait cycle and chair-rising. Implant kinetics (in terms of polyethylene contact areas and contact pressure), polyethylene and tibial bone stresses were calculated under three different loading conditions for each design.ResultsThe tibial stress distribution in the different regions of interest of the tibia remains relatively homogeneous regardless of the type of design used. The main relevant difference was observed between the mobile and fixed-bearing models, as the contact areas were significantly different between these models in the different loading conditions. As a consequence, significant changes in the stress distribution were observed at the interface between the prosthetic components, but no significant changes were noted on the tibial bone. Moreover, the different models exhibited a symmetrical medial and lateral distribution of the contact areas, which was not always common among all the currently available prostheses (i.e. medial pivot designs).ConclusionThe changes of the prosthetic implant did not induce a big variation of the stress distribution in the different regions of the tibial bone, while they significantly changed the distribution of stress at the interface between the prosthetic components.

Relating matrix stress to local stress on a hard microstructural inclusion for understanding cleavage fracture in high strength steel

Macroscale cleavage fracture toughness of high strength steels is strongly related to the fracture of hard microstructural inclusions. Therefore, an accurate determination of the local stress on these inclusions based on the matrix stress is necessary for the statistical modelling of macroscale cleavage fracture. This paper presents analytical equations to quantitatively estimate the stress of the microstructural inclusions from the far-field stress of the matrix. The analytical equations account for the inclusion shape, the inclusion orientation, the far-field stress state and matrix material properties. Finite element modelling of a representative volume element containing a hard inclusion shows that the equations provide an accurate representation of the local stress state. The equations are implemented into a multi-barrier model and compared with CTOD experiments with two different levels of constraint.

Alternation between taxonomically divergent hosts is not the major determinant of flavivirus evolution.

Flaviviruses display diverse epidemiological and ecological features. Tick-borne and mosquito-borne flaviviruses (TBFV and MBFV, respectively) are important human pathogens that alternate replication in invertebrate vectors and vertebrate hosts. The Flavivirus genus also includes insect-specific viruses (ISFVs) and viruses with unknown invertebrate hosts. It is generally accepted that viruses that alternate between taxonomically different hosts evolve slowly and that the evolution of MBFVs and TBFVs is dominated by strong constraints, with limited episodes of positive selection. We exploited the availability of flavivirus genomes to test these hypotheses and to compare their rates and patterns of evolution. We estimated the substitution rates of CFAV and CxFV (two ISFVs) and, by taking into account the time-frame of measurement, compared them with those of other flaviviruses. Results indicated that CFAV and CxFV display relatively different substitution rates. However, these data, together with estimates for single-host members of the Flaviviridae family, indicated that MBFVs do not display relatively slower evolution. Conversely, TBFVs displayed some of lowest substitution rates among flaviviruses. Analysis of selective patterns over longer evolutionary time-frames confirmed that MBFVs evolve under strong purifying selection. Interestingly, TBFVs and ISFVs did not show extremely different levels of constraint, although TBFVs alternate among hosts, whereas ISFVs do not. Additional results showed that episodic positive selection drove the evolution of MBFVs, despite their high constraint. Positive selection was also detected on two branches of the TBFVs phylogeny that define the seabird clade. Thus, positive selection was much more common during the evolution of arthropod-borne flaviviruses than previously thought. Overall, our data indicate that flavivirus evolutionary patterns are complex and most likely determined by multiple factors, not limited to the alternation between taxonomically divergent hosts. The frequency of both positive and purifying selection, especially in MBFVs, suggests that a minority of sites in the viral polyprotein experience weak constraint and can evolve to generate new viral phenotypes and possibly promote adaptation to new hosts.

Posterior stability in posterior-stabilized vs medially congruent total knee replacement: A radiological comparison of two polyethylene designs in a single model

Objective:The purpose of this radiological study was to assess the posterior laxity of a single model of a total knee arthroplasty design (TKA) having a medially constrained (MC) or a Posterior-Stabilized (PS) polyethylene insert using a well-documented stress x-ray. To the authors knowledge, this is the first report evaluating MC TKA outcomes according to the “kneeling view.”Materials and Methods:Sixty patients with non-traumatic primary knee osteoarthritis undergoing TKA were first matched by age, sex, BMI and diagnosis and then divided in two groups: group A (37 knees) received a MC TKA and group B (23 knees) a PS implant made by the same manufacturer. In all cases the posterior cruciate ligament (PCL) was resected. All patients underwent the same postoperative “kneeling view” and were also clinically evaluated according to the Knee Society Score (KSS) and Oxford Knee Score (OKS). Radiographic measurements were taken by tracing a line along the posterior cortex of the tibia and then measuring the perpendicular distance to a point marked at the posterior corner of Blumensaat’s line.Results:At 12 months minimum FU, no statistically significant differences were found between the two groups in all the clinical scores. There was a statistically significant difference on kneeling view values between the two groups (P = 0.0002): the mean value in the MC group was −1.97 ± 3.8 mm while was −5.6 ± 3.1 mm in the PS group. In both groups, the average position of the posterior cortex of the tibia was anterior to the posterior corner of Blumensaat’s line, showing absence of instability in flexion.Conclusion:This study highlighted that the PCL removal, accompanied by a precise surgical technique, did not increase the instability in flexion in two groups of patients having the same TKA design but polyethylene inserts characterized by different levels of constraint.

Cementless Metaphyseal Sleeve Fixation in Revision Knee Arthroplasty: Our Experience with an Arabic Population at the Midterm.

Objective Metaphyseal sleeve (MS) fixation in revision knee arthroplasty (RKA) among Western populations has been reported with very encouraging outcomes. The aim of this study was to report our experience with the use of MS in RKA among an Arabic population. Clinical and radiographic outcomes and implant survivorship were reported at a minimum follow-up of 2 years and a mean follow-up of 4.1 years. Methods A retrospective analysis was conducted on prospectively collected data of patients who underwent RKA with a MS in combination with a cementless stem (femoral or tibial). Range of motion (ROM) and Knee Society Score (KSS) were obtained pre- and postoperatively. Complications, occurrence of stem-tip pain, and implant survival were documented. Knee radiographs were obtained to evaluate the alignment and osseointegration or loosening of the MS. Results A total of 52 sleeves (27 tibial and 25 femoral) implanted in 27 RKAs (27 patients) were included. The mean follow-up period was 4.1 ± 1.8 (2–7.5) years. Postoperatively, the ROM improved from 89.3 ± 9.2 to 106.3 ± 11.4 (p = 0.19) and the KSS also significantly improved, from 102.9 ± 35.6 to 130.2 ± 33.7 (p < 0.001). One patient (3.7%) developed heterotopic ossification, and another one (3.7 %) had a stem-tip pain on the tibial side; both were managed conservatively. One patient (3.7 %) sustained a fracture and required reoperation. None of the sleeves showed progressive radiolucent lines, and none required revision. The aseptic survivorship and overall survivorship at a mean of 4.1 years were 100% and 96.3%, respectively. Conclusion MS provided successful midterm outcomes that were maintained in obese patients with different levels of constraint. Our series supports their use as a viable option in RKA.

Analysis of Biomechanical Differences Between Condylar Constrained Knee and Rotating Hinged Implants: A Numerical Study

BackgroundDifferent levels of constraint for total knee arthroplasty can be considered for revision surgeries. While prior studies have assessed the clinical impact and patient outcomes of condylar constrained knee (CCK) and rotating hinged (RTH) implants, nowadays little is known about the biomechanical effects induced by different levels of constraint on bone stress and implant micromotions. MethodsCCK and RTH implant models were analyzed using a previously validated numerical model. Each system was investigated during a squat and a lunge motor task. The force in the joint, the bone and implant stresses, and micromotions in this latter were analyzed and compared among designs. ResultsDifferent activities induced similar bone stress distributions in both implants. The RTH implant induces mostly high stress compared to the CCK implant, especially in the region close to tip of the stem. However, in the proximal tibia, the stresses achieved with the CCK implant is higher than the one calculated for the RTH design, due to the presence of the post-cam system. Accordingly, the condylar constrained design shows higher implant micromotions due to the greater torsional constraint. ConclusionDifferent levels of constraint in revision arthroplasty were always associated with different biomechanical outputs. RTH implants are characterized by higher tibial stress especially in the region close to the stem tip; condylar implants, instead, increase the proximal tibial stress and therefore implant micromotions, as a result of the presence of the post-cam mechanism. Surgeons will have to consider these findings to guarantee the best outcome for the patient and the related change in the bone stress and implant fixation induced by different levels of constrain in a total knee arthroplasty.

Numerical insights on the seismic behavior of a non-isolated historical masonry tower

In this paper, numerical insights on the seismic behavior of a non-isolated historical masonry tower are presented and discussed. The tower under study is the main tower of the fortress of San Felice sul Panaro, a town located near the city of Modena (Italy). Such a tower is surrounded by adjacent structural elements and, therefore, is not isolated. This historical monument has been hit by the devastating seismic sequence occurred in May 2012 in the Northern part of the Emilia region (the so-called “Emilia earthquake”), showing a huge and widespread damage. Here, in order to understand the behavior of the structure, its interaction with the adjacent buildings and the reasons of the occurred damage, advanced numerical analyses (both nonlinear static and dynamic) are performed on a 3D finite element model with different levels of constraint supplied by the adjacent structural elements and a detailed comparison between the simulated damage and the actual one is carried out. The results of the conducted numerical campaign show a good agreement with the actual crack pattern, particularly for the model of the tower that considers the adjacent structural elements.

Revision Total Knee Arthroplasty Using a Constrained Condylar Knee Prosthesis Combined with a Posterior Stabilized Articular Surface.

Intraoperative assessment of valgus-varus stability is crucial for choosing articular surfaces with different levels of constraint. Legacy constrained condylar knee (CCK) prostheses are readily available to assemble and use with a CCK articular surface or a posterior stabilized (PS) articular surface in revision knee arthroplasty surgeries. We wanted to validate outcomes of revision total knee arthroplasty (TKA) using legacy CCK prostheses combined with a PS articular surface. Thirty-seven patients were enrolled and followed up for more than 2 years. Range of motion (ROM), the Knee Society score (KSS), the Knee Society functional score (KSS-F), and the Western Ontario and McMaster Universities Arthritis Index (WOMAC) were used to evaluate outcomes. Follow-up was a mean of 86.5 months (range: 28-152 months). The mean age of the participants was 69.8 years (range: 31-86 years). The mean ROM was 110.5 degrees, the KSS was 86.2 points, the KSS-F was 68.3 points, and the WOMAC score was 22.6 points. Seven participants had implant failures: five because of delayed infections and two because of posterior dislocations. In conclusion, revision TKA using a CCK prosthesis combined with a PS articular surface might provide satisfactory mid-term outcomes. Delayed infection was the most common cause of implant failure. Dislocation might occur in middle-old or older patients despite careful intraoperative examination of valgus-varus stability, extension-flexion gap balancing, and signs of recurvatum.

Correlation of circumferentially notched and smooth specimen fatigue test results in two nickel base superalloys

Prediction of the fatigue lives of components in engineered products is an important area of study; fatigue failure of a component may have product safety implications. Nearly all components contain stress concentration features and fatigue cracks will typically develop from these stress concentrations. Therefore, it is important that fatigue life prediction methods take into account the presence of stress concentrations. This article compares two methods of correlating fatigue test results between smooth and notched specimens in order to be better able to predict the fatigue lives of full-scale components. The first method uses the Neuber analysis approach to predict the strain range and mean strain at the root of the notch; the second uses elastic-plastic finite element analysis of the notched specimens. Two circumferentially notched specimen geometries are considered, with Kt values of 2.19 and 3.43. The analyses show that the Neuber method under-predicts the fatigue lives of the notched specimens, whereas a closer correlation is obtained using the finite element models. This is explained in terms of the different levels of constraint on yielding in a circumferentially notched specimen relative to the pure shear loading that is the basis of the Neuber analysis. Four methods of enhancing the finite element correlations are described. The first uses a method developed by Peterson to define a fatigue stress concentration factor. The second uses a mean stress and stress range approach developed by Smith, Watson and Topper. The third uses a critical distance approach developed by Pluvinage. The final method takes into account the volume of highly stressed material at the root of the notch using an approach first described by Waters and Norris to define a fatigue stress concentration factor. This approach has many parallels with the strain energy density approach.

Modalités et enjeux du traitement sous contrainte auprès des toxicomanes

This article is exploring different forms of constraint that are exerted in the field of drug addiction treatment. The objective of this article is to establish benchmarks and to stimulate reflection about the ethical and clinical implications of those constraints in the field of drug addiction treatment. This article is presenting a critical review of different forms of constraint that can be exerted in Canada in regard to the treatment of drug addiction. In the first section of the article, a definition of therapeutic intervention is proposed, that includes the dimension of power, which justifies the importance of considering the coercive aspects of treatment. The second section, which represents the core section of the paper, is devoted to the presentation of different levels of constraint that can be distinguished in regard to drug addicts who are under treatment. Three levels of constraint are exposed: judicial constraint, institutional constraint and relational constraint. The coercive aspect of treatment can then be recognized as a combination of all tree levels of constraint. Judicial constraint refers to any form of constraint in which the court or the judge is imposing or recommending treatment. This particular level of constraint can take different forms, such as therapeutic remands, conditions of a probation order, conditions of a conditional sentence of imprisonment, and coercive treatment such as the ones provided through drug courts. Institutional constraint refers to any form of constraint exerted within any institutional setting, such as correctional facilities and programs offered in community. Correctional facilities being limited by their own specific mission, it might have a major impact on the way the objectives of treatment are defined. Those limitations can then be considered as a form of constraint, in which drug users don't have much space to express their personal needs. Finally, relational constraint refers to any form of constraint in which the drug addict might be coerced to treatment under the pressure of people from the immediate environment, such as members of family, friends or employers. Even if this form of constraint is not as obvious as the ones exerted by court and correctional facilities, it has to be considered by practitioners who are evaluating the motivation of drug addicts under treatment. Considering the diversity of constraints that are exerted on drug addicts who are under treatment, it appears that we should be always aware of the ethical and clinical challenges facing practitioners every day. The recognition of those constraints can also help to understand how important it is to consider the institutional and social context in which treatment is being provided.

MALE DOMINANCE, FEMALE MATE CHOICE, AND INTERSEXUAL CONFLICT IN THE ROSE BITTERLING (RHODEUS OCELLATUS)

An intersexual conflict arises when males and females differ in their reproductive interests. Although experimental studies have shown that females often mate with dominant males, it may not always be in the interest of a female to do so. Here we investigated the impact of male dominance on female mate choice and offspring growth and survival in the rose bitterling (Rhodeus ocellatus), a freshwater fish with a resource-based mating system. Three experimental mating trials were conducted using males of known dominance rank, but with different levels of constraint on male behavior. Thus, females were able to choose among; (1) males that were isolated from each other; (2) males that could see and smell each other, but could not directly interact; (3) males that could interact fully. Using a combination of behavioral observation and parentage analyses it was shown that female preferences did not correspond with male dominance and that male aggression and dominance constrained female mate choice, resulting in a potential intersexual conflict. The survival of offspring to independence was significantly correlated with female mate preferences, but not with male dominance. A lack of strong congruence in female preference for males suggested a role for parental haplotype compatibility in mate choice.

Sensitivity of Fatigue Crack Growth Data to Specimen Geometry

The formulations of fatigue crack growth prediction are still mostly based on phenomenological models. A commonly used formula in the field of high cycle fatigue is the Paris- Erdogan law. For given experimental conditions (such as temperature, stress ratio or environmental conditions) the parameters C and m have to be experimentally determined and considered as material constants. Thus, for a given material, the fatigue crack growth rate (FCGR) depends only on the applied range of the stress intensity factor. In a threshold region a significant shift in the data of the fatigue crack propagation rate can be observed. The shift is induced by different test specimen geometry. To analyses it the authors will present their own laboratory fatigue crack growth rate test data measured on two different specimens with different levels of constraint and for different steels. It is demonstrated that fatigue characteristics (i.e. C, m and Kth) obtained from different specimen geometries are not only properties of the materials but depends on the specimen geometry.

Quantification of the effect of specimen geometry on the fatigue crack growth response by two-parameter fracture mechanics

Abstract Discrepancies in fatigue crack growth rate and threshold values observed in different specimen geometries are analyzed and discussed. To explain the discrepancies, a phenomenological approach is suggested going out from the assumption of linear elastic fracture mechanics. To this aim, two-parameter constraint-based fracture mechanics is used and the different levels of constraint in the vicinity of the fatigue crack tip are characterized by means of the T-stress. The results of the theoretical analyses correspond to the presented experimental data. It is concluded that under small scale yielding conditions (corresponding to high cycle loading) low level of the constraint (corresponding to negative values of the T-stress) substantially increases the rate of the fatigue crack propagation. The results presented make it possible to relate the experimentally measured data obtained on the specimens with different geometries and thereby contribute to more reliable estimates of the residual fatigue life of structures.

Accounting For Effects Of Constraint On Propagation Of A Fatigue Crack

The paper describes the application of two parameter constraint-based fracture mechanics to the behavior of fatigue cracks. The different levels of constraint in the vicinity of the tip of a fatigue crack are quantified by means of the T-stress. The paper seeks to quanti~ the experimentally observed effect of the specimen geometry on the rate of propagation of a fatigue crack. To this aim a modified Paris law that takes the different values of the corresponding constraint parameter T into account is then suggested. It is shown that, depending upon the material properties, the geome~, and the loading of the specimen, a constraint may cause a difference of as much as 100°/0 in the rate of propagation of a fatigue crack for extreme values of the T-stress, The problem is solved numerically by means of the finite element method, and results are compared with data obtained experimentally using two specimens with different values of the T-stress (a center cracked and a compact tension test specimen).

Sexual reproduction in the cork oak ( Quercus suber L). II. Crossing intra- and interspecific barriers

Intraspecific barriers promote outcrossing while interspecific mechanisms may contribute to the isolation of species; both control the exchange of genes between plants. In this paper we establish that post-pollination mechanisms promote outcross and act at different temporal and spatial levels to control seed set and quality in Quercus species. Controlled pollinations were performed to investigate intraspecific crossing barriers in Q. suber and pollen-pistil interactions following interspecific pollinations with some simpatric Quercus species. Cytological data of intraspecific crosses in Q. suber and Q. ilex have shown different kinetics on pollen tube growth after self and outcross pollination, but pollen tubes were able to reach the base of the styles in both species and seed set was successful. Although some pre-zygotic interaction is occurring at the style, the most important interaction takes place at ovary. The cross between Q. ilex and Q. suber is possible only in one direction, revealing a case of unilateral incongruity. We show that the lack of seed set observed in the cross Q. suber×Q. ilex is due to the inability of pollen tubes to penetrate the transmitting tissue after germination. With Q. suber mainly as female parent, pollinations with other simpatric Quercus species have shown different levels of constraint on pollen tube progression at stigma and style levels. Eventual hybridisation between Quercus species will depend on the compatibility of pollen-pistil interactions, on the competitive ability of pollen genotypes, and, most important, on the overlapping of geographical, phenological and ecological factors. Differences in seed set and seed allocation was evident in all crosses, and was particularly outstanding in interspecific and in self intraspecific crosses, determining the ultimate level of seed production and quality in Quercus species.

Evolution of the larval cuticle proteins coded by the secondary sex chromosome pair:X2 andneo-Y ofDrosophila miranda: I. Comparison at the DNA sequence level

The larval cuticle proteins (LCPs) are encoded by a multigene family, Lcp1-4, located at the right arm of the metacentric autosome 2 (2R) in Drosophila melanogaster. Due to a chromosome fusion the Lcp locus of Drosophila miranda is situated on a pair of secondary sex chromosomes, the X2 and neo-Y chromosomes. Comparing the deduced amino acid sequences of the autosomal D. melanogaster loci with the sex-chromosomal loci of D. miranda, we were able to trace the evolution of the Lcp loci with respect to their different chromosomal inheritance. The length of the signal peptide is conserved in all four LCPs, while the size of the mature LCPs varies. Conserved protein motifs became obvious from the alignment, indicating regions of structural and functional importance. Analyzing intra- and interspecific sequence similarities of the Lcp gene families allowed us to reconstruct the phylogeny of the gene cluster. Alignment with cuticle amino acid sequences originating from divergent insect species reveals motifs already present in the primordial insect LCPs. These motifs indicate different levels of constraint acting during the evolution of the LCPs.

Workstation design and postural stress part 2: A case study

An evaluation of the musculoskeletal problems associated with seated workstations was undertaken for employees of the Human Sciences Research Council. A sample of 37 workers was studied for 14 days to determine which symptoms were due to chronic disorders and which were linked to postural stress or constrained posture as a result of workstation and task design. Techniques used included two subjective comfort ratings, clinical examinations by physiotherapists, anthropometric and workstation measurement, and video recordings of subjects’ posture over time. Subjects were selected from four occupations characterised by different levels of constraint in their work posture; data-entry typists, typists, programmers and researchers.Examinations revealed that 68% of the presenting symptoms were not related to any known previous trauma or pathology. Of these problems 86% were reported to be occupationally aggravated or related. The findings confirmed the hypothesis that postural constraint is accompanied by an increased likelihood of developing chronic musculoskeletal disorders.* The concepts of postural stress and postural constraint and their relationship to the development of muscle strain are discussed in Part 1: Background to occupational syndromes.