Luis Gracia

Influence of socioeconomic factors on fitness and fatness in Spanish adolescents: The AVENA study

OBJECTIVE This study was to examine the influence of socioeconomic status on fitness and fatness in Spanish adolescents. SUBJECTS AND METHODS A total of 1 795 adolescents (833 boys) aged 12.5-18.5 years from the AVENA study participated in this study. The following physical fitness components were assessed: muscular strength (standing long jump), speed-agility (4 × 10 m shuttle run) and cardiorespiratory fitness (20 m shuttle run). Total and central body fat was assessed using skinfold thickness and waist circumference, respectively. Both parents reported their educational and professional level. RESULTS Girls with higher paternal educational level and boys with higher either maternal or paternal professional level had higher muscular strength levels (all P<0.05). Speed-agility and cardiorespiratory fitness were not associated with parental educational or professional levels in boys. In contrast, girls with higher paternal educational level or higher parental professional level had higher levels in both fitness components (all P<0.05). A higher maternal educational level was associated with lower total and central body fat in boys (all P<0.05), but not in girls. We observed a small effect size (Cohens d∼0.2) in most of these associations. CONCLUSIONS Our results suggest modest associations of high socioeconomic status with better fitness and fatness levels in Spanish adolescents. These associations greatly depend on the socioeconomic status and fitness parameters studied.

Imposing essential boundary conditions in the natural element method by means of density-scaled?-shapes

A new method is proposed for the ‘exact’ imposition of essential boundary conditions in the context of the natural element method (NEM). This is a new technique in the field of Computational Mechanics and can be considered as a meshless method. Unlike most of these methods, the NE shape functions are strictly interpolant and the essential boundary conditions can be imposed by directly substituting the corresponding terms in the system of equations. However, these shape functions are not strictly linear over non-convex boundaries and the approach does not make the test functions vanish over the whole essential boundary region. A modification of the initial NEM version is considered based on α-shapes and α-complexes, which are widely used in the field of scientific visualization. Using α-shapes in the context of the NEM allows the construction of models entirely in terms of nodes and also ensures the linear precision of the interpolant over convex and non-convex boundaries. Results on some benchmark problems are presented after a theoretical description of the method. Copyright

Male osteoporosis: A review.

Osteoporosis in men is a heterogeneous disease that has received little attention. However, one third of worldwide hip fractures occur in the male population. This problem is more prevalent in people over 70 years of age. The etiology can be idiopathic or secondary to hypogonadism, vitamin D deficiency and inadequate calcium intake, hormonal treatments for prostate cancer, use of toxic and every disease or drug use that alters bone metabolism.Risk factors such as a previous history of fragility fracture should be assessed for the diagnosis. However, risk factors in men are very heterogeneous. There are significant differences in the pharmacological treatment of osteoporosis between men and women fundamentally due to the level of evidence in published trials supporting each treatment. New treatments will offer new therapeutic prospects. The goal of this work is a revision of the present status knowledge about male osteoporosis.

Study of crack propagation in orthotropic materials by using the boundary element method

Abstract The application of the Boundary Element Method (BEM) to the computation of stress intensity factors (SIF) and the crack propagation angle in orthotropic materials is the aim of this paper. The computer program includes isoparametric linear, quadratic and quarter-point-tractionsingular elements in order to obtain the stress distribution around the crack tips. A multidomain approach is followed in order to avoid the geometric singularity that appears in the double-node method. Different methods to compute the SIF are compared for several cases. Finally, the maximum circumferential stress approach is used to obtain the crack propagation angle in a mixed-mode propagation problem in an orthotropic material.

Study of bone remodeling of two models of femoral cementless stems by means of DEXA and finite elements

BackgroundA hip replacement with a cemented or cementless femoral stem produces an effect on the bone called adaptive remodelling, attributable to mechanical and biological factors. All of the cementless prostheses designs try to achieve an optimal load transfer in order to avoid stress-shielding, which produces an osteopenia.Long-term densitometric studies taken after implanting ABG-I and ABG-II stems confirm that the changes made to the design and alloy of the ABG-II stem help produce less proximal atrophy of the femur. The simulation with FE allowed us to study the biomechanical behaviour of two stems. The aim of this study was, if possible, to correlate the biological and mechanical findings.MethodsBoth models with prostheses ABG-I and II have been simulated in five different moments of time which coincide with the DEXA measurements: postoperative, 6 months, 1, 3 and 5 years, in addition to the healthy femur as the initial reference. For the complete comparative analysis of both stems, all of the possible combinations of bone mass (group I and group II of pacients in two controlled studies for ABG-I and II stems, respectively), prosthetic geometry (ABG-I and ABG-II) and stem material (Wrought Titanium or TMZF) were simulated.Results and DiscussionIn both groups of bone mass an increase of stress in the area of the cancellous bone is produced, which coincides with the end of the HA coating, as a consequence of the bottleneck effect which is produced in the transmission of loads, and corresponds to Gruen zones 2 and 6, where no osteopenia can be seen in contrast to zones 1 and 7.ConclusionsIn this study it is shown that the ABG-II stem is more effective than the ABG-I given that it generates higher tensional values on the bone, due to which proximal bone atrophy diminishes. This biomechanical behaviour with an improved transmission of loads confirmed by means of FE simulation corresponds to the biological findings obtained with Dual-Energy X-Ray Absorptiometry (DEXA).

Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

BackgroundPrimary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces.A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied.MethodsThe tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed.ResultsThe mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw), 564,05 N (Group 2; 9 × 28), 614,95 N (Group 3; 9 × 35), 651,14 N (Group 4; 10 × 28) and 664,99 (Group 5; 10 × 35). No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P < 0.001).ConclusionsLonger and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm) do not achieve optimal fixation and should be implanted only with special requirements.

EVALUATION OF THE PROBABILITY DISTRIBUTION OF CRACK PROPAGATION LIFE IN METAL FATIGUE BY MEANS OF PROBABILISTIC FINITE ELEMENT METHOD AND B-MODELS

Abstract In this paper, a new model for the prediction of the cumulative distribution function of fatigue life of structural elements during the crack propagation stage is established. This problem is considered as a cumulative damage process following the probabilistic approach of Bogdanoff and Kozin (B-models). The initial and final crack lengths, the crack propagation angle, the material fracture and elastic parameters and the external loads have been the random variables considered here. The theoretical bases of the model and the procedure to construct it are described in the forthcoming paragraphs such as several examples for mode I problems including the comparison with experimental results.

Prevalence of osteoporotic vertebral fracture in Spanish women over age 45

The aim of this work is to study the prevalence of osteoporotic vertebral fractures in Spanish women over 45 years of age, based on the selection of a nationwide sample. An observational, cross-sectional, multicenter study was conducted during 2006, in all of Spains regions. The sample analyzed was of 5000 individuals, representative of the female population over age 45 in Spain. A questionnaire was used to determine which factors are most often associated with vertebral fractures. We also assessed whether the Prevalent Vertebral Fracture Index, proposed by Vogt, is useful in indicating a possible osteoporotic vertebral fracture. Five hundred orthopedic surgeons, from various Spanish regions, were trained in different aspects of the study: inclusion and exclusion criteria, management of the risk factor questionnaire, and implementation of the Vogt questionnaire. The number of fracture cases was 1549 (31.79%). 528 Women (34.08%) had a single vertebral fracture, and 1021 (65.92%) had multiple vertebral fractures. The following factors were statistically significantly associated with vertebral fracture: age, late menarche, early menopause, diabetes mellitus, hyperparathyroidism, rheumatoid arthritis, height loss, daily physical activity, corticosteroid therapy, personal history of osteoporotic fracture and previous diagnosis of osteoporosis. The differences in Vogt score according to age and fracture status were statistically significant. The conclusion of the study is that vertebral osteoporotic fracture in the female Spanish population is frequent. The high prevalence in the Spanish population older than 60 years is probably related to malnutrition in the period from 1936 to 1952.

Applications of finite element simulation in orthopedic and trauma surgery

Research in different areas of orthopedic and trauma surgery requires a methodology that allows both a more economic approach and the ability to reproduce different situations in an easy way. Simulation models have been introduced recently in bioengineering and could become an essential tool in the study of any physiological unity, regardless of its complexity. The main problem in modeling with finite elements simulation is to achieve an accurate reproduction of the anatomy and a perfect correlation of the different structures, in any region of the human body. Authors have developed a mixed technique, joining the use of a three-dimensional laser scanner Roland Picza captured together with computed tomography (CT) and 3D CT images, to achieve a perfect reproduction of the anatomy. Finite element (FE) simulation lets us know the biomechanical changes that take place after hip prostheses or osteosynthesis implantation and biological responses of bone to biomechanical changes. The simulation models are able to predict changes in bone stress distribution around the implant, so allowing preventing future pathologies. The development of a FE model of lumbar spine is another interesting application of the simulation. The model allows research on the lumbar spine, not only in physiological conditions but also simulating different load conditions, to assess the impact on biomechanics. Different degrees of disc degeneration can also be simulated to determine the impact on adjacent anatomical elements. Finally, FE models may be useful to test different fixation systems, i.e., pedicular screws, interbody devices or rigid fixations compared with the dynamic ones. We have also developed models of lumbar spine and hip joint to predict the occurrence of osteoporotic fractures, based on densitometric determinations and specific biomechanical models, including approaches from damage and fracture mechanics. FE simulations also allow us to predict the behavior of orthopedic splints applied to the correction of deformities, providing the recovering force-displacement and angle-moment curves that characterize the mechanical behavior of the splint in the overall range of movement.

A simple method for the synthesis of 2D and 3D mechanisms with kinematic constraints

A general procedure for the synthesis of mechanisms is presented here. This approach minimises the error between the actual path of one or several points of the mechanism and the paths for each of them predefined by a certain number of points. It is also possible to consider kinematic constraints on velocity, acceleration and jerk. The optimisation method uses a sequence of quadratic problems with an analytical definition of the objective function, constraints and their gradients, while the hessians are computed by finite differences.