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The principals of classical mechanics are applied to the study of the resistance of materials to fracture when subject to a certain load. Bone has been, for a long time, the object of study in the field of mechanics in order to understand and resolve problems of fracture associated with deficient mechanical behaviour which may exist due to factors such as age or certain pathologies. The great quantity of specific vocabulary used in biomechanics, derived as it is from the terminology of mechanical engineering, makes it very difficult, on occasion, for researchers specialising in bone and mineral metabolism to interpret information available in the literature on the resistance of bone. The objective of this work is to describe as briefly and concisely as possible the main concepts and fundamental principles used in biomechanics, focused on their application to bone tissue. In addition, the main mechanical trials carried out on whole bones or on samples of trabecular or cortical bone are reviewed. [ABSTRACT FROM AUTHOR]

Introduction: Osteoarthritis is a chronic joint disease; isometric exercise leads to the development of mechanical work and isokinetic exercise leads to better joint mobility. Objectives: To compare the effectiveness of isometric versus isokinetic therapeutic exercises in patients with knee osteoarthritis. Material and methods: Quasiexperimental study in a population of 45 to 75 year old patients with a diagnosis of knee osteoarthritis. Group 1 (experimental) was put under isokinetic exercises and group 2 (control) under isometric exercises. The sample size was of 33 patients per group; the allocation to the experimentation or control group was nonrandom, but stratified by degrees of knee osteoarthritis. The effectiveness of the exercise was measured in three dimensions: muscle strength, joint range and pain. The intervention lasted eight weeks and the physical activity was carried out every third day. The statistical analysis included averages, standard deviation, percentage, Chi square test, z test for two populations, t test for two independent populations and twin t test. Results: The analysis of muscle strength comparing the categories independently demonstrates differences at 8 weeks; 33.3% of the isokinetic exercise is in the normal category and 15.2% in the isometric exercise (p= 0.04). There was not difference of joint range between groups, despite finding a stage I range in 100.0% of the isokinetic group and 97.0% in the isometric (p> 0.05) group. Pain was milder in the isokinetic exercise group at 8 weeks (p= 0.01) Conclusions: Isokinetic exercises have a greater effectiveness than isometric exercises for muscle strength and pain in patients with knee osteoarthritis. However, other studies with randomized designs are needed. [ABSTRACT FROM AUTHOR]

The use of acrylic bone cement in the total hip replacement is a common procedure to fix artificial prosthesis to bone structure. Acrylic cement has been studied for nearly forty years and the prosthesis long term durability indicates that the clinical efficiency of these cements at 12-15 years of being implanted is about 80%. One of the new alternatives studied in the field of bone cement is related to acrylic cement modified with bioactive fillers in order to increase their long term use. In this paper we analyze the influence of three types of silanized hydroxyapatite in the mechanical and setting behaviour of poly(methyl methacrylate-co-styrene) bone cements. Physical and mechanical properties such as density, compression and tensile strength of the formulations were studied. The results indicate that the density is increased with the content of fillers and the mechanical behaviour is affected by the content and the type of HA. The presence of agglomerated particles as fillers in the matrix (when less than 50% of fillers is used) produces a decrease of compression and tensile strengths while the tensile modulus increases with the content of fillers. As a preliminary result, an in vitro bioactive behavior of the formulations was obtained by the inmersion of the samples in simulated body fluid. [ABSTRACT FROM AUTHOR]

Mechanical properties of a new low-cost unilateral multiaxial external fixator (ATLAS) developed for our group are presented. This is a double-bar fixator assembled with six-degrees-of-freedom connectors so that the entire fixator allows six degrees of freedom between bone fragments. A computational and experimental procedure was developed to obtain the interfragmentary flexibility matrix of the fixator. This study was also undertaken with other three fixators, two imported and one national frequently used in our region. The stiffness of the new fixator was in the range of stiffnesses obtained for the others. Even with the double-bar configuration, which gives good stability and stiffness to the assembly, the ATLAS fixator allows six degrees of freedom between bone fragments, so that the surgeon can reduce the fracture accurately. From the biomechanical point of view, this fixator is ready for clinical evaluation. [ABSTRACT FROM AUTHOR]