Fracture+Fixation+Manual

Fracture+Fixation+Manual - 125:315 BME Measurements and...

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125:315 BME Measurements and Analysis Laboratory Spring 2010 Fracture Fixation
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125:315 BME Measurements and Analysis Laboratory: Fracture Fixation Spring 2010 2 I. Objectives The objective of this laboratory experiment is to: 1. Use a mechanical testing machine in a proper manner, demonstrating familiarity with its basic controls and functions. 2. Apply the theory of bending to determine Young’s elastic modulus (E) of a material, as well as the moment of inertia (I) and flexural rigidity (EI) of a structure. 3. Identify the five fundamental loads: compression, tension, shear, bending and torsion. II. Introduction Numerous biomechanical issues arise in the design of fracture fixation plates. One main issue is bending rigidity of the plate vs. bending rigidity of the bone. This is important because load sharing between bone plate and bone, which is influenced by the bending rigidity of plate vs. bone, is thought to have important biological implications. As bone healing progresses, the plate should not be so rigid as to overprotect the bone from functional loading; this overprotection has been correlated with local osteopenia (porosity) of the bone and potential for refracture when the plate is removed. While bones and plates are generally subjected to more than just bending loads in vivo, this experiment centers on bending properties. Specifically, we address some of the factors involved in designing a bone plate for a given bone. II.1 The Structure and Functions of Bones The function of a given bone determines its structure. The shafts of the long bones are composed of strong cortical bone. The shock absorbing capability of vertebrae is due to its relatively high trabecular bone content. Trabecular bone develops four types of structure, depending on whether it must resist relatively high or relatively low forces and whether the primary loading is axial (tension or compression) or asymmetric (bending). Because of this, the strength and elasticity of trabecular bone differ considerably with location in the body, as well as with the age and health of the individual [1]. Both cortical and trabecular bone are anisotropic; that is, they demonstrate different strength and stiffness in response to forces applied from different directions. Bone is strongest in resisting compressive stress and weakest in resisting shear stress as shown in Figure 5.1 [1]. The collagen fibers of bone, like those of tendons, have great tensile strength, whereas the calcium salts have great compressional strength [2]. Figure 5.1 Relative bone strength in resisting compression, tension and shear [1].
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125:315 BME Measurements and Analysis Laboratory: Fracture Fixation Spring 2010 3 II.2 Mechanical Loads on the Human Body Muscle forces, gravitational force, and bone-breaking force such as that encountered in a skiing accident all affect the human body differently which is determined by the direction and duration as well as the magnitude of the given force [1]. Compression
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Fracture+Fixation+Manual - 125:315 BME Measurements and...

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