Multi-axial Fatigue of Trabecular Bone with Respect to Normal Walking

Trabecular bone plays an important role in skeleton structures. Some analysis such as numerical, analytical or experimental analysis applies, to predict fatigue life of trabecular bone. In this study, numerical analysis is performed to predict fatigue life of trabecular bone subjected to axial compression mixed with torsional load due to gait loading. Objective of study is established to predict fatigue life of bone structure. Considerably, trabecular bone makes useful contribution all over the body because of load tolerating duty. Effect of multi-axial and discrete load due to normal walking is highly demanded clinically. The scope of this study is to compare the fatigue behaviour of trabecular bone faced with multi-axial and discrete load. Analysing fatigue life of trabecular bone based on average bodyweight in this decade; make a useful contribution for human being and their health, especially for those who suffered from osteoporosis disease.

Normal walking is the most action impose on the skeleton structure. The microarchitecture of trabecular bone plays an important role respect to mechanical properties. Analyse the fatigue behaviour of the trabecular bone respect to physiological activity (Normal Walking), subjected to combination of axial compression and torsional (multi-axial) load counted as the main aim of this study. The osteoclast is responsible for modelling and remodelling of bone and is defined as a large multinucleate bone cell that absorbs bone tissue during growth and healing. Irregularities and disorders in trabecular bone cause to reduction of bone mass and its architecture. The standard method applied to extract bone structures properties is 2D section of bone biopsies. Tetrahedrons technique is applied to calculate bone volume (BV), total volume (TV) is the volume of whole bone structures. Trabecular bone has a significant portion in respect of resisting compression and shear. Data extracted from experimental test is depends on many parameters such as geometry of bone and measurement of strain. Trabecular architecture has a specific properties respect to tension loading. Almost all load due to physiological activates are counted as cyclic loading. Lifetimes were found to be highly dependent on the axis of loading and are drastically reduced for off-axis loading.

Simulation of trabecular bone starting by micro CT-scan data and using Mimics software to construct the corresponded part of structure will be included. In this chapter, explanation of choosing sample of bone for Micro CT-scan will be covered. Computer tomography produces a volume of data that can be manipulated through a process known as “Windowing” in order to demonstrate various bodily structures based on their ability to block the X-ray beam. In this chapter after reconstructing bone in the Mimic software, trabecular bone model built up in size of 10 mm as radius and 20 mm as height.

Stress-strain analysis in multi-axial loading is considered then fatigue life prediction of trabecular bone is represented. Vertical model subjected to axial load is faced with lower stress amplitude and effective plastic strain as well. Effective plastic strain in trabecular bone is known as a crucial data for tracking crack nucleation point and damage behaviour under different types of load. Since Combination of axial and torsional load on trabecular bone make life of bone shorter than imposing each load separately, this part of study consider the trend of stress and strain within the structure. Volumetric strain and effective plastic strain data were combined to extract data for strain amplitude axis and number of cycles to failure data computed numerically used as number of cycles to failure for x-axis in four load amplitude. Since trabecular bone is not withstand against load as structure subjected to axial load can, so it would be expected that fatigue life in torsional load is decrease drastically in compare with axial load. In static analysis trabecular bone was subjected to axial load two parameter monitored which were stress versus volumetric strain and effective plastic strain that is the crucial factor of damage initiation within structure. Results show that trabecular bone subjected to axial load has considerable fatigue life which in 40 % of total load it reaches to 1226.80 cycles approximately, however, this value for torsional load reach to 42 cycles and for multi-axial 38 cycles. Torsional load known as the most effective load, which causes damage within struts and trabeculae.

Analysis of fatigue life of bone support us in various aims such as design artificial trabecular bone fatigue life estimation was performed by applying strain-based method, results show that fatigue is altered based on different type of load; femoral head of bovine trabecular bone was used in this analysis. In dynamic analysis also S-N curve extracted, results show that trabecular bone follow Coffin-Manson law and counted as reliable method for estimation of fatigue life of trabecular bone. Trabecular bone sample subjected to axial, torsional and multi-axial load, has especial stress distribution history within the structure. This finding also clear that, our simulated model has same results in compare with the experimental part. This analysis concerned about load type and its amplitude, however, bone morphological indices is counted as one another important part that can effect on fatigue life of bone. Analysis of different types of load such as axial, torsional and multi-axial in different anatomical sites and analyse its in-phase and out of phase that effect on fatigue life considerably will be expected for those are interested in such area.