Adaptive Bone Remodeling of Proximal femur Trabecular Bone to Identify Influence of Different Loading Patterns

Abstract

PURPOSE: Bone structures are changing continuously. Approximately 10% of total amount of bone structure is replaced every year. In this study, a stress-based bone remodeling model has been proposed to predict the rod-plate architecture of human femur trabecular bone. METHODS: The cortical bone has been considered as a solid structure. All remodeling processes occur in trabecular bone, are represented by a three-dimensional network of interconnected rods with circular cross-sections and are initially uniform. The basis for the proposed remodeling technique is to keep the local stresses in the trabecular bone in predefined boundary stresses. Either enhancing existing beam elements and changing beam structure into plates or removing the beam elements from unnecessary dense regions controlled the stresses. Two cases of material properties have been considered for the bone material: isotropic and transversely isotropic. Walking, stair climbing and stumbling as three different loading patterns have been applied in this study. RESULTS: It is shown that the material properties have minor effect on the final morphology of trabecular bone. Moreover, as the magnitude of the load applied at the proximal femur increases, the trabecular structure becomes denser in critical zones. Bone volume fraction and bone density at the critical regions of the converged structure was compared with previously measured data obtained from combinations of Dual X-ray Absorptiometry and Computed Tomography. Our results indicated a high density region in the femoral head (BV/TV= 0.557) and a low density region in the femoral neck (BV/TV=0.124). Also, the low density medullary cavity was predicted in the converged models. CONCLUSION: Our findings were in good agreement with natural volume fractions reported by other studies. Stumbling loading condition resulted in the highest density; whereas walking loading condition which considered as a routine daily activity, results in the least internal density in different regions. Therefore, the proposed model can help to understand the structural effects of different individual loading patterns on the bone density and structure. Furthermore, the proposed model provides insight into selecting exercises which can be used to increase bone density at different regions of the proximal femur.