Daisuke Tawara

Mechanical evaluation by patient-specific finite element analyses demonstrates therapeutic effects for osteoporotic vertebrae.

Osteoporosis can lead to bone compressive fractures in the lower lumbar vertebrae. In order to assess the recovery of vertebral strength during drug treatment for osteoporosis, it is necessary not only to measure the bone mass but also to perform patient-specific mechanical analyses, since the strength of osteoporotic vertebrae is strongly dependent on patient-specific factors, such as bone shape and bone density distribution in cancellous bone, which are related to stress distribution in the vertebrae. In the present study, patient-specific general (not voxel) finite element analyses of osteoporotic vertebrae during drug treatment were performed over time. We compared changes in bone density and compressive principal strain distribution in a relative manner using models for the first lumbar vertebra based on computer tomography images of four patients at three time points (before therapy, and after 6 and 12 months of therapy). The patient-specific mechanical analyses indicated that increases in bone density and decreases in compressive principal strain were significant in some osteoporotic vertebrae. The data suggested that the vertebrae were strengthened structurally and the drug treatment was effective in preventing compression fractures. The effectiveness of patient-specific mechanical analyses for providing useful and important information for the prognosis of osteoporosis is demonstrated.

In Silico Analysis of the Biomechanical Stability of Commercially Pure Ti and Ti-15Mo Plates for the Treatment of Mandibular Angle Fracture

PURPOSE To investigate the influence of different materials and fixation methods on maximum principal stress (MPS) and displacement in reconstruction plates using in silico 3-dimensional finite element analysis (3D-FEA). MATERIALS AND METHODS Computer-assisted designed (CAD) models of the mandible and teeth were constructed. Champy and AO/ASIF plates and fixation screws were designed with CAD software. 3D-FEA was performed by image-based CAE software. Maximum and minimum values of biomechanical stability, MPS, and displacement distribution were compared in Champy and AO/ASIF plates made from commercially pure titanium grade 2 (cp-Ti) and a titanium-and-molybdenum (14.47% wt) alloy (Ti-15Mo). RESULTS For plates fixed on a model of a fractured left angle of the mandible, the maximum and minimum values of MPS in the cp-Ti-constructed Champy plate, upper AO/ASIF plate, and lower AO/ASIF plate were 19.5 and 20.3%, 15.2 and 25.3%, and 21.4 and 4.6% lower, respectively, than those for plates made from Ti-15Mo. In the same model, the maximum and minimum values of displacement in the cp-Ti-constructed Champy plate, upper AO/ASIF plate, and lower AO/ASIF plate were 1.6 and 3.8%, 3.1 and 2.7%, and 5.4 and 10.4% higher, respectively, than those for plates made from Ti-15Mo. CONCLUSIONS This in silico 3D-FEA shows that Ti-15Mo plates have greater load-bearing capability.

Stochastic Multi-Scale Finite Element Analysis of the Drilling Force of Trabecular Bone During Oral Implant Surgery

To avoid procedural accidents during/after oral implant surgery in a jawbone (e.g., perforation of the lingual side due to an inadequate drilling angle or scratching the mandibular canal), it is im...

Predicting changes in mechanical properties of trabecular bone by adaptive remodeling.

Abstract Because changes in the mechanical properties of bone are closely related to trabecular bone remodeling, methods that consider the temporal morphological changes induced by adaptive remodeling of trabecular bone are needed to estimate long-term fracture risk and bone quality in osteoporosis. We simulated bone remodeling using simplified and pig trabecular bone models and estimated the morphology of healthy and osteoporotic cases. We then displayed the fracture risk of the remodeled models based on a cumulative histogram from high stress. The histogram showed more elements had higher stresses in the osteoporosis model, indicating that the osteoporosis model had a greater risk.

Estimation of Changes in Mechanical Bone Quality by Multi-scale Analysis with Remodeling Simulation

Mechanical bone quality and its related load-supporting function at the macro-scale is a result of adaptation, which is achieved by trabecular bone remodeling at the microscale. The increase in fracture risk in patients with osteoporosis is a clear example of this structure/function relationship, where decreased bone mass as a result of structural changes during remodeling leads to changes in the stress distribution of trabecular bone. This stress distribution is closely associated with the morphology and orientation of the nano-scale biological apatite (BAp) crystallite - the main factor determining bone quality. It is therefore important to evaluate both the changes in mechanical bone quality and bone mass when predicting fracture risk. We propose a computational model of remodeling and multi-scale stress analysis of trabecular bone based on homogenization techniques, considering the mechanical properties of the BAp crystallite orientation to be anisotropic. We first identified morphological changes in healthy and osteoporotic cases, and then performed a multi-scale stress analysis for the remodeled osteoporotic trabecular bone to elucidate changes in mechanical bone quality leading to fracture risk. Our results demonstrate that the load-supporting function of remodeled bone correlates with mechanical adaptability to external loads through remodeling, despite a progressive decrease in bone mass. These findings suggest the potential to use changes in mechanical bone quality as a predictor of fracture risk. The availability of these simulation methods for bone quality evaluation is discussed.

REMODELING SIMULATION ESTIMATES CHANGES IN MECHANICAL PROPERTIES OF OSTEOPOROTIC BONES

Osteoporosis causes bone fracture due to changes in the stress distribution of the trabecular bone with structural change as well as a decrease in bone mass. It arises from an imbalance in bone remodeling which involves the coupling of bone formation and resorption by osteoblast/osteoclast [Cowin SC, 1991]. Therefore, an evaluation of mechanical properties of the trabecular bone with its morphological change by remodeling is necessary to estimate the long-term fracture risk. In this study, we simulated bone remodeling of a pig trabecular bone model and estimated morphology of healthy and osteoporotic cases using our proposed mathematical model of bone remodeling [Adachi T, 2001]. We also evaluated fracture risks using a cumulative histogram of high stress. Potential of evaluation of change in mechanical properties of the trabecular bone considering its remodeling is discussed.