The effect of mechanical stimuli on numerical simulation of bone remodeling / 医用生物力学

Objective To study the effect of three different kinds of mechanical stimuli (i.e. strain energy density, equivalent stress and equivalent strain) on numerical simulation of bone remodeling. Methods A two-dimensional finite element model of the proximal femur was constructed. Based on the mechanostat theory and finite element method, the inner structure of the proximal femur and its density distributions under the three different stimuli were predicted. Then the simulation results were compared quantitatively with calculation results obtained from CT images. ResultsThe predicted density distributions on the proximal femur under different stimuli were all well matched with the real structure of the proximal femur. By comparing the values and shapes of the calculated bone density curves, the predictions from the model using equivalent stress as mechanical stimuli were mostly consistent with the CT images. ConclusionsThe equivalent stress might play a leading role in mechano-regulation algorithms of bone remodeling. The accurate prediction of bone remodeling process will provide a theoretical basis for clinical practices such as orthopedic surgery, treatment of bone diseases and personalized design and optimization of prosthesis.

Biomechanical effects on sacroiliac fusion for treating low back pain / 医用生物力学

Objective Based on the finite element method, both sacroiliac fusion and sacroiliac contact models were built to compare the biomechanical differences between the two models and to explore the biomechanical mechanism in the treatment of low back pain by sacroiliac fusion. Methods Two pelvic finite element models were constructed, including the pelvic ring, sacrum, part of the femur, ligaments, cartilage and joint contact. The sacroiliac joints were set to be contact in one model and fusion in the other, respectively. Differences in mechanical conduction on the pelvic ring and the stress on the sacroiliac cartilage under 500 N load between the two models were explored. Results For the fusion model, stresses and displacement on the sacroiliac joint were significantly lower than that of the contact model, especially on the sacroiliac cartilage, where the displacement was reduced by 261% from 0.83 mm to 0.23 mm, and the stresses reduced by 32% from 6.6 MPa to 5.0 MPa. However, the transfer of stress on the pelvic ring was relatively more concentrated in the fusion model. Conclusions Sacroiliac fusion may provide better therapeutic effects on the treatment of low back pain, but the risk of disc herniation and femoral head necrosis must be assessed seriously in advance.