Construction of a finite element model based on lunate sagittal Micro-CT images and its stress analysis / 中国组织工程研究

ABSTRACT

BACKGROUND: Biomechanical mechanisms are complex, and previous studiers focus on the stress conduction in the carpus. However, the stress distribution and characteristics of trabecula in the carpus are rarely reported.OBJECTIVE: To investigate the stress distribution and deformation characteristics of the normal lunate through a two-dimensional sagittal finite element model.METHODS: A normal cadaveric lunate sample was scanned with Micro-CT and the central sagittal image was chosen for further finite element analysis (FEA). The chosen image was processed and imported into the finite element analysis software (Ansys 14.0). A two-dimensional sagittal finite element model of the lunate bone was established. Axial pressure was applied to the model with the wrist held in different positions, and nine regions of interests (ROIs) were identified, for which stress and displacement nephograms were created. These included the first principal stress (S1, the maximum stress in a principal plane), the third principal stress (S3, the minimal stress in a principal plane), shear stress (SXY, the component of stress coplanar with a material cross section), von Mises stress (SEQV, yielding begins when the elastic energy of distortion reaches a critical value)and displacement of each ROI (UY, displacement on the vertical plane of the lunate) which were calculated and compared.RESULTS AND CONCLUSION: (1) The stresses on ROIs located in the proximal and volar cortices of the lunate bone were much higher than those in the distal and dorsal cortices. At the proximal lunate, S1 was less than S3; however at the distal lunate, S1 was greater than S3. The ROIs of the distal and proximal ends of the lunate bone received much higher stress than the ROIs of the middle part. As for axial trabecular displacement,both distal and proximal ROIs were compressed by axial pressure. However, the dorsal and the volar parts of the proximal lunate moved in different directions at different wrist postures. Besides, the stress values and magnitudes of displacement were elevated in wrist flexion and extension compared to neutral position.Furthermore, the stress concentration zones (the proximal volar ROI, the proximal dorsal ROI, the distal volar ROI, and the distal dorsal ROI) had different directions of shear stress and displacement in different wrist postures. (2) These results suggest that when stress is loaded on a normal lunate model, four stress concentration zones, the proximal volar ROI, the proximal dorsal ROI, the distal volar ROI, and the distal dorsal ROI are found. The wrist postures can significantly affect the value and distribution of axial stress on the sagittal lunate.