A novel screw head design of pedicle screw for reducing the correction loss in patients with thoracolumbar vertebral fractures: a biomechanical study

Bin Ye, Ming Yan, Huiyang Zhu, Wei Duan, Xueyu Hu, Zhengxu Ye, Zhuojing Luo
2016 Journal of Orthopaedic Translation  
appear to be most critical. We hypothesized that the developed fracture prediction tool would be able to identify the fracture risk from these critical lesions. The aim of this study was to analyse porcine femurs affected by simulated AVN lesions to understand loading on subsequent failure of bone as well as the assessment of geometric and material parameters on fracture risk. Methods: A computational tool was created which predicted the stress and strain of the bone structure under loading and
more » ... e under loading and its susceptibility to geometric and material properties. Beam theory was used to calculate the maximum loading force at which the bone was likely to fracture. The forces acting on the upper femur were simplified and merged to a single static joint contact force pointing to the centre of the femoral head. Geometric and material properties such as Young's modulus were derived from non-invasive three dimensional computed tomography images (QCT) using a material model. Fifteen porcine femurs were compression tested until failure, where apart from the control samples each femur had an artificial lesion at one of two different positions within the femoral head, lateral and medial to the fovea. The predicted fracture load and location was compared with experimental results. Results: The predicted fracture load and site correlated well with the experimental data. When analysing fracture at the neck, the predicted fracture loads for the lesion affected femurs were lower throughout. Lesions within the subchondral area had a huge impact on the stability. This trend has been seen in the computational as well as in the experimental data. The predicted fracture load was up to 50% lower within the femoral heads which had a lesion lateral to the fovea. Experimentally as well as computationally there was no difference between the control samples and the heads affected by a lesion medial to the fovea. Discussion: This in-vitro study demonstrated that fracture prediction based on beam theory is a viable tool to predict fracture. The tool correctly identified the femoral neck and points at the head as fracture sites. The lesion position plays an important role and lesions lateral to the fovea in the weight bearing area are more severe. Slippage of the epiphyseal plate decreased the stability of the porcine femurs indeterminably and made an exact calculation of the fracture load more difficult. http://dx.
doi:10.1016/j.jot.2016.06.055 fatcat:22pdk6zcnjdmzah35ubsyae5va