Simulation And Experimental Study Of Forces In Sternum Sawing For Thoracotomy

Median sternotomy is the standard approach for open heart surgery.The current surgery has problems such as large damage to the incision interface and difficult healing of the bone tissue.In this paper,combined with clinical needs,the simulation and experimental research on the sternum sawing force are carried out.The main contents and conclusions are as follows:Aiming at the structural characteristics of sternum anisotropic viscoelastic biocomposite structure,a composite constitutive mechanical physics model of bone tissue based on bone unit reinforcement was established.The UTQUS VUMAT subroutine was used for secondary development,and the bone tissue composite was modeled as a macroscopic whole.The subroutine included the constitutive model of the orthotropic material,the stress-strain relationship,the stress update.and the stiffness degradation,damage initiation,failure criteria and unit deletion,etc.,using the progressive damage analysis method,overcome the limitations of the elastoplastic constitutive model of bone cutting simulation,and solve the convergence problem caused by excessive distortion of material elements in bone cutting simulation.Based on the above-mentioned bone tissue constitutive model,the finite element method was used to simulate the three-dimensional dynamic simulation process of sternal sawing,and the mechanism of sternal bone sawing was systematically studied.The simulation analysis found that the material damage during the bone sawing process is mainly realized as elastic brittle fracture,and the plastic deformation is small,and the chip shape is chopped and chipped.In the sawing three-way force component,the sawing resistance is much greater than the feed resistance and lateral force.The presence of the bone unit enhances the strength of the bone tissue,and the sawing force is greatest when the sawing direction and the angle of the bone unit are close to 90°.The increase in the sawing depth increases the number of teeth participating in the sawing at the same time,and the sawing force is significantly increased.The sternal sawing experiment was designed,and the trend of the experiment and simulation results was roughly consistent,which verified the validity of the simulation model.The experimental results show that the sawing frequency is the main factor affecting the sawing force.When the sawing frequency is small,the change of the sawing force is not obvious.When the sawing frequency is more than 8000 times/min,the sawing force gradually increases as the sawing frequency increases.The feed rate has little effect on the sawing resistance,and the feed resistance increases with the increase of the feed rate,and the excessive feed rate causes the sternum saw to flutter.The optimal process parameters for sternal sawing are a feed rate of approximately 1.2 mm/s and a sawing frequency of 6000 to 7000 beats/min.At this time,the mechanical damage to the bone tissue is small without affecting the surgical efficiency.The above research work constructs the sternum simulation model and systematically reveals the influence of the sternum sawing parameters on the sawing force,and provides a scientific theoretical basis for the reasonable operation of doctors in sternal thoracotomy to reduce sternal injury.