Finite Element Analysis Of Absorbable Sheath To Prevent Stress Shielding Of Interlocking Intramedullary Nail

Domestic and foreign researchers believe that the traditional interlocking intramedullary nail fixation is a strong static fixation,the disadvantage is that it can produce stress shielding effect.At present,the mainstream solution is to achieve the transformation of interlocking intramedullary nail from static to dynamic fixation.The commonly used method in the clinic is the screws of one end of the intramedullary nail are removed in the metaphase of fracture healing to make fracture ends produce fretting and pressure to stimulate the growth of callus,but this requires patients to undergo surgery again.In order to avoid the defects mentioned above,the nail with absorbable sheath(AS nail)is designed in this study by combining the absorbable sheath with the common metal nail(CM nail).The basic principle of the AS nail is the absorbable sheath sheathed on the common metal nail using the degradation of absorbable materials to reduce the stress shielding effect of the interlocking intramedullary nail.In this paper,the effect of AS nail is verified by the method of finite element analysis and mechanical experiment.The specific research content and results are as follows:(1)Establishment and validation of finite element model of normal human femur and goat femur.In this part,the finite element model of human and goat femur was established,and the strain gauge experiment of goat femur was completed.By comparing the finite element simulation results with the existing authoritative data and the strain gauge experimental data,the accuracy of the finite element model of human and goat femur is verified respectively.(2)The finite element analysis of internal fixation model of human femoral interlocking intramedullary nail.In this part,the finite element model of internal fixation of human femoral interlocking intramedullary nail with the AS nail and the CM nail was established respectively;The stress and longitudinal displacement of the callus at the fracture site and the stress shielding rate of the fracture fixation with the two kinds of nails were analyzed at the 0,1,3,6,9 and 12 months after fracture healing;The strength and reliability of the AS nail,the CM nail and the interlocking intramedullary nail in different periods of fracture healing were analyzed and verified.The results showed that in the early stage of fracture healing,the strength of the AS nail and the CM nail are both high,which can provide a stable mechanical environment for the broken end of the fracture.In the middle and later stage,due to the degradation of absorbable sheath in the AS nail group caused the fracture ends produced fretting and pressure.Compared with the traditional static CM nail fixation group,the stress shielding effect of the interlocking intramedullary nail on fracture ends was reduced more effectively.(3)Finite element analysis of femoral internal fixation model of goats and mechanical experiment validation.In this part,the finite element model of internal fixation of goat femoral interlocking intramedullary nail with the AS nail and the CM nail was established respectively,and the stress shielding rate of the two kinds of nails on fracture ends was analyzed during different healing period;The vertical compression test of the femur(after taking the nail)at different stages of fracture healing was completed.The relationship between the stress and longitudinal displacement of callus at the broken ends of goat femur in finite element simulation and the maximum bearing capacity of femur during vertical compression was comparatively analyzed.The results showed that the stress shielding rate of the AS nail group on fracture ends was less than that of the CM nail group;The callus stress and longitudinal displacement of the AS nail group were positively correlated with the bearing capacity of the femur,and all were greater than the CM nail group.(4)The introduction of animal experiment about the interlocking intramedullary nail fixation used in the femur of goat.This section introduces the experimental equipment needed for the implantation of goat femoral interlocking intramedullary nail and the entire surgical procedure.Through the observation of the X-ray films of the AS nail group and the CM nail group in the postoperative period,we further verified the feasibility of using the AS nail to reduce the stress shielding effect of the interlocking intramedullary nail.