Biomechanical Study On Optimization Of Screw Placement Strategy In Adolescent Idiopathic Scoliosis

?Background?Adolescent Idiopathic Scoliosis(AIS)is a kind of spinal deformity disease with unknown etiology,mainly in the growth and development period,seriously affecting the physical and mental health of teenagers,and gradually being valued by people.Although the etiology of AIS is not yet clear,the occurrence and development of the disease and the choice of treatment methods are closely related to the biomechanical characteristics of the spine.During the evolution of the disease,the imbalance of vertebral body development and the instability of the base caused by the tilt and rotation of the spine and pelvis all have an important impact on the further aggravation of the Angle.From the perspective of treatment methods supported by various theories,the development of supports and the continuous progress of surgical treatment methods such as pedicle screw internal fixation are all taking biomechanical characteristics as important research objects.Among them,the development of pedicle screw internal fixation orthopedic technology has brought the treatment of AIS into a new stage,and the surgical effect and the long-term quality of life of patients have been greatly improved,which can be said to be the "gold standard" of the current surgical treatment of AIS.Although the internal fixation technology is effective,but the expensive cost makes many patients daunting,miss the best treatment period or even give up surgery.In actual surgery,for patients from poor families,many spine surgeons choose to reduce the number of screw placement,in order to minimize the cost of surgery,reduce the burden of patients.However,in the process of surgery,it is often only based on personal experience,and the number and position of reduced screws are relatively random,which lacks the support of biomechanical research evidence.Moreover,the long-term effect of reducing the number of screws on the patient's condition is unclear.?Objectives?This study used the existing by verifying the three dimensional finite element model of the spine,the pedicle screws data substitution,simulating clinical commonly used several kinds of selective scheme,nailing through a lot of observing the operation situation,as far as possible when the computer simulation of joint action,gathering on the nail,on the bar,screw rod,the springback,lock the whole process of the stress data,comparing the pros and cons of various solutions through real-time computer mechanics cloud,to explore the best scheme for nailing,verified and long-term follow-up and returns the clinical work,in order to obtain the best applicable of the selective nailing.?Methods?1.The pedicle screw,nut and rod models were established.2.Determine the strategy for selective nailing3.Simulation of surgical procedures and analysis?Results?1.Pull out force: this study selected largest stress of pedicle screws,in pedicle screw length direction selection section of 20 different computing each section of the nails,orthopaedic way 1 nail maximum output of 12.4 N,orthopaedic way 2 nails maximum output of 15.7 N,orthopaedic way 3 nails maximum output of 28.6 N.In terms of nail pulling force,orthopaedic mode 1 was the best and orthopaedic mode 3 was the worst.2.Contact stress: The contact stress of the rod and the pedicle screw is sliding contact.The force of the pedicle screw in different parts can be directly seen from the contact stress of the rod.Figure 10 shows the contact stress of different orthopaedic modes.It can be found from the figure that the contact stress of orthopaedic mode 1 is distributed widely at both ends of the rod,and the maximum contact stress is 256.9MPa.On the other hand,it is proved that in the process of rod rotating,the two ends of the rod bear the largest force,which should be the focus of attention.The contact stress of orthopaedic mode 2 was 277.8mpa,and the value and distribution were similar to that of orthopaedic mode 1.The contact stress occurred at the place where the rod came into contact with the pedicle screw,and the stress distribution at both ends of the rod was large.On the other hand,it was confirmed that the stress at both ends of the rod was the largest in the process of rod rotation,which should be the focus.Orthopaedic way 3 ways of contact force distribution and orthopaedic 1 and 2 are similar,the maximum contact stress is 305.2 MPa,are larger than the other two types of orthopaedic,contact stress occurred in good contact with pedicle screw,the ends of the rod stress distribution is larger,on the other hand,demonstrated in the process of turning bar,bar the ends of the largest stress,should be to focus on the parts.It can be found from figure 10 that the distribution of contact stress is the maximum at both ends of the rod,and this part should be the key part,which is prone to failure and fracture of the nail rod.From the point of contact stress value,the contact stress of orthopaedic mode 1 and 2 is similar,while the contact stress of orthopaedic mode 3 is obviously greater than that of orthopaedic mode 1 and 2.This indicates that orthopaedic mode 3 is the most prone to nail rod failure.The results were consistent with the maximum pulling stress of pedicle screw.?Conclusions?In the interval of alternating screw placement,the extractive force and contact stress of the screw rod are the minimum,and the mechanical properties are better than the whole screw placement method,which can be used for AIS surgery and orthopedic treatment.