The Unilateral Atlantoaxial Pedicle Screw Fixation For Traumatic Atlantoaxial Instability:Finite Element Analysis And Clinical Application

Objective: 1.To establish an upper cervical spine model by finite element analysis and verify the validity of the model.2.To study the biomechanical stabilities of unilateral atlantoaxial pedicle screw fixation combined with structural bone graft on the established model.3.To evaluate the feasibility,safety and efficacy of the unilateral atlantoaxial transpedicle screw fixation technique combined with structural iliac bone graft in the surgical treatment of unstable atlas fractures.Methods: 1.The volunteer was scanned with thin-slice CT.The CT data was imported into the computer to reconstruct the 3D point cloud model of the cervical spine,and to compose an editable geometrical solid model.Then,we parameterize the image information and establish the upper cervical spine model,namely the normal model.The normal group model images were edited to get Jefferson fracture finite element model.3.44 adult patients with unstable atlas fractures between Jan.2012 to Jun.2016 were recruited in this study.All cases were divided as group A and group B.Group A was undergoing unilateral atlanto-axial transpedicle screws fixation technique.Group B was undergoing bilateral atlanto-axial transpedicle screws fixation technique.Clinical and surgical evaluation including surgery time,blood loses,hospital stay,costs,success rate,postoperative atlant-oaxial stability and complication were performed.Functional outcomes of preoperation,6-month and final follow-up were evaluated by visual analog scale(VAS)and Japanese Orthopaedic Association Scores(JOA)..Bone grafting fusion was also evaluated.Results 1.A complete upper cervical spine model was established.The validity of the model was verified by comparing with the data in the literature.2.By comparing the activity of each segment and the maximum stress of the implant,it was concluded that unilateral atlantoaxial pedicle screws fixation combined with single cortical bone iliac bone graft has obvious advantages in flexion and extension activities.The degree of activity of the segment is well controlled,and the activity of the adjacent segment is not substantially affected.In the lateral bending and torsion activities,unilateral placement technique and bilateral placement technique have their own advantages.3.All the patients were followed-up,ranged from 14 to 48 months(average,28.4 months).The average operation time of group A was(123.35±18.21)mins,blood loss was(218.45±80.16)ml,hospital stay was(7.05±1.02)d,hospitalization expense was(4.57±0.88)ten thousand yuan,success rate was 100%,postoperative atlant-oaxial stability of all patients was abtained and there was no complication.The average operation time of group B was(173.35±12.44)mins,blood loss was(318.16±61.67)ml,hospital stay was(7.22±0.82)d,hospitalization expense was(6.73±0.17)ten thousand yuan,success rate was 100%,postoperative atlant-oaxial stability of all patients was abtained and there was no complication.there were significantly statistical differences between two groups in operation time,blood loss,hospital stay and hospitalization expenses(P<0.01).there were no significantly statistical differences between two groups in hospital stay,success rate,postoperative atlant-oaxial stability,cpmplication,VAS and JOA(P>0.05).Conclusion The unilateral atlantoaxial pedicle screws fixation combined with single cortical bone iliac bone graft technique and bilateral screw fixation technique both can play a role in fixation and stability of the fracture segment.In the aspect of biomechanical stability,it is a supplement to the method of atlantoaxial fusion with screw-rod constructs.Both unilateral and bilateral atlantoaxial transpedicle screws fixation technique combined with structural iliac bone graft have good clinical results for unstable atlas fractures.But unilateral atlanto-axial transpedicle screws fixation group has shorter operation time,less blood loses and less hospital costs.This operation was an alternative method in the surgical treatment of one-side pedicle dysplasia or comminuted lateral mass fracture and other unstable atlas fractures.