| Purpose1.To design a new type of atlas screw by measuring the CT parameters of the atlas.2.Pull force test was performed on the new screw in vitro specimens to compare its biomechanics.3.Evaluation of biomechanics of new atlas screws by finite element method.4.Biomechanics of different installing modes of crosslink with C1-C2 pedicle screw-rod fixation were tested on cadavers.5.Biomechanics and stress distribution of crosslink in C1-C2PSR were analyzed by finite element method.6.To compare the clinical efficacy of different installation modes of transverse connection combined with C1-C2PSR in the treatment of atlantoaxial dislocation.Methods1.CT data of 60 adults were selected,and the cortical bone thickness(AB,CD,EF,GH),the distance between entry and exit point(AD,EH),and the thickness of vertebral artery groove(VGH)of pedicle and lateral mass were measured by Mimics software.A new type of screw with double and triple thread was designed.2.Eighteen fresh atlas specimens were used for pedicle and lateral mass fixation with triple,double,and single thread screws,respectively,and the screw pulling strength was compared.3.CT data of a normal human atlas were selected,and software was used to fix the pedicle and lateral mass of single and double cortical pedicle screws with triple,double and single thread screws in normal and osteoporosis models,and the screw extraction force and stress distribution were measured.4.Complete group(A)and instability model(B)were established for 6 fresh occipitocervical specimens.group C was established by C1-C2PSR which was performed for group B,hR-R CL and hS-S CL were installed for group C which established group D and E(upper crosslink E1,lower crosslink E2,left upper and right lower crosslink E3,left lower and right upper crosslink E4 and X crosslink E5).Each group of ROM was loaded,tested and analyzed.5.The above 9 finite element models were established,the ROM and internal fixed stress peaks were measured,and stress cloud maps were extracted.6.Thirty-two patients with atlantoaxial dislocation were treated with hS-SCL+C1-C2PSR in 7 cases,hR-RCL+C1-C2PSR in 12 cases,and C1-C2PSR in 13 cases.Operation time,blood loss,complications,neurological function,and bone graft fusion were compared.Results1.AB:3.87±0.64mm,CD:2.47±0.63mm,AD:29.21±1.93mm,EF:3.69±0.65mm,GH:2.64±0.48mm,EH:16.88±1.23mm,VGH:4.41±0.28mm.There was no statistical difference between left and right,P>0.05.2.The maximum pull-out force of the triple threaded bicortical pedicle fixation was the largest,Pearson correlation analysis showed a positive correlation between the pull-out force and screw length.3.The screw maximum pull force:Triple thread>double thread>single thread;There was statistical difference between single and double cortical fixation and diameter 4.0mm and 3.5mm;the screw stress was distributed in the caudal and middle parts.4.Under flexion and extension states,the ROM was group C=D=E<A<B;Under lateral flexion and rotation states,the ROM was group E5=E3/E4<E1/E2=D<C<A<B.5.Under lateral flexion and rotation states,Compared with no crosslink group,the ROM of crosslink group decreased by 33.3%～47.4%and 76.4%～92.6%respectively,the ROM decreased most in E5 group.The crosslink stress is distributed at both ends.6.There were no significant differences in blood loss,operation time and neurological function recovery among the three groups,Bone graft fusion:the crosslink group was earlier than the non-crosslink group,There was no statistical difference between hS-S CL group and hR-R CL group(P>0.05).Conclusion1.The new atlas screw design is feasible.2.The same mode of screw fixation strength:triple thread>double thread>single thread;Diameter 4.0mm is better than 3.5mm;Bicortical fixation is stronger than monocortical fixation.3.E5 group has the strongest anti-rotation stability,but the two ends of the crosslink may be more prone to breakage.4.The crosslink group had earlier bone graft fusion,and the hS-SCL group and hR-RCL group had similar efficacy,but the former group was more convenient to install. |
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