Basic Research And Clinical Application Of Cervical Translaminar Screw

OBJECTIVE 1.To analyze the imaging anatomy of translaminar screw in cervical spine(C2-C7),to compare the differences of surrounding osseous structures of the spinal canal between developmental cervical stenosis and normal people based on the anatomical measurement,and to summarize the acceptance rates of translaminar screws at each level.2.To test the feasibility and biomechanical properties of the innovative techniques of cervical translaminar screw in the biomechanical experiment.3.To describe the techniques and indications of cervical translaminar screw in clinical application with typical cases.METHODS 1.The research objects were divided into two groups: the developmental cervical stenosis(DCS)group and the normal control(NC)group.The anatomical measurement of the surrounding osseous structures of spinal canal at C2-C7 segments was performed by three-dimensional CT reconstruction,including multiple parameters with pedicle,lateral mass and lamina.The statistical significances of the parameters between the two groups were compared respectively.Eventually,we performed the analysisof the acceptance rates with different diameters translaminar screw at different levels.2.We innovatively proposed the unilateral C1 double-screw and ipsilateral C2 PS combined with contralateral C2 LS-rod fixation technique(Group C)for atlantoaxial instability.To analyze its feasibility and to evaluate its biomechanical properties,we measured the anatomical parameters of the C1 double-screw,and compared the biomechanical flexibility with traditional bilateral C1-C2 pedicle screws(Group B)and unilateral C1-C2 pedicle screws(Group A),respectively.3.We also innovatively proposed the unilateral PS combined with a contralateral translaminar screw(UPS+CTLS)technique for short-segment fixation at the subaxial cervical spine.To study its feasibility and to evaluate its biomechanical properties,its biomechanical flexibility was compared with bilateral mass screws(BMSs)and bilateral pedicle screws(BPSs).Then,the pullout strength test was performed for the PSs,LMSs and translaminar screws(TLSs)using seven isolated C4 and C5 vertebrae.4.We described several types of hybrid fixations combined with translaminar screw that can be applied to various clinical cases,and discussed the surgical procedures and their corresponding indications.RESULTS 1.Anatomical measurement at C2 level showed that the parameters of PW and LW were significantly higher in DCS group than inNC group.However,the PTA was significantly smaller in DCS group than in NC group.The other parameters had no significant differences between the groups.Anatomical measurement at the subaxial cervical spine showed that,SCSD and VBSD were significantly different between groups at all levels.The parameters of width in PW,LW and LMW were significantly higher in DCS group than in NC group at all levels,except LMW in C7.Measurement of anatomical angles showed significantly smaller PTA in DCS group than in NC group at all levels.In contrast,LTA was statistically more obtuse(higher degree)in the DCS group at C4-6.Unexpectedly,except LML in C5,there were no significant differences in LL and LML at all levels,which is inconsistent with previous reports.However,PL was statistically shorter in the DCS group at all levels.Eventually,DCS group had higher acceptance rates of TLS than NC group at all levels.2.Results of morphological measurement of C1 double-screw suggested that,the working thickness of the C1 PS was ≤3.5 mm in only 1(1/15=6.7%)specimen and the other parameters were >3.5 mm in all specimens.In the ROM test,all fixation groups showed significantly reduced flexibility in all directions compared with both the intact and destabilization groups.Further,Groups B and C were found to have better stability in all directions than Group A.However,no significant differences were observed between Groups B and C.3.Biomechanical test in the subaxial cervical showed that,the UPS+CTLSgroup showed no significant difference from the BMS group in the three-plane ROM or from the BPS group in the axial rotation or flexion-extension ROM but showed a significantly greater lateral bending ROM than the BPS group.The pullout strength test showed that both C4 and C5 TLSs exhibited strength similar to that of LMSs but poorer than that of PSs.4.The hybrid fixation techniques of C2 translaminar screws has no obvious technical difficulty in clinical application,and the CT measurement is recommended to be a precondition for the use of subaxial cervical translaminar screw due to the limitation of laminar anatomical conditions.CONCLUSIONS 1.The surrounding osseous structure of spinal canal was significantly thicker in DCS group than in normal group,thus larger screw in diameter may be recommended in DCS patient.2.The novel technique of unilateral C1 double-screw and ipsilateral C2 PS combined with contralateral C2 LS-rod fixation provided better stability than unilateral PS-rod fixation,while is similar as the bilateral PS-rod fixation.This may be a feasible salvage method that provides a new insight for atlantoaxial instability.3.Fixation with the hybrid UPS+CTLS construct performed a comparative sffectiveness with the BMS fixation in our biomechanical tests,and mayplay a clinical role when BPS or BMS placement is not feasible for short-segment fixation.4.The translaminar screw can be used as an alternative technique combined with various screw fixation techniques in clinical application.It is recommended to perform CT scan preoperatively to analyze the anatomical structure of the lamina.