BACKGROUND:At present,the surgical treatment of atlantoaxial dislocation mainly adopts the posterior atlantoaxial screw-rod internal fixation system for lifting and reduction.During the operation,the curvature of the connecting rod is often increased to increase the drop between the atlantoaxial vertebrae to improve the reduction effect,but it increases the difficulty and risk of surgery.The axis pivot screw directly increases the reduction drop between the atlantoaxial vertebrae,but the extent to which it increases the reduction capacity is unclear.OBJECTIVE:To test the reduction ability of axis pivot screw and compare it with ordinary screw.METHODS:Six fresh human craniocervical specimens were used in study.The joint capsules of two lateral mass joints and atlanto-odontoid joint and transverse ligament were removed to make an atlantoaxial instability model.Three kinds of internal fixation were performed successively on both sides of the axis of each specimen:uniaxial axis pivot screws(group A),multi-axial axis pivot screws(group B)and ordinary screws(group C).Flexible ultra-thin film pressure sensors were placed in the anterior atlanto-odontoid space.Two connecting rods with the same curvature were placed to simulate the lifting and reduction,and the pressure of the anterior atlanto-odontoid space was obtained.Comparative analysis was conducted among the three groups.RESULTS AND CONCLUSION:(1)The anterior atlanto-odontoid space pressure of groups A-C was(97.59±8.58),(60.43±5.09),and(22.74±0.81)N,respectively.There were significant differences among the three groups(F=251.603,P=0.000).The pairwise comparison among the three groups showed significant differences(P=0.000).(2)The axis pivot screw applied to the posterior atlantoaxial screw-rod internal fixation system can improve the reduction capacity compared with the common cervical posterior screw,and the uniaxial axis pivot screw has more reduction capacity than the multi-axis uniaxial axis pivot screw to improve the posterior atlantoaxial screw-rod internal fixation system.

BACKGROUND:At present,the surgical treatment of atlantoaxial dislocation mainly adopts the posterior atlantoaxial screw-rod internal fixation system for lifting and reduction.During the operation,the curvature of the connecting rod is often increased to increase the drop between the atlantoaxial vertebrae to improve the reduction effect,but it increases the difficulty and risk of surgery.The axis pivot screw directly increases the reduction drop between the atlantoaxial vertebrae,but the extent to which it increases the reduction capacity is unclear.OBJECTIVE:To test the reduction ability of axis pivot screw and compare it with ordinary screw.METHODS:Six fresh human craniocervical specimens were used in study.The joint capsules of two lateral mass joints and atlanto-odontoid joint and transverse ligament were removed to make an atlantoaxial instability model.Three kinds of internal fixation were performed successively on both sides of the axis of each specimen:uniaxial axis pivot screws(group A),multi-axial axis pivot screws(group B)and ordinary screws(group C).Flexible ultra-thin film pressure sensors were placed in the anterior atlanto-odontoid space.Two connecting rods with the same curvature were placed to simulate the lifting and reduction,and the pressure of the anterior atlanto-odontoid space was obtained.Comparative analysis was conducted among the three groups.RESULTS AND CONCLUSION:(1)The anterior atlanto-odontoid space pressure of groups A-C was(97.59±8.58),(60.43±5.09),and(22.74±0.81)N,respectively.There were significant differences among the three groups(F=251.603,P=0.000).The pairwise comparison among the three groups showed significant differences(P=0.000).(2)The axis pivot screw applied to the posterior atlantoaxial screw-rod internal fixation system can improve the reduction capacity compared with the common cervical posterior screw,and the uniaxial axis pivot screw has more reduction capacity than the multi-axis uniaxial axis pivot screw to improve the posterior atlantoaxial screw-rod internal fixation system.