Biomechanical Comparison Of TAPR-â…¢ System And Posterior Pedicle Screw-rods System In Atlantoaxial

BackgroundUpper cervical spine disorders have been plaguing clinician. Irreducible atlantoaxial dislocation (IAAD) with ventral spinal cord compression is difficult to treat, in particular basilar invagination, because of the odontoid process moves up, ventral spinal cord severely compression can be decompression through reduction of atlantoaxial to the anatomic position of pull-down the dens. The current operation mode of transoral approach of craniovertebral junction site of lesion, from direct anterior release of hyperplastic scar, callus tissue, and anterior or posterior reset, and the dislocation under the condition of atlantoaxial reduction to normal anatomical position or will be moved to the foramen magnum of the odontoid drop, restoration of vertebral canal the effective cross-sectional area, can effectively relieve the extension of ventral spinal cord compression, the compression of spinal cord decompression extension effectively, and then fixed, fusion of the corresponding segment. Current transoral atlantoaxial reduction plate system (TARP-III) and posterior atlantoaxial screw-rods (plate) technology are the most mature fixation with a reset function for atlantoaxial dislocation. However, anterior or posterior fixation methods still have relatively extensive controversy. However, it is unknown about the stability and the pull-down strength of axis between anterior Transoral Atlantoaxial Reduction Plate system (TARP-Ⅲ) and posterior atlantoaxial pedicle screw-rod system in atlantoaxial. No comparative in vitro biomechanical testing has been previously done to evaluate the axis pull-down forces during the anterior and posterior reduction procedure and the stability between anterior Transoral Atlantoaxial Reduction Plate system (TARP-Ⅲ) and posterior atlantoaxial pedicle screw-rod system in atlantoaxial. In the present study, we evaluated the stability and the pull-down strength of axis between anterior Transoral Atlantoaxial Reduction Plate system (TARP-III) and posterior atlantoaxial pedicle screw-rod system in atlantoaxial and provide biomechanical basis for clinical application.Materials and Methods1. Six fresh human cadaveric atlantoaxial complex specimens with intact ligaments (C0-C3) were tested and made cervical complete state experimental model, double plastic sealed and stored at-20degrees temperature refrigerator spare. Internal fixation materials are titanium alloy (TARP-III plate system, posterior cervical spine pedicle screw-rod system by Shandong Weigao orthopaedic materials company).The specimens were divided into A groups:normal group, group B:atlantoaxial anterior TARP system fixation group, group C:posterior pedicle screw fixation group. Each group of6specimens, each specimen in each specimen are respectively fixed, the3groups of experiments by random principle, firstly tested specimens in the control groups, then each specimen with anterior and posterior fixation system, tested the flexion/extension, the left/right side flexion, left/right axial rotation of6kinds of physiological sports, excluding inner fixation effect, after each experiment, specimens in non destructive motion testing experiments can be restored to the state before the experiment.In non destructive manner using gait analysis system (Motion Analysis,6Eagle system, the United States of America mumbo jumbo motion analysis technology company) were measured. Specimen after fixation, in C1, C2vertebral body on the3fluorescent Mark with C1and C2plane marker (3points determine a plane). Then the specimens applying2.0Nm pure couple distance, measurement under different states of C1, C2segmental flexion/extension, the left/right side flexion, left/right axial rotation of6kinds of physiological movement, composed of six fluorescent photosensitive camera capture C1, C2segment in0load and the maximum load (2.0Nm) state trajectory. Through computer analysis system for measuring C1, C2segment angular displacement of ROM. Each test was repeated3times for loading/unloading cycle, in third cycles of kinematic measurement, in order to reduce the influence of viscoelastic specimen. If any one direction ROM increased significantly, the segmental instability, internal fixation system provided by the fixing effect is poor; instead, it indicates that the segment internal fixation system is able to provide a stable, fixed effect. The results of the test will be flexion/extension, the left/right side flexion, left/right axial rotation of6kinds of physiological movement into flexion extension, lateral flexion, rotation of three-dimensional movement and calculate different fixed model ROM values of the mean and the standard deviation.Repeated measures analysis of variance were statistically compared, statistical tests of significance level=0.05, P<0.05, showed that there were statistically significant differences in materials and methods.2. Six fresh human cadaveric atlantoaxial complex specimens with intact ligaments (C0-C3) were tested and made cervical complete state experimental model, double plastic sealed and stored at-20degrees temperature refrigerator spare. Internal fixation materials are titanium alloy (TARP-Ⅲ plate system, posterior cervical spine pedicle screw-rod system by Shandong Weigao orthopaedic materials company). The specimens were divided into group A:anterior TARP system fixed group, group B:posterior pedicle screw fixation group. Successively underwent anterior TARP system fixation and posterior atlantoaxial pedicle screw rod system fixation, and relevant biomechanical measurement. All specimens in random sequence are respectively fixed on the BOSE material testing machine (ELF-3510AT. Bose. Inc, USA), embedded processing good specimens are on edge of axis odontoid part and the displacement sensor is connected to the lower edge of the fixed, mechanical sensor. Anterior TARP-III system fixed in atlantoaxial combined with the distraction reduction device, simulation operation of distraction reduction process, in the reset pivot arm is equal on both sides by sequentially applying distraction load (60N/80N/100N), BOSE material testing machine records generated in the process of spreading axis drop separating force and atlantoaxial of inter vertebral separation displacement, similarly to the posterior pedicle screw rod system fixation to atlantoaxial, the connecting rod is placed in the screw tail groove, tightening the C2tail run, C1tail risk is screwed into the screw tail half, make the connection rod in the pedicle screw tail groove sliding up and down, and drive the atlantoaxial on separation. Using the distraction device on both sides simultaneously applied with equal force of anterior distraction, BOSE material testing machine records generated in the process of spreading axis drop separating force and displacement of the atlantoaxial of inter vertebral separation.Paired t test was used for statistical comparison, statistical tests of significance level is0.05.P<0.05showed the difference was statistically significant.Results1. Fixed before and two different fixation of atlantoaxial between flexion/extension range of motion results in flexion/extension state, its stability order:B, C> A, A and B, C, P<0.001indicates anterior TARP system fixation and posterior pedicle screw fixation the group with normal atlantoaxial group there was significant difference between B, C; P=0.074>0.05, TARP system fixed group and that of anterior posterior pedicle screw fixation group showed no significant difference between.Under the condition of different fixation of atlantoaxial between left/right lateral flexion range of motion results showed the left/right side flexion range of motion:B. C>A, A and B, C, P<0.001indicates anterior TARP system fixation and posterior pedicle screw fixation group and normal atlantoaxial group and there was significant difference between comparison between B, C; P=0.671>0.05, TARP system fixed group and that of anterior posterior pedicle screw fixation group showed no significant difference between.Under the condition of different fixation of atlantoaxial between left/right rotation range of motion results showed a left/right rotation range of motion:B, C> A, A and B, C, P<0.001indicates anterior TARP system fixation and posterior pedicle screw fixation group and normal atlantoaxial group and there was significant difference between comparison between B, C; P=0.061>0.05, showed the difference in stiffness between the TARP group and pedicle screw-rod group was not statistically significant.2. Biomechanical testing results show:the anterior TARP III system fixed restoration in anterior respectively, applying different distraction load (60N/80N/100N) when TARP III system on the anterior atlantoaxial inter vertebral separating force generated by (on the axis resulting drop separation force) average value is:(26.11±2.08) N、(36.08±2.40) N、(45.01±2.26)N; in the atlantoaxial inter vertebral resulting separation displacement average value is:(0.87±0.07)mm、(1.07±0.07)mm、(1.14±0.06)mm. In the posterior pedicle screw fixation of atlantoaxial reduction and fixation, intervertebral separating force generated by (on the axis resulting drop separation force) average value is:(22.09±1.45)N、(29.77±2.36)N、(40.80±3.41) N; in atlantoaxial inter vertebral resulting separation displacement average value is:(0.82±0.07) mm、(1.01±0.08) mm、(1.06±0.08) mm. On axis under pulling force and displacement of the anterior atlantoaxial posterior inter vertebral separation, paired t test statistical comparison group, P<0.05, the difference was statistically significant.Conclusion1. The TARP-Ⅲ system fixation and pedicle screw-rods fixation methods were significantly stiffer than the control group. The anterior TARP-Ⅲ system provided stiffness equal to posterior pedicle screw-rods fixation.2. Transoral atlantoaxial reduction plate system (TARP) provides the pull-down strength of axis reduction significantly superior to atlantoaxial pedicle screw-rods system. In situations in which the use of salvaging fixation is required, the surgeon should anticipate a significant increase in the reduction force compared with posterior pedicle screw-rods system.3. Experimentally,, in a three-dimensional stability, the anterior TARP-Ⅲ system provided stiffness equal to posterior pedicle screw-rods fixation; on the pull-down strength of axis reduction performance of TARP system with the posterior screw-rod system performed better, with good biomechanical properties. And the TARP system fixation technique simplifies the operation steps, obviating the need for excision of odontoid process, avoids the injury to the spinal cord, spinal nerve, cerebrospinal fluid leakage caused by the operation complications, reduce operation risk. Therefore, the TARP system seems reasonable that the reliable and rigid fixation can be considered good procedures for stabilizing the atlantoaxial joints.