Biomechanical Study of Cortical Bone Trajectory Screws in Intervertebral Fixation of Lumbar Tuberculosis

Abstract BackgroundWe aimed to explore the biomechanical stability and advantages of cortical bone trajectory (CBT) screws in the treatment of lumbar spine tuberculosis and provide biomechanical basis for the choice of clinical fixation methods. Methods16 pig spine specimens (T12-L5) were selected to simulate the lumbar spine(L2-L3) tuberculosis bone destruction model in vitro. The 16 specimens were randomly divided into 4 groups, and short segments (pedicle screws of the diseased vertebrae) were assigned respectively. Fixation (group A), short-segment fixation (group B), fixation with pedicle screw (group C), fixation with CBT screw (group D), 4 specimens in each group , Each specimen in each group was subjected to biomechanical testing in the state of complete specimen (state 1) and L2-3 spinal tuberculosis model bone graft fusion and internal fixation (state 2). Load each specimen on the spine 3D exercise machine, respectively apply moments of 2N·m, 2.5N·m, 1N·m, 3N·m, meanwhile record the movement of the specimens in the four directions of flexion，extension，lateral bending and torsion ROM, compare Simultaneously analyze each group of ROM. ResultsThe ROMs of flexion, extension, lateral bending, and torsion in group A in state 1 and state 3 modes were （8.47±1.76）°、 （7.01±1.10）°、 （5.03±0.92）°、 （4.48±0.41）°and （4.78±0.07）°、 （2.91±0.16）°、 （2.66±0.09）°、 （2.23±0.05）°; the ROMs of flexion, extension, lateral bending and torsion in group B in state 1 and state 3 modes were （7.32±0.75）°、 （5.35±0.69）°、 （3.44±0.51）°、 （3.36±1.02）°and（3.51±0.29）°、 （1.74±0.04）°、 （1.53±0.31）°、 （1.23±0.08）°; The ROMs of flexion, extension, lateral bending, and torsion in group C in state 1 and state 3 modes were （10.01±0.39）°、 （9.05±0.25）°、 （7.42±1.06）°、 （6.92±1.15）°and （7.21±0.17）°、 （5.07±0.02）°、 （5.12±0.74）°、 （4.58±0.01）°; The ROMs of flexion, extension, lateral bending, and torsion in group D in state 1 and state 3 modes were （9.20±1.37）°、 （7.38±0.88）°、 （6.89±1.22）°、 （6.00±0.52）°and （6.06±0.16）°、 （3.99±0.02）°、 （3.85±0.08）°、 （3.47±0.10）°. The ROM value of each fixed mode group under the state of bone graft fusion and internal fixation was lower than that of the intact state, and the difference was statistically significant (P<0.05)，The t values are 4.531, 5.346, 6.008, 4.149; 9.481, 16.181, 11.814, 4.769; 4.349, 8.002, 4.473, 4.800; 5.041, 4.146, 12.232, 10.58. ConclusionCBT screw disease intervertebral fixation can not only provide sufficient mechanical stability, but also provide stronger stability when using the same fixed segment, and The fixed segments are minimized.