Immediate Biomechanical Analysis Of Three Different Lumbar Interbody Fusion Methods Combined With Pedicle Screw Fixation For Pig Lumbar Vertebrae Simulated L3/4 Lumbar Spine In Vitro

Background: Posterior lumbar discectomy,decompression,interbody fusion and pedicle screw internal fixation are common methods for the treatment of lumbar degenerative diseases.In the past,the simulated lumbar degeneration in vitro was fixed with pedicle screw,and the biomechanical evaluation of the intervertebral fusion was mostly used to evaluate the flexion and extension of spine specimens.Loading was applied to measure the displacement of the specimens,and the stability of the specimens was evaluated by the displacement value.In vitro simulation of L3/4degeneration of lumbar spine,posterior lumbar discectomy,bone graft,PEEK fusion cage and titanium cage implantation fusion,stress and strain analysis immediately after pedicle screw fixation are rarely reported.Objective: To establish a degenerative model of L3/4 lumbar spine in vitro,and to compare and analyze the biomechanical effects of three different posterior interbody fusion methods combined with pedicle screw fixation on the edge and adjacent segments of the fixation site immediately,so as to perform L3/4 degenerative posterior vertebral fusion combined with pedicle screw fixation and intervertebral fusion in clinic.The selection of combination mode and the design of new fusion device provide biomechanical theoretical basis.Methods: A total of 18 boars were selected.The boars were killed the fresh spinal specimens of the pig’s chest 15 to lumber 6 were taken out,simulating the T12-S1 spine of the human body,and making an in vitro model.They were randomly divided into 3 groups: posterior intervertebral discectomy,intervertebral bone graft fusion and pedicle screw fixation group(bone graft group);posterior intervertebraldiscectomy,intervertebral Titanium cage fusion and pedicle screw fixation group(Titanium cage group);posterior intervertebral discectomy,intervertebral PEEK cage fusion and pedicle screw fixation group(PEEK cage group).Resistance strain gauges were pasted at the same measuring points before and after the fusion of the three groups of specimens.The strain values of the three groups were measured by strain electrical measurement at the same measuring points before and after the fusion of the three groups of specimens.The strain values of the three groups were calculated according to the material mechanics formula under the conditions of forward bending,backward extension,left bending and right bending.Stress values of each measuring point before and after specimen fixation.Results: Strain Electrical measurements of each group showed that the strain and stress of the titanium cage group in the forward bending,extension,left bending and right bending of the titanium cage group were all smaller than those in the bone graft group and the PEEK cage group in the simulated L3/4 degeneration model.Under the same bending moment,the strain and stress of each measuring point in the PEEK cage group were less than those in the bone graft group under the conditions of flexion,extension,left bending and right bending,and the difference was significant.Conclusion: Immediately after posterior L3/4 discectomy,bone graft group,PEEK fusion cage group and titanium cage group were treated with interbody fusion and pedicle screw fixation respectively,the strain and stress of fusion and fixation segments and adjacent segments were affected differently by different interbody fusion methods,which resulted in different biomechanical stability of spine.Choosing appropriate implants can minimize the influence of posterior interbody fusion combined with pedicle screw fixation on strain and stress of adjacent segments,so as to reduce the probability of degeneration of adjacent segments.