Biomechanics Comparison And Analysis Of Fusion With Non-fusion Fixation Of Lumbar Spine

ObjectTo investigate the biomechanical effects of Isola pedicle screw internal fixation and DIAM fixation for Lumbar Spine.The Isola pedicle screw internal fixation system is used to imitate the fusion fixation. The DIAM is one of non-fusion fixation devices.MethodNine fresh cadaveric lumbers specimens L1-L5, maintaining interosseous membrane, discs, intervertebral joint capsule, ligaments and removing sacrospinous muscle, psoas major muscle, were divided into three groups:Normal specimens, the DIAM group and the Isola system group. The specimen mechanical parameters which correlate to load under conditions such as axial compression, flex, extension and lateral bending, were tested and collected.ResultsFrom the results of lumbar vertebrae, disc and facets on the load-strain, both the DIAM and Isola pedicle screws system can stable the spine. DIAM, in addition to increasing the role of spinal stability, make the zygapophysiales more uniform in extension position, increasing the carrying capacity of the rear structure. The spine gets more stably.From the results of lumbar vertebrae, disc and facets on stress intensity, DIAM stress intensity is close to normal stress. Isola fixation system has the same effect, but stress intensity losts too large. Stress shielding effect comes up, which makes adverse effects. From the results of lumbar intervertebral and disc displacement under the physiological load, both the DIAM and Isola play a role in stabilizing the spine. DIAM is more close to the normal specimens than the Isola pedicle screws system, and therefore the Isola pedicle screws system increased the compensation of displacement of adjacent segments, thus increasing the possibility of ASD.From the results of physiological axial load and lumbar disc levels of shear rigidity, both the two systems have strong resistance to compression and shear deformation. DIAM is close to physiological conditions, Isola pedicle screw fixation system is stronger. However, excessive enhancement will increase the load of adjacent segments. From the results of lumbar spine torque stiffness, Isola pedicle screw system has a very good torsional capacity. DIAM is relatively weakly, and it’s torsional stiffness can not meet the need of anti-torque, which restrains its indications.ConclusionBoth the DIAM and Isola pedicle screw system can improve the spinal stabilization. Furtherrmore, the spinal which the DIAM is used in is closed to normal situation, compared to fusion fixation.The Isola system fixed solidly, but the rang of motion lost partially and stess shielding comes up, increasing the stress and degeneration of adjacent segments. Non-fusion fixation is poor in resisting torsion, compared to fusion fixation.