Biomechanical Fixation Properties Of The Cortical Bone Trajectory Screws In The Osteoporotic Lumbar Spine

Objective With the rapid growth of the elderly population,osteoporosis has become one of the most common public health problems and major medical problems.Osteoporosis also leads to degeneration of the facet joints,degeneration of the intervertebral disc,stenosis of the intervertebral space,and bone remodeling.These degenerative changes can cause spinal deformities,changes in stress distribution,and may lead to degenerative segmental instability and subluxation,such as spinal stenosis,degenerative lumbar spondylolisthesis,and scoliosis.As the average life expectancy increases,older patients who require spinal surgery are also increasing.Osteoporosis is prone to progressive spinal deformity and potential neurological damage in elderly patients,selecting optimal strategies for improving fixation in the osteoporotic lumbar spine remains an important issue in clinical research.Cortical bone trajectory(CBT)screws have been proven to enhance screw pullout strength.However,the biomechanical efficacy of these screws remains understudied.The aim of this study was to evaluate the biomechanical efficacy of CBT screws in the osteoporotic lumbar spine.Methods A total of 31 vertebrae from 14 cadaveric lumbar spines were obtained.All specimens were measured by computed tomography,while the diameter of their pedicles,excluding those of vertebral bodies with very small pedicle developments,was calculated.After measuring bone mineral density(BMD),the CBT screw was randomly inserted into one side,while the traditional trajectory(TT)screw was inserted into the contralateral side.The maximum insertional torque was recorded after the screw insertion.A total of21 vertebrae were subjected to a pullout testing at a rate of 5 mm/min,while 10 vertebrae were subjected to a cyclic fatigue testing.Each construct was loaded until exceeding 5mm.Results The average BMD was 0.567±0.101 g/cm~2.The CBT screw had a higher maximum insertional torque(t=5.78,p<0.001,0.333 Nm vs.0.188 Nm)and higher axial pullout strength than the TT screw(t=7.41,p<0.001,394 N vs.241 N).Increased BMD was not significantly associated with a higher pullout load.Compared with the TT screw,the CBT screw showed better resistance to fatigue testing and required more cycles to exceed 5 mm(t=5.62,p<0.001,6161 cycles vs.3639 cycles).The failure load for displacing the screws was also significantly greater for the CBT screw than for the TT screw(t=5.75,p<0.001,443 N vs.317 N).Conclusion The CBT screw had a better biomechanical fixation performance in the osteoporotic lumbar spine compared with the standard pedicle screw.