چكيده به لاتين
Vertebral fusion in the spine means connecting the vertebrae. In this type of surgery, two or more vertebrae may be connected to eliminate pain, instability, or other symptoms of spinal diseases. For many years, lumbar interbody fusion has been used for treating degenerative lumbar diseases such as disc degeneration, degenerative spinal stenosis, and lumbar spondylolisthesis. Osteoporosis is the most common problem for lumbar interbody fusion with pedicle screws, and it causes spinal injuries because most patients who need lumbar interbody fusion are old, have osteoporosis, and vertebrae are the most common place of bone fracture.
This study investigates the fusion phenomenon on a three-vertebral model consisting of the second, third, and fourth lumbar vertebrae, two intervertebral discs, and an implant system including four pedicle screws and two connecting rods have been considered according to the bone density index. Three types of screws were considered for four types of bone quality, and von-mises stresses were investigated in 4 types of flexion, extension, lateral bending, and twisting movements, and the best type of screw among the investigated options was found in the vertebra with osteoporosis and selected. Then, the maximum von-mises stress and the displacement resulting from the selection of two types of materials, titanium, and polyetheretherketone, for connecting rods in contact with the selected screw were compared and reported so that the best situation for choosing the combination of the pedicle screw and connecting rod for an Osteoporotic bone in different types of bone density should be suggested.
The results show that the pedicle screw with a diameter of 6.0 mm and a length of 45 mm enables minimum stress distribution on the bone-screw joint contact surface, considering the four types of movement. Also, a comparative study of stabilizing implant systems showed that both spine implant systems reduce stress distribution in all models. However, the value of stress distribution with the stabilization system based on the polyetheretherketone connecting rod decreases over time with the increase in osteoporosis. Finally, it was concluded that the spinal implant system based on a polyetheretherketone connecting rod has significantly reduced the stress on the whole model and seems to be a better option in stress reduction and load sharing for cases with the poor bone quality compared to a titanium spinal implant system.
The observations and data shown in the results can help researchers and clinicians accurately identify vertebral implants to minimize screw breakage or loosening and stress distribution at the screw-bone contact surfaces. This work may help to design new vertebral implants and identify the aftereffects of fusion with different bone densities.
