| BackgroundNitinol shape memory alloy has shape memory and super-elastic characteristics and has been widely used in medicine, but reported not much in the field of spine surgery, mainly in the application of idiopathic scoliosis anterior U-shaped memory alloy nail. PLA General Hospital began to use memory alloy rod to treat scoliosissince the1980s, experienced first-generation and second-generation shape memory alloy system, but based on the consideration of the toxicity of nickel, shape memory alloy rod is not widely used in clinical applications. Foreign scholars also conducted animal studies of memory alloy rods, but no clinical reports. In recent yearsthe PLA General Hospital first usedthe shape memory alloy rods as a tool in correcting scoliosis, and has been clinically provensafety and effectiveness. In these applications the shape memory alloy rod as a tool was placed in concave side of the scoliosis, the effect of using in the convex side and bilateral sideof the scoliosis is unknown; in order to increase the ability of derotationmemory alloy rods of rectangular cross-section were designed, the effect has not yet been verificated. Finite element analysis method as a new research method has an increasingly important role in the study of spinal deformitybecause of its non-invasive, simple and reproducible. In this study, we attempt to solve the above problemsby means of finite element analysis method.Object1. Create a memory alloy rod correction finite element model of idiopathic scoliosis and verified.2. On the finite element model of adolescent idiopathic scoliosis simulatethe correcting process using shape memory alloy rod on concave side, convex side and both side of the scoliosis spine, the simulation results were compared and analyzed. 3. the design and conduct of scoliosis finite element simulation of the new rectangular shape memory alloy rods and compared with the circular shape memory alloy rodsMethod1. A patient with adolescent idiopathic scoliosis (LENKE1type) was choosed as the object of study. The patientundergone CT scan from cervical spine to the sacral, the data (dicom) was collected. Then used MIMICS, Rapidform, ABAQUS software to build three-dimensional finite element model of the spine. On the finite element model of adolescent idiopathic scoliosis simulatethe correcting process using shape memory alloy rod on concave side.Simulation results were compared with the clinical results to validate the model.2. On the finite element model of adolescent idiopathic scoliosis simulatethe correcting process using shape memory alloy rod on concave side, convex side and both side of the scoliosis spine, the simulation results were compared and analyzed. Outcome measure includedchange of Cobb angle, vertebral displacement of each method.3. According to the circular memory rod design experience and pedicle screw tail cap size, rectangular new alloy rod was designed; the cross-section was5.5x7.5mm rectangle. Then on the finite element model, simulated rectangular memory rod with multiaxial pedicle screws, rectangular shape memory alloy rods with monoaxial pedicle screws.The results were compared with the effect of circular memory alloy rods correction.Result1. Idiopathic scoliosis finite element model wassuccessfully established. The simulation of the memory alloy rod on the concave side of the scoliosis correcting procedure was successfully. Compared with actual clinical outcomes,the model was proved to be validity.2. Three different corrective method (concave side, convex side, both sides) using shape memory alloy rods were successfully simulated.According to the data, both rods have bigger correction in coronal plane, but the concave side correction has super ability to correct sagittal alignment. 3. Simulation of corrective procedures by a rectangular shape memory alloy rod with multiaxial and monoaxial pedicle screws was successfully conducted. Compared to the circular memory rod,rectangular shape memory alloy rod with multiaxial pedicle screws has the similar results, but the rectangular shape memory alloy rod with monoaxial pedicle rod has greater correction in rotation deformity in cross section plane.ConclusionFinite element analysis can be successfully applied to idiopathic scoliosis studies;higher clinical similarities with the actual situation, the tool can be used as a simulation model and analysis of the results. In the finite element simulation resultswith memory alloy rods bilateral memory alloy rods were strongerin the coronal plane. The new rectangular shape memory alloy rods with monoaxial pedicle screws in deformity correction in cross-section may have an advantage. |
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