| Summary: | 碩士 === 國立陽明大學 === 物理治療暨輔助科技學系 === 97 === Fusion with spinal internal fixator was used to treat instability of the lumbar spine. Several clinical studies have indicated that the fusion may accelerate degeneration at adjacent levels. The DYNESYS, a dynamic spinal internal fixator, is therefore designed to maintain intersegmental stability and prevent adjacent segment from degeneration. However, according to previous studies, adjacent segment degeneration and screw breakage still occurred after surgery due to the high stiffness of DYNESYS. Therefore, the purpose of this study was to investigate whether the stability of the lumbar spine could remain and the stress of the adjacent disc could release through decreasing the cord pretension of DYNESYS.
Finite element (FE) software, ANSYS, was used to build an intact lumbar spine (INT) model, implanting different cord pretensions of DYNESYS, defined as 300N (PT300) , 200N (PT200) , and 100N (PT100) , in L3-L4 motion segment of the lumbar spine. Preload 150N on L1 and pure moments incrementally were applied in order to make the flexion, extension, torsion and lateral bending of ROM reached 20, 15, 8 and 20 degrees in each model. The following analysis was comparing the Lumbar ROMs, disc stresses, facet joint contact forces, screw stresses and screw fatigue life in four FE models.
Comparing with INT, the DYNESYS models provided sufficient stability at surgical level with four physiological motions; in addition, PT100 had the performance close to INT and decreased lumbar ROMs to 13-78% and facet joint contact forces to 9-84% at the surgical level. At the both adjacent levels, except for extension, lumbar range of motions (ROMs) and disc stresses of PT100 had the performance close to INT. The maximum difference, comparing with PT300, reached 5% and 9%, respectively. Besides, PT100 had minimal screw stress under flexion, torsion, and lateral bending among three DYNESYS models. The results of screw fatigue life were the same in each DYNESYS model.
Our study found DYNESYS models could not restore normal physiological motions in the lumbar spine. But PT100 was able to provide lumbar ROMs, adjacent disc stresses and facet joint contact forces that approached the performance of INT. This study suggests that applying pretension of 100N to cord in implanting DYNESYS is a better consideration in making clinical decision.
|
|---|
