A three-dimensional finite element analysis of the biomechanical properties of a new lumbar spondylolysis repair device

English Keywords:Lumbar spondylolysis  Internal fixation system  Finite element analysis  Biomechanics

English Abstract:

  【Abstract】 Objectives: To evaluate the biomechanical properties of a new lumbar spondylolysis repair device by three-dimensional finite element analysis. Methods: A nonlinear finite element model of L3-S1 segment(A) was constructed on the 3D reconstruction of the lumbar CT data extracted from a healthy volunteer and was verified. Based on this, L5 spondylolysis model(B), pedicle screw-U-shaped rod fixation model(C), and the new lumbar spondylolysis repair device model(D) were established. The freedom of the lower surface of S1 vertebral body of the four models were constrained. The axial compression forces of 500N and moment loads of 10N·m were applied to the upper surface of L3 vertebral body to simulate six motion states of lumbar flexion, extension, left and right bending and rotation. The range of motion(ROM) of lumbar spine, the stress of L5 spinous process root, and axial pressure of isthmus were compared between models under different motion states. Results: The ROM of model A at L4-L5 and L5-S1 segments were similar to those reported previously, demonstrating the effectiveness of this model. At all motion states, the ROMs of models C and D decreased by 16.46%-55.98% and 17.48%-40.65% than model B, respectively; the average ROM of model D was 0.44° larger than that of model C. Comparing with model C, the maximum stresses of the L5 spinous process of the model D decreased by 12.71%, 54.95%, 58.46%, 53.97%, 46.91%, and 72.34%, respectively，which can reduce the risks of L5 spinous process fracture; and the axial pressures of lumbar isthmus increased by 236.51%, 282.51%, 216.98%, 231.47%, 294.03%, and 138.91%, respectively, which may accelerate bone healing more effectively. Conclusions: The new lumbar spondylolysis repair device could better stabilize lumbar spondylolysis while preserving the ROM of lumbar spine. As compared with pedicle screw-U-shaped rod, the new lumbar spondylolysis repair device might provide sufficient mechanical stability and reduce the risk of spinous process fracture.