Lightning Podiums: Value and Outcomes in Spinal Surgery - Room 801B

Presented by: Z.-P. Luo

Author(s):

X.-D. Cui(1), W. Zhang(1), H.-T. Li(1), G.-D. Chen(1), H.-L. Yang(1), Z.-P. Luo(1)

(1) Orthopaedic Institute,Department of Orthopaedics,the First Affiliated Hospital,Soochow University, Suzhou, China

Abstract

Background: Thoracolumbar compression fractures are frequently-occurring disease in spinal fractures, though posterior pedicle screw systems can effectively restore the fractured vertebral body height and reconstruct spinal stability. The complications like bone defect formed during fractured vertebral healing cannot be neglected.

Objective: To investigate the biomechanical effects of different types of vertebral bone defect after posterior instrumentation removed.

Methods: A nonlinear three-dimentional finite element (FE) model of thoracolumbar T12-L2 with four screw paths was developed as the intact model with posterior instrumentation removed. Base on this intact model, simulated models were divided into two groups: (i) vertebral defect with different size of cavity-like holes (small, mediun, large) and (ii) vertebral defect with five different cavity positions (central, anterior, posterior, superior, inferior). The vertebral defect were set at the L1 vertebral body. The von Mises stress distribution of each models were collected and analyzed. Torque of 10Nm torque and loading force of 400N in the axial direction were imposed on the superior surface of the T12 endplate to produce flexion, extension, lateral bending and axial rotation.

Results: Different mechanical parameters on the cancellous, endplate and cortical bone were calculated to evaluate the differences among the vertebral defect models. In the cavity size group, the stress distribute was mainly concentrate around the cavity and had a tendency of increasing with the cavity size. In the cavity position group, superior, center and inferior cavities had more influence than the anterior and posterior cavity positon models. In all models, the maximum stress around the cavity has little difference, the maximum stress on the cancellous bone around the cavity was 2.016 MPa in the large-size cavity model, 1.6 fold than the intact model, while at cartilage endplate the maximum stress was 9.406 MPa at inferior cavity model 1.7 fold than the 5.615 MPa at posterior cavity model.

Conclusion: The present study showed the clinical application of different FE models of vertebral defect in the thoracolumbar spine. Even though there was an increase in stress concentration in the central cancellous bone around the cavity, the maximum stress distributed around the cavity showed little difference between the different vertebral defect models and the stress distribution of the vertebral defect as a whole did not change. Thus, the manifestation of vertebral defect did not increase the risk factor of instability and subsequent fracture deformity.