Biomechanical properties of a novel nonfusion artificial vertebral body for anterior lumbar vertebra resection and internal fixation

The aim of the study was to evaluate the biomechanical properties of a novel nonfused artificial vertebral body in treating lumbar diseases and to compare with those of the fusion artificial vertebral body. An intact finite element model of the L1–L5 lumbar spine was constructed and validated. Then, the finite element models of the fusion group and nonfusion group were constructed by replacing the L3 vertebral body and adjacent intervertebral discs with prostheses. For all finite element models, an axial preload of 500 N and another 10 N m imposed on the superior surface of L1. The range of motion and stress peaks in the adjacent discs, endplates, and facet joints were compared among the three groups. The ranges of motion of the L1–2 and L4–5 discs in flexion, extension, left lateral bending, right lateral bending, left rotation and right rotation were greater in the fusion group than those in the intact group and nonfusion group. The fusion group induced the greatest stress peaks in the adjacent discs and adjacent facet joints compared to the intact group and nonfusion group. The nonfused artificial vertebral body could better retain mobility of the surgical site after implantation (3.6°–8.7°), avoid increased mobility and stress of the adjacent discs and facet joints.

Finite Element Analysis of Stability of Internal Fixation Reconstruction Methods for Lumbar Total Vertebral Resection

Objective To compare the effect of different fixation methods on spinal stability after total en bloc spondylectomy(TES) of lumbar spine.Method The finite element models were established based on the CT scan of a healthy volunteer. After the validity of the models was confirmed, the models with different posterior fixation methods of the lumbar spine were established with and without the artificial vertebral body, respectively. The motions of flexion, extension, lateral bending and rotation under supine and standing conditions were simulated. The angular displacement of T11-L3 and stress of internal fixations were compared and analyzed.Results The finite element models of spinal reconstruction after TES were obtained. When the anterior support existed, the movement of the spine after TES was not affected by the gravity of the upper body. The movements in the opposite direction on the same plane were similar. All three methods provided enough stability to the spine. The improved short-segment fixation shared stress of the artificial vertebral body with no obvious negative effect. The long-segment fixation had stronger fixation effect with the huge loss of the range of motion of lumbar spine. When the anterior support failed, obvious rotation showed in lateral bending in all models. The short-segment fixation and the long-segment fixation failed to maintain the spinal stability with fixations breakage or functional loss. The improved short-segment fixations showed strong ability in maintaining the spinal stability. The vertebral body screws can prevent the failure of anterior fixation by sharing great stress of the whole internal fixation system. The improved short-segment had huge advantages over the others.Conclusion After TES, the improved short-segment fixation can provide more stability to the spine. The vertebral body screws can prevent the failure of the internal fixation by reducing the stress of the anterior support. This fixation method should be promoted in clinical practice while the effect requires more observation.

A Novel Anterior Transpedicular Screw Artificial Vertebral Body System for Lower Cervical Spine Fixation: A Finite Element Study

A finite element model was used to compare the biomechanical properties of a novel anterior transpedicular screw artificial vertebral body system (AVBS) with a conventional anterior screw plate system (ASPS) for fixation in the lower cervical spine. A model of the intact cervical spine (C3–C7) was established. AVBS or ASPS constructs were implanted between C4 and C6. The models were loaded in three-dimensional (3D) motion. The Von Mises stress distribution in the internal fixators was evaluated, as well as the range of motion (ROM) and facet joint force. The models were generated and analyzed by mimics, geomagic studio, and ansys software. The intact model of the lower cervical spine consisted of 286,382 elements. The model was validated against previously reported cadaveric experimental data. In the ASPS model, stress was concentrated at the connection between the screw and plate and the connection between the titanium mesh and adjacent vertebral body. In the AVBS model, stress was evenly distributed. Compared to the intact cervical spine model, the ROM of the whole specimen after fixation with both constructs is decreased by approximately 3 deg. ROM of adjacent segments is increased by approximately 5 deg. Facet joint force of the ASPS and AVBS models was higher than those of the intact cervical spine model, especially in extension and lateral bending. AVBS fixation represents a novel reconstruction approach for the lower cervical spine. AVBS provides better stability and lower risk for internal fixator failure compared with traditional ASPS fixation.