Biomechanical effects of over lordotic curvature after spinal fusion on adjacent intervertebral discs under continuous compressive load. (March 2020)

• Record Type: Journal Article
• Authors: Wang, Wei; Pei, Baoqing; Pei, Yuyang; Li, Hui; Lu, Shibao; Wu, Xueqing; Wu, Nan; Shi, Zhenpeng; Hao, Yan; Fan, Yubo
• Is Part Of: Clinical biomechanics. Volume 73(2020)
• Page Start: 149
• Page End: 156
• Publication Date: 2020-03
• Subjects: Over-lordotic curvature -- Compressive creep -- Finite element -- Spinal fusion -- Adjacent intervertebral disc; Biomechanics -- Periodicals; Osteopathic medicine -- Periodicals; Biomechanics -- Periodicals; Osteopathic Medicine -- Periodicals; 612.76
• DOI: 10.1016/j.clinbiomech.2020.01.002
• Languages: English
• ISSNs: 0268-0033

Abstract

Abstract: Background: To investigate the effects of over-lordotic curvature after lumbar fusion on the stress and deformations of the adjacent intervertebral discs under constant compressive loads. Methods: Two-level ovine specimens—including three vertebral bodies with two discs—were divided into two groups: Group A (to observe external deformation) and Group B (to observe internal stress and deformations of the discs). Each group consisted of three models: a) intact model, b) increased stiffness + unchanged curvature fusion model, and c) increased stiffness + curvature fusion model. Models were tested at a vertebral pressure of 0.4 MPa for 30 min. Creep deformations and stress distributions in the superior adjacent intervertebral discs were analysed using finite element models. Findings: Stiffness angle of the curvature model was increased by 5° and compared with the intact and stiffness models. In Group A, there was no significant deformation in the superior and adjacent intervertebral discs ( P > 0.05), whereas creep deformations of the Group B discs increased significantly. Maximum deformations, with increases of approximately 3.7-fold and 2.8-fold in the vertical and horizontal directions, respectively, occurred at the anterior annulus fibrosus. The vertical and sagittal stress concentrations at the anterior annulus fibrosus had maximum differences of 1.0 MPa and 1.2 MPa, respectively. Interpretations: Under a continuous compressive load, over-lordotic fusion significantly increases the stress and deformation gradient of the nucleus polposus and annulus fibrosus in the superior, adjacent intervertebral disc, increasing the risk of damage and secondary degeneration of these discs when subjected to daily static loads. Highlights: The effects of over-lordotic curvature on intervertebral discs were investigated. The stress deformation in ovine lumbar specimens was analysed. Results indicate that the curvature increases stress and deformation gradients. The curvature increases the risk of degeneration in intervertebral discs.