Investigation of Alterations in the Lumbar Disc Biomechanics at the Adjacent Segments After Spinal Fusion Using a Combined In Vivo and In Silico Approach

• Published in: Annals of biomedical engineering 2021-02, Vol.49 (2), p.601-616
• Main Authors: Zhou, Chaochao, Cha, Thomas, Wang, Wei, Guo, Runsheng, Li, Guoan
• Format: Article
• Language: English
• Subjects: Biochemistry; Biological and Medical Physics; Biomechanics; Biomedical and Life Sciences; Biomedical Engineering and Bioengineering; Biomedicine; Biophysics; Boundary conditions; Classical Mechanics; Confidence intervals; Degeneration; Finite element method; Fluoroscopic imaging; In vivo methods and tests; Intervertebral discs; Lamella; Mathematical models; Original Article; Segments; Surgery; Three dimensional models
• ISSN: 0090-6964; 1573-9686
• DOI: 10.1007/s10439-020-02588-9

The development of adjacent segment degeneration (ASD) is a major concern after lumbar spinal fusion surgery, but the causative mechanisms remain unclear. This study used a combined in vivo and in silico method to investigate the changes of anatomical dimensions and biomechanical responses of the adjacent segment (L3-4) after spinal fusion (L4-S1) in five patients under weight-bearing upright standing conditions. The in vivo adjacent disc height changes before and after fusion were measured using a dual fluoroscopic imaging system (DFIS), and the measured in vivo intervertebral positions and orientations were used as displacement boundary conditions of the patient-specific three-dimensional (3D) finite element (FE) disc models to simulate the biomechanical responses of adjacent discs to fusion of the diseased segments. Our data (represented by medians and 95% confidence intervals) showed that a significant decrease by − 0.8 (− 1.2, − 0.4) mm ( p < 0.05) in the adjacent disc heights occurred at the posterior region after fusion. The significant increases in disc tissue strains and stresses, 0.32 (0.21, 0.43) mm/mm ( p < 0.05) and 1.70 (1.07, 3.60) MPa ( p < 0.05), respectively, after fusion were found in the posterolateral portions of the outermost annular lamella. The intradiscal pressure of the adjacent disc was significantly increased by 0.29 (0.13, 0.47) MPa after fusion ( p < 0.05). This study demonstrated that fusion could cause alterations in adjacent disc biomechanics, and the combined in vivo and in silico method could be a valuable tool for the quantitative assessment of ASD after fusion.