Effects of different severities of disc degeneration on the range of motion of cervical spine

AIMS AND OBJECTIVES: The human spine degenerates with age. Intervertebral disc degeneration occurs in the cervical spine. The objective of this study is to determine the effects of degenerative disc diseases on the range of motion (ROM) of the human cervical spinal column using a validated finite-element model. MATERIALS AND METHODS: The validated intact and healthy C2–T1 finite-element model simulated the cortical shell, cancellous core, posterior elements of the vertebrae, and spinal ligaments (longitudinal, capsular, spinous and ligamentum flava, and nucleus and annulus of the discs). Three different stages of the disc disease, that is, mild, moderate, and severe, were simulated at the C5–C6, C6–C7, and C5–C6–C7 discs, respectively, and they were termed as upper single level, lower single level, and bi-level (BL) models, respectively. The material properties and geometry of the disc(s) were altered to simulate the different stages of degeneration. The external mechanical loading was applied in the sagittal mode, via flexion–extension motions and the magnitude was 2.0 Nm for each mode. They were applied to each of the healthy and disc degeneration models, and for each of the three severities of degeneration. The ROM at adjacent and index levels was extracted and normalized with respect to the healthy (baseline) spine. RESULTS: A nonuniform distribution in the ROM was found for different disc degeneration states, segmental levels, and flexion–extension loading modes. The specific results for each and level are reported in the results section of the paper. CONCLUSION: Closer follow-up times may be necessary in symptomatic patients with progressive disease, especially with BL involvements.