The higher cellular elastic modulus of the nucleus pulposus with degenerative changes in the cervical intervertebral discs.

Abstract

Our study aims to explore the association between the elastic modulus of nucleus pulposus cells (NPCs) and degenerative changes in the cervical intervertebral discs (IVDs). Primary human NPCs were isolated from 21 degenerative IVDs that underwent anterior cervical decompression and fusion. The clinical degeneration degree of IVDs were assessed by a qualitative approach based on MRIs and a quantitative method based on the radiographs after all elastic modulus of NPCs were measured. On the basis of the degree of cervical IVDs degeneration, subjects were divided into mild (n = 6), moderate (n = 10) and severe (n = 5) degeneration groups. Atomic force microscopy were used to acquire morphology and force displacement curves. Force curves were fitted using the Sneddon model to extract the cellular elastic modulus. In our study, the elastic modulus increased significantly in mild, moderate, and severe groups (46.75 ± 17.87, 50.34 ± 25.97, and 72.63 ± 25.82 kPa, respectively) in accordance with the degree of cervical IVD degeneration (P < 0.05). In particularly, when the degree of height loss was enhanced because of IVD degeneration, the elastic modulus was also significantly increased in the groups (45.24 ± 19.90, 53.39 ± 26.78, and 70.68 ± 25.43 kPa, respectively; P < 0.05). The micromechanics of NPCs was associated with the macroscopic behavior in the IVDs. The cellular elastic modulus of NPCs, which could be influenced by age, sex and IVD segment of the subjects, increased with the aggravation of IVDs degeneration and the reduction of discs height.