Biomechanical evaluation of oblique pulling manipulation on C5/6 intervertebral discs with different levels of degeneration

Abstract

BACKGROUND: The oblique pulling manipulation has good therapeutic effects on cervical spondylosis, but its biomechanical mechanism of action on intervertebral discs with different degrees of degeneration is not clear. OBJECTIVE: To explore the biomechanical mechanism of the oblique pulling manipulation on the discs with different degrees of degeneration through three-dimensional finite element model. METHODS: The motion capture system was used to measure the kinematic parameters of the key steps during the oblique pulling manipulation, and a three-dimensional finite element model of the whole cervical spine of the C5/6 mildly, moderately, and severely degenerated intervertebral discs was established. The kinematic parameters were converted into moments and loaded onto the whole cervical spine of the mildly, moderately, and severely degenerated intervertebral discs in a step-by-step manner, so as to obtain the biomechanical parameters of the stress-strain of each structure during the simulated oblique pulling manipulation. RESULTS AND CONCLUSION: (1) In the simulation of the oblique pulling manipulation to the right side, with the increase of disc degeneration, the Von-Mise stress of the annulus fibrosus gradually increased, and the stress was concentrated on the right lateral side of the annulus fibrosus; the Von-Mise stress of the nucleus pulposus decreased, and the stress was concentrated at the junction of the nucleus pulposus and annulus fibrosus; the overall displacement of the intervertebral disc decreased, the stress of the left facet joint decreased, and the Von-Mise stress of the spinal cord increased, with the stress concentrated in the upper cervical spine. (2) In the simulation of the oblique pulling manipulation to the right side, with the increase of disc degeneration, the overall strain of the C5/6 intervertebral disc, the intradiscal pressure of the nucleus pulposus, and the stress of the left nerve root decreased, while the shear force of the intervertebral disc increased, the relative distance between the left nerve root and the intervertebral disc increased, and the relative distance between the right nerve root and the intervertebral disc did not change significantly. (3) The results indicate that the cervical oblique pulling manipulation improves the biomechanical imbalance of mildly and moderately degenerated intervertebral discs by adjusting the stress of the facet joints and increasing the distance between nerve roots, but for severely degenerated intervertebral discs, it should be used with caution due to the sharp increase of annulus fibrosus stress and the risk of spinal cord compression.

1. Introduction

Neck pain is a health problem affecting a considerable portion of the global population. A comprehensive assessment of global neck, shoulder, and back pain indicates that more than one-third of people worldwide experience neck pain lasting at least three months [1]. Various cervical structures may cause neck pain due to degenerative changes, but most studies suggest that intervertebral disc degeneration is the most important underlying cause [2]. SUZUKI et al. [3] found that C5/6 is the most common degenerative segment through MRI evaluation of a large number of patients with neck pain symptoms.

Currently, there are many treatment methods for cervical disc degenerative diseases [4-6], among which cervical oblique pulling manipulation is one of the effective clinical treatments. It improves facet joint disorders and restores the dynamic and static balance of the cervical spine through overall regulation, thereby improving cervical function and reducing pain [7-9]. However, when it comes to cervical degenerative diseases caused by disc degeneration, the application of oblique pulling manipulation requires more caution, otherwise serious complications may occur. In recent years, finite element analysis has shifted from macroscopic mechanical simulation to patient-specific biomechanical prediction. For example, WISNESKI et al. [10] combined deep learning and dynamic finite element to construct personalized degenerated disc models, achieving prediction of manipulation treatment effects (area under the curve AUC=0.91); LIN et al. [11] further coupled motion capture and finite element inverse analysis to quantify the stress dispersion effect of oblique pulling manipulation on the annulus fibrosus (peak reduction 17.3%). However, the influence of the material property gradient unique to degenerated discs on biomechanical responses still needs to be refined, especially the interaction mechanism of shear force mutation on the spinal cord/nerve root microenvironment remains unclear [12-13]. Currently, most studies focus on the biomechanical mechanisms of massage manipulation on normal intervertebral discs [14-16].