Biomechanical characteristics of cervical spine movement in cervical spondylotic myelopathy analyzed based on motion capture and Opensim simulation technology

Abstract

BACKGROUND: Previous studies have confirmed that neck muscle strength and intervertebral stress can influence the progression of cervical spine degeneration. However, no quantitative analysis has been conducted to examine the interaction between the biomechanical changes in cervical spondylotic myelopathy and cervical vertebral stress and paravertebral muscles. OBJECTIVE: To explore the cervical spine movement patterns of patients with cervical spondylotic myelopathy based on biomechanical principles, quantify the synergistic imbalance effects between paraspinal muscle strength and intervertebral stress in these patients, and discuss and reveal the dialectical relationship between the traditional Chinese medicine theory of “musculoskeletal imbalance” and the modern biomechanical concept of “dynamic and static imbalance” in cervical spondylotic myelopathy. METHODS: Twenty patients with cervical spondylotic myelopathy (CSM group) from the orthopedic outpatient and inpatient departments of the First Affiliated Hospital of Guangxi University of Chinese Medicine and ten healthy individuals (healthy group) from the health examination center and “preventive treatment of disease” center were enrolled. Age and sex were recorded. Cervical spine 6-degree-of-freedom motion data were collected using motion capture and Opensim virtual simulation models, with three repeated measurements. After data optimization, forward dynamics tool algorithms were used to quantify range of motion, peak motion angle changes, vertebral pressure center distribution, average muscle strength, average maximum joint pressure, and average maximum joint shear force in both groups. RESULTS AND CONCLUSION: (1) There were no statistically significant differences in sex and age between the two groups. (2) In left rotation, right rotation, and extension directions, the peak motion angle changes in the CSM group were significantly smaller than those in the healthy group; in lateral flexion, rotation, and extension directions, the range of motion in the CSM group was significantly larger than that in the healthy group. (3) Comparison of pressure centers at C4 and C5 indicated that the joint pressure center in CSM patients was more diffuse. (4) The average muscle strength in CSM patients was much lower than that in healthy individuals. (5) The maximum joint pressure at C4-C6 during extension in CSM patients was significantly greater than that in the healthy group, while the maximum joint pressure at C3-C7 during flexion, lateral flexion, and rotation was smaller than that in the healthy group; the average maximum joint shear force at C4-C7 during lateral flexion and rotation in the healthy group was greater than that in the CSM group. (6) These findings suggest that during neck movement, CSM patients exhibit decreased neck muscle strength and baseline vertebral stress imbalance, which alters the stress on the facet joints and pressure center distribution, accelerates the degeneration of bony structures and muscles, and disrupts cervical stability. The biomechanical changes in CSM are correlated with the “musculoskeletal imbalance” and “dynamic and static imbalance” theories.

1. Introduction

Cervical spondylotic myelopathy (CSM) is a neurological disorder characterized by limb numbness and muscle weakness, primarily resulting from degenerative changes in the cervical vertebrae and intervertebral discs [1-6]. Currently, surgical decompression is considered the main method to prevent disease progression in Western medicine. However, there remain many uncertainties regarding the optimal timing and prognosis of surgery, and postoperative residual symptoms are not uncommon, indicating that even surgery carries significant clinical risks [7-9]. Therefore, early diagnosis and treatment of CSM are of great clinical importance.

In modern traditional Chinese medicine (TCM) theory, CSM falls under the categories of 'Bi syndrome', 'Wei syndrome', and 'Jing syndrome' [10]. Classical TCM texts also recognize a similar relationship between tendons and bones, stating that 'tendons bind bones, and bones support tendons'. Under physiological conditions, the tendon system maintains motor homeostasis through a dual mechanism: bony structure constraint and joint movement coordination. The interaction between tendons and bones exhibits a yin-yang dialectical relationship: the dynamic unity of restriction and synergy ultimately forms a 'dynamic-static equilibrium' compatible with skeletal stability and soft tissue elasticity [11]. The core pathological change in cervical spondylosis lies in the biomechanical imbalance of the musculoskeletal system: dynamic constraint failure, attenuation of tendon-muscle mechanical function; static alignment disorder, abnormal stress on intervertebral joints. The synergistic effect of these two factors disrupts the dynamic-static balance and accelerates the degenerative process [12].

'Tendon dislocation' essentially refers to the failure of dynamic soft tissue constraints: muscle spasm and tissue adhesion lead to displacement of the tendon system, resulting in decreased muscle force transmission efficiency and significantly reduced cervical stability.