Exploring the characteristics of neck muscle strength and activation in patients with cervical spondylotic radiculopathy using motion capture-Opensim digital simulation technology

Abstract

BACKGROUND: Modern research suggests that the “muscle-bone imbalance” in cervical spondylotic radiculopathy is associated with changes in the performance of cervical muscles due to biomechanical alterations of the head and neck. However, most studies have focused on static analysis of the cervical spine, lacking dynamic quantitative data on neck muscle strength and activation. OBJECTIVE: To investigate the differences in muscle strength and muscle activation during cervical spine movement between patients with cervical spondylotic radiculopathy and healthy individuals from a biomechanical perspective. METHODS: From October 1, 2023 to March 1, 2024, 10 volunteers were recruited from the orthopedic outpatient or inpatient department and health examination center of the First Affiliated Hospital of Guangxi University of Chinese Medicine, including 5 patients with cervical spondylotic radiculopathy (cervical spondylotic radiculopathy group) and 5 healthy individuals (healthy control group). Inertial motion capture sensors were used to capture the motion data of the neck in six degrees of freedom: flexion, extension, left lateral flexion, right lateral flexion, left rotation, and right rotation. Each movement was repeated three times, yielding 18 sets of data per subject. Based on MRI-derived muscle parameters of patients and healthy individuals, OpenSim head-neck musculoskeletal models were respectively established. After preprocessing, the captured neck motion data were imported into the OpenSim simulation model to calculate and compare the neck muscle strength and muscle activation levels between the two groups. RESULTS AND CONCLUSION: (1) The healthy control group showed orderly synergistic activation of muscle groups, while the cervical spondylotic radiculopathy group exhibited disordered synergistic activation patterns, characterized by insufficient activation of the affected side muscles, excessive compensation of the healthy side, and significantly reduced synergy of core muscles such as the sternocleidomastoid, middle and upper trapezius, and longus colli. In the cervical spondylotic radiculopathy group, during extension, the muscle strength of the sternocleidomastoid, middle trapezius, longus capitis, and upper trapezius was lower than that of the healthy control group (P < 0.05). During flexion, the muscle strength of the sternocleidomastoid, longus capitis, longus colli, levator scapulae, multifidus, splenius cervicis, splenius capitis, and middle/upper trapezius was lower than that of the healthy control group (P < 0.05). During left lateral flexion, the muscle strength of the sternocleidomastoid, longus capitis, longus colli, scalene, levator scapulae, multifidus, splenius cervicis, splenius capitis, and middle/upper trapezius was lower than that of the healthy control group (P < 0.05). During right lateral flexion, the muscle strength of the longus colli and upper trapezius was lower than that of the healthy control group (P < 0.05). During left rotation, the muscle strength of the levator scapulae was lower than that of the healthy control group (P < 0.05). During right rotation, the muscle strength of the longus colli was lower than that of the healthy control group (P < 0.05). (2) These findings indicate that patients with cervical spondylotic radiculopathy exhibit muscle synergy imbalance in all directions of cervical spine movement. The imbalance is characterized by degeneration of the affected side muscles and nerves, reduced muscle strength and coordination, while the healthy side muscles and nerves compensate for the functional insufficiency of the affected side, leading to over-control. Among the muscle groups involved in cervical spine movement, the degeneration of the sternocleidomastoid and middle/upper trapezius is the most significant, which is one of the important features causing cervical spondylotic radiculopathy.

1. Introduction

Cervical spondylotic radiculopathy (CSR) is primarily caused by compression of the spinal nerve roots due to degenerative changes in the cervical spine, posing a significant health threat to the general population [1-3]. Studies have shown that CSR has a high incidence among middle-aged and elderly individuals [4-5], leading to symptoms such as neck pain, radiating arm pain, and neurological dysfunction, which greatly impair patients' quality of life [6-9]. With the rapid proliferation of modern electronic devices, prolonged poor posture such as looking down has increased the burden on the cervical spine, accelerating degeneration and making the disease more prevalent in younger populations [10-13].

Current evidence indicates that conservative treatments (e.g., physical therapy, analgesic therapy) achieve a short-term effective rate of approximately 58% in relieving radicular pain [14], but they fail to address the mechanical compression of nerve roots and the biomechanical imbalance of intervertebral joints [15]. Consequently, 39%-63% of patients with persistent pain and neurological deficits eventually require surgical intervention [16]. Although surgery can be effective in certain cases, it carries risks and is not suitable for all patients [4,17]. Therefore, a deeper understanding of the biomechanical imbalance mechanisms in CSR, particularly the role of neck muscle strength and activation in dynamic cervical balance and disease progression, is crucial for optimizing treatment strategies [18].

Traditional Chinese medicine orthopedics attributes CSR to 'muscle-bone imbalance,' while modern research suggests that this imbalance is related to changes in cervical muscle performance due to biomechanical alterations of the head and neck [18]. However, existing studies lack quantitative data on cervical muscle strength and activation, failing to intuitively reveal the intrinsic biomechanical characteristics of 'muscle-bone imbalance' in CSR patients. Motion capture technology can precisely record human movement trajectories, and when integrated with simulation models, it can realistically reproduce human motion, overcoming the limitations of traditional imaging and more accurately presenting biomechanical properties during movement.