The present study discerned notable alterations in cervical longus among patients who underwent ACDF surgery, characterized by a reduced muscle volume, diminished AxCSA, and an enlarged RLS. Conversely, no significant changes were observed in the muscle volume of cervical extensors between the preoperative data and the postoperative data at each follow-up time point. However, there were significant differences in the muscle volume of cervical extensors between preoperative and postoperative follow-up time points. The reduction in the volume of cervical longus may be attributed to several potential causes. In the course of ACDF surgery, unavoidable soft tissue damage occurs in the anterior portion of the neck due to the application of surgical instruments. This damage encompasses stretching injuries to the muscle tissue, stimulation of the paravertebral muscles by surgical implants, and thermal damage resulting from the use of high-frequency electrotome [
13]. The injury to the cervical longus and subsequent scar repair of muscle tissue following ACDF surgery may contribute to the observed reduction in the volume of the cervical longus and AxCSA of the operative segment to a certain extent. While the necessity of postoperative cervical collar use remains a subject of debate, it is customary for patients to don a cervical collar during the initial postoperative period. The primary objective is to limit neck movements, thereby aiming to enhance fusion rates [
14]. The utilization of a cervical collar can elicit discernible alterations in the neck region, potentially leading to muscle atrophy. Individuals exhibiting heightened apprehension of pain may actively abstain from engaging in physical activities anticipated to induce or exacerbate pain—a phenomenon recognized as fear-avoidance beliefs [
15]. Fear-avoidance behavior can potentially engender deficiencies in the postoperative rehabilitation exercise and hinder the functional recovery of affected patients. This, in turn, may contribute to a reduction in the volume of the cervical longus. Additionally, the fusion of cervical segments may result in a diminished range of motion, thereby influencing the volumetric changes observed in cervical muscles. Consequently, alterations in the cervical longus may be attributed to a combination of muscle disuse and inhibition [
8,
16]. Intervertebral disk degeneration and its associated inflammatory mediators emerge as pivotal factors influencing the structural alterations observed in paravertebral muscles [
17,
18]. A prior animal study has demonstrated that intervertebral disk degeneration, coupled with associated inflammatory changes, can induce atrophy of the Lumbar Multifidus [
19]. Diverse inflammatory mediators can intricately contribute to the promotion of muscle fat infiltration and fibrosis, ultimately culminating in muscle atrophy and degeneration [
17,
19]. The findings from animal studies align fundamentally with the observations of muscle atrophy and fat infiltration in human studies [
20‐
22]. The findings of this study indicate that, compared with the preoperative data, the postoperative cross-sectional area and muscle volume of cervical extensors showed no significant changes, while CESA/VBA experienced a minor reduction at the 3rd and 12th months post-operation, followed by a slight increase at the final follow-up. There is a significant intergroup difference in the measurements of CESA/VBA between the preoperative and postoperative assessments. ACDF serves the purpose of reconstructing cervical vertebral stability; however, the fusion of cervical vertebrae in the operative segments results in the loss of their original mobility. Consequently, an augmented mechanical stress in adjacent cervical segments ensues, potentially contributing to an accelerated degeneration of intervertebral disks in these neighboring segments [
23,
24]. The aforementioned accelerated degeneration of the cervical intervertebral disk could be a contributing factor to the observed declining trend in the muscle volume of cervical extensors. Additionally, the reduction in neck movement caused by factors such as postoperative wearing of cervical collar may lead to atrophy of the cervical extensors. Subsequent factors, such as increased neck activity and rehabilitation exercises, may contribute to an increase in the volume of cervical extensors. The postoperative increase in RLS suggests a transformation in the cross-sectional shape of the cervical longus from a “round” configuration to an “oval” configuration following ACDF. A prior investigation has substantiated that ACDF possesses the capability to rectify the curvature of the cervical spine, thereby augmenting cervical lordosis, particularly in patients exhibiting sagittal imbalance of the cervical spine. Furthermore, the extent of correction in cervical curvature post-surgery is more pronounced in cases where the cervical curvature is initially smaller [
25]. Such alteration in cervical curvature exerts a specific elongating influence on the cervical longus. Under these circumstances, both volume and muscle bundle reconstruction of the cervical longus occur, as there is no discernible change in the sarcolemma. Consequently, the cervical longus exhibits a diminished thickness compared to its preoperative state. Additionally, a previous investigation into degenerative cervical spine disease revealed that individuals with chronic neck pain presented a broader ovoid shape of the cervical multifidus when compared to their healthy counterparts [
6]. Hence, cervical pain could be regarded as a potential influencing factor capable of altering the morphology of deep cervical muscles. Additionally, various factors may influence the neck muscles post-ACDF, including patient age, gender, the cervical spine segment of the surgery, and the duration of the operation. This study conducted a detailed investigation into the changes in the cervical longus and cervical extensor muscles post-ACDF across different cervical spine segments. Regarding the impact of age, gender, and operation duration on post-ACDF neck muscles, relevant clinical studies indicate: (1) The influence of gender does not seem to exert a substantial impact on the clinically meaningful recovery subsequent to single-level ACDF [
26]; (2) a study found that patients’ age is one of the factors affecting the effectiveness of ACDF surgery. Younger patients achieved better surgical outcomes in terms of cervical lordosis correction and graft height loss after ACDF. The correction of cervical lordosis and loss of graft height are closely related to changes in cervical muscles. Therefore, this result also indicates that patient age is one of the factors influencing post-ACDF changes in cervical muscles [
27]; (3) a study revealed that prolonging the duration of single-level ACDF surgery is associated with an increased incidence of postoperative swallowing difficulties. However, the observed differences did not reach statistical significance, possibly attributed to the limited number of cases. The manifestation of postoperative swallowing difficulties, to a certain extent, reflects the severity of damage to cervical muscles. Thus, the duration of surgery may indeed exert an impact on cervical muscle function [
28].