[Abstract] To discuss the importance of cervical hyperextension MRI in the diagnosis of cervical spondylosis. In the clinical diagnosis and treatment of cervical spondylosis, cervical neutral MRI is one of the most important imaging examinations, which is often used to understand the diameter of the cervical spinal canal and pathological changes of the spinal cord to guide clinical diagnosis and treatment. However, some patients have clear clinical symptoms and signs of spinal cord cervical spondylosis, but there is no significant narrowing of the cervical spinal canal and no significant compression of the spinal cord on neutral MRI. MRI of the cervical spine in the hyperextension position can reveal that most of these patients have compression of the cervical spinal cord in the hyperextension position. MRI in cervical hyperextension is important in the diagnosis and treatment of spinal cord cervical spondylosis to prevent misdiagnosis and omission. Cervical spondylosis is a clinical syndrome caused by cervical degeneration of the cervical disc, hypertrophy and hyperplasia of the cervical spine, and cervical injury, resulting in a series of symptoms due to irritation or compression of the cervical spinal cord, cervical nerves and blood vessels. Cervical MRI is a three-dimensional imaging, which is a noninvasive examination easily accepted by patients and has a high resolution of soft tissues. T2WI can clearly show the intensity and extent of signals in the spinal cord and morphological changes of nerve roots, providing a reliable basis for surgical treatment [1]. In the clinical diagnosis and treatment of spinal cord cervical spondylosis, cervical neutral MRI is one of the most important imaging examinations and is often used to understand the diameter of the cervical spinal canal and pathological changes in the spinal cord to guide clinical diagnosis and treatment. However, some patients have clear clinical symptoms and signs of spinal cord cervical spondylosis, but there is no significant narrowing of the cervical spinal canal and no significant compression of the spinal cord on neutral MRI. In such patients, MRI of the cervical spine in the hyperextension position was performed to study whether there was significant stenosis of the cervical spinal canal and whether there was significant compression of the spinal cord. The imaging basis for determining spinal cord cervical spondylosis includes narrowing of the cervical spinal canal sagittal diameter and compression of the cervical spinal cord. It is currently believed that the normal lower limit of the sagittal diameter of the cervical spinal canal should be about 1l mm [2], but the sagittal diameter of the cervical spinal canal is not constant in different positions. In cervical extension, the spinal canal is shortened and the spinal cord cross-section is increased; in hyperflexion, the spinal canal is elongated and the spinal cord cross-section is decreased [3-4]. Dynamic MRI of the cervical spine in patients with cervical degeneration revealed that the sagittal diameter of the cervical spinal canal at the vertebral body level was arranged as follows: hyperextension > neutral > hyperflexion, which was considered to be due to the thickening of the cervical spinal cord and dural sac diameter in hyperextension, as well as the narrowing of the spinal canal volume due to the degenerative bulging or herniated disc and the posteriorly folded and invaginated ligamentum flavum [5-6]. Domestic and international studies have confirmed that cervical flexion and extension movements cause an increase in spinal canal stenosis and are more pronounced in posterior extension than in anterior flexion [7]. According to these findings, cervical hyperextension MRI was added to such patients, and patients who showed significant cervical spinal cord compression after performing hyperextension MRI had absolute indications for surgery in combination with symptoms and signs. Patients who underwent surgery were in remission, indicating the importance of cervical hyperextension MRI in the clinical diagnosis and treatment of cervical spondylosis of the spinal cord [7]. The morphological size of the spinal cord also changes in normal individuals during physiological extension and flexion movements. The length of the spinal cord will elongate in flexion and shorten in posterior extension, and the cross-section of the spinal cord will also change, elongating and thinning in forward flexion and thickening in posterior extension, but the spinal cord is not compressed by the change in the physiological dynamic sagittal diameter of the spinal canal because of the small change and the buffer gap of the subarachnoid space of the dural sac [8-10]. In patients with cervical spondylosis, the effective cushion space around the spinal cord becomes smaller due to changes in the environment around the spinal cord, especially in the degenerative intervertebral junction structures mentioned above, which can easily cause compressive injury to the spinal cord itself, and during posterior extension movements, the sagittal diameter of the spinal canal becomes smaller and the cross-sectional area decreases, but the area of the corresponding plane of the spinal cord increases [11-13]. In the reduced effective space of the spinal canal, the anteriorly protruding intervertebral disc tissue, bony redundancy and hypertrophied posterior longitudinal ligaments and the posteriorly thickened and wrinkled anteriorly convex ligamentum flavum together form a compression effect on the anterior and posterior aspects of the spinal cord, which is known as the “clamping effect” [9], and the sagittal diameter of the spinal canal can be reduced by more than 30% [14], if accompanied by straightening of the cervical curvature, formation of bony bridges or fixation of the motion segment. The stenosis can be more pronounced if it is accompanied by cervical curvature straightening, bone bridge formation, or motor segment fixation [15]. [Conclusion] For patients with spinal cord-type cervical spondylosis, routine cervical hyperextension MRI is recommended to facilitate diagnosis and treatment and prevent misdiagnosis and omission.