Pathomechanism, pathogenesis, and results of treatment in cervical spondylotic myelopathy caused by dynamic canal stenosis. In this study, the pathomechanism and pathogenesis of dynamic canal stenosis caused by cervical instability in patients with cervical spondylotic myelopathy and the validity of the concept of instability are clarified by analyzing the results of treatment in 53 cases. In cases of cervical spondylotic myelopathy caused by dynamic canal stenosis, the authors found that the posterior slide of the vertebral body occurs as a result of degeneration in the cervical spine due to aging changes, and that the dynamic sagittal diameter of the spinal canal decreases with an increase of the degree of posterior slide. This is followed by gradual aggravation of the clinical symptoms. Continuous cervical traction was found to be the first choice of treatment. Surgical treatment is indicated in cases in which the traction was ineffective, or even when it was effective, in cases in which the Japanese Orthopaedic Association (JOA) score remained low or when there was a tendency toward rapid aggravation of symptoms. It was demonstrated that the shorter the duration of the myelopathy, the better the results of treatment obtained. A limit of the dynamic sagittal diameter of the spinal canal of 12 mm was considered as valid. 