Researchers conducted a retrospective study. For a study, they sought to determine the clinical and imaging outcomes following anterior cervical decompression and fusion as a foundation for preventing C5 palsy. From 2001 to 2018, 239 patients with cervical myelopathy had anterior cervical decompression and fusion at the facility, including at the C4–C5 disc level. After surgery, 12 of these patients (5.0%) developed C5 palsy. Patients with and without C5 palsy had their clinical characteristics and imaging results examined. The sagittal alignment of the cervical spine was kyphotic in patients with C5 palsy, the breadth of the C5 intervertebral foramen was narrower, and the lateral decompressed line was wider beyond the medial half of the Luschka joint in patients with C5 palsy. Patients with and without C5 palsy had no significant differences in age, sex, disease, number of fused segments, decompression width, or anterior spinal cord displacement. The outcomes suggest that the pathomechanism of C5 palsy was affected by the placement of the lateral decompression line, particularly in patients with cervical kyphosis and a narrow C5 intervertebral foramen. C5 root kinking between the intervertebral foramen and the posterior margin of the spine may result from excessive lateral decompression beyond the Luchka joint. In both anterior and posterior methods, this pathomechanism may be identical. The medial line of the Luschka joint should be established intraoperatively to avoid C5 palsy, and decompression should be conducted within the Luschka joints to avoid C5 palsy. Medial foraminotomy should be employed in situations requiring extensive decompression, such as those involving substantial ossification of the posterior longitudinal ligament, lateral osteophytes, and symptomatic foraminal stenosis.