Developmental and dynamic canal stenosis as radiologic factors affecting surgical results of anterior cervical fusion for myelopathy

Study Design. The correlation between preoperative and postoperative latera l functional radiograms and clinical results was analyzed in 74 cases of my elopathy treated by anterior cervical fusion. Objectives. To clarify the correlation between clinical results and radiolo gic findings (developmental and dynamic stenosis). Summary of Background Data. Although radiologic changes have been reported at the disc level adjacent to anterior cervical fusion, the question of whe ther these radiologic findings affect the clinical results of anterior fusi on has not been resolved. Methods. The "deteriorated" results group (28 cases) was composed of cases with deterioration of 2 points or more in the Japan Orthopedic Association score at follow-up compared with the postoperative best score; The "good" r esults group (46 cases) exhibited a recovery rate of greater than or equal to 50%. The two groups were compared in lateral functional roentgenograms o n which the sagittal canal diameter in each vertebra and the diameter betwe en the inferoposterior lip of the vertebral body and the anterior margin of the lamina of the distal vertebra in the extended neck were measured. A di ameter of less than 12 mm was defined as developmental canal stenosis or dy namic canal stenosis. Results. Fifty-four percent of the cases in the deteriorated results group had developmental canal stenosis, whereas the same findings were identified in only 2% of the cases in the good results group (P < 0.01). Preoperative dynamic canal stenosis at the disc level adjacent to the fusion was found in 64% of the patients in the deteriorated results group and in only 4% of the patients in the good results group (P < 0.01). Conclusions. Patients in the deteriorated results group showed a higher inc idence of preoperative developmental and/or dynamic canal stenosis at the a djacent disc level than those in the the good results group. These results indicate that patients with preoperative developmental canal stenosis are n ot suitable candidates for anterior cervical fusion. When dynamic canal ste nosis is found below or above the level of fusion, simultaneous fusion is r ecommended to avoid deterioration of the myelopathy.