Kyphotic malalignment after anterior cervical fusion is one of the factors promoting the degenerative process in adjacent intervertebral levels

The aim of this study was to determine whether postoperative malalignment of the cervical spine after anterior interbody fusion surgery promotes degenerative changes in the neighboring intervertebral discs. Forty-two patients who underwent anterior interbody fusion surgery for cervical spondylosis and disc herniation (34 men, 8 women) were followed for an average of 9.8 years. The average age at surgery was 50.2 years. Twenty-three patients underwent a single-level fusion, 17 underwent two-level fusion, and 2 had three levels fused. The Japanese Orthopaedic Association cervical myelopathy score, with a normal score 17 points, was 11.7 before surgery and 14.9 at follow-up. Neurological status was significantly improved postoperatively, and the improvement was preserved thereafter in most cases (paired t-test, P < 0.001). Degenerative changes were evident on radiological examination in the levels adjacent to the fused segment in 21 of the 42 (50%) patients. Eight of these 21 patients demonstrated neurological deterioration caused by an adjacent disc lesion. A total of 43% of the patients with adjacent-level degeneration had malalignment of the cervical spine, such as kyphosis or sigmoid curvature. In addition, degenerative change in adjacent intervertebral levels was observed in 77% of kyphoses of the fused segment. These were statistically significant (Fisher exact method, P < 0.05, P < 0.04, respectively). Our findings suggest that one of the factors promoting degenerative change in adjacent intervertebral levels after anterior cervical fusion for degenerative disorders is postoperative kyphotic change in the cervical spine and the fused segment.