A retrospective study to reveal the effect of surgical correction of cervical kyphosis on thoraco-lumbo-pelvic sagittal alignment

Recent studies suggest that cervical lordosis is influenced by thoracic kyphosis and that T1 slope is a key factor determining cervical sagittal alignment. However, no previous study has investigated the influence of cervical kyphosis correction on the remaining spinopelvic balance. The purpose of this study is to assess the effect of surgical correction of cervical kyphosis on thoraco-lumbo-pelvic alignment. Fifty-five patients who underwent a parts per thousand yen2 level cervical fusions for cervical radiculopathy or myelopathy were included. All patients had regional or global cervical kyphosis, which was surgically corrected into lordosis. Radiographic measurements were made using whole spine standing lateral radigraphs pre- and postoperatively to analyze various sagittal parameters. The visual analogue scale (VAS) for neck pain and the neck disability index (NDI) were calculated. The paired t test was used to compare pre- and post-operative radiographic measures and functional scores. Correlations between changes in cervical sagittal parameters and those of other sagittal parameters were analyzed by Pearson's correlation method. Preoperative kyphosis (11.4A degrees +/- 8.3A degrees) was corrected into lordosis (-9.3A degrees +/- 8.1A degrees). The average fusion levels were 3.3 +/- 1.0. With increasing C2-C7 lordosis after surgery (from -3.4A degrees +/- 10.0A degrees to -15A degrees +/- 7.9A degrees), C0-C2 lordosis decreased significantly (from -34.6A degrees +/- 8.2A degrees to -27.7A degrees +/- 8.0A degrees) (P < 0.001). Thoracic kyphosis (from 24.8 +/- 13.9A degrees to 33.5 +/- 11.9A degrees) and T1 slope (from 12.8A degrees +/- 7.9A degrees to 20.4A degrees +/- 5.2A degrees) significantly increased after surgery (P < 0.001). However, other parameters did not significantly change (P > 0.05). Neck pain VAS and NDI scores (31.8 +/- 16.2) significantly improved (P < 0.001). The degree of increasing C2-C7 lordosis by surgical correction was negatively correlated with changes in both thoracic kyphosis and T1 slope (P < 0.01). Surgical correction of cervical kyphosis affects T1 slope and thoracic kyphosis, but not lumbo-pelvic alignment. These results indicate that the compensatory mechanisms to minimize positive sagittal malalignment of the head may occur mainly in the thoracic, and not in the lumbosacral spine.