Impact of cervical kyphosis on segmental motion and symptomatic adjacent segment degeneration: a long-term follow-up data of more than 5 years.

Purpose: This study was performed to assess the impact of cervical kyphosis on the locations of average center of rotation (COR) of each level preoperatively and to investigate whether uncorrected cervical kyphosis increases the incidence of symptomatic adjacent segment degeneration (ASD) after anterior cervical decompression and fusion (ACDF).

Methods: We retrospectively analyzed all patients surgically treated for cervical myelopathy, radiculopathy, or deformity at a single institution from 2012 to 2018. They were divided into cervical kyphosis and cervical lordosis cohorts. Propensity score matching was performed. Preoperative cervical segmental and postoperative adjacent segment CORs were measured. Development of symptomatic ASD in all patients was assessed after > 5 years of follow-up.

Results: Among 412 patients with cervical lordosis and 47 patients with S-type cervical kyphosis, we established 37 matched pairs before and after surgery. In total, 368 COR locations were measured. Uncorrected kyphosis was identified in seven patients. The CORs of the cervical spine were located farther forward and upward in the cervical kyphosis group than in the control group (p < 0.05). At 1-year visit after ACDF, the locations of the adjacent COR showed no significant differences between the cervical postoperative lordosis group and control group. The incidence of symptomatic ASD was significantly higher in the uncorrected kyphosis group than in the corrected kyphosis group (42.9% vs. 2.5%, p = 0.001) and lordosis group (42.9% vs. 1.9%, p < 0.001).

Conclusions: Cervical kyphosis can impact the locations of COR and increase the incidence of symptomatic ASD. Kyphosis correction is needed during ACDF in patients with cervical kyphosis.