Risk factor analysis of postoperative kyphotic change in subaxial cervical alignment after upper cervical fixation.

Objective: Little is known about the risk factors for postoperative subaxial cervical kyphosis following craniovertebral junction (CVJ) fixation. The object of this study was to evaluate postoperative changes in cervical alignment and to identify the risk factors for postoperative kyphotic change in the subaxial cervical spine after CVJ fixation.

Methods: One hundred fifteen patients were retrospectively analyzed for postoperative subaxial kyphosis after CVJ fixation. Relations between subaxial kyphosis and radiological risk factors, including segmental angles and ranges of motion (ROMs) at C0-1, C1-2, and C2-7, and clinical factors, such as age, sex, etiology, occipital fixation, extensor muscle resection at C2, additional C1-2 posterior wiring, and subaxial laminoplasty, were investigated. Univariate and multivariate logistic regression analyses were conducted to identify the risk factors for postoperative kyphotic changes in the subaxial cervical spine.

Results: The C2-7 angle change was more than -10° in 30 (26.1%) of the 115 patients. Risk factor analysis showed CVJ fixation combined with subaxial laminoplasty (OR 9.336, 95% CI 1.484-58.734, p = 0.017) and a small ROM at the C0-1 segment (OR 0.836, 95% CI 0.757-0.923, p < 0.01) were related to postoperative subaxial kyphotic change. On the other hand, age, sex, resection of the C2 extensor muscle, rheumatoid arthritis, additional C1-2 posterior wiring, and postoperative segmental angles were not risk factors for postoperative subaxial kyphosis.

Conclusions: Subaxial alignment change is not uncommon after CVJ fixation. Muscle detachment at the C2 spinous process was not a risk factor of kyphotic change. The study findings suggest that a small ROM at the C0-1 segment with or without occipital fixation and combined subaxial laminoplasty are risk factors for subaxial kyphotic change.