Preoperative T1 Slope as a Predictor of Change in Cervical Alignment and Range of Motion After Cervical Disc Arthroplasty

BACKGROUND: This study analyzed the effect of preoperative T1 slope on cervical alignment and range of motion (ROM) after cervical disc arthroplasty (CDA) in patients with cervical degenerative disease. MATERIAL/METHODS: This retrospective study included 32 patients with single-level symptomatic cervical disc disease who underwent CDA with the Mobi-C cervical disc prosthesis and had a mean follow-up of 26.8±6.4 months. Standing lateral, flexion, and extension X-rays of the cervical spine were obtained preoperatively and postoperatively at 24-month follow-up. Simple linear regression analysis was used to assess the impact of preoperative T1 slope on changes from preoperative values in radiologic parameters. RESULTS: Compared to preoperative values, at 24-month follow-up, there was a significant increase in mean functional spinal unit (FSU) angle (+7.4°), upper adjacent segment (UAS) angle (+3.1°), and overall cervical alignment (C2–C7 angle) (+6.3°), and a significant decrease in mean lower adjacent segment (LAS) angle (−2.4°). Mean ROM of the FSU (−3.6°), LAS (−3.0°), and overall cervical spine (−11.5°) significantly decreased, and mean ROM of the UAS (+1.6°) significantly increased. There were significant correlations between preoperative T1 slope and mean change from preoperative value in FSU angle, C2–C7 angle, and ROM of the overall cervical spine (C2–C7). CONCLUSIONS: T1 slope is useful for evaluating changes in the FSU angle, C2–C7 angle, and ROM of the overall cervical spine following CDA with the Mobi-C disc. Patients with a large preoperative T1 slope may be good candidates for CDA with the Mobi-C prosthesis due its motion maintenance and the fact that it has little adverse impact on sagittal alignment. It also could be a good option in terms of sagittal alignment improvement or motion maintenance for patients with kyphosis.