Change in Segmental Alignment Following 1- to 3- level Anterior Cervical Diskectomy and Fusion (ACDF) Is Predicted by Baseline Alignment and Interbody Placement

Introduction: ACDF allows for direct and indirect neural element decompression and correction of segmental alignment among patients treated for degenerative cervical spine disease. The effects of baseline alignment and construct details on segmental realignment remains unknown. Thus, we sought to evaluate the influence of preoperative alignment and cage design on change in segmental alignment following ACDF.

Methods: Patients treated at a single tertiary care system with 1-to-3-level ACDF for degenerative pathologies were identified and data were collected on demographics, construct details, and pre-and postoperative alignment. The primary outcomes of interest were change in disc height, change in segmental lordosis, and segmental lordosis on first postoperative upright radiographs. Multivariable linear regressions were performed to identify independently significant predictors of these outcomes at the p< 0.05 threshold. Results were reported as β coefficients with 95% confidence intervals.

Results: One hundred patients (median 60.8yr; 54% male) treated at 144 levels were included. The most frequently treated levels were C5/6 (32.6%), C4/5 (22.9%), C3/4 (20.8%), and C6/7 (20.8%); titanium interbodies were used in 81.3% of cases with anterior plate fixation in 96.5%, an integrated fixation in the remainder. Disc height improvement positively correlated with greater preoperative C2-7 lordosis (β=0.16/°;[0.07,0.26];p=0.001) and greater cage lordosis (β=0.60/°;[0.19,1.01]; p=0.005), and it negatively correlated with greater preoperative segmental lordosis (β=-1.19/°;[-1.51,-0.87];p < 0.001), greater posterior disc height (β=-1.01/mm;[-1.68,-0.34];p=0.004), and greater distance between the graft and anterior edge of the cranial level (β=-0.22/mm;[-0.41,-0.02];p=0.03). Segmental lordosis increase was positively predicted by greater cage height (β=1.13/mm;[0.33,1.93]p= 0.007) and preoperative C2-7 lordosis (β=0.16/°;[0.06,0.25];p=0.002), while negatively influenced by greater preoperative segmental lordosis (β= -1.31/°;[-1.62,-1.01];p < 0.001) and increased distance from the anterior lip of the cranial vertebra (β=-0.22;[-0.41,-0.03];p = 0.024).

Conclusion : Segmental realignment and disc height restoration following ACDF were best predicted by a combination of baseline cervical alignment, preoperative segmental lordosis, cage properties (lordosis, height), and construct preparation. Specifically, anterior placement of the interbody within the disc space positive predicted both disc height restoration and improvement in segmental lordosis.